shoc-backend/SeaHaven.Services/Helpers/WorkOrderMediaFileRules.cs

using Microsoft.AspNetCore.Http;
using Data.SeaHavenIndustries.Enums;
using System.IO.Compression;

namespace SeaHaven.Services.Helpers
{
    /// <summary>SH-116 media type allowlist for board work-order uploads.</summary>
    public static class WorkOrderMediaFileRules
    {
        private static readonly HashSet<string> AllowedContentTypes = new(StringComparer.OrdinalIgnoreCase)
        {
            "image/jpeg",
            "image/jpg",
            "image/png",
            "video/mp4",
            "video/quicktime",
            "application/pdf",
            "application/msword",
            "application/vnd.openxmlformats-officedocument.wordprocessingml.document"
        };

        private static readonly Dictionary<string, HashSet<string>> ExtensionsByContentType =
            new(StringComparer.OrdinalIgnoreCase)
            {
                ["image/jpeg"] = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { ".jpg", ".jpeg" },
                ["image/png"] = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { ".png" },
                ["video/mp4"] = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { ".mp4" },
                ["video/quicktime"] = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { ".mov" },
                ["application/pdf"] = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { ".pdf" },
                ["application/msword"] = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { ".doc" },
                ["application/vnd.openxmlformats-officedocument.wordprocessingml.document"] =
                    new HashSet<string>(StringComparer.OrdinalIgnoreCase) { ".docx" }
            };

        // A browser fills the multipart part's Content-Type from File.type, which mobile
        // browsers leave empty (or the client sends octet-stream) when the OS cannot
        // classify a picked file. Only then is the type resolved from the extension; the
        // category rule, extension pairing, and magic-byte signature still decide.
        private static readonly HashSet<string> UndeterminedContentTypes =
            new(StringComparer.OrdinalIgnoreCase) { string.Empty, "application/octet-stream" };

        private static string? ResolveContentType(string declaredType, string extension)
        {
            if (!UndeterminedContentTypes.Contains(declaredType))
                return AllowedContentTypes.Contains(declaredType) ? declaredType : null;

            foreach (var (contentType, extensions) in ExtensionsByContentType)
            {
                if (extensions.Contains(extension))
                    return contentType;
            }

            return null;
        }

        private static string CanonicalContentType(string contentType)
        {
            if (contentType.Equals("image/jpg", StringComparison.OrdinalIgnoreCase))
                return "image/jpeg";
            return contentType;
        }

        public static bool IsAllowed(
            IFormFile file,
            WorkOrderMediaCategory? category = WorkOrderMediaCategory.Extra)
        {
            if (file == null || file.Length <= 0)
                return false;

            var declaredType = (file.ContentType ?? string.Empty).Trim();
            var extension = Path.GetExtension(file.FileName ?? string.Empty);
            var resolvedType = ResolveContentType(declaredType, extension);
            if (resolvedType == null)
                return false;

            var contentType = CanonicalContentType(resolvedType);
            var resolvedCategory = category ?? WorkOrderMediaCategory.Extra;
            if (IsDocument(contentType)
                && resolvedCategory is not WorkOrderMediaCategory.Extra and not WorkOrderMediaCategory.Aveta)
            {
                return false;
            }

            if (string.IsNullOrWhiteSpace(extension)
                || !ExtensionsByContentType.TryGetValue(contentType, out var allowedExtensions)
                || !allowedExtensions.Contains(extension))
            {
                return false;
            }

            try
            {
                using var stream = file.OpenReadStream();
                var headerLength = (int)Math.Min(Math.Max(file.Length, 0), 512);
                if (headerLength == 0)
                    return false;

                var header = new byte[headerLength];
                var read = stream.Read(header, 0, header.Length);
                if (read <= 0)
                    return false;

                if (read < header.Length)
                    Array.Resize(ref header, read);

                if (IsDocx(contentType))
                    return IsWordDocumentArchive(stream);

                return MatchesSignature(contentType, header);
            }
            catch
            {
                return false;
            }
        }

        public static void EnsureAllowed(
            IFormFile file,
            WorkOrderMediaCategory? category = WorkOrderMediaCategory.Extra)
        {
            if (!IsAllowed(file, category))
            {
                throw new Exceptions.WorkOrderBoardValidationException(
                    "UnsupportedMediaType",
                    "Supported file types are JPG, PNG, MP4, MOV, PDF, DOC, and DOCX for Extra Docs; photos accept media only.");
            }
        }

        internal static bool MatchesSignature(string contentType, byte[] bytes)
        {
            if (bytes.Length == 0)
                return false;

            if (contentType.Equals("image/png", StringComparison.OrdinalIgnoreCase))
            {
                return bytes.Length >= 8
                    && bytes[0] == 0x89 && bytes[1] == 0x50 && bytes[2] == 0x4E && bytes[3] == 0x47
                    && bytes[4] == 0x0D && bytes[5] == 0x0A && bytes[6] == 0x1A && bytes[7] == 0x0A;
            }

            if (contentType.Equals("image/jpeg", StringComparison.OrdinalIgnoreCase))
            {
                return bytes.Length >= 3 && bytes[0] == 0xFF && bytes[1] == 0xD8 && bytes[2] == 0xFF;
            }

            if (contentType.Equals("application/pdf", StringComparison.OrdinalIgnoreCase))
            {
                // %PDF-
                return bytes.Length >= 5
                    && bytes[0] == 0x25 && bytes[1] == 0x50 && bytes[2] == 0x44
                    && bytes[3] == 0x46 && bytes[4] == 0x2D;
            }

            if (contentType.Equals("video/mp4", StringComparison.OrdinalIgnoreCase)
                || contentType.Equals("video/quicktime", StringComparison.OrdinalIgnoreCase))
            {
                return HasFtypBox(bytes);
            }

            if (contentType.Equals("application/pdf", StringComparison.OrdinalIgnoreCase))
                return bytes.Length >= 4 && bytes.AsSpan(0, 4).SequenceEqual("%PDF"u8);

            if (contentType.Equals("application/msword", StringComparison.OrdinalIgnoreCase))
            {
                ReadOnlySpan<byte> oleSignature = stackalloc byte[]
                {
                    0xD0, 0xCF, 0x11, 0xE0, 0xA1, 0xB1, 0x1A, 0xE1
                };
                return bytes.Length >= oleSignature.Length
                    && bytes.AsSpan(0, oleSignature.Length).SequenceEqual(oleSignature);
            }

            return false;
        }

        private static bool IsDocument(string contentType)
            => contentType.Equals("application/pdf", StringComparison.OrdinalIgnoreCase)
                || contentType.Equals("application/msword", StringComparison.OrdinalIgnoreCase)
                || IsDocx(contentType);

        private static bool IsDocx(string contentType)
            => contentType.Equals(
                "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
                StringComparison.OrdinalIgnoreCase);

        private static bool IsWordDocumentArchive(Stream stream)
        {
            if (!stream.CanSeek)
                return false;

            stream.Position = 0;
            using var archive = new ZipArchive(stream, ZipArchiveMode.Read, leaveOpen: true);
            return archive.Entries.Any(entry =>
                entry.FullName.StartsWith("word/", StringComparison.OrdinalIgnoreCase));
        }

        private static bool HasFtypBox(byte[] bytes)
        {
            if (bytes.Length < 12)
                return false;

            // ISO BMFF: [size:4][ftyp:4][major_brand:4]...
            return bytes[4] == (byte)'f'
                && bytes[5] == (byte)'t'
                && bytes[6] == (byte)'y'
                && bytes[7] == (byte)'p';
        }
    }
}