<?php
header('Content-Type: application/json');
require_once __DIR__ . '/../db/config.php';
session_start();

$user_id = $_SESSION['user_id'] ?? null;
if (!$user_id) {
    echo json_encode(['success' => false, 'error' => 'Not logged in']);
    exit;
}

$startup_id = $_POST['startup_id'] ?? null;

if (!$startup_id) {
    echo json_encode(['success' => false, 'error' => 'Startup ID is required']);
    exit;
}

try {
    // Check if already following
    $stmt = db()->prepare("SELECT 1 FROM startup_followers WHERE startup_id = ? AND user_id = ?");
    $stmt->execute([$startup_id, $user_id]);
    $is_following = (bool)$stmt->fetch();

    if (!$is_following) {
        // Follow
        $stmt = db()->prepare("INSERT IGNORE INTO startup_followers (startup_id, user_id) VALUES (?, ?)");
        $stmt->execute([$startup_id, $user_id]);
        $action_result = 'followed';
    } else {
        // Unfollow
        $stmt = db()->prepare("DELETE FROM startup_followers WHERE startup_id = ? AND user_id = ?");
        $stmt->execute([$startup_id, $user_id]);
        $action_result = 'unfollowed';
    }

    // Update denormalized count
    $stmt = db()->prepare("UPDATE startups SET followers_count = (SELECT COUNT(*) FROM startup_followers WHERE startup_id = ?) WHERE id = ?");
    $stmt->execute([$startup_id, $startup_id]);
    
    // Get new count
    $stmt = db()->prepare("SELECT followers_count FROM startups WHERE id = ?");
    $stmt->execute([$startup_id]);
    $new_count = $stmt->fetchColumn();
    
    echo json_encode([
        'success' => true, 
        'action' => $action_result,
        'new_count' => (int)$new_count,
        'followers_count' => (int)$new_count // redundancy for both frontend versions
    ]);
} catch (Exception $e) {
    echo json_encode(['success' => false, 'error' => $e->getMessage()]);
}