/// The HTTP client, built on `package:http`.
///
/// Retry policy: 429 and the transient 5xx in [retriableStatus], plus network
/// failures, are retried with exponentially backed-off, jittered waits. 400 and
/// 404 are deliberately absent from that set — both are definitive answers
/// about the request, so retrying returns the same thing more slowly while
/// burning someone else's quota.
library;

import 'dart:async';
import 'dart:convert';
import 'dart:math';

import 'package:http/http.dart' as http;

import 'csv.dart';
import 'errors.dart';
import 'models.dart';
import 'version.dart';

/// Where the public API lives.
const String defaultBaseUrl = 'https://cep.is';

/// How many CEPs the `/csv` endpoint accepts in one request.
const int maxBatch = 500;

/// The statuses worth trying again. 400 and 404 are deliberately absent.
const Set<int> retriableStatus = <int>{429, 500, 502, 503, 504};

const String _accept = 'application/json, text/csv;q=0.9, */*;q=0.1';

final RegExp _digitsOnly = RegExp(r'^\d{8}$');

final RegExp _separators = RegExp(r'[-.\s]');

final RegExp _imfFixdate = RegExp(
  r'^[A-Za-z]{3},\s+(\d{2})\s+([A-Za-z]{3})\s+(\d{4})\s+'
  r'(\d{2}):(\d{2}):(\d{2})\s+GMT$',
);

const Map<String, int> _months = <String, int>{
  'jan': 1,
  'feb': 2,
  'mar': 3,
  'apr': 4,
  'may': 5,
  'jun': 6,
  'jul': 7,
  'aug': 8,
  'sep': 9,
  'oct': 10,
  'nov': 11,
  'dec': 12,
};

/// Returns the CEP's 8 digits, accepting the mask.
///
/// `'01001-000'`, `'01001000'` and `' 01001-000 '` all become `'01001000'`.
///
/// Throws [InvalidCepException] unless exactly 8 digits remain. This runs
/// **before** any request: a 7-digit CEP is the caller's bug, and spending a
/// round trip for the server to say so wastes both sides' time.
String normalizeCep(String value) {
  final cleaned = value.trim().replaceAll(_separators, '');
  if (!_digitsOnly.hasMatch(cleaned)) {
    throw InvalidCepException(
      "CEP must be 8 digits, got '$value'",
      source: value,
    );
  }
  return cleaned;
}

