import fsp from 'node:fs/promises';
import path from 'node:path';
import crypto from 'node:crypto';
import { joinRel, normalizeRelPath, safeJoin, sessionRoot } from './paths.mjs';
import { setFileMeta } from './fs-tree.mjs';

const sessions = new Map();

function sessionFile(ctx, id) {
  return path.join(sessionRoot(ctx), `${id}.part`);
}

function sessionMetaFile(ctx, id) {
  return path.join(sessionRoot(ctx), `${id}.json`);
}

export async function ensureSessionDir(ctx) {
  await fsp.mkdir(sessionRoot(ctx), { recursive: true });
}

export async function createUploadSession(ctx, { relPath, totalSize, prefix = '', clientMeta = {} }) {
  await ensureSessionDir(ctx);
  const id = crypto.randomBytes(8).toString('hex');
  const rel = joinRel(prefix, normalizeRelPath(relPath));
  const meta = {
    id,
    rel,
    totalSize: Number(totalSize),
    received: 0,
    clientMeta,
    createdAt: Date.now(),
    userId: ctx.userId,
  };
  await fsp.writeFile(sessionMetaFile(ctx, id), JSON.stringify(meta));
  await fsp.writeFile(sessionFile(ctx, id), Buffer.alloc(0));
  sessions.set(`${ctx.userId}:${id}`, meta);
  return meta;
}

async function loadSession(ctx, id) {
  const key = `${ctx.userId}:${id}`;
  if (sessions.has(key)) return sessions.get(key);
  const raw = await fsp.readFile(sessionMetaFile(ctx, id), 'utf8');
  const meta = JSON.parse(raw);
  if (meta.userId && meta.userId !== ctx.userId) {
    throw new Error('session not found');
  }
  sessions.set(key, meta);
  return meta;
}

export async function appendUploadChunk(ctx, id, buffer, offset) {
  const meta = await loadSession(ctx, id);
  const file = sessionFile(ctx, id);
  const handle = await fsp.open(file, 'r+');
  try {
    await handle.write(buffer, 0, buffer.length, Number(offset));
  } finally {
    await handle.close();
  }
  meta.received = Math.max(meta.received, Number(offset) + buffer.length);
  await fsp.writeFile(sessionMetaFile(ctx, id), JSON.stringify(meta));
  return meta;
}

export async function completeUploadSession(ctx, id) {
  const meta = await loadSession(ctx, id);
  const part = sessionFile(ctx, id);
  const stat = await fsp.stat(part);
  if (stat.size < meta.totalSize) throw new Error('incomplete');
  const dest = safeJoin(ctx.uploadDir, meta.rel);
  await fsp.mkdir(path.dirname(dest), { recursive: true });
  await fsp.rename(part, dest);
  await fsp.unlink(sessionMetaFile(ctx, id)).catch(() => {});
  sessions.delete(`${ctx.userId}:${id}`);
  if (meta.clientMeta?.clientId) {
    await setFileMeta(ctx, meta.rel, meta.clientMeta);
  }
  return { saved: meta.rel, size: stat.size };
}

export async function getSession(ctx, id) {
  return loadSession(ctx, id);
}