using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Options;
using StardewModdingAPI.Toolkit;
using StardewModdingAPI.Toolkit.Framework.Clients.WebApi;
using StardewModdingAPI.Toolkit.Framework.Clients.Wiki;
using StardewModdingAPI.Toolkit.Framework.ModData;
using StardewModdingAPI.Toolkit.Framework.UpdateData;
using StardewModdingAPI.Web.Framework;
using StardewModdingAPI.Web.Framework.Caching;
using StardewModdingAPI.Web.Framework.Caching.Mods;
using StardewModdingAPI.Web.Framework.Caching.Wiki;
using StardewModdingAPI.Web.Framework.Clients;
using StardewModdingAPI.Web.Framework.Clients.Chucklefish;
using StardewModdingAPI.Web.Framework.Clients.CurseForge;
using StardewModdingAPI.Web.Framework.Clients.GitHub;
using StardewModdingAPI.Web.Framework.Clients.ModDrop;
using StardewModdingAPI.Web.Framework.Clients.Nexus;
using StardewModdingAPI.Web.Framework.ConfigModels;

namespace StardewModdingAPI.Web.Controllers
{
    /// <summary>Provides an API to perform mod update checks.</summary>
    [Produces("application/json")]
    [Route("api/v{version:semanticVersion}/mods")]
    internal class ModsApiController : Controller
    {
        /*********
        ** Fields
        *********/
        /// <summary>The mod sites which provide mod metadata.</summary>
        private readonly ModSiteManager ModSites;

        /// <summary>The cache in which to store wiki data.</summary>
        private readonly IWikiCacheRepository WikiCache;

        /// <summary>The cache in which to store mod data.</summary>
        private readonly IModCacheRepository ModCache;

        /// <summary>The config settings for mod update checks.</summary>
        private readonly IOptions<ModUpdateCheckConfig> Config;

        /// <summary>The internal mod metadata list.</summary>
        private readonly ModDatabase ModDatabase;


        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        /// <param name="environment">The web hosting environment.</param>
        /// <param name="wikiCache">The cache in which to store wiki data.</param>
        /// <param name="modCache">The cache in which to store mod metadata.</param>
        /// <param name="config">The config settings for mod update checks.</param>
        /// <param name="chucklefish">The Chucklefish API client.</param>
        /// <param name="curseForge">The CurseForge API client.</param>
        /// <param name="github">The GitHub API client.</param>
        /// <param name="modDrop">The ModDrop API client.</param>
        /// <param name="nexus">The Nexus API client.</param>
        public ModsApiController(IWebHostEnvironment environment, IWikiCacheRepository wikiCache, IModCacheRepository modCache, IOptions<ModUpdateCheckConfig> config, IChucklefishClient chucklefish, ICurseForgeClient curseForge, IGitHubClient github, IModDropClient modDrop, INexusClient nexus)
        {
            this.ModDatabase = new ModToolkit().GetModDatabase(Path.Combine(environment.WebRootPath, "SMAPI.metadata.json"));

            this.WikiCache = wikiCache;
            this.ModCache = modCache;
            this.Config = config;
            this.ModSites = new ModSiteManager(new IModSiteClient[] { chucklefish, curseForge, github, modDrop, nexus });
        }

        /// <summary>Fetch version metadata for the given mods.</summary>
        /// <param name="model">The mod search criteria.</param>
        /// <param name="version">The requested API version.</param>
        [HttpPost]
        public async Task<IEnumerable<ModEntryModel>> PostAsync([FromBody] ModSearchModel? model, [FromRoute] string version)
        {
            if (model?.Mods == null)
                return Array.Empty<ModEntryModel>();

            ModUpdateCheckConfig config = this.Config.Value;

            // fetch wiki data
            WikiModEntry[] wikiData = this.WikiCache.GetWikiMods().Select(p => p.Data).ToArray();
            IDictionary<string, ModEntryModel> mods = new Dictionary<string, ModEntryModel>(StringComparer.CurrentCultureIgnoreCase);
            foreach (ModSearchEntryModel mod in model.Mods)
            {
                if (string.IsNullOrWhiteSpace(mod.ID))
                    continue;

                // special case: if this is an update check for the official SMAPI repo, check the Nexus mod page for beta versions
                if (mod.ID == config.SmapiInfo.ID && mod.UpdateKeys.Any(key => key == config.SmapiInfo.DefaultUpdateKey) && mod.InstalledVersion?.IsPrerelease() == true)
                    mod.AddUpdateKeys(config.SmapiInfo.AddBetaUpdateKeys);

