packages/flutter_tools/lib/src/web/devfs_proxy.dart

// 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 'package:yaml/yaml.dart';

import '../base/logger.dart';

/// Represents a rule for proxying requests based on a specific pattern.
///
/// Subclasses must implement the [matches], [replace], and [targetUri] members.
sealed class ProxyRule {
  static const _kLogEntryPrefix = '[ProxyRule]';
  static const _kTarget = 'target';
  static const _kRegex = 'regex';
  static const _kPrefix = 'prefix';
  static const _kReplace = 'replace';

  /// Checks if the given [path] matches the rule's pattern.
  bool matches(String path);

  /// Replaces the matched part of the [path] according to the rule's logic.
  /// If no replacement is needed, it returns the original path.
  String replace(String path);

  /// Returns the target URI to which the request should be proxied.
  Uri get targetUri;

  /// If both or neither 'prefix' and 'regex' are defined, it logs an error and returns null.
  /// Otherwise, it tries to create a [PrefixProxyRule] or [RegexProxyRule] based on the [yaml] keys.
  static ProxyRule? fromYaml(YamlMap yaml, Logger logger) {
    if (PrefixProxyRule.canHandle(yaml) && RegexProxyRule.canHandle(yaml)) {
      logger.printError(
        '$_kLogEntryPrefix Both $_kPrefix and $_kRegex are defined in the proxy rule YAML.'
        ' Only one should be used.',
      );
      return null;
    } else if (PrefixProxyRule.canHandle(yaml)) {
      return PrefixProxyRule.fromYaml(yaml, logger);
    } else if (RegexProxyRule.canHandle(yaml)) {
      return RegexProxyRule.fromYaml(yaml, logger);
    } else {
      logger.printError('$_kLogEntryPrefix Invalid proxy rule in YAML: $yaml');
      return null;
    }
  }

  /// Rewrites [requestUri] for the target URI.
  ///
  /// 1. Getting the base target URI from the rule.
  /// 2. Replacing the request path according to the rule's replacement logic.
  /// 3. Resolving the final target URL by combining the target URI, the rewritten
  ///    request path and the request query
  Uri finalTargetUri(Uri requestUri) {
    final String rewrittenPath = replace(requestUri.path);
    return targetUri.resolveUri(Uri(path: rewrittenPath, query: requestUri.query));
  }
}

/// A [ProxyRule] implementation that uses regular expressions for matching and
/// replacement.
///
/// This rule matches paths against a provided regular expression [_pattern].
/// If a [_replacement] string is provided, it replaces parts of the matched
/// path based on regex group capturing.
class RegexProxyRule extends ProxyRule {
  /// Creates a [RegexProxyRule] with the given regular expression [_pattern],
  /// [target] URI base, and optional [_replacement] string.
  RegexProxyRule({required this._pattern, required String target, this._replacement})
    : targetUri = Uri.parse(target);

  final RegExp _pattern;
  final String? _replacement;
  @override
  /// The target URI to which the request should be proxied.
  final Uri targetUri;

  @override
  bool matches(String path) {
    return _pattern.hasMatch(path);
  }

  @override
  String replace(String path) {
    if (_replacement == null) {
      return path;
    }
    return path.replaceAllMapped(_pattern, (Match match) {
      String result = _replacement;
      for (var i = 0; i <= match.groupCount; i++) {
        result = result.replaceAll('\$$i', match.group(i) ?? '');
      }
      return result;
    });
  }

  @override
  String toString() {
    return '{${ProxyRule._kRegex}: ${_pattern.pattern}, ${ProxyRule._kTarget}: $targetUri, ${ProxyRule._kReplace}: ${_replacement ?? 'null'}}';
  }

  /// Checks if the given [yaml] can be handled by this rule.
  /// It requires the 'regex' key to be present and non-empty.
  static bool canHandle(YamlMap yaml) {
    return yaml.containsKey(ProxyRule._kRegex) &&
        yaml[ProxyRule._kRegex] is String &&
        (yaml[ProxyRule._kRegex] as String).isNotEmpty;
  }

  /// Attempts to create a [RegexProxyRule] from the provided [yaml] map.
  /// If the 'regex' or 'target' keys are missing or invalid, it logs an error
  /// and returns null.
  /// If the 'regex' is invalid, it logs a warning and treats it as a string.
  static RegexProxyRule? fromYaml(YamlMap yaml, Logger effectiveLogger) {
    final regex = yaml[ProxyRule._kRegex] as String?;
    final target = yaml[ProxyRule._kTarget] as String?;
    final replacement = yaml[ProxyRule._kReplace] as String?;
    if (regex == null || regex.isEmpty) {
      return null;
    } else if (target == null || target.isEmpty) {
      effectiveLogger.printError(
        '${ProxyRule._kLogEntryPrefix} Invalid ${ProxyRule._kTarget} for '
        '${ProxyRule._kRegex}: $regex. ${ProxyRule._kTarget} cannot be null',
      );
      return null;
    }
    RegExp? pattern;
    try {
      pattern = RegExp(regex.trim());
    } on FormatException catch (e) {
      pattern = RegExp(RegExp.escape(regex));
      effectiveLogger.printWarning(
        '${ProxyRule._kLogEntryPrefix} Invalid regex pattern in ${ProxyRule._kRegex}: $regex. '
        'Treating $regex as string. Error: $e',
      );
    }
    return RegexProxyRule(pattern: pattern, target: target, replacement: replacement?.trim());
  }
}

/// A [ProxyRule] implementation that matches paths starting with a specific prefix.
///
/// If a [_replacement] string is provided, it replaces the prefix in the matched path.
class PrefixProxyRule extends RegexProxyRule {
  /// Creates a [PrefixProxyRule] with the given [prefix] prefix, [target] URI base,
  /// and optional [replacement] string.
  PrefixProxyRule({required String prefix, required super.target, super.replacement})
    : super(pattern: RegExp('^${RegExp.escape(prefix)}'));

  @override
  String toString() {
    return '{${ProxyRule._kPrefix}: ${_pattern.pattern}, ${ProxyRule._kTarget}: $targetUri, ${ProxyRule._kReplace}: ${_replacement ?? 'null'}}';
  }

  /// Checks if the given [yaml] can be handled by this rule.
  /// It requires the 'prefix' key to be present and non-empty.
  static bool canHandle(YamlMap yaml) {
    return yaml.containsKey(ProxyRule._kPrefix) &&
        yaml[ProxyRule._kPrefix] is String &&
        (yaml[ProxyRule._kPrefix] as String).isNotEmpty;
  }

  /// Attempts to create a [PrefixProxyRule] from the provided [yaml] map.
  /// If the 'prefix' or 'target' keys are missing or invalid, it logs an error
  /// and returns null.
  static PrefixProxyRule? fromYaml(YamlMap yaml, Logger effectiveLogger) {
    final prefix = yaml[ProxyRule._kPrefix] as String?;
    final target = yaml[ProxyRule._kTarget] as String?;
    final replacement = yaml[ProxyRule._kReplace] as String?;
    if (prefix == null || prefix.isEmpty) {
      return null;
    } else if (target == null || target.isEmpty) {
      effectiveLogger.printError(
        '${ProxyRule._kLogEntryPrefix} Invalid ${ProxyRule._kTarget} for '
        '${ProxyRule._kPrefix}: $prefix. ${ProxyRule._kTarget} cannot be null',
      );
      return null;
    }
    return PrefixProxyRule(prefix: prefix, target: target, replacement: replacement?.trim());
  }
}