'use strict';
const { cppdb } = require('../util');
const controllers = new WeakMap();

module.exports = function transaction(fn) {
	if (typeof fn !== 'function') throw new TypeError('Expected first argument to be a function');

	const db = this[cppdb];
	const controller = getController(db, this);
	const { apply } = Function.prototype;

	// Each version of the transaction function has these same properties
	const properties = {
		default: { value: wrapTransaction(apply, fn, db, controller.default) },
		deferred: { value: wrapTransaction(apply, fn, db, controller.deferred) },
		immediate: { value: wrapTransaction(apply, fn, db, controller.immediate) },
		exclusive: { value: wrapTransaction(apply, fn, db, controller.exclusive) },
		database: { value: this, enumerable: true },
	};

	Object.defineProperties(properties.default.value, properties);
	Object.defineProperties(properties.deferred.value, properties);
	Object.defineProperties(properties.immediate.value, properties);
	Object.defineProperties(properties.exclusive.value, properties);

	// Return the default version of the transaction function
	return properties.default.value;
};

// Return the database's cached transaction controller, or create a new one
const getController = (db, self) => {
	let controller = controllers.get(db);
	if (!controller) {
		const shared = {
			commit: db.prepare('COMMIT', self, false),
			rollback: db.prepare('ROLLBACK', self, false),
			savepoint: db.prepare('SAVEPOINT `\t_bs3.\t`', self, false),
			release: db.prepare('RELEASE `\t_bs3.\t`', self, false),
			rollbackTo: db.prepare('ROLLBACK TO `\t_bs3.\t`', self, false),
		};
		controllers.set(db, controller = {
			default: Object.assign({ begin: db.prepare('BEGIN', self, false) }, shared),
			deferred: Object.assign({ begin: db.prepare('BEGIN DEFERRED', self, false) }, shared),
			immediate: Object.assign({ begin: db.prepare('BEGIN IMMEDIATE', self, false) }, shared),
			exclusive: Object.assign({ begin: db.prepare('BEGIN EXCLUSIVE', self, false) }, shared),
		});
	}
	return controller;
};

// Return a new transaction function by wrapping the given function
const wrapTransaction = (apply, fn, db, { begin, commit, rollback, savepoint, release, rollbackTo }) => function sqliteTransaction() {
	let before, after, undo;
	if (db.inTransaction) {
		before = savepoint;
		after = release;
		undo = rollbackTo;
	} else {
		before = begin;
		after = commit;
		undo = rollback;
	}
	before.run();
	try {
		const result = apply.call(fn, this, arguments);
		if (result && typeof result.then === 'function') {
			throw new TypeError('Transaction function cannot return a promise');
		}
		after.run();
		return result;
	} catch (ex) {
		if (db.inTransaction) {
			undo.run();
			if (undo !== rollback) after.run();
		}
		throw ex;
	}
};