                // fetch result
                ModEntryModel result = await this.GetModData(mod, wikiData, model.IncludeExtendedMetadata, model.ApiVersion);
                if (!model.IncludeExtendedMetadata && (model.ApiVersion == null || mod.InstalledVersion == null))
                {
                    result.Errors = result.Errors
                        .Concat(new[] { $"This API can't suggest an update because {nameof(model.ApiVersion)} or {nameof(mod.InstalledVersion)} are null, and you didn't specify {nameof(model.IncludeExtendedMetadata)} to get other info. See the SMAPI technical docs for usage." })
                        .ToArray();
                }

                mods[mod.ID] = result;
            }

            // return data
            return mods.Values;
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Get the metadata for a mod.</summary>
        /// <param name="search">The mod data to match.</param>
        /// <param name="wikiData">The wiki data.</param>
        /// <param name="includeExtendedMetadata">Whether to include extended metadata for each mod.</param>
        /// <param name="apiVersion">The SMAPI version installed by the player.</param>
        /// <returns>Returns the mod data if found, else <c>null</c>.</returns>
        private async Task<ModEntryModel> GetModData(ModSearchEntryModel search, WikiModEntry[] wikiData, bool includeExtendedMetadata, ISemanticVersion? apiVersion)
        {
            // cross-reference data
            ModDataRecord? record = this.ModDatabase.Get(search.ID);
            WikiModEntry? wikiEntry = wikiData.FirstOrDefault(entry => entry.ID.Contains(search.ID.Trim(), StringComparer.OrdinalIgnoreCase));
            UpdateKey[] updateKeys = this.GetUpdateKeys(search.UpdateKeys, record, wikiEntry).ToArray();
            ModOverrideConfig? overrides = this.Config.Value.ModOverrides.FirstOrDefault(p => p.ID.Equals(search.ID.Trim(), StringComparison.OrdinalIgnoreCase));
            bool allowNonStandardVersions = overrides?.AllowNonStandardVersions ?? false;

            // SMAPI versions with a '-beta' tag indicate major changes that may need beta mod versions.
            // This doesn't apply to normal prerelease versions which have an '-alpha' tag.
            bool isSmapiBeta = apiVersion != null && apiVersion.IsPrerelease() && apiVersion.PrereleaseTag.StartsWith("beta");

            // get latest versions
            ModEntryModel result = new(search.ID);
            IList<string> errors = new List<string>();
            ModEntryVersionModel? main = null;
            ModEntryVersionModel? optional = null;
            ModEntryVersionModel? unofficial = null;
            ModEntryVersionModel? unofficialForBeta = null;
            foreach (UpdateKey updateKey in updateKeys)
            {
                // validate update key
                if (!updateKey.LooksValid)
                {
                    errors.Add($"The update key '{updateKey}' isn't in a valid format. It should contain the site key and mod ID like 'Nexus:541', with an optional subkey like 'Nexus:541@subkey'.");
                    continue;
                }

                // fetch data
                ModInfoModel data = await this.GetInfoForUpdateKeyAsync(updateKey, allowNonStandardVersions, wikiEntry?.Overrides?.ChangeRemoteVersions);
                if (data.Status != RemoteModStatus.Ok)
                {
                    errors.Add(data.Error ?? data.Status.ToString());
                    continue;
                }

                // if there's only a prerelease version (e.g. from GitHub), don't override the main version
                ISemanticVersion? curMain = data.Version;
                ISemanticVersion? curPreview = data.PreviewVersion;
                if (curPreview == null && curMain?.IsPrerelease() == true)
                {
                    curPreview = curMain;
                    curMain = null;
                }

                // handle versions
                if (this.IsNewer(curMain, main?.Version))
                    main = new ModEntryVersionModel(curMain, data.Url!);
                if (this.IsNewer(curPreview, optional?.Version))
                    optional = new ModEntryVersionModel(curPreview, data.Url!);
            }

            // get unofficial version
            if (wikiEntry?.Compatibility.UnofficialVersion != null && this.IsNewer(wikiEntry.Compatibility.UnofficialVersion, main?.Version) && this.IsNewer(wikiEntry.Compatibility.UnofficialVersion, optional?.Version))
                unofficial = new ModEntryVersionModel(wikiEntry.Compatibility.UnofficialVersion, $"{this.Url.PlainAction("Index", "Mods", absoluteUrl: true)}#{wikiEntry.Anchor}");

