using Microsoft.IdentityModel.Tokens;
using System;
using System.Collections.Generic;
using System.Security.Claims;
using System.Text;
using System.IdentityModel.Tokens.Jwt;
using Traffic.Data.ViewModels;
using Microsoft.Extensions.Configuration;
using Traffic.Data.Enums;

namespace Traffic.Service.Helpers
{
    public class JwtHelpers
    {
        private readonly IConfiguration _configuration;

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

        public string GenerateToken(AccountUserViewModel admin, int expireDays = 30)
        {
            var issuer = _configuration.GetValue<string>("JwtSettings:Issuer");
            var signKey = _configuration.GetValue<string>("JwtSettings:SignKey");

            // 設定要加入到 JWT Token 中的聲明資訊(Claims)
            var claims = new List<Claim>();

            // 在 RFC 7519 規格中(Section#4)，總共定義了 7 個預設的 Claims，我們應該只用的到兩種！
            //claims.Add(new Claim(JwtRegisteredClaimNames.Iss, issuer));
            claims.Add(new Claim(JwtRegisteredClaimNames.NameId, admin.Id.ToString())); // member.Identity.Name
            claims.Add(new Claim(JwtRegisteredClaimNames.Name, admin.Account.ToString())); // member.Identity.Name
            claims.Add(new Claim(JwtRegisteredClaimNames.GivenName, admin.Name.ToString())); // member.Identity.Name
            //claims.Add(new Claim(JwtRegisteredClaimNames.Aud, "The Audience"));
            //claims.Add(new Claim(JwtRegisteredClaimNames.Exp, DateTimeOffset.UtcNow.AddMinutes(30).ToUnixTimeSeconds().ToString()));
            //claims.Add(new Claim(JwtRegisteredClaimNames.Nbf, DateTimeOffset.UtcNow.ToUnixTimeSeconds().ToString())); // 必須為數字
            //claims.Add(new Claim(JwtRegisteredClaimNames.Iat, DateTimeOffset.UtcNow.ToUnixTimeSeconds().ToString())); // 必須為數字
            claims.Add(new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString())); // JWT ID

            // 網路上常看到的這個 NameId 設定是多餘的
            //claims.Add(new Claim(JwtRegisteredClaimNames.NameId, memberName));

            // 這個 Claim 也以直接被 JwtRegisteredClaimNames.Sub 取代，所以也是多餘的
            //claims.Add(new Claim(ClaimTypes.Name, memberName));

            // 你可以自行擴充 "roles" 加入登入者該有的角色
            switch (admin.Role)
            {
                case (int)Auth.Admin:
                    claims.Add(new Claim("roles", "Admin"));
                    break;
                case (int)Auth.User:
                    claims.Add(new Claim("roles", "User"));
                    break;
                default:
                    break;
            }

            var memberClaimsIdentity = new ClaimsIdentity(claims);

            // 建立一組對稱式加密的金鑰，主要用於 JWT 簽章之用
            var securityKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(signKey));

            // HmacSha256 有要求必須要大於 128 bits，所以 key 不能太短，至少要 16 字元以上
            // https://stackoverflow.com/questions/47279947/idx10603-the-algorithm-hs256-requires-the-securitykey-keysize-to-be-greater
            var signingCredentials = new SigningCredentials(securityKey, SecurityAlgorithms.HmacSha256Signature);

            // 建立 SecurityTokenDescriptor
            var tokenDescriptor = new SecurityTokenDescriptor
            {
                Issuer = issuer,
                //Audience = issuer, // 由於你的 API 受眾通常沒有區分特別對象，因此通常不太需要設定，也不太需要驗證
                //NotBefore = DateTime.Now, // 預設值就是 DateTime.Now
                //IssuedAt = DateTime.Now, // 預設值就是 DateTime.Now
                Subject = memberClaimsIdentity,
                Expires = DateTime.Now.AddDays(expireDays),
                SigningCredentials = signingCredentials
            };

            // 產出所需要的 JWT securityToken 物件，並取得序列化後的 Token 結果(字串格式)
            var tokenHandler = new JwtSecurityTokenHandler();
            var securityToken = tokenHandler.CreateToken(tokenDescriptor);
            var serializeToken = tokenHandler.WriteToken(securityToken);

            return serializeToken;
        }
    }
}