import fs from 'fs/promises';
import path from 'path';
import os from 'os';
import { spawn } from 'child_process';
import pkg from 'lodash';
import { fileURLToPath } from 'url';
import utils from '@serverlessinc/sf-core/src/utils.js';
const { log, style } = utils;
const logger = log.get('sls:dev:local-lambda');

const { flatten } = pkg;
let __dirname = path.dirname(fileURLToPath(import.meta.url));
if (__dirname.endsWith('dist')) {
  __dirname = path.join(__dirname, '../lib/plugins/aws/dev/local-lambda');
}
/**
 * This is the main Local Lambda class that will be used to invoke local lambda functions.
 * Each instance of this class represents a single lambda function instance that can be invoked.
 *
 * @class
 * @param {Object} [config={}] - The configuration object for the Local Lambda.
 * @param {string} config.handler - The AWS Lambda handler.
 * @param {string} config.runtime - The AWS Lambda runtime.
 * @param {Object} [config.environment={}] - An object representing environment variables to set for the local lambda instance in addition to the current process environment.
 * @param {string} config.serviceAbsolutePath - The absolute path to the service directory.
 *
 * @property {string} handler - The AWS Lambda handler.
 * @property {string} runtime - The AWS Lambda runtime.
 * @property {Object} environment - The local lambda environment variables.
 * @property {string} serviceAbsolutePath - The absolute path to the service directory.
 *
 * @example
 * const config = {
 *   handler: 'index.handler',
 *   runtime: 'nodejs20.x',
 *   environment: { FOO: 'BAR' },
 *   serviceAbsolutePath: '~/path/to/service'
 * };
 *
 * const localLambda = new LocalLambda(config);
 */
class LocalLambda {
  constructor(config = {}) {
    this.serviceAbsolutePath = config.serviceAbsolutePath;

    const supportedRuntimes = flatten(
      runtimeWrappers.map((runtimeWrapper) => runtimeWrapper.versions)
    );

    if (!supportedRuntimes.includes(config.runtime)) {
      throw new Error(`Unsupported runtime: "${config.runtime}"`);
    }

    this.handler = config.handler;
    this.runtime = config.runtime;
    this.environment = {
      ...process.env,
      ...(config.environment || {}),
    };
    this.invocationColorFn = config.invocationColorFn;
  }

  /**
   * Asynchronously retrieves the absolute path of the handler file, considering possible file extensions.
   *
   * This method constructs the absolute path of the handler file based on the handler name provided in the class instance,
   * the service's absolute path, and the runtime environment. It checks for possible file extensions that match the runtime
   * environment's expected file types and returns the first matching handler file's absolute path.
   *
   * @async
   * @returns {Promise<string>} A promise that resolves to the absolute path of the handler file.
   * If no files are found, an error will be thrown.
   *
   * @example
   * const handlerFileAbsolutePath = await localLambda.getHandlerFileAbsolutePath();
   * console.log(handlerFileAbsolutePath); // Outputs: "/path/to/service/handler.js"
   */
  async getHandlerFileAbsolutePath() {
    // Extract the handler file name without the extension.
    const handlerFileName = this.handler.split('.')[0];

    // Construct the absolute path to the handler file without the extension.
    const handlerFileAbsolutePathWithoutExtension = path.resolve(
      this.serviceAbsolutePath,
      handlerFileName
    );

    // Get a list of possible extensions based on the specified runtime
    // ex. ['.js', '.mjs', '.js', '.ts']
    const possibleExtensions = flatten(
      runtimeWrappers
        .filter((runtimeWrapper) => runtimeWrapper.versions.includes(this.runtime))
        .map((possibleRuntime) => possibleRuntime.extensions)
    );

    // Get a list of possible handler file paths with the different extensions
    // and check to see which one exists
    const possibleHandlerFiles = await Promise.all(
      possibleExtensions.map(async (ext) => {
        return {
          path: `${handlerFileAbsolutePathWithoutExtension}${ext}`,
          exists: await fileExists(`${handlerFileAbsolutePathWithoutExtension}${ext}`),
        };
      })
    );

    // Find the handler file that actually exists
    const handlerFileAbsolutePath = possibleHandlerFiles.find((file) => file.exists)?.path;

