using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using StardewModdingAPI.Toolkit.Serialization;
using StardewModdingAPI.Toolkit.Serialization.Models;
using StardewModdingAPI.Toolkit.Utilities.PathLookups;

namespace StardewModdingAPI.Toolkit.Framework.ModScanning
{
    /// <summary>Scans folders for mod data.</summary>
    public class ModScanner
    {
        /*********
        ** Fields
        *********/
        /// <summary>The JSON helper with which to read manifests.</summary>
        private readonly JsonHelper JsonHelper;

        /// <summary>A list of filesystem entry names to ignore when checking whether a folder should be treated as a mod.</summary>
        private readonly HashSet<Regex> IgnoreFilesystemNames = new()
        {
            new Regex(@"^__folder_managed_by_vortex$", RegexOptions.Compiled | RegexOptions.IgnoreCase), // Vortex mod manager
            new Regex(@"(?:^\._|^\.DS_Store$|^__MACOSX$|^mcs$)", RegexOptions.Compiled | RegexOptions.IgnoreCase), // macOS
            new Regex(@"^(?:desktop\.ini|Thumbs\.db)$", RegexOptions.Compiled | RegexOptions.IgnoreCase) // Windows
        };

        /// <summary>A list of file extensions to ignore when searching for mod files.</summary>
        private readonly HashSet<string> IgnoreFileExtensions = new(StringComparer.OrdinalIgnoreCase)
        {
            // text
            ".doc",
            ".docx",
            ".md",
            ".rtf",
            ".txt",

            // images
            ".bmp",
            ".gif",
            ".ico",
            ".jpeg",
            ".jpg",
            ".png",
            ".psd",
            ".tif",

            // archives
            ".rar",
            ".zip",

            // backup files
            ".backup",
            ".bak",
            ".old",

            // Windows shortcut files
            ".url",
            ".lnk"
        };

        /// <summary>The extensions for packed content files.</summary>
        private readonly HashSet<string> StrictXnbModExtensions = new(StringComparer.OrdinalIgnoreCase)
        {
            ".xgs",
            ".xnb",
            ".xsb",
            ".xwb"
        };

        /// <summary>The extensions for files which an XNB mod may contain, in addition to <see cref="StrictXnbModExtensions"/>.</summary>
        private readonly HashSet<string> PotentialXnbModExtensions = new(StringComparer.OrdinalIgnoreCase)
        {
            ".json",
            ".yaml"
        };

        /// <summary>The name of the marker file added by Vortex to indicate it's managing the folder.</summary>
        private readonly string VortexMarkerFileName = "__folder_managed_by_vortex";

        /// <summary>The name for a mod's configuration JSON file.</summary>
        private readonly string ConfigFileName = "config.json";


        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        /// <param name="jsonHelper">The JSON helper with which to read manifests.</param>
        public ModScanner(JsonHelper jsonHelper)
        {
            this.JsonHelper = jsonHelper;
        }

        /// <summary>Extract information about all mods in the given folder.</summary>
        /// <param name="rootPath">The root folder containing mods.</param>
        /// <param name="useCaseInsensitiveFilePaths">Whether to match file paths case-insensitively, even on Linux.</param>
        public IEnumerable<ModFolder> GetModFolders(string rootPath, bool useCaseInsensitiveFilePaths)
        {
            DirectoryInfo root = new(rootPath);
            return this.GetModFolders(root, root, useCaseInsensitiveFilePaths);
        }

        /// <summary>Extract information about all mods in the given folder.</summary>
        /// <param name="rootPath">The root folder containing mods. Only the <paramref name="modPath"/> will be searched, but this field allows it to be treated as a potential mod folder of its own.</param>
        /// <param name="modPath">The mod path to search.</param>
        /// <param name="useCaseInsensitiveFilePaths">Whether to match file paths case-insensitively, even on Linux.</param>
        public IEnumerable<ModFolder> GetModFolders(string rootPath, string modPath, bool useCaseInsensitiveFilePaths)
        {
            return this.GetModFolders(root: new DirectoryInfo(rootPath), folder: new DirectoryInfo(modPath), useCaseInsensitiveFilePaths: useCaseInsensitiveFilePaths);
        }

        /// <summary>Extract information from a mod folder.</summary>
        /// <param name="root">The root folder containing mods.</param>
        /// <param name="searchFolder">The folder to search for a mod.</param>
        public ModFolder ReadFolder(DirectoryInfo root, DirectoryInfo searchFolder)
        {
            // find manifest.json
            FileInfo? manifestFile = this.FindManifest(searchFolder);

