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

with lib;

let
  cfg = config.services.home-assistant;

  # cfg.config != null can be assumed here
  configJSON = pkgs.writeText "configuration.json"
    (builtins.toJSON (if cfg.applyDefaultConfig then
    (recursiveUpdate defaultConfig cfg.config) else cfg.config));
  configFile = pkgs.runCommand "configuration.yaml" { preferLocalBuild = true; } ''
    ${pkgs.remarshal}/bin/json2yaml -i ${configJSON} -o $out
  '';

  lovelaceConfigJSON = pkgs.writeText "ui-lovelace.json"
    (builtins.toJSON cfg.lovelaceConfig);
  lovelaceConfigFile = pkgs.runCommand "ui-lovelace.yaml" { preferLocalBuild = true; } ''
    ${pkgs.remarshal}/bin/json2yaml -i ${lovelaceConfigJSON} -o $out
  '';

  availableComponents = cfg.package.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";
  #   ...
  # } ];
  #
  # Beginning with 0.87 Home Assistant is migrating their components to the
  # scheme "platform.subComponent", e.g. "hue.light" instead of "light.hue".
  # See https://developers.home-assistant.io/blog/2019/02/19/the-great-migration.html.
  # Hence, we also check whether we find an entry in the config when interpreting
  # the first part of the path as the component.
  useComponentPlatform = component:
    let
      path = splitString "." component;
      # old: platform is the last part of path
      parentConfig = attrByPath (init path) null cfg.config;
      platform = last path;
      # new: platform is the first part of the path
      parentConfig' = attrByPath (tail path) null cfg.config;
      platform' = head path;
    in
      (isList parentConfig && any (item: item.platform or null == platform) parentConfig)
      || (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 = cfg.port;
  } // optionalAttrs (cfg.lovelaceConfig != null) {
    lovelace.mode = "yaml";
  };

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>.
      '';
    };

    configWritable = mkOption {
      default = false;
      type = types.bool;
      description = ''
        Whether to make <filename>configuration.yaml</filename> writable.
        This only has an effect if <option>config</option> is set.
        This will allow you to edit it from Home Assistant's web interface.
        However, bear in mind that it will be overwritten at every start of the service.
      '';
    };

    lovelaceConfig = mkOption {
      default = null;
      type = with types; nullOr attrs;
      # from https://www.home-assistant.io/lovelace/yaml-mode/
      example = literalExample ''
        {
          title = "My Awesome Home";
          views = [ {
            title = "Example";
            cards = [ {
              type = "markdown";
              title = "Lovelace";
              content = "Welcome to your **Lovelace UI**.";
            } ];
          } ];
        }
      '';
      description = ''
        Your <filename>ui-lovelace.yaml</filename> as a Nix attribute set.
        Setting this option will automatically add
        <literal>lovelace.mode = "yaml";</literal> to your <option>config</option>.
        Beware that setting this option will delete your previous <filename>ui-lovelace.yaml</filename>
      '';
    };

    lovelaceConfigWritable = mkOption {
      default = false;
      type = types.bool;
      description = ''
        Whether to make <filename>ui-lovelace.yaml</filename> writable.
        This only has an effect if <option>lovelaceConfig</option> is set.
        This will allow you to edit it from Home Assistant's web interface.
        However, bear in mind that it will be overwritten at every start of the service.
      '';
    };

    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 = optionalString (cfg.config != null) (if cfg.configWritable then ''
        cp --no-preserve=mode ${configFile} "${cfg.configDir}/configuration.yaml"
      '' else ''
        rm -f "${cfg.configDir}/configuration.yaml"
        ln -s ${configFile} "${cfg.configDir}/configuration.yaml"
      '') + optionalString (cfg.lovelaceConfig != null) (if cfg.lovelaceConfigWritable then ''
        cp --no-preserve=mode ${lovelaceConfigFile} "${cfg.configDir}/ui-lovelace.yaml"
      '' else ''
        rm -f "${cfg.configDir}/ui-lovelace.yaml"
        ln -s ${lovelaceConfigFile} "${cfg.configDir}/ui-lovelace.yaml"
      '');
      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;
  };
}