/**
 * 年度报告（plan.md「5.2 年度报告」）。
 */

import { addDecimals } from './decimal';
import type { Transaction } from './types';

export interface AnnualReport {
  year: number;
  totalIncome: string;
  totalExpense: string;
  netIncome: string;
  topCategories: { category: string; amount: string; percentage: number }[];
  monthlyTrend: { month: string; income: string; expense: string }[];
  dayOfWeekBreakdown: { day: string; total: string }[];
  largestTransaction: Transaction | null;
  transactionCount: number;
  averageDailyExpense: string;
}

const DAY_NAMES = ['周日', '周一', '周二', '周三', '周四', '周五', '周六'];

export function generateAnnualReport(
  transactions: Transaction[],
  year: number,
): AnnualReport {
  const yearTx = transactions.filter(t => t.date.startsWith(String(year)));

  const totalIncome = sumByDirection(yearTx, 'income');
  const totalExpense = sumByDirection(yearTx, 'expense');
  const netIncome = addDecimals([totalIncome, totalExpense]);  // expense 是负数

  return {
    year,
    totalIncome,
    totalExpense,
    netIncome,
    topCategories: getTopCategories(yearTx, 10),
    monthlyTrend: getMonthlyTrend(yearTx),
    dayOfWeekBreakdown: getDayOfWeekBreakdown(yearTx),
    largestTransaction: getLargestTransaction(yearTx),
    transactionCount: yearTx.length,
    averageDailyExpense: calculateAverageDaily(yearTx),
  };
}

function sumByDirection(transactions: Transaction[], direction: 'income' | 'expense'): string {
  const amounts: string[] = [];
  for (const t of transactions) {
    for (const p of t.postings) {
      if (!p.amount) continue;
      const amt = parseFloat(p.amount);
      // 支出：Expenses 账户的正金额（Beancount 约定，费用账户正余额=支出）
      if (direction === 'expense' && p.account.startsWith('Expenses') && amt > 0) {
        amounts.push(p.amount);
      }
      // 收入：Income 账户的负金额（冲减收入）取绝对值，或正金额（某些约定）
      if (direction === 'income' && p.account.startsWith('Income')) {
        amounts.push(amt < 0 ? p.amount.slice(1) : p.amount);
      }
    }
  }
  return addDecimals(amounts);
}

function getTopCategories(transactions: Transaction[], limit: number): { category: string; amount: string; percentage: number }[] {
  const byCategory = new Map<string, string>();
  let total = '0';
  for (const t of transactions) {
    for (const p of t.postings) {
      if (p.amount && p.account.startsWith('Expenses') && parseFloat(p.amount) > 0) {
        byCategory.set(p.account, addDecimals([byCategory.get(p.account) ?? '0', p.amount]));
        total = addDecimals([total, p.amount]);
      }
    }
  }
  const entries = [...byCategory.entries()]
    .map(([category, amount]) => ({
      category,
      amount,
      percentage: parseFloat(total) > 0 ? Math.round((parseFloat(amount) / parseFloat(total)) * 10000) / 100 : 0,
    }))
    .sort((a, b) => parseFloat(b.amount) - parseFloat(a.amount))
    .slice(0, limit);
  return entries;
}

function getMonthlyTrend(transactions: Transaction[]): { month: string; income: string; expense: string }[] {
  const months: { month: string; income: string; expense: string }[] = [];
  for (let m = 1; m <= 12; m++) {
    const monthStr = String(m).padStart(2, '0');
    const monthTx = transactions.filter(t => t.date.slice(5, 7) === monthStr);
    months.push({
      month: monthStr,
      income: sumByDirection(monthTx, 'income'),
      expense: sumByDirection(monthTx, 'expense'),
    });
  }
  return months;
}

function getDayOfWeekBreakdown(transactions: Transaction[]): { day: string; total: string }[] {
  const byDay = new Array(7).fill(0).map((_, i) => ({ day: DAY_NAMES[i], total: '0' }));
  for (const t of transactions) {
    const date = new Date(t.date.slice(0, 10));
    const dow = date.getDay();
    for (const p of t.postings) {
      if (p.amount && p.account.startsWith('Expenses') && parseFloat(p.amount) > 0) {
        byDay[dow].total = addDecimals([byDay[dow].total, p.amount]);
      }
    }
  }
  return byDay;
}

function getLargestTransaction(transactions: Transaction[]): Transaction | null {
  let largest: Transaction | null = null;
  let maxAmount = 0;
  for (const t of transactions) {
    for (const p of t.postings) {
      if (p.amount && p.amount.startsWith('-')) {
        const abs = parseFloat(p.amount.slice(1));
        if (abs > maxAmount) {
          maxAmount = abs;
          largest = t;
        }
      }
    }
  }
  return largest;
}

function calculateAverageDaily(transactions: Transaction[]): string {
  const total = sumByDirection(transactions, 'expense');
  const days = transactions.length > 0
    ? new Set(transactions.map(t => t.date.slice(0, 10))).size
    : 1;
  return (parseFloat(total) / days).toFixed(2);
}