/**
 * 预算管理页面（plan.md「1.1 budget/index」+ 决策 1 双轨制）。
 *
 * 功能：预算列表(含进度条) + 添加/编辑/删除。
 * 进度计算调用 calculateBudgetProgress 纯函数,展示已用/剩余/百分比。
 */
import React, { useState } from 'react';
import { Alert, Pressable, ScrollView, StyleSheet, Text, View } from 'react-native';
import { SafeAreaView } from 'react-native-safe-area-context';
import { useRouter } from 'expo-router';
import { Ionicons } from '@expo/vector-icons';
import { useTheme } from '../../theme';
import { useLedgerStore } from '../../store/ledgerStore';
import { useMetadataStore, generateId } from '../../store/metadataStore';
import { useT } from '../../i18n';
import { Card } from '../../components/Card';
import { FormModal, type FormField } from '../../components/FormModal';
import { calculateBudgetProgress } from '../../domain/budgets';
import type { Budget } from '../../domain/budgets';

type ModalMode = { type: 'add' } | { type: 'edit'; budget: Budget } | null;

export default function BudgetScreen() {
  const { theme } = useTheme();
  const t = useT();
  const router = useRouter();

  const budgets = useMetadataStore(s => s.budgets);
  const addBudget = useMetadataStore(s => s.addBudget);
  const updateBudget = useMetadataStore(s => s.updateBudget);
  const removeBudget = useMetadataStore(s => s.removeBudget);
  const ledger = useLedgerStore(s => s.ledger);

  const [modal, setModal] = useState<ModalMode>(null);

  const transactions = ledger?.transactions ?? [];
  const today = new Date().toISOString().slice(0, 10);

  const handleDelete = (budget: Budget) => {
    Alert.alert(t('budget.deleteTitle'), t('budget.deleteConfirm', { name: budget.name }), [
      { text: t('common.cancel'), style: 'cancel' },
      { text: t('common.delete'), style: 'destructive', onPress: () => removeBudget(budget.id) },
    ]);
  };

  const handleConfirm = (values: Record<string, string>) => {
    const name = values.name?.trim() || t('budget.unnamed');
    const amount = values.amount?.trim() || '0';
    const period = (values.period as Budget['period']) || 'monthly';
    const categoryAccount = values.categoryAccount?.trim() || undefined;
    const startDate = values.startDate?.trim() || today;

    const amtNum = parseFloat(amount);
    if (isNaN(amtNum) || amtNum <= 0) {
      Alert.alert(t('budget.invalidAmountTitle'), t('budget.invalidAmountDesc'));
      return;
    }

    if (modal?.type === 'add') {
      addBudget({ id: generateId('bud'), name, amount, period, categoryAccount, startDate });
    } else if (modal?.type === 'edit') {
      updateBudget(modal.budget.id, { name, amount, period, categoryAccount, startDate });
    }
    setModal(null);
  };

  const periodLabel = (p: string) => p === 'monthly' ? t('budget.periodMonthly') : p === 'weekly' ? t('budget.periodWeekly') : t('budget.periodYearly');

  const editFields: FormField[] = modal?.type === 'edit' ? [
    { key: 'name', label: t('budget.fieldName'), placeholder: t('budget.fieldNamePlaceholder'), defaultValue: modal.budget.name },
    { key: 'amount', label: t('budget.fieldAmount'), placeholder: t('budget.fieldAmountPlaceholder'), defaultValue: modal.budget.amount, keyboardType: 'decimal-pad' },
    { key: 'period', label: t('budget.fieldPeriod'), placeholder: 'monthly', defaultValue: modal.budget.period },
    { key: 'categoryAccount', label: t('budget.fieldCategoryAccount'), placeholder: t('budget.fieldCategoryPlaceholder'), defaultValue: modal.budget.categoryAccount ?? '' },
    { key: 'startDate', label: t('budget.fieldStartDate'), placeholder: '2026-01-01', defaultValue: modal.budget.startDate },
  ] : [];

