techdocs: Replace nodegit with isomorphic-git

TechDocs needs 4 functions from the git library
1. To clone 2. To get the commit timestamp for HEAD 3. To fetch 4. To merge two branches

Created necessary commands in the new SCM client and reordered them alphabetically for convenience

packages/backend-common/src/scm/git.ts

@@ -37,6 +37,45 @@ class SCM {
     },
   ) {}
 
+  async add({ dir, filepath }: { dir: string; filepath: string }) {
+    this.config.logger?.info(`Adding file {dir=${dir},filepath=${filepath}}`);
+
+    return git.add({ fs, dir, filepath });
+  }
+
+  async addRemote({
+    dir,
+    url,
+    remoteName,
+  }: {
+    dir: string;
+    remoteName: string;
+    url: string;
+  }) {
+    this.config.logger?.info(
+      `Creating new remote {dir=${dir},remoteName=${remoteName},url=${url}}`,
+    );
+    return git.addRemote({ fs, dir, remote: remoteName, url });
+  }
+
+  async commit({
+    dir,
+    message,
+    author,
+    committer,
+  }: {
+    dir: string;
+    message: string;
+    author: { name: string; email: string };
+    committer: { name: string; email: string };
+  }) {
+    this.config.logger?.info(
+      `Committing file to repo {dir=${dir},message=${message}}`,
+    );
+
+    return git.commit({ fs, dir, message, author, committer });
+  }
+
   async clone({ url, dir }: { url: string; dir: string }) {
     this.config.logger?.info(`Cloning repo {dir=${dir},url=${url}}`);
     return git.clone({
@@ -62,6 +101,39 @@ class SCM {
     });
   }
 
+  // https://isomorphic-git.org/docs/en/currentBranch
+  async currentBranch({ dir, fullName }: { dir: string; fullName?: boolean }) {
+    const fullname = fullName ?? false;
+    return git.currentBranch({ fs, dir, fullname });
+  }
+
+  // https://isomorphic-git.org/docs/en/fetch
+  async fetch({ dir, remote }: { dir: string; remote?: string }) {
+    const remoteValue = remote ?? 'origin';
+    this.config.logger?.info(
+      `Fetching remote=${remoteValue} for repository {dir=${dir}}`,
+    );
+    return git.fetch({
+      fs,
+      http,
+      dir,
+      remote: remoteValue,
+      onProgress: event => {
+        const total = event.total
+          ? `${Math.round((event.loaded / event.total) * 100)}%`
+          : event.loaded;
+        this.config.logger?.info(`status={${event.phase},total={${total}}}`);
+      },
+      headers: {
+        'user-agent': 'git/@isomorphic-git',
+      },
+      onAuth: () => ({
+        username: this.config.username,
+        password: this.config.password,
+      }),
+    });
+  }
+
   async init({ dir }: { dir: string }) {
     this.config.logger?.info(`Init git repository {dir=${dir}}`);
 
@@ -71,43 +143,21 @@ class SCM {
     });
   }
 
-  async add({ dir, filepath }: { dir: string; filepath: string }) {
-    this.config.logger?.info(`Adding file {dir=${dir},filepath=${filepath}}`);
-
-    return git.add({ fs, dir, filepath });
-  }
-
-  async commit({
+  // https://isomorphic-git.org/docs/en/merge
+  async merge({
     dir,
-    message,
-    author,
-    committer,
+    headBranch,
+    baseBranch,
   }: {
     dir: string;
-    message: string;
-    author: { name: string; email: string };
-    committer: { name: string; email: string };
+    headBranch: string;
+    baseBranch?: string;
   }) {
     this.config.logger?.info(
-      `Committing file to repo {dir=${dir},message=${message}}`,
+      `Merging branch '${headBranch}' into '${baseBranch}' for repository {dir=${dir}}`,
     );
-
-    return git.commit({ fs, dir, message, author, committer });
-  }
-
-  async addRemote({
-    dir,
-    url,
-    remoteName,
-  }: {
-    dir: string;
-    remoteName: string;
-    url: string;
-  }) {
-    this.config.logger?.info(
-      `Creating new remote {dir=${dir},remoteName=${remoteName},url=${url}}`,
-    );
-    return git.addRemote({ fs, dir, remote: remoteName, url });
+    // If baseBranch is undefined, current branch is used.
+    return git.merge({ fs, dir, ours: baseBranch, theirs: headBranch });
   }
 
   async push({ dir, remoteName }: { dir: string; remoteName: string }) {
@@ -134,6 +184,16 @@ class SCM {
       }),
     });
   }
+
+  // https://isomorphic-git.org/docs/en/readCommit
+  async readCommit({ dir, sha }: { dir: string; sha: string }) {
+    return git.readCommit({ fs, dir, oid: sha });
+  }
+
+  // https://isomorphic-git.org/docs/en/resolveRef
+  async resolveRef({ dir, ref }: { dir: string; ref: string }) {
+    return git.resolveRef({ fs, dir, ref });
+  }
 }
 
 // TODO(blam): This could potentially become something like for URL