{ modulePath, name, description ? null, wrappedPackageName ? null
, unwrappedPackageName ? null, platforms, visible ? false
, enableBookmarks ? true }:

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

with lib;

let

  inherit (pkgs.stdenv.hostPlatform) isDarwin;

  appName = name;

  moduleName = concatStringsSep "." modulePath;

  cfg = getAttrFromPath modulePath config;

  jsonFormat = pkgs.formats.json { };

  supportedPlatforms = flatten (attrVals (attrNames platforms) lib.platforms);

  isWrapped = versionAtLeast config.home.stateVersion "19.09"
    && wrappedPackageName != null;

  defaultPackageName =
    if isWrapped then wrappedPackageName else unwrappedPackageName;

  packageName = if wrappedPackageName != null then
    wrappedPackageName
  else
    unwrappedPackageName;

  profilesPath =
    if isDarwin then "${cfg.configPath}/Profiles" else cfg.configPath;

  nativeMessagingHostsPath = if isDarwin then
    "${cfg.vendorPath}/NativeMessagingHosts"
  else
    "${cfg.vendorPath}/native-messaging-hosts";

  nativeMessagingHostsJoined = pkgs.symlinkJoin {
    name = "ff_native-messaging-hosts";
    paths = [
      # Link a .keep file to keep the directory around
      (pkgs.writeTextDir "lib/mozilla/native-messaging-hosts/.keep" "")
      # Link package configured native messaging hosts (entire browser actually)
      cfg.finalPackage
    ]
    # Link user configured native messaging hosts
      ++ cfg.nativeMessagingHosts;
  };

  # The extensions path shared by all profiles; will not be supported
  # by future browser versions.
  extensionPath = "extensions/{ec8030f7-c20a-464f-9b0e-13a3a9e97384}";

  profiles = flip mapAttrs' cfg.profiles (_: profile:
    nameValuePair "Profile${toString profile.id}" {
      Name = profile.name;
      Path = if isDarwin then "Profiles/${profile.path}" else profile.path;
      IsRelative = 1;
      Default = if profile.isDefault then 1 else 0;
    }) // {
      General = {
        StartWithLastProfile = 1;
      } // lib.optionalAttrs (cfg.profileVersion != null) {
        Version = cfg.profileVersion;
      };
    };

  profilesIni = generators.toINI { } profiles;

  userPrefValue = pref:
    builtins.toJSON (if isBool pref || isInt pref || isString pref then
      pref
    else
      builtins.toJSON pref);

  mkUserJs = prePrefs: prefs: extraPrefs: bookmarks:
    let
      prefs' = lib.optionalAttrs ([ ] != bookmarks) {
        "browser.bookmarks.file" = toString (browserBookmarksFile bookmarks);
        "browser.places.importBookmarksHTML" = true;
      } // prefs;
    in ''
      // Generated by Home Manager.

      ${prePrefs}

      ${concatStrings (mapAttrsToList (name: value: ''
        user_pref("${name}", ${userPrefValue value});
      '') prefs')}

      ${extraPrefs}
    '';

  mkContainersJson = containers:
    let
      containerToIdentity = _: container: {
        userContextId = container.id;
        name = container.name;
        icon = container.icon;
        color = container.color;
        public = true;
      };
    in ''
      ${builtins.toJSON {
        version = 5;
        lastUserContextId =
          foldlAttrs (acc: _: value: if value.id > acc then value.id else acc) 0
          containers;
        identities = mapAttrsToList containerToIdentity containers ++ [
          {
            userContextId = 4294967294; # 2^32 - 2
            name = "userContextIdInternal.thumbnail";
            icon = "";
            color = "";
            accessKey = "";
            public = false;
          }
          {
            userContextId = 4294967295; # 2^32 - 1
            name = "userContextIdInternal.webextStorageLocal";
            icon = "";
            color = "";
            accessKey = "";
            public = false;
          }
        ];
      }}
    '';

  browserBookmarksFile = bookmarks:
    let
      indent = level:
        lib.concatStringsSep "" (map (lib.const "  ") (lib.range 1 level));

