using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using DCIT.Core.Models;

namespace DCIT.Core.Services
{
    public sealed class TemporaryFileCleanupService
    {
        private static readonly Regex AtomicTempFilePattern = new Regex(@"\.tmp-[0-9a-fA-F]{32}(?=\.)", RegexOptions.Compiled | RegexOptions.IgnoreCase);
        private readonly string _tempRoot;

        public TemporaryFileCleanupService()
            : this(Path.Combine(Path.GetTempPath(), "DCIT"))
        {
        }

        public TemporaryFileCleanupService(string tempRoot)
        {
            _tempRoot = string.IsNullOrWhiteSpace(tempRoot)
                ? Path.Combine(Path.GetTempPath(), "DCIT")
                : tempRoot;
        }

        public TemporaryCleanupResult Cleanup(AppConfig config)
        {
            var result = new TemporaryCleanupResult();
            CleanupDedicatedTempDirectory(Path.Combine(_tempRoot, "processing"), result);
            CleanupDedicatedTempDirectory(Path.Combine(_tempRoot, "extract"), result);

            var configuredOutputDirectories = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
            AddDirectory(configuredOutputDirectories, config == null || config.ReplacePage == null ? null : config.ReplacePage.OutputDirectory);
            AddDirectory(configuredOutputDirectories, config == null || config.RestorePage == null ? null : config.RestorePage.RestoreDirectory);

            foreach (var directory in configuredOutputDirectories)
            {
                CleanupAtomicTempFiles(directory, result);
            }

            return result;
        }

        private static void AddDirectory(ISet<string> directories, string path)
        {
            if (string.IsNullOrWhiteSpace(path))
            {
                return;
            }

            try
            {
                directories.Add(Path.GetFullPath(path));
            }
            catch
            {
            }
        }

        private static void CleanupAtomicTempFiles(string rootDirectory, TemporaryCleanupResult result)
        {
            if (string.IsNullOrWhiteSpace(rootDirectory) || !Directory.Exists(rootDirectory))
            {
                return;
            }

            IEnumerable<string> files;
            try
            {
                files = Directory.EnumerateFiles(rootDirectory, "*", SearchOption.AllDirectories)
                    .Where(path => IsAtomicTempFile(Path.GetFileName(path)));
            }
            catch (Exception ex)
            {
                result.Failures.Add("无法扫描目录 " + rootDirectory + ": " + ex.Message);
                return;
            }

            foreach (var file in files)
            {
                TryDeleteFile(file, result);
            }
        }

        private static bool IsAtomicTempFile(string fileName)
        {
            return !string.IsNullOrWhiteSpace(fileName) && AtomicTempFilePattern.IsMatch(fileName);
        }

        private static void CleanupDedicatedTempDirectory(string rootDirectory, TemporaryCleanupResult result)
        {
            if (string.IsNullOrWhiteSpace(rootDirectory) || !Directory.Exists(rootDirectory))
            {
                return;
            }

            IEnumerable<string> files;
            try
            {
                files = Directory.EnumerateFiles(rootDirectory, "*", SearchOption.AllDirectories).ToList();
            }
            catch (Exception ex)
            {
                result.Failures.Add("无法扫描目录 " + rootDirectory + ": " + ex.Message);
                return;
            }

            foreach (var file in files)
            {
                TryDeleteFile(file, result);
            }

            TryDeleteEmptyDirectories(rootDirectory, result);
        }

        private static void TryDeleteEmptyDirectories(string rootDirectory, TemporaryCleanupResult result)
        {
            IEnumerable<string> directories;
            try
            {
                directories = Directory.EnumerateDirectories(rootDirectory, "*", SearchOption.AllDirectories)
                    .OrderByDescending(path => path.Length)
                    .ToList();
            }
            catch (Exception ex)
            {
                result.Failures.Add("无法枚举临时目录 " + rootDirectory + ": " + ex.Message);
                return;
            }

            foreach (var directory in directories)
            {
                try
                {
                    if (!Directory.EnumerateFileSystemEntries(directory).Any())
                    {
                        Directory.Delete(directory);
                    }
                }
                catch (Exception ex)
                {
                    result.Failures.Add("无法删除临时目录 " + directory + ": " + ex.Message);
                }
            }

            try
            {
                if (!Directory.EnumerateFileSystemEntries(rootDirectory).Any())
                {
                    Directory.Delete(rootDirectory);
                }
            }
            catch (Exception ex)
            {
                result.Failures.Add("无法删除临时目录 " + rootDirectory + ": " + ex.Message);
            }
        }

        private static void TryDeleteFile(string filePath, TemporaryCleanupResult result)
        {
            try
            {
                if (File.Exists(filePath))
                {
                    File.Delete(filePath);
                    result.RemovedFiles.Add(filePath);
                }
            }
            catch (Exception ex)
            {
                result.Failures.Add("无法删除临时文件 " + filePath + ": " + ex.Message);
            }
        }
    }

    public sealed class TemporaryCleanupResult
    {
        public IList<string> RemovedFiles { get; } = new List<string>();

        public IList<string> Failures { get; } = new List<string>();
    }
}