using System.IdentityModel.Tokens.Jwt;
using System.Security.Claims;
using System.Text;
using System.Text.Json;
using Microsoft.IdentityModel.Tokens;
using Microsoft.SelfService.Portal.Core.API.Models;

namespace Microsoft.SelfService.Portal.Core.API.Services
{
    public class ApiTokenService
    {
        private readonly IConfiguration _configuration;

        public ApiTokenService(IConfiguration configuration)
        {
            _configuration = configuration;
        }

        public int TokenLifetimeSeconds =>
            _configuration.GetValue<int?>("Authentication:OnPremClientCredentials:TokenLifetimeSeconds") ?? 3600;

        public string Issuer =>
            _configuration["Authentication:OnPremClientCredentials:Issuer"] ?? "Microsoft.SelfService.Portal.Core.API";

        public string Audience =>
            _configuration["Authentication:OnPremClientCredentials:Audience"] ?? "Microsoft.SelfService.Portal.Core.API";

        public ApiTokenCreateResult CreateAccessToken(ApiClientModel client, IReadOnlyCollection<string> scopes)
        {
            return CreateAccessToken(client.ClientId, client.ClientId, scopes);
        }

        public ApiTokenCreateResult CreateAccessToken(string subject, string? clientId, IReadOnlyCollection<string> scopes)
        {
            var signingKey = GetSigningKey();
            var credentials = new SigningCredentials(signingKey, SecurityAlgorithms.HmacSha256);
            var now = DateTime.UtcNow;
            var jti = Guid.NewGuid().ToString("N");
            var expiresAt = now.AddSeconds(TokenLifetimeSeconds);

            var claims = new List<Claim>
            {
                new(JwtRegisteredClaimNames.Sub, subject),
                new(JwtRegisteredClaimNames.Jti, jti)
            };

            if (!string.IsNullOrWhiteSpace(clientId))
            {
                claims.Add(new Claim("client_id", clientId));
            }

            foreach (var scope in scopes)
            {
                claims.Add(new Claim("scope", scope));
            }

            var token = new JwtSecurityToken(
                issuer: Issuer,
                audience: Audience,
                claims: claims,
                notBefore: now,
                expires: expiresAt,
                signingCredentials: credentials);

            return new ApiTokenCreateResult
            {
                AccessToken = new JwtSecurityTokenHandler().WriteToken(token),
                Jti = jti,
                IssuedAt = now,
                ExpiresAt = expiresAt
            };
        }

        public IReadOnlyCollection<string> ReadClientScopes(ApiClientModel client)
        {
            if (string.IsNullOrWhiteSpace(client.ScopesJson))
            {
                return Array.Empty<string>();
            }

            return JsonSerializer.Deserialize<string[]>(client.ScopesJson) ?? Array.Empty<string>();
        }

        public IReadOnlyCollection<string> ResolveRequestedScopes(ApiClientModel client, string? requestedScope)
        {
            var allowedScopes = ReadClientScopes(client);
            if (string.IsNullOrWhiteSpace(requestedScope))
            {
                return allowedScopes;
            }

            var requestedScopes = requestedScope
                .Split(' ', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
                .Distinct(StringComparer.OrdinalIgnoreCase)
                .ToArray();

            if (requestedScopes.Any(scope => !allowedScopes.Contains(scope, StringComparer.OrdinalIgnoreCase)))
            {
                throw new InvalidOperationException("Requested scope is not allowed for this client.");
            }

            return requestedScopes;
        }

        public IReadOnlyCollection<string> ResolveRequestedUserScopes(string? requestedScope)
        {
            if (string.IsNullOrWhiteSpace(requestedScope))
            {
                throw new InvalidOperationException("At least one scope is required.");
            }

            var allowedScopes = ReadAllowedTokenScopes();
            var requestedScopes = requestedScope
                .Split(' ', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
                .Distinct(StringComparer.OrdinalIgnoreCase)
                .ToArray();

            if (requestedScopes.Length == 0)
            {
                throw new InvalidOperationException("At least one scope is required.");
            }

            if (requestedScopes.Any(scope => !allowedScopes.Contains(scope, StringComparer.OrdinalIgnoreCase)))
            {
                throw new InvalidOperationException("Requested scope is not allowed.");
            }

            return requestedScopes;
        }

        public IReadOnlyCollection<string> ReadAllowedTokenScopes()
        {
            var configuredScopes = _configuration.GetSection("Authentication:OnPremClientCredentials:AllowedTokenScopes").Get<string[]>();
            if (configuredScopes != null && configuredScopes.Length > 0)
            {
                return configuredScopes;
            }

            return
            [
                "deployment.read",
                "deployment.write",
                "queue.process",
                "template.read",
                "credential.resolve",
                "token.manage",
                "token.admin"
            ];
        }

        public SymmetricSecurityKey GetSigningKey()
        {
            var signingKey = _configuration["Authentication:OnPremClientCredentials:SigningKey"];
            if (string.IsNullOrWhiteSpace(signingKey))
            {
                signingKey = "DevelopmentOnly-OnPremClientCredentials-SigningKey-ChangeMe";
            }

            return new SymmetricSecurityKey(Encoding.UTF8.GetBytes(signingKey));
        }
    }
}