using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;
using Yavsc.Blogspot;

namespace Yavsc.Api.Client;

/// <summary>
/// High-level client for the Blog subsystem of the Yavsc API
/// (deployed at <c>https://blogs.pschneider.fr</c>). All transport
/// concerns — base URL, JSON serialisation, Bearer auth, silent
/// refresh on 401, request body shaping — are delegated to
/// <see cref="YavscApiClient"/>, which lives in the consuming
/// application (PostIt). This class is a thin DTO↔path mapper,
/// nothing more.
///
/// <para><b>URL convention.</b> <see cref="YavscApiClient"/>'s
/// <c>BaseAddress</c> already terminates with <c>/api/v1/</c>
/// (see <c>Settings.ApiUrl</c>). The path prefix below is
/// therefore <i>relative</i> to that version segment: a prefix of
/// <c>"blog"</c> resolves to <c>…/api/v1/blog</c>, which matches
/// the <c>[Route(APIPrefix + "/blog")]</c> attribute on
/// <c>Yavsc.Blogs.Controllers.BlogApiController</c>. Do not
/// re-include the <c>api/</c> segment here — that produced 404s
/// in the past (see commit "PostIt: fix blog API double-prefix").</para>
///
/// The class is intentionally non-IDisposable: it does not own the
/// <see cref="YavscApiClient"/> it depends on. Lifetimes are managed
/// by the consumer (typically a singleton service registered with
/// the application).
/// </summary>
public sealed class BlogApiClient
{
    private const string DefaultPathPrefix = "blogspot";

    private readonly IYavscApiClient _api;
    private readonly Uri _baseAddress;
    private readonly string _pathPrefix;

    public BlogApiClient(IYavscApiClient api, string blogsBaseAddress, string pathPrefix = DefaultPathPrefix)
    {
        _api = api ?? throw new ArgumentNullException(nameof(api));
        if (string.IsNullOrEmpty(blogsBaseAddress))
            throw new ArgumentException("Base address is required.", nameof(blogsBaseAddress));

        // e.g. "https://blogs.pschneider.fr/api/v1/" — keep the
        // trailing slash so relative paths ("posts") resolve correctly.
        _baseAddress = new Uri(blogsBaseAddress);
        api.Http.BaseAddress = _baseAddress;

        _pathPrefix = pathPrefix?.TrimStart('/') ?? DefaultPathPrefix;
    }

    public Task<List<BlogPostDto>> GetPostsAsync(int start = 0, int take = 25, CancellationToken ct = default)
        => _api.CallAsync<List<BlogPostDto>>(
            HttpMethod.Get,
            $"{_pathPrefix}?start={start}&take={take}",
            ct: ct);

    public Task<BlogPostDto?> GetPostAsync(long id, CancellationToken ct = default)
        => _api.CallAsync<BlogPostDto?>(HttpMethod.Get, $"{_pathPrefix}/{id}", ct: ct);

    public Task<BlogPostDto?> CreatePostAsync(
        BlogPostDto post,
        IReadOnlyCollection<BlogUploadFile>? files = null,
        CancellationToken ct = default)
        => SendPostAsync(HttpMethod.Post, _pathPrefix, post, files, ct);

    public Task UpdatePostAsync(
        long id,
        BlogPostDto post,
        IReadOnlyCollection<BlogUploadFile>? files = null,
        CancellationToken ct = default)
        => SendPostAsync(HttpMethod.Put, $"{_pathPrefix}/{id}", post, files, ct);

    public Task DeletePostAsync(long id, CancellationToken ct = default)
        => _api.CallAsync(HttpMethod.Delete, $"{_pathPrefix}/{id}", ct: ct);

    /// <summary>
    /// Set a post's publication state. <c>true</c> publishes
    /// it (visible to anonymous readers via
    /// <c>PermissionHandler.IsPublic</c>); <c>false</c> takes
    /// it back to draft. Idempotent: the resulting state
    /// matches the call, regardless of the previous state.
    /// </summary>
    public Task SetPublishAsync(long id, bool publish, CancellationToken ct = default)
        => _api.CallAsync(HttpMethod.Put, $"{_pathPrefix}/{id}/publish",
            body: new { publish }, ct: ct);

    private Task<BlogPostDto?> SendPostAsync(
        HttpMethod method,
        string path,
        BlogPostDto post,
        IReadOnlyCollection<BlogUploadFile>? files,
        CancellationToken ct)
    {
        if (files is null || files.Count == 0)
            return _api.CallAsync<BlogPostDto?>(method, path, body: post, ct: ct);

        return _api.CallAsync<BlogPostDto?>(method, path, () => CreateMultipartContent(post, files), ct: ct);
    }

    private static HttpContent CreateMultipartContent(BlogPostDto post, IReadOnlyCollection<BlogUploadFile> files)
    {
        var content = new MultipartFormDataContent();
        var blogJson = JsonSerializer.Serialize(post, new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.WhenWritingNull,
        });

        content.Add(new StringContent(blogJson), "blog");

        foreach (var file in files)
        {
            var fileContent = new ByteArrayContent(file.Content);
            fileContent.Headers.ContentType = new MediaTypeHeaderValue(
                string.IsNullOrWhiteSpace(file.ContentType) ? "application/octet-stream" : file.ContentType);
            content.Add(fileContent, "file", file.FileName);
        }

        return content;
    }
}