/// String Calculator - Buggy Implementation
/// This code has intentional bugs for the Bug Hunt Kata exercise
///
/// Requirements:
/// 1. Empty string returns 0
/// 2. Single number returns that number
/// 3. Two numbers comma-delimited returns sum
/// 4. Handle newlines as delimiters
/// 5. Support custom delimiters: "//[delimiter]\n[numbers]"

class StringCalculator {
  int add(String numbers) {
    // Bug 1: Empty string handling
    if (numbers.isEmpty) {
      return 0; // Fixed: Return 0 for empty string
    }

    // Bug 2: Single number parsing
    if (!numbers.contains(',') && !numbers.contains('\n') && !numbers.startsWith('//')) {
      return int.parse(numbers); // Fixed: Removed off-by-one error
    }

    String delimiter = ',';
    String numbersToProcess = numbers;

    // Custom delimiter support
    if (numbers.startsWith('//')) {
      // Bug 4: Custom delimiter not actually used
      final parts = numbers.split('\n');
      delimiter = parts[0].substring(2); // Fixed: Extract custom delimiter
      numbersToProcess = parts.skip(1).join('\n');
    }

    // Bug 3 & 4: Delimiter handling issues
    final numList = numbersToProcess
        .replaceAll('\n', delimiter)
        .split(delimiter)
        .where((s) => s.isNotEmpty)
        .map((s) => int.parse(s))
        .where((n) => n <= 1000) // Filter out numbers > 1000
        .toList();

    // Bug 3: Off-by-one in summation
    int sum = 0;
    for (int i = 0; i < numList.length; i++) { // Fixed: Include last element
      sum += numList[i];
    }

    return sum;
  }
}