using System.Security.Claims;
using System.Security.Cryptography;
using System.Text;
using System.Text.Encodings.Web;
using Application.Abstractions.Data;
using Microsoft.AspNetCore.Authentication;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Infrastructure.Authentication;

/// <summary>
/// Personal Access Token (PAT) Bearer scheme.
/// Header: Authorization: Bearer dpot_pat_xxxxx
/// </summary>
public sealed class ApiKeyAuthenticationHandler(
    IOptionsMonitor<AuthenticationSchemeOptions> options,
    ILoggerFactory logger,
    UrlEncoder encoder,
    IAppDbContext db
) : AuthenticationHandler<AuthenticationSchemeOptions>(options, logger, encoder)
{
    public const string SchemeName = "ApiKey";
    public const string TokenPrefix = "dpot_pat_";

    private readonly IAppDbContext _db = db;

    protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
    {
        if (!Request.Headers.TryGetValue("Authorization", out var authHeader))
        {
            return AuthenticateResult.NoResult();
        }

        var auth = authHeader.ToString();
        if (string.IsNullOrEmpty(auth) || !auth.StartsWith("Bearer ", StringComparison.OrdinalIgnoreCase))
        {
            return AuthenticateResult.NoResult();
        }

        var token = auth.Substring("Bearer ".Length).Trim();
        if (!token.StartsWith(TokenPrefix, StringComparison.Ordinal))
        {
            // Not a PAT — let other schemes try.
            return AuthenticateResult.NoResult();
        }

        var hash = HashToken(token);
        var pat = await _db.ApiPersonalAccessToken
            .AsTracking()
            .FirstOrDefaultAsync(c => c.TokenHash == hash, Context.RequestAborted);

        if (pat is null)
        {
            return AuthenticateResult.Fail("Invalid API key.");
        }

        if (!pat.IsActive)
        {
            return AuthenticateResult.Fail("API key is revoked or expired.");
        }

        pat.TouchLastUsed();
        await _db.SaveChangesAsync(Context.RequestAborted);

        var claims = new List<Claim>
        {
            new(ClaimTypes.NameIdentifier, pat.OwnerMemberID.ToString()),
            new("token_id", pat.ID.ToString()),
            new("token_type", "pat"),
            new("scope", pat.ScopesCsv)
        };

        foreach (var s in pat.ScopesCsv.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries))
        {
            claims.Add(new Claim("scp", s));
        }

        var identity = new ClaimsIdentity(claims, Scheme.Name);
        var principal = new ClaimsPrincipal(identity);
        var ticket = new AuthenticationTicket(principal, Scheme.Name);
        return AuthenticateResult.Success(ticket);
    }

    public static string HashToken(string token)
    {
        var bytes = Encoding.UTF8.GetBytes(token);
        var hash = SHA256.HashData(bytes);
        return Convert.ToHexString(hash).ToLowerInvariant();
    }
}