    // If none of the possible handler files exist, throw an error
    if (!handlerFileAbsolutePath) {
      throw new Error(`Handler "${this.handler}" not found in service directory`);
    }

    return handlerFileAbsolutePath;
  }

  /**
   * Asynchronously invokes the specified handler function with the provided event object, executing it in a child process
   * based on the runtime environment configuration.
   *
   * The function captures and filters the child process's stdout and stderr streams, extracting the execution result
   * encapsulated between '__RESULT_START__' and '__RESULT_END__' delimiters.
   *
   * @async
   * @param {Object} [event={}] - The event object to be passed to the handler function. Defaults to an empty object if not provided.
   * @param {Object} [context={}] - The context object to be passed to the handler function. Defaults to an empty object if not provided.
   * @returns {Promise<any>} A promise that resolves with the result of the handler function's execution.
   *
   * @example
   * const event = { key: 'value' }; // Example event object
   * const context = { key: 'value' }; // Example context object
   * const result = await instance.invoke(event, context);
   * console.log(result); // Outputs the handler's execution result
   */
  async invoke(event = {}, context = {}) {
    // get the absolute path of the handler file set in the class instance
    const handlerFileAbsolutePath = await this.getHandlerFileAbsolutePath();

    // extract the handler name from the handler string
    const handlerName = this.handler.split('.')[1];

    // find the runtime wrapper that supports the handler file extension
    const runtimeWrapper = runtimeWrappers.find((runtimeWrapper) =>
      runtimeWrapper.extensions.includes(path.extname(handlerFileAbsolutePath))
    );

    return new Promise((resolve, reject) => {
      /**
       * Construct the arguments to be passed to the child process:
       *   - The handler file's absolute path to be imported by the wrapper
       *   - The handler function name to be called by the wrapper
       *   - The event that will be passed as an argument to the handler function
       *   - The context that will be passed as a second argument to the handler function
       */
      const argsString = JSON.stringify({
        handlerFileAbsolutePath,
        handlerName,
        event,
        context,
      });

      const childEnv = { ...this.environment };

      // Spawn a child process to execute the runtime wrapper and set the specified environment variables
      const child = spawn(
        runtimeWrapper.command,
        [...runtimeWrapper.arguments, runtimeWrapper.path, argsString],
        {
          env: childEnv,
          cwd: this.serviceAbsolutePath,
        }
      );

      // Write standard output
      child.stdout.on('data', (data) => {
        logger.notice(`${this.invocationColorFn('─')} ${data.toString().trim()}`);
      });

      // Write error output
      child.stderr.on('data', (data) => {
        logger.notice(`${this.invocationColorFn('─')} ${style.error(data.toString().trim())}`);
      });

      // Handles child process errors, not user function errors
      child.on('error', (error) => {
        logger.notice(
          `${this.invocationColorFn('─')} ${style.error(`Child process error: ${error.message}`)}`
        );
      });

      child.on('close', async (code) => {
        try {
          const result = await getInvocationResult(child.pid);

          resolve(result);
        } catch (error) {
          reject(error);
        }
      });
    });
  }
}

/**
 * Gets the invocation result from the temporary file created by the runtime wrapper,
 * then deletes the file for cleanup. The result is parsed from JSON and returned.
 *
 * @param {*} childProcessId - The ID of the child process that executed the runtime wrapper to construct the unique file name.
 *
 * @returns {Promise<any>} A promise that resolves with the parsed result from the temporary file.
 */
const getInvocationResult = async (childProcessId) => {
  const filePath = path.join(os.tmpdir(), `sls_${childProcessId}.json`);

  const result = await fs.readFile(filePath, 'utf8');

  // delete the temporary file after reading its contents
  await fs.unlink(filePath);

  return JSON.parse(result);
};

/**
 * Asynchronously checks if a file exists at the specified file path.
 *
 * @async
 * @function fileExists
 * @param {string} filePath - The path to the file whose existence is to be checked.
 * @returns {Promise<boolean>} A promise that resolves to `true` if the file exists, or `false` if it does not.
 * @example
 * async function checkFile() {
 *   const exists = await fileExists('./example.txt');
 *   console.log(exists ? 'File exists' : 'File does not exist');
 * }
 */
const fileExists = async (filePath) => {
  try {
    await fs.access(filePath, fs.constants.F_OK);
    return true;
  } catch (error) {
    return false;
  }
};

/**
 * This is a list of runtime wrappers that we currently support.
 * It is easily extensible to support more runtimes.
 * Each wrapper has a:
 *   - Command to be executed (e.g. 'node', 'ts-node')
 *   - Path to the wrapper file that the command will execute
 *   - List of runtime versions that the wrapper supports
 *   - List of file extensions that the wrapper supports
 */
const runtimeWrappers = [
  {
    command: 'node',
    arguments: [],
    path: path.join(__dirname, 'runtime-wrappers/node.cjs'),
    versions: ['nodejs14.x', 'nodejs16.x', 'nodejs18.x', 'nodejs20.x'],
    extensions: ['.js', '.mjs', '.cjs', '.ts', '.mts', '.cts'],
  },
];

export default LocalLambda;