using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using PowderCoating.Application.Interfaces;

namespace PowderCoating.Application.Services;

/// <summary>
/// On-premises file storage service that saves, retrieves, and deletes files under the
/// application's <c>wwwroot/uploads/</c> directory. This service is the legacy storage path for
/// self-hosted deployments; cloud-hosted tenants use <see cref="AzureBlobStorageService"/> instead.
/// All file names are prefixed with a new GUID to prevent collisions and block path traversal
/// attacks that embed directory separators in the original file name.
/// </summary>
public class FileService : IFileService
{
    private const string UploadsRootFolder = "uploads";
    private readonly IWebHostEnvironment _environment;
    private readonly ILogger<FileService> _logger;

    /// <summary>
    /// Initializes the service with the hosting environment (provides <c>WebRootPath</c>) and logger.
    /// </summary>
    public FileService(IWebHostEnvironment environment, ILogger<FileService> logger)
    {
        _environment = environment;
        _logger = logger;
    }

    /// <summary>
    /// Validates and saves an uploaded file to the specified subfolder under <c>wwwroot/uploads/</c>.
    /// Validation order: null/empty check, size limit, then extension allowlist. The original file
    /// name is sanitised with <see cref="Path.GetFileName"/> to strip any directory components before
    /// prepending the GUID prefix, preventing path traversal if the browser supplies a name with
    /// slashes. The target subfolder is resolved and confined under <c>wwwroot/uploads/</c> before
    /// any file system access occurs. Returns a relative path (from <c>wwwroot</c>) suitable for
    /// storing in the database.
    /// </summary>
    public async Task<(bool Success, string FilePath, string ErrorMessage)> SaveFileAsync(
        IFormFile file,
        string subfolder,
        string[] allowedExtensions,
        long maxFileSize)
    {
        try
        {
            // Validate file
            if (file == null || file.Length == 0)
            {
                return (false, string.Empty, "No file was uploaded.");
            }

            // Validate file size
            if (file.Length > maxFileSize)
            {
                var maxSizeMB = maxFileSize / (1024 * 1024);
                return (false, string.Empty, $"File size exceeds the maximum allowed size of {maxSizeMB} MB.");
            }

            // Validate file extension
            var extension = Path.GetExtension(file.FileName).ToLowerInvariant();
            if (string.IsNullOrEmpty(extension) || !allowedExtensions.Contains(extension))
            {
                var allowedExts = string.Join(", ", allowedExtensions);
                return (false, string.Empty, $"Invalid file type. Allowed types: {allowedExts}");
            }

            // Create upload directory if it doesn't exist
            // NOTE: WebRootPath is read-only on Azure Linux App Service; this service is legacy
            // and should only be called for on-premises deployments. New uploads use Azure Blob.
            if (!TryResolveUploadSubfolder(subfolder, out var uploadPath, out var relativeSubfolder, out var subfolderError))
            {
                return (false, string.Empty, subfolderError);
            }

            if (!Directory.Exists(uploadPath))
            {
                try
                {
                    Directory.CreateDirectory(uploadPath);
                    _logger.LogInformation("Created upload directory: {UploadPath}", uploadPath);
                }
                catch (Exception ex)
                {
                    _logger.LogWarning(ex, "Could not create upload directory {UploadPath} — filesystem may be read-only", uploadPath);
                    return (false, string.Empty, "File storage is not available in this environment.");
                }
            }

            // Generate unique filename — strip directory components from the original name
            // to prevent path traversal if the browser sends a filename with slashes.
            var safeOriginalName = Path.GetFileName(file.FileName);
            var uniqueFileName = $"{Guid.NewGuid()}-{safeOriginalName}";
            var filePath = Path.Combine(uploadPath, uniqueFileName);

            // Save the file
            using (var stream = new FileStream(filePath, FileMode.Create))
            {
                await file.CopyToAsync(stream);
            }

            // Return relative path from wwwroot
            var relativePath = Path.Combine(UploadsRootFolder, relativeSubfolder, uniqueFileName).Replace("\\", "/");

            _logger.LogInformation("File saved successfully: {FilePath}", relativePath);
            return (true, relativePath, string.Empty);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error saving file: {FileName}", file?.FileName);
            return (false, string.Empty, "An error occurred while saving the file.");
        }
    }

    /// <summary>
    /// Deletes a file given its relative path from <c>wwwroot</c>.
    /// Returns success if the file does not exist (idempotent) so that callers do not need to check
    /// existence before calling. The relative path is normalized and must remain under
    /// <c>wwwroot/uploads/</c>; paths outside that root are rejected.
    /// </summary>
    public async Task<(bool Success, string ErrorMessage)> DeleteFileAsync(string filePath)
    {
        try
        {
            if (string.IsNullOrWhiteSpace(filePath))
            {
                return (false, "File path is required.");
            }

            if (!TryResolveLegacyUploadPath(filePath, out var fullPath, out var pathError))
            {
                return (false, pathError);
            }

            if (!File.Exists(fullPath))
            {
                _logger.LogWarning("File not found for deletion: {FilePath}", filePath);
                return (true, string.Empty); // Consider it successful if file doesn't exist
            }

            await Task.Run(() => File.Delete(fullPath));

            _logger.LogInformation("File deleted successfully: {FilePath}", filePath);
            return (true, string.Empty);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error deleting file: {FilePath}", filePath);
            return (false, "An error occurred while deleting the file.");
        }
    }

