// TODO(stuartmorgan): Remove this. See https://github.com/flutter/flutter/issues/174722.
// ignore_for_file: public_member_api_docs

import '../mustache.dart' as m;

class TemplateException implements m.TemplateException {
  TemplateException(this.message, this.templateName, this.source, this.offset);

  @override
  final String message;
  @override
  final String? templateName;
  @override
  final String? source;
  @override
  final int? offset;

  bool _isUpdated = false;
  late int _line;
  late int _column;
  late String _context;

  @override
  int get line {
    _update();
    return _line;
  }

  @override
  int get column {
    _update();
    return _column;
  }

  @override
  String get context {
    _update();
    return _context;
  }

  @override
  String toString() {
    final List<Object?> list = <Object?>[];
    if (templateName != null) {
      list.add(templateName);
    }
    list.add(line);
    list.add(column);
    final String location = list.isEmpty ? '' : ' (${list.join(':')})';
    return '$message$location\n$context';
  }

  // This source code is a modified version of FormatException.toString().
  void _update() {
    if (_isUpdated) {
      return;
    }
    _isUpdated = true;

    if (source == null ||
        offset == null ||
        (offset! < 0 || offset! > source!.length)) {
      return;
    }

    // Find line and character column.
    int lineNum = 1;
    int lineStart = 0;
    bool lastWasCR = false;
    for (int i = 0; i < offset!; i++) {
      final int char = source!.codeUnitAt(i);
      if (char == 0x0a) {
        if (lineStart != i || !lastWasCR) {
          lineNum += 1;
        }
        lineStart = i + 1;
        lastWasCR = false;
      } else if (char == 0x0d) {
        lineNum++;
        lineStart = i + 1;
        lastWasCR = true;
      }
    }

    _line = lineNum;
    _column = offset! - lineStart + 1;

    // Find context.
    int lineEnd = source!.length;
    for (int i = offset!; i < source!.length; i++) {
      final int char = source!.codeUnitAt(i);
      if (char == 0x0a || char == 0x0d) {
        lineEnd = i;
        break;
      }
    }
    final int length = lineEnd - lineStart;
    int start = lineStart;
    int end = lineEnd;
    String prefix = '';
    String postfix = '';
    if (length > 78) {
      // Can't show entire line. Try to anchor at the nearest end, if
      // one is within reach.
      final int index = offset! - lineStart;
      if (index < 75) {
        end = start + 75;
        postfix = '...';
      } else if (end - offset! < 75) {
        start = end - 75;
        prefix = '...';
      } else {
        // Neither end is near, just pick an area around the offset.
        start = offset! - 36;
        end = offset! + 36;
        prefix = postfix = '...';
      }
    }
    final String slice = source!.substring(start, end);
    final int markOffset = offset! - start + prefix.length;

    _context = "$prefix$slice$postfix\n${" " * markOffset}^\n";
  }
}