import { DatabaseSync } from 'node:sqlite'
import { mkdirSync, readFileSync, writeFileSync, existsSync } from 'fs'
import { resolve } from 'path'
import { homedir } from 'os'

const DB_DIR = resolve(homedir(), '.hermes-web-ui')
const DB_PATH = resolve(DB_DIR, 'hermes-web-ui.db')
const JSON_PATH = resolve(DB_DIR, 'hermes-web-ui.json')

// --- SQLite availability check ---

const SQLITE_AVAILABLE = (() => {
  const [major, minor] = process.versions.node.split('.').map(Number)
  return major > 22 || (major === 22 && minor >= 5)
})()

export function isSqliteAvailable(): boolean {
  return SQLITE_AVAILABLE
}

// --- SQLite backend ---

let _db: DatabaseSync | null = null

export function getDb(): DatabaseSync | null {
  if (!SQLITE_AVAILABLE) return null
  if (!_db) {
    mkdirSync(DB_DIR, { recursive: true })
    _db = new DatabaseSync(DB_PATH)
    _db.exec('PRAGMA journal_mode=WAL')
    _db.exec('PRAGMA foreign_keys=ON')
  }
  return _db
}

/**
 * Ensure a table's schema matches the expected definition.
 * - Creates the table if it does not exist
 * - Adds missing columns (ALTER TABLE ADD COLUMN)
 * - Drops extra columns (ALTER TABLE DROP COLUMN, SQLite 3.35+)
 *
 * No-op when SQLite is not available.
 */
export function ensureTable(tableName: string, schema: Record<string, string>): void {
  const db = getDb()
  if (!db) return

  const colDefs = Object.entries(schema)
    .map(([col, def]) => `"${col}" ${def}`)
    .join(', ')

  db.exec(`CREATE TABLE IF NOT EXISTS "${tableName}" (${colDefs})`)

  const rows = db.prepare(`PRAGMA table_info("${tableName}")`).all() as Array<{ name: string }>
  const existingCols = new Set(rows.map(r => r.name))
  const expectedCols = new Set(Object.keys(schema))

  for (const col of expectedCols) {
    if (!existingCols.has(col)) {
      db.exec(`ALTER TABLE "${tableName}" ADD COLUMN "${col}" ${schema[col]}`)
    }
  }

  for (const col of existingCols) {
    if (!expectedCols.has(col)) {
      db.exec(`ALTER TABLE "${tableName}" DROP COLUMN "${col}"`)
    }
  }
}

// --- JSON fallback backend ---

type JsonData = Record<string, Record<string, Record<string, any>>>

function readJsonStore(): JsonData {
  if (!existsSync(JSON_PATH)) return {}
  try {
    return JSON.parse(readFileSync(JSON_PATH, 'utf-8'))
  } catch {
    return {}
  }
}

function writeJsonStore(data: JsonData): void {
  mkdirSync(DB_DIR, { recursive: true })
  writeFileSync(JSON_PATH, JSON.stringify(data, null, 2), 'utf-8')
}

/**
 * Get a record from the JSON store.
 * @param table  Table name (namespace)
 * @param key    Primary key
 */
export function jsonGet(table: string, key: string): Record<string, any> | undefined {
  const data = readJsonStore()
  return data[table]?.[key]
}

/**
 * Set a record in the JSON store.
 * @param table  Table name (namespace)
 * @param key    Primary key
 * @param value  Record data
 */
export function jsonSet(table: string, key: string, value: Record<string, any>): void {
  const data = readJsonStore()
  if (!data[table]) data[table] = {}
  data[table][key] = value
  writeJsonStore(data)
}

/**
 * Get all records from a table in the JSON store.
 */
export function jsonGetAll(table: string): Record<string, Record<string, any>> {
  const data = readJsonStore()
  return data[table] || {}
}

/**
 * Delete a record from the JSON store.
 */
export function jsonDelete(table: string, key: string): void {
  const data = readJsonStore()
  if (data[table]) {
    delete data[table][key]
    writeJsonStore(data)
  }
}

/**
 * Get the storage path for debugging.
 */
export function getStoragePath(): string {
  return SQLITE_AVAILABLE ? DB_PATH : JSON_PATH
}