    /// <summary>
    /// Reads a file from disk and returns its raw bytes along with a derived MIME content type.
    /// Intended for serving files that are stored under the legacy <c>wwwroot/uploads/</c> path but
    /// are otherwise not directly exposed through the static-files middleware.
    /// </summary>
    public async Task<(bool Success, byte[] FileContent, string ContentType, string ErrorMessage)> GetFileAsync(string filePath)
    {
        try
        {
            if (string.IsNullOrWhiteSpace(filePath))
            {
                return (false, Array.Empty<byte>(), string.Empty, "File path is required.");
            }

            if (!TryResolveLegacyUploadPath(filePath, out var fullPath, out var pathError))
            {
                return (false, Array.Empty<byte>(), string.Empty, pathError);
            }

            if (!File.Exists(fullPath))
            {
                _logger.LogWarning("File not found: {FilePath}", filePath);
                return (false, Array.Empty<byte>(), string.Empty, "File not found.");
            }

            var fileBytes = await File.ReadAllBytesAsync(fullPath);
            var contentType = GetContentType(filePath);

            return (true, fileBytes, contentType, string.Empty);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error retrieving file: {FilePath}", filePath);
            return (false, Array.Empty<byte>(), string.Empty, "An error occurred while retrieving the file.");
        }
    }

    /// <summary>
    /// Checks whether a file exists at the given <c>wwwroot/uploads/</c>-relative path without reading it.
    /// Used by views and controllers to conditionally show download links only when the file is present.
    /// </summary>
    public bool FileExists(string filePath)
    {
        if (string.IsNullOrWhiteSpace(filePath))
        {
            return false;
        }

        if (!TryResolveLegacyUploadPath(filePath, out var fullPath, out _))
        {
            return false;
        }

        return File.Exists(fullPath);
    }

    /// <summary>
    /// Maps a file name or path to its MIME content type based on the extension.
    /// Falls back to <c>application/octet-stream</c> for unrecognised extensions so the browser
    /// triggers a download rather than attempting to render an unknown format inline.
    /// </summary>
    public string GetContentType(string fileName)
    {
        var extension = Path.GetExtension(fileName).ToLowerInvariant();

        return extension switch
        {
            ".pdf" => "application/pdf",
            ".doc" => "application/msword",
            ".docx" => "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
            ".xls" => "application/vnd.ms-excel",
            ".xlsx" => "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
            ".jpg" or ".jpeg" => "image/jpeg",
            ".png" => "image/png",
            ".gif" => "image/gif",
            ".webp" => "image/webp",
            _ => "application/octet-stream"
        };
    }

    private bool TryResolveUploadSubfolder(
        string subfolder,
        out string uploadPath,
        out string relativeSubfolder,
        out string errorMessage)
    {
        uploadPath = string.Empty;
        relativeSubfolder = string.Empty;
        errorMessage = string.Empty;

        if (string.IsNullOrWhiteSpace(subfolder))
        {
            errorMessage = "Upload subfolder is required.";
            return false;
        }

        if (!TryGetUploadsRootPath(out var uploadsRoot, out errorMessage))
        {
            return false;
        }

        var normalizedSubfolder = subfolder.Replace('\\', '/').Trim('/');
        var resolvedPath = Path.GetFullPath(
            Path.Combine(uploadsRoot, normalizedSubfolder.Replace('/', Path.DirectorySeparatorChar)));

        if (!IsWithinDirectory(resolvedPath, uploadsRoot))
        {
            errorMessage = "Invalid upload subfolder.";
            _logger.LogWarning("Rejected upload subfolder outside uploads root: {Subfolder}", subfolder);
            return false;
        }

        relativeSubfolder = Path.GetRelativePath(uploadsRoot, resolvedPath).Replace("\\", "/");
        uploadPath = resolvedPath;
        return true;
    }

    private bool TryResolveLegacyUploadPath(string filePath, out string fullPath, out string errorMessage)
    {
        fullPath = string.Empty;
        errorMessage = string.Empty;

        if (!TryGetUploadsRootPath(out var uploadsRoot, out errorMessage))
        {
            return false;
        }

        var normalizedRelativePath = filePath.Replace('\\', '/').TrimStart('/');
        if (!normalizedRelativePath.StartsWith($"{UploadsRootFolder}/", StringComparison.OrdinalIgnoreCase))
        {
            errorMessage = "Invalid file path.";
            _logger.LogWarning("Rejected legacy file path outside uploads root: {FilePath}", filePath);
            return false;
        }

        var resolvedPath = Path.GetFullPath(
            Path.Combine(_environment.WebRootPath, normalizedRelativePath.Replace('/', Path.DirectorySeparatorChar)));

        if (!IsWithinDirectory(resolvedPath, uploadsRoot))
        {
            errorMessage = "Invalid file path.";
            _logger.LogWarning("Rejected path traversal attempt for legacy file path: {FilePath}", filePath);
            return false;
        }

        fullPath = resolvedPath;
        return true;
    }

    private bool TryGetUploadsRootPath(out string uploadsRoot, out string errorMessage)
    {
        uploadsRoot = string.Empty;
        errorMessage = string.Empty;

        if (string.IsNullOrWhiteSpace(_environment.WebRootPath))
        {
            errorMessage = "File storage is not available in this environment.";
            _logger.LogWarning("WebRootPath is not configured for the legacy file service.");
            return false;
        }

        uploadsRoot = Path.GetFullPath(Path.Combine(_environment.WebRootPath, UploadsRootFolder));
        return true;
    }

    private static bool IsWithinDirectory(string candidatePath, string rootPath)
    {
        var normalizedRoot = rootPath.TrimEnd(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar)
            + Path.DirectorySeparatorChar;
        return candidatePath.StartsWith(normalizedRoot, StringComparison.OrdinalIgnoreCase);
    }
}