// Copyright (c) 2016 Timothy Farrell
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

function tryJSON(type, destination, id, data) {
	const packet = [type, destination, id, data];
	try {
		return JSON.stringify(packet);
	} catch (e) {
		return packet;
	}
}

function getPaths(obj, prefix = '') {
	return Object.keys(obj)
		.map(key => {
			const prop = obj[key];
			const path = `${prefix}${key}`;
			if (typeof prop === 'function') {
				return path;
			}
			return getPaths(prop, path + '.');
		})
		.reduce((a, b) => a.concat(b), []);
}

function traverseObj(obj, pathStr, assignValue) {
	const path = pathStr.split('.');
	const last = path.pop();
	const ptr = path.reduce(
		(acc, next) => (acc[next] === undefined ? (acc[next] = {}) : acc[next]),
		obj
	);
	if (assignValue) {
		return (ptr[last] = assignValue);
	}
	return ptr[last];
}

export function WorkerPortal(context, worker, isSlave, serialize) {
	const responseMap = new Map();
	const _worker = worker || self;
	const contextIndex = getPaths(context);
	const methods = contextIndex.map(path => traverseObj(context, path));
	const _serialize = serialize
		? (type, destination, id, params) => serialize(type, destination, id, params, tryJSON)
		: tryJSON;
	let callCount = 0;
	let enabled = false;

	function post(type, id, destination, params) {
		_worker.postMessage(_serialize(type, destination, id, params));
	}

	function dispatcher(evt) {
		let data;
		try {
			data = JSON.parse(evt.data);
		} catch (e) {
			data = evt.data;
		}
		const destination = data[1];
		const id = data[2];
		const params = data[3];

		function _resolve(value) {
			post(1, id, 0, value);
		}
		function _reject(e) {
			post(1, id, 1, {
				message: e.message,
				name: e.name,
				stack: e.stack
			});
		}

		// If we have received an RPC response, satisfy the promise.
		if (data[0]) {
			if (responseMap.has(id)) {
				const responses = responseMap.get(id);
				responseMap.delete(id);
				responses[destination](params);
			}
			return;
		}

		// If we have received an RPC call, execute and respond.
		let thennable;
		try {
			thennable = methods[destination].apply(null, params);
		} catch (e) {
			_reject(e);
		}
		if (thennable && typeof thennable.then === 'function') {
			thennable.then(_resolve).catch(_reject);
		} else {
			_resolve(thennable);
		}
	}

	function injectionPointFactory(fnId, callbackFactory) {
		return function(...args) {
			return new Promise((resolve, reject) => {
				if (!enabled && fnId !== 0) {
					reject(new Error('Portal disabled'));
				}
				const id = callCount;
				callCount += 1;
				responseMap.set(id, [callbackFactory ? callbackFactory(resolve) : resolve, reject]);
				post(0, id, fnId, args);
			});
		};
	}

	function resolveExternalInterfaceFactory(resolve) {
		return (linkedFunctionNames, ...rest) => {
			const externalInterface = {};
			linkedFunctionNames.forEach((pathStr, index) => {
				traverseObj(externalInterface, pathStr, injectionPointFactory(index));
			});
			enabled = true;
			resolve(externalInterface);
			return contextIndex;
		};
	}

	function cleanup() {
		enabled = false;
		_worker.removeEventListener('message', dispatcher);
		for (let key of responseMap.keys()) {
			try {
				responseMap.get(key)[1](new Error('Portal cleanup called.'));
			} catch (e) {}
		}
	}

	_worker.addEventListener('message', dispatcher);

	if (isSlave) {
		return new Promise(resolve => {
			contextIndex.splice(0, 0, '__init', '__cleanupSlave');
			methods.splice(0, 0, resolveExternalInterfaceFactory(resolve), cleanup);
		});
	}

	return injectionPointFactory(0, resolveExternalInterfaceFactory)(contextIndex).then(api =>
		Object.assign(api, {
			_cleanup: injectionPointFactory(1, resolve => resolve(cleanup()))
		})
	);
}