LinqOverview.cs

using System.Diagnostics.CodeAnalysis;
using System.Net.Http.Json;
using System.Text.Json.Serialization;

var httpClient = new HttpClient();

try
{
    // Section 1 - async I/O
    /**
     *  1. Sending a GET request to "https://jsonplaceholder.typicode.com/posts"
     *  2. Validating that a 200 response was provided - if not, we get an exception
     *  3. Based on the provided generic type (in this case IEnumerable<Post>) we essentially convert the string content of the response to
     *     a valid C# object.
     *  4. Assign that object to the variable `posts`
     **/
    var posts = await httpClient.GetFromJsonAsync<IEnumerable<Post>>("https://jsonplaceholder.typicode.com/posts") ?? throw new Exception("Posts failed to retrieve");

    /** Section 2 - LINQ
     * LINQ is a very elegant way of filtering, mapping and reducing data
     *  - Filter (.Where) = As the name implies, filter. The .Where method is the default means of filtering a collection
     *  - Mapping (.Select) = The process of taking in an input collection and for each item transforming the contents of the collection
     *  - Reducing (.Aggregate) = Bottom of the iceberg, reducing is technically a superset of the previously mentioned two but essentially is taking an input and completely "reducing" that input to something else
     */

    // Basic example of filtering
    var allPostsWithMoreThan30CharactersInTitle = posts.Where(post => post.Title.Length > 30);
    PrintPosts(allPostsWithMoreThan30CharactersInTitle);

    // For individual items, use First/FirstOrDefault
    var firstBigPost = posts.FirstOrDefault(post => post.Title.Length > 30);
    if (firstBigPost != null)
    {
        PrintPosts([firstBigPost]);
    }

    // LINQ is important because it's IMMUTABLE, anything that happens in LINQ doesn't screw with the underlying collection
    // This is also a potential PERFORMANCE ISSUE, however we will let you know if that is the case (premature optimisation is the root of all evil)
    // LINQ essentially iterates over every item in a collection and runs the provided function, this means that with bigger collections - you get poorer performance

    // Mapping is the process of taking in an input and returning a modified output
    var postAnalytics = posts.Select(post => new PostAnalytics(post));
    foreach (var analytics in postAnalytics)
    {
        PrintAnalytics(analytics);
    }

    // You can "chain" LINQ methods
    var allPostsWithMoreThan30CharactersInTitleAnalytics = posts
        .Where(post => post.Title.Length > 30)
        .Select(post => new PostAnalytics(post));


    // Aggregate/Reduce is the most powerful of the bunch but it's a pest to write sometimes and nowhere near as clean
    // as its cousins.
    var postSummary = posts.Aggregate(
        new PostCollectionSummary(), 
        (summary, post) => 
        {
            summary.PostCount += 1;

            // If I haven't found a post yet OR the current post is longer, update the lengthiest post
            if (summary.LengthiestPost == null || post.Title.Length > summary.LengthiestPost.Title.Length)
            {
                summary.LengthiestPost = post;
            }

            return summary;
        });
)
    Console.WriteLine($"SUMMARY | COUNT: {postSummary.PostCount} | Lengthiest Post: {postSummary.LengthiestPost?.Title}");

}
// Exception is the base class for all exceptions
// If you provide a specific type that isn't exception, it will only catch that type and all sub-classes
catch (Exception ex)
{
    Console.WriteLine($"Something went wrong ({ex.Message})");
}

static void PrintPosts(IEnumerable<Post> posts)
{
    foreach (var post in posts)
    {
        Console.WriteLine($"Post #{post.Id} - {post.Title}");
    }
}

static void PrintAnalytics(PostAnalytics postAnalytics)
{
    Console.WriteLine($"Title Length: {postAnalytics.TitleLength}, Vowel Count: {postAnalytics.VowelCountKinda}");
}

// {
//     "userId": 1,
//     "id": 1,
//     "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",

public sealed class Post
{
    [JsonPropertyName("id")]
    public int Id { get; set; } = 0;

    [JsonPropertyName("title")]
    public string Title { get; set; } = string.Empty;
}

public sealed record PostAnalytics(Post post)
{
    public int TitleLength => post.Title.Length;
    public int VowelCountKinda => post.Title.ToLower().Count(c => c == 'a' || c == 'i' || c == 'o');
}

public sealed class PostCollectionSummary
{
    public int PostCount { get; set; }
    public Post? LengthiestPost { get; set; }
}