using System.Collections.Generic;
using System.Linq;

namespace InternshipSystem.Api.Service
{
    public class FileValidator
    {
        private readonly List<(string Mime, byte[] Signature)> validFileTypes;

        public FileValidator()
        {
            validFileTypes = new List<(string, byte[])> {
                ("application/pdf", new byte[] { 0x25, 0x50, 0x44, 0x46 }),
                ("image/jpeg", new byte[] { 0xFF, 0xD8, 0xFF, 0xDB }),
                ("image/jpeg", new byte[] { 0xFF, 0xD8, 0xFF, 0xE0 }),
                ("image/jpeg", new byte[] { 0xFF, 0xD8, 0xFF, 0xE1 })
            };
        }

        public bool IsValidFile(byte[] scan)
        {
            return IsFileValidType(scan);
        }

        private bool IsFileValidType(byte[] scan)
        {
            return GetFileMime(scan) != null;
        }

        public string GetFileMime(byte[] scan)
        {
            var header = scan[..4];

            return validFileTypes.FirstOrDefault(sig => sig.Signature.SequenceEqual(header)).Mime;
        }
    }
}