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

  eachBlockbook = config.services.blockbook-frontend;

  blockbookOpts = { config, lib, name, ...}: {

    options = {

      enable = lib.mkEnableOption "blockbook-frontend application";

      package = lib.mkPackageOption pkgs "blockbook" { };

      user = lib.mkOption {
        type = lib.types.str;
        default = "blockbook-frontend-${name}";
        description = "The user as which to run blockbook-frontend-${name}.";
      };

      group = lib.mkOption {
        type = lib.types.str;
        default = "${config.user}";
        description = "The group as which to run blockbook-frontend-${name}.";
      };

      certFile = lib.mkOption {
        type = lib.types.nullOr lib.types.path;
        default = null;
        example = "/etc/secrets/blockbook-frontend-${name}/certFile";
        description = ''
          To enable SSL, specify path to the name of certificate files without extension.
          Expecting {file}`certFile.crt` and {file}`certFile.key`.
        '';
      };

      configFile = lib.mkOption {
        type = with lib.types; nullOr path;
        default = null;
        example = "${config.dataDir}/config.json";
        description = "Location of the blockbook configuration file.";
      };

      coinName = lib.mkOption {
        type = lib.types.str;
        default = "Bitcoin";
        description = ''
          See <https://github.com/trezor/blockbook/blob/master/bchain/coins/blockchain.go#L61>
          for current of coins supported in master (Note: may differ from release).
        '';
      };

      cssDir = lib.mkOption {
        type = lib.types.path;
        default = "${config.package}/share/css/";
        defaultText = lib.literalExpression ''"''${package}/share/css/"'';
        example = lib.literalExpression ''"''${dataDir}/static/css/"'';
        description = ''
          Location of the dir with {file}`main.css` CSS file.
          By default, the one shipped with the package is used.
        '';
      };

      dataDir = lib.mkOption {
        type = lib.types.path;
        default = "/var/lib/blockbook-frontend-${name}";
        description = "Location of blockbook-frontend-${name} data directory.";
      };

      debug = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = "Debug mode, return more verbose errors, reload templates on each request.";
      };

      internal = lib.mkOption {
        type = lib.types.nullOr lib.types.str;
        default = ":9030";
        description = "Internal http server binding `[address]:port`.";
      };

      messageQueueBinding = lib.mkOption {
        type = lib.types.str;
        default = "tcp://127.0.0.1:38330";
        description = "Message Queue Binding `address:port`.";
      };

      public = lib.mkOption {
        type = lib.types.nullOr lib.types.str;
        default = ":9130";
        description = "Public http server binding `[address]:port`.";
      };

      rpc = {
        url = lib.mkOption {
          type = lib.types.str;
          default = "http://127.0.0.1";
          description = "URL for JSON-RPC connections.";
        };

        port = lib.mkOption {
          type = lib.types.port;
          default = 8030;
          description = "Port for JSON-RPC connections.";
        };

        user = lib.mkOption {
          type = lib.types.str;
          default = "rpc";
          description = "Username for JSON-RPC connections.";
        };

        password = lib.mkOption {
          type = lib.types.str;
          default = "rpc";
          description = ''
            RPC password for JSON-RPC connections.
            Warning: this is stored in cleartext in the Nix store!!!
            Use `configFile` or `passwordFile` if needed.
          '';
        };

        passwordFile = lib.mkOption {
          type = lib.types.nullOr lib.types.path;
          default = null;
          description = ''
            File containing password of the RPC user.
            Note: This options is ignored when `configFile` is used.
          '';
        };
      };

      sync = lib.mkOption {
        type = lib.types.bool;
        default = true;
        description = "Synchronizes until tip, if together with zeromq, keeps index synchronized.";
      };

      templateDir = lib.mkOption {
        type = lib.types.path;
        default = "${config.package}/share/templates/";
        defaultText = lib.literalExpression ''"''${package}/share/templates/"'';
        example = lib.literalExpression ''"''${dataDir}/templates/static/"'';
        description = "Location of the HTML templates. By default, ones shipped with the package are used.";
      };

      extraConfig = lib.mkOption {
        type = lib.types.attrs;
        default = {};
        example = lib.literalExpression '' {
          "alternative_estimate_fee" = "whatthefee-disabled";
          "alternative_estimate_fee_params" = "{\"url\": \"https://whatthefee.io/data.json\", \"periodSeconds\": 60}";
          "fiat_rates" = "coingecko";
          "fiat_rates_params" = "{\"url\": \"https://api.coingecko.com/api/v3\", \"coin\": \"bitcoin\", \"periodSeconds\": 60}";
          "coin_shortcut" = "BTC";
          "coin_label" = "Bitcoin";
          "parse" = true;
          "subversion" = "";
          "address_format" = "";
          "xpub_magic" = 76067358;
          "xpub_magic_segwit_p2sh" = 77429938;
          "xpub_magic_segwit_native" = 78792518;
          "mempool_workers" = 8;
          "mempool_sub_workers" = 2;
          "block_addresses_to_keep" = 300;
        }'';
        description = ''
          Additional configurations to be appended to {file}`coin.conf`.
          Overrides any already defined configuration options.
          See <https://github.com/trezor/blockbook/tree/master/configs/coins>
          for current configuration options supported in master (Note: may differ from release).
        '';
      };

      extraCmdLineOptions = lib.mkOption {
        type = lib.types.listOf lib.types.str;
        default = [];
        example = [ "-workers=1" "-dbcache=0" "-logtosderr" ];
        description = ''
          Extra command line options to pass to Blockbook.
          Run blockbook --help to list all available options.
        '';
      };
    };
  };
in
{
  # interface

  options = {
    services.blockbook-frontend = lib.mkOption {
      type = lib.types.attrsOf (lib.types.submodule blockbookOpts);
      default = {};
      description = "Specification of one or more blockbook-frontend instances.";
    };
  };

  # implementation

  config = lib.mkIf (eachBlockbook != {}) {

    systemd.services = lib.mapAttrs' (blockbookName: cfg: (
      lib.nameValuePair "blockbook-frontend-${blockbookName}" (
        let
          configFile = if cfg.configFile != null then cfg.configFile else
            pkgs.writeText "config.conf" (builtins.toJSON ( {
                coin_name = "${cfg.coinName}";
                rpc_user = "${cfg.rpc.user}";
                rpc_pass = "${cfg.rpc.password}";
                rpc_url = "${cfg.rpc.url}:${toString cfg.rpc.port}";
                message_queue_binding = "${cfg.messageQueueBinding}";
              } // cfg.extraConfig)
            );
        in {
          description = "blockbook-frontend-${blockbookName} daemon";
          after = [ "network.target" ];
          wantedBy = [ "multi-user.target" ];
          preStart = ''
            ln -sf ${cfg.templateDir} ${cfg.dataDir}/static/
            ln -sf ${cfg.cssDir} ${cfg.dataDir}/static/
            ${lib.optionalString (cfg.rpc.passwordFile != null && cfg.configFile == null) ''
              CONFIGTMP=$(mktemp)
              ${pkgs.jq}/bin/jq ".rpc_pass = \"$(cat ${cfg.rpc.passwordFile})\"" ${configFile} > $CONFIGTMP
              mv $CONFIGTMP ${cfg.dataDir}/${blockbookName}-config.json
            ''}
          '';
          serviceConfig = {
            User = cfg.user;
            Group = cfg.group;
            ExecStart = ''
               ${cfg.package}/bin/blockbook \
               ${if (cfg.rpc.passwordFile != null && cfg.configFile == null) then
               "-blockchaincfg=${cfg.dataDir}/${blockbookName}-config.json"
               else
               "-blockchaincfg=${configFile}"
               } \
               -datadir=${cfg.dataDir} \
               ${lib.optionalString (cfg.sync != false) "-sync"} \
               ${lib.optionalString (cfg.certFile != null) "-certfile=${toString cfg.certFile}"} \
               ${lib.optionalString (cfg.debug != false) "-debug"} \
               ${lib.optionalString (cfg.internal != null) "-internal=${toString cfg.internal}"} \
               ${lib.optionalString (cfg.public != null) "-public=${toString cfg.public}"} \
               ${toString cfg.extraCmdLineOptions}
            '';
            Restart = "on-failure";
            WorkingDirectory = cfg.dataDir;
            LimitNOFILE = 65536;
          };
        }
    ) )) eachBlockbook;

    systemd.tmpfiles.rules = lib.flatten (lib.mapAttrsToList (blockbookName: cfg: [
      "d ${cfg.dataDir} 0750 ${cfg.user} ${cfg.group} - -"
      "d ${cfg.dataDir}/static 0750 ${cfg.user} ${cfg.group} - -"
    ]) eachBlockbook);

    users.users = lib.mapAttrs' (blockbookName: cfg: (
      lib.nameValuePair "blockbook-frontend-${blockbookName}" {
      name = cfg.user;
      group = cfg.group;
      home = cfg.dataDir;
      isSystemUser = true;
    })) eachBlockbook;

    users.groups = lib.mapAttrs' (instanceName: cfg: (
      lib.nameValuePair "${cfg.group}" { })) eachBlockbook;
  };

  meta.maintainers = with lib.maintainers; [ _1000101 ];

}