using System.Diagnostics;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using PowderCoating.Application.Configuration;
using PowderCoating.Application.Interfaces;

namespace PowderCoating.Application.Services;

/// <summary>
/// One-time migration utility that copies files from the legacy local filesystem
/// (<c>wwwroot/media/</c>) to Azure Blob Storage containers, then optionally
/// deletes the originals.
/// <para>
/// The migration is <strong>idempotent</strong>: if a blob already exists in Azure
/// it is skipped (not overwritten).  This means the operation is safe to run
/// multiple times — for example if a previous run was interrupted part-way through.
/// </para>
/// <para>
/// Container assignment is inferred from the relative path of each file
/// (see <see cref="DetermineContainer"/>).  Files that do not match any known
/// path pattern are reported as failures but do not abort the overall run.
/// </para>
/// </summary>
public class StorageMigrationService : IStorageMigrationService
{
    private readonly IAzureBlobStorageService _blobService;
    private readonly StorageSettings _settings;
    private readonly ILogger<StorageMigrationService> _logger;

    /// <summary>
    /// Initialises the service with the blob storage provider, storage
    /// configuration, and a logger for per-file progress messages.
    /// </summary>
    public StorageMigrationService(
        IAzureBlobStorageService blobService,
        IOptions<StorageSettings> settings,
        ILogger<StorageMigrationService> logger)
    {
        _blobService = blobService;
        _settings = settings.Value;
        _logger = logger;
    }

    /// <summary>
    /// Recursively enumerates all files under <paramref name="mediaBasePath"/>,
    /// determines the correct Azure Blob Storage container for each file, and
    /// uploads those that do not already exist in Azure.
    /// </summary>
    /// <param name="mediaBasePath">
    /// Absolute path to the root media directory on the local filesystem
    /// (e.g. <c>C:\app\wwwroot\media</c>).
    /// </param>
    /// <param name="deleteLocalAfterMigration">
    /// When <c>true</c>, the local file is deleted immediately after a successful
    /// upload.  Defaults to <c>false</c> so a dry-run can be performed first.
    /// <strong>Warning:</strong> set to <c>true</c> only after verifying the
    /// migration result — deleted local files cannot be recovered without a backup.
    /// </param>
    /// <returns>
    /// A <see cref="StorageMigrationResult"/> summarising how many files were
    /// migrated, skipped (already in Azure), and failed, along with total bytes
    /// transferred and elapsed time.
    /// </returns>
    public async Task<StorageMigrationResult> MigrateFilesystemToAzureAsync(
        string mediaBasePath,
        bool deleteLocalAfterMigration = false)
    {
        var result = new StorageMigrationResult();
        var stopwatch = Stopwatch.StartNew();

        if (!Directory.Exists(mediaBasePath))
        {
            result.Errors.Add($"Media directory not found: {mediaBasePath}");
            result.Duration = stopwatch.Elapsed;
            return result;
        }

        var allFiles = Directory.EnumerateFiles(mediaBasePath, "*.*", SearchOption.AllDirectories).ToList();
        _logger.LogInformation("Starting filesystem-to-Azure migration. Found {Count} files in {Path}", allFiles.Count, mediaBasePath);

        foreach (var fullPath in allFiles)
        {
            var relativePath = Path.GetRelativePath(mediaBasePath, fullPath).Replace("\\", "/");
            var container = DetermineContainer(relativePath);

            if (container is null)
            {
                _logger.LogWarning("Could not determine container for file: {RelativePath} — skipping", relativePath);
                result.Errors.Add($"Unknown file type (no matching container): {relativePath}");
                result.Failed++;
                result.Files.Add(new MigratedFileEntry
                {
                    RelativePath = relativePath,
                    Container = "unknown",
                    FileSize = new FileInfo(fullPath).Length,
                    Status = MigrationFileStatus.Failed
                });
                continue;
            }

            try
            {
                var fileInfo = new FileInfo(fullPath);

                // Skip if blob already exists in Azure
                var alreadyExists = await _blobService.ExistsAsync(container, relativePath);
                if (alreadyExists)
                {
                    _logger.LogDebug("Blob already exists, skipping: {Container}/{BlobName}", container, relativePath);
                    result.Skipped++;
                    result.Files.Add(new MigratedFileEntry
                    {
                        RelativePath = relativePath,
                        Container = container,
                        FileSize = fileInfo.Length,
                        Status = MigrationFileStatus.Skipped
                    });
                    continue;
                }

                var contentType = GetContentType(Path.GetExtension(fullPath).ToLowerInvariant());

