// File-based persistence adapter for Tasks, Projects, and Artifacts (JSON on disk, per-task locks).
import { promises as fs } from "fs";
import path from "path";
import crypto from "crypto";
import type { TaskRecord, ProjectRecord, Artifact, ChatMessage } from "@/lib/types";
import { inferTaskTitle } from "@/lib/task-title";

const DATA_DIR = path.join(process.cwd(), ".data");
const TASKS_DIR = path.join(DATA_DIR, "tasks");
const ARTIFACTS_DIR = path.join(DATA_DIR, "artifacts");
const PROJECTS_FILE = path.join(DATA_DIR, "projects.json");

// ---- tiny per-key sequential lock ----
const locks = new Map<string, Promise<unknown>>();
function withLock<T>(key: string, fn: () => Promise<T>): Promise<T> {
  const prev = locks.get(key) ?? Promise.resolve();
  const next = prev.then(fn, fn);
  locks.set(
    key,
    next.catch(() => undefined).finally(() => {
      if (locks.get(key) === next) locks.delete(key);
    }),
  );
  return next;
}

// ---- id helpers ----
function randomHex(len: number): string {
  return crypto.randomBytes(Math.ceil(len / 2)).toString("hex").slice(0, len);
}
function projectId(): string { return `proj_${randomHex(10)}`; }
function taskId(): string { return `sess_${randomHex(12)}`; }
export function artifactId(): string { return `art_${randomHex(12)}`; }

// ---- fs helpers ----
async function ensureDirs(): Promise<void> {
  await fs.mkdir(TASKS_DIR, { recursive: true });
  await fs.mkdir(ARTIFACTS_DIR, { recursive: true });
}

async function readJson<T>(file: string): Promise<T | null> {
  try {
    const buf = await fs.readFile(file, "utf8");
    return JSON.parse(buf) as T;
  } catch (err) {
    if ((err as NodeJS.ErrnoException).code === "ENOENT") return null;
    throw err;
  }
}

async function writeJsonAtomic(file: string, value: unknown): Promise<void> {
  await fs.mkdir(path.dirname(file), { recursive: true });
  const tmp = `${file}.${process.pid}.${randomHex(6)}.tmp`;
  await fs.writeFile(tmp, JSON.stringify(value, null, 2), "utf8");
  await fs.rename(tmp, file);
}

function taskFile(id: string): string {
  return path.join(TASKS_DIR, `${id}.json`);
}

// ---- projects ----
async function readProjects(): Promise<ProjectRecord[]> {
  await ensureDirs();
  const existing = await readJson<ProjectRecord[]>(PROJECTS_FILE);
  return existing ?? [];
}

async function writeProjects(projects: ProjectRecord[]): Promise<void> {
  await writeJsonAtomic(PROJECTS_FILE, projects);
}

export async function ensureDefaultProject(): Promise<ProjectRecord> {
  return withLock("projects", async () => {
    const projects = await readProjects();
    if (projects.length > 0) return projects[0];
    const proj: ProjectRecord = {
      id: projectId(),
      name: "Default",
      createdAt: Date.now(),
    };
    await writeProjects([proj]);
    return proj;
  });
}

export async function listProjects(): Promise<ProjectRecord[]> {
  const projects = await readProjects();
  if (projects.length === 0) {
    const def = await ensureDefaultProject();
    return [def];
  }
  return projects;
}

async function getProject(id: string): Promise<ProjectRecord | null> {
  const projects = await readProjects();
  return projects.find((p) => p.id === id) ?? null;
}

