import 'dart:async';
import 'dart:convert';
import 'dart:html' as html;
import 'dart:typed_data';

import '../layout/layout_controller.dart';
import '../session/log_buffer.dart';
import '../session/packet_buffer.dart';
import 'csv_exporter_base.dart';

export 'csv_exporter_base.dart';

/// Web CSV exporter: builds a Blob in memory and triggers a download.
///
/// Yields between chunks so the main thread doesn't lock during large exports.
class CsvExporterImpl implements CsvExporter {
  static const int _chunkRows = 1000;

  @override
  Future<ExportResult> exportData({
    required PacketBuffer buffer,
    required LayoutController layout,
    ProgressCallback? onProgress,
  }) async {
    final builder = CsvRowBuilder(layout);
    final chunks = <String>[];
    chunks.add('${builder.dataHeader()}\n');
    final total = buffer.length;
    final sb = StringBuffer();
    var written = 0;
    for (var i = 0; i < total; i++) {
      sb.writeln(builder.dataRow(buffer[i]));
      written++;
      if (written % _chunkRows == 0) {
        chunks.add(sb.toString());
        sb.clear();
        onProgress?.call(written / total);
        await Future<void>.delayed(Duration.zero);
      }
    }
    if (sb.isNotEmpty) chunks.add(sb.toString());

    final ts = DateTime.now().toIso8601String().replaceAll(':', '-');
    final filename = 'telemetry_data_$ts.csv';
    final bytes = _toBytes(chunks);
    _triggerDownload(filename, bytes);
    onProgress?.call(1.0);
    return ExportResult(path: filename, bytesWritten: bytes.length);
  }

  @override
  Future<ExportResult> exportLog({
    required LogBuffer buffer,
    ProgressCallback? onProgress,
  }) async {
    final builder = CsvRowBuilder(_NoLayoutPlaceholder());
    final chunks = <String>[];
    chunks.add('${builder.logHeader()}\n');
    final total = buffer.length;
    final sb = StringBuffer();
    var written = 0;
    for (final entry in buffer.iterate()) {
      sb.writeln(builder.logRow(entry));
      written++;
      if (written % _chunkRows == 0) {
        chunks.add(sb.toString());
        sb.clear();
        onProgress?.call(written / total);
        await Future<void>.delayed(Duration.zero);
      }
    }
    if (sb.isNotEmpty) chunks.add(sb.toString());

    final ts = DateTime.now().toIso8601String().replaceAll(':', '-');
    final filename = 'telemetry_log_$ts.csv';
    final bytes = _toBytes(chunks);
    _triggerDownload(filename, bytes);
    onProgress?.call(1.0);
    return ExportResult(path: filename, bytesWritten: bytes.length);
  }

  Uint8List _toBytes(List<String> chunks) {
    final encoder = utf8.encoder;
    final encoded = chunks.map(encoder.convert).toList();
    final total = encoded.fold<int>(0, (s, c) => s + c.length);
    final out = Uint8List(total);
    var off = 0;
    for (final c in encoded) {
      out.setRange(off, off + c.length, c);
      off += c.length;
    }
    return out;
  }

  void _triggerDownload(String filename, Uint8List bytes) {
    final blob = html.Blob([bytes], 'text/csv');
    final url = html.Url.createObjectUrlFromBlob(blob);
    final anchor = html.AnchorElement(href: url)
      ..download = filename
      ..style.display = 'none';
    html.document.body!.append(anchor);
    anchor.click();
    anchor.remove();
    html.Url.revokeObjectUrl(url);
  }
}

class _NoLayoutPlaceholder implements LayoutController {
  @override
  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
}