<?php
/**
 * Send Invitations - AJAX Handler
 * Location: /clients/send-invitations.php
 * 
 * Sends email invitations to all members of a selection via SendGrid.
 * Supports first send + up to 2 resends (3 total dispatches).
 * Updates survey_urls, selection, and project statuses.
 * 
 * POST params:
 *   selection_id      - Required
 *   incentive_amount  - Optional override (first send only)
 *   dispatch_type     - 'first' (default) or 'resend'
 * 
 * Returns: JSON { success, sent_count, failed_count, skipped_count, dispatch_number, errors[], message }
 * 
 * Resend Rules:
 *   - 2nd dispatch: Not within 24 hours of 1st dispatch
 *   - 3rd dispatch: Not within 72 hours of 1st dispatch AND not within 48 hours of 2nd dispatch
 *   - Resend only goes to members whose survey_urls status = 'sent' (not taken at all)
 *   - Reminder emails have subject "REMINDER: ..."
 *   - mail_dispatch_wave is tracked on survey_urls for performance analysis
 */
ini_set('display_errors', 0);
error_reporting(E_ALL);
ini_set('log_errors', 1);

// Long-running mailer: bypass PHP default 30s time limit and keep running
// even if the browser disconnects. Ensures DB transaction commits cleanly
// even when sending to large selections.
set_time_limit(0);
ignore_user_abort(true);

require_once 'client-session.php';
require_once 'panel-db-config.php';
require_once 'sendgrid-config.php';
requireClientLogin();

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

if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
    echo json_encode(['success' => false, 'message' => 'Invalid request method']);
    exit;
}

try {
    $pdo = getClientDBConnection();
    $panelPdo = getPanelDBConnection();

    $selection_id = isset($_POST['selection_id']) ? (int)$_POST['selection_id'] : 0;
    $incentive_override = isset($_POST['incentive_amount']) ? (float)$_POST['incentive_amount'] : 0;
    $dispatch_type = isset($_POST['dispatch_type']) ? $_POST['dispatch_type'] : 'first';

    if (!$selection_id) {
        throw new Exception('Invalid selection ID');
    }

    // 1. Get selection + project details
    $stmt = $pdo->prepare("
        SELECT ps.*, p.project_name, p.project_id AS project_code, p.eloi, p.id AS proj_id,
               p.status AS project_status, p.made_live_at
        FROM project_selections ps
        JOIN projects p ON ps.project_id = p.id
        WHERE ps.id = ? AND ps.client_id = ?
    ");
    $stmt->execute([$selection_id, $_SESSION['client_id']]);
    $selection = $stmt->fetch(PDO::FETCH_ASSOC);

    if (!$selection) {
        throw new Exception('Selection not found or unauthorized');
    }

    $eloi = (int)$selection['eloi'];
    $default_incentive = calculateDefaultIncentive($eloi);
    $dispatch_count = (int)($selection['mail_dispatch_count'] ?? 0);

    // ======================================================
    // RESEND FLOW
    // ======================================================
    if ($dispatch_type === 'resend') {

        // Must be live or hold (invitations already sent)
        if (!in_array($selection['status'], ['live', 'hold'])) {
            throw new Exception('Selection must be live or on hold to resend invitations. Current status: ' . $selection['status']);
        }

        if (empty($selection['invitations_sent_at'])) {
            throw new Exception('First invitations have not been sent yet.');
        }

        // Check dispatch count limits
        if ($dispatch_count >= 3) {
            throw new Exception('Maximum of 3 dispatches (1 original + 2 reminders) have already been sent for this selection.');
        }

        $now = time();
        $first_sent_at = strtotime($selection['invitations_sent_at']);
        $second_sent_at = !empty($selection['second_dispatch_at']) ? strtotime($selection['second_dispatch_at']) : null;

