<?php

declare(strict_types=1);

// Test logic for eager loading without mocking complex dependencies
test('eager loading performance simulation shows query reduction', function () {
    // Simulate N+1 problem vs eager loading performance

    // Scenario: 100 users, each with posts and profile
    $userCount = 100;
    $avgPostsPerUser = 5;
    $profilePerUser = 1;

    // N+1 Problem Simulation
    $n1QueriesLazy = 1 + ($userCount * 2); // 1 query for users + 1 query per user for posts + 1 query per user for profile

    // Eager Loading Simulation
    $eagerQueries = 1 + 2; // 1 query for users + 1 batch query for posts + 1 batch query for profiles

    $queryReduction = ($n1QueriesLazy - $eagerQueries) / $n1QueriesLazy;

    expect($eagerQueries)->toBeLessThan($n1QueriesLazy);
    expect($queryReduction)->toBeGreaterThan(0.95); // Over 95% query reduction

    // Real numbers: 201 queries vs 3 queries = 98.5% reduction!
});

test('batch loading logic groups related entities correctly', function () {
    // Simulate the batch loading grouping logic

    // Users data
    $users = [
        ['id' => 1, 'name' => 'Alice'],
        ['id' => 2, 'name' => 'Bob'],
        ['id' => 3, 'name' => 'Charlie'],
    ];

    // Posts data (simulating database result)
    $allPosts = [
        ['id' => 1, 'user_id' => 1, 'title' => 'Alice Post 1'],
        ['id' => 2, 'user_id' => 1, 'title' => 'Alice Post 2'],
        ['id' => 3, 'user_id' => 2, 'title' => 'Bob Post 1'],
        ['id' => 4, 'user_id' => 3, 'title' => 'Charlie Post 1'],
        ['id' => 5, 'user_id' => 3, 'title' => 'Charlie Post 2'],
        ['id' => 6, 'user_id' => 3, 'title' => 'Charlie Post 3'],
    ];

    // Simulate batch loading grouping (what our implementation does)
    $postsByUserId = [];
    foreach ($allPosts as $post) {
        $userId = $post['user_id'];
        if (! isset($postsByUserId[$userId])) {
            $postsByUserId[$userId] = [];
        }
        $postsByUserId[$userId][] = $post;
    }

    // Verify correct grouping
    expect($postsByUserId[1])->toHaveCount(2); // Alice has 2 posts
    expect($postsByUserId[2])->toHaveCount(1); // Bob has 1 post
    expect($postsByUserId[3])->toHaveCount(3); // Charlie has 3 posts

    // Verify no posts are lost
    $totalPosts = array_sum(array_map('count', $postsByUserId));
    expect($totalPosts)->toBe(count($allPosts));

    // Verify all users can get their posts
    foreach ($users as $user) {
        $userId = $user['id'];
        $userPosts = $postsByUserId[$userId] ?? [];

        // Each post should belong to the correct user
        foreach ($userPosts as $post) {
            expect($post['user_id'])->toBe($userId);
        }
    }
});

test('belongsTo relation batching reduces queries', function () {
    // Simulate belongsTo relation (posts belonging to categories)

    $posts = [
        ['id' => 1, 'title' => 'Post 1', 'category_id' => 1],
        ['id' => 2, 'title' => 'Post 2', 'category_id' => 2],
        ['id' => 3, 'title' => 'Post 3', 'category_id' => 1],
        ['id' => 4, 'title' => 'Post 4', 'category_id' => 3],
        ['id' => 5, 'title' => 'Post 5', 'category_id' => 2],
    ];

    // Without batching: 1 query per post for category = 5 queries
    $lazyQueries = count($posts);

    // With batching: Collect all unique category_ids, then 1 IN query
    $categoryIds = array_unique(array_column($posts, 'category_id'));
    $batchQueries = 1; // Single IN query: SELECT * FROM categories WHERE id IN (1,2,3)

    expect($batchQueries)->toBeLessThan($lazyQueries);
    expect(count($categoryIds))->toBeLessThan(count($posts)); // Proof that we're reducing queries

    // Simulate batch loading result
    $categories = [
        ['id' => 1, 'name' => 'Tech'],
        ['id' => 2, 'name' => 'Science'],
        ['id' => 3, 'name' => 'Art'],
    ];

    // Index by ID for fast lookup (what our implementation does)
    $categoriesById = [];
    foreach ($categories as $category) {
        $categoriesById[$category['id']] = $category;
    }

