using System;
using System.Diagnostics.CodeAnalysis;
using System.Net;
using System.Net.Http.Headers;
using System.Threading.Tasks;
using Pathoschild.Http.Client;
using StardewModdingAPI.Toolkit;
using StardewModdingAPI.Toolkit.Framework.UpdateData;
using StardewModdingAPI.Web.Framework.Clients.UpdateManifest.ResponseModels;

namespace StardewModdingAPI.Web.Framework.Clients.UpdateManifest
{
    /// <summary>An API client for fetching update metadata from an arbitrary JSON URL.</summary>
    internal class UpdateManifestClient : IUpdateManifestClient
    {
        /*********
        ** Fields
        *********/
        /// <summary>The underlying HTTP client.</summary>
        private readonly IClient Client;


        /*********
        ** Accessors
        *********/
        /// <summary>The unique key for the mod site.</summary>
        public ModSiteKey SiteKey => ModSiteKey.UpdateManifest;


        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        /// <param name="userAgent">The user agent for the API client.</param>
        public UpdateManifestClient(string userAgent)
        {
            this.Client = new FluentClient()
                .SetUserAgent(userAgent);

            this.Client.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/plain"));
        }

        /// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
        public void Dispose()
        {
            this.Client.Dispose();
        }

        /// <inheritdoc/>
        [SuppressMessage("ReSharper", "ConditionIsAlwaysTrueOrFalseAccordingToNullableAPIContract", Justification = "This is the method which ensures the annotations are correct.")]
        public async Task<IModPage?> GetModData(string id)
        {
            // get raw update manifest
            UpdateManifestModel? manifest;
            try
            {
                manifest = await this.Client.GetAsync(id).As<UpdateManifestModel?>();
                if (manifest is null)
                    return this.GetFormatError(id, "manifest can't be empty");
            }
            catch (ApiException ex) when (ex.Status == HttpStatusCode.NotFound)
            {
                return new GenericModPage(this.SiteKey, id).SetError(RemoteModStatus.DoesNotExist, $"No update manifest found at {id}");
            }
            catch (Exception ex)
            {
                return this.GetFormatError(id, ex.Message);
            }

            // validate
            if (!SemanticVersion.TryParse(manifest.Format, out _))
                return this.GetFormatError(id, $"invalid format version '{manifest.Format}'");
            foreach (UpdateManifestModModel mod in manifest.Mods.Values)
            {
                if (mod is null)
                    return this.GetFormatError(id, "a mod record can't be null");
                if (string.IsNullOrWhiteSpace(mod.ModPageUrl))
                    return this.GetFormatError(id, $"all mods must have a {nameof(mod.ModPageUrl)} value");
                foreach (UpdateManifestVersionModel? version in mod.Versions)
                {
                    if (version is null)
                        return this.GetFormatError(id, "a version record can't be null");
                    if (string.IsNullOrWhiteSpace(version.Version))
                        return this.GetFormatError(id, $"all version records must have a {nameof(version.Version)} field");
                    if (!SemanticVersion.TryParse(version.Version, out _))
                        return this.GetFormatError(id, $"invalid mod version '{version.Version}'");
                }
            }

            // build model
            return new UpdateManifestModPage(id, manifest);
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Get a mod page instance with an error indicating the update manifest is invalid.</summary>
        /// <param name="url">The full URL to the update manifest.</param>
        /// <param name="reason">A human-readable reason phrase indicating why it's invalid.</param>
        private IModPage GetFormatError(string url, string reason)
        {
            return new GenericModPage(this.SiteKey, url).SetError(RemoteModStatus.InvalidData, $"The update manifest at {url} is invalid ({reason})");
        }
    }
}