chore: Added changes for discard (#38152)

## Description
- Added implementation for discard

Fixes #37438

## Automation

/ok-to-test tags="@tag.Git"

### 🔍 Cypress test results
<!-- This is an auto-generated comment: Cypress test results  -->
> [!TIP]
> 🟢 🟢 🟢 All cypress tests have passed! 🎉 🎉 🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/12314835405>
> Commit: 0db248a
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=12314835405&attempt=1"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.Git`
> Spec:
> <hr>Fri, 13 Dec 2024 12:18:45 UTC
<!-- end of auto-generated comment: Cypress test results  -->


## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [ ] No


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Introduced a method to discard changes associated with a specified
branched artifact.
  - Added functionality to recreate artifact JSON from the last commit.

- **Bug Fixes**
- Enhanced handling of lock requirements in Git operations, allowing for
null values.

- **Documentation**
- Updated method signatures and added descriptions for new
functionalities.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

app/server/appsmith-server/src/main/java/com/appsmith/server/git/GitRedisUtils.java

@@ -69,7 +69,7 @@ public Mono<Boolean> releaseFileLock(String defaultApplicationId) {
      * @return : Boolean for whether the lock is acquired
      */
     // TODO @Manish add artifactType reference in incoming prs.
-    public Mono<Boolean> acquireGitLock(String baseArtifactId, String commandName, boolean isLockRequired) {
+    public Mono<Boolean> acquireGitLock(String baseArtifactId, String commandName, Boolean isLockRequired) {
         if (!Boolean.TRUE.equals(isLockRequired)) {
             return Mono.just(Boolean.TRUE);
         }

app/server/appsmith-server/src/main/java/com/appsmith/server/git/central/CentralGitServiceCE.java

@@ -31,4 +31,6 @@ Mono<String> fetchRemoteChanges(
             ArtifactType artifactType,
             GitType gitType,
             RefType refType);
+
+    Mono<? extends Artifact> discardChanges(String branchedArtifactId, ArtifactType artifactType, GitType gitType);
 }

app/server/appsmith-server/src/main/java/com/appsmith/server/git/central/CentralGitServiceCEImpl.java

@@ -1112,4 +1112,84 @@ private Mono<? extends Artifact> updateArtifactWithGitMetadataGivenPermission(
                 .getArtifactHelper(artifact.getArtifactType())
                 .saveArtifact(artifact);
     }
+
+    /**
+     * Resets the artifact to last commit, all uncommitted changes are lost in the process.
+     * @param branchedArtifactId : id of the branchedArtifact
+     * @param artifactType type of the artifact
+     * @param gitType what is the intended implementation type
+     * @return : a publisher of an artifact.
+     */
+    @Override
+    public Mono<? extends Artifact> discardChanges(
+            String branchedArtifactId, ArtifactType artifactType, GitType gitType) {
+
+        if (!hasText(branchedArtifactId)) {
+            return Mono.error(new AppsmithException(AppsmithError.INVALID_PARAMETER, FieldName.ARTIFACT_ID));
+        }
+
+        GitArtifactHelper<?> gitArtifactHelper = gitArtifactHelperResolver.getArtifactHelper(artifactType);
+        AclPermission artifactEditPermission = gitArtifactHelper.getArtifactEditPermission();
+
+        Mono<? extends Artifact> branchedArtifactMonoCached =
+                gitArtifactHelper.getArtifactById(branchedArtifactId, artifactEditPermission);
+
+        Mono<? extends Artifact> recreatedArtifactFromLastCommit;
+
+        // Rehydrate the artifact from local file system
+        recreatedArtifactFromLastCommit = branchedArtifactMonoCached
+                .flatMap(branchedArtifact -> {
+                    GitArtifactMetadata branchedGitData = branchedArtifact.getGitArtifactMetadata();
+                    if (branchedGitData == null || !hasText(branchedGitData.getDefaultArtifactId())) {
+                        return Mono.error(
+                                new AppsmithException(AppsmithError.INVALID_GIT_CONFIGURATION, GIT_CONFIG_ERROR));
+                    }
+
+                    return Mono.just(branchedArtifact)
+                            .doFinally(signalType -> gitRedisUtils.acquireGitLock(
+                                    branchedGitData.getDefaultArtifactId(),
+                                    GitConstants.GitCommandConstants.DISCARD,
+                                    TRUE));
+                })
+                .flatMap(branchedArtifact -> {
+                    GitArtifactMetadata branchedGitData = branchedArtifact.getGitArtifactMetadata();
+                    ArtifactJsonTransformationDTO jsonTransformationDTO = new ArtifactJsonTransformationDTO();
+                    // Because this operation is only valid for branches
+                    jsonTransformationDTO.setArtifactType(artifactType);
+                    jsonTransformationDTO.setRefType(RefType.BRANCH);
+                    jsonTransformationDTO.setWorkspaceId(branchedArtifact.getWorkspaceId());
+                    jsonTransformationDTO.setBaseArtifactId(branchedGitData.getDefaultArtifactId());
+                    jsonTransformationDTO.setRefName(branchedGitData.getRefName());
+                    jsonTransformationDTO.setRepoName(branchedGitData.getRepoName());
+
+                    GitHandlingService gitHandlingService = gitHandlingServiceResolver.getGitHandlingService(gitType);
+
+                    return gitHandlingService
+                            .recreateArtifactJsonFromLastCommit(jsonTransformationDTO)
+                            .onErrorResume(throwable -> {
+                                log.error("Git recreate ArtifactJsonFailed : {}", throwable.getMessage());
+                                return Mono.error(
+                                        new AppsmithException(
+                                                AppsmithError.GIT_ACTION_FAILED,
+                                                "discard changes",
+                                                "Please create a new branch and resolve conflicts in the remote repository before proceeding."));
+                            })
+                            .flatMap(artifactExchangeJson -> importService.importArtifactInWorkspaceFromGit(
+                                    branchedArtifact.getWorkspaceId(),
+                                    branchedArtifact.getId(),
+                                    artifactExchangeJson,
+                                    branchedGitData.getBranchName()))
+                            // Update the last deployed status after the rebase
+                            .flatMap(importedArtifact -> gitArtifactHelper.publishArtifact(importedArtifact, true));
+                })
+                .flatMap(branchedArtifact -> gitAnalyticsUtils
+                        .addAnalyticsForGitOperation(AnalyticsEvents.GIT_DISCARD_CHANGES, branchedArtifact, null)
+                        .doFinally(signalType -> gitRedisUtils.releaseFileLock(
+                                branchedArtifact.getGitArtifactMetadata().getDefaultArtifactId(), TRUE)))
+                .name(GitSpan.OPS_DISCARD_CHANGES)
+                .tap(Micrometer.observation(observationRegistry));
+
+        return Mono.create(sink ->
+                recreatedArtifactFromLastCommit.subscribe(sink::success, sink::error, null, sink.currentContext()));
+    }
 }

