/// Month-grid helpers for the transactions heatmap.
library;

DateTime dateOnly(DateTime date) => DateTime(date.year, date.month, date.day);

DateTime monthStart(DateTime date) => DateTime(date.year, date.month);

bool isSameDay(DateTime a, DateTime b) =>
    a.year == b.year && a.month == b.month && a.day == b.day;

bool isSameMonth(DateTime a, DateTime b) =>
    a.year == b.year && a.month == b.month;

DateTime addMonths(DateTime month, int delta) =>
    DateTime(month.year, month.month + delta);

/// Monday-first calendar cells for [month], padded with nulls to full weeks.
List<DateTime?> monthGrid(DateTime month) {
  final start = DateTime(month.year, month.month, 1);
  final daysInMonth = DateTime(month.year, month.month + 1, 0).day;
  final leading = start.weekday - DateTime.monday;
  final cells = <DateTime?>[
    ...List<DateTime?>.filled(leading, null),
    for (var day = 1; day <= daysInMonth; day++)
      DateTime(month.year, month.month, day),
  ];
  while (cells.length % 7 != 0) {
    cells.add(null);
  }
  return cells;
}

/// How many transactions landed on each calendar day.
Map<DateTime, int> txCountsByDay(Iterable<DateTime> dates) {
  final counts = <DateTime, int>{};
  for (final date in dates) {
    final key = dateOnly(date);
    counts[key] = (counts[key] ?? 0) + 1;
  }
  return counts;
}

/// GitHub-style 0–4 intensity from a transaction count.
int heatmapLevel(int count) {
  if (count <= 0) return 0;
  if (count >= 4) return 4;
  return count;
}