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

using Microsoft.Extensions.FileProviders;
using Microsoft.Extensions.Primitives;

// ReSharper disable once CheckNamespace
namespace kwd.gist
{
    /// <summary>
    /// Resolves file system paths using case-aware path.
    /// </summary>
    public class CaseAwareFileProvider : IFileProvider, IDisposable
    {
        private readonly PhysicalFileProvider _provider;

        public CaseAwareFileProvider(string root)
        {
            if (!Path.IsPathRooted(root))
            {
                throw new ArgumentException("The path must be absolute.", nameof(root));
            }

            var pathRoot = Path.GetPathRoot(root);

            var matchCase = ResolvePath(pathRoot, root.Substring(pathRoot.Length));

            _provider = new PhysicalFileProvider(matchCase);
        }

        public string Root => _provider.Root;

        public IFileInfo GetFileInfo(string subpath)
        {
            var matchCase = ResolvePath(_provider.Root, subpath)
                .Substring(_provider.Root.Length);

            return _provider.GetFileInfo(matchCase);
        }

        public IDirectoryContents GetDirectoryContents(string subpath)
        {
            var matchCase = ResolvePath(_provider.Root, subpath)
                .Substring(_provider.Root.Length);

            return _provider.GetDirectoryContents(matchCase);
        }

        public IChangeToken Watch(string filter) =>
            _provider.Watch(filter);

        public void Dispose() => _provider.Dispose();

        private static string ResolvePath(string root, params string[] subPath)
        {
            root = root ?? string.Empty;

            if (root != string.Empty && !Directory.Exists(root))
            {
                return Path.Combine(root, Path.Combine(subPath));
            }

            var pathSegments = subPath
                .SelectMany(x => x.Split(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar))
                .Where(x => !string.IsNullOrEmpty(x))
                .ToArray();

            var segments = new Queue<string>(pathSegments);
            var cur = root;

            while (segments.Any())
            {
                var next = segments.Dequeue();
                var part = Path.GetFileName(Directory.GetFileSystemEntries(cur, next).FirstOrDefault());
                if (part != null)
                {
                    cur = Path.Combine(cur, part);
                }
                else
                {
                    cur = Path.Combine(new[]
                        {cur, next}.Concat(segments).ToArray());
                    break;
                }
            }

            return cur;
        }
    }
}