                (bool Success, string ErrorMessage) uploadResult;
                await using (var stream = File.OpenRead(fullPath))
                {
                    uploadResult = await _blobService.UploadAsync(container, relativePath, stream, contentType);
                }

                if (!uploadResult.Success)
                {
                    result.Failed++;
                    result.Errors.Add($"Upload failed for {relativePath}: {uploadResult.ErrorMessage}");
                    result.Files.Add(new MigratedFileEntry
                    {
                        RelativePath = relativePath,
                        Container = container,
                        FileSize = fileInfo.Length,
                        Status = MigrationFileStatus.Failed
                    });
                    continue;
                }

                result.Migrated++;
                result.BytesMigrated += fileInfo.Length;
                result.Files.Add(new MigratedFileEntry
                {
                    RelativePath = relativePath,
                    Container = container,
                    FileSize = fileInfo.Length,
                    Status = MigrationFileStatus.Migrated
                });

                if (deleteLocalAfterMigration)
                {
                    File.Delete(fullPath);
                    _logger.LogInformation("Deleted local file after migration: {FullPath}", fullPath);
                }

                _logger.LogInformation("Migrated: {RelativePath} → {Container}", relativePath, container);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Error migrating file: {RelativePath}", relativePath);
                result.Failed++;
                result.Errors.Add($"Exception for {relativePath}: {ex.Message}");
                result.Files.Add(new MigratedFileEntry
                {
                    RelativePath = relativePath,
                    Container = container,
                    FileSize = 0,
                    Status = MigrationFileStatus.Failed
                });
            }
        }

        stopwatch.Stop();
        result.Duration = stopwatch.Elapsed;

        _logger.LogInformation(
            "Migration complete. Migrated: {Migrated}, Skipped: {Skipped}, Failed: {Failed}, Duration: {Duration}",
            result.Migrated, result.Skipped, result.Failed, result.Duration);

        return result;
    }

    /// <summary>
    /// Determines which Azure Blob Storage container a local file belongs in by
    /// inspecting its path segments.  The mapping mirrors the blob naming
    /// conventions used by each file service:
    /// <list type="bullet">
    ///   <item><c>/profile-photos/</c> → <c>profileimages</c> container</item>
    ///   <item><c>/job-photos/</c> → <c>jobimages</c> container</item>
    ///   <item><c>/equipment-manuals/</c> → <c>manuals</c> container</item>
    ///   <item><c>company-logo</c> (anywhere in path) → <c>companylogos</c> container</item>
    /// </list>
    /// Returns <c>null</c> for files that do not match any known pattern; the
    /// caller treats these as failures and continues with the next file.
    /// </summary>
    /// <param name="relativePath">
    /// Path of the file relative to the media root, with forward slashes.
    /// </param>
    /// <returns>Container name, or <c>null</c> if no match is found.</returns>
    private string? DetermineContainer(string relativePath)
    {
        if (relativePath.Contains("/profile-photos/"))   return _settings.Containers.ProfileImages;
        if (relativePath.Contains("/job-photos/"))       return _settings.Containers.JobImages;
        if (relativePath.Contains("/equipment-manuals/"))return _settings.Containers.Manuals;
        if (relativePath.Contains("company-logo"))       return _settings.Containers.CompanyLogos;
        return null;
    }

    /// <summary>
    /// Maps a lowercase file extension to its canonical MIME content type for
    /// the <c>Content-Type</c> metadata stored with each Azure blob.  Correct
    /// MIME types ensure browsers handle downloads appropriately (inline vs.
    /// prompt for application) when blobs are accessed via signed URLs.
    /// </summary>
    /// <param name="extension">Lowercase file extension including the leading dot.</param>
    /// <returns>MIME type string, or <c>application/octet-stream</c> as a safe fallback.</returns>
    private static string GetContentType(string extension) => extension switch
    {
        ".jpg" or ".jpeg"  => "image/jpeg",
        ".png"             => "image/png",
        ".gif"             => "image/gif",
        ".webp"            => "image/webp",
        ".svg"             => "image/svg+xml",
        ".pdf"             => "application/pdf",
        ".doc"             => "application/msword",
        ".docx"            => "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
        ".txt"             => "text/plain",
        _                  => "application/octet-stream"
    };
}