/// Client for the cep.is API.
///
/// Reuse one instance: the configuration is immutable and no method keeps state
/// between calls, so it is safe to share anywhere in an isolate.
///
/// ```dart
/// final client = Client(totalTimeout: Duration(seconds: 15));
/// final address = await client.lookup('01001-000');
/// ```
///
/// Call [close] when done, unless you passed your own `httpClient` — then it is
/// yours to close.
class Client {
  /// Creates a client.
  ///
  /// [baseUrl] is where the API lives. Point it at a local instance (the API
  /// repo brings one up on `http://localhost:8080` with `just up`) or at a test
  /// server. It is the only parameter that usually changes between
  /// environments. A trailing slash is stripped, so it cannot produce doubled
  /// separators that some proxies normalise and others 404.
  ///
  /// [timeout] bounds a **single attempt** — request and body read together.
  /// `package:http` reads the whole response before returning, so this is one
  /// deadline over the exchange rather than one per socket operation. The cap
  /// on the whole call, retries and waits included, is [totalTimeout].
  ///
  /// [maxAttempts] counts the first attempt; `1` disables retrying. The default
  /// of `3` covers the common case (one transient failure) without turning a
  /// real outage into a long wait.
  ///
  /// [backoffBase] is the base of the exponential wait. The actual wait is
  /// drawn from `[0, base * 2^(n-1)]` — *full jitter*. The randomness is not
  /// decoration: without it, N clients that fail together come back together
  /// and reproduce the spike that took the service down.
  ///
  /// [backoffMax] caps each individual wait. It applies to a server-sent
  /// `Retry-After` too, or a `Retry-After: 3600` from a misconfigured proxy
  /// would park the caller for an hour.
  ///
  /// [totalTimeout] caps the whole call, attempts and waits included. `null`
  /// leaves [maxAttempts] as the only bound. Set it in code serving a web
  /// request: without it the worst case is `maxAttempts * timeout` plus the sum
  /// of the backoffs. When this cap is what cuts an attempt short, the error
  /// reported is still the API's last real answer rather than the truncation —
  /// a 503 you already know about is a better diagnosis than a timeout this
  /// client caused itself.
  ///
  /// [userAgent] overrides the `User-Agent`. The default identifies the library
  /// and its version, which is what lets the server diagnose an old client
  /// misbehaving.
  ///
  /// [httpClient] replaces the transport — pass one to share a connection pool,
  /// or to use a platform-native implementation such as `cupertino_http` or
  /// `cronet_http` under Flutter. A client passed here is never closed by
  /// [close].
  ///
  /// Throws [ArgumentError] for a non-positive duration or fewer than one
  /// attempt.
  Client({
    String baseUrl = defaultBaseUrl,
    Duration timeout = const Duration(seconds: 10),
    int maxAttempts = 3,
    Duration backoffBase = const Duration(milliseconds: 500),
    Duration backoffMax = const Duration(seconds: 8),
    Duration? totalTimeout,
    String? userAgent,
    http.Client? httpClient,
  })  : baseUrl = _stripTrailingSlashes(baseUrl),
        timeout = _positive(timeout, 'timeout'),
        maxAttempts = _atLeastOne(maxAttempts),
        backoffBase = _positive(backoffBase, 'backoffBase'),
        backoffMax = _positive(backoffMax, 'backoffMax'),
        totalTimeout = totalTimeout == null
            ? null
            : _positive(totalTimeout, 'totalTimeout'),
        userAgent = userAgent ?? 'cepis-dart/$packageVersion (+https://cep.is)',
        _http = httpClient ?? http.Client(),
        _ownsHttp = httpClient == null;

  /// The API root, without a trailing slash.
  final String baseUrl;

  /// How long a single attempt may take, request and body read together.
  final Duration timeout;

  /// How many attempts in total, counting the first.
  final int maxAttempts;

  /// Base of the exponential wait.
  final Duration backoffBase;

  /// Cap on each individual wait, a server-sent `Retry-After` included.
  final Duration backoffMax;

  /// Cap on the whole call, or `null` for none.
  final Duration? totalTimeout;

  /// The `User-Agent` sent with every request.
  final String userAgent;

  final http.Client _http;
  final bool _ownsHttp;
  final Random _random = Random();

  /// Looks up a single CEP.
  ///
  /// ```dart
  /// final address = await client.lookup('01001-000');
  /// address.localidade; // 'São Paulo'
  /// ```
  ///
  /// A 400 from the API surfaces as [InvalidCepException] carrying the API's
  /// own message: the format already passed local validation, so the server
  /// knows something this client does not.
  ///
  /// Throws [InvalidCepException] when the CEP is not 8 digits — no request is
  /// made; [CepNotFoundException] when it is well-formed but absent from the
  /// database; [RateLimitedException] on 429 after every attempt;
  /// [ServerException] on 5xx after every attempt; [NetworkException] when the
  /// request never completed; [InvalidResponseException] on a success status
  /// with an unreadable body.
  Future<Address> lookup(String cep) async {
    final number = normalizeCep(cep);
    final reply = await _request(_uri('/$number'));

    if (reply.status == 404) {
      throw CepNotFoundException(
        'CEP $number does not exist in the DNE database',
        cep: number,
      );
    }
    if (reply.status == 400) {
      throw InvalidCepException(
        _errorMessage(reply.body, 'CEP $number rejected'),
        source: cep,
      );
    }

