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

let
  inherit (lib)
    filterAttrs
    foldl
    imap1
    mapAttrsToList
    mkEnableOption
    mkIf
    mkMerge
    mkOption
    mkPackageOption
    types
    ;
in
{
  options = {
    services.intake = {
      package = mkPackageOption pkgs "intake" { };

      extraPackages = mkOption {
        type = types.listOf types.package;
        default = [ ];
        description = "Extra packages available to all enabled users and their intake services.";
      };

      users = mkOption {
        description = "User intake service definitions.";
        default = { };
        type = types.attrsOf (
          types.submodule {
            options = {
              enable = mkEnableOption "intake, a universal and extensible feed aggregator.";

              dataDir = mkOption {
                type = types.str;
                default = "/home/$USER/.local/share/intake";
                description = "The data directory for this user's intake service.";
              };

              listen.addr = mkOption {
                type = types.str;
                default = "127.0.0.1";
                description = "The listen address for this user's intake service.";
              };

              listen.port = mkOption {
                type = types.port;
                default = 80;
                description = "The listen port for this user's intake service.";
              };

              extraPackages = mkOption {
                type = types.listOf types.package;
                default = [ ];
                description = "Extra packages available to this user and their intake service.";
              };
            };
          }
        );
      };
    };
  };

  config =
    let
      intakeCfg = config.services.intake;
      enabledUsers = filterAttrs (userName: userCfg: userCfg.enable) intakeCfg.users;
      enabledUserNames = mapAttrsToList (userName: userCfg: userName) enabledUsers;
      userPackages =
        userName:
        [ intakeCfg.package ] ++ intakeCfg.extraPackages ++ intakeCfg.users.${userName}.extraPackages;
    in
    {
      # Apply the overlay so intake is included in pkgs.
      nixpkgs.overlays = [ flake.overlays.default ];

      # Give every intake user the shared packages and their user-specific packages.
      users.users =
        let
          addPackagesToUser = userName: {
            ${userName}.packages = userPackages userName;
          };
        in
        mkMerge (map addPackagesToUser enabledUserNames);

      # Define a user service for each configured user
      systemd.services =
        let
          runScript =
            userName:
            let
              listen = enabledUsers.${userName}.listen;
            in
            pkgs.writeShellScript "intake-run.sh" ''
              mkdir -p $INTAKE_DATA_DIR
              ${intakeCfg.package}/bin/intake serve --addr ${listen.addr} --port ${toString listen.port}
            '';
          # systemd service definition for a single user, given `services.intake.users.userName` = `userCfg`
          userServiceConfig = userName: userCfg: {
            "intake-${userName}" = {
              description = "Intake service for user ${userName}";
              script = "${runScript userName}";
              path = config.environment.systemPackages ++ intakeCfg.extraPackages ++ userCfg.extraPackages;
              environment = {
                INTAKE_DATA_DIR = "/home/${userName}/.local/share/intake";
              };
              serviceConfig = {
                User = userName;
                Type = "simple";
              };
              wantedBy = [ "multi-user.target" ];
              after = [ "network.target" ];
              enable = userCfg.enable;
            };
          };
        in
        mkMerge (mapAttrsToList userServiceConfig enabledUsers);
    };
}