// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';

import '../base/context.dart';
import '../convert.dart';
import '../globals.dart';
import 'common.dart';
import 'file_system.dart';
import 'io.dart';
import 'platform.dart';

const int kNetworkProblemExitCode = 50;

typedef HttpClientFactory = HttpClient Function();

/// Download a file from the given URL.
///
/// If a destination file is not provided, returns the bytes.
///
/// If a destination file is provided, streams the bytes to that file and
/// returns an empty list.
///
/// If [maxAttempts] is exceeded, returns null.
Future<List<int>> fetchUrl(Uri url, {
  int maxAttempts,
  File destFile,
}) async {
  int attempts = 0;
  int durationSeconds = 1;
  while (true) {
    attempts += 1;
    _MemoryIOSink memorySink;
    IOSink sink;
    if (destFile == null) {
      memorySink = _MemoryIOSink();
      sink = memorySink;
    } else {
      sink = destFile.openWrite();
    }

    final bool result = await _attempt(
      url,
      destSink: sink,
    );
    if (result) {
      return memorySink?.writes?.takeBytes() ?? <int>[];
    }

    if (maxAttempts != null && attempts >= maxAttempts) {
      printStatus('Download failed -- retry $attempts');
      return null;
    }
    printStatus('Download failed -- attempting retry $attempts in '
        '$durationSeconds second${ durationSeconds == 1 ? "" : "s"}...');
    await Future<void>.delayed(Duration(seconds: durationSeconds));
    if (durationSeconds < 64) {
      durationSeconds *= 2;
    }
  }
}

/// Check if the given URL points to a valid endpoint.
Future<bool> doesRemoteFileExist(Uri url) async => await _attempt(url, onlyHeaders: true);

// Returns true on success and false on failure.
Future<bool> _attempt(Uri url, {
  IOSink destSink,
  bool onlyHeaders = false,
}) async {
  assert(onlyHeaders || destSink != null);
  printTrace('Downloading: $url');
  HttpClient httpClient;
  if (context.get<HttpClientFactory>() != null) {
    httpClient = context.get<HttpClientFactory>()();
  } else {
    httpClient = HttpClient();
  }
  HttpClientRequest request;
  HttpClientResponse response;
  try {
    if (onlyHeaders) {
      request = await httpClient.headUrl(url);
    } else {
      request = await httpClient.getUrl(url);
    }
    response = await request.close();
  } on ArgumentError catch (error) {
    final String overrideUrl = platform.environment['FLUTTER_STORAGE_BASE_URL'];
    if (overrideUrl != null && url.toString().contains(overrideUrl)) {
      printError(error.toString());
      throwToolExit(
        'The value of FLUTTER_STORAGE_BASE_URL ($overrideUrl) could not be '
        'parsed as a valid url. Please see https://flutter.dev/community/china '
        'for an example of how to use it.\n'
        'Full URL: $url',
        exitCode: kNetworkProblemExitCode,);
    }
    printError(error.toString());
    rethrow;
  } on HandshakeException catch (error) {
    printTrace(error.toString());
    throwToolExit(
      'Could not authenticate download server. You may be experiencing a man-in-the-middle attack,\n'
      'your network may be compromised, or you may have malware installed on your computer.\n'
      'URL: $url',
      exitCode: kNetworkProblemExitCode,
    );
  } on SocketException catch (error) {
    printTrace('Download error: $error');
    return false;
  } on HttpException catch (error) {
    printTrace('Download error: $error');
    return false;
  }
  assert(response != null);

  // If we're making a HEAD request, we're only checking to see if the URL is
  // valid.
  if (onlyHeaders) {
    return response.statusCode == HttpStatus.ok;
  }
  if (response.statusCode != HttpStatus.ok) {
    if (response.statusCode > 0 && response.statusCode < 500) {
      throwToolExit(
        'Download failed.\n'
        'URL: $url\n'
        'Error: ${response.statusCode} ${response.reasonPhrase}',
        exitCode: kNetworkProblemExitCode,
      );
    }
    // 5xx errors are server errors and we can try again
    printTrace('Download error: ${response.statusCode} ${response.reasonPhrase}');
    return false;
  }
  printTrace('Received response from server, collecting bytes...');
  try {
    assert(destSink != null);
    await response.forEach(destSink.add);
    return true;
  } on IOException catch (error) {
    printTrace('Download error: $error');
    return false;
  } finally {
    await destSink?.flush();
    await destSink?.close();
  }
}

/// An IOSink that collects whatever is written to it.
class _MemoryIOSink implements IOSink {
  @override
  Encoding encoding = utf8;

  final BytesBuilder writes = BytesBuilder(copy: false);

  @override
  void add(List<int> data) {
    writes.add(data);
  }

  @override
  Future<void> addStream(Stream<List<int>> stream) {
    final Completer<void> completer = Completer<void>();
    stream.listen(add).onDone(completer.complete);
    return completer.future;
  }

  @override
  void writeCharCode(int charCode) {
    add(<int>[charCode]);
  }

  @override
  void write(Object obj) {
    add(encoding.encode('$obj'));
  }

  @override
  void writeln([ Object obj = '' ]) {
    add(encoding.encode('$obj\n'));
  }

  @override
  void writeAll(Iterable<dynamic> objects, [ String separator = '' ]) {
    bool addSeparator = false;
    for (dynamic object in objects) {
      if (addSeparator) {
        write(separator);
      }
      write(object);
      addSeparator = true;
    }
  }

  @override
  void addError(dynamic error, [ StackTrace stackTrace ]) {
    throw UnimplementedError();
  }

  @override
  Future<void> get done => close();

  @override
  Future<void> close() async { }

  @override
  Future<void> flush() async { }
}