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

with lib;

let
  cfg = config.services.home-assistant;

  # cfg.config != null can be assumed here
  configFile = pkgs.writeText "configuration.json"
    (builtins.toJSON (if cfg.applyDefaultConfig then
    (lib.recursiveUpdate defaultConfig cfg.config) else cfg.config));

  availableComponents = pkgs.home-assistant.availableComponents;

  # Given component "parentConfig.platform", returns whether config.parentConfig
  # is a list containing a set with set.platform == "platform".
  #
  # For example, the component sensor.luftdaten is used as follows:
  # config.sensor = [ {
  #   platform = "luftdaten";
  #   ...
  # } ];
  useComponentPlatform = component:
    let
      path = splitString "." component;
      parentConfig = attrByPath (init path) null cfg.config;
      platform = last path;
    in isList parentConfig && any
      (item: item.platform or null == platform)
      parentConfig;

  # Returns whether component is used in config
  useComponent = component:
    hasAttrByPath (splitString "." component) cfg.config
    || useComponentPlatform component;

  # List of components used in config
  extraComponents = filter useComponent availableComponents;

  package = if (cfg.autoExtraComponents && cfg.config != null)
    then (cfg.package.override { inherit extraComponents; })
    else cfg.package;

  # If you are changing this, please update the description in applyDefaultConfig
  defaultConfig = {
    homeassistant.time_zone = config.time.timeZone;
    http.server_port = (toString cfg.port);
  };

in {
  meta.maintainers = with maintainers; [ dotlambda ];

  options.services.home-assistant = {
    enable = mkEnableOption "Home Assistant";

    configDir = mkOption {
      default = "/var/lib/hass";
      type = types.path;
      description = "The config directory, where your <filename>configuration.yaml</filename> is located.";
    };

    port = mkOption {
      default = 8123;
      type = types.int;
      description = "The port on which to listen.";
    };

    applyDefaultConfig = mkOption {
      default = true;
      type = types.bool;
      description = ''
        Setting this option enables a few configuration options for HA based on NixOS configuration (such as time zone) to avoid having to manually specify configuration we already have.
        </para>
        <para>
        Currently one side effect of enabling this is that the <literal>http</literal> component will be enabled.
        </para>
        <para>
        This only takes effect if <literal>config != null</literal> in order to ensure that a manually managed <filename>configuration.yaml</filename> is not overwritten.
      '';
    };

    config = mkOption {
      default = null;
      type = with types; nullOr attrs;
      example = literalExample ''
        {
          homeassistant = {
            name = "Home";
            time_zone = "UTC";
          };
          frontend = { };
          http = { };
          feedreader.urls = [ "https://nixos.org/blogs.xml" ];
        }
      '';
      description = ''
        Your <filename>configuration.yaml</filename> as a Nix attribute set.
        Beware that setting this option will delete your previous <filename>configuration.yaml</filename>.
      '';
    };

    package = mkOption {
      default = pkgs.home-assistant;
      defaultText = "pkgs.home-assistant";
      type = types.package;
      example = literalExample ''
        pkgs.home-assistant.override {
          extraPackages = ps: with ps; [ colorlog ];
        }
      '';
      description = ''
        Home Assistant package to use.
        Override <literal>extraPackages</literal> or <literal>extraComponents</literal> in order to add additional dependencies.
        If you specify <option>config</option> and do not set <option>autoExtraComponents</option>
        to <literal>false</literal>, overriding <literal>extraComponents</literal> will have no effect.
      '';
    };

    autoExtraComponents = mkOption {
      default = true;
      type = types.bool;
      description = ''
        If set to <literal>true</literal>, the components used in <literal>config</literal>
        are set as the specified package's <literal>extraComponents</literal>.
        This in turn adds all packaged dependencies to the derivation.
        You might still see import errors in your log.
        In this case, you will need to package the necessary dependencies yourself
        or ask for someone else to package them.
        If a dependency is packaged but not automatically added to this list,
        you might need to specify it in <literal>extraPackages</literal>.
      '';
    };

    openFirewall = mkOption {
      default = false;
      type = types.bool;
      description = "Whether to open the firewall for the specified port.";
    };
  };

  config = mkIf cfg.enable {
    networking.firewall.allowedTCPPorts = mkIf cfg.openFirewall [ cfg.port ];

    systemd.services.home-assistant = {
      description = "Home Assistant";
      after = [ "network.target" ];
      preStart = lib.optionalString (cfg.config != null) ''
        config=${cfg.configDir}/configuration.yaml
        rm -f $config
        ${pkgs.remarshal}/bin/json2yaml -i ${configFile} -o $config
        chmod 444 $config
      '';
      serviceConfig = {
        ExecStart = "${package}/bin/hass --config '${cfg.configDir}'";
        User = "hass";
        Group = "hass";
        Restart = "on-failure";
        ProtectSystem = "strict";
        ReadWritePaths = "${cfg.configDir}";
        KillSignal = "SIGINT";
        PrivateTmp = true;
        RemoveIPC = true;
      };
      path = [
        "/run/wrappers" # needed for ping
      ];
    };

    systemd.targets.home-assistant = rec {
      description = "Home Assistant";
      wantedBy = [ "multi-user.target" ];
      wants = [ "home-assistant.service" ];
      after = wants;
    };

    users.users.hass = {
      home = cfg.configDir;
      createHome = true;
      group = "hass";
      uid = config.ids.uids.hass;
    };

    users.groups.hass.gid = config.ids.gids.hass;
  };
}