import Database from 'better-sqlite3';
import path from 'path';
import fs from 'fs';

const SCHEMA = `
CREATE TABLE IF NOT EXISTS nodes (
  id TEXT PRIMARY KEY,
  kind TEXT NOT NULL,
  title TEXT NOT NULL,
  content TEXT NOT NULL DEFAULT '',
  status TEXT,
  tags TEXT DEFAULT '[]',
  metadata TEXT DEFAULT '{}',
  embedding BLOB,
  created_at INTEGER NOT NULL,
  updated_at INTEGER NOT NULL,
  is_stale INTEGER DEFAULT 0
);

CREATE TABLE IF NOT EXISTS edges (
  id TEXT PRIMARY KEY,
  from_id TEXT NOT NULL REFERENCES nodes(id) ON DELETE CASCADE,
  to_id TEXT NOT NULL REFERENCES nodes(id) ON DELETE CASCADE,
  type TEXT NOT NULL,
  metadata TEXT DEFAULT '{}',
  created_at INTEGER NOT NULL
);

CREATE TABLE IF NOT EXISTS node_tags (
  node_id TEXT NOT NULL REFERENCES nodes(id) ON DELETE CASCADE,
  tag TEXT NOT NULL,
  PRIMARY KEY (node_id, tag)
);

CREATE INDEX IF NOT EXISTS idx_nodes_kind ON nodes(kind);
CREATE INDEX IF NOT EXISTS idx_nodes_status ON nodes(status);
CREATE INDEX IF NOT EXISTS idx_nodes_created ON nodes(created_at DESC);
CREATE INDEX IF NOT EXISTS idx_nodes_stale ON nodes(is_stale);
CREATE INDEX IF NOT EXISTS idx_edges_from ON edges(from_id);
CREATE INDEX IF NOT EXISTS idx_edges_to ON edges(to_id);
CREATE INDEX IF NOT EXISTS idx_edges_type ON edges(type);
CREATE INDEX IF NOT EXISTS idx_tags_tag ON node_tags(tag);
`;

let _db: Database.Database | null = null;

export function getMemoryDir(): string {
  return path.join(process.cwd(), '.memory');
}

export function getDb(): Database.Database {
  if (_db) return _db;

  const dir = getMemoryDir();
  if (!fs.existsSync(dir)) {
    fs.mkdirSync(dir, { recursive: true });
  }

  _db = new Database(path.join(dir, 'cortex.db'));
  _db.pragma('journal_mode = WAL');
  _db.pragma('foreign_keys = ON');
  _db.exec(SCHEMA);

  // Migration: add last_accessed_at column
  const cols = _db.prepare("PRAGMA table_info(nodes)").all() as any[];
  if (!cols.some((c: any) => c.name === 'last_accessed_at')) {
    _db.exec('ALTER TABLE nodes ADD COLUMN last_accessed_at INTEGER');
    _db.exec('UPDATE nodes SET last_accessed_at = updated_at WHERE last_accessed_at IS NULL');
  }

  return _db;
}

export function closeDb(): void {
  if (_db) {
    _db.close();
    _db = null;
  }
}