Onyx.js

/* eslint-disable no-continue */
import _ from 'underscore';
import Str from 'expensify-common/lib/str';
import {deepEqual} from 'fast-equals';
import lodashGet from 'lodash/get';
import Storage from './storage';
import * as Logger from './Logger';
import cache from './OnyxCache';
import createDeferredTask from './createDeferredTask';
import fastMerge from './fastMerge';
import * as PerformanceUtils from './metrics/PerformanceUtils';

// Method constants
const METHOD = {
    SET: 'set',
    MERGE: 'merge',
    MERGE_COLLECTION: 'mergecollection',
    CLEAR: 'clear',
};

// Keeps track of the last connectionID that was used so we can keep incrementing it
let lastConnectionID = 0;

// Holds a mapping of all the react components that want their state subscribed to a store key
const callbackToStateMapping = {};

// Stores all of the keys that Onyx can use. Must be defined in init().
let onyxKeys = {};

// Holds a list of keys that have been directly subscribed to or recently modified from least to most recent
let recentlyAccessedKeys = [];

// Holds a list of keys that are safe to remove when we reach max storage. If a key does not match with
// whatever appears in this list it will NEVER be a candidate for eviction.
let evictionAllowList = [];

// Holds a map of keys and connectionID arrays whose keys will never be automatically evicted as
// long as we have at least one subscriber that returns false for the canEvict property.
const evictionBlocklist = {};

// Optional user-provided key value states set when Onyx initializes or clears
let defaultKeyStates = {};

// Connections can be made before `Onyx.init`. They would wait for this task before resolving
const deferredInitTask = createDeferredTask();

/**
 * Uses a selector string or function to return a simplified version of sourceData
 * @param {Mixed} sourceData
 * @param {String|Function} selector
 *      If it's a string, the selector is passed to lodashGet on the sourceData
 *      If it's a function, it is passed the sourceData and it should return the simplified data
 * @returns {Mixed}
 */
const getSubsetOfData = (sourceData, selector) => (_.isFunction(selector)
    ? selector(sourceData)
    : lodashGet(sourceData, selector));

/**
 * Takes a collection of items (eg. {testKey_1:{a:'a'}, testKey_2:{b:'b'}})
 * and runs it through a reducer function to return a subset of the data according to a selector.
 * The resulting collection will only contain items that are returned by the selector.
 * @param {Object} collection
 * @param {String|Function} selector (see method docs for getSubsetOfData() for full details)
 * @returns {Object}
 */
const reduceCollectionWithSelector = (collection, selector) => _.reduce(collection, (finalCollection, item, key) => {
    // eslint-disable-next-line no-param-reassign
    finalCollection[key] = getSubsetOfData(item, selector);

    return finalCollection;
}, {});

/**
 * Get some data from the store
 *
 * @private
 * @param {string} key
 * @returns {Promise<*>}
 */
function get(key) {
    // When we already have the value in cache - resolve right away
    if (cache.hasCacheForKey(key)) {
        return Promise.resolve(cache.getValue(key));
    }

    const taskName = `get:${key}`;

    // When a value retrieving task for this key is still running hook to it
    if (cache.hasPendingTask(taskName)) {
        return cache.getTaskPromise(taskName);
    }

    // Otherwise retrieve the value from storage and capture a promise to aid concurrent usages
    const promise = Storage.getItem(key)
        .then((val) => {
            cache.set(key, val);
            return val;
        })
        .catch(err => Logger.logInfo(`Unable to get item from persistent storage. Key: ${key} Error: ${err}`));

    return cache.captureTask(taskName, promise);
}

/**
 * Returns current key names stored in persisted storage
 * @private
 * @returns {Promise<string[]>}
 */
function getAllKeys() {
    // When we've already read stored keys, resolve right away
    const storedKeys = cache.getAllKeys();
    if (storedKeys.length > 0) {
        return Promise.resolve(storedKeys);
    }

    const taskName = 'getAllKeys';

    // When a value retrieving task for all keys is still running hook to it
    if (cache.hasPendingTask(taskName)) {
        return cache.getTaskPromise(taskName);
    }

    // Otherwise retrieve the keys from storage and capture a promise to aid concurrent usages
    const promise = Storage.getAllKeys()
        .then((keys) => {
            _.each(keys, key => cache.addKey(key));
            return keys;
        });

    return cache.captureTask(taskName, promise);
}

/**
 * Checks to see if the a subscriber's supplied key
 * is associated with a collection of keys.
 *
 * @private
 * @param {String} key
 * @returns {Boolean}
 */
function isCollectionKey(key) {
    return _.contains(_.values(onyxKeys.COLLECTION), key);
}

/**
 * @param {String} collectionKey
 * @param {String} key
 * @returns {Boolean}
 */
function isCollectionMemberKey(collectionKey, key) {
    return Str.startsWith(key, collectionKey) && key.length > collectionKey.length;
}

/**
 * Checks to see if a provided key is the exact configured key of our connected subscriber
 * or if the provided key is a collection member key (in case our configured key is a "collection key")
 *
 * @private
 * @param {String} configKey
 * @param {String} key
 * @return {Boolean}
 */
function isKeyMatch(configKey, key) {
    return isCollectionKey(configKey)
        ? Str.startsWith(key, configKey)
        : configKey === key;
}

/**
 * Checks to see if this key has been flagged as
 * safe for removal.
 *
 * @private
 * @param {String} testKey
 * @returns {Boolean}
 */
function isSafeEvictionKey(testKey) {
    return _.some(evictionAllowList, key => isKeyMatch(key, testKey));
}

/**
 * Remove a key from the recently accessed key list.
 *
 * @private
 * @param {String} key
 */
function removeLastAccessedKey(key) {
    recentlyAccessedKeys = _.without(recentlyAccessedKeys, key);
}