            // get unofficial version for beta
            if (wikiEntry is { HasBetaInfo: true })
            {
                if (wikiEntry.BetaCompatibility.Status == WikiCompatibilityStatus.Unofficial)
                {
                    if (wikiEntry.BetaCompatibility.UnofficialVersion != null)
                    {
                        unofficialForBeta = (wikiEntry.BetaCompatibility.UnofficialVersion != null && this.IsNewer(wikiEntry.BetaCompatibility.UnofficialVersion, main?.Version) && this.IsNewer(wikiEntry.BetaCompatibility.UnofficialVersion, optional?.Version))
                            ? new ModEntryVersionModel(wikiEntry.BetaCompatibility.UnofficialVersion, $"{this.Url.PlainAction("Index", "Mods", absoluteUrl: true)}#{wikiEntry.Anchor}")
                            : null;
                    }
                    else
                        unofficialForBeta = unofficial;
                }
            }

            // fallback to preview if latest is invalid
            if (main == null && optional != null)
            {
                main = optional;
                optional = null;
            }

            // special cases
            if (overrides?.SetUrl != null)
            {
                if (main != null)
                    main = new(main.Version, overrides.SetUrl);
                if (optional != null)
                    optional = new(optional.Version, overrides.SetUrl);
            }

            // get recommended update (if any)
            ISemanticVersion? installedVersion = this.ModSites.GetMappedVersion(search.InstalledVersion?.ToString(), wikiEntry?.Overrides?.ChangeLocalVersions, allowNonStandard: allowNonStandardVersions);
            if (apiVersion != null && installedVersion != null)
            {
                // get newer versions
                List<ModEntryVersionModel> updates = new List<ModEntryVersionModel>();
                if (this.IsRecommendedUpdate(installedVersion, main?.Version, useBetaChannel: true))
                    updates.Add(main);
                if (this.IsRecommendedUpdate(installedVersion, optional?.Version, useBetaChannel: isSmapiBeta || installedVersion.IsPrerelease() || search.IsBroken))
                    updates.Add(optional);
                if (this.IsRecommendedUpdate(installedVersion, unofficial?.Version, useBetaChannel: true))
                    updates.Add(unofficial);
                if (this.IsRecommendedUpdate(installedVersion, unofficialForBeta?.Version, useBetaChannel: apiVersion.IsPrerelease()))
                    updates.Add(unofficialForBeta);

                // get newest version
                ModEntryVersionModel? newest = null;
                foreach (ModEntryVersionModel update in updates)
                {
                    if (newest == null || update.Version.IsNewerThan(newest.Version))
                        newest = update;
                }

                // set field
                result.SuggestedUpdate = newest != null
                    ? new ModEntryVersionModel(newest.Version, newest.Url)
                    : null;
            }

            // add extended metadata
            if (includeExtendedMetadata)
                result.Metadata = new ModExtendedMetadataModel(wikiEntry, record, main: main, optional: optional, unofficial: unofficial, unofficialForBeta: unofficialForBeta);

            // add result
            result.Errors = errors.ToArray();
            return result;
        }

        /// <summary>Get whether a given version should be offered to the user as an update.</summary>
        /// <param name="currentVersion">The current semantic version.</param>
        /// <param name="newVersion">The target semantic version.</param>
        /// <param name="useBetaChannel">Whether the user enabled the beta channel and should be offered prerelease updates.</param>
        private bool IsRecommendedUpdate(ISemanticVersion currentVersion, [NotNullWhen(true)] ISemanticVersion? newVersion, bool useBetaChannel)
        {
            return
                newVersion != null
                && newVersion.IsNewerThan(currentVersion)
                && (useBetaChannel || !newVersion.IsPrerelease());
        }

        /// <summary>Get whether a <paramref name="current"/> version is newer than an <paramref name="other"/> version.</summary>
        /// <param name="current">The current version.</param>
        /// <param name="other">The other version.</param>
        private bool IsNewer([NotNullWhen(true)] ISemanticVersion? current, ISemanticVersion? other)
        {
            return current != null && (other == null || other.IsOlderThan(current));
        }

