using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using StardewModdingAPI.Toolkit;
using StardewModdingAPI.Toolkit.Framework.Clients.Wiki;
using StardewModdingAPI.Toolkit.Framework.UpdateData;
using StardewModdingAPI.Web.Framework.Clients;

namespace StardewModdingAPI.Web.Framework
{
    /// <summary>Handles fetching data from mod sites.</summary>
    internal class ModSiteManager
    {
        /*********
        ** Fields
        *********/
        /// <summary>The mod sites which provide mod metadata.</summary>
        private readonly IDictionary<ModSiteKey, IModSiteClient> ModSites;


        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        /// <param name="modSites">The mod sites which provide mod metadata.</param>
        public ModSiteManager(IModSiteClient[] modSites)
        {
            this.ModSites = modSites.ToDictionary(p => p.SiteKey);
        }

        /// <summary>Get the mod info for an update key.</summary>
        /// <param name="updateKey">The namespaced update key.</param>
        public async Task<IModPage> GetModPageAsync(UpdateKey updateKey)
        {
            if (!updateKey.LooksValid)
                return new GenericModPage(updateKey.Site, updateKey.ID!).SetError(RemoteModStatus.DoesNotExist, $"Invalid update key '{updateKey}'.");

            // get site
            if (!this.ModSites.TryGetValue(updateKey.Site, out IModSiteClient? client))
                return new GenericModPage(updateKey.Site, updateKey.ID).SetError(RemoteModStatus.DoesNotExist, $"There's no mod site with key '{updateKey.Site}'. Expected one of [{string.Join(", ", this.ModSites.Keys)}].");

            // fetch mod
            IModPage? mod;
            try
            {
                mod = await client.GetModData(updateKey.ID);
            }
            catch (Exception ex)
            {
                mod = new GenericModPage(updateKey.Site, updateKey.ID).SetError(RemoteModStatus.TemporaryError, ex.ToString());
            }

            // handle errors
            return mod ?? new GenericModPage(updateKey.Site, updateKey.ID).SetError(RemoteModStatus.DoesNotExist, $"Found no {updateKey.Site} mod with ID '{updateKey.ID}'.");
        }

        /// <summary>Parse version info for the given mod page info.</summary>
        /// <param name="page">The mod page info.</param>
        /// <param name="updateKey">The update key to match in available files.</param>
        /// <param name="mapRemoteVersions">The changes to apply to remote versions for update checks.</param>
        /// <param name="allowNonStandardVersions">Whether to allow non-standard versions.</param>
        public ModInfoModel GetPageVersions(IModPage page, UpdateKey updateKey, bool allowNonStandardVersions, ChangeDescriptor? mapRemoteVersions)
        {
            // get ID to show in errors
            string displayId = page.RequireSubkey
                ? page.Id + updateKey.Subkey
                : page.Id;

            // validate
            ModInfoModel model = new();
            if (!page.IsValid)
                return model.SetError(page.Status, page.Error);
            if (page.RequireSubkey && updateKey.Subkey is null)
                return model.SetError(RemoteModStatus.RequiredSubkeyMissing, $"The {page.Site} mod with ID '{displayId}' requires an update subkey indicating which mod to fetch.");

            // add basic info (unless it's a manifest, in which case the 'mod page' is the JSON file)
            if (updateKey.Site != ModSiteKey.UpdateManifest)
                model.SetBasicInfo(page.Name, page.Url);

            // fetch versions
            bool hasVersions = this.TryGetLatestVersions(page, updateKey.Subkey, allowNonStandardVersions, mapRemoteVersions, out ISemanticVersion? mainVersion, out ISemanticVersion? previewVersion, out string? mainModPageUrl, out string? previewModPageUrl);
            if (!hasVersions)
                return model.SetError(RemoteModStatus.InvalidData, $"The {page.Site} mod with ID '{displayId}' has no valid versions.");

            // apply mod page info
            model.SetBasicInfo(
                name: page.GetName(updateKey.Subkey) ?? page.Name,
                url: page.GetUrl(updateKey.Subkey) ?? page.Url
            );

            // return info
            return model
                .SetMainVersion(mainVersion!, mainModPageUrl)
                .SetPreviewVersion(previewVersion, previewModPageUrl);
        }

        /// <summary>Get a semantic local version for update checks.</summary>
        /// <param name="version">The version to parse.</param>
        /// <param name="map">Changes to apply to the raw version, if any.</param>
        /// <param name="allowNonStandard">Whether to allow non-standard versions.</param>
        public ISemanticVersion? GetMappedVersion(string? version, ChangeDescriptor? map, bool allowNonStandard)
        {
            // try mapped version
            string? rawNewVersion = this.GetRawMappedVersion(version, map);
            if (SemanticVersion.TryParse(rawNewVersion, allowNonStandard, out ISemanticVersion? parsedNew))
                return parsedNew;

