<?php
/**
 * Validate Manual Selection IDs
 * AJAX endpoint: POST with JSON body { project_id, user_ids[] }
 * 
 * Checks:
 * 1. Which IDs exist in panel DB and are active + email verified
 * 2. Which valid IDs are already in other selections for this project
 * 3. Returns available-to-add count (valid - already assigned)
 */
require_once 'client-session.php';
require_once 'panel-db-config.php';
requireClientLogin();

header('Content-Type: application/json');

try {
    $input = json_decode(file_get_contents('php://input'), true);
    
    $project_id = (int)($input['project_id'] ?? 0);
    $user_ids = $input['user_ids'] ?? [];
    
    if (!$project_id) {
        throw new Exception('Invalid project ID');
    }
    
    if (empty($user_ids) || !is_array($user_ids)) {
        throw new Exception('No user IDs provided');
    }
    
    // Sanitize IDs
    $user_ids = array_map('intval', $user_ids);
    $user_ids = array_unique(array_filter($user_ids, function($id) { return $id > 0; }));
    $total_uploaded = count($user_ids);
    
    if ($total_uploaded === 0) {
        throw new Exception('No valid numeric IDs found');
    }
    
    $pdo = getClientDBConnection();    // shop DB
    $panelPdo = getPanelDBConnection(); // panel DB
    
    // Verify project belongs to this client
    $stmt = $pdo->prepare("SELECT id, project_id FROM projects WHERE id = ? AND client_id = ?");
    $stmt->execute([$project_id, $_SESSION['client_id']]);
    if (!$stmt->fetch()) {
        throw new Exception('Unauthorized');
    }
    
    // Step 1: Check which IDs exist in panel DB and are active + email_verified
    // Process in batches of 1000 to avoid query limits
    $valid_user_ids = [];
    $batches = array_chunk($user_ids, 1000);
    
    foreach ($batches as $batch) {
        $placeholders = str_repeat('?,', count($batch) - 1) . '?';
        $stmt = $panelPdo->prepare("
            SELECT id FROM users 
            WHERE id IN ($placeholders) 
            AND status = 'active' 
            AND email_verified = 1
        ");
        $stmt->execute($batch);
        $valid_user_ids = array_merge($valid_user_ids, $stmt->fetchAll(PDO::FETCH_COLUMN));
    }
    
    $valid_active = count($valid_user_ids);
    $not_found = $total_uploaded - $valid_active;
    
    // Step 2: Check which valid IDs are already in selections for this project
    $already_in_selections = 0;
    $already_ids = [];
    
    if (!empty($valid_user_ids)) {
        // Get all selection IDs for this project
        $stmt = $pdo->prepare("SELECT id FROM project_selections WHERE project_id = ?");
        $stmt->execute([$project_id]);
        $project_selection_ids = $stmt->fetchAll(PDO::FETCH_COLUMN);
        
        if (!empty($project_selection_ids)) {
            // Find which valid_user_ids are already members of these selections
            $selPlaceholders = str_repeat('?,', count($project_selection_ids) - 1) . '?';
            
            // Process in batches
            $valid_batches = array_chunk($valid_user_ids, 1000);
            foreach ($valid_batches as $batch) {
                $userPlaceholders = str_repeat('?,', count($batch) - 1) . '?';
                $stmt = $pdo->prepare("
                    SELECT DISTINCT user_id FROM selection_members 
                    WHERE selection_id IN ($selPlaceholders) 
                    AND user_id IN ($userPlaceholders)
                ");
                $params = array_merge($project_selection_ids, $batch);
                $stmt->execute($params);
                $already_ids = array_merge($already_ids, $stmt->fetchAll(PDO::FETCH_COLUMN));
            }
            $already_ids = array_unique($already_ids);
            $already_in_selections = count($already_ids);
        }
    }
    
    // Step 3: Compute available to add (valid minus already assigned)
    $available_ids = array_diff($valid_user_ids, $already_ids);
    $available_to_add = count($available_ids);
    
    echo json_encode([
        'total_uploaded' => $total_uploaded,
        'valid_active' => $valid_active,
        'not_found' => $not_found,
        'already_in_selections' => $already_in_selections,
        'available_to_add' => $available_to_add,
        'valid_user_ids' => array_values($available_ids) // only the ones actually available
    ]);
    
} catch (Exception $e) {
    http_response_code(400);
    echo json_encode(['error' => $e->getMessage()]);
}