/**
 * lib/db.ts
 * Singleton libSQL (SQLite) client. Call getDb() anywhere on the server.
 *
 * WAL journal mode is set for better concurrency.
 * On first boot, existing meta.json / users.json are imported and renamed
 * to *.migrated so the one-time import never runs twice.
 */
import { createClient, type Client } from '@libsql/client'
import path from 'path'
import fs from 'fs'

const DATA_DIR = path.join(process.cwd(), 'data')
const DB_URL = `file:${path.join(DATA_DIR, 'backerup.db')}`

let _client: Client | null = null

export function getDb(): Client {
  if (_client) return _client
  fs.mkdirSync(DATA_DIR, { recursive: true })
  _client = createClient({ url: DB_URL })
  // Fire-and-forget: migrations run before first real query via ensureReady()
  return _client
}

/** Call once at startup (or await before first query if needed). */
let _ready: Promise<void> | null = null

export function ensureReady(): Promise<void> {
  if (_ready) return _ready
  _ready = (async () => {
    const db = getDb()
    await applyMigrations(db)
    await importLegacyJson(db)
  })()
  return _ready
}

// ── Schema ────────────────────────────────────────────────────────────────────

async function applyMigrations(db: Client): Promise<void> {
  await db.executeMultiple(`
    PRAGMA journal_mode = WAL;
    PRAGMA foreign_keys = ON;
    PRAGMA synchronous = NORMAL;

    CREATE TABLE IF NOT EXISTS files (
      token          TEXT PRIMARY KEY,
      original_name  TEXT NOT NULL,
      display_name   TEXT,
      size           INTEGER NOT NULL,
      type           TEXT NOT NULL,
      uploaded_at    TEXT NOT NULL,
      description    TEXT,
      group_name     TEXT,
      container_name TEXT,
      image          TEXT
    );

    CREATE TABLE IF NOT EXISTS users (
      id             TEXT PRIMARY KEY,
      username       TEXT NOT NULL UNIQUE COLLATE NOCASE,
      password_hash  TEXT NOT NULL,
      salt           TEXT NOT NULL,
      role           TEXT NOT NULL DEFAULT 'user',
      created_at     TEXT NOT NULL
    );
  `)
}

// ── One-time JSON → SQLite import ─────────────────────────────────────────────

async function importLegacyJson(db: Client): Promise<void> {
  const metaPath = path.join(DATA_DIR, 'meta.json')
  if (fs.existsSync(metaPath)) {
    try {
      const { rows } = await db.execute('SELECT COUNT(*) as cnt FROM files')
      if ((rows[0].cnt as number) === 0) {
        type OldRecord = {
          token: string; originalName: string; displayName?: string; size: number
          type: string; uploadedAt: string; description?: string; group?: string
          containerName?: string; image?: string
        }
        const records = JSON.parse(fs.readFileSync(metaPath, 'utf-8')) as OldRecord[]
        for (const r of records) {
          await db.execute({
            sql: `INSERT OR IGNORE INTO files
                  (token,original_name,display_name,size,type,uploaded_at,description,group_name,container_name,image)
                  VALUES (?,?,?,?,?,?,?,?,?,?)`,
            args: [r.token, r.originalName, r.displayName ?? null, r.size, r.type,
                   r.uploadedAt, r.description ?? null, r.group ?? null,
                   r.containerName ?? null, r.image ?? null],
          })
        }
        fs.renameSync(metaPath, metaPath + '.migrated')
        console.log(`[db] Imported ${records.length} file records from meta.json`)
      }
    } catch (e) {
      console.error('[db] Failed to import meta.json:', e)
    }
  }

  const usersPath = path.join(DATA_DIR, 'users.json')
  if (fs.existsSync(usersPath)) {
    try {
      const { rows } = await db.execute('SELECT COUNT(*) as cnt FROM users')
      if ((rows[0].cnt as number) === 0) {
        type OldUser = {
          id: string; username: string; passwordHash: string; salt: string
          role: string; createdAt: string
        }
        const users = JSON.parse(fs.readFileSync(usersPath, 'utf-8')) as OldUser[]
        for (const u of users) {
          await db.execute({
            sql: `INSERT OR IGNORE INTO users (id,username,password_hash,salt,role,created_at)
                  VALUES (?,?,?,?,?,?)`,
            args: [u.id, u.username, u.passwordHash, u.salt, u.role, u.createdAt],
          })
        }
        fs.renameSync(usersPath, usersPath + '.migrated')
        console.log(`[db] Imported ${users.length} users from users.json`)
      }
    } catch (e) {
      console.error('[db] Failed to import users.json:', e)
    }
  }
}