    // Verify we can resolve all post categories
    foreach ($posts as $post) {
        $categoryId = $post['category_id'];
        expect($categoriesById)->toHaveKey($categoryId);
        expect($categoriesById[$categoryId]['id'])->toBe($categoryId);
    }
});

test('one-to-one relation batching works correctly', function () {
    // Simulate one-to-one relation (users with profiles)

    $users = [
        ['id' => 1, 'name' => 'Alice'],
        ['id' => 2, 'name' => 'Bob'],
        ['id' => 3, 'name' => 'Charlie'],
    ];

    $profiles = [
        ['id' => 1, 'user_id' => 1, 'bio' => 'Alice bio'],
        ['id' => 2, 'user_id' => 2, 'bio' => 'Bob bio'],
        ['id' => 3, 'user_id' => 3, 'bio' => 'Charlie bio'],
    ];

    // Batch loading: Single query with IN clause
    $userIds = array_column($users, 'id');
    $batchQuery = "SELECT * FROM profiles WHERE user_id IN (" . implode(',', $userIds) . ")";

    expect($batchQuery)->toContain('IN (1,2,3)');

    // Group profiles by user_id (one-to-one, so each user has max 1 profile)
    $profileByUserId = [];
    foreach ($profiles as $profile) {
        $profileByUserId[$profile['user_id']] = $profile;
    }

    // Verify one-to-one relationship
    expect($profileByUserId)->toHaveCount(3);
    expect($profileByUserId[1]['bio'])->toBe('Alice bio');
    expect($profileByUserId[2]['bio'])->toBe('Bob bio');
    expect($profileByUserId[3]['bio'])->toBe('Charlie bio');
});

test('eager loading handles missing relations gracefully', function () {
    // Test scenario where some entities don't have relations

    $users = [
        ['id' => 1, 'name' => 'Alice'],
        ['id' => 2, 'name' => 'Bob'],
        ['id' => 3, 'name' => 'Charlie'],
    ];

    // Only some users have posts
    $posts = [
        ['id' => 1, 'user_id' => 1, 'title' => 'Alice Post'],
        ['id' => 2, 'user_id' => 3, 'title' => 'Charlie Post'],
        // Bob (user_id: 2) has no posts
    ];

    // Group posts by user_id
    $postsByUserId = [];
    foreach ($posts as $post) {
        $userId = $post['user_id'];
        if (! isset($postsByUserId[$userId])) {
            $postsByUserId[$userId] = [];
        }
        $postsByUserId[$userId][] = $post;
    }

    // Assign relations to users
    $usersWithPosts = [];
    foreach ($users as $user) {
        $userId = $user['id'];
        $usersWithPosts[] = [
            'user' => $user,
            'posts' => $postsByUserId[$userId] ?? [], // Default to empty array if no posts
        ];
    }

    // Verify handling of missing relations
    expect($usersWithPosts[0]['posts'])->toHaveCount(1); // Alice has 1 post
    expect($usersWithPosts[1]['posts'])->toHaveCount(0); // Bob has 0 posts
    expect($usersWithPosts[2]['posts'])->toHaveCount(1); // Charlie has 1 post

    // Verify no user is missing from result
    expect($usersWithPosts)->toHaveCount(3);
});

test('complex eager loading scenario performance calculation', function () {
    // Real-world scenario: Blog system with nested relations

    $postCount = 50;
    $avgCommentsPerPost = 8;
    $avgTagsPerPost = 3;
    $avgCategoriesPerPost = 1; // belongsTo relation

    // Without eager loading (N+1 problem)
    $lazyQueries = 1; // Posts query
    $lazyQueries += $postCount; // 1 query per post for category (belongsTo)
    $lazyQueries += $postCount; // 1 query per post for comments (hasMany)
    $lazyQueries += $postCount; // 1 query per post for tags (hasMany)
    // Total: 1 + 50 + 50 + 50 = 151 queries

    // With eager loading
    $eagerQueries = 1; // Posts query
    $eagerQueries += 1; // Batch query for all categories (IN clause)
    $eagerQueries += 1; // Batch query for all comments (WHERE post_id IN ...)
    $eagerQueries += 1; // Batch query for all tags (JOIN with pivot table)
    // Total: 4 queries

    $performanceGain = ($lazyQueries - $eagerQueries) / $lazyQueries;

    expect($eagerQueries)->toBe(4);
    expect($lazyQueries)->toBe(151);
    expect($performanceGain)->toBeGreaterThan(0.97); // Over 97% query reduction!

    // Database load reduction
    $loadReduction = $lazyQueries / $eagerQueries;
    expect($loadReduction)->toBeGreaterThan(35); // 37.75x fewer queries
});