        // Validate time gaps
        if ($dispatch_count == 1) {
            // 2nd dispatch: must be at least 24 hours after 1st
            $min_time = $first_sent_at + (24 * 3600);
            if ($now < $min_time) {
                $remaining = $min_time - $now;
                $hours = floor($remaining / 3600);
                $mins = ceil(($remaining % 3600) / 60);
                throw new Exception("Cannot send 2nd dispatch yet. Must wait at least 24 hours after the first send. Time remaining: {$hours}h {$mins}m.");
            }
        } elseif ($dispatch_count == 2) {
            // 3rd dispatch: must be at least 48 hours after 2nd
            $min_time = $second_sent_at + (48 * 3600);

            if ($now < $min_time) {
                $remaining = $min_time - $now;
                $hours = floor($remaining / 3600);
                $mins = ceil(($remaining % 3600) / 60);
                throw new Exception("Cannot send 3rd dispatch yet. Must wait at least 48 hours after the second send. Time remaining: {$hours}h {$mins}m.");
            }
        }

        $new_dispatch_number = $dispatch_count + 1;

        // Get URLs that are still in 'sent' status (not taken at all)
        // "Taken" = any status beyond 'sent': clicked, complete, partial, screenout, quotafull, timeout
        $stmt = $pdo->prepare("
            SELECT id, rr_proxy_url, unique_identifier, sent_to_user_id
            FROM survey_urls
            WHERE assigned_to_selection_id = ? 
              AND status = 'sent'
            ORDER BY id ASC
        ");
        $stmt->execute([$selection_id]);
        $pending_urls = $stmt->fetchAll(PDO::FETCH_ASSOC);

        if (empty($pending_urls)) {
            throw new Exception('No pending recipients found. All members have already taken the survey or their URLs have a terminal status.');
        }

        // Get emails from panel DB
        $user_ids = array_column($pending_urls, 'sent_to_user_id');
        $user_ids = array_filter($user_ids); // remove nulls
        if (empty($user_ids)) {
            throw new Exception('No valid user IDs found for resend.');
        }
        $placeholders = implode(',', array_fill(0, count($user_ids), '?'));
        $stmt = $panelPdo->prepare("SELECT id, email FROM users WHERE id IN ($placeholders) AND status = 'active'");
        $stmt->execute(array_values($user_ids));
        $email_map = $stmt->fetchAll(PDO::FETCH_KEY_PAIR);

        // Use incentive from original send
        $incentive = $selection['incentive_amount'] ?? $default_incentive;

        // Build REMINDER subject
        $subject = 'REMINDER: Invitation: Your Online Survey Opportunity from Relevant Reflex India';

        $sent_count = 0;
        $failed_count = 0;
        $skipped_count = 0;
        $errors = [];
        $totalQueued = count($pending_urls);
        $ordinal = $new_dispatch_number == 2 ? '2nd' : '3rd';

        // ─── STEP 1: Tiny header transaction — bump dispatch count + activity logs ───
        // Commits in <100ms so it always succeeds before any timeout.
        $pdo->beginTransaction();

        if ($new_dispatch_number == 2) {
            $stmt = $pdo->prepare("
                UPDATE project_selections
                SET mail_dispatch_count = 2,
                    second_dispatch_at = NOW()
                WHERE id = ?
            ");
            $stmt->execute([$selection_id]);
        } elseif ($new_dispatch_number == 3) {
            $stmt = $pdo->prepare("
                UPDATE project_selections
                SET mail_dispatch_count = 3,
                    third_dispatch_at = NOW()
                WHERE id = ?
            ");
            $stmt->execute([$selection_id]);
        }

        $detailsQueued = json_encode([
            'dispatch_number' => $new_dispatch_number,
            'queued' => $totalQueued,
            'type' => 'reminder'
        ]);

        $stmt = $pdo->prepare("
            INSERT INTO selection_activity_log (selection_id, action, description, performed_by, created_at)
            VALUES (?, ?, ?, ?, NOW())
        ");
        $stmt->execute([$selection_id, 'reminder_dispatch_' . $new_dispatch_number, $detailsQueued, $_SESSION['client_id']]);

