using System.Security.Cryptography;
using Application.Abstractions.Data;
using Application.Abstractions.Kyc;
using Application.Abstractions.Messaging;
using Domain.Entities.Developers;
using Domain.Entities.Developers.ValueObject;
using Microsoft.EntityFrameworkCore;
using SharedKernel.Results;

namespace Application.Features.Api.Developers.Profile.StartKyc;

internal sealed class Handler(IAppDbContext db, INiceAuthClient nice) : ICommandHandler<Command, Result<Response>>
{
    public async Task<Result<Response>> Handle(Command request, CancellationToken ct)
    {
        var dev = await db.Developer
            .AsTracking()
            .FirstOrDefaultAsync(c => c.MemberID == request.MemberID, ct);

        if (dev is null)
        {
            return Result.Failure<Response>(Error.NotFound(
                "Developer.NotFound",
                "회사 정보를 먼저 입력해 주세요."));
        }

        if (dev.KycStatus == KycStatus.Verified)
        {
            return Result.Failure<Response>(Error.Conflict(
                "Developer.AlreadyVerified",
                "이미 본인인증이 완료되었어요."));
        }

        // 기존 Pending 중 만료된 세션은 Expired 로 정리 (DB 위생)
        var now = DateTime.UtcNow;
        var stale = await db.NiceAuthSession
            .AsTracking()
            .Where(c => c.DeveloperID == dev.ID && c.Status == NiceAuthSessionStatus.Pending && c.ExpiresAt <= now)
            .ToListAsync(ct);
        foreach (var s in stale)
        {
            s.MarkExpired();
        }

        var sessionToken = GenerateSessionToken();

        var urlResult = await nice.RequestAuthUrlAsync(sessionToken, ct);
        if (urlResult.IsFailure)
        {
            return Result.Failure<Response>(urlResult.Error);
        }
        var info = urlResult.Value;

        var session = NiceAuthSession.Create(
            dev.ID,
            sessionToken,
            info.RequestNo,
            info.TransactionId,
            info.Ticket,
            info.Iterators);
        await db.NiceAuthSession.AddAsync(session, ct);

        dev.MarkKycPending();
        await db.SaveChangesAsync(ct);

        return Result.Success(new Response(info.AuthUrl, sessionToken));
    }

    /// <summary>
    /// SessionToken: 16 byte CSPRNG → URL-safe Base64 no-padding (22 char).
    /// NICE return_url path segment 로 embed 되므로 URL-safe 문자만 사용.
    /// </summary>
    private static string GenerateSessionToken()
    {
        var bytes = RandomNumberGenerator.GetBytes(16);
        return Convert.ToBase64String(bytes)
            .Replace('+', '-')
            .Replace('/', '_')
            .TrimEnd('=');
    }
}