using System.Security.Cryptography;
using System.Text;
using JobTrackerApi.Data;
using Microsoft.EntityFrameworkCore;

namespace JobTrackerApi.Services;

public static class AvatarStorage
{
    private const string FilePrefix = "file:";

    public static async Task<string> StageAsync(string dataRoot, string userId, byte[] bytes, CancellationToken cancellationToken)
    {
        var key = Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(userId))).ToLowerInvariant();
        var folder = Path.Combine(dataRoot, "Avatars", key);
        Directory.CreateDirectory(folder);
        var path = Path.Combine(folder, $"avatar-{Guid.NewGuid():N}.png");
        try { await File.WriteAllBytesAsync(path, bytes, cancellationToken); }
        catch
        {
            TryDelete(FilePrefix + path);
            throw;
        }
        return FilePrefix + path;
    }

    public static IEnumerable<string> PortraitFiles(string dataRoot, string ownerKey)
    {
        var root = Path.Combine(dataRoot, "Avatars");
        var folder = Path.Combine(root, ownerKey);
        if (ownerKey.Length != 64 || !ownerKey.All(Uri.IsHexDigit)
            || !Directory.Exists(folder) || (File.GetAttributes(root) & FileAttributes.ReparsePoint) != 0
            || (File.GetAttributes(folder) & FileAttributes.ReparsePoint) != 0) yield break;
        foreach (var path in Directory.EnumerateFiles(folder, "avatar*", new EnumerationOptions { AttributesToSkip = FileAttributes.ReparsePoint, IgnoreInaccessible = true }))
        {
            var name = Path.GetFileName(path);
            if (name is "avatar.png" or "avatar.jpg" or "avatar.webp"
                || (name.StartsWith("avatar-", StringComparison.Ordinal) && name.EndsWith(".png", StringComparison.Ordinal)
                    && name.Length == 43 && Guid.TryParseExact(name[7..^4], "N", out _))) yield return path;
        }
    }

    public static async Task<int> SweepOrphansAsync(JobTrackerContext db, string dataRoot, DateTimeOffset now, CancellationToken token)
    {
        var root = Path.Combine(dataRoot, "Avatars");
        if (!Directory.Exists(root) || (File.GetAttributes(root) & FileAttributes.ReparsePoint) != 0) return 0;
        var candidates = Directory.EnumerateDirectories(root, "*", new EnumerationOptions { AttributesToSkip = FileAttributes.ReparsePoint, IgnoreInaccessible = true })
            .Take(1000).SelectMany(folder => PortraitFiles(dataRoot, Path.GetFileName(folder)).Take(1000))
            .Where(path => File.GetLastWriteTimeUtc(path) <= now.AddDays(-1).UtcDateTime)
            .Take(1000).Select(path => FilePrefix + Path.GetFullPath(path)).ToList();
        var referenced = (await db.Users.AsNoTracking().Where(user => candidates.Contains(user.AvatarImageDataUrl!))
            .Select(user => user.AvatarImageDataUrl!).ToListAsync(token))
            .ToHashSet(OperatingSystem.IsWindows() ? StringComparer.OrdinalIgnoreCase : StringComparer.Ordinal);
        var removed = 0;
        foreach (var candidate in candidates)
        {
            token.ThrowIfCancellationRequested();
            if (!referenced.Contains(candidate) && TryDelete(candidate)) removed++;
        }
        return removed;
    }

    public static bool TryDelete(string? value)
    {
        try { Delete(value); return true; }
        catch (IOException) { return false; }
        catch (UnauthorizedAccessException) { return false; }
    }

    public static async Task<string> StoreAsync(string dataRoot, string userId, byte[] bytes, string contentType, CancellationToken cancellationToken)
    {
        var userKey = Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(userId))).ToLowerInvariant();
        var folder = Path.Combine(dataRoot, "Avatars", userKey);
        Directory.CreateDirectory(folder);
        var extension = contentType switch { "image/png" => ".png", "image/webp" => ".webp", _ => ".jpg" };
        var path = Path.Combine(folder, "avatar" + extension);
        foreach (var old in Directory.EnumerateFiles(folder, "avatar.*")) if (!string.Equals(old, path, StringComparison.OrdinalIgnoreCase)) File.Delete(old);
        await File.WriteAllBytesAsync(path, bytes, cancellationToken);
        return FilePrefix + path;
    }

    public static string? Resolve(string? value)
    {
        if (string.IsNullOrWhiteSpace(value) || !value.StartsWith(FilePrefix, StringComparison.Ordinal)) return value;
        var path = value[FilePrefix.Length..];
        if (!File.Exists(path)) return null;
        var contentType = Path.GetExtension(path).ToLowerInvariant() switch { ".png" => "image/png", ".webp" => "image/webp", _ => "image/jpeg" };
        return $"data:{contentType};base64,{Convert.ToBase64String(File.ReadAllBytes(path))}";
    }

    public static void Delete(string? value)
    {
        if (value?.StartsWith(FilePrefix, StringComparison.Ordinal) != true) return;
        var path = value[FilePrefix.Length..];
        if (File.Exists(path)) File.Delete(path);
    }
}