        /// <summary>Get the mod info for an update key.</summary>
        /// <param name="updateKey">The namespaced update key.</param>
        /// <param name="allowNonStandardVersions">Whether to allow non-standard versions.</param>
        /// <param name="mapRemoteVersions">The changes to apply to remote versions for update checks.</param>
        private async Task<ModInfoModel> GetInfoForUpdateKeyAsync(UpdateKey updateKey, bool allowNonStandardVersions, ChangeDescriptor? mapRemoteVersions)
        {
            if (!updateKey.LooksValid)
                return new ModInfoModel().SetError(RemoteModStatus.DoesNotExist, $"Invalid update key '{updateKey}'.");

            // get mod page
            IModPage page;
            {
                bool isCached =
                    this.ModCache.TryGetMod(updateKey.Site, updateKey.ID, out Cached<IModPage>? cachedMod)
                    && !this.ModCache.IsStale(cachedMod.LastUpdated, cachedMod.Data.Status == RemoteModStatus.TemporaryError ? this.Config.Value.ErrorCacheMinutes : this.Config.Value.SuccessCacheMinutes);

                if (isCached)
                    page = cachedMod!.Data;
                else
                {
                    page = await this.ModSites.GetModPageAsync(updateKey);
                    this.ModCache.SaveMod(updateKey.Site, updateKey.ID, page);
                }
            }

            // get version info
            return this.ModSites.GetPageVersions(page, updateKey.Subkey, allowNonStandardVersions, mapRemoteVersions);
        }

        /// <summary>Get update keys based on the available mod metadata, while maintaining the precedence order.</summary>
        /// <param name="specifiedKeys">The specified update keys.</param>
        /// <param name="record">The mod's entry in SMAPI's internal database.</param>
        /// <param name="entry">The mod's entry in the wiki list.</param>
        private IEnumerable<UpdateKey> GetUpdateKeys(string[]? specifiedKeys, ModDataRecord? record, WikiModEntry? entry)
        {
            // get unique update keys
            List<UpdateKey> updateKeys = this.GetUnfilteredUpdateKeys(specifiedKeys, record, entry)
                .Select(UpdateKey.Parse)
                .Distinct()
                .ToList();

            // apply overrides from wiki
            if (entry?.Overrides?.ChangeUpdateKeys?.HasChanges == true)
            {
                List<string> newKeys = updateKeys.Select(p => p.ToString()).ToList();
                entry.Overrides.ChangeUpdateKeys.Apply(newKeys);
                updateKeys = newKeys.Select(UpdateKey.Parse).ToList();
            }

            // if the list has both an update key (like "Nexus:2400") and subkey (like "Nexus:2400@subkey") for the same page, the subkey takes priority
            {
                var removeKeys = new HashSet<UpdateKey>();
                foreach (UpdateKey key in updateKeys)
                {
                    if (key.Subkey != null)
                        removeKeys.Add(new UpdateKey(key.Site, key.ID, null));
                }
                if (removeKeys.Any())
                    updateKeys.RemoveAll(removeKeys.Contains);
            }

            return updateKeys;
        }

        /// <summary>Get every available update key based on the available mod metadata, including duplicates and keys which should be filtered.</summary>
        /// <param name="specifiedKeys">The specified update keys.</param>
        /// <param name="record">The mod's entry in SMAPI's internal database.</param>
        /// <param name="entry">The mod's entry in the wiki list.</param>
        private IEnumerable<string> GetUnfilteredUpdateKeys(string[]? specifiedKeys, ModDataRecord? record, WikiModEntry? entry)
        {
            // specified update keys
            foreach (string key in specifiedKeys ?? Array.Empty<string>())
            {
                if (!string.IsNullOrWhiteSpace(key))
                    yield return key.Trim();
            }

            // default update key
            {
                string? defaultKey = record?.GetDefaultUpdateKey();
                if (!string.IsNullOrWhiteSpace(defaultKey))
                    yield return defaultKey;
            }

            // wiki metadata
            if (entry != null)
            {
                if (entry.NexusID.HasValue)
                    yield return UpdateKey.GetString(ModSiteKey.Nexus, entry.NexusID.ToString());
                if (entry.ModDropID.HasValue)
                    yield return UpdateKey.GetString(ModSiteKey.ModDrop, entry.ModDropID.ToString());
                if (entry.CurseForgeID.HasValue)
                    yield return UpdateKey.GetString(ModSiteKey.CurseForge, entry.CurseForgeID.ToString());
                if (entry.ChucklefishID.HasValue)
                    yield return UpdateKey.GetString(ModSiteKey.Chucklefish, entry.ChucklefishID.ToString());
            }
        }
    }
}