      bookmarkToHTML = indentLevel: bookmark:
        ''
          ${indent indentLevel}<DT><A HREF="${
            escapeXML bookmark.url
          }" ADD_DATE="1" LAST_MODIFIED="1"${
            lib.optionalString (bookmark.keyword != null)
            " SHORTCUTURL=\"${escapeXML bookmark.keyword}\""
          }${
            lib.optionalString (bookmark.tags != [ ])
            " TAGS=\"${escapeXML (concatStringsSep "," bookmark.tags)}\""
          }>${escapeXML bookmark.name}</A>'';

      directoryToHTML = indentLevel: directory: ''
        ${indent indentLevel}<DT>${
          if directory.toolbar then
            ''
              <H3 ADD_DATE="1" LAST_MODIFIED="1" PERSONAL_TOOLBAR_FOLDER="true">Bookmarks Toolbar''
          else
            ''<H3 ADD_DATE="1" LAST_MODIFIED="1">${escapeXML directory.name}''
        }</H3>
        ${indent indentLevel}<DL><p>
        ${allItemsToHTML (indentLevel + 1) directory.bookmarks}
        ${indent indentLevel}</DL><p>'';

      itemToHTMLOrRecurse = indentLevel: item:
        if item ? "url" then
          bookmarkToHTML indentLevel item
        else
          directoryToHTML indentLevel item;

      allItemsToHTML = indentLevel: bookmarks:
        lib.concatStringsSep "\n"
        (map (itemToHTMLOrRecurse indentLevel) bookmarks);

      bookmarkEntries = allItemsToHTML 1 bookmarks;
    in pkgs.writeText "${packageName}-bookmarks.html" ''
      <!DOCTYPE NETSCAPE-Bookmark-file-1>
      <!-- This is an automatically generated file.
        It will be read and overwritten.
        DO NOT EDIT! -->
      <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=UTF-8">
      <TITLE>Bookmarks</TITLE>
      <H1>Bookmarks Menu</H1>
      <DL><p>
      ${bookmarkEntries}
      </DL>
    '';

  mkNoDuplicateAssertion = entities: entityKind:
    (let
      # Return an attribute set with entity IDs as keys and a list of
      # entity names with corresponding ID as value. An ID is present in
      # the result only if more than one entity has it. The argument
      # entities is a list of AttrSet of one id/name pair.
      findDuplicateIds = entities:
        filterAttrs (_entityId: entityNames: length entityNames != 1)
        (zipAttrs entities);

      duplicates = findDuplicateIds (mapAttrsToList
        (entityName: entity: { "${toString entity.id}" = entityName; })
        entities);

      mkMsg = entityId: entityNames:
        "  - ID ${entityId} is used by " + concatStringsSep ", " entityNames;
    in {
      assertion = duplicates == { };
      message = ''
        Must not have a ${appName} ${entityKind} with an existing ID but
      '' + concatStringsSep "\n" (mapAttrsToList mkMsg duplicates);
    });

  wrapPackage = package:
    let
      # The configuration expected by the Firefox wrapper.
      fcfg = { enableGnomeExtensions = cfg.enableGnomeExtensions; };

      # A bit of hackery to force a config into the wrapper.
      browserName =
        package.browserName or (builtins.parseDrvName package.name).name;

      # The configuration expected by the Firefox wrapper builder.
      bcfg = setAttrByPath [ browserName ] fcfg;

    in if package == null then
      null
    else if isDarwin then
      package
    else if isWrapped then
      package.override (old: {
        cfg = old.cfg or { } // fcfg;
        extraPolicies = (old.extraPolicies or { }) // cfg.policies;
      })
    else
      (pkgs.wrapFirefox.override { config = bcfg; }) package { };

in {
  options = setAttrByPath modulePath {
    enable = mkOption {
      type = types.bool;
      default = false;
      example = true;
      description = ''
        Whether to enable ${appName}.${
          optionalString (description != null) " ${description}"
        }
        ${optionalString (!visible)
        "See `programs.firefox` for more configuration options."}
      '';
    };

