/// Project future balances from recurring templates.
library;

import '../models/bank.dart';
import '../models/transaction_meta.dart';
import 'tx_calendar.dart';

/// One monthly recurring item used for look-ahead forecasts.
class RecurringItem {
  const RecurringItem({
    required this.templateId,
    required this.description,
    required this.amount,
    required this.currency,
    required this.dayOfMonth,
    this.ruleSummary = '',
    this.sourceTxId,
    this.labelIds = const [],
  });

  final String templateId;
  final String description;
  final double amount;
  final String currency;
  final int dayOfMonth;
  final String ruleSummary;
  final String? sourceTxId;
  final List<String> labelIds;
}

/// Build projection items from first-class [templates].
List<RecurringItem> recurringItemsFromTemplates({
  required Iterable<RecurringTemplate> templates,
  required List<BankTransaction> transactions,
  required bool Function(BankTransaction tx) isInternalTransfer,
  required List<String> Function(BankTransaction tx) labelIdsFor,
  String Function(String? labelId)? labelName,
}) {
  return [
    for (final tpl in templates)
      RecurringItem(
        templateId: tpl.id,
        description: tpl.name,
        amount: resolveRecurringAmount(
          template: tpl,
          transactions: transactions,
          isInternalTransfer: isInternalTransfer,
          labelIdsFor: labelIdsFor,
        ),
        currency: tpl.currency,
        dayOfMonth: tpl.dayOfMonth.clamp(1, 28),
        ruleSummary: recurringRuleSummary(
          template: tpl,
          labelName: labelName,
        ),
        sourceTxId: tpl.sourceTxId,
        labelIds: [
          if (tpl.labelId != null && tpl.labelId!.isNotEmpty) tpl.labelId!,
        ],
      ),
  ];
}

String recurringRuleSummary({
  required RecurringTemplate template,
  String Function(String? labelId)? labelName,
}) {
  switch (template.amountRule) {
    case RecurringAmountRule.lastValue:
      return 'Last value';
    case RecurringAmountRule.avgLastTxs:
      return 'Avg last ${template.avgCount} matching';
    case RecurringAmountRule.labelAvgMonths:
      final name = labelName?.call(template.labelId) ?? 'label';
      return 'Avg ${template.avgCount} mo · $name';
  }
}

/// Resolve projected amount for [template] from bank history.
double resolveRecurringAmount({
  required RecurringTemplate template,
  required List<BankTransaction> transactions,
  required bool Function(BankTransaction tx) isInternalTransfer,
  required List<String> Function(BankTransaction tx) labelIdsFor,
}) {
  switch (template.amountRule) {
    case RecurringAmountRule.lastValue:
      return _lastMerchantAmount(
            template: template,
            transactions: transactions,
          ) ??
          0;
    case RecurringAmountRule.avgLastTxs:
      return avgLastMatchingTxs(
        count: template.avgCount,
        transactions: transactions,
        merchantKey: template.merchantKey,
        sourceTxId: template.sourceTxId,
      );
    case RecurringAmountRule.labelAvgMonths:
      final labelId = template.labelId;
      if (labelId == null || labelId.isEmpty) return 0;
      return avgLabelMonths(
        labelId: labelId,
        months: template.avgCount,
        transactions: transactions,
        isInternalTransfer: isInternalTransfer,
        labelIdsFor: labelIdsFor,
      );
  }
}

double? _lastMerchantAmount({
  required RecurringTemplate template,
  required List<BankTransaction> transactions,
}) {
  if (template.sourceTxId != null) {
    for (final tx in transactions) {
      if (tx.id == template.sourceTxId) return tx.amount;
    }
  }
  final key = template.merchantKey;
  if (key.isEmpty) return null;
  BankTransaction? latest;
  DateTime? latestDate;
  for (final tx in transactions) {
    if (tx.merchantKey != key) continue;
    final date = DateTime.tryParse(tx.date);
    if (date == null) continue;
    if (latest == null || date.isAfter(latestDate!)) {
      latest = tx;
      latestDate = date;
    }
  }
  return latest?.amount;
}

