const { ono } = require('@jsdevtools/ono');

const {
  ResolverError,
  ParserError,
  UnmatchedParserError,
  UnmatchedResolverError,
  isHandledError,
} = require('./util/errors');
const plugins = require('./util/plugins');
const url = require('./util/url');

/**
 * Reads and parses the specified file path or URL.
 *
 * @param {string} path - This path MUST already be resolved, since `read` doesn't know the resolution context
 * @param {$Refs} $refs
 * @param {$RefParserOptions} options
 *
 * @returns {Promise}
 * The promise resolves with the parsed file contents, NOT the raw (Buffer) contents.
 */
module.exports = async function parse(path, $refs, options) {
  // Remove the URL fragment, if any
  // eslint-disable-next-line no-param-reassign
  path = url.stripHash(path);

  // Add a new $Ref for this file, even though we don't have the value yet.
  // This ensures that we don't simultaneously read & parse the same file multiple times
  const $ref = $refs._add(path);

  // This "file object" will be passed to all resolvers and parsers.
  const file = {
    url: path,
    extension: url.getExtension(path),
  };

  // Read the file and then parse the data
  try {
    const resolver = await readFile(file, options, $refs);
    $ref.pathType = resolver.plugin.name;
    file.data = resolver.result;

    const parser = await parseFile(file, options, $refs);
    $ref.value = parser.result;

    return parser.result;
  } catch (err) {
    if (isHandledError(err)) {
      $ref.value = err;
    }

    throw err;
  }
};

/**
 * Reads the given file, using the configured resolver plugins
 *
 * @param {object} file           - An object containing information about the referenced file
 * @param {string} file.url       - The full URL of the referenced file
 * @param {string} file.extension - The lowercased file extension (e.g. ".txt", ".html", etc.)
 * @param {$RefParserOptions} options
 *
 * @returns {Promise}
 * The promise resolves with the raw file contents and the resolver that was used.
 */
function readFile(file, options, $refs) {
  return new Promise((resolve, reject) => {
    // console.log('Reading %s', file.url);

    // Find the resolvers that can read this file
    let resolvers = plugins.all(options.resolve);
    resolvers = plugins.filter(resolvers, 'canRead', file);

    // Run the resolvers, in order, until one of them succeeds
    plugins.sort(resolvers);
    plugins.run(resolvers, 'read', file, $refs).then(resolve, onError);

    function onError(err) {
      if (!err && options.continueOnError) {
        // No resolver could be matched
        reject(new UnmatchedResolverError(file.url));
      } else if (!err || !('error' in err)) {
        // Throw a generic, friendly error.
        reject(ono.syntax(`Unable to resolve $ref pointer "${file.url}"`));
      } else if (err.error instanceof ResolverError) {
        // Throw the original error, if it's one of our own (user-friendly) errors.
        reject(err.error);
      } else {
        reject(new ResolverError(err, file.url));
      }
    }
  });
}

/**
 * Parses the given file's contents, using the configured parser plugins.
 *
 * @param {object} file           - An object containing information about the referenced file
 * @param {string} file.url       - The full URL of the referenced file
 * @param {string} file.extension - The lowercased file extension (e.g. ".txt", ".html", etc.)
 * @param {*}      file.data      - The file contents. This will be whatever data type was returned by the resolver
 * @param {$RefParserOptions} options
 *
 * @returns {Promise}
 * The promise resolves with the parsed file contents and the parser that was used.
 */
function parseFile(file, options, $refs) {
  return new Promise((resolve, reject) => {
    // console.log('Parsing %s', file.url);

    // Find the parsers that can read this file type.
    // If none of the parsers are an exact match for this file, then we'll try ALL of them.
    // This handles situations where the file IS a supported type, just with an unknown extension.
    const allParsers = plugins.all(options.parse);
    const filteredParsers = plugins.filter(allParsers, 'canParse', file);
    const parsers = filteredParsers.length > 0 ? filteredParsers : allParsers;

    // Run the parsers, in order, until one of them succeeds
    plugins.sort(parsers);
    plugins.run(parsers, 'parse', file, $refs).then(onParsed, onError);

    function onParsed(parser) {
      if (!parser.plugin.allowEmpty && isEmpty(parser.result)) {
        reject(ono.syntax(`Error parsing "${file.url}" as ${parser.plugin.name}. \nParsed value is empty`));
      } else {
        resolve(parser);
      }
    }

    function onError(err) {
      if (!err && options.continueOnError) {
        // No resolver could be matched
        reject(new UnmatchedParserError(file.url));
      } else if (!err || !('error' in err)) {
        reject(ono.syntax(`Unable to parse ${file.url}`));
      } else if (err.error instanceof ParserError) {
        reject(err.error);
      } else {
        reject(new ParserError(err.error.message, file.url));
      }
    }
  });
}

/**
 * Determines whether the parsed value is "empty".
 *
 * @param {*} value
 * @returns {boolean}
 */
function isEmpty(value) {
  return (
    value === undefined ||
    (typeof value === 'object' && Object.keys(value).length === 0) ||
    (typeof value === 'string' && value.trim().length === 0) ||
    (Buffer.isBuffer(value) && value.length === 0)
  );
}