    package = mkOption {
      inherit visible;
      type = with types; nullOr package;
      default = pkgs.${defaultPackageName};
      defaultText = literalExpression "pkgs.${packageName}";
      example = literalExpression ''
        pkgs.${packageName}.override {
          # See nixpkgs' firefox/wrapper.nix to check which options you can use
          nativeMessagingHosts = [
            # Gnome shell native connector
            pkgs.gnome-browser-connector
            # Tridactyl native connector
            pkgs.tridactyl-native
          ];
        }
      '';
      description = ''
        The ${appName} package to use. If state version ≥ 19.09 then
        this should be a wrapped ${appName} package. For earlier state
        versions it should be an unwrapped ${appName} package.
        Set to `null` to disable installing ${appName}.
      '';
    };

    languagePacks = mkOption {
      type = types.listOf types.str;
      default = [ ];
      description = ''
        The language packs to install. Available language codes can be found
        on the releases page:
        `https://releases.mozilla.org/pub/firefox/releases/''${version}/linux-x86_64/xpi/`,
        replacing `''${version}` with the version of ${appName} you have.
      '';
      example = [ "en-GB" "de" ];
    };

    name = mkOption {
      internal = true;
      type = types.str;
      default = name;
      example = "Firefox";
      description = "The name of the browser.";
    };

    wrappedPackageName = mkOption {
      internal = true;
      type = with types; nullOr str;
      default = wrappedPackageName;
      description = "Name of the wrapped browser package.";
    };

    vendorPath = mkOption {
      internal = true;
      type = with types; nullOr str;
      default = with platforms;
        if isDarwin then
          darwin.vendorPath or null
        else
          linux.vendorPath or null;
      example = ".mozilla";
      description =
        "Directory containing the native messaging hosts directory.";
    };

    configPath = mkOption {
      internal = true;
      type = types.str;
      default = with platforms;
        if isDarwin then darwin.configPath else linux.configPath;
      example = ".mozilla/firefox";
      description = "Directory containing the ${appName} configuration files.";
    };

    nativeMessagingHosts = optionalAttrs (cfg.vendorPath != null) (mkOption {
      inherit visible;
      type = types.listOf types.package;
      default = [ ];
      description = ''
        Additional packages containing native messaging hosts that should be
        made available to ${appName} extensions.
      '';
    });

    finalPackage = mkOption {
      inherit visible;
      type = with types; nullOr package;
      readOnly = true;
      description = "Resulting ${appName} package.";
    };

    policies = optionalAttrs (wrappedPackageName != null) (mkOption {
      inherit visible;
      type = types.attrsOf jsonFormat.type;
      default = { };
      description =
        "[See list of policies](https://mozilla.github.io/policy-templates/).";
      example = {
        DefaultDownloadDirectory = "\${home}/Downloads";
        BlockAboutConfig = true;
      };
    });

    profileVersion = mkOption {
      internal = true;
      type = types.nullOr types.ints.unsigned;
      default = if isDarwin then null else 2;
      description = "profile version, set null for nix-darwin";
    };

    profiles = mkOption {
      inherit visible;
      type = types.attrsOf (types.submodule ({ config, name, ... }: {
        options = {
          name = mkOption {
            type = types.str;
            default = name;
            description = "Profile name.";
          };

          id = mkOption {
            type = types.ints.unsigned;
            default = 0;
            description = ''
              Profile ID. This should be set to a unique number per profile.
            '';
          };

          preConfig = mkOption {
            type = types.lines;
            default = "";
            description = ''
              Extra preferences to add to {file}`user.js`, before
              [](#opt-programs.firefox.profiles._name_.settings).

