const fs = require('fs');
const path = require('path');
const { spawn } = require('child_process');

const BACKUPS_DIR = path.join(__dirname, '..', '..', 'backups');
const USERS_FILE = path.join(__dirname, '..', '..', 'users.json');
const AUDIT_LOG_FILE = path.join(__dirname, '..', '..', 'audit.log');
const SETTINGS_FILE = path.join(__dirname, '..', '..', 'settings.json');
const BACKUP_PREFIX = 'backup-';

function ensureBackupsDir() {
    fs.mkdirSync(BACKUPS_DIR, { recursive: true });
}

function makeBackupStamp() {
    return new Date().toISOString().replace(/[:.]/g, '-');
}

async function collectAppSnapshot(pool, actor = 'system') {
    const tablesResult = await pool.query(`
        SELECT table_name
        FROM information_schema.tables
        WHERE table_schema = 'public'
        ORDER BY table_name
    `);

    const tables = [];
    for (const row of tablesResult.rows) {
        const tableName = row.table_name;
        const structure = await pool.query(`
            SELECT
                c.column_name AS name,
                c.data_type AS type,
                c.is_nullable AS nullable,
                c.column_default AS default_value
            FROM information_schema.columns c
            WHERE c.table_name = $1 AND c.table_schema = 'public'
            ORDER BY c.ordinal_position
        `, [tableName]);
        const data = await pool.query(`SELECT * FROM "${tableName}"`);
        tables.push({
            name: tableName,
            structure: structure.rows,
            rows: data.rows,
        });
    }

    return {
        meta: {
            createdAt: new Date().toISOString(),
            createdBy: actor,
            version: 1,
        },
        users: fs.existsSync(USERS_FILE) ? JSON.parse(fs.readFileSync(USERS_FILE, 'utf8')) : { users: [] },
        settings: fs.existsSync(SETTINGS_FILE) ? JSON.parse(fs.readFileSync(SETTINGS_FILE, 'utf8')) : null,
        audit: fs.existsSync(AUDIT_LOG_FILE)
            ? fs.readFileSync(AUDIT_LOG_FILE, 'utf8').split(/\r?\n/).filter(Boolean)
            : [],
        tables,
    };
}

function runPgDump() {
    return new Promise((resolve, reject) => {
        const args = [
            '-h', process.env.DB_HOST || 'db',
            '-p', String(process.env.DB_PORT || '5432'),
            '-U', process.env.DB_USER || 'postgres',
            '-d', process.env.DB_NAME || 'postgres',
            '--clean',
            '--if-exists',
            '--no-owner',
            '--no-privileges',
        ];

        const child = spawn('pg_dump', args, {
            env: {
                ...process.env,
                PGPASSWORD: process.env.DB_PASSWORD || '',
            },
            stdio: ['ignore', 'pipe', 'pipe'],
        });

        const stdout = [];
        const stderr = [];
        child.stdout.on('data', (chunk) => stdout.push(chunk));
        child.stderr.on('data', (chunk) => stderr.push(chunk));
        child.on('error', reject);
        child.on('close', (code) => {
            if (code !== 0) {
                reject(new Error(Buffer.concat(stderr).toString('utf8') || `pg_dump exited with code ${code}`));
                return;
            }
            resolve(Buffer.concat(stdout).toString('utf8'));
        });
    });
}

function formatBackupEntry(filePath, filename) {
    const stats = fs.statSync(filePath);
    const kind = filename.endsWith('.sql') ? 'database' : 'application';
    const match = filename.match(/^backup-(.+?)-(db|app)\.(sql|json)$/);
    return {
        filename,
        size: stats.size,
        createdAt: stats.birthtime.toISOString(),
        kind,
        bundle: match ? match[1] : null,
    };
}

function pruneBackups(keepLast = 14) {
    ensureBackupsDir();
    const maxFiles = Math.max(1, keepLast) * 2;
    const files = fs.readdirSync(BACKUPS_DIR)
        .filter((name) => name.startsWith(BACKUP_PREFIX) && (name.endsWith('.json') || name.endsWith('.sql')))
        .map((name) => ({
            name,
            filePath: path.join(BACKUPS_DIR, name),
            mtimeMs: fs.statSync(path.join(BACKUPS_DIR, name)).mtimeMs,
        }))
        .sort((a, b) => b.mtimeMs - a.mtimeMs);

    files.slice(maxFiles).forEach((file) => {
        fs.unlinkSync(file.filePath);
    });
}

async function createBackup(pool, actor = 'system', options = {}) {
    ensureBackupsDir();
    const stamp = makeBackupStamp();
    const createdAt = new Date().toISOString();
    const includeAppSnapshot = options.includeAppSnapshot !== false;
    const files = [];

    const sqlDump = await runPgDump();
    const sqlFilename = `${BACKUP_PREFIX}${stamp}-db.sql`;
    const sqlPath = path.join(BACKUPS_DIR, sqlFilename);
    fs.writeFileSync(sqlPath, sqlDump, 'utf8');
    files.push(formatBackupEntry(sqlPath, sqlFilename));

    if (includeAppSnapshot) {
        const snapshot = await collectAppSnapshot(pool, actor);
        const jsonFilename = `${BACKUP_PREFIX}${stamp}-app.json`;
        const jsonPath = path.join(BACKUPS_DIR, jsonFilename);
        fs.writeFileSync(jsonPath, JSON.stringify(snapshot, null, 2), 'utf8');
        files.push(formatBackupEntry(jsonPath, jsonFilename));
    }

    if (options.keepLast) {
        pruneBackups(options.keepLast);
    }

    return {
        createdAt,
        files,
    };
}

function listBackups() {
    ensureBackupsDir();
    return fs.readdirSync(BACKUPS_DIR)
        .filter((name) => name.startsWith(BACKUP_PREFIX) && (name.endsWith('.json') || name.endsWith('.sql')))
        .map((name) => formatBackupEntry(path.join(BACKUPS_DIR, name), name))
        .sort((a, b) => b.createdAt.localeCompare(a.createdAt));
}

function getBackupPath(filename) {
    const filePath = path.join(BACKUPS_DIR, filename);
    if (!filePath.startsWith(BACKUPS_DIR) || !fs.existsSync(filePath)) {
        throw new Error('Backup not found');
    }
    return filePath;
}

module.exports = {
    BACKUPS_DIR,
    createBackup,
    getBackupPath,
    listBackups,
    pruneBackups,
};