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

$action = $_POST['action'] ?? null;
$projectId = $_POST['projectId'] ?? null;

if (!$action || !$projectId) {
    redirect_with_error('forecasting.php', $projectId, 'Invalid request.');
}

function redirect_with_error($page, $projectId, $message) {
    $version = $_POST['version'] ?? null;
    $query = http_build_query(array_filter([
        'projectId' => $projectId,
        'version' => $version,
        'error' => $message
    ]));
    header("Location: {$page}?{$query}");
    exit();
}

function redirect_with_success($page, $projectId, $message) {
    $version = $_POST['version'] ?? null;
    $query = http_build_query(array_filter([
        'projectId' => $projectId,
        'version' => $version,
        'success' => $message
    ]));
    header("Location: {$page}?{$query}");
    exit();
}

function get_months($startDate, $endDate) {
    $start = new DateTime($startDate);
    $end = new DateTime($endDate);
    $interval = new DateInterval('P1M');
    $period = new DatePeriod($start, $interval, $end->modify('+1 month'));
    $months = [];
    foreach ($period as $dt) {
        $months[] = $dt->format('Y-m-01');
    }
    return $months;
}

try {
    $pdo = db();

    switch ($action) {
        case 'new_version':
            // Find the latest version number
            $stmt = $pdo->prepare("SELECT MAX(versionNumber) as max_version FROM forecasting WHERE projectId = :projectId");
            $stmt->execute([':projectId' => $projectId]);
            $latest_version_num = $stmt->fetchColumn();
            $new_version_num = $latest_version_num + 1;

            // Get the ID of the latest version to clone from
            $stmt = $pdo->prepare("SELECT id FROM forecasting WHERE projectId = :projectId AND versionNumber = :versionNumber");
            $stmt->execute([':projectId' => $projectId, ':versionNumber' => $latest_version_num]);
            $latest_version_id = $stmt->fetchColumn();

            $pdo->beginTransaction();

            // Create the new forecasting version
            $stmt = $pdo->prepare("INSERT INTO forecasting (projectId, versionNumber, createdAt) VALUES (:projectId, :versionNumber, NOW())");
            $stmt->execute([':projectId' => $projectId, ':versionNumber' => $new_version_num]);
            $new_version_id = $pdo->lastInsertId();

            // Clone allocations from the latest version if it exists
            if ($latest_version_id) {
                $clone_sql = "INSERT INTO forecastAllocation (forecastingId, rosterId, resourceName, level, month, allocatedDays) 
                              SELECT :new_version_id, rosterId, resourceName, level, month, allocatedDays 
                              FROM forecastAllocation WHERE forecastingId = :latest_version_id";
                $stmt = $pdo->prepare($clone_sql);
                $stmt->execute([':new_version_id' => $new_version_id, ':latest_version_id' => $latest_version_id]);
            }

            $pdo->commit();
            redirect_with_success('forecasting.php', $projectId, 'New version created successfully.', ['version' => $new_version_num]);
            break;

        case 'add_resource':
            $forecastingId = $_POST['forecastingId'] ?? null;
            $rosterId = $_POST['rosterId'] ?? null;

            if (!$forecastingId || !$rosterId) {
                redirect_with_error('forecasting.php', $projectId, 'Missing data for adding resource.');
            }

            // Fetch project and roster details
            $stmt = $pdo->prepare("SELECT startDate, endDate FROM projects WHERE id = :projectId");
            $stmt->execute([':projectId' => $projectId]);
            $project = $stmt->fetch(PDO::FETCH_ASSOC);

            $stmt = $pdo->prepare("SELECT fullNameEn, `level` FROM roster WHERE id = :rosterId");
            $stmt->execute([':rosterId' => $rosterId]);
            $roster = $stmt->fetch(PDO::FETCH_ASSOC);

            if (!$project || !$roster) {
                redirect_with_error('forecasting.php', $projectId, 'Project or resource not found.');
            }

            $months = get_months($project['startDate'], $project['endDate']);
            $insert_sql = "INSERT INTO forecastAllocation (forecastingId, rosterId, resourceName, level, month, allocatedDays) VALUES (:forecastingId, :rosterId, :resourceName, :level, :month, 0)";
            $stmt = $pdo->prepare($insert_sql);

            $pdo->beginTransaction();
            foreach ($months as $month) {
                $stmt->execute([
                    ':forecastingId' => $forecastingId,
                    ':rosterId' => $rosterId,
                    ':resourceName' => $roster['fullNameEn'],
                    ':level' => $roster['level'],
                    ':month' => $month
                ]);
            }
            $pdo->commit();

            redirect_with_success('forecasting.php', $projectId, 'Resource added to forecast.');
            break;

        case 'remove_resource':
            $forecastingId = $_POST['forecastingId'] ?? null;
            $rosterId = $_POST['rosterId'] ?? null;

            if (!$forecastingId || !$rosterId) {
                redirect_with_error('forecasting.php', $projectId, 'Missing data for removing resource.');
            }

            $sql = "DELETE FROM forecastAllocation WHERE forecastingId = :forecastingId AND rosterId = :rosterId";
            $stmt = $pdo->prepare($sql);
            $stmt->execute([':forecastingId' => $forecastingId, ':rosterId' => $rosterId]);

            redirect_with_success('forecasting.php', $projectId, 'Resource removed from forecast.');
            break;

        case 'update_allocation':
            header('Content-Type: application/json');
            $forecastingId = $_POST['forecastingId'] ?? null;
            $rosterId = $_POST['rosterId'] ?? null;
            $month = $_POST['month'] ?? null;
            $allocatedDays = $_POST['allocatedDays'] ?? null;

            if (!$forecastingId || !$rosterId || !$month || !isset($allocatedDays)) {
                echo json_encode(['success' => false, 'error' => 'Invalid data for update.']);
                exit();
            }

            // Use INSERT ... ON DUPLICATE KEY UPDATE to handle both new and existing cells
            $sql = "INSERT INTO forecastAllocation (forecastingId, rosterId, month, allocatedDays, resourceName, level) 
                    VALUES (:forecastingId, :rosterId, :month, :allocatedDays, 
                            (SELECT fullNameEn FROM roster WHERE id = :rosterId), 
                            (SELECT `level` FROM roster WHERE id = :rosterId))
                    ON DUPLICATE KEY UPDATE allocatedDays = :allocatedDays";
            
            // We need a unique key on (forecastingId, rosterId, month) for this to work.
            // Let's assume it exists. If not, we need to add it.
            // ALTER TABLE forecastAllocation ADD UNIQUE KEY `unique_allocation` (`forecastingId`, `rosterId`, `month`);

            $stmt = $pdo->prepare($sql);
            $stmt->execute([
                ':forecastingId' => $forecastingId,
                ':rosterId' => $rosterId,
                ':month' => $month,
                ':allocatedDays' => $allocatedDays
            ]);

            echo json_encode(['success' => true]);
            exit();

        default:
            redirect_with_error('forecasting.php', $projectId, 'Invalid action specified.');
            break;
    }

} catch (PDOException $e) {
    if ($pdo->inTransaction()) {
        $pdo->rollBack();
    }
    if ($action === 'update_allocation') {
        header('Content-Type: application/json');
        echo json_encode(['success' => false, 'error' => 'Database error: ' . $e->getMessage()]);
    } else {
        redirect_with_error('forecasting.php', $projectId, 'Database error: ' . $e->getMessage());
    }
    exit();
}