feat: extract commit generation logic into dedicated module

Moves all commit message generation logic from the main extension
file into a new `commitGenerator.ts` module, including:

- Multi-repo orchestration with QuickPick selection
- Filtering repositories that have changes
- Single-repository generation with progress reporting
- Streaming AI response handling with abort support
- Developer note inclusion in prompts
- Diff truncation based on configurable max size

src/commitGenerator.ts

@@ -0,0 +1,162 @@
+import * as path from "path"
+import * as vscode from "vscode"
+import { getGitDiffStagedFirst } from "./git"
+import { createProvider } from "./providers"
+
+let abortController: AbortController | undefined
+
+export async function generateCommitMsg(scm?: vscode.SourceControl): Promise<void> {
+  try {
+    const gitExtension = vscode.extensions.getExtension("vscode.git")?.exports
+    if (!gitExtension) {
+      throw new Error("Git extension not found")
+    }
+
+    const git = gitExtension.getAPI(1)
+    if (git.repositories.length === 0) {
+      throw new Error("No Git repositories available")
+    }
+
+    // If invoked from SCM panel button, a specific repo is provided
+    if (scm) {
+      const repository = git.getRepository(scm.rootUri)
+      if (!repository) {
+        throw new Error("Repository not found for the selected SCM")
+      }
+      await generateForRepository(repository)
+      return
+    }
+
+    await orchestrateMultiRepo(git.repositories)
+  } catch (error) {
+    const msg = error instanceof Error ? error.message : String(error)
+    vscode.window.showErrorMessage(`[Zemit] ${msg}`)
+  }
+}
+
+export function abortGeneration(): void {
+  abortController?.abort()
+  vscode.commands.executeCommand("setContext", "aiCommit.isGenerating", false)
+}
+
+// ─── Multi-repo orchestration ─────────────────────────────────────────────────
+
+async function orchestrateMultiRepo(repos: unknown[]): Promise<void> {
+  const reposWithChanges = await filterReposWithChanges(repos)
+
+  if (reposWithChanges.length === 0) {
+    vscode.window.showInformationMessage("[Zemit] No changes found in any repository.")
+    return
+  }
+
+  if (reposWithChanges.length === 1) {
+    await generateForRepository(reposWithChanges[0])
+    return
+  }
+
+  const items = reposWithChanges.map((repo: any) => ({
+    label: repo.rootUri.fsPath.split(path.sep).pop() || repo.rootUri.fsPath,
+    description: repo.rootUri.fsPath,
+    repo,
+  }))
+
+  items.unshift({
+    label: "$(git-commit) All repositories with changes",
+    description: `Generate for ${reposWithChanges.length} repositories`,
+    repo: null as any,
+  })
+
+  const selection = await vscode.window.showQuickPick(items, {
+    placeHolder: "Select a repository to generate a commit message for",
+  })
+
+  if (!selection) return
+
+  if (selection.repo === null) {
+    for (const repo of reposWithChanges) {
+      await generateForRepository(repo).catch(() => {})
+    }
+  } else {
+    await generateForRepository(selection.repo)
+  }
+}
+
+async function filterReposWithChanges(repos: unknown[]): Promise<unknown[]> {
+  const result = []
+  for (const repo of repos) {
+    try {
+      const diff = await getGitDiffStagedFirst((repo as any).rootUri.fsPath)
+      if (diff) result.push(repo)
+    } catch {
+      // repo has no changes — skip
+    }
+  }
+  return result
+}
+
+// ─── Generation for a single repository ──────────────────────────────────────
+
+async function generateForRepository(repository: any): Promise<void> {
+  const repoPath = repository.rootUri.fsPath
+  const repoName = repoPath.split(path.sep).pop() || "repository"
+  const diff = await getGitDiffStagedFirst(repoPath)
+
+  await vscode.window.withProgress(
+    {
+      location: vscode.ProgressLocation.SourceControl,
+      title: `Zemit: Generating commit message for ${repoName}...`,
+      cancellable: true,
+    },
+    (_progress, token) => performGeneration(repository.inputBox, diff, token),
+  )
+}
+
+async function performGeneration(
+  inputBox: any,
+  diff: string,
+  token: vscode.CancellationToken,
+): Promise<void> {
+  const config = vscode.workspace.getConfiguration("aiCommit")
+  const maxDiffSize = config.get<number>("maxDiffSize", 5000)
+  const style = config.get<string>("commitStyle", "conventional")
+
+  const truncatedDiff =
+    diff.length > maxDiffSize ? diff.substring(0, maxDiffSize) + "\n\n[Diff truncated due to size]" : diff
+
+  // Include any existing user note in the prompt
+  const existingNote = inputBox.value?.trim() || ""
+
+  let prompt = truncatedDiff
+  if (existingNote) {
+    prompt = `Developer note (use if relevant): ${existingNote}\n\n${prompt}`
+  }
+
+  abortController = new AbortController()
+  token.onCancellationRequested(() => abortController?.abort())
+
+  try {
+    await vscode.commands.executeCommand("setContext", "aiCommit.isGenerating", true)
+
+    const provider = createProvider(config)
+    let response = ""
+
+    for await (const chunk of provider.generateCommitMessage(prompt, style, abortController.signal)) {
+      if (token.isCancellationRequested) break
+      response += chunk
+      inputBox.value = cleanCommitMessage(response)
+    }
+
+    if (!inputBox.value) {
+      throw new Error("The AI returned an empty response")
+    }
+  } finally {
+    await vscode.commands.executeCommand("setContext", "aiCommit.isGenerating", false)
+  }
+}
+
+function cleanCommitMessage(str: string): string {
+  return str
+    .trim()
+    .replace(/^```[^\n]*\n?|```$/g, "")
+    .trim()
+}