using System.Net.Http.Json;
using System.Text.Json;
using Elternbeirat.Contracts;

namespace Elternbeirat.PocketBase;

/// <summary>
///     Reads published content from a PocketBase instance over its REST API.
/// </summary>
/// <remarks>
///     <para>
///         There is one method per collection (pages, posts, events, faqs). Each returns
///         only records with <c>public = true</c> and leaves filtering and sorting to
///         PocketBase via query parameters.
///     </para>
///     <para>
///         Register the class as a typed client via <c>AddHttpClient</c>, with
///         <see cref="HttpClient.BaseAddress"/> set to the PocketBase base URL.
///     </para>
/// </remarks>
/// <param name="http">
///     The HTTP client; its <see cref="HttpClient.BaseAddress"/> must point to PocketBase.
/// </param>
public sealed class PocketBaseClient(HttpClient http)
{
    /// <summary>
    ///     Serializer options that map PocketBase UTC dates to Berlin wall-clock time.
    /// </summary>
    private static readonly JsonSerializerOptions JsonOptions = CreateJsonOptions();

    /// <summary>
    ///     Gets all public pages, ordered by <see cref="Page.Order"/>.
    /// </summary>
    /// <param name="ct">
    ///     A token to cancel the request.
    /// </param>
    /// <returns>
    ///     The public pages, or an empty list if there are none.
    /// </returns>
    /// <exception cref="HttpRequestException">
    ///     PocketBase could not be reached or returned a non-success status code.
    /// </exception>
    /// <exception cref="JsonException">
    ///     The response could not be deserialized.
    /// </exception>
    /// <exception cref="OperationCanceledException">
    ///     <paramref name="ct"/> was canceled or the request timed out.
    /// </exception>
    public Task<IReadOnlyList<Page>> GetPagesAsync(CancellationToken ct = default)
        => GetRecordsAsync<Page>("pages", "order", ct);

    /// <summary>
    ///     Gets all public posts, ordered by <see cref="Post.Date"/>, newest first.
    /// </summary>
    /// <inheritdoc cref="GetPagesAsync" path="/param"/>
    /// <returns>
    ///     The public posts, or an empty list if there are none.
    /// </returns>
    /// <inheritdoc cref="GetPagesAsync" path="/exception"/>
    public Task<IReadOnlyList<Post>> GetPostsAsync(CancellationToken ct = default)
        => GetRecordsAsync<Post>("posts", "-date", ct);

    /// <summary>
    ///     Gets all public events, ordered by <see cref="Event.Start"/>, earliest first.
    /// </summary>
    /// <inheritdoc cref="GetPagesAsync" path="/param"/>
    /// <returns>
    ///     The public events, or an empty list if there are none.
    /// </returns>
    /// <inheritdoc cref="GetPagesAsync" path="/exception"/>
    public Task<IReadOnlyList<Event>> GetEventsAsync(CancellationToken ct = default)
        => GetRecordsAsync<Event>("events", "start", ct);

    /// <summary>
    ///     Gets all public FAQ entries, ordered by <see cref="Faq.Topic"/>.
    /// </summary>
    /// <inheritdoc cref="GetPagesAsync" path="/param"/>
    /// <returns>
    ///     The public FAQ entries, or an empty list if there are none.
    /// </returns>
    /// <inheritdoc cref="GetPagesAsync" path="/exception"/>
    public Task<IReadOnlyList<Faq>> GetFaqsAsync(CancellationToken ct = default)
        => GetRecordsAsync<Faq>("faqs", "topic", ct);

    /// <summary>
    ///     Creates the serializer options with the date converters registered: the
    ///     wall-clock ones for points in time and the calendar-day one for plain dates.
    /// </summary>
    /// <returns>
    ///     The configured options.
    /// </returns>
    private static JsonSerializerOptions CreateJsonOptions()
    {
        var options = new JsonSerializerOptions
        {
            PropertyNameCaseInsensitive = true,
        };
        options.Converters.Add(new LocalDateTimeConverter());
        options.Converters.Add(new NullableLocalDateTimeConverter());
        options.Converters.Add(new DateOnlyConverter());
        return options;
    }

    /// <summary>
    ///     Gets all public records of a collection in a single request.
    /// </summary>
    /// <typeparam name="T">
    ///     The record type to deserialize into.
    /// </typeparam>
    /// <param name="collection">
    ///     The PocketBase collection name, e.g. <c>"posts"</c>.
    /// </param>
    /// <param name="sort">
    ///     The PocketBase sort expression; a leading <c>-</c> sorts descending.
    /// </param>
    /// <param name="ct">
    ///     A token to cancel the request.
    /// </param>
    /// <returns>
    ///     The public records, or an empty list if there are none.
    /// </returns>
    private async Task<IReadOnlyList<T>> GetRecordsAsync<T>(
        string collection,
        string sort,
        CancellationToken ct)
    {
        // filter=public=true keeps drafts out; perPage is large enough to fetch
        // every record in a single page given the small content volume.
        var url = $"/api/collections/{collection}/records"
                  + $"?perPage=500&filter={Uri.EscapeDataString("public=true")}"
                  + $"&sort={Uri.EscapeDataString(sort)}";

        var result = await http.GetFromJsonAsync<RecordList<T>>(url, JsonOptions, ct);
        return result?.Items ?? [];
    }
}