import * as vscode from "vscode";
import { ActorSnapshot, formatSnapshot } from "./protocol";
import { canEditActor, parseSnapshotEdit, SnapshotEdit } from "./snapshotEdits";

interface DocumentSnapshot {
  session: number;
  endpoint: string;
  actor: ActorSnapshot;
  capturedAt: string;
  connected: boolean;
  removed: boolean;
  mtime: number;
}

export class SnapshotDocuments implements vscode.FileSystemProvider {
  private readonly changes = new vscode.EventEmitter<vscode.FileChangeEvent[]>();
  readonly onDidChangeFile = this.changes.event;
  private readonly documents = new Map<string, DocumentSnapshot>();
  private readonly baselines = new Map<string, string>();

  constructor(
    private readonly save: (session: number, actor: string, edit: SnapshotEdit) => Promise<void>,
    private readonly warn: (message: string) => void,
  ) {}

  set(session: number, endpoint: string, actor: ActorSnapshot): vscode.Uri {
    const uri = vscode.Uri.from({
      scheme: "runa",
      authority: String(session),
      path: `/actors/${actor.actor_ref}.json`,
    });
    const previous = this.documents.get(uri.toString());
    this.documents.set(uri.toString(), {
      session,
      endpoint,
      actor,
      capturedAt: new Date().toISOString(),
      connected: true,
      removed: false,
      mtime: Math.max(Date.now(), (previous?.mtime ?? 0) + 1),
    });
    this.changed(uri);
    return uri;
  }

  refresh(session: number, endpoint: string, actors: ActorSnapshot[]): void {
    const byRef = new Map(actors.map((actor) => [actor.actor_ref, actor]));
    for (const [key, snapshot] of this.documents) {
      const actor = byRef.get(snapshot.actor.actor_ref);
      if (snapshot.session !== session) continue;
      if (actor) this.set(session, endpoint, actor);
      else if (!snapshot.removed) {
        snapshot.removed = true;
        snapshot.mtime++;
        this.changed(vscode.Uri.parse(key));
      }
    }
  }

  disconnect(session: number): void {
    for (const [key, snapshot] of this.documents) {
      if (snapshot.session === session) {
        snapshot.connected = false;
        snapshot.mtime++;
        this.changed(vscode.Uri.parse(key));
      }
    }
  }

  private changed(uri: vscode.Uri): void {
    this.changes.fire([{ type: vscode.FileChangeType.Changed, uri }]);
  }

  private snapshot(uri: vscode.Uri): DocumentSnapshot {
    const snapshot = this.documents.get(uri.toString());
    if (!snapshot) throw vscode.FileSystemError.FileNotFound(uri);
    return snapshot;
  }

  private text(snapshot: DocumentSnapshot): string {
    return formatSnapshot(
      snapshot.actor,
      snapshot.endpoint,
      snapshot.capturedAt,
      snapshot.connected,
      snapshot.removed,
    );
  }

  stat(uri: vscode.Uri): vscode.FileStat {
    if (this.isDirectory(uri))
      return { type: vscode.FileType.Directory, ctime: 0, mtime: 0, size: 0 };
    const snapshot = this.snapshot(uri);
    return {
      type: vscode.FileType.File,
      ctime: 0,
      mtime: snapshot.mtime,
      size: Buffer.byteLength(this.text(snapshot)),
      permissions:
        snapshot.connected && !snapshot.removed && canEditActor(snapshot.actor)
          ? undefined
          : vscode.FilePermission.Readonly,
    };
  }

  readFile(uri: vscode.Uri): Uint8Array {
    const text = this.text(this.snapshot(uri));
    const dirty = vscode.workspace.textDocuments.some(
      (document) => document.uri.toString() === uri.toString() && document.isDirty,
    );
    if (!dirty) this.baselines.set(uri.toString(), text);
    return Buffer.from(text);
  }

  async writeFile(uri: vscode.Uri, content: Uint8Array): Promise<void> {
    const snapshot = this.snapshot(uri);
    if (!snapshot.connected || snapshot.removed || !canEditActor(snapshot.actor))
      throw vscode.FileSystemError.NoPermissions(
        "Actor must be paused or failed with no active invocation, and not removed or disconnected",
      );
    const baseline = this.baselines.get(uri.toString());
    if (baseline === undefined)
      throw vscode.FileSystemError.Unavailable("Inspect the actor before editing");
    const edit = parseSnapshotEdit(Buffer.from(content).toString("utf8"), baseline);
    await this.save(snapshot.session, snapshot.actor.actor_ref, edit);
    if (edit.discarded.length)
      this.warn(`Discarded read-only inspection fields: ${edit.discarded.join(", ")}`);
    this.changed(uri);
  }

  didSave(document: vscode.TextDocument): void {
    if (document.uri.scheme !== "runa" || document.isDirty) return;
    const snapshot = this.snapshot(document.uri);
    // Notify after the save completes so VS Code reloads the now-clean editor.
    snapshot.mtime = Math.max(Date.now(), snapshot.mtime + 1);
    this.changed(document.uri);
  }

  watch(): vscode.Disposable {
    return new vscode.Disposable(() => {});
  }
  private isDirectory(uri: vscode.Uri): boolean {
    return (
      uri.scheme === "runa" &&
      (uri.path === "/" || uri.path === "/actors") &&
      [...this.documents.values()].some((snapshot) => String(snapshot.session) === uri.authority)
    );
  }

  readDirectory(uri: vscode.Uri): [string, vscode.FileType][] {
    if (!this.isDirectory(uri)) throw vscode.FileSystemError.FileNotADirectory(uri);
    if (uri.path === "/") return [["actors", vscode.FileType.Directory]];
    return [...this.documents.values()]
      .filter((snapshot) => String(snapshot.session) === uri.authority)
      .map((snapshot) => [`${snapshot.actor.actor_ref}.json`, vscode.FileType.File]);
  }
  createDirectory(uri: vscode.Uri): void {
    if (!this.isDirectory(uri))
      throw vscode.FileSystemError.NoPermissions("Actor snapshot directories cannot be created");
  }
  delete(): never {
    throw vscode.FileSystemError.NoPermissions("Actor snapshots cannot be deleted");
  }
  rename(): never {
    throw vscode.FileSystemError.NoPermissions("Actor snapshots cannot be renamed");
  }
  dispose(): void {
    this.changes.dispose();
    this.documents.clear();
    this.baselines.clear();
  }
}