/**
 * Add a key to the list of recently accessed keys. The least
 * recently accessed key should be at the head and the most
 * recently accessed key at the tail.
 *
 * @private
 * @param {String} key
 */
function addLastAccessedKey(key) {
    // Only specific keys belong in this list since we cannot remove an entire collection.
    if (isCollectionKey(key) || !isSafeEvictionKey(key)) {
        return;
    }

    removeLastAccessedKey(key);
    recentlyAccessedKeys.push(key);
}

/**
 * Removes a key previously added to this list
 * which will enable it to be deleted again.
 *
 * @private
 * @param {String} key
 * @param {Number} connectionID
 */
function removeFromEvictionBlockList(key, connectionID) {
    evictionBlocklist[key] = _.without(evictionBlocklist[key] || [], connectionID);

    // Remove the key if there are no more subscribers
    if (evictionBlocklist[key].length === 0) {
        delete evictionBlocklist[key];
    }
}

/**
 * Keys added to this list can never be deleted.
 *
 * @private
 * @param {String} key
 * @param {Number} connectionID
 */
function addToEvictionBlockList(key, connectionID) {
    removeFromEvictionBlockList(key, connectionID);

    if (!evictionBlocklist[key]) {
        evictionBlocklist[key] = [];
    }

    evictionBlocklist[key].push(connectionID);
}

/**
 * Take all the keys that are safe to evict and add them to
 * the recently accessed list when initializing the app. This
 * enables keys that have not recently been accessed to be
 * removed.
 *
 * @private
 * @returns {Promise}
 */
function addAllSafeEvictionKeysToRecentlyAccessedList() {
    return getAllKeys()
        .then((keys) => {
            _.each(evictionAllowList, (safeEvictionKey) => {
                _.each(keys, (key) => {
                    if (!isKeyMatch(safeEvictionKey, key)) {
                        return;
                    }
                    addLastAccessedKey(key);
                });
            });
        });
}

/**
 * @private
 * @param {String} collectionKey
 * @returns {Object}
 */
function getCachedCollection(collectionKey) {
    const collectionMemberKeys = _.filter(cache.getAllKeys(), (
        storedKey => isCollectionMemberKey(collectionKey, storedKey)
    ));

    return _.reduce(collectionMemberKeys, (prev, curr) => {
        const cachedValue = cache.getValue(curr);
        if (!cachedValue) {
            return prev;
        }

        // eslint-disable-next-line no-param-reassign
        prev[curr] = cachedValue;
        return prev;
    }, {});
}

/**
 * When a collection of keys change, search for any callbacks matching the collection key and trigger those callbacks
 *
 * @private
 * @param {String} collectionKey
 * @param {Object} partialCollection - a partial collection of grouped member keys
 */
function keysChanged(collectionKey, partialCollection) {
    // We are iterating over all subscribers similar to keyChanged(). However, we are looking for subscribers who are subscribing to either a collection key or
    // individual collection key member for the collection that is being updated. It is important to note that the collection parameter cane be a PARTIAL collection
    // and does not represent all of the combined keys and values for a collection key. It is just the "new" data that was merged in via mergeCollection().
    const stateMappingKeys = _.keys(callbackToStateMapping);
    for (let i = 0; i < stateMappingKeys.length; i++) {
        const subscriber = callbackToStateMapping[stateMappingKeys[i]];
        if (!subscriber) {
            continue;
        }

        // Skip iteration if we do not have a collection key or a collection member key on this subscriber
        if (!Str.startsWith(subscriber.key, collectionKey)) {
            continue;
        }

        /**
         * e.g. Onyx.connect({key: ONYXKEYS.COLLECTION.REPORT, callback: ...});
         */
        const isSubscribedToCollectionKey = subscriber.key === collectionKey;

        /**
         * e.g. Onyx.connect({key: `${ONYXKEYS.COLLECTION.REPORT}{reportID}`, callback: ...});
         */
        const isSubscribedToCollectionMemberKey = isCollectionMemberKey(collectionKey, subscriber.key);

        // We prepare the "cached collection" which is the entire collection + the new partial data that
        // was merged in via mergeCollection().
        const cachedCollection = getCachedCollection(collectionKey);

        // Regular Onyx.connect() subscriber found.
        if (_.isFunction(subscriber.callback)) {
            // If they are subscribed to the collection key and using waitForCollectionCallback then we'll
            // send the whole cached collection.
            if (isSubscribedToCollectionKey) {
                if (subscriber.waitForCollectionCallback) {
                    subscriber.callback(cachedCollection);
                    continue;
                }

                // If they are not using waitForCollectionCallback then we notify the subscriber with
                // the new merged data but only for any keys in the partial collection.
                const dataKeys = _.keys(partialCollection);
                for (let j = 0; j < dataKeys.length; j++) {
                    const dataKey = dataKeys[j];
                    subscriber.callback(cachedCollection[dataKey], dataKey);
                }
                continue;
            }

            // And if the subscriber is specifically only tracking a particular collection member key then we will
            // notify them with the cached data for that key only.
            if (isSubscribedToCollectionMemberKey) {
                subscriber.callback(cachedCollection[subscriber.key], subscriber.key);
                continue;
            }

            continue;
        }

        // React component subscriber found.
        if (subscriber.withOnyxInstance) {
            // We are subscribed to a collection key so we must update the data in state with the new
            // collection member key values from the partial update.
            if (isSubscribedToCollectionKey) {
                // If the subscriber has a selector, then the component's state must only be updated with the data
                // returned by the selector.
                if (subscriber.selector) {
                    subscriber.withOnyxInstance.setState((prevState) => {
                        const previousData = reduceCollectionWithSelector(prevState[subscriber.statePropertyName], subscriber.selector);
                        const newData = reduceCollectionWithSelector(cachedCollection, subscriber.selector);

                        if (!deepEqual(previousData, newData)) {
                            return {
                                [subscriber.statePropertyName]: newData,
                            };
                        }
                        return null;
                    });
                    continue;
                }

                subscriber.withOnyxInstance.setState((prevState) => {
                    const finalCollection = _.clone(prevState[subscriber.statePropertyName] || {});
                    const dataKeys = _.keys(partialCollection);
                    for (let j = 0; j < dataKeys.length; j++) {
                        const dataKey = dataKeys[j];
                        finalCollection[dataKey] = cachedCollection[dataKey];
                    }

                    PerformanceUtils.logSetStateCall(subscriber, prevState[subscriber.statePropertyName], finalCollection, 'keysChanged', collectionKey);
                    return {
                        [subscriber.statePropertyName]: finalCollection,
                    };
                });
                continue;
            }

            // If a React component is only interested in a single key then we can set the cached value directly to the state name.
            if (isSubscribedToCollectionMemberKey) {
                // However, we only want to update this subscriber if the partial data contains a change.
                // Otherwise, we would update them with a value they already have and trigger an unnecessary re-render.
                const dataFromCollection = partialCollection[subscriber.key];
                if (_.isUndefined(dataFromCollection)) {
                    continue;
                }

                // If the subscriber has a selector, then the component's state must only be updated with the data
                // returned by the selector and the state should only change when the subset of data changes from what
                // it was previously.
                if (subscriber.selector) {
                    subscriber.withOnyxInstance.setState((prevState) => {
                        const prevData = prevState[subscriber.statePropertyName];
                        const newData = getSubsetOfData(cachedCollection[subscriber.key], subscriber.selector);
                        if (!deepEqual(prevData, newData)) {
                            PerformanceUtils.logSetStateCall(subscriber, prevData, newData, 'keysChanged', collectionKey);
                            return {
                                [subscriber.statePropertyName]: newData,
                            };
                        }

                        return null;
                    });
                    continue;
                }

                subscriber.withOnyxInstance.setState((prevState) => {
                    const data = cachedCollection[subscriber.key];
                    const previousData = prevState[subscriber.statePropertyName];
                    if (data === previousData) {
                        return null;
                    }

                    PerformanceUtils.logSetStateCall(subscriber, previousData, data, 'keysChanged', collectionKey);
                    return {
                        [subscriber.statePropertyName]: data,
                    };
                });
            }
        }
    }
}

/**
 * When a key change happens, search for any callbacks matching the key or collection key and trigger those callbacks
 *
 * @example
 * keyChanged(key, value, subscriber => subscriber.initWithStoredValues === false)
 *
 * @private
 * @param {String} key
 * @param {*} data
 * @param {Function} [canUpdateSubscriber] only subscribers that pass this truth test will be updated
 */
function keyChanged(key, data, canUpdateSubscriber) {
    // Add or remove this key from the recentlyAccessedKeys lists
    if (!_.isNull(data)) {
        addLastAccessedKey(key);
    } else {
        removeLastAccessedKey(key);
    }

    // We are iterating over all subscribers to see if they are interested in the key that has just changed. If the subscriber's  key is a collection key then we will
    // notify them if the key that changed is a collection member. Or if it is a regular key notify them when there is an exact match. Depending on whether the subscriber
    // was connected via withOnyx we will call setState() directly on the withOnyx instance. If it is a regular connection we will pass the data to the provided callback.
    const stateMappingKeys = _.keys(callbackToStateMapping);
    for (let i = 0; i < stateMappingKeys.length; i++) {
        const subscriber = callbackToStateMapping[stateMappingKeys[i]];
        if (!subscriber || !isKeyMatch(subscriber.key, key) || (_.isFunction(canUpdateSubscriber) && !canUpdateSubscriber(subscriber))) {
            continue;
        }

        // Subscriber is a regular call to connect() and provided a callback
        if (_.isFunction(subscriber.callback)) {
            if (isCollectionKey(subscriber.key) && subscriber.waitForCollectionCallback) {
                const cachedCollection = getCachedCollection(subscriber.key);
                cachedCollection[key] = data;
                subscriber.callback(cachedCollection);
                continue;
            }

            subscriber.callback(data, key);
            continue;
        }

        // Subscriber connected via withOnyx() HOC
        if (subscriber.withOnyxInstance) {
            // Check if we are subscribing to a collection key and overwrite the collection member key value in state
            if (isCollectionKey(subscriber.key)) {
                // If the subscriber has a selector, then the consumer of this data must only be given the data
                // returned by the selector and only when the selected data has changed.
                if (subscriber.selector) {
                    subscriber.withOnyxInstance.setState((prevState) => {
                        const prevData = prevState[subscriber.statePropertyName];
                        const newData = {
                            [key]: getSubsetOfData(data, subscriber.selector),
                        };
                        const prevDataWithNewData = {
                            ...prevData,
                            [key]: getSubsetOfData(data, subscriber.selector),
                        };
                        if (!deepEqual(prevData, prevDataWithNewData)) {
                            PerformanceUtils.logSetStateCall(subscriber, prevData, newData, 'keyChanged', key);
                            return {
                                [subscriber.statePropertyName]: prevDataWithNewData,
                            };
                        }
                        return null;
                    });
                    continue;
                }

                subscriber.withOnyxInstance.setState((prevState) => {
                    const collection = prevState[subscriber.statePropertyName] || {};
                    const newCollection = {
                        ...collection,
                        [key]: data,
                    };
                    PerformanceUtils.logSetStateCall(subscriber, collection, newCollection, 'keyChanged', key);
                    return {
                        [subscriber.statePropertyName]: newCollection,
                    };
                });
                continue;
            }

            // If the subscriber has a selector, then the component's state must only be updated with the data
            // returned by the selector and only if the selected data has changed.
            if (subscriber.selector) {
                subscriber.withOnyxInstance.setState((prevState) => {
                    const previousValue = getSubsetOfData(prevState[subscriber.statePropertyName], subscriber.selector);
                    const newValue = getSubsetOfData(data, subscriber.selector);
                    if (!deepEqual(previousValue, newValue)) {
                        return {
                            [subscriber.statePropertyName]: newValue,
                        };
                    }
                    return null;
                });
                continue;
            }

            // If we did not match on a collection key then we just set the new data to the state property
            subscriber.withOnyxInstance.setState((prevState) => {
                const previousData = prevState[subscriber.statePropertyName];
                if (previousData === data) {
                    return null;
                }

                PerformanceUtils.logSetStateCall(subscriber, previousData, data, 'keyChanged', key);
                return {
                    [subscriber.statePropertyName]: data,
                };
            });
            continue;
        }

        console.error('Warning: Found a matching subscriber to a key that changed, but no callback or withOnyxInstance could be found.');
    }
}