        $stmt = $pdo->prepare("
            INSERT INTO project_activity_log (project_id, client_id, action, details, ip_address, created_at)
            VALUES (?, ?, ?, ?, ?, NOW())
        ");
        $stmt->execute([$selection['proj_id'], $_SESSION['client_id'], 'reminder_dispatch_' . $new_dispatch_number, $detailsQueued, $_SERVER['REMOTE_ADDR'] ?? '']);

        $pdo->commit();

        // ─── STEP 2: Send JSON response IMMEDIATELY (before the long send) ───
        $response = json_encode([
            'success'          => true,
            'sent_count'       => $totalQueued,
            'failed_count'     => 0,
            'skipped_count'    => 0,
            'dispatch_number'  => $new_dispatch_number,
            'errors'           => [],
            'message'          => "Sending {$ordinal} dispatch reminder to {$totalQueued} recipient(s) in background. Page will refresh shortly to show delivery progress."
        ]);
        header('Content-Type: application/json');
        header('Connection: close');
        header('Content-Length: ' . strlen($response));
        echo $response;

        // ─── STEP 3: Detach from HTTP request — script keeps running ───
        if (function_exists('session_write_close')) { @session_write_close(); }
        if (function_exists('fastcgi_finish_request')) {
            fastcgi_finish_request();
        } else {
            while (ob_get_level() > 0) { @ob_end_flush(); }
            @flush();
        }

        // ─── STEP 4: Background send loop — autocommit per email ───
        // No outer transaction: each successful email's UPDATE survives
        // even if the worker is later killed by LiteSpeed/PHP-FPM timeout.
        foreach ($pending_urls as $item) {
            $user_id = $item['sent_to_user_id'];
            $url_id  = $item['id'];

            if (!$user_id || !isset($email_map[$user_id])) {
                $skipped_count++;
                continue;
            }

            $email = $email_map[$user_id];
            $html  = buildReminderEmail($item['rr_proxy_url'], $eloi, $incentive);

            $result = sendEmailViaSendGrid($email, $subject, $html);

            if ($result['success']) {
                $stmt = $pdo->prepare("
                    UPDATE survey_urls
                    SET mail_dispatch_wave = ?,
                        sent_at = NOW()
                    WHERE id = ?
                ");
                $stmt->execute([$new_dispatch_number, $url_id]);
                $sent_count++;
            } else {
                $failed_count++;
                error_log("SendGrid resend error for $email: " . $result['message']);
            }
        }

        // ─── STEP 5: Best-effort final log (may not run if killed; safe) ───
        try {
            $finalDetails = json_encode([
                'dispatch_number' => $new_dispatch_number,
                'sent' => $sent_count,
                'failed' => $failed_count,
                'skipped' => $skipped_count,
                'type' => 'reminder_completed'
            ]);
            $stmt = $pdo->prepare("
                INSERT INTO selection_activity_log (selection_id, action, description, performed_by, created_at)
                VALUES (?, ?, ?, ?, NOW())
            ");
            $stmt->execute([$selection_id, 'reminder_dispatch_' . $new_dispatch_number . '_completed', $finalDetails, $_SESSION['client_id'] ?? null]);
        } catch (Exception $e) { /* swallow — best-effort only */ }
        exit;
    }

    // ======================================================
    // FIRST SEND FLOW (existing logic, preserved exactly)
    // ======================================================

    // 2. Validate selection status — must be 'targeted' (URLs fully assigned)
    if (!in_array($selection['status'], ['targeted', 'draft'])) {
        if ($selection['status'] === 'live') {
            throw new Exception('Invitations have already been sent for this selection');
        }
        throw new Exception('Selection must be in "targeted" status to send invitations. Current: ' . $selection['status']);
    }

