// ========================================================================
//
// Copyright (C) 2017-2018 MARC CHEVALDONNE
//                         marc.chevaldonne.free.fr
//
// Module        : TokenController.cs
// Author        : Marc Chevaldonné
// Creation date : 2018-02-12
//
// ========================================================================

using AlertWebAPI.Models;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.IdentityModel.Tokens;
using System;
using System.Diagnostics;
using System.IdentityModel.Tokens.Jwt;
using System.Linq;
using System.Text;

namespace AlertWebAPI.Controllers
{
    /// <summary>
    /// allows to create a token on the alert database by authenticating 
    /// </summary>
    [Route("api/token")]
    public class TokenController : Controller
    {
        private IConfiguration _config;

        /// <summary>
        /// context allowing to access the database containing the logins and passwords
        /// </summary>
        private readonly UserDbContext context;

        /// <summary>
        /// constructor
        /// </summary>
        /// <param name="config"></param>
        public TokenController(IConfiguration config)
        {
            _config = config;

            //creates the context to the Users database
            this.context = new UserDbContext();

            //if the users database is empty, creates a fake user and adds it to the database
            StubData();
        }

        [Conditional("DEBUG")]
        private void StubData()
        {
            if (context.Users.Count() == 0)
            {
                InitializeData(context);
                context.SaveChanges();
            }
        }

        /// <summary>
        /// creates stub data for the users database
        /// </summary>
        /// <param name="context"></param>
        private void InitializeData(UserDbContext context)
        {
            context.Users.Add(new User
            {
                Name = "Dwight Schrute",
                UserName = "dwight",
                Password = "boss",
                Email = "dwight.schrute@dundlermifflin.com"
            });
        }

        /// <summary>
        /// creates a token for accessing the alert database
        /// [AllowAnonymous] authorizes anonymous access to this method
        /// </summary>
        /// <param name="login">username/password of the user asking for a token</param>
        /// <returns>a token to access the alert database</returns>
        [AllowAnonymous]
        [HttpPost]
        public IActionResult CreateToken([FromBody]Login login)
        {
            IActionResult response = Unauthorized();

            //tries to authenticate with the login data
            var user = Authenticate(login);

            //if authentication succeeds, builds a token and returns it
            if (user != null)
            {
                var tokenString = BuildToken(user);
                response = Ok(new { token = tokenString });
            }

            //else, returns a Status401Unauthorized response
            return response;
        }

        /// <summary>
        /// builds the token with the user data
        /// note that it uses the config file (Key and Issuer), defined in appsettings.json
        /// </summary>
        /// <param name="user">the user who will get the token</param>
        /// <returns>the token built</returns>
        private string BuildToken(User user)
        {
            var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_config["Jwt:Key"]));
            var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);

            var token = new JwtSecurityToken(_config["Jwt:Issuer"],
              _config["Jwt:Issuer"],
              expires: DateTime.Now.AddMinutes(30),
              signingCredentials: creds);

            return new JwtSecurityTokenHandler().WriteToken(token);
        }

        /// <summary>
        /// authenticates the login/password
        /// </summary>
        /// <param name="login">login/password to authenticate</param>
        /// <returns>the user if authentication succeeds, null if not</returns>
        private User Authenticate(Login login)
        {
            User user = null;

            //retrieves the first user in the database with the given login and password
            user = context.Users.FirstOrDefault(u => u.UserName == login.Username && u.Password == login.Password);

            //methods without users database and hard-saved login/password
            //if (login.Username == "dwight" && login.Password == "boss")
            //{
            //    user = new User { Name = "Dwight Schrute", Email = "dwight.schrute@dundlermifflin.com" };
            //}
            return user;
        }
    }
}