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

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

with lib;

let

  inherit (pkgs.stdenv.hostPlatform) isDarwin;

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

      ${concatStrings (mapAttrsToList (name: value: ''
        user_pref("${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 = 4;
        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 ${name} ${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 ${name}.${
          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 ${name} package to use. If state version ≥ 19.09 then
        this should be a wrapped ${name} package. For earlier state
        versions it should be an unwrapped ${name} package.
        Set to `null` to disable installing ${name}.
      '';
    };

    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 Firefox 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 ${name} 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 ${name} extensions.
      '';
    });

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

          settings = mkOption {
            type = types.attrsOf (jsonFormat.type // {
              description =
                "${name} 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 ${name} preferences.

              ${name} 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 ${name} 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 ${name} user content CSS.";
            example = ''
              /* Hide scrollbar in FF Quantum */
              *{scrollbar-width:none !important}
            '';
          };

          bookmarks = mkOption {
            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 = cfg.name;
                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 Firefox 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 ${name} 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 ${name} add-ons.

              Note that it is necessary to manually enable these extensions
              inside ${name} 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 ${name} 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 ${cfg.name} 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.settings != { }
        || profile.extraConfig != "" || profile.bookmarks != [ ]) {
          text =
            mkUserJs 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 = 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);
    };
  });
}