using System;
using System.Collections.Generic;
using System.IO;

namespace StardewModdingAPI.Toolkit.Utilities.PathLookups
{
    /// <summary>An API for case-insensitive file lookups within a root directory.</summary>
    internal class CaseInsensitiveFileLookup : IFileLookup
    {
        /*********
        ** Fields
        *********/
        /// <summary>The root directory path for relative paths.</summary>
        private readonly string RootPath;

        /// <summary>A case-insensitive lookup of file paths within the <see cref="RootPath"/>. Each path is listed in both file path and asset name format, so it's usable in both contexts without needing to re-parse paths.</summary>
        private readonly Lazy<Dictionary<string, string>> RelativePathCache;

        /// <summary>The case-insensitive file lookups by root path.</summary>
        private static readonly Dictionary<string, CaseInsensitiveFileLookup> CachedRoots = new(StringComparer.OrdinalIgnoreCase);


        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        /// <param name="rootPath">The root directory path for relative paths.</param>
        /// <param name="searchOption">Which directories to scan from the root.</param>
        public CaseInsensitiveFileLookup(string rootPath, SearchOption searchOption = SearchOption.AllDirectories)
        {
            this.RootPath = PathUtilities.NormalizePath(rootPath);
            this.RelativePathCache = new(() => this.GetRelativePathCache(searchOption));
        }

        /// <inheritdoc />
        public FileInfo GetFile(string relativePath)
        {
            // invalid path
            if (string.IsNullOrWhiteSpace(relativePath))
                throw new InvalidOperationException("Can't get a file from an empty relative path.");

            // already cached
            if (this.RelativePathCache.Value.TryGetValue(relativePath, out string? resolved))
                return new(Path.Combine(this.RootPath, resolved));

            // keep capitalization as-is
            FileInfo file = new(Path.Combine(this.RootPath, relativePath));
            if (file.Exists)
                this.RelativePathCache.Value[relativePath] = relativePath;
            return file;
        }

        /// <inheritdoc />
        public void Add(string relativePath)
        {
            // skip if cache isn't created yet (no need to add files manually in that case)
            if (!this.RelativePathCache.IsValueCreated)
                return;

            // skip if already cached
            if (this.RelativePathCache.Value.ContainsKey(relativePath))
                return;

            // make sure path exists
            relativePath = PathUtilities.NormalizePath(relativePath);
            if (!File.Exists(Path.Combine(this.RootPath, relativePath)))
                throw new InvalidOperationException($"Can't add relative path '{relativePath}' to the case-insensitive cache for '{this.RootPath}' because that file doesn't exist.");

            // cache path
            this.RelativePathCache.Value[relativePath] = relativePath;
        }

        /// <summary>Get a cached dictionary of relative paths within a root path, for case-insensitive file lookups.</summary>
        /// <param name="rootPath">The root path to scan.</param>
        public static CaseInsensitiveFileLookup GetCachedFor(string rootPath)
        {
            rootPath = PathUtilities.NormalizePath(rootPath);

            if (!CaseInsensitiveFileLookup.CachedRoots.TryGetValue(rootPath, out CaseInsensitiveFileLookup? cache))
                CaseInsensitiveFileLookup.CachedRoots[rootPath] = cache = new CaseInsensitiveFileLookup(rootPath);

            return cache;
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Get a case-insensitive lookup of file paths (see <see cref="RelativePathCache"/>).</summary>
        /// <param name="searchOption">Which directories to scan from the root.</param>
        private Dictionary<string, string> GetRelativePathCache(SearchOption searchOption)
        {
            Dictionary<string, string> cache = new(StringComparer.OrdinalIgnoreCase);

            foreach (string path in Directory.EnumerateFiles(this.RootPath, "*", searchOption))
            {
                string relativePath = path.Substring(this.RootPath.Length + 1);
                cache[relativePath] = relativePath;
            }

            return cache;
        }
    }
}