app/server/appsmith-server/src/main/java/com/appsmith/server/git/central/GitHandlingServiceCE.java

@@ -58,4 +58,7 @@ Mono<Tuple2<? extends Artifact, String>> commitArtifact(
             Artifact branchedArtifact, CommitDTO commitDTO, ArtifactJsonTransformationDTO jsonTransformationDTO);
 
     Mono<String> fetchRemoteChanges(ArtifactJsonTransformationDTO jsonTransformationDTO, GitAuth gitAuth);
+
+    Mono<? extends ArtifactExchangeJson> recreateArtifactJsonFromLastCommit(
+            ArtifactJsonTransformationDTO jsonTransformationDTO);
 }

app/server/appsmith-server/src/main/java/com/appsmith/server/git/fs/GitFSServiceCEImpl.java

@@ -598,4 +598,23 @@ public Mono<String> fetchRemoteChanges(ArtifactJsonTransformationDTO jsonTransfo
 
         return checkoutBranchMono.then(Mono.defer(() -> fetchRemoteMono));
     }
+
+    @Override
+    public Mono<? extends ArtifactExchangeJson> recreateArtifactJsonFromLastCommit(
+            ArtifactJsonTransformationDTO jsonTransformationDTO) {
+
+        String workspaceId = jsonTransformationDTO.getWorkspaceId();
+        String baseArtifactId = jsonTransformationDTO.getBaseArtifactId();
+        String repoName = jsonTransformationDTO.getRepoName();
+        String refName = jsonTransformationDTO.getRefName();
+
+        ArtifactType artifactType = jsonTransformationDTO.getArtifactType();
+        GitArtifactHelper<?> gitArtifactHelper = gitArtifactHelperResolver.getArtifactHelper(artifactType);
+        Path repoSuffix = gitArtifactHelper.getRepoSuffixPath(workspaceId, baseArtifactId, repoName);
+
+        return fsGitHandler.rebaseBranch(repoSuffix, refName).flatMap(rebaseStatus -> {
+            return commonGitFileUtils.reconstructArtifactExchangeJsonFromGitRepoWithAnalytics(
+                    workspaceId, baseArtifactId, repoName, refName, artifactType);
+        });
+    }
 }