            // set appropriate invalid-mod error
            if (manifestFile == null)
            {
                FileInfo[] files = this.RecursivelyGetFiles(searchFolder).ToArray();
                FileInfo[] relevantFiles = files.Where(this.IsRelevant).ToArray();

                // empty Vortex folder
                // (this filters relevant files internally so it can check for the normally-ignored Vortex marker file)
                if (this.IsEmptyVortexFolder(files))
                    return new ModFolder(root, searchFolder, ModType.Invalid, null, ModParseError.EmptyVortexFolder, "it's an empty Vortex folder (is the mod disabled in Vortex?).");

                // empty folder
                if (!relevantFiles.Any())
                    return new ModFolder(root, searchFolder, ModType.Invalid, null, ModParseError.EmptyFolder, "it's an empty folder.");

                // XNB mod
                if (this.IsXnbMod(relevantFiles))
                    return new ModFolder(root, searchFolder, ModType.Xnb, null, ModParseError.XnbMod, "it's not a SMAPI mod (see https://smapi.io/xnb for info).");

                // SMAPI installer
                if (relevantFiles.Any(p => p.Name is "install on Linux.sh" or "install on macOS.command" or "install on Windows.bat"))
                    return new ModFolder(root, searchFolder, ModType.Invalid, null, ModParseError.ManifestMissing, "the SMAPI installer isn't a mod (you can delete this folder after running the installer file).");

                // not a mod?
                return new ModFolder(root, searchFolder, ModType.Invalid, null, ModParseError.ManifestMissing, "it contains files, but none of them are manifest.json.");
            }

            // read mod info
            Manifest? manifest = null;
            ModParseError error = ModParseError.None;
            string? errorText = null;
            {
                try
                {
                    if (!this.JsonHelper.ReadJsonFileIfExists<Manifest>(manifestFile.FullName, out manifest))
                    {
                        error = ModParseError.ManifestInvalid;
                        errorText = "its manifest is invalid.";
                    }
                }
                catch (SParseException ex)
                {
                    error = ModParseError.ManifestInvalid;
                    errorText = $"parsing its manifest failed: {ex.Message}";
                }
                catch (Exception ex)
                {
                    error = ModParseError.ManifestInvalid;
                    errorText = $"parsing its manifest failed:\n{ex}";
                }
            }

            // get mod type
            ModType type;
            {
                bool isContentPack = !string.IsNullOrWhiteSpace(manifest?.ContentPackFor?.UniqueID);
                bool isSmapi = !string.IsNullOrWhiteSpace(manifest?.EntryDll);

                if (isContentPack == isSmapi)
                    type = ModType.Invalid;
                else if (isContentPack)
                    type = ModType.ContentPack;
                else
                    type = ModType.Smapi;
            }

            // build result
            return new ModFolder(root, manifestFile.Directory!, type, manifest, error, errorText);
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Recursively extract information about all mods in the given folder.</summary>
        /// <param name="root">The root mod folder.</param>
        /// <param name="folder">The folder to search for mods.</param>
        /// <param name="useCaseInsensitiveFilePaths">Whether to match file paths case-insensitively, even on Linux.</param>
        private IEnumerable<ModFolder> GetModFolders(DirectoryInfo root, DirectoryInfo folder, bool useCaseInsensitiveFilePaths)
        {
            bool isRoot = folder.FullName == root.FullName;

            // skip
            if (!isRoot)
            {
                if (folder.Name.StartsWith("."))
                {
                    yield return new ModFolder(root, folder, ModType.Ignored, null, ModParseError.IgnoredFolder, "ignored folder because its name starts with a dot.");
                    yield break;
                }
                if (!this.IsRelevant(folder))
                    yield break;
            }

            // find mods in subfolders
            if (this.IsModSearchFolder(root, folder))
            {
                IEnumerable<ModFolder> subfolders = folder.EnumerateDirectories().SelectMany(sub => this.GetModFolders(root, sub, useCaseInsensitiveFilePaths));
                if (!isRoot)
                    subfolders = this.TryConsolidate(root, folder, subfolders.ToArray());
                foreach (ModFolder subfolder in subfolders)
                    yield return subfolder;
            }

            // treat as mod folder
            else
                yield return this.ReadFolder(root, folder);
        }

