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

namespace HashCalculator.GUI
{
    internal class FileSystemSuggestions
    {
        private static readonly Dictionary<string, InputEntryType> Mapping = new Dictionary<string, InputEntryType>(StringComparer.OrdinalIgnoreCase)
        {
            { ".big", InputEntryType.BigFile },
            { ".xml", InputEntryType.XmlFile },
            { ".w3x", InputEntryType.XmlFile },
            { ".manifest", InputEntryType.ManifestFile },
        };

        private Search _search = new Search();

        [SuppressMessage("Microsoft.Performance", "CA1031")]
        public IEnumerable<InputEntry> ProvideFileSystemSuggestions(string? path)
        {
            var empty = Enumerable.Empty<InputEntry>();

            if (string.IsNullOrWhiteSpace(path) || path == null)
            {
                return empty;
            }

            path = Environment.ExpandEnvironmentVariables(path);

            if (path.IndexOfAny(Path.GetInvalidPathChars()) != -1)
            {
                return empty;
            }

            _search.Update(path);

            if (!_search.IsValidPath)
            {
                return empty;
            }

            var currentFiles = new List<InputEntry>();
            string? fileName;
            string? currentFullPath = null;
            try
            {
                var currentFile = new FileInfo(path);
                fileName = currentFile.Name;
                if (currentFile.Exists)
                {
                    currentFullPath = currentFile.FullName;
                    var type = CheckExtension(currentFile);
                    if (type is InputEntryType entryType)
                    {
                        currentFiles.Add(new InputEntry(entryType, path, currentFullPath));
                    }
                    currentFiles.Add(new InputEntry(InputEntryType.BinaryFile, path, currentFullPath));
                }
            }
            catch
            {
                return empty;
            }

            var alternatives = empty;
            try
            {
                var directories = from directory in _search.AllDirectories
                                  where directory.Name.StartsWith(fileName, StringComparison.OrdinalIgnoreCase)
                                  select new InputEntry(InputEntryType.Path, _search.GetInputStyleName(directory), directory.FullName);

                var otherFiles = from file in _search.AllFiles
                                 where file.Name.StartsWith(fileName, StringComparison.OrdinalIgnoreCase)
                                 where file.FullName != currentFullPath
                                 select file;

                var supportedFiles = from file in otherFiles
                                     let type = CheckExtension(file)
                                     where type.HasValue
                                     select new InputEntry(type.Value, _search.GetInputStyleName(file), file.FullName);

                var binaryFiles = from file in otherFiles
                                  select new InputEntry(InputEntryType.BinaryFile, _search.GetInputStyleName(file), file.FullName);

                alternatives = supportedFiles.Concat(directories).Concat(binaryFiles).ToArray();
            }
            catch { }

            return currentFiles.Concat(alternatives);
        }

        private static InputEntryType? CheckExtension(FileInfo info)
        {
            if (Mapping.TryGetValue(info.Extension, out var type))
            {
                return type;
            }

            return null;
        }
    }

    internal sealed class Search
    {
        private string? _inputBaseDirectory;
        public bool IsValidPath => _inputBaseDirectory != null;
        public IEnumerable<DirectoryInfo> AllDirectories { get; private set; }
        public IEnumerable<FileInfo> AllFiles { get; private set; }

        public Search()
        {
            AllDirectories = Array.Empty<DirectoryInfo>();
            AllFiles = Array.Empty<FileInfo>();
        }

        public string GetInputStyleName(FileSystemInfo entry)
        {
            if (_inputBaseDirectory == null)
            {
                throw new InvalidOperationException();
            }

            return Path.Combine(_inputBaseDirectory, entry.Name);
        }

        [SuppressMessage("Microsoft.Performance", "CA1031")]
        public void Update(string path)
        {
            string? newBaseDirectory = null;
            try
            {
                if (Path.GetFileName(path).IndexOfAny(Path.GetInvalidFileNameChars()) != -1)
                {
                    _inputBaseDirectory = null;
                    return;
                }

                newBaseDirectory = Path.GetDirectoryName(path);
                var rootDirectory = Path.GetPathRoot(path);
                if(string.IsNullOrEmpty(newBaseDirectory) && !string.IsNullOrEmpty(rootDirectory))
                {
                    var last = rootDirectory.LastOrDefault();
                    if (last != Path.DirectorySeparatorChar && last != Path.AltDirectorySeparatorChar)
                    {
                        rootDirectory += Path.DirectorySeparatorChar;
                    }
                    newBaseDirectory = rootDirectory;
                }
            }
            catch
            {
                _inputBaseDirectory = null;
            }

            if (newBaseDirectory == null)
            {
                return;
            }

            if (newBaseDirectory == _inputBaseDirectory)
            {
                return;
            }

            _inputBaseDirectory = newBaseDirectory;
            Update();
        }

        [SuppressMessage("Microsoft.Performance", "CA1031")]
        private void Update()
        {
            AllDirectories = Enumerable.Empty<DirectoryInfo>();
            AllFiles = Enumerable.Empty<FileInfo>();
            try
            {
                var actualPath = _inputBaseDirectory!.Length == 0
                    ? "."
                    : _inputBaseDirectory;
                var directory = new DirectoryInfo(actualPath);
                if (directory.Exists)
                {
                    AllDirectories = directory.EnumerateDirectories();
                    AllFiles = directory.EnumerateFiles();
                }
            }
            catch { }
        }
    }
}