{ pkgs, lib, config, ... }:
let
  passwordStoreDir = "/etc/passwords";
  passwordHash = password: builtins.hashString "sha256" "${password.path}\n${builtins.toString password.selector}\n${builtins.toString password.transform}";
  passwordStorePath = password: "${passwordStoreDir}/${passwordHash password}";
  describePassword = password: password.path
    + (if password.selector != null then " -> ${password.selector}" else "")
    + (if password.transform != null then " | (${password.transform})" else "");
  passwordFiles = builtins.attrValues config.vivarium.passwordFiles;
in
{
  config = {
    system = {
      activationScripts.secrets = {
        deps = [ "users" "groups" ];
        supportsDryActivation = false; # TODO
        text =
          let
            readPassword = password: "cat ${lib.strings.escapeShellArg (passwordStorePath password)}";
            # Using awk's ENVIRON so it should resist any input?
            pipeSubstitute = k: v: ''K=${lib.strings.escapeShellArg k} V="$(${v})" awk '{ gsub (ENVIRON["K"], ENVIRON["V"]); print }' '';
            subsitutePassword = variable: password: pipeSubstitute variable (readPassword password);
            subsitutePasswordFile = passwordFile: lib.mapAttrsToList subsitutePassword passwordFile.passwords;
            renderPasswordFile = passwordFