vscode-cowriting-plugin/src/diffViewController.ts

/**
 * DiffViewController — F6 diff-view toggle (spec §6.2/§6.4). Owns the baseline
 * lifecycle (initialize at first track / advance at every machine landing / pin
 * on demand), serves the baseline as a readonly `cowriting-baseline:` virtual
 * document, and toggles a native vscode.diff (baseline left, the LIVE document
 * right). A pure view: never mutates the document, sidecar, or attribution
 * state (INV-19). Baselines persist via the vscode-free BaselineStore; if
 * storage is unavailable the controller degrades to in-memory baselines + one
 * warning (reload survival is lost; the toggle still works) — §6.5 PUC-5.
 */
import * as path from "node:path";
import * as vscode from "vscode";
import { BaselineStore, type Baseline, type BaselineReason } from "./baselineStore";

export const BASELINE_SCHEME = "cowriting-baseline";

export class DiffViewController implements vscode.Disposable {
  private readonly disposables: vscode.Disposable[] = [];
  /** Source of truth for the content provider; mirrors what the store persists. */
  private readonly baselines = new Map<string, Baseline>();
  private readonly onDidChangeEmitter = new vscode.EventEmitter<vscode.Uri>();
  private storageWarned = false;

  constructor(
    private readonly store: BaselineStore | null,
    private readonly rootDir: string,
  ) {
    const provider: vscode.TextDocumentContentProvider = {
      onDidChange: this.onDidChangeEmitter.event,
      provideTextDocumentContent: (uri) => {
        const docPath = this.docPathFromBaselineUri(uri);
        return this.baselines.get(docPath)?.text ?? "";
      },
    };
    this.disposables.push(
      this.onDidChangeEmitter,
      vscode.workspace.registerTextDocumentContentProvider(BASELINE_SCHEME, provider),
      vscode.commands.registerCommand("cowriting.toggleDiffView", () =>
        this.toggle(vscode.window.activeTextEditor),
      ),
      vscode.commands.registerCommand("cowriting.pinDiffBaseline", () =>
        this.pinCommand(vscode.window.activeTextEditor),
      ),
    );
  }

  // ---- tracking / uri helpers --------------------------------------------------------

  private isTracked(document: vscode.TextDocument): boolean {
    return document.uri.scheme === "file" && document.uri.fsPath.startsWith(this.rootDir);
  }
  private docPathOf(uri: vscode.Uri): string {
    return vscode.workspace.asRelativePath(uri, false);
  }
  /** The readonly virtual-doc URI whose content the provider serves for this doc. */
  private baselineUri(docPath: string): vscode.Uri {
    return vscode.Uri.from({ scheme: BASELINE_SCHEME, path: "/" + docPath });
  }
  private docPathFromBaselineUri(uri: vscode.Uri): string {
    return uri.path.replace(/^\//, "");
  }

  // ---- baseline lifecycle (§6.4) -----------------------------------------------------

  /** First sight of a tracked doc: load the stored baseline, else capture `opened`. */
  ensureBaseline(document: vscode.TextDocument): void {
    if (!this.isTracked(document)) return;
    const docPath = this.docPathOf(document.uri);
    if (this.baselines.has(docPath)) return;
    if (this.store) {
      try {
        const stored = this.store.load(docPath);
        if (stored) {
          this.baselines.set(docPath, stored);
          return;
        }
      } catch {
        this.warnStorageOnce();
      }
    }
    this.capture(document, "opened");
  }

  /** Machine landing (INV-18): re-capture so landed text never shows as a change. */
  advance(document: vscode.TextDocument): void {
    if (!this.isTracked(document)) return;
    this.capture(document, "machine-landing");
  }

  /** Human pin: baseline := now; the open diff visibly empties (left = right). */
  pin(document: vscode.TextDocument): void {
    if (!this.isTracked(document)) return;
    this.capture(document, "pinned");
  }