    return Address.fromJson(_json(reply.body));
  }

  /// Looks up many CEPs in one batch.
  ///
  /// Returns a list of **the same length and in the same order** as the input.
  /// A CEP that does not exist becomes `null` at its position — it does not
  /// vanish from the list, and it does not throw. That is the right difference
  /// from [lookup]: in a batch of a thousand, one bad CEP must not cost the
  /// other nine hundred and ninety-nine.
  ///
  /// A malformed CEP also becomes `null`, for the same reason, rather than
  /// throwing [InvalidCepException]. To know *which* one was malformed,
  /// validate first with [normalizeCep].
  ///
  /// Input is chunked into blocks of [maxBatch] automatically.
  ///
  /// **Batches carry no coordinate.** The endpoint behind this is CSV, and the
  /// CSV has no `geo` column. Every [Address] returned here has a `null`
  /// [Address.geo], including for CEPs that do have one. Need the coordinate?
  /// Use [lookup], one at a time.
  Future<List<Address?>> lookupMany(List<String> ceps) async {
    if (ceps.isEmpty) {
      return <Address?>[];
    }

    final result = <Address?>[];
    for (var start = 0; start < ceps.length; start += maxBatch) {
      final end = min(start + maxBatch, ceps.length);
      result.addAll(await _lookupChunk(ceps.sublist(start, end)));
    }
    return result;
  }

  /// Queries `GET /health`: does the API answer, and with which database.
  ///
  /// Does not throw for an API reporting itself degraded — that arrives in
  /// [Health.status], and checking health is exactly when you want the
  /// diagnosis rather than an exception. Network failures still throw.
  Future<Health> health() async {
    final reply = await _request(
      _uri('/health'),
      acceptedStatus: const <int>[200, 503],
    );
    return Health.fromJson(_json(reply.body));
  }

  /// Releases the underlying transport.
  ///
  /// Does nothing when the transport was supplied through the `httpClient`
  /// parameter: that one belongs to the caller.
  void close() {
    if (_ownsHttp) {
      _http.close();
    }
  }

  Future<List<Address?>> _lookupChunk(List<String> ceps) async {
    final reply = await _request(
      _uri('/csv', <String, String>{'ceps': ceps.join(',')}),
    );

    final rows = <Address?>[];
    for (final record in parseCsv(reply.body)) {
      if ((record['localidade'] ?? '').trim().isEmpty) {
        rows.add(null);
        continue;
      }
      rows.add(Address.fromJson(record));
    }

    while (rows.length < ceps.length) {
      rows.add(null);
    }
    return rows.sublist(0, ceps.length);
  }

  Uri _uri(String path, [Map<String, String>? query]) {
    final uri = Uri.parse('$baseUrl$path');
    return query == null ? uri : uri.replace(queryParameters: query);
  }

  Map<String, dynamic> _json(String body) {
    final Object? data;
    try {
      data = jsonDecode(body);
    } on FormatException {
      throw InvalidResponseException(
        'response is not valid JSON — something between you and the API is '
        'answering instead of it: ${_snippet(body)}',
      );
    }
    if (data is! Map<String, dynamic>) {
      throw InvalidResponseException(
        'expected a JSON object, got ${data.runtimeType}',
      );
    }
    return data;
  }

  Duration _backoff(int attempt, Duration? retryAfter) {
    if (retryAfter != null) {
      return retryAfter < backoffMax ? retryAfter : backoffMax;
    }
    final exponent = attempt - 1 > 30 ? 30 : attempt - 1;
    final ceiling = min(
      backoffBase.inMicroseconds * (1 << exponent),
      backoffMax.inMicroseconds,
    );
    return Duration(microseconds: _random.nextInt(max(ceiling, 1)));
  }

