finance_app/app/Http/Controllers/Api/DashboardController.php

<?php

namespace App\Http\Controllers\Api;

use App\Models\Expense;
use Illuminate\Support\Facades\Auth;
use Carbon\Carbon;
use App\Http\Controllers\Controller;
use Illuminate\Support\Facades\DB;

class DashboardController extends Controller
{
    public function index()
    {
        $userId = Auth::id();
        $now    = Carbon::now();

        $latestMonth = $now->copy();
        $latestYear = $latestMonth->year;

        // 1. 本月基礎統計 (用一個查詢同時撈出「總金額」與「總筆數」)
        $monthStats = Expense::where('user_id', $userId)
            ->whereYear('date',  $latestYear)
            ->whereMonth('date', $latestMonth)
            ->selectRaw('SUM(amount) as total_amount, COUNT(id) as total_count')
            ->first();

        if (!$monthStats || $monthStats->total_amount == 0) {
            // 改用 first() 確保能抓到單筆資料
            $latestExpense = Expense::where('user_id', $userId)->latest('date')->first();

            if ($latestExpense) {
                $targetDate = Carbon::parse($latestExpense->date);
                $latestYear = $targetDate->year;
                $latestMonth = $targetDate->month;

                // 重新撈取該月份的統計資料
                $monthStats = Expense::where('user_id', $userId)
                    ->whereYear('date', $latestYear)
                    ->whereMonth('date', $latestMonth)
                    ->selectRaw('SUM(amount) as total_amount, COUNT(id) as total_count')
                    ->first();
            }
        }

        $monthlyTotal = (float) ($monthStats->total_amount ?? 0);
        $monthlyCount = (int) ($monthStats->total_count ?? 0);

        // 2. 本月分類統計（圓餅圖）- 保持集合操作即可
        $categoryStats = Expense::with('category')
            ->where('user_id', $userId)
            ->whereYear('date',  $latestYear)
            ->whereMonth('date', $latestMonth)
            ->get()
            ->groupBy(fn($e) => $e->category?->name ?? '未分類')
            ->map(fn($group, $name) => [
                'name'   => $name,
                'total'  => (float) $group->sum('amount'),
                'color'  => $group->first()->category?->color ?? '#6B7280',
            ])
            ->values();

        // 3. 近 6 個月趨勢優化：一次性撈出半年內的所有資料，避免 6 次 SQL 查詢
        $sixMonthsAgo = $now->copy()->subMonths(5)->startOfMonth();
        $endOfCurrentMonth = $now->copy()->endOfMonth();

        // 建立近 6 個月的初始月份清單（例如 ['2026/01' => 0.0, '2026/02' => 0.0 ... ]）
        $monthlyTrendData = collect(range(5, 0))->mapWithKeys(function ($i) use ($now) {
            $monthStr = $now->copy()->subMonths($i)->format('Y/m');
            return [$monthStr => 0.0];
        })->toArray();

        // ➔ (A) 撈取一般消費 (未開啟分攤)
        $isPostgres = DB::connection()->getDriverName() === 'pgsql';
        $dateGroupRaw = $isPostgres ? "to_char(date, 'YYYY/MM')" : "DATE_FORMAT(date, '%Y/%m')";

        $normalExpenses = Expense::where('user_id', $userId)
            ->where('is_amortized', false)
            ->where('date', '>=', $sixMonthsAgo)
            ->selectRaw("{$dateGroupRaw} as month, SUM(amount) as total")
            ->groupBy('month')
            ->get();

        foreach ($normalExpenses as $expense) {
            if (array_key_exists($expense->month, $monthlyTrendData)) {
                $monthlyTrendData[$expense->month] += (float) $expense->total;
            }
        }

        // ➔ (B) 智慧分攤消費 (處理跨月、跨年、半年繳大魔王 🎯)
        // 撈出所有歸屬期間有交集到這 6 個月範圍內的分攤費用
        $amortizedExpenses = Expense::where('user_id', $userId)
            ->where('is_amortized', true)
            ->where(function ($query) use ($sixMonthsAgo, $endOfCurrentMonth) {
                $query->where('period_start', '<=', $endOfCurrentMonth)
                    ->where('period_end', '>=', $sixMonthsAgo);
            })
            ->get();

        foreach ($amortizedExpenses as $expense) {
            $start = Carbon::parse($expense->period_start)->startOfMonth();
            $end = Carbon::parse($expense->period_end)->endOfMonth();

            // 計算這筆費用的總跨月份數 (至少為 1 個月)
            $totalMonths = max(1, $start->diffInMonths($end) + 1);
            // 算出每月平均攤提金額
            $monthlyShare = (float) $expense->amount / $totalMonths;

            // 跑這 6 個月的迴圈，看有沒有落在這筆費用的歸屬區間內
            foreach ($monthlyTrendData as $monthStr => &$currentTotal) {
                $currentMonthObj = Carbon::createFromFormat('Y/m', $monthStr)->startOfMonth();

                // 如果圖表上的這個月份，剛好在費用的歸屬起訖之內，就把每月平均金額灌進去！
                if ($currentMonthObj->betweenIncluded($start, $end)) {
                    $currentTotal += $monthlyShare;
                }
            }
        }

        // 轉回前端圖表要的格式
        $monthlyTrend = collect($monthlyTrendData)->map(function ($total, $monthStr) {
            return [
                'month' => $monthStr,
                'total' => round($total, 2), // 四捨五入到小數點兩位
            ];
        })->values();

        return response()->json([
            'monthlyTotal'  => $monthlyTotal,
            'monthlyCount'  => $monthlyCount,
            'categoryStats' => $categoryStats,
            'monthlyTrend'  => $monthlyTrend,
        ]);
    }
}