import '../models/habit.dart';
import '../models/tracker_entry.dart';

/// fn-weekly-minimum-ratio
///
/// Computes the share of done check-ins in the last 7 days that used the
/// habit's "minimum" dose variant. Useful for L2-conditional habits where the
/// user picks a minimum option on bad-condition days. A high ratio is fine
/// (the protocol's whole point), but it also signals the user is mostly
/// running on minimum dose — a context the UI can surface.
///
/// Returns 0.0 when there are no done entries in the window (no division by
/// zero).
class WeeklyMinimumRatio {
  final int totalDone;
  final int minimumUsed;
  final double ratio; // 0.0..1.0
  final DateTime windowStart; // inclusive, YYYY-MM-DD == windowStart
  final DateTime windowEnd; // inclusive

  const WeeklyMinimumRatio({
    required this.totalDone,
    required this.minimumUsed,
    required this.ratio,
    required this.windowStart,
    required this.windowEnd,
  });
}

/// Pure function: caller resolves the variant rows and passes them in.
///
/// - [entries] should already be filtered to the habit and to value=done.
/// - [variantsById] maps variant_id → variant (only minimums need to be
///   present, but a full map is fine).
/// - [asOf] is treated as the inclusive end of the 7-day window.
WeeklyMinimumRatio computeWeeklyMinimumRatio({
  required Iterable<TrackerEntryModel> entries,
  required Map<String, HabitDoseVariantModel> variantsById,
  required DateTime asOf,
}) {
  final end = DateTime(asOf.year, asOf.month, asOf.day);
  final start = end.subtract(const Duration(days: 6));

  var totalDone = 0;
  var minimumUsed = 0;

  for (final e in entries) {
    if (e.value != TrackerValue.done) continue;
    final d = DateTime.parse(e.date);
    if (d.isBefore(start) || d.isAfter(end)) continue;
    totalDone += 1;
    final vId = e.variantId;
    if (vId == null) continue;
    final v = variantsById[vId];
    if (v != null && v.isMinimum) minimumUsed += 1;
  }

  final ratio = totalDone == 0 ? 0.0 : minimumUsed / totalDone;
  return WeeklyMinimumRatio(
    totalDone: totalDone,
    minimumUsed: minimumUsed,
    ratio: ratio,
    windowStart: start,
    windowEnd: end,
  );
}