  Future<_Reply> _request(
    Uri url, {
    List<int> acceptedStatus = const <int>[200],
  }) async {
    final elapsed = Stopwatch()..start();
    final budget = totalTimeout;

    int? lastStatus;
    Duration? lastRetryAfter;
    Object? lastFailure;

    for (var attempt = 1; attempt <= maxAttempts; attempt++) {
      var deadline = timeout;
      var truncated = false;
      if (budget != null) {
        final remaining = budget - elapsed.elapsed;
        if (remaining <= Duration.zero) {
          break;
        }
        if (remaining < deadline) {
          deadline = remaining;
          truncated = true;
        }
      }

      try {
        final response = await _http.get(
          url,
          headers: <String, String>{
            'User-Agent': userAgent,
            'Accept': _accept,
          },
        ).timeout(deadline);

        if (acceptedStatus.contains(response.statusCode) ||
            !retriableStatus.contains(response.statusCode)) {
          return _Reply(response.statusCode, _decode(response.bodyBytes));
        }

        lastStatus = response.statusCode;
        lastRetryAfter = _retryAfter(response.headers['retry-after']);
        lastFailure = null;
      } on Exception catch (error) {
        if (truncated && error is TimeoutException && lastStatus != null) {
          break;
        }
        lastFailure = error;
        lastStatus = null;
        lastRetryAfter = null;
      }

      if (attempt == maxAttempts) {
        break;
      }

      var wait = _backoff(attempt, lastRetryAfter);
      if (budget != null) {
        final remaining = budget - elapsed.elapsed;
        if (remaining <= Duration.zero) {
          break;
        }
        if (remaining < wait) {
          wait = remaining;
        }
      }
      await Future<void>.delayed(wait);
    }

    final suffix = '(after $maxAttempts attempt(s))';
    if (lastStatus == 429) {
      throw RateLimitedException(
        'rate limit reached at $url $suffix',
        retryAfter: lastRetryAfter,
      );
    }
    if (lastStatus != null) {
      throw ServerException(
        'the API answered $lastStatus at $url $suffix',
        status: lastStatus,
      );
    }
    throw NetworkException(
      'could not reach $url $suffix: $lastFailure',
      cause: lastFailure,
    );
  }

  static String _stripTrailingSlashes(String value) {
    var end = value.length;
    while (end > 0 && value[end - 1] == '/') {
      end--;
    }
    return value.substring(0, end);
  }

  static Duration _positive(Duration value, String name) {
    if (value <= Duration.zero) {
      throw ArgumentError.value(value, name, 'must be > 0');
    }
    return value;
  }

  static int _atLeastOne(int value) {
    if (value < 1) {
      throw ArgumentError.value(value, 'maxAttempts', 'must be >= 1');
    }
    return value;
  }
}

class _Reply {
  const _Reply(this.status, this.body);

  final int status;
  final String body;
}

String _decode(List<int> bytes) => utf8.decode(bytes, allowMalformed: true);

String _snippet(String body) =>
    body.length <= 120 ? body : '${body.substring(0, 120)}…';

String _errorMessage(String body, String fallback) {
  try {
    final Object? data = jsonDecode(body);
    if (data is Map<String, dynamic>) {
      final message = data['mensagem'];
      if (message is String && message.isNotEmpty) {
        return message;
      }
    }
  } on FormatException {
    return fallback;
  }
  return fallback;
}

Duration? _retryAfter(String? value) {
  if (value == null) {
    return null;
  }
  final header = value.trim();
  if (header.isEmpty) {
    return null;
  }

  final seconds = double.tryParse(header);
  if (seconds != null) {
    if (seconds <= 0) {
      return Duration.zero;
    }
    return Duration(microseconds: (seconds * 1000000).round());
  }

  final match = _imfFixdate.firstMatch(header);
  if (match == null) {
    return null;
  }
  final month = _months[match.group(2)!.toLowerCase()];
  if (month == null) {
    return null;
  }
  final target = DateTime.utc(
    int.parse(match.group(3)!),
    month,
    int.parse(match.group(1)!),
    int.parse(match.group(4)!),
    int.parse(match.group(5)!),
    int.parse(match.group(6)!),
  );
  final delta = target.difference(DateTime.now().toUtc());
  return delta.isNegative ? Duration.zero : delta;
}