// ---- tasks ----
export async function createTask(
  projectIdArg: string,
  firstMessage: string,
): Promise<TaskRecord> {
  const project = await getProject(projectIdArg);
  if (!project) throw new Error(`Project not found: ${projectIdArg}`);

  const id = taskId();
  const now = Date.now();
  const title = inferTaskTitle(firstMessage);
  const firstMsg: ChatMessage = {
    id: `msg_${randomHex(10)}`,
    role: "user",
    content: firstMessage,
  };
  const task: TaskRecord = {
    id,
    projectId: projectIdArg,
    title,
    createdAt: now,
    updatedAt: now,
    messages: [firstMsg],
    artifacts: [],
  };
  return withLock(`task:${id}`, async () => {
    await writeJsonAtomic(taskFile(id), task);
    return task;
  });
}

export async function getTask(id: string): Promise<TaskRecord | null> {
  return readJson<TaskRecord>(taskFile(id));
}

export async function appendMessage(
  id: string,
  message: ChatMessage,
): Promise<TaskRecord> {
  return withLock(`task:${id}`, async () => {
    const task = await readJson<TaskRecord>(taskFile(id));
    if (!task) throw new Error(`Task not found: ${id}`);
    task.messages.push(message);
    task.updatedAt = Date.now();
    await writeJsonAtomic(taskFile(id), task);
    return task;
  });
}

export async function updateTask(
  id: string,
  patch: Partial<TaskRecord>,
): Promise<TaskRecord> {
  return withLock(`task:${id}`, async () => {
    const task = await readJson<TaskRecord>(taskFile(id));
    if (!task) throw new Error(`Task not found: ${id}`);
    const next: TaskRecord = {
      ...task,
      ...(patch.title !== undefined ? { title: patch.title } : {}),
      ...(patch.messages !== undefined ? { messages: patch.messages } : {}),
      ...(patch.artifacts !== undefined ? { artifacts: patch.artifacts } : {}),
      id: task.id,
      projectId: task.projectId,
      createdAt: task.createdAt,
      updatedAt: Date.now(),
    };
    await writeJsonAtomic(taskFile(id), next);
    return next;
  });
}

export async function listTasks(projectIdArg: string): Promise<TaskRecord[]> {
  await ensureDirs();
  const entries = await fs.readdir(TASKS_DIR).catch(() => [] as string[]);
  const tasks: TaskRecord[] = [];
  for (const entry of entries) {
    if (!entry.endsWith(".json")) continue;
    const task = await readJson<TaskRecord>(path.join(TASKS_DIR, entry));
    if (task && task.projectId === projectIdArg) tasks.push(task);
  }
  tasks.sort((a, b) => b.updatedAt - a.updatedAt);
  return tasks;
}

// ---- artifacts ----
interface ArtifactMeta {
  artifact: Artifact;
  taskId: string;
  filename: string;
}

function artifactDir(id: string): string {
  return path.join(ARTIFACTS_DIR, id);
}

export async function saveArtifact(
  taskIdArg: string,
  artifact: Artifact,
  body: Buffer | string,
): Promise<void> {
  const task = await getTask(taskIdArg);
  if (!task) throw new Error(`Task not found: ${taskIdArg}`);

  const dir = artifactDir(artifact.id);
  await fs.mkdir(dir, { recursive: true });
  const filename = artifact.name || "artifact.bin";
  const safeName = path.basename(filename);
  const blobPath = path.join(dir, safeName);
  const data = typeof body === "string" ? Buffer.from(body, "utf8") : body;
  await fs.writeFile(blobPath, data);

  const meta: ArtifactMeta = { artifact, taskId: taskIdArg, filename: safeName };
  await writeJsonAtomic(path.join(dir, "meta.json"), meta);

  await withLock(`task:${taskIdArg}`, async () => {
    const t = await readJson<TaskRecord>(taskFile(taskIdArg));
    if (!t) return;
    const idx = t.artifacts.findIndex((a) => a.id === artifact.id);
    if (idx >= 0) t.artifacts[idx] = artifact;
    else t.artifacts.push(artifact);
    t.updatedAt = Date.now();
    await writeJsonAtomic(taskFile(taskIdArg), t);
  });
}

export async function readArtifact(
  id: string,
): Promise<{ artifact: Artifact; body: Buffer } | null> {
  const dir = artifactDir(id);
  const meta = await readJson<ArtifactMeta>(path.join(dir, "meta.json"));
  if (!meta) return null;
  const blobPath = path.join(dir, meta.filename);
  try {
    const body = await fs.readFile(blobPath);
    return { artifact: meta.artifact, body };
  } catch (err) {
    if ((err as NodeJS.ErrnoException).code === "ENOENT") return null;
    throw err;
  }
}