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

with lib;
let
  cfg = config.modules.syncthing;

  # Helper function to create a serviceConfig entry if the condition is met
  mkServiceConfigOption = name: value: mkIf (value != null) { "${name}" = value; };

  # Construct the settings object for Syncthing
  syncthingSettings = mkMerge [
    # GUI configuration
    (mkIf cfg.gui.enable {
      gui = mkMerge [
        (mkIf (cfg.gui.user != null) {
          user = cfg.gui.user;
        })
      ];
    })

    # Devices configuration
    (mkIf (cfg.devices != {}) {
      devices = mapAttrs (name: device: {
        id = device.id;
      } // optionalAttrs (device.name != null) {
        name = device.name;
      } // optionalAttrs (device.addresses != []) {
        addresses = device.addresses;
      }) cfg.devices;
    })

    # Folders configuration
    (mkIf (cfg.folders != {}) {
      folders = mapAttrs (name: folder: {
        path = folder.path;
        devices = folder.devices;
      } // optionalAttrs (folder.ignorePerms != null) {
        ignorePerms = folder.ignorePerms;
      } // optionalAttrs (folder.type != null) {
        type = folder.type;
      } // optionalAttrs (folder.rescanIntervalS != null) {
        rescanIntervalS = folder.rescanIntervalS;
      } // optionalAttrs (folder.versioning != null) {
        versioning = folder.versioning;
      }) cfg.folders;
    })

    # Extra options
    cfg.extraOptions
  ];
in
{
  options = {
    modules.syncthing = {
      enable = mkEnableOption "Deploy syncthing";

      openDefaultPorts = mkOption {
        type = types.bool;
        default = true;
        description = "Open ports in the firewall for Syncthing";
      };

      disableDefaultFolder = mkOption {
        type = types.bool;
        default = true;
        description = "Don't create default ~/Sync folder";
      };

      gui = {
        enable = mkEnableOption "Enable GUI configuration";

        user = mkOption {
          type = types.nullOr types.str;
          default = null;
          description = "GUI username";
          example = "myuser";
        };

        passwordFile = mkOption {
          type = types.nullOr types.path;
          default = null;
          description = "Path to file containing GUI password";
          example = "config.age.secrets.syncthing-gui-password.path";
        };
      };

      identity = {
        keyPath = mkOption {
          type = types.nullOr types.path;
          default = null;
          description = "Path to Syncthing private key for stable device ID";
          example = "config.age.secrets.syncthing-key.path";
        };

        certPath = mkOption {
          type = types.nullOr types.path;
          default = null;
          description = "Path to Syncthing certificate for stable device ID";
          example = "config.age.secrets.syncthing-cert.path";
        };
      };

      devices = mkOption {
        type = types.attrsOf (types.submodule {
          options = {
            id = mkOption {
              type = types.str;
              description = "Device ID";
              example = "DMWVMM6-MKEQVB4-I4UZTRH-5A6E24O-XHQTL3K-AAI5R5L-MXNMUGX-QTGRHQ2";
            };

            name = mkOption {
              type = types.nullOr types.str;
              default = null;
              description = "Device name (optional)";
            };

            addresses = mkOption {
              type = types.listOf types.str;
              default = [];
              description = "Device addresses";
              example = [ "tcp://192.168.1.100:22000" ];
            };
          };
        });
        default = {};
        description = "Syncthing devices configuration";
        example = {
          "laptop" = {
            id = "DMWVMM6-MKEQVB4-I4UZTRH-5A6E24O-XHQTL3K-AAI5R5L-MXNMUGX-QTGRHQ2";
          };
          "phone" = {
            id = "ANOTHER-DEVICE-ID-GOES-HERE";
            addresses = [ "tcp://192.168.1.101:22000" ];
          };
        };
      };

      folders = mkOption {
        type = types.attrsOf (types.submodule {
          options = {
            path = mkOption {
              type = types.str;
              description = "Local folder path";
              example = "/home/myuser/Documents";
            };

            devices = mkOption {
              type = types.listOf (types.either types.str (types.submodule {
                options = {
                  name = mkOption {
                    type = types.str;
                    description = "Device name";
                  };

                  encryptionPasswordFile = mkOption {
                    type = types.path;
                    description = "Path to file containing encryption password";
                  };
                };
              }));
              default = [];
              description = "List of devices that can access this folder";
              example = [ "laptop" "phone" ];
            };

            ignorePerms = mkOption {
              type = types.nullOr types.bool;
              default = null;
              description = "Whether to ignore file permissions";
            };

            type = mkOption {
              type = types.nullOr (types.enum [ "sendreceive" "sendonly" "receiveonly" ]);
              default = null;
              description = "Folder type";
            };

            rescanIntervalS = mkOption {
              type = types.nullOr types.int;
              default = null;
              description = "Rescan interval in seconds";
            };

            versioning = mkOption {
              type = types.nullOr (types.submodule {
                options = {
                  type = mkOption {
                    type = types.enum [ "external" "simple" "staggered" "trashcan" ];
                    description = "Versioning type";
                  };

                  params = mkOption {
                    type = types.attrsOf types.str;
                    default = {};
                    description = "Versioning parameters";
                  };
                };
              });
              default = null;
              description = "Folder versioning configuration";
            };
          };
        });
        default = {};
        description = "Syncthing folders configuration";
        example = {
          "Documents" = {
            path = "/home/myuser/Documents";
            devices = [ "laptop" "phone" ];
            ignorePerms = false;
          };
          "Sensitive" = {
            path = "/home/myuser/Sensitive";
            devices = [
              "laptop"
              {
                name = "phone";
                encryptionPasswordFile = "/run/secrets/syncthing-sensitive-password";
              }
            ];
          };
        };
      };

      extraOptions = mkOption {
        type = types.attrsOf types.anything;
        default = {};
        description = "Additional Syncthing configuration options";
      };
    };
  };

  config = mkIf cfg.enable {
    services.syncthing = {
      enable = true;
      openDefaultPorts = cfg.openDefaultPorts;
      # Set stable identity if provided
      key = mkIf (cfg.identity.keyPath != null) cfg.identity.keyPath;
      cert = mkIf (cfg.identity.certPath != null) cfg.identity.certPath;
      # Combine all settings
      settings = syncthingSettings;
    };

    # Configure systemd service options collectively
    systemd.services.syncthing = {
      # Add environment variable to disable default folder creation
      environment.STNODEFAULTFOLDER = mkIf cfg.disableDefaultFolder "true";

      # Add supplementary groups for secret access
      serviceConfig.SupplementaryGroups = [ "syncthing-secrets" ];
    };

    # Create a group for accessing secrets
    users.groups.syncthing-secrets = {};
  };
}