/**
 * Sends the data obtained from the keys to the connection. It either:
 *     - sets state on the withOnyxInstances
 *     - triggers the callback function
 *
 * @private
 * @param {Object} mapping
 * @param {Object} [mapping.withOnyxInstance]
 * @param {String} [mapping.statePropertyName]
 * @param {Function} [mapping.callback]
 * @param {String} [mapping.selector]
 * @param {*|null} val
 * @param {String} matchedKey
 */
function sendDataToConnection(mapping, val, matchedKey) {
    // If the mapping no longer exists then we should not send any data.
    // This means our subscriber disconnected or withOnyx wrapped component unmounted.
    if (!callbackToStateMapping[mapping.connectionID]) {
        return;
    }

    if (mapping.withOnyxInstance) {
        let newData = val;

        // If the mapping has a selector, then the component's state must only be updated with the data
        // returned by the selector.
        if (mapping.selector) {
            if (isCollectionKey(mapping.key)) {
                newData = reduceCollectionWithSelector(val, mapping.selector);
            } else {
                newData = getSubsetOfData(val, mapping.selector);
            }
        }

        PerformanceUtils.logSetStateCall(mapping, null, newData, 'sendDataToConnection');
        mapping.withOnyxInstance.setWithOnyxState(mapping.statePropertyName, newData);
        return;
    }

    if (_.isFunction(mapping.callback)) {
        mapping.callback(val, matchedKey);
    }
}

/**
 * We check to see if this key is flagged as safe for eviction and add it to the recentlyAccessedKeys list so that when we
 * run out of storage the least recently accessed key can be removed.
 *
 * @private
 * @param {Object} mapping
 */
function addKeyToRecentlyAccessedIfNeeded(mapping) {
    if (!isSafeEvictionKey(mapping.key)) {
        return;
    }

    // Try to free some cache whenever we connect to a safe eviction key
    cache.removeLeastRecentlyUsedKeys();

    if (mapping.withOnyxInstance && !isCollectionKey(mapping.key)) {
        // All React components subscribing to a key flagged as a safe eviction key must implement the canEvict property.
        if (_.isUndefined(mapping.canEvict)) {
            throw new Error(
                `Cannot subscribe to safe eviction key '${mapping.key}' without providing a canEvict value.`,
            );
        }

        addLastAccessedKey(mapping.key);
    }
}

/**
 * Gets the data for a given an array of matching keys, combines them into an object, and sends the result back to the subscriber.
 *
 * @private
 * @param {Array} matchingKeys
 * @param {Object} mapping
 */
function getCollectionDataAndSendAsObject(matchingKeys, mapping) {
    Promise.all(_.map(matchingKeys, key => get(key)))
        .then(values => _.reduce(values, (finalObject, value, i) => {
            // eslint-disable-next-line no-param-reassign
            finalObject[matchingKeys[i]] = value;
            return finalObject;
        }, {}))
        .then(val => sendDataToConnection(mapping, val));
}

/**
 * Subscribes a react component's state directly to a store key
 *
 * @example
 * const connectionID = Onyx.connect({
 *     key: ONYXKEYS.SESSION,
 *     callback: onSessionChange,
 * });
 *
 * @param {Object} mapping the mapping information to connect Onyx to the components state
 * @param {String} mapping.key ONYXKEY to subscribe to
 * @param {String} [mapping.statePropertyName] the name of the property in the state to connect the data to
 * @param {Object} [mapping.withOnyxInstance] whose setState() method will be called with any changed data
 *      This is used by React components to connect to Onyx
 * @param {Function} [mapping.callback] a method that will be called with changed data
 *      This is used by any non-React code to connect to Onyx
 * @param {Boolean} [mapping.initWithStoredValues] If set to false, then no data will be prefilled into the
 *  component
 * @param {Boolean} [mapping.waitForCollectionCallback] If set to true, it will return the entire collection to the callback as a single object
 * @param {String|Function} [mapping.selector] THIS PARAM IS ONLY USED WITH withOnyx(). If included, this will be used to subscribe to a subset of an Onyx key's data.
 *       If the selector is a string, the selector is passed to lodashGet on the sourceData. If the selector is a function, the sourceData is passed to the selector and should return the
 *       simplified data. Using this setting on `withOnyx` can have very positive performance benefits because the component will only re-render when the subset of data changes.
 *       Otherwise, any change of data on any property would normally cause the component to re-render (and that can be expensive from a performance standpoint).
 * @returns {Number} an ID to use when calling disconnect
 */
function connect(mapping) {
    const connectionID = lastConnectionID++;
    callbackToStateMapping[connectionID] = mapping;
    callbackToStateMapping[connectionID].connectionID = connectionID;

    if (mapping.initWithStoredValues === false) {
        return connectionID;
    }

    // Commit connection only after init passes
    deferredInitTask.promise
        .then(() => addKeyToRecentlyAccessedIfNeeded(mapping))
        .then(getAllKeys)
        .then((keys) => {
            // We search all the keys in storage to see if any are a "match" for the subscriber we are connecting so that we
            // can send data back to the subscriber. Note that multiple keys can match as a subscriber could either be
            // subscribed to a "collection key" or a single key.
            const matchingKeys = _.filter(keys, key => isKeyMatch(mapping.key, key));

            // If the key being connected to does not exist we initialize the value with null. For subscribers that connected
            // directly via connect() they will simply get a null value sent to them without any information about which key matched
            // since there are none matched. In withOnyx() we wait for all connected keys to return a value before rendering the child
            // component. This null value will be filtered out so that the connected component can utilize defaultProps.
            if (matchingKeys.length === 0) {
                sendDataToConnection(mapping, null);
                return;
            }

            // When using a callback subscriber we will either trigger the provided callback for each key we find or combine all values
            // into an object and just make a single call. The latter behavior is enabled by providing a waitForCollectionCallback key
            // combined with a subscription to a collection key.
            if (_.isFunction(mapping.callback)) {
                if (isCollectionKey(mapping.key)) {
                    if (mapping.waitForCollectionCallback) {
                        getCollectionDataAndSendAsObject(matchingKeys, mapping);
                        return;
                    }