              Use [](#opt-programs.firefox.profiles._name_.extraConfig), unless
              you want to overwrite in
              [](#opt-programs.firefox.profiles._name_.settings), then use this
              option.
            '';
          };

          settings = mkOption {
            type = types.attrsOf (jsonFormat.type // {
              description =
                "${appName} preference (int, bool, string, and also attrs, list, float as a JSON string)";
            });
            default = { };
            example = literalExpression ''
              {
                "browser.startup.homepage" = "https://nixos.org";
                "browser.search.region" = "GB";
                "browser.search.isUS" = false;
                "distribution.searchplugins.defaultLocale" = "en-GB";
                "general.useragent.locale" = "en-GB";
                "browser.bookmarks.showMobileBookmarks" = true;
                "browser.newtabpage.pinned" = [{
                  title = "NixOS";
                  url = "https://nixos.org";
                }];
              }
            '';
            description = ''
              Attribute set of ${appName} preferences.

              ${appName} only supports int, bool, and string types for
              preferences, but home-manager will automatically
              convert all other JSON-compatible values into strings.
            '';
          };

          extraConfig = mkOption {
            type = types.lines;
            default = "";
            description = ''
              Extra preferences to add to {file}`user.js`.
            '';
          };

          userChrome = mkOption {
            type = types.lines;
            default = "";
            description = "Custom ${appName} user chrome CSS.";
            example = ''
              /* Hide tab bar in FF Quantum */
              @-moz-document url(chrome://browser/content/browser.xul), url(chrome://browser/content/browser.xhtml) {
                #TabsToolbar {
                  visibility: collapse !important;
                  margin-bottom: 21px !important;
                }

                #sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] #sidebar-header {
                  visibility: collapse !important;
                }
              }
            '';
          };

          userContent = mkOption {
            type = types.lines;
            default = "";
            description = "Custom ${appName} user content CSS.";
            example = ''
              /* Hide scrollbar in FF Quantum */
              *{scrollbar-width:none !important}
            '';
          };

          bookmarks = mkOption {
            internal = !enableBookmarks;
            type = let
              bookmarkSubmodule = types.submodule ({ config, name, ... }: {
                options = {
                  name = mkOption {
                    type = types.str;
                    default = name;
                    description = "Bookmark name.";
                  };

                  tags = mkOption {
                    type = types.listOf types.str;
                    default = [ ];
                    description = "Bookmark tags.";
                  };

                  keyword = mkOption {
                    type = types.nullOr types.str;
                    default = null;
                    description = "Bookmark search keyword.";
                  };

                  url = mkOption {
                    type = types.str;
                    description = "Bookmark url, use %s for search terms.";
                  };
                };
              }) // {
                description = "bookmark submodule";
              };

              bookmarkType = types.addCheck bookmarkSubmodule (x: x ? "url");

              directoryType = types.submodule ({ config, name, ... }: {
                options = {
                  name = mkOption {
                    type = types.str;
                    default = name;
                    description = "Directory name.";
                  };

                  bookmarks = mkOption {
                    type = types.listOf nodeType;
                    default = [ ];
                    description = "Bookmarks within directory.";
                  };

                  toolbar = mkOption {
                    type = types.bool;
                    default = false;
                    description = ''
                      Make this the toolbar directory. Note, this does _not_
                      mean that this directory will be added to the toolbar,
                      this directory _is_ the toolbar.
                    '';
                  };
                };
              }) // {
                description = "directory submodule";
              };

              nodeType = types.either bookmarkType directoryType;
            in with types;
            coercedTo (attrsOf nodeType) attrValues (listOf nodeType);
            default = [ ];
            example = literalExpression ''
              [
                {
                  name = "wikipedia";
                  tags = [ "wiki" ];
                  keyword = "wiki";
                  url = "https://en.wikipedia.org/wiki/Special:Search?search=%s&go=Go";
                }
                {
                  name = "kernel.org";
                  url = "https://www.kernel.org";
                }
                {
                  name = "Nix sites";
                  toolbar = true;
                  bookmarks = [
                    {
                      name = "homepage";
                      url = "https://nixos.org/";
                    }
                    {
                      name = "wiki";
                      tags = [ "wiki" "nix" ];
                      url = "https://wiki.nixos.org/";
                    }
                  ];
                }
              ]
            '';
            description = ''
              Preloaded bookmarks. Note, this may silently overwrite any
              previously existing bookmarks!
            '';
          };

