/**
 * Copyright 2018 The AMP HTML Authors. All Rights Reserved.
 *
 * 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.
 */
'use strict';

const URL = require('url').URL;
const {join, resolve} = require('path');

const DUMMY_HOST = 'https://example.com';

/**
 * Resolves a given URL / path against an optional base. The base can either specify an URL or
 * a relative filesystem path. It's also possible to pass a function for calculating the image
 * path.
 */
class PathResolver {
  /**
   * Create a PathResolver.
   * @param {string|function}  [base=''] - relative path or base URL
   */
  constructor(base = '') {
    if (typeof base === 'function') {
      this.implementation = base;
    } else {
      this.implementation = this.createStaticResolver(base);
    }
  }

  /**
   * Resolves the given path against the base.
   *
   * @param {string} path - an absolute or relative URL
   * @param {Object} params - the params object getting passed when calling ampOptimizer.transformHtml(html, params)
   * @returns {string}
   */
  resolve(path, params) {
    return this.implementation(path, params);
  }

  createStaticResolver(base) {
    let baseSpecifiesHost = false;
    try {
      new URL(base);
      baseSpecifiesHost = true;
    } catch (_) {
      // base is not a valid host
    }
    return (path) => {
      try {
        if (baseSpecifiesHost) {
          return new URL(path, base).toString();
        } else {
          return new URL(path).toString();
        }
      } catch (_) {
        // path and base specify a relative path
      }
      // remove query params to be able to find a file on the local filesystem
      path = new URL(path, DUMMY_HOST).pathname.substring(1);
      // resolve path to make debugging easier in case a file cannot be found locally
      return resolve(join(base, path));
    };
  }
}

module.exports = PathResolver;