                    // We did not opt into using waitForCollectionCallback mode so the callback is called for every matching key.
                    for (let i = 0; i < matchingKeys.length; i++) {
                        get(matchingKeys[i]).then(val => sendDataToConnection(mapping, val, matchingKeys[i]));
                    }
                    return;
                }

                // If we are not subscribed to a collection key then there's only a single key to send an update for.
                get(mapping.key).then(val => sendDataToConnection(mapping, val, mapping.key));
                return;
            }

            // If we have a withOnyxInstance that means a React component has subscribed via the withOnyx() HOC and we need to
            // group collection key member data into an object.
            if (mapping.withOnyxInstance) {
                if (isCollectionKey(mapping.key)) {
                    getCollectionDataAndSendAsObject(matchingKeys, mapping);
                    return;
                }

                // If the subscriber is not using a collection key then we just send a single value back to the subscriber
                get(mapping.key).then(val => sendDataToConnection(mapping, val, mapping.key));
                return;
            }

            console.error('Warning: Onyx.connect() was found without a callback or withOnyxInstance');
        });

    // The connectionID is returned back to the caller so that it can be used to clean up the connection when it's no longer needed
    // by calling Onyx.disconnect(connectionID).
    return connectionID;
}

/**
 * Remove the listener for a react component
 * @example
 * Onyx.disconnect(connectionID);
 *
 * @param {Number} connectionID unique id returned by call to Onyx.connect()
 * @param {String} [keyToRemoveFromEvictionBlocklist]
 */
function disconnect(connectionID, keyToRemoveFromEvictionBlocklist) {
    if (!callbackToStateMapping[connectionID]) {
        return;
    }

    // Remove this key from the eviction block list as we are no longer
    // subscribing to it and it should be safe to delete again
    if (keyToRemoveFromEvictionBlocklist) {
        removeFromEvictionBlockList(keyToRemoveFromEvictionBlocklist, connectionID);
    }

    delete callbackToStateMapping[connectionID];
}

/**
 * This method mostly exists for historical reasons as this library was initially designed without a memory cache and one was added later.
 * For this reason, Onyx works more similar to what you might expect from a native AsyncStorage with reads, writes, etc all becoming
 * available async. Since we have code in our main applications that might expect things to work this way it's not safe to change this
 * behavior just yet.
 *
 * @example
 * notifySubscribersOnNextTick(key, value, subscriber => subscriber.initWithStoredValues === false)
 *
 * @param {String} key
 * @param {*} value
 * @param {Function} [canUpdateSubscriber] only subscribers that pass this truth test will be updated
 */
// eslint-disable-next-line rulesdir/no-negated-variables
function notifySubscribersOnNextTick(key, value, canUpdateSubscriber) {
    Promise.resolve().then(() => keyChanged(key, value, canUpdateSubscriber));
}

/**
 * This method is similar to notifySubscribersOnNextTick but it is built for working specifically with collections
 * so that keysChanged() is triggered for the collection and not keyChanged(). If this was not done, then the
 * subscriber callbacks receive the data in a different format than they normally expect and it breaks code.
 *
 * @param {String} key
 * @param {*} value
 */
// eslint-disable-next-line rulesdir/no-negated-variables
function notifyCollectionSubscribersOnNextTick(key, value) {
    Promise.resolve().then(() => keysChanged(key, value));
}

/**
 * Remove a key from Onyx and update the subscribers
 *
 * @private
 * @param {String} key
 * @return {Promise}
 */
function remove(key) {
    // Cache the fact that the value was removed
    cache.set(key, null);
    notifySubscribersOnNextTick(key, null);
    return Storage.removeItem(key);
}

/**
 * If we fail to set or merge we must handle this by
 * evicting some data from Onyx and then retrying to do
 * whatever it is we attempted to do.
 *
 * @private
 * @param {Error} error
 * @param {Function} onyxMethod
 * @param  {...any} args
 * @return {Promise}
 */
function evictStorageAndRetry(error, onyxMethod, ...args) {
    Logger.logInfo(`Handled error: ${error}`);

    if (error && Str.startsWith(error.message, 'Failed to execute \'put\' on \'IDBObjectStore\'')) {
        Logger.logAlert('Attempted to set invalid data set in Onyx. Please ensure all data is serializable.');
        throw error;
    }

    // Find the first key that we can remove that has no subscribers in our blocklist
    const keyForRemoval = _.find(recentlyAccessedKeys, key => !evictionBlocklist[key]);

    if (!keyForRemoval) {
        Logger.logAlert('Out of storage. But found no acceptable keys to remove.');
        throw error;
    }

    // Remove the least recently viewed key that is not currently being accessed and retry.
    Logger.logInfo(`Out of storage. Evicting least recently accessed key (${keyForRemoval}) and retrying.`);
    return remove(keyForRemoval)
        .then(() => onyxMethod(...args));
}

/**
 * Write a value to our store with the given key
 *
 * @param {String} key ONYXKEY to set
 * @param {*} value value to store
 *
 * @returns {Promise}
 */
function set(key, value) {
    // Logging properties only since values could be sensitive things we don't want to log
    Logger.logInfo(`set() called for key: ${key}${_.isObject(value) ? ` properties: ${_.keys(value).join(',')}` : ''}`);

    // eslint-disable-next-line no-use-before-define
    if (hasPendingMergeForKey(key)) {
        Logger.logAlert(`Onyx.set() called after Onyx.merge() for key: ${key}. It is recommended to use set() or merge() not both.`);
    }

    // If the value in the cache is the same as what we have then do not update subscribers unless they
    // have initWithStoredValues: false then they MUST get all updates even if nothing has changed.
    if (!cache.hasValueChanged(key, value)) {
        cache.addToAccessedKeys(key);
        notifySubscribersOnNextTick(key, value, subscriber => subscriber.initWithStoredValues === false);
        return Promise.resolve();
    }

    // Adds the key to cache when it's not available
    cache.set(key, value);
    notifySubscribersOnNextTick(key, value);

