using System.Globalization;
using System.Net;
using System.Security.Cryptography;
using Microsoft.Data.Sqlite;
using SQLitePCL;

namespace AuthProxy;

public static class Program {
  private const string COOKIE_NAME = "__Secure-Token";

  private static readonly string s_loginHtmlCache = File.ReadAllText(Path.Combine(
      AppDomain.CurrentDomain.BaseDirectory, "login.html"));
  private static readonly string? s_domain = Environment
    .GetEnvironmentVariable("AUTH_DOMAIN");
  private static readonly string s_db = Environment
    .GetEnvironmentVariable("AUTH_DB") ?? "credentials.db";
  private static readonly long s_lifetime = long.Parse(Environment
    .GetEnvironmentVariable("AUTH_LIFETIME") ?? "7",
      CultureInfo.InvariantCulture) * 60 * 60 * 24;
  private static readonly string? s_password = Environment
    .GetEnvironmentVariable("AUTH_PASSWORD");
  private static readonly int s_port = int.Parse(Environment
    .GetEnvironmentVariable("AUTH_PORT") ?? "5000",
      CultureInfo.InvariantCulture);

  private static string ConnectionString { get => $"Data Source={s_db}"; }

  public static void Main(string[] args) {
    var app = Initialize(args);
    app.UseSession();

    app.MapGet("/auth/check", async (context) => {
      var token = context.Request.Cookies[COOKIE_NAME];
      if (!TokenIsValid(token)) {
        context.Response.ContentType = "text/plain";
        context.Response.StatusCode = (int)HttpStatusCode.Unauthorized;
        await context.Response.WriteAsync("unauthorized");
        return;
      }

      context.Response.ContentType = "text/plain";
      context.Response.StatusCode = (int)HttpStatusCode.OK;
      await context.Response.WriteAsync("authorized");
    });

    app.MapGet("/auth/login", async (context) => {
      context.Response.ContentType = "text/html";
      context.Response.StatusCode = (int)HttpStatusCode.OK;
      await context.Response.WriteAsync(s_loginHtmlCache);
    });

    app.MapGet("/auth/logout", (context) => {
      if (context.Request.Cookies[COOKIE_NAME] == null)
        return Task.CompletedTask;

      var cookieOpts = new CookieOptions {
        Path = "/",
        Secure = true,
        HttpOnly = true,
        SameSite = SameSiteMode.None,
        MaxAge = TimeSpan.FromSeconds(s_lifetime),
      };
      if (!string.IsNullOrEmpty(s_domain)) {
        cookieOpts.Domain = s_domain;
      }

      context.Response.Cookies.Append(COOKIE_NAME, string.Empty, cookieOpts);

      context.Response.Redirect("/");
      return Task.CompletedTask;
    });

    app.MapPost("/auth/password", async (context) => {
      if (context.Request.Form.TryGetValue("password", out var reqPassword)
          && !string.IsNullOrEmpty(s_password)
          && string.Equals(reqPassword.FirstOrDefault(), s_password, StringComparison.Ordinal)) {
        var cookieOpts = new CookieOptions {
          Path = "/",
          Secure = true,
          HttpOnly = true,
          SameSite = SameSiteMode.None,
          MaxAge = TimeSpan.FromSeconds(s_lifetime),
        };
        if (!string.IsNullOrEmpty(s_domain)) {
          cookieOpts.Domain = s_domain;
        }

        using var connection = new SqliteConnection(ConnectionString);
        await connection.OpenAsync();
        context.Response.Cookies.Append(
            COOKIE_NAME,
            GenerateToken(connection),
            cookieOpts);
        if (!context.Request.Form.TryGetValue("target", out var target)
            || string.IsNullOrEmpty(target.FirstOrDefault())) {
          target = [];
        }

        context.Response.Redirect(target.FirstOrDefault() ?? "/");
      } else {
        context.Response.StatusCode = 401;
        await context.Response.WriteAsJsonAsync(new { error = "bad password" });
      }
    });

    app.Run($"http://0.0.0.0:{s_port}");
  }

  private static string GenerateToken(SqliteConnection connection) {
    var rng = RandomNumberGenerator.Create();
    var bytes = new byte[32];
    rng.GetBytes(bytes);
    var token = Convert.ToBase64String(bytes);
    using var cmd = new SqliteCommand(@"insert into tokens (token) values (@Token)",
        connection);
    var param = cmd.CreateParameter();
    param.ParameterName = "@Token";
    param.Value = token;
    cmd.Parameters.Add(param);
    cmd.ExecuteNonQuery();
    return token;
  }

  private static bool TokenIsValid(string? token) {
    if (string.IsNullOrWhiteSpace(token)) return false;

    using var connection = new SqliteConnection(ConnectionString);
    connection.Open();
    using var cmd = new SqliteCommand(
        @"select 1 from tokens where
          token=@Token
          and julianday(created_date, @Timeout) > julianday(CURRENT_TIMESTAMP)",
        connection);
    var tokenParam = cmd.CreateParameter();
    tokenParam.ParameterName = "@Token";
    tokenParam.Value = token;
    var timeoutParam = cmd.CreateParameter();
    timeoutParam.ParameterName = "@Timeout";
    timeoutParam.Value = $"+{s_lifetime} seconds";
    cmd.Parameters.Add(tokenParam);
    cmd.Parameters.Add(timeoutParam);
    return cmd.ExecuteScalar() != null;
  }

  private static void RemoveExpiredTokens() {
    using var connection = new SqliteConnection(ConnectionString);
    connection.Open();
    using var cmd = new SqliteCommand(
        @"delete from tokens where
          julianday(created_date, @Timeout) < julianday(CURRENT_TIMESTAMP)",
          connection);
    var timeoutParam = cmd.CreateParameter();
    timeoutParam.ParameterName = "@Timeout";
    timeoutParam.Value = $"+{s_lifetime} seconds";
    cmd.Parameters.Add(timeoutParam);
    cmd.ExecuteNonQuery();
  }

  private static WebApplication Initialize(string[] args) {
    Batteries.Init();

    using var connection = new SqliteConnection(ConnectionString);
    connection.Open();
    using (var cmd = new SqliteCommand(
        @"select 1 from sqlite_master
          where type='table' and name='tokens'",
        connection)) {
      var exists = cmd.ExecuteScalar();
      if (exists == null) {
        var schemaPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "schema.sql");
        if (!File.Exists(schemaPath)) {
          throw new FileNotFoundException(schemaPath);
        }

        var schema = File.ReadAllText(schemaPath);
        using var schemaCmd = new SqliteCommand(schema, connection);
        schemaCmd.ExecuteNonQuery();
      }
    }

    RemoveExpiredTokens();

    var builder = WebApplication.CreateBuilder(args);
    builder.Services.AddDistributedMemoryCache();
    builder.Services.AddSession();
    return builder.Build();
  }
}