  /** Capture buffer text at this epoch, persist, and refresh any open diff's left side. */
  private capture(document: vscode.TextDocument, reason: BaselineReason): void {
    const docPath = this.docPathOf(document.uri);
    const baseline: Baseline = {
      docPath,
      text: document.getText(),
      capturedAt: new Date().toISOString(),
      reason,
    };
    this.baselines.set(docPath, baseline);
    if (this.store) {
      try {
        this.store.save(docPath, baseline);
      } catch {
        this.warnStorageOnce();
      }
    }
    // An open diff re-requests the left side when its baseline URI changes.
    this.onDidChangeEmitter.fire(this.baselineUri(docPath));
  }

  private warnStorageOnce(): void {
    if (this.storageWarned) return;
    this.storageWarned = true;
    void vscode.window.showWarningMessage(
      "Cowriting: diff-view storage is unavailable — baselines are kept in memory only and won't survive a reload.",
    );
  }

  // ---- commands (toggle implemented in SLICE-3, Task 4) ------------------------------

  private pinCommand(editor: vscode.TextEditor | undefined): void {
    if (!editor || !this.isTracked(editor.document)) {
      void vscode.window.showWarningMessage("Cowriting: open a tracked workspace document to pin its diff baseline.");
      return;
    }
    this.pin(editor.document);
  }

  // ---- test-facing surface (§6.4) ----------------------------------------------------

  getBaseline(docPath: string): { text: string; reason: BaselineReason; capturedAt: string } | undefined {
    const b = this.baselines.get(docPath);
    return b ? { text: b.text, reason: b.reason, capturedAt: b.capturedAt } : undefined;
  }
  /** Absolute on-disk path of this doc's persisted baseline, or undefined if in-memory. */
  baselineFilePath(docPath: string): string | undefined {
    return this.store?.baselinePath(docPath);
  }

  // ---- toggle UX (§6.5 PUC-1) --------------------------------------------------------

  /**
   * If this doc's baseline diff is the active/open tab → close it and reveal the
   * normal editor; if the active editor is a tracked doc with no diff open →
   * open vscode.diff (baseline left, the live document right). Untracked → warn,
   * no diff.
   */
  private async toggle(editor: vscode.TextEditor | undefined): Promise<void> {
    if (!editor || !this.isTracked(editor.document)) {
      void vscode.window.showWarningMessage(
        "Cowriting: open a tracked workspace document to toggle its diff view.",
      );
      return;
    }
    const document = editor.document;
    const docPath = this.docPathOf(document.uri);
    const openTab = this.findDiffTab(document.uri);
    if (openTab) {
      await vscode.window.tabGroups.close(openTab);
      await vscode.window.showTextDocument(document, { preview: false });
      return;
    }
    this.ensureBaseline(document);
    const baseline = this.baselines.get(docPath)!;
    const title = `${path.basename(docPath)} — my changes since ${this.epochLabel(baseline)}`;
    await vscode.commands.executeCommand(
      "vscode.diff",
      this.baselineUri(docPath),
      document.uri,
      title,
      { preview: false },
    );
  }

  /** The open baseline-diff tab for this document, if any. */
  private findDiffTab(modified: vscode.Uri): vscode.Tab | undefined {
    for (const group of vscode.window.tabGroups.all) {
      for (const tab of group.tabs) {
        const input = tab.input;
        if (
          input instanceof vscode.TabInputTextDiff &&
          input.original.scheme === BASELINE_SCHEME &&
          input.modified.toString() === modified.toString()
        ) {
          return tab;
        }
      }
    }
    return undefined;
  }

  /** Human-readable epoch for the diff tab title (§5 / §6.5). */
  private epochLabel(baseline: Baseline): string {
    const time = new Date(baseline.capturedAt).toLocaleTimeString();
    switch (baseline.reason) {
      case "opened":
        return `opened ${time}`;
      case "machine-landing":
        return `Claude landed ${time}`;
      case "pinned":
        return `pinned ${time}`;
    }
  }

  /**
   * Test-facing (§6.4): is this doc's baseline diff currently open in any tab
   * group? The diff's `modified` side is the document's own file: URI.
   */
  isDiffOpen(docPath: string): boolean {
    return this.findDiffTab(vscode.Uri.file(path.join(this.rootDir, docPath))) !== undefined;
  }

  dispose(): void {
    for (const d of this.disposables) d.dispose();
  }
}