          path = mkOption {
            type = types.str;
            default = name;
            description = "Profile path.";
          };

          isDefault = mkOption {
            type = types.bool;
            default = config.id == 0;
            defaultText = "true if profile ID is 0";
            description = "Whether this is a default profile.";
          };

          search = mkOption {
            type = types.submodule (args:
              import ./profiles/search.nix {
                inherit (args) config;
                inherit lib pkgs appName;
                package = cfg.finalPackage;
                modulePath = modulePath ++ [ "profiles" name "search" ];
                profilePath = config.path;
              });
            default = { };
            description = "Declarative search engine configuration.";
          };

          containersForce = mkOption {
            type = types.bool;
            default = false;
            description = ''
              Whether to force replace the existing containers configuration.
              This is recommended since ${appName} will replace the symlink on
              every launch, but note that you'll lose any existing configuration
              by enabling this.
            '';
          };

          containers = mkOption {
            type = types.attrsOf (types.submodule ({ name, ... }: {
              options = {
                name = mkOption {
                  type = types.str;
                  default = name;
                  description = "Container name, e.g., shopping.";
                };

                id = mkOption {
                  type = types.ints.unsigned;
                  default = 0;
                  description = ''
                    Container ID. This should be set to a unique number per container in this profile.
                  '';
                };

                # List of colors at
                # https://searchfox.org/mozilla-central/rev/5ad226c7379b0564c76dc3b54b44985356f94c5a/toolkit/components/extensions/parent/ext-contextualIdentities.js#32
                color = mkOption {
                  type = types.enum [
                    "blue"
                    "turquoise"
                    "green"
                    "yellow"
                    "orange"
                    "red"
                    "pink"
                    "purple"
                    "toolbar"
                  ];
                  default = "pink";
                  description = "Container color.";
                };

                icon = mkOption {
                  type = types.enum [
                    "briefcase"
                    "cart"
                    "circle"
                    "dollar"
                    "fence"
                    "fingerprint"
                    "gift"
                    "vacation"
                    "food"
                    "fruit"
                    "pet"
                    "tree"
                    "chill"
                  ];
                  default = "fruit";
                  description = "Container icon.";
                };
              };
            }));
            default = { };
            example = {
              "shopping" = {
                id = 1;
                color = "blue";
                icon = "cart";
              };
              "dangerous" = {
                id = 2;
                color = "red";
                icon = "fruit";
              };
            };
            description = ''
              Attribute set of container configurations. See
              [Multi-Account
              Containers](https://support.mozilla.org/en-US/kb/containers)
              for more information.
            '';
          };

          extensions = mkOption {
            type = types.listOf types.package;
            default = [ ];
            example = literalExpression ''
              with pkgs.nur.repos.rycee.firefox-addons; [
                privacy-badger
              ]
            '';
            description = ''
              List of ${appName} add-on packages to install for this profile.
              Some pre-packaged add-ons are accessible from the
              [Nix User Repository](https://github.com/nix-community/NUR).
              Once you have NUR installed run

              ```console
              $ nix-env -f '<nixpkgs>' -qaP -A nur.repos.rycee.firefox-addons
              ```

              to list the available ${appName} add-ons.

              Note that it is necessary to manually enable these extensions
              inside ${appName} after the first installation.

              To automatically enable extensions add
              `"extensions.autoDisableScopes" = 0;`
              to
              [{option}`${moduleName}.profiles.<profile>.settings`](#opt-${moduleName}.profiles._name_.settings)
            '';
          };

        };
      }));
      default = { };
      description = "Attribute set of ${appName} profiles.";
    };

    enableGnomeExtensions = mkOption {
      inherit visible;
      type = types.bool;
      default = false;
      description = ''
        Whether to enable the GNOME Shell native host connector. Note, you
        also need to set the NixOS option
        `services.gnome.gnome-browser-connector.enable` to
        `true`.
      '';
    };
  };

  config = mkIf cfg.enable ({
    assertions = [
      (hm.assertions.assertPlatform moduleName pkgs supportedPlatforms)

