<?php
require_once __DIR__ . '/db/config.php';

// --- DATA FETCHING & CALCULATION ---
$project = null;
$project_id = $_GET['project_id'] ?? null;
$financial_data = [];
$months = [];
$metrics = ["Opening Balance", "Billings", "WIP", "Expenses", "Cost", "NSR", "Margin"];

if (!$project_id) {
    header("HTTP/1.0 400 Bad Request");
    echo "Project ID is required.";
    exit;
}

try {
    $pdo = db();
    $stmt = $pdo->prepare("SELECT * FROM projects WHERE id = :id");
    $stmt->execute([':id' => $project_id]);
    $project = $stmt->fetch(PDO::FETCH_ASSOC);

    if ($project) {
        function get_month_range($start_date_str, $end_date_str) {
            $months = [];
            if (empty($start_date_str) || empty($end_date_str)) return $months;
            $start = new DateTime($start_date_str);
            $end = new DateTime($end_date_str);
            $current = clone $start;
            $current->modify('first day of this month');
            while ($current <= $end) {
                $months[] = $current->format('Y-m-01');
                $current->modify('+1 month');
            }
            return $months;
        }
        $months = get_month_range($project['startDate'], $project['endDate']);

        // --- Financial Calculations ---

        // 1. Fetch base monthly data
        $monthly_costs = [];
        $monthly_wip = [];

        $forecast_stmt = $pdo->prepare("SELECT id FROM forecasting WHERE projectId = :pid ORDER BY versionNumber DESC LIMIT 1");
        $forecast_stmt->execute([':pid' => $project_id]);
        $latest_forecast = $forecast_stmt->fetch(PDO::FETCH_ASSOC);

        if ($latest_forecast) {
            $fid = $latest_forecast['id'];
            
            // Base Monthly Cost
            $cost_sql = "SELECT fa.month, SUM(fa.allocatedDays * (r.totalMonthlyCost / 20)) FROM forecastAllocation fa JOIN roster r ON fa.rosterId = r.id WHERE fa.forecastingId = :fid GROUP BY fa.month";
            $cost_stmt = $pdo->prepare($cost_sql);
            $cost_stmt->execute([':fid' => $fid]);
            $monthly_costs = $cost_stmt->fetchAll(PDO::FETCH_KEY_PAIR);

            // Base Monthly WIP
            $recoverability_decimal = $project['recoverability'] / 100;
            $wip_sql = "SELECT fa.month, SUM(fa.allocatedDays * (r.grossRevenue * (1 - :recoverability))) as wip FROM forecastAllocation fa JOIN roster r ON fa.rosterId = r.id WHERE fa.forecastingId = :fid GROUP BY fa.month";
            $wip_stmt = $pdo->prepare($wip_sql);
            $wip_stmt->execute([':fid' => $fid, ':recoverability' => $recoverability_decimal]);
            $monthly_wip = $wip_stmt->fetchAll(PDO::FETCH_KEY_PAIR);
        }

        // Base Monthly Billings
        $billing_stmt = $pdo->prepare("SELECT month, amount FROM billingMonthly WHERE projectId = :pid");
        $billing_stmt->execute([':pid' => $project_id]);
        $monthly_billing = $billing_stmt->fetchAll(PDO::FETCH_KEY_PAIR);

        // Base Monthly Expenses
        $expenses_stmt = $pdo->prepare("SELECT month, amount FROM expensesMonthly WHERE projectId = :pid");
        $expenses_stmt->execute([':pid' => $project_id]);
        $monthly_expenses = $expenses_stmt->fetchAll(PDO::FETCH_KEY_PAIR);

        // 2. Calculate cumulative values month by month
        $cumulative_billing = 0;
        $cumulative_cost = 0;
        $cumulative_expenses = 0;
        $previous_month_wip = 0;

        foreach ($months as $month) {
            // --- Opening Balance ---
            $opening_balance = $previous_month_wip;
            $financial_data['Opening Balance'][$month] = $opening_balance;

            // --- Base Data ---
            $cost = $monthly_costs[$month] ?? 0;
            $base_monthly_wip = $monthly_wip[$month] ?? 0;
            $billing = $monthly_billing[$month] ?? 0;
            $expenses = $monthly_expenses[$month] ?? 0;

            // --- Cumulative Metrics ---
            $cumulative_billing += $billing;
            $financial_data['Billings'][$month] = $cumulative_billing;

            $cumulative_cost += $cost;
            $financial_data['Cost'][$month] = $cumulative_cost;

            $cumulative_expenses += $expenses;
            $financial_data['Expenses'][$month] = $cumulative_expenses;

            // --- WIP (Closing Balance) ---
            $final_opening_balance = $financial_data['Opening Balance'][$month];
            $current_wip = $final_opening_balance + $expenses + $base_monthly_wip - $billing;
            $financial_data['WIP'][$month] = $current_wip;

            // --- Calculated Metrics (NSR and Margin) ---
            $nsr = $financial_data['WIP'][$month] + $financial_data['Billings'][$month] - $financial_data['Opening Balance'][$month] - $financial_data['Expenses'][$month];
            $financial_data['NSR'][$month] = $nsr;

            $final_nsr = $financial_data['NSR'][$month];
            $final_cost = $financial_data['Cost'][$month];
            $margin = ($final_nsr != 0) ? (($final_nsr - $final_cost) / $final_nsr) : 0;
            $financial_data['Margin'][$month] = $margin;

            // --- Carry-over for next iteration ---
            $previous_month_wip = $financial_data['WIP'][$month];
        }
    }
} catch (PDOException $e) {
    header("HTTP/1.0 500 Internal Server Error");
    echo "Database error: " . $e->getMessage();
    exit;
}

if (!$project) {
    header("HTTP/1.0 404 Not Found");
    echo "Project not found.";
    exit;
}

// --- CSV EXPORT ---
$filename = "project_finance_" . preg_replace('/[^a-zA-Z0-9_]/', '_', $project['name']) . ".csv";

header('Content-Type: text/csv');
header('Content-Disposition: attachment; filename="' . $filename . '"');

$output = fopen('php://output', 'w');

// Header row
$header = ['Metric'];
foreach ($months as $month) {
    $header[] = date('M Y', strtotime($month));
}
fputcsv($output, $header);

// Data rows
foreach ($metrics as $metric) {
    $row = [$metric];
    foreach ($months as $month) {
        $row[] = number_format($financial_data[$metric][$month] ?? 0, 2);
    }
    fputcsv($output, $row);
}

fclose($output);
exit;