/**
 * This task builds OpenLayers with the Closure Compiler.
 */
var fs = require('fs');
var path = require('path');

var async = require('async');
var closure = require('closure-util');
var fse = require('fs-extra');
var nomnom = require('nomnom');

var generateExports = require('./generate-exports');

var log = closure.log;
var root = path.join(__dirname, '..');


/**
 * Assert that a provided config object is valid.
 * @param {Object} config Build configuration object.
 * @param {function(Error)} callback Called with an error if config is invalid.
 */
function assertValidConfig(config, callback) {
  process.nextTick(function() {
    if (!Array.isArray(config.exports)) {
      callback(new Error('Config missing "exports" array'));
      return;
    }
    if (typeof config.compile !== 'object') {
      callback(new Error('Config missing "compile" object'));
      return;
    }
    callback(null);
  });
}


/**
 * Read the build configuration file.
 * @param {string} configPath Path to config file.
 * @param {function(Error, Object)} callback Callback.
 */
function readConfig(configPath, callback) {
  fs.readFile(configPath, function(err, data) {
    if (err) {
      if (err.code === 'ENOENT') {
        err = new Error('Unable to find config file: ' + configPath);
      }
      callback(err);
      return;
    }
    var config;
    try {
      config = JSON.parse(String(data));
    } catch (err2) {
      callback(new Error('Trouble parsing config as JSON: ' + err2.message));
      return;
    }
    callback(null, config);
  });
}


/**
 * Get the list of sources sorted in dependency order.
 * @param {function(Error, Array.<string>)} callback Called with a list of paths
 *     or any error.
 */
function getDependencies(callback) {
  log.info('ol', 'Parsing dependencies');
  closure.getDependencies({lib: ['src/**/*.js']}, function(err, paths) {
    if (err) {
      callback(err);
      return;
    }
    paths.push(path.join(root, 'build', 'exports.js'));
    callback(null, paths);
  });
}


/**
 * Run the compiler.
 * @param {Object} options Options for Closure Compiler.
 * @param {Array.<string>} paths List of paths to source files.
 * @param {function(Error, string)} callback Called with the compiled output or
 *     any error.
 */
function build(options, paths, callback) {
  log.info('ol', 'Compiling ' + paths.length + ' sources');
  options.js = paths;
  closure.compile(options, callback);
}


/**
 * Generate a build of the library.
 * @param {Object} config Build configuration object.  Must have an "exports"
 *     array and a "compile" object with options for the compiler.
 * @param {function(Error, string)} callback Called with the compiled source
 *     or any error.
 */
function main(config, callback) {
  async.waterfall([
    assertValidConfig.bind(null, config),
    generateExports.bind(null, config.exports),
    getDependencies,
    build.bind(null, config.compile)
  ], callback);
}


/**
 * If running this module directly, read the config file and call the main
 * function.
 */
if (require.main === module) {
  var options = nomnom.options({
    config: {
      position: 0,
      required: true,
      help: 'Path to JSON config file'
    },
    output: {
      position: 1,
      required: true,
      help: 'Output file path'
    },
    loglevel: {
      abbr: 'l',
      choices: ['silly', 'verbose', 'info', 'warn', 'error'],
      default: 'info',
      help: 'Log level',
      metavar: 'LEVEL'
    }
  }).parse();

  /**
   * Set the log level.
   * @type {string}
   */
  log.level = options.loglevel;

  // read the config, run the main function, and write the output file
  async.waterfall([
    readConfig.bind(null, options.config),
    main,
    fse.outputFile.bind(fse, options.output)
  ], function(err) {
    if (err) {
      log.error(err.message);
      process.exit(1);
    } else {
      process.exit(0);
    }
  });
}


/**
 * Export main function.
 */
module.exports = main;