            // return original version
            return SemanticVersion.TryParse(version, allowNonStandard, out ISemanticVersion? parsedOld)
                ? parsedOld
                : null;
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Get the mod version numbers for the given mod.</summary>
        /// <param name="mod">The mod to check.</param>
        /// <param name="subkey">The optional update subkey to match in available files. (If no file names or descriptions contain the subkey, it'll be ignored.)</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>
        /// <param name="main">The main mod version.</param>
        /// <param name="preview">The latest prerelease version, if newer than <paramref name="main"/>.</param>
        /// <param name="mainModPageUrl">The mod page URL from which <paramref name="main"/> can be downloaded, if different from the <see cref="mod"/>'s URL.</param>
        /// <param name="previewModPageUrl">The mod page URL from which <paramref name="preview"/> can be downloaded, if different from the <see cref="mod"/>'s URL.</param>
        private bool TryGetLatestVersions(IModPage? mod, string? subkey, bool allowNonStandardVersions, ChangeDescriptor? mapRemoteVersions, [NotNullWhen(true)] out ISemanticVersion? main, out ISemanticVersion? preview, out string? mainModPageUrl, out string? previewModPageUrl)
        {
            main = null;
            preview = null;
            mainModPageUrl = null;
            previewModPageUrl = null;
            if (mod is null)
                return false;

            // parse all versions from the mod page
            IEnumerable<(IModDownload? download, ISemanticVersion? version)> GetAllVersions()
            {
                ISemanticVersion? ParseAndMapVersion(string? raw)
                {
                    raw = this.NormalizeVersion(raw);
                    return this.GetMappedVersion(raw, mapRemoteVersions, allowNonStandardVersions);
                }

                // get mod version
                ISemanticVersion? modVersion = ParseAndMapVersion(mod.Version);
                if (modVersion != null)
                    yield return (download: null, version: modVersion);

                // get file versions
                foreach (IModDownload download in mod.Downloads)
                {
                    ISemanticVersion? cur = ParseAndMapVersion(download.Version);
                    if (cur != null)
                        yield return (download, cur);
                }
            }
            var versions = GetAllVersions()
                .OrderByDescending(p => p.version, SemanticVersionComparer.Instance)
                .ToArray();

            // get main + preview versions
            void TryGetVersions([NotNullWhen(true)] out ISemanticVersion? mainVersion, out ISemanticVersion? previewVersion, out string? mainUrl, out string? previewUrl, Func<(IModDownload? download, ISemanticVersion? version), bool>? filter = null)
            {
                mainVersion = null;
                previewVersion = null;
                mainUrl = null;
                previewUrl = null;

                // get latest main + preview version
                foreach ((IModDownload? download, ISemanticVersion? version) entry in versions)
                {
                    if (entry.version is null || filter?.Invoke(entry) == false)
                        continue;

                    if (entry.version.IsPrerelease())
                    {
                        if (previewVersion is null)
                        {
                            previewVersion = entry.version;
                            previewUrl = entry.download?.ModPageUrl;
                        }
                    }
                    else
                    {
                        mainVersion = entry.version;
                        mainUrl = entry.download?.ModPageUrl;
                        break; // any others will be older since entries are sorted by version
                    }
                }

                // normalize values
                if (previewVersion is not null)
                {
                    if (mainVersion is null)
                    {
                        // if every version is prerelease, latest one is the main version
                        mainVersion = previewVersion;
                        mainUrl = previewUrl;
                    }
                    if (!previewVersion.IsNewerThan(mainVersion))
                    {
                        previewVersion = null;
                        previewUrl = null;
                    }
                }
            }

            // get versions for subkey
            if (subkey is not null)
                TryGetVersions(out main, out preview, out mainModPageUrl, out previewModPageUrl, filter: entry => entry.download?.MatchesSubkey(subkey) == true);

            // fallback to non-subkey versions
            if (main is null && !mod.RequireSubkey)
                TryGetVersions(out main, out preview, out mainModPageUrl, out previewModPageUrl);
            return main != null;
        }

        /// <summary>Get a semantic local version for update checks.</summary>
        /// <param name="version">The version to map.</param>
        /// <param name="map">Changes to apply to the raw version, if any.</param>
        private string? GetRawMappedVersion(string? version, ChangeDescriptor? map)
        {
            if (version == null || map?.HasChanges != true)
                return version;

            var mapped = new List<string> { version };
            map.Apply(mapped);

            return mapped.FirstOrDefault();
        }

        /// <summary>Normalize a version string.</summary>
        /// <param name="version">The version to normalize.</param>
        private string? NormalizeVersion(string? version)
        {
            if (string.IsNullOrWhiteSpace(version))
                return null;

            version = version.Trim();
            if (Regex.IsMatch(version, @"^v\d", RegexOptions.CultureInvariant | RegexOptions.IgnoreCase)) // common version prefix
                version = version.Substring(1);

            return version;
        }
    }
}