using System.Security.Cryptography;
using System.Text;
using LanguageExt.Common;
using MediatR;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Options;
using W542.GandalfReborn.Commands;
using W542.GandalfReborn.Data.Database.Repositories;
using W542.GandalfReborn.Data.Dto;
using W542.GandalfReborn.Extensions;
using W542.GandalfReborn.Handlers.Commands;

namespace W542.GandalfReborn.Handlers.Security;

public class GetTokensCommandHandler(IAuthCodeRepository authCodeRepository, TimeProvider timeProvider, IMediator mediator) : IGrCommandHandler<GetTokensCommand, Result<TokenDto>>
{
    public async Task<Result<TokenDto>> Handle(GetTokensCommand command, CancellationToken cancellationToken)
    {
        var authCode = await authCodeRepository
            .Query(q => q.Where(x => x.Code == command.AuthCode))
            .SingleOrDefaultAsync(cancellationToken);
        
        if (authCode is null)
        {
            return "Auth code could not be found.".AsErrorResult<TokenDto>();
        }

        if (authCode.Expiration <= timeProvider.GetUtcNow())
        {
            await authCodeRepository
                .Query(q => q.Where(x => x.Id == authCode.Id))
                .ExecuteDeleteAsync(cancellationToken);
            
            return "Auth code is expired.".AsErrorResult<TokenDto>();
        }

        switch (authCode.Algorithm)
        {
            case "S256":
                var proofKeyBytes = Encoding.UTF8.GetBytes(command.ProofKey);
                var sha256Bytes = SHA256.HashData(proofKeyBytes);
                var hexProofKey = BitConverter.ToString(sha256Bytes).Replace("-", string.Empty).ToLower();
                if (authCode.Challenge != hexProofKey)
                    return "Code challenge failed.".AsErrorResult<TokenDto>();
                break;

            default:
                return $"Algorithm '{authCode.Algorithm}' not supported".AsErrorResult<TokenDto>();
        }

        await authCodeRepository
            .Query(q => q.Where(x => x.Id == authCode.Id))
            .ExecuteDeleteAsync(cancellationToken);
        
        return await mediator.Send(new CreateTokensCommand {SubjectId = authCode.SubjectId}, cancellationToken);
    }
}