    // Write the thing to persistent storage, which will trigger a storage event for any other tabs open on this domain
    return Storage.setItem(key, value)
        .catch(error => evictStorageAndRetry(error, set, key, value));
}

/**
 * Storage expects array like: [["@MyApp_user", value_1], ["@MyApp_key", value_2]]
 * This method transforms an object like {'@MyApp_user': myUserValue, '@MyApp_key': myKeyValue}
 * to an array of key-value pairs in the above format
 * @private
 * @param {Record} data
 * @return {Array} an array of key - value pairs <[key, value]>
 */
function prepareKeyValuePairsForStorage(data) {
    return _.map(data, (value, key) => [key, value]);
}

/**
 * Sets multiple keys and values
 *
 * @example Onyx.multiSet({'key1': 'a', 'key2': 'b'});
 *
 * @param {Object} data object keyed by ONYXKEYS and the values to set
 * @returns {Promise}
 */
function multiSet(data) {
    const keyValuePairs = prepareKeyValuePairsForStorage(data);

    _.each(data, (val, key) => {
        // Update cache and optimistically inform subscribers on the next tick
        cache.set(key, val);
        notifySubscribersOnNextTick(key, val);
    });

    return Storage.multiSet(keyValuePairs)
        .catch(error => evictStorageAndRetry(error, multiSet, data));
}

// Key/value store of Onyx key and arrays of values to merge
const mergeQueue = {};

/**
 * @private
 * @param {String} key
 * @returns {Boolean}
 */
function hasPendingMergeForKey(key) {
    return Boolean(mergeQueue[key]);
}

/**
 * Given an Onyx key and value this method will combine all queued
 * value updates and return a single value. Merge attempts are
 * batched. They must occur after a single call to get() so we
 * can avoid race conditions.
 *
 * @private
 * @param {String} key
 * @param {*} data
 *
 * @returns {*}
 */
function applyMerge(key, data) {
    const mergeValues = mergeQueue[key];
    if (_.isArray(data) || _.every(mergeValues, _.isArray)) {
        // Array values will always just concatenate
        // more items onto the end of the array
        return _.reduce(mergeValues, (modifiedData, mergeValue) => [
            ...modifiedData,
            ...mergeValue,
        ], data || []);
    }

    if (_.isObject(data) || _.every(mergeValues, _.isObject)) {
        // Object values are merged one after the other
        return _.reduce(mergeValues, (modifiedData, mergeValue) => {
            // lodash adds a small overhead so we don't use it here
            // eslint-disable-next-line prefer-object-spread, rulesdir/prefer-underscore-method
            const newData = Object.assign({}, fastMerge(modifiedData, mergeValue));

            // We will also delete any object keys that are undefined or null.
            // Deleting keys is not supported by AsyncStorage so we do it this way.
            // Remove all first level keys that are explicitly set to null.
            return _.omit(newData, (value, finalObjectKey) => _.isNull(mergeValue[finalObjectKey]));
        }, data || {});
    }

    // If we have anything else we can't merge it so we'll
    // simply return the last value that was queued
    return _.last(mergeValues);
}

/**
 * Merge a new value into an existing value at a key.
 *
 * The types of values that can be merged are `Object` and `Array`. To set another type of value use `Onyx.set()`. Merge
 * behavior uses lodash/merge under the hood for `Object` and simple concatenation for `Array`. However, it's important
 * to note that if you have an array value property on an `Object` that the default behavior of lodash/merge is not to
 * concatenate. See here: https://github.com/lodash/lodash/issues/2872
 *
 * Calls to `Onyx.merge()` are batched so that any calls performed in a single tick will stack in a queue and get
 * applied in the order they were called. Note: `Onyx.set()` calls do not work this way so use caution when mixing
 * `Onyx.merge()` and `Onyx.set()`.
 *
 * @example
 * Onyx.merge(ONYXKEYS.EMPLOYEE_LIST, ['Joe']); // -> ['Joe']
 * Onyx.merge(ONYXKEYS.EMPLOYEE_LIST, ['Jack']); // -> ['Joe', 'Jack']
 * Onyx.merge(ONYXKEYS.POLICY, {id: 1}); // -> {id: 1}
 * Onyx.merge(ONYXKEYS.POLICY, {name: 'My Workspace'}); // -> {id: 1, name: 'My Workspace'}
 *
 * @param {String} key ONYXKEYS key
 * @param {(Object|Array)} value Object or Array value to merge
 * @returns {Promise}
 */
function merge(key, value) {
    if (mergeQueue[key]) {
        mergeQueue[key].push(value);
        return Promise.resolve();
    }

    mergeQueue[key] = [value];
    return get(key)
        .then((data) => {
            try {
                const modifiedData = applyMerge(key, data);

                // Clean up the write queue so we
                // don't apply these changes again
                delete mergeQueue[key];

                return set(key, modifiedData);
            } catch (error) {
                Logger.logAlert(`An error occurred while applying merge for key: ${key}, Error: ${error}`);
            }

            return Promise.resolve();
        });
}

/**
 * Merge user provided default key value pairs.
 * @private
 * @returns {Promise}
 */
function initializeWithDefaultKeyStates() {
    return Storage.multiGet(_.keys(defaultKeyStates))
        .then((pairs) => {
            const asObject = _.object(pairs);

            const merged = fastMerge(asObject, defaultKeyStates);
            cache.merge(merged);
            _.each(merged, (val, key) => keyChanged(key, val));
        });
}

/**
 * Clear out all the data in the store
 *
 * Note that calling Onyx.clear() and then Onyx.set() on a key with a default
 * key state may store an unexpected value in Storage.
 *
 * E.g.
 * Onyx.clear();
 * Onyx.set(ONYXKEYS.DEFAULT_KEY, 'default');
 * Storage.getItem(ONYXKEYS.DEFAULT_KEY)
 *     .then((storedValue) => console.log(storedValue));
 * null is logged instead of the expected 'default'
 *
 * Onyx.set() might call Storage.setItem() before Onyx.clear() calls
 * Storage.setItem(). Use Onyx.merge() instead if possible. Onyx.merge() calls
 * Onyx.get(key) before calling Storage.setItem() via Onyx.set().
 * Storage.setItem() from Onyx.clear() will have already finished and the merged
 * value will be saved to storage after the default value.
 *
 * @param {Array} keysToPreserve is a list of ONYXKEYS that should not be cleared with the rest of the data
 * @returns {Promise<void>}
 */
function clear(keysToPreserve = []) {
    return getAllKeys()
        .then((keys) => {
            const keyValuesToReset = [];
            const defaultKeys = _.keys(defaultKeyStates);

