vscode-cowriting-plugin/src/diffViewController.ts

/**
 * DiffViewController — the baseline router (native-surfaces migration, spec
 * §6.4, INV-7). Resolves each coedited document's review baseline to one of two
 * modes: **head** (git-tracked — the baseline is the `HEAD` blob, re-read on
 * every commit, never persisted) or **snapshot** (untracked/no-repo — captured
 * on coediting-entry, re-pinned on demand by "Mark Changes as Reviewed").
 * Baselines are established ONLY for documents the CoeditingRegistry has
 * entered (INV-10) — opening a file no longer captures one (the retired
 * `ensureBaseline`/#17 behavior). The shipped machine-landing advance (#48,
 * INV-18) is retired too: a landed Claude edit stays a visible change-since-
 * baseline until the file is committed (head mode) or reviewed (snapshot
 * mode) — spec INV-7's note, D21. 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 SNAPSHOT
 * baseline in VS Code's per-extension GLOBAL storage keyed by a hash of the
 * document URI (INV-7: head-mode baselines are storage-free — never
 * persisted); 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";
import type { GitBaselineAdapter } from "./gitBaseline";
import type { CoeditingRegistry } from "./coeditingRegistry";

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>();
  /** Which mode each established document resolved to (INV-7). */
  private readonly modes = new Map<string, "head" | "snapshot">();
  /** F7 (additive): fires on every baseline capture (establish / head-refresh /
   *  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,
    private readonly git: GitBaselineAdapter,
    registry: CoeditingRegistry,
  ) {
    this.disposables.push(
      this.onDidChangeBaselineEmitter,
      vscode.commands.registerCommand("cowriting.markReviewed", () =>
        this.pinCommand(vscode.window.activeTextEditor),
      ),
      // INV-10: a baseline is established only once its document ENTERS
      // coediting; exiting keeps the stored baseline as-is (PUC-7).
      registry.onDidChange(({ uri, coediting }) => {
        if (!coediting) return;
        const doc = vscode.workspace.textDocuments.find((d) => d.uri.toString() === uri);
        if (doc) void this.establish(doc);
      }),
      // A commit on a watched repo may advance a head-mode baseline (D13).
      git.onDidChangeHead(() => void this.refreshHeadBaselines()),
    );
    // Restore already-coediting documents (e.g. after an extension host reload).
    for (const key of registry.list()) {
      const doc = vscode.workspace.textDocuments.find((d) => d.uri.toString() === key);
      if (doc) void this.establish(doc);
    }
  }

  // ---- 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 SNAPSHOT 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, INV-7) -----------------------------------------------

  /**
   * Resolve this document's baseline mode and (re)establish its baseline.
   * git-tracked (a HEAD blob resolves) → **head** mode, baseline = HEAD, never
   * persisted. Otherwise → **snapshot** mode: load a previously-stored
   * snapshot, else capture the buffer now (`"entered"`). Called once when a
   * document enters coediting (registry.enter) and at startup for documents
   * already coediting.
   */
  async establish(document: vscode.TextDocument): Promise<void> {
    if (!this.isDiffable(document)) return;
    const key = this.uriKey(document);
    const head = await this.git.headFor(document.uri);
    if (head) {
      this.modes.set(key, "head");
      this.setBaseline(key, head.text, "head");
      return;
    }
    this.modes.set(key, "snapshot");
    if (this.store && this.isPersistable(document)) {
      const stored = this.tryLoad(key); // existing load path, legacy reasons normalized
      if (stored) {
        this.baselines.set(key, stored);
        this.fire(key);
        return;
      }
    }
    this.capture(document, "entered");
  }

  /** The mode a document's baseline resolved to, or undefined before `establish`. */
  modeOf(uriString: string): "head" | "snapshot" | undefined {
    return this.modes.get(uriString);
  }

  /** Re-read HEAD for every head-mode document; a commit advances the baseline (D13). */
  private async refreshHeadBaselines(): Promise<void> {
    for (const [key, mode] of this.modes) {
      if (mode !== "head") continue;
      const doc = vscode.workspace.textDocuments.find((d) => d.uri.toString() === key);
      if (!doc) continue;
      const head = await this.git.headFor(doc.uri);
      if (head && head.text !== this.baselines.get(key)?.text) {
        this.setBaseline(key, head.text, "head"); // commit advanced the baseline (D13)
      }
    }
  }

  /** Human pin ("Mark Changes as Reviewed", D14): snapshot mode only — a
   *  git-tracked (head-mode) baseline advances only by commit. */
  pin(document: vscode.TextDocument): void {
    if (!this.isDiffable(document)) return;
    const key = this.uriKey(document);
    if (this.modes.get(key) !== "snapshot") {
      void vscode.window.showWarningMessage(
        "Cowriting: this document is git-tracked — commit to advance the baseline.",
      );
      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)) {
      this.trySave(key, baseline);
    }
    this.fire(key);
  }

  /** Set a baseline from resolved text directly (head mode — no document buffer read). */
  private setBaseline(key: string, text: string, reason: BaselineReason): void {
    const baseline: Baseline = { uri: key, text, capturedAt: new Date().toISOString(), reason };
    this.baselines.set(key, baseline);
    // head-mode baselines are storage-free (INV-7); persist only snapshots.
    if (reason !== "head" && this.store) this.trySave(key, baseline);
    this.fire(key);
  }

  private tryLoad(key: string): Baseline | null {
    try {
      return this.store!.load(this.storageKey(key));
    } catch {
      this.warnStorageOnce();
      return null;
    }
  }

  private trySave(key: string, baseline: Baseline): void {
    try {
      this.store!.save(this.storageKey(key), baseline);
    } catch {
      this.warnStorageOnce();
    }
  }

  private fire(key: string): void {
    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 mark its changes as reviewed.");
      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();
  }
}