import 'dart:async';
import 'dart:io' show HttpDate;
import 'package:angel_framework/angel_framework.dart';
import 'package:convert/convert.dart';
import 'package:crypto/crypto.dart';
import 'package:file/file.dart';
import 'virtual_directory.dart';

/// Generates an MD5 ETag from the given buffer.
String md5Etag(List<int> buf) {
  return hex.encode(md5.convert(buf).bytes);
}

/// Returns a string representation of the given [CacheAccessLevel].
String accessLevelToString(CacheAccessLevel accessLevel) {
  switch (accessLevel) {
    case CacheAccessLevel.PRIVATE:
      return 'private';
    case CacheAccessLevel.PUBLIC:
      return 'public';
    default:
      throw new ArgumentError('Unrecognized cache access level: $accessLevel');
  }
}

/// A `VirtualDirectory` that also sets `Cache-Control` headers.
class CachingVirtualDirectory extends VirtualDirectory {
  final Map<String, String> _etags = {};

  /// Either `PUBLIC` or `PRIVATE`.
  final CacheAccessLevel accessLevel;

  /// If `true`, responses will always have `private, max-age=0` as their `Cache-Control` header.
  final bool noCache;

  /// If `true` (default), `Cache-Control` headers will only be set if the application is in production mode.
  final bool onlyInProduction;

  /// If `true` (default), ETags will be computed and sent along with responses.
  final bool useEtags;

  /// The `max-age` for `Cache-Control`.
  ///
  /// Set this to `null` to leave no `Expires` header on responses.
  final int maxAge;

  CachingVirtualDirectory(Angel app, FileSystem fileSystem,
      {this.accessLevel: CacheAccessLevel.PUBLIC,
      Directory source,
      bool debug,
      Iterable<String> indexFileNames,
      this.maxAge: 0,
      this.noCache: false,
      this.onlyInProduction: false,
      this.useEtags: true,
      bool allowDirectoryListing,
      bool useBuffer: false,
      String publicPath,
      callback(File file, RequestContext req, ResponseContext res)})
      : super(app, fileSystem,
            source: source,
            indexFileNames: indexFileNames ?? ['index.html'],
            publicPath: publicPath ?? '/',
            callback: callback,
            allowDirectoryListing: allowDirectoryListing,
            useBuffer: useBuffer);

  @override
  Future<bool> serveFile(
      File file, FileStat stat, RequestContext req, ResponseContext res) {
    res.headers['accept-ranges'] = 'bytes';

    if (onlyInProduction == true && req.app.isProduction != true) {
      return super.serveFile(file, stat, req, res);
    }

    bool shouldNotCache = noCache == true;

    if (!shouldNotCache) {
      shouldNotCache = req.headers.value('cache-control') == 'no-cache' ||
          req.headers.value('pragma') == 'no-cache';
    }

    if (shouldNotCache) {
      res.headers['cache-control'] = 'private, max-age=0, no-cache';
      return super.serveFile(file, stat, req, res);
    } else {
      var ifModified = req.headers.ifModifiedSince;
      bool ifRange = false;

      try {
        ifModified = HttpDate.parse(req.headers.value('if-range'));
        ifRange = true;
      } catch (_) {
        // Fail silently...
      }

      if (ifModified != null) {
        try {
          var ifModifiedSince = ifModified;

          if (ifModifiedSince.compareTo(stat.modified) >= 0) {
            res.statusCode = 304;
            setCachedHeaders(stat.modified, req, res);

            if (useEtags && _etags.containsKey(file.absolute.path))
              res.headers['ETag'] = _etags[file.absolute.path];

            if (ifRange) {
              // Send the 206 like normal
              res.statusCode = 206;
              return super.serveFile(file, stat, req, res);
            }

            return new Future.value(false);
          } else if (ifRange) {
            // Return 200, just send the whole thing.
            return res.streamFile(file).then((_) => false);
          }
        } catch (_) {
          throw new AngelHttpException.badRequest(
              message:
                  'Invalid date for ${ifRange ? 'if-range' : 'if-not-modified-since'} header.');
        }
      }

      // If-modified didn't work; try etags

      if (useEtags == true) {
        var etagsToMatchAgainst = req.headers['if-none-match'];
        ifRange = false;

        if (etagsToMatchAgainst?.isNotEmpty != true) {
          etagsToMatchAgainst = req.headers['if-range'];
          ifRange = etagsToMatchAgainst?.isNotEmpty == true;
        }

        if (etagsToMatchAgainst?.isNotEmpty == true) {
          bool hasBeenModified = false;

          for (var etag in etagsToMatchAgainst) {
            if (etag == '*')
              hasBeenModified = true;
            else {
              hasBeenModified = !_etags.containsKey(file.absolute.path) ||
                  _etags[file.absolute.path] != etag;
            }
          }

          if (!ifRange) {
            if (!hasBeenModified) {
              res.statusCode = 304;
              setCachedHeaders(stat.modified, req, res);
              return new Future.value(false);
            }
          } else {
            if (!hasBeenModified) {
              // Continue serving like a regular range...
              return super.serveFile(file, stat, req, res);
            } else {
              // Otherwise, send the whole thing.
              return res.streamFile(file).then((_) => false);
            }
          }
        }
      }

      return file.readAsBytes().then((buf) {
        if (useEtags) {
          res.headers['ETag'] = _etags[file.absolute.path] = md5Etag(buf);
        }
        //res.statusCode = 200;
        res.headers
          ..['content-type'] = res.app.mimeTypeResolver.lookup(file.path) ??
              'application/octet-stream';
        setCachedHeaders(stat.modified, req, res);
        res.add(buf);
        return false;
      });
    }
  }

  void setCachedHeaders(
      DateTime modified, RequestContext req, ResponseContext res) {
    var privacy = accessLevelToString(accessLevel ?? CacheAccessLevel.PUBLIC);

    res.headers
      ..['cache-control'] = '$privacy, max-age=${maxAge ?? 0}'
      ..['last-modified'] = HttpDate.format(modified);

    if (maxAge != null) {
      var expiry = new DateTime.now().add(new Duration(seconds: maxAge ?? 0));
      res.headers['expires'] = HttpDate.format(expiry);
    }
  }
}

enum CacheAccessLevel { PUBLIC, PRIVATE }