vscode-cowriting-plugin/src/diffViewController.ts

/**
 * DiffViewController — F6 baseline data layer (spec §6.4/§6.7). Owns the baseline
 * lifecycle (initialize at first sight / advance at every machine landing / pin
 * on demand) and serves it to F7/F10 via `getBaseline` + the additive
 * `onDidChangeBaseline` event. A pure data layer: never mutates the document,
 * sidecar, or attribution state (INV-19).
 *
 * The F6 two-pane `vscode.diff` *view* (toggle UI + the `cowriting-baseline:`
 * virtual document) was removed in #34 once F10 made the rendered preview the
 * single review surface; only the baseline store survives here (spec §6.7).
 *
 * The baseline works on ANY text document, not just workspace files — it needs no
 * `.threads/` sidecar, only a stable doc identity + a storage home. So it has
 * its OWN diffable predicate (any `file:` or `untitled:` doc), decoupled from
 * F2's workspace `isTracked`. Persistable docs (`file:`) keep their baseline in
 * VS Code's per-extension GLOBAL storage keyed by a hash of the document URI;
 * untitled buffers have no durable identity, so their baseline is in-memory
 * only (lost on reload) — the same degrade the storage-unavailable path uses.
 */
import { createHash } from "node:crypto";
import * as vscode from "vscode";
import { BaselineStore, type Baseline, type BaselineReason } from "./baselineStore";

export class DiffViewController implements vscode.Disposable {
  private readonly disposables: vscode.Disposable[] = [];
  /** Source of truth for the baseline, keyed by `document.uri.toString()`. */
  private readonly baselines = new Map<string, Baseline>();
  /** F7 (additive): fires on every baseline capture (open / advance / pin) so
   *  the track-changes preview refreshes without polling. Carries the real
   *  document URI. */
  private readonly onDidChangeBaselineEmitter = new vscode.EventEmitter<{ uri: string }>();
  readonly onDidChangeBaseline = this.onDidChangeBaselineEmitter.event;
  private storageWarned = false;

  constructor(private readonly store: BaselineStore | null) {
    this.disposables.push(
      this.onDidChangeBaselineEmitter,
      vscode.commands.registerCommand("cowriting.pinDiffBaseline", () =>
        this.pinCommand(vscode.window.activeTextEditor),
      ),
      // F6 captures a baseline for any diffable doc the moment it is first seen,
      // independent of the workspace gate (so "opened" is the open-time text).
      vscode.workspace.onDidOpenTextDocument((d) => this.ensureBaseline(d)),
    );
    for (const d of vscode.workspace.textDocuments) this.ensureBaseline(d);
  }

  // ---- diffability / identity --------------------------------------------------------

  /** Any text document F6 tracks a baseline for: a saved file OR an unsaved buffer. */
  private isDiffable(document: vscode.TextDocument): boolean {
    return document.uri.scheme === "file" || document.uri.scheme === "untitled";
  }
  /** Only `file:` docs have a durable identity to persist a baseline against. */
  private isPersistable(document: vscode.TextDocument): boolean {
    return document.uri.scheme === "file";
  }
  /** In-memory map key — the full document URI. */
  private uriKey(document: vscode.TextDocument): string {
    return document.uri.toString();
  }
  /** Filesystem-safe storage key for a persistable doc: sha256 of its URI. */
  private storageKey(uriKey: string): string {
    return createHash("sha256").update(uriKey).digest("hex");
  }

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

  /** First sight of a diffable doc: load the stored baseline, else capture `opened`. */
  ensureBaseline(document: vscode.TextDocument): void {
    if (!this.isDiffable(document)) return;
    const key = this.uriKey(document);
    if (this.baselines.has(key)) return;
    if (this.store && this.isPersistable(document)) {
      try {
        const stored = this.store.load(this.storageKey(key));
        if (stored) {
          this.baselines.set(key, 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.isDiffable(document)) return;
    this.capture(document, "machine-landing");
  }

  /** Human pin: baseline := now; the preview's change-marks empty (left = right). */
  pin(document: vscode.TextDocument): void {
    if (!this.isDiffable(document)) return;
    this.capture(document, "pinned");
  }

  /** Capture buffer text at this epoch, persist (if persistable), notify F7/F10. */
  private capture(document: vscode.TextDocument, reason: BaselineReason): void {
    const key = this.uriKey(document);
    const baseline: Baseline = { uri: key, text: document.getText(), capturedAt: new Date().toISOString(), reason };
    this.baselines.set(key, baseline);
    if (this.store && this.isPersistable(document)) {
      try {
        this.store.save(this.storageKey(key), baseline);
      } catch {
        this.warnStorageOnce();
      }
    }
    this.onDidChangeBaselineEmitter.fire({ uri: key });
  }

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

  private pinCommand(editor: vscode.TextEditor | undefined): void {
    if (!editor || !this.isDiffable(editor.document)) {
      void vscode.window.showWarningMessage("Cowriting: focus a text editor to pin its review baseline.");
      return;
    }
    this.pin(editor.document);
  }

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

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

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