{ config, lib, pkgs, ... }:

let
  inherit (lib)
    genAttrs
    maintainers
    mkAliasOptionModule
    mkEnableOption
    mkIf
    mkOption
    types
    ;
  cfg = config.services.nginx.tailscaleAuth;
  cfgAuth = config.services.tailscaleAuth;
in
{
  imports = [
    (mkAliasOptionModule [ "services" "nginx" "tailscaleAuth" "package" ] [ "services" "tailscaleAuth" "package" ])
    (mkAliasOptionModule [ "services" "nginx" "tailscaleAuth" "user" ] [ "services" "tailscaleAuth" "user" ])
    (mkAliasOptionModule [ "services" "nginx" "tailscaleAuth" "group" ] [ "services" "tailscaleAuth" "group" ])
    (mkAliasOptionModule [ "services" "nginx" "tailscaleAuth" "socketPath" ] [ "services" "tailscaleAuth" "socketPath" ])
  ];

  options.services.nginx.tailscaleAuth = {
    enable = mkEnableOption "Enable tailscale.nginx-auth, to authenticate nginx users via tailscale.";

    expectedTailnet = mkOption {
      default = "";
      type = types.nullOr types.str;
      example = "tailnet012345.ts.net";
      description = ''
        If you want to prevent node sharing from allowing users to access services
        across tailnets, declare your expected tailnets domain here.
      '';
    };

    virtualHosts = mkOption {
      type = types.listOf types.str;
      default = [];
      description = ''
        A list of nginx virtual hosts to put behind tailscale.nginx-auth
      '';
    };
  };

  config = mkIf cfg.enable {
    services.tailscaleAuth.enable = true;
    services.nginx.enable = true;

    users.users.${config.services.nginx.user}.extraGroups = [ cfgAuth.group ];

    systemd.services.tailscale-nginx-auth = {
      after = [ "nginx.service" ];
      wants = [ "nginx.service" ];
    };

    services.nginx.virtualHosts = genAttrs
      cfg.virtualHosts
      (vhost: {
        locations."/auth" = {
          extraConfig = ''
            internal;

            proxy_pass http://unix:${cfgAuth.socketPath};
            proxy_pass_request_body off;

            # Upstream uses $http_host here, but we are using gixy to check nginx configurations
            # gixy wants us to use $host: https://github.com/yandex/gixy/blob/master/docs/en/plugins/hostspoofing.md
            proxy_set_header Host $host;
            proxy_set_header Remote-Addr $remote_addr;
            proxy_set_header Remote-Port $remote_port;
            proxy_set_header Original-URI $request_uri;
            proxy_set_header X-Scheme                $scheme;
            proxy_set_header X-Auth-Request-Redirect $scheme://$host$request_uri;
          '';
        };
        locations."/".extraConfig = ''
          auth_request /auth;
          auth_request_set $auth_user $upstream_http_tailscale_user;
          auth_request_set $auth_name $upstream_http_tailscale_name;
          auth_request_set $auth_login $upstream_http_tailscale_login;
          auth_request_set $auth_tailnet $upstream_http_tailscale_tailnet;
          auth_request_set $auth_profile_picture $upstream_http_tailscale_profile_picture;

          proxy_set_header X-Webauth-User "$auth_user";
          proxy_set_header X-Webauth-Name "$auth_name";
          proxy_set_header X-Webauth-Login "$auth_login";
          proxy_set_header X-Webauth-Tailnet "$auth_tailnet";
          proxy_set_header X-Webauth-Profile-Picture "$auth_profile_picture";

          ${lib.optionalString (cfg.expectedTailnet != "") ''proxy_set_header Expected-Tailnet "${cfg.expectedTailnet}";''}
        '';
      });
  };

  meta.maintainers = with maintainers; [ phaer ];

}