            // Get all the values for the keys that need to be preserved. These key/value pairs will be set
            // in Onyx after the database is cleared().
            const keyValuesToPreserve = _.reduce(keysToPreserve, (finalArray, keyToPreserve) => {
                finalArray.push([keyToPreserve, cache.getValue(keyToPreserve)]);
                return finalArray;
            }, []);

            // The only keys that should not be cleared are:
            // 1. Anything specifically passed in keysToPreserve (because some keys like language preferences, offline
            //      status, or activeClients need to remain in Onyx even when signed out)
            // 2. Any keys with a default state (because they need to remain in Onyx as their default, and setting them
            //      to null would cause unknown behavior)
            const keysToClear = _.difference(keys, keysToPreserve, defaultKeys);
            keyValuesToReset.push(..._.map(keysToClear, key => [key, null]));

            // Remove any keysToPreserve from the defaultKeyStates because if they are passed in it has been explicitly
            // called out to preserve those values instead of resetting them back
            // to the default.
            const defaultKeyValuePairs = _.pairs(_.omit(defaultKeyStates, ...keysToPreserve));

            // Add the default key value pairs to the keyValuesToReset so that they get set back to their default values
            // when we clear Onyx
            keyValuesToReset.push(...defaultKeyValuePairs);

            // We now have all the key/values that need to be reset, but we're not done yet!
            // There will be two groups of key/values and they each need to be updated a little bit differently.
            // Collection keys need to be notified differently than non collection keys
            const keyValuesToResetAsCollection = {};
            const keyValuesToResetIndividually = {};

            // Make sure that we also reset the cache values before clearing the values from storage.
            // We do this before clearing Storage so that any call to clear() followed by merge() on a key with a
            // default state results in the merged value getting saved, since the update from the merge() call would
            // happen on the tick after the update from this clear()
            _.each(keyValuesToReset, (keyValue) => {
                const key = keyValue[0];
                const value = keyValue[1];
                cache.set(key, value);

                const collectionKey = key.substring(0, key.indexOf('_') + 1);
                if (collectionKey) {
                    if (!keyValuesToResetAsCollection[collectionKey]) {
                        keyValuesToResetAsCollection[collectionKey] = {};
                    }
                    keyValuesToResetAsCollection[collectionKey][key] = value;
                    return;
                }

                keyValuesToResetIndividually[key] = value;
            });

            // Notify the subscribers for each key/value group so they can receive the new values
            _.each(keyValuesToResetIndividually, (value, key) => {
                notifySubscribersOnNextTick(key, value);
            });
            _.each(keyValuesToResetAsCollection, (value, key) => {
                notifyCollectionSubscribersOnNextTick(key, value);
            });

            // Call clear() and make sure that the default key/values and the key/values from the parameter
            // are preserved in storage. This makes sure to always leave storage in a state that contains
            // all the default values and any additional values that we want to remain after the database is cleared.
            return Storage.clear()
                .then(() => Storage.multiSet(defaultKeyValuePairs.concat(keyValuesToPreserve)));
        });
}

/**
 * Merges a collection based on their keys
 *
 * @example
 *
 * Onyx.mergeCollection(ONYXKEYS.COLLECTION.REPORT, {
 *     [`${ONYXKEYS.COLLECTION.REPORT}1`]: report1,
 *     [`${ONYXKEYS.COLLECTION.REPORT}2`]: report2,
 * });
 *
 * @param {String} collectionKey e.g. `ONYXKEYS.COLLECTION.REPORT`
 * @param {Object} collection Object collection keyed by individual collection member keys and values
 * @returns {Promise}
 */
function mergeCollection(collectionKey, collection) {
    if (!_.isObject(collection) || _.isArray(collection) || _.isEmpty(collection)) {
        Logger.logInfo('mergeCollection() called with invalid or empty value. Skipping this update.');
        return Promise.resolve();
    }

    // Confirm all the collection keys belong to the same parent
    _.each(collection, (_data, dataKey) => {
        if (isKeyMatch(collectionKey, dataKey)) {
            return;
        }

        throw new Error(`Provided collection doesn't have all its data belonging to the same parent. CollectionKey: ${collectionKey}, DataKey: ${dataKey}`);
    });

    return getAllKeys()
        .then((persistedKeys) => {
            // Split to keys that exist in storage and keys that don't
            const [existingKeys, newKeys] = _.chain(collection)
                .keys()
                .partition(key => persistedKeys.includes(key))
                .value();

            const existingKeyCollection = _.pick(collection, existingKeys);
            const newCollection = _.pick(collection, newKeys);
            const keyValuePairsForExistingCollection = prepareKeyValuePairsForStorage(existingKeyCollection);
            const keyValuePairsForNewCollection = prepareKeyValuePairsForStorage(newCollection);

            const promises = [];

            // New keys will be added via multiSet while existing keys will be updated using multiMerge
            // This is because setting a key that doesn't exist yet with multiMerge will throw errors
            if (keyValuePairsForExistingCollection.length > 0) {
                promises.push(Storage.multiMerge(keyValuePairsForExistingCollection));
            }

            if (keyValuePairsForNewCollection.length > 0) {
                promises.push(Storage.multiSet(keyValuePairsForNewCollection));
            }

            // Prefill cache if necessary by calling get() on any existing keys and then merge original data to cache
            // and update all subscribers
            Promise.all(_.map(existingKeys, get)).then(() => {
                cache.merge(collection);
                keysChanged(collectionKey, collection);
            });

            return Promise.all(promises)
                .catch(error => evictStorageAndRetry(error, mergeCollection, collection));
        });
}

