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

<?php

namespace App\Http\Controllers\Api;

use App\Http\Controllers\Controller;
use App\Models\InvestmentHolding;
use Illuminate\Http\Request;

class InvestmentTransactionController extends Controller
{
    public function index(Request $request, string $holdingId)
    {
        $holding = InvestmentHolding::whereHas('account', function ($q) use ($request) {
            $q->where('user_id', $request->user()->id);
        })->findOrFail($holdingId);

        return response()->json($holding->transactions()->orderBy('traded_at', 'desc')->get());
    }

    public function store(Request $request, string $holdingId)
    {
        $holding = InvestmentHolding::whereHas('account', function ($q) use ($request) {
            $q->where('user_id', $request->user()->id);
        })->findOrFail($holdingId);

        $validated = $request->validate([
            'action' => 'required|in:buy,sell',
            'shares' => 'nullable|numeric|min:0',
            'price' => 'nullable|numeric|min:0',
            'fee' => 'nullable|numeric|min:0',
            'tax' => 'nullable|numeric|min:0',
            'traded_at' => 'required|date',
            'note' => 'nullable|string',
            'amount' => 'nullable|numeric|min:0', // 實際投入金額（基金用）
            'nav' => 'nullable|numeric|min:0',    // 淨值（基金用）
        ]);

        $transaction = $holding->transactions()->create($validated);

        // 更新持倉的 shares 和 avg_cost
        $this->recalculateHolding($holding);

        return response()->json($transaction, 201);
    }

    public function destroy(Request $request, string $holdingId, string $id)
    {
        $holding = InvestmentHolding::whereHas('account', function ($q) use ($request) {
            $q->where('user_id', $request->user()->id);
        })->findOrFail($holdingId);

        $transaction = $holding->transactions()->findOrFail($id);
        $transaction->delete();

        $this->recalculateHolding($holding);

        return response()->json(null, 204);
    }

    // 每次買賣後重新計算平均成本和持有股數
    private function recalculateHolding(InvestmentHolding $holding): void
    {
        $transactions = $holding->transactions()->orderBy('traded_at')->get();

        $totalUnits = 0;
        $totalCost = 0;
        $presentUnits = 0;


        foreach ($transactions as $tx) {
            if ($tx->action === 'buy') {
                if ($holding->type === 'fund') {
                    $units = $tx->nav > 0 ? $tx->amount / $tx->nav : 0;
                    $totalCost += $tx->amount + $tx->fee;
                    $presentUnits += $units;
                    $totalUnits += $units;
                } else {
                    $totalCost += $tx->shares * $tx->price + $tx->fee;
                    $presentUnits += $tx->shares;
                    $totalUnits += $tx->shares;
                }
            }  else {
                if ($holding->type === 'fund') {
                    $units = $tx->nav > 0 ? $tx->amount / $tx->nav : 0;
                    $totalUnits -= $units;
                } else {
                    $totalUnits -= $tx->shares;
                }
            }
            
        }
        
        $holding->update([
            'shares'   => max(0, $totalUnits), // 總持有股數
            'avg_cost' => $presentUnits > 0 ? $totalCost / $presentUnits : 0,
        ]);
    }
}