/**
 * Copyright (c) Microsoft Corporation.
 *
 * 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.
 */

import fs from 'fs';
import path from 'path';

import { createGuid } from './utils/crypto';
import { ZipFile } from './utils/zipFile';

import type { HeadersArray } from '../utils/isomorphic/types';
import type * as har from '@trace/har';

const redirectStatus = [301, 302, 303, 307, 308];

export class HarBackend {
  readonly id: string;
  private _harFile: har.HARFile;
  private _zipFile: ZipFile | null;
  private _baseDir: string | null;

  constructor(harFile: har.HARFile, baseDir: string | null, zipFile: ZipFile | null) {
    this.id = createGuid();
    this._harFile = harFile;
    this._baseDir = baseDir;
    this._zipFile = zipFile;
  }

  async lookup(url: string, method: string, headers: HeadersArray, postData: Buffer | undefined, isNavigationRequest: boolean): Promise<{
      action: 'error' | 'redirect' | 'fulfill' | 'noentry',
      message?: string,
      redirectURL?: string,
      status?: number,
      headers?: HeadersArray,
      body?: Buffer }> {
    let entry;
    try {
      entry = await this._harFindResponse(url, method, headers, postData);
    } catch (e) {
      return { action: 'error', message: 'HAR error: ' + e.message };
    }

    if (!entry)
      return { action: 'noentry' };

    // If navigation is being redirected, restart it with the final url to ensure the document's url changes.
    if (entry.request.url !== url && isNavigationRequest)
      return { action: 'redirect', redirectURL: entry.request.url };

    const response = entry.response;
    try {
      const buffer = await this._loadContent(response.content);
      return {
        action: 'fulfill',
        status: response.status,
        headers: response.headers,
        body: buffer,
      };
    } catch (e) {
      return { action: 'error', message: e.message };
    }
  }

  private async _loadContent(content: { text?: string, encoding?: string, _file?: string }): Promise<Buffer> {
    const file = content._file;
    let buffer: Buffer;
    if (file) {
      if (this._zipFile)
        buffer = await this._zipFile.read(file);
      else
        buffer = await fs.promises.readFile(path.resolve(this._baseDir!, file));
    } else {
      buffer = Buffer.from(content.text || '', content.encoding === 'base64' ? 'base64' : 'utf-8');
    }
    return buffer;
  }

  private async _harFindResponse(url: string, method: string, headers: HeadersArray, postData: Buffer | undefined): Promise<har.Entry | undefined> {
    const harLog = this._harFile.log;
    const visited = new Set<har.Entry>();
    while (true) {
      const entries: har.Entry[] = [];
      for (const candidate of harLog.entries) {
        if (candidate.request.url !== url || candidate.request.method !== method)
          continue;
        if (method === 'POST' && postData && candidate.request.postData) {
          const buffer = await this._loadContent(candidate.request.postData);
          if (!buffer.equals(postData)) {
            const boundary = multipartBoundary(headers);
            if (!boundary)
              continue;
            const candidataBoundary = multipartBoundary(candidate.request.headers);
            if (!candidataBoundary)
              continue;
            // Try to match multipart/form-data ignroing boundary as it changes between requests.
            if (postData.toString().replaceAll(boundary, '') !== buffer.toString().replaceAll(candidataBoundary, ''))
              continue;
          }
        }
        entries.push(candidate);
      }

      if (!entries.length)
        return;

      let entry = entries[0];

      // Disambiguate using headers - then one with most matching headers wins.
      if (entries.length > 1) {
        const list: { candidate: har.Entry, matchingHeaders: number }[] = [];
        for (const candidate of entries) {
          const matchingHeaders = countMatchingHeaders(candidate.request.headers, headers);
          list.push({ candidate, matchingHeaders });
        }
        list.sort((a, b) => b.matchingHeaders - a.matchingHeaders);
        entry = list[0].candidate;
      }

      if (visited.has(entry))
        throw new Error(`Found redirect cycle for ${url}`);

      visited.add(entry);

      // Follow redirects.
      const locationHeader = entry.response.headers.find(h => h.name.toLowerCase() === 'location');
      if (redirectStatus.includes(entry.response.status) && locationHeader) {
        const locationURL = new URL(locationHeader.value, url);
        url = locationURL.toString();
        if ((entry.response.status === 301 || entry.response.status === 302) && method === 'POST' ||
          entry.response.status === 303 && !['GET', 'HEAD'].includes(method)) {
          // HTTP-redirect fetch step 13 (https://fetch.spec.whatwg.org/#http-redirect-fetch)
          method = 'GET';
        }
        continue;
      }

      return entry;
    }
  }

  dispose() {
    this._zipFile?.close();
  }
}

function countMatchingHeaders(harHeaders: har.Header[], headers: HeadersArray): number {
  const set = new Set(headers.map(h => h.name.toLowerCase() + ':' + h.value));
  let matches = 0;
  for (const h of harHeaders) {
    if (set.has(h.name.toLowerCase() + ':' + h.value))
      ++matches;
  }
  return matches;
}

function multipartBoundary(headers: HeadersArray) {
  const contentType = headers.find(h => h.name.toLowerCase() === 'content-type');
  if (!contentType?.value.includes('multipart/form-data'))
    return undefined;
  const boundary = contentType.value.match(/boundary=(\S+)/);
  if (boundary)
    return boundary[1];
  return undefined;
}