/**
 * Insert API responses and lifecycle data into Onyx
 *
 * @param {Array} data An array of objects with shape {onyxMethod: oneOf('set', 'merge', 'mergeCollection'), key: string, value: *}
 * @returns {Promise} resolves when all operations are complete
 */
function update(data) {
    // First, validate the Onyx object is in the format we expect
    _.each(data, ({onyxMethod, key}) => {
        if (!_.contains([METHOD.CLEAR, METHOD.SET, METHOD.MERGE, METHOD.MERGE_COLLECTION], onyxMethod)) {
            throw new Error(`Invalid onyxMethod ${onyxMethod} in Onyx update.`);
        }
        if (onyxMethod !== METHOD.CLEAR && !_.isString(key)) {
            throw new Error(`Invalid ${typeof key} key provided in Onyx update. Onyx key must be of type string.`);
        }
    });

    const promises = [];

    _.each(data, ({onyxMethod, key, value}) => {
        switch (onyxMethod) {
            case METHOD.SET:
                promises.push(set(key, value));
                break;
            case METHOD.MERGE:
                promises.push(merge(key, value));
                break;
            case METHOD.MERGE_COLLECTION:
                promises.push(mergeCollection(key, value));
                break;
            case METHOD.CLEAR:
                promises.push(clear());
                break;
            default:
                break;
        }
    });

    return Promise.all(promises);
}

/**
 * Initialize the store with actions and listening for storage events
 *
 * @param {Object} [options={}] config object
 * @param {Object} [options.keys={}] `ONYXKEYS` constants object
 * @param {Object} [options.initialKeyStates={}] initial data to set when `init()` and `clear()` is called
 * @param {String[]} [options.safeEvictionKeys=[]] This is an array of keys
 * (individual or collection patterns) that when provided to Onyx are flagged
 * as "safe" for removal. Any components subscribing to these keys must also
 * implement a canEvict option. See the README for more info.
 * @param {Number} [options.maxCachedKeysCount=55] Sets how many recent keys should we try to keep in cache
 * Setting this to 0 would practically mean no cache
 * We try to free cache when we connect to a safe eviction key
 * @param {Boolean} [options.captureMetrics] Enables Onyx benchmarking and exposes the get/print/reset functions
 * @param {Boolean} [options.shouldSyncMultipleInstances] Auto synchronize storage events between multiple instances
 * of Onyx running in different tabs/windows. Defaults to true for platforms that support local storage (web/desktop)
 * @param {Boolean} [options.debugSetState] Enables debugging setState() calls to connected components.
 * @example
 * Onyx.init({
 *     keys: ONYXKEYS,
 *     initialKeyStates: {
 *         [ONYXKEYS.SESSION]: {loading: false},
 *     },
 * });
 */
function init({
    keys = {},
    initialKeyStates = {},
    safeEvictionKeys = [],
    maxCachedKeysCount = 1000,
    captureMetrics = false,
    shouldSyncMultipleInstances = Boolean(global.localStorage),
    debugSetState = false,
} = {}) {
    if (captureMetrics) {
        // The code here is only bundled and applied when the captureMetrics is set
        // eslint-disable-next-line no-use-before-define
        applyDecorators();
    }

    if (debugSetState) {
        PerformanceUtils.setShouldDebugSetState(true);
    }

    if (maxCachedKeysCount > 0) {
        cache.setRecentKeysLimit(maxCachedKeysCount);
    }

    // Let Onyx know about all of our keys
    onyxKeys = keys;

    // Set our default key states to use when initializing and clearing Onyx data
    defaultKeyStates = initialKeyStates;

    // Let Onyx know about which keys are safe to evict
    evictionAllowList = safeEvictionKeys;

    // Initialize all of our keys with data provided then give green light to any pending connections
    Promise.all([
        addAllSafeEvictionKeysToRecentlyAccessedList(),
        initializeWithDefaultKeyStates(),
    ])
        .then(deferredInitTask.resolve);

    if (shouldSyncMultipleInstances && _.isFunction(Storage.keepInstancesSync)) {
        Storage.keepInstancesSync((key, value) => {
            cache.set(key, value);
            keyChanged(key, value);
        });
    }
}

const Onyx = {
    connect,
    disconnect,
    set,
    multiSet,
    merge,
    mergeCollection,
    update,
    clear,
    init,
    registerLogger: Logger.registerLogger,
    addToEvictionBlockList,
    removeFromEvictionBlockList,
    isSafeEvictionKey,
    METHOD,
};

/**
 * Apply calls statistic decorators to benchmark Onyx
 *
 * @private
 */
function applyDecorators() {
    // We're requiring the script dynamically here so that it's only evaluated when decorators are used
    const decorate = require('./metrics');

    // Re-assign with decorated functions
    /* eslint-disable no-func-assign */
    get = decorate.decorateWithMetrics(get, 'Onyx:get');
    set = decorate.decorateWithMetrics(set, 'Onyx:set');
    multiSet = decorate.decorateWithMetrics(multiSet, 'Onyx:multiSet');
    clear = decorate.decorateWithMetrics(clear, 'Onyx:clear');
    merge = decorate.decorateWithMetrics(merge, 'Onyx:merge');
    mergeCollection = decorate.decorateWithMetrics(mergeCollection, 'Onyx:mergeCollection');
    getAllKeys = decorate.decorateWithMetrics(getAllKeys, 'Onyx:getAllKeys');
    initializeWithDefaultKeyStates = decorate.decorateWithMetrics(initializeWithDefaultKeyStates, 'Onyx:defaults');
    update = decorate.decorateWithMetrics(update, 'Onyx:update');
    /* eslint-enable */

    // Re-expose decorated methods
    /* eslint-disable rulesdir/prefer-actions-set-data */
    Onyx.set = set;
    Onyx.multiSet = multiSet;
    Onyx.clear = clear;
    Onyx.merge = merge;
    Onyx.mergeCollection = mergeCollection;
    Onyx.update = update;
    /* eslint-enable */

    // Expose stats methods on Onyx
    Onyx.getMetrics = decorate.getMetrics;
    Onyx.resetMetrics = decorate.resetMetrics;
    Onyx.printMetrics = decorate.printMetrics;
}

export default Onyx;