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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,12 @@ | ||
| // @flow | ||
| import type { FSA } from 'types/redux'; | ||
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| export const UNDO = 'UNDO'; | ||
| export function undo(): FSA { | ||
| return { type: UNDO, payload: null }; | ||
| } | ||
|
|
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| export const REDO = 'REDO'; | ||
| export function redo(): FSA { | ||
| return { type: REDO, payload: null }; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,116 @@ | ||
| // @flow | ||
| import type { FSA } from 'types/redux'; | ||
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| import { pick, takeRight, set, get, last } from 'lodash'; | ||
| import { UNDO, REDO } from 'actions/undoHistory'; | ||
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| export type UndoHistoryConfig = { | ||
| reducerName: string, | ||
| limit?: number, | ||
| actionsToWatch: string[], | ||
| whitelist: string[], | ||
| }; | ||
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| export type UndoHistoryState = { | ||
| past: Object[], | ||
| present: ?Object, | ||
| future: Object[], | ||
| }; | ||
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| // Call the reducer with empty action to populate the initial state | ||
| const initialState: UndoHistoryState = { | ||
| past: [], | ||
| present: undefined, // Don't pretend to know the present | ||
| future: [], | ||
| }; | ||
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| // Update undo history using the action and app states | ||
| // Basically a reducer but not really, as it needs to know the previous state. | ||
| // Passing state in even though state === presentAppState[config.reducerName] as the "reducer" | ||
| // doesn't need to know that. | ||
| export function computeUndoStacks<T: Object>( | ||
| state: UndoHistoryState = initialState, | ||
| action: FSA, | ||
| previousAppState: T, | ||
| presentAppState: T, | ||
| config: UndoHistoryConfig, | ||
| ): UndoHistoryState { | ||
| const { past, present, future } = state; | ||
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| // If action is undo/redoable, store state | ||
| if (config.actionsToWatch.includes(action.type)) { | ||
| // Append actual present to past, and drop history past config.limit | ||
| // Limit only enforced here since undo/redo only shift the history around without adding new history | ||
| const appendedPast = [...past, pick(previousAppState, config.whitelist)]; | ||
| const newPast = 'limit' in config ? takeRight(appendedPast, config.limit) : appendedPast; | ||
|
|
||
| return { | ||
| past: newPast, | ||
| present: pick(presentAppState, config.whitelist), | ||
| future: [], | ||
| }; | ||
| } | ||
|
|
||
| switch (action.type) { | ||
| case UNDO: { | ||
| // Abort if no past, or present is unknown | ||
| if (past.length === 0 || !present) return state; | ||
| const previous = last(past); | ||
| const newPast = past.slice(0, past.length - 1); | ||
| return { | ||
| past: newPast, | ||
| present: previous, | ||
| future: [present, ...future], | ||
| }; | ||
| } | ||
| case REDO: { | ||
| // Abort if no future, or present is unknown | ||
| if (future.length === 0 || !present) return state; | ||
| const next = future[0]; | ||
| const newFuture = future.slice(1); | ||
| return { | ||
| past: [...past, present], | ||
| present: next, | ||
| future: newFuture, | ||
| }; | ||
| } | ||
| default: { | ||
| return state; | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // Copy all keyPaths in present into a new copy of state | ||
| export function mergePresent<T: Object>(state: T, present: Object, keyPaths: string[]): T { | ||
| const newState = { ...state }; | ||
| keyPaths.forEach((path) => { | ||
| const presentValue = get(present, path); | ||
| if (presentValue) set(newState, path, presentValue); | ||
| }); | ||
| return newState; | ||
| } | ||
|
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| // Given a config object, returns function which compute new state after | ||
| // undoing/redoing/storing present as required by action. | ||
| export default function createUndoReducer(config: UndoHistoryConfig) { | ||
| return <T: Object>(previousState: T, presentState: T, action: FSA) => { | ||
| // Calculate un/redone history | ||
| const undoHistoryState = presentState[config.reducerName]; | ||
| const updatedHistory = computeUndoStacks( | ||
| undoHistoryState, | ||
| action, | ||
| previousState, | ||
| presentState, | ||
| config, | ||
| ); | ||
| const updatedState = { ...presentState, [config.reducerName]: updatedHistory }; | ||
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| // Applies undo and redo actions on overall app state | ||
| // Applies updatedHistory.present to state if action.type === {UNDO,REDO} | ||
| // Assumes updatedHistory.present is the final present state | ||
| if ((action.type === UNDO || action.type === REDO) && updatedHistory.present) { | ||
| return mergePresent(updatedState, updatedHistory.present, config.whitelist); | ||
| } | ||
| return updatedState; | ||
| }; | ||
| } |
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