        /// <summary>Consolidate adjacent folders into one mod folder, if possible.</summary>
        /// <param name="root">The folder containing both parent and subfolders.</param>
        /// <param name="parentFolder">The parent folder to consolidate, if possible.</param>
        /// <param name="subfolders">The subfolders to consolidate, if possible.</param>
        private IEnumerable<ModFolder> TryConsolidate(DirectoryInfo root, DirectoryInfo parentFolder, ModFolder[] subfolders)
        {
            if (subfolders.Length > 1)
            {
                // a collection of empty folders
                if (subfolders.All(p => p.ManifestParseError == ModParseError.EmptyFolder))
                    return new[] { new ModFolder(root, parentFolder, ModType.Invalid, null, ModParseError.EmptyFolder, subfolders[0].ManifestParseErrorText) };

                // an XNB mod
                if (subfolders.All(p => p.Type == ModType.Xnb || p.ManifestParseError == ModParseError.EmptyFolder))
                    return new[] { new ModFolder(root, parentFolder, ModType.Xnb, null, ModParseError.XnbMod, subfolders[0].ManifestParseErrorText) };
            }

            return subfolders;
        }

        /// <summary>Find the manifest for a mod folder.</summary>
        /// <param name="folder">The folder to search.</param>
        private FileInfo? FindManifest(DirectoryInfo folder)
        {
            // check for conventional manifest in current folder
            const string defaultName = "manifest.json";
            FileInfo file = new(Path.Combine(folder.FullName, defaultName));
            if (file.Exists)
                return file;

            // check for manifest with incorrect capitalization
            {
                CaseInsensitivePathLookup pathLookup = new(folder.FullName, SearchOption.TopDirectoryOnly); // don't use GetCachedFor, since we only need it temporarily
                string realName = pathLookup.GetFilePath(defaultName);
                if (realName != defaultName)
                    file = new(Path.Combine(folder.FullName, realName));
            }
            if (file.Exists)
                return file;

            // not found
            return null;
        }

        /// <summary>Get whether a given folder should be treated as a search folder (i.e. look for subfolders containing mods).</summary>
        /// <param name="root">The root mod folder.</param>
        /// <param name="folder">The folder to search for mods.</param>
        private bool IsModSearchFolder(DirectoryInfo root, DirectoryInfo folder)
        {
            if (root.FullName == folder.FullName)
                return true;

            DirectoryInfo[] subfolders = folder.GetDirectories().Where(this.IsRelevant).ToArray();
            FileInfo[] files = folder.GetFiles().Where(this.IsRelevant).ToArray();
            return subfolders.Any() && !files.Any();
        }

        /// <summary>Recursively get all files in a folder.</summary>
        /// <param name="folder">The root folder to search.</param>
        private IEnumerable<FileInfo> RecursivelyGetFiles(DirectoryInfo folder)
        {
            foreach (FileSystemInfo entry in folder.GetFileSystemInfos())
            {
                if (entry is DirectoryInfo && !this.IsRelevant(entry))
                    continue;

                if (entry is FileInfo file)
                    yield return file;

                if (entry is DirectoryInfo subfolder)
                {
                    foreach (FileInfo subfolderFile in this.RecursivelyGetFiles(subfolder))
                        yield return subfolderFile;
                }
            }
        }

        /// <summary>Get whether a file or folder is relevant when deciding how to process a mod folder.</summary>
        /// <param name="entry">The file or folder.</param>
        private bool IsRelevant(FileSystemInfo entry)
        {
            // ignored file extensions and any files starting with "."
            if ((entry is FileInfo file) && (this.IgnoreFileExtensions.Contains(file.Extension) || file.Name.StartsWith(".")))
                return false;

            // ignored entry name
            return !this.IgnoreFilesystemNames.Any(p => p.IsMatch(entry.Name));
        }

        /// <summary>Get whether a set of files looks like an XNB mod.</summary>
        /// <param name="files">The files in the mod.</param>
        private bool IsXnbMod(IEnumerable<FileInfo> files)
        {
            bool hasXnbFile = false;

            foreach (FileInfo file in files.Where(this.IsRelevant))
            {
                if (this.StrictXnbModExtensions.Contains(file.Extension))
                {
                    hasXnbFile = true;
                    continue;
                }

                if (!this.PotentialXnbModExtensions.Contains(file.Extension))
                    return false;
            }

            return hasXnbFile;
        }

        /// <summary>Get whether a set of files looks like an XNB mod.</summary>
        /// <param name="files">The files in the mod.</param>
        private bool IsEmptyVortexFolder(IEnumerable<FileInfo> files)
        {
            bool hasVortexMarker = false;

            foreach (FileInfo file in files)
            {
                if (file.Name == this.VortexMarkerFileName)
                {
                    hasVortexMarker = true;
                    continue;
                }

                if (this.IsRelevant(file) && file.Name != this.ConfigFileName)
                    return false;
            }

            return hasVortexMarker;
        }
    }
}