/// Average of the last [count] txs that match the selected source
/// (same similar-pattern + flow as apply-to-similar).
double avgLastMatchingTxs({
  required int count,
  required List<BankTransaction> transactions,
  String merchantKey = '',
  String? sourceTxId,
}) {
  final n = count.clamp(1, 36);
  BankTransaction? prototype;
  if (sourceTxId != null && sourceTxId.isNotEmpty) {
    for (final tx in transactions) {
      if (tx.id == sourceTxId) {
        prototype = tx;
        break;
      }
    }
  }
  if (prototype == null && merchantKey.isNotEmpty) {
    DateTime? latestDate;
    for (final tx in transactions) {
      if (tx.merchantKey != merchantKey) continue;
      final date = DateTime.tryParse(tx.date);
      if (date == null) continue;
      if (prototype == null || date.isAfter(latestDate!)) {
        prototype = tx;
        latestDate = date;
      }
    }
  }
  if (prototype == null) return 0;

  final criteria = SimilarMatchCriteria(
    pattern: defaultSimilarPattern(prototype.description),
    flow: prototype.amount < 0
        ? TxFlowFilter.expense
        : prototype.amount > 0
            ? TxFlowFilter.income
            : TxFlowFilter.all,
  );

  final matches = <({BankTransaction tx, DateTime date})>[];
  for (final tx in transactions) {
    if (!txMatchesSimilarCriteria(tx, criteria)) continue;
    final date = DateTime.tryParse(tx.date);
    if (date == null) continue;
    matches.add((tx: tx, date: date));
  }
  if (matches.isEmpty) return prototype.amount;
  matches.sort((a, b) => b.date.compareTo(a.date));
  final take = matches.take(n).toList(growable: false);
  final sum = take.fold<double>(0, (s, e) => s + e.tx.amount);
  return sum / take.length;
}

/// Average monthly signed total for [labelId] over the last [months] completed months.
double avgLabelMonths({
  required String labelId,
  required int months,
  required List<BankTransaction> transactions,
  required bool Function(BankTransaction tx) isInternalTransfer,
  required List<String> Function(BankTransaction tx) labelIdsFor,
  DateTime? now,
}) {
  final n = months.clamp(1, 36);
  final today = dateOnly(now ?? DateTime.now());
  final currentMonth = monthStart(today);
  final totals = <DateTime, double>{};
  for (var i = 1; i <= n; i++) {
    totals[addMonths(currentMonth, -i)] = 0;
  }

  for (final tx in transactions) {
    if (isInternalTransfer(tx)) continue;
    final date = DateTime.tryParse(tx.date);
    if (date == null) continue;
    final key = monthStart(date);
    if (!totals.containsKey(key)) continue;
    final ids = labelIdsFor(tx);
    if (!ids.contains(labelId)) continue;
    totals[key] = (totals[key] ?? 0) + tx.amount;
  }

  final sum = totals.values.fold<double>(0, (s, v) => s + v);
  return sum / n;
}

/// Occurrences of [items] with dates in `(from, to]` (exclusive start, inclusive end).
List<({RecurringItem item, DateTime date})> projectedOccurrences({
  required List<RecurringItem> items,
  required DateTime from,
  required DateTime to,
}) {
  final start = dateOnly(from);
  final end = dateOnly(to);
  if (!end.isAfter(start)) return const [];

  final out = <({RecurringItem item, DateTime date})>[];
  var cursor = monthStart(start);
  final lastMonth = monthStart(end);

  while (!cursor.isAfter(lastMonth)) {
    final daysInMonth = DateTime(cursor.year, cursor.month + 1, 0).day;
    for (final item in items) {
      final day = item.dayOfMonth.clamp(1, daysInMonth);
      final date = DateTime(cursor.year, cursor.month, day);
      if (date.isAfter(start) && !date.isAfter(end)) {
        out.add((item: item, date: date));
      }
    }
    cursor = addMonths(cursor, 1);
  }

  out.sort((a, b) => a.date.compareTo(b.date));
  return out;
}

/// Current balance plus projected recurring amounts through [throughDate].
double predictBalance({
  required double currentBalance,
  required DateTime from,
  required DateTime throughDate,
  required List<RecurringItem> items,
}) {
  final projected = projectedOccurrences(
    items: items,
    from: from,
    to: throughDate,
  );
  return projected.fold<double>(
    currentBalance,
    (sum, row) => sum + row.item.amount,
  );
}