  return (
    <SafeAreaView style={[styles.page, { backgroundColor: theme.colors.bgPrimary }]} edges={['top']}>
      <View style={styles.header}>
        <Pressable onPress={() => router.back()}><Ionicons name="arrow-back" size={24} color={theme.colors.fgPrimary} /></Pressable>
        <Text style={[theme.typography.h2, { color: theme.colors.fgPrimary, flex: 1, marginLeft: 8 }]}>{t('budget.title')}</Text>
      </View>
      <ScrollView contentContainerStyle={styles.content}>
        <Pressable onPress={() => setModal({ type: 'add' })} style={styles.addBtn}>
          <Ionicons name="add-circle" size={20} color={theme.colors.accent} />
          <Text style={[theme.typography.body, { color: theme.colors.accent, marginLeft: 6 }]}>{t('budget.add')}</Text>
        </Pressable>
        {budgets.map(budget => {
          const progress = calculateBudgetProgress(budget, transactions, today);
          return (
            <Pressable
              key={budget.id}
              onPress={() => setModal({ type: 'edit', budget })}
              onLongPress={() => handleDelete(budget)}
            >
              <Card title={budget.name}>
                <View style={styles.budgetRow}>
                  <Text style={[theme.typography.body, { color: theme.colors.fgPrimary }]}>
                    {t('budget.yuanPer', { amount: budget.amount, period: periodLabel(budget.period) })}
                  </Text>
                  <Text style={[theme.typography.caption, {
                    color: progress.overBudget ? theme.colors.error : theme.colors.fgSecondary,
                  }]}>
                    {t('budget.used', { spent: progress.spent, pct: progress.percentage.toFixed(0) })}
                  </Text>
                </View>
                {/* 进度条 */}
                <View style={[styles.barWrap, { backgroundColor: theme.colors.bgTertiary }]}>
                  <View style={[
                    styles.bar,
                    {
                      width: `${Math.min(progress.percentage, 100)}%`,
                      backgroundColor: progress.overBudget ? theme.colors.error : theme.colors.accent,
                    },
                  ]} />
                </View>
                {budget.categoryAccount && (
                  <Text style={[theme.typography.caption, { color: theme.colors.fgSecondary, marginTop: 4 }]}>
                    {budget.categoryAccount}
                  </Text>
                )}
              </Card>
            </Pressable>
          );
        })}
        {budgets.length === 0 && (
          <Text style={[theme.typography.caption, { color: theme.colors.fgSecondary, textAlign: 'center', marginTop: 20 }]}>
            {t('budget.empty')}
          </Text>
        )}
        <Text style={[theme.typography.caption, { color: theme.colors.fgSecondary, textAlign: 'center', marginTop: 8 }]}>
          {t('common.clickEditLongDelete')}
        </Text>
      </ScrollView>

      <FormModal
        visible={modal !== null}
        title={modal?.type === 'edit' ? t('budget.editTitle') : t('budget.add')}
        fields={modal?.type === 'edit' ? editFields : [
          { key: 'name', label: t('budget.fieldName'), placeholder: t('budget.fieldNamePlaceholder') },
          { key: 'amount', label: t('budget.fieldAmount'), placeholder: t('budget.fieldAmountPlaceholder'), keyboardType: 'decimal-pad' },
          { key: 'period', label: t('budget.fieldPeriod'), placeholder: 'monthly' },
          { key: 'categoryAccount', label: t('budget.fieldCategoryAccount'), placeholder: t('budget.fieldCategoryPlaceholder') },
          { key: 'startDate', label: t('budget.fieldStartDate'), placeholder: '2026-01-01' },
        ]}
        onConfirm={handleConfirm}
        onCancel={() => setModal(null)}
      />
    </SafeAreaView>
  );
}

const styles = StyleSheet.create({
  page: { flex: 1 },
  header: { flexDirection: 'row', alignItems: 'center', paddingHorizontal: 16, paddingTop: 8, paddingBottom: 12 },
  content: { padding: 16, gap: 12 },
  addBtn: { flexDirection: 'row', alignItems: 'center' },
  budgetRow: { flexDirection: 'row', justifyContent: 'space-between', alignItems: 'center' },
  barWrap: { height: 8, borderRadius: 4, overflow: 'hidden', marginTop: 8 },
  bar: { height: '100%', borderRadius: 4 },
});