    // 3. Get member count
    $stmt = $pdo->prepare("SELECT COUNT(*) FROM selection_members WHERE selection_id = ?");
    $stmt->execute([$selection_id]);
    $member_count = (int)$stmt->fetchColumn();

    if ($member_count === 0) {
        throw new Exception('No members in this selection');
    }

    // 4. Get assigned URL count for this selection
    $stmt = $pdo->prepare("
        SELECT COUNT(*) FROM survey_urls 
        WHERE assigned_to_selection_id = ? AND status = 'assigned'
    ");
    $stmt->execute([$selection_id]);
    $assigned_count = (int)$stmt->fetchColumn();

    if ($assigned_count < $member_count) {
        throw new Exception("Not all members have URLs assigned. Members: $member_count, URLs assigned: $assigned_count");
    }

    // 5. Calculate & validate incentive
    $incentive = $incentive_override > 0 ? $incentive_override : $default_incentive;

    if ($incentive < $default_incentive) {
        throw new Exception("Incentive cannot be less than ₹" . number_format($default_incentive, 0) . " (default for {$eloi} min LOI)");
    }

    // 6. Get all assigned URLs for this selection
    $stmt = $pdo->prepare("
        SELECT id, rr_proxy_url, unique_identifier
        FROM survey_urls
        WHERE assigned_to_selection_id = ? AND status = 'assigned'
        ORDER BY id ASC
    ");
    $stmt->execute([$selection_id]);
    $urls = $stmt->fetchAll(PDO::FETCH_ASSOC);

    // 7. Get all member user_ids for this selection (ordered to pair with URLs)
    $stmt = $pdo->prepare("
        SELECT user_id FROM selection_members 
        WHERE selection_id = ? 
        ORDER BY id ASC
    ");
    $stmt->execute([$selection_id]);
    $members = $stmt->fetchAll(PDO::FETCH_COLUMN);

    // 8. Pair members with URLs
    $send_queue = [];
    for ($i = 0; $i < count($members); $i++) {
        if (!isset($urls[$i])) break;
        $send_queue[] = [
            'user_id'    => $members[$i],
            'url_id'     => $urls[$i]['id'],
            'proxy_url'  => $urls[$i]['rr_proxy_url'],
            'unique_id'  => $urls[$i]['unique_identifier']
        ];
    }

    if (empty($send_queue)) {
        throw new Exception('No URL-member pairs available to send');
    }

    // 9. Look up member emails from panel DB
    $user_ids = array_column($send_queue, 'user_id');
    $placeholders = implode(',', array_fill(0, count($user_ids), '?'));
    $stmt = $panelPdo->prepare("SELECT id, email FROM users WHERE id IN ($placeholders) AND status = 'active'");
    $stmt->execute($user_ids);
    $email_map = $stmt->fetchAll(PDO::FETCH_KEY_PAIR); // id => email

    // 10. Send emails
    $subject = 'Invitation: Your Online Survey Opportunity from Relevant Reflex India';
    $sent_count = 0;
    $failed_count = 0;
    $errors = [];
    $totalQueued = count($send_queue);

    // ─── STEP 1: Tiny header transaction — mark selection live + project live + log ───
    // Commits in <100ms so it always succeeds before any timeout.
    $pdo->beginTransaction();

    $stmt = $pdo->prepare("
        UPDATE project_selections
        SET status = 'live',
            incentive_amount = ?,
            invitations_sent_at = NOW(),
            mail_dispatch_count = 1,
            launched_at = CASE WHEN launched_at IS NULL THEN NOW() ELSE launched_at END
        WHERE id = ?
    ");
    $stmt->execute([$incentive, $selection_id]);

    if ($selection['project_status'] !== 'Live') {
        $stmt = $pdo->prepare("
            UPDATE projects
            SET status = 'Live',
                made_live_at = CASE WHEN made_live_at IS NULL THEN NOW() ELSE made_live_at END
            WHERE id = ?
        ");
        $stmt->execute([$selection['proj_id']]);
    }

    $detailsQueued = json_encode([
        'dispatch_number' => 1,
        'queued' => $totalQueued,
        'incentive' => $incentive,
        'eloi' => $eloi
    ]);

    $stmt = $pdo->prepare("
        INSERT INTO selection_activity_log (selection_id, action, description, performed_by, created_at)
        VALUES (?, 'invitations_sent', ?, ?, NOW())
    ");
    $stmt->execute([$selection_id, $detailsQueued, $_SESSION['client_id']]);

    $stmt = $pdo->prepare("
        INSERT INTO project_activity_log (project_id, client_id, action, details, ip_address, created_at)
        VALUES (?, ?, 'invitations_sent', ?, ?, NOW())
    ");
    $stmt->execute([$selection['proj_id'], $_SESSION['client_id'], $detailsQueued, $_SERVER['REMOTE_ADDR'] ?? '']);

    $pdo->commit();

    // ─── STEP 2: Send JSON response IMMEDIATELY (before the long send loop) ───
    $response = json_encode([
        'success'         => true,
        'sent_count'      => $totalQueued,
        'failed_count'    => 0,
        'dispatch_number' => 1,
        'errors'          => [],
        'incentive'       => $incentive,
        'message'         => "Sending invitations to {$totalQueued} recipient(s) in background. The selection is now live; emails will continue to deliver over the next few minutes. Refresh the page to see updated delivery status."
    ]);
    header('Content-Type: application/json');
    header('Connection: close');
    header('Content-Length: ' . strlen($response));
    echo $response;

    // ─── STEP 3: Detach from HTTP request — script keeps running ───
    if (function_exists('session_write_close')) { @session_write_close(); }
    if (function_exists('fastcgi_finish_request')) {
        fastcgi_finish_request();
    } else {
        while (ob_get_level() > 0) { @ob_end_flush(); }
        @flush();
    }

    // ─── STEP 4: Background send loop — autocommit per email ───
    // No outer transaction: each successful email's UPDATE survives
    // even if the worker is later killed by LiteSpeed/PHP-FPM timeout.
    foreach ($send_queue as $item) {
        $user_id = $item['user_id'];
        $url_id  = $item['url_id'];

        if (!isset($email_map[$user_id])) {
            $failed_count++;
            continue;
        }

        $email = $email_map[$user_id];
        $html  = buildInvitationEmail($item['proxy_url'], $eloi, $incentive);

        $result = sendEmailViaSendGrid($email, $subject, $html);

        if ($result['success']) {
            $stmt = $pdo->prepare("
                UPDATE survey_urls
                SET status = 'sent',
                    is_sent = 1,
                    sent_to_user_id = ?,
                    sent_at = NOW(),
                    mail_dispatch_wave = 1
                WHERE id = ?
            ");
            $stmt->execute([$user_id, $url_id]);
            $sent_count++;
        } else {
            $failed_count++;
            error_log("SendGrid error for $email: " . $result['message']);
        }
    }

    // ─── STEP 5: Best-effort final log (may not run if killed; safe) ───
    try {
        $finalDetails = json_encode([
            'dispatch_number' => 1,
            'sent' => $sent_count,
            'failed' => $failed_count,
            'incentive' => $incentive,
            'eloi' => $eloi,
            'type' => 'invitations_completed'
        ]);
        $stmt = $pdo->prepare("
            INSERT INTO selection_activity_log (selection_id, action, description, performed_by, created_at)
            VALUES (?, 'invitations_completed', ?, ?, NOW())
        ");
        $stmt->execute([$selection_id, $finalDetails, $_SESSION['client_id'] ?? null]);
    } catch (Exception $e) { /* swallow — best-effort only */ }
    exit;

} catch (Exception $e) {
    if (isset($pdo) && $pdo->inTransaction()) {
        $pdo->rollBack();
    }
    error_log("Send invitations error: " . $e->getMessage());
    echo json_encode([
        'success' => false,
        'message' => $e->getMessage()
    ]);
}