      (let
        defaults =
          catAttrs "name" (filter (a: a.isDefault) (attrValues cfg.profiles));
      in {
        assertion = cfg.profiles == { } || length defaults == 1;
        message = "Must have exactly one default ${appName} profile but found "
          + toString (length defaults) + optionalString (length defaults > 1)
          (", namely " + concatStringsSep ", " defaults);
      })

      (let
        getContainers = profiles:
          flatten
          (mapAttrsToList (_: value: (attrValues value.containers)) profiles);

        findInvalidContainerIds = profiles:
          filter (container: container.id >= 4294967294)
          (getContainers profiles);
      in {
        assertion = cfg.profiles == { }
          || length (findInvalidContainerIds cfg.profiles) == 0;
        message = "Container id must be smaller than 4294967294 (2^32 - 2)";
      })

      {
        assertion = cfg.languagePacks == [ ] || cfg.package != null;
        message = ''
          'programs.firefox.languagePacks' requires 'programs.firefox.package'
          to be set to a non-null value.
        '';
      }

      (mkNoDuplicateAssertion cfg.profiles "profile")
    ] ++ (mapAttrsToList
      (_: profile: mkNoDuplicateAssertion profile.containers "container")
      cfg.profiles);

    warnings = optional (cfg.enableGnomeExtensions or false) ''
      Using '${moduleName}.enableGnomeExtensions' has been deprecated and
      will be removed in the future. Please change to overriding the package
      configuration using '${moduleName}.package' instead. You can refer to
      its example for how to do this.
    '';

    home.packages = lib.optional (cfg.finalPackage != null) cfg.finalPackage;

    home.file = mkMerge ([{
      "${cfg.configPath}/profiles.ini" =
        mkIf (cfg.profiles != { }) { text = profilesIni; };
    }] ++ optional (cfg.vendorPath != null) {
      "${nativeMessagingHostsPath}" = {
        source =
          "${nativeMessagingHostsJoined}/lib/mozilla/native-messaging-hosts";
        recursive = true;
      };
    } ++ flip mapAttrsToList cfg.profiles (_: profile: {
      "${profilesPath}/${profile.path}/.keep".text = "";

      "${profilesPath}/${profile.path}/chrome/userChrome.css" =
        mkIf (profile.userChrome != "") { text = profile.userChrome; };

      "${profilesPath}/${profile.path}/chrome/userContent.css" =
        mkIf (profile.userContent != "") { text = profile.userContent; };

      "${profilesPath}/${profile.path}/user.js" = mkIf (profile.preConfig != ""
        || profile.settings != { } || profile.extraConfig != ""
        || profile.bookmarks != [ ]) {
          text = mkUserJs profile.preConfig profile.settings profile.extraConfig
            profile.bookmarks;
        };

      "${profilesPath}/${profile.path}/containers.json" =
        mkIf (profile.containers != { }) {
          text = mkContainersJson profile.containers;
          force = profile.containersForce;
        };

      "${profilesPath}/${profile.path}/search.json.mozlz4" =
        mkIf (profile.search.enable) {
          enable = profile.search.enable;
          force = profile.search.force;
          source = profile.search.file;
        };

      "${profilesPath}/${profile.path}/extensions" =
        mkIf (profile.extensions != [ ]) {
          source = let
            extensionsEnvPkg = pkgs.buildEnv {
              name = "hm-firefox-extensions";
              paths = profile.extensions;
            };
          in "${extensionsEnvPkg}/share/mozilla/${extensionPath}";
          recursive = true;
          force = true;
        };
    }));
  } // setAttrByPath modulePath {
    finalPackage = wrapPackage cfg.package;

    policies = {
      ExtensionSettings = lib.mkIf (cfg.languagePacks != [ ]) (listToAttrs (map
        (lang:
          nameValuePair "langpack-${lang}@firefox.mozilla.org" {
            installation_mode = "normal_installed";
            install_url =
              "https://releases.mozilla.org/pub/firefox/releases/${cfg.package.version}/linux-x86_64/xpi/${lang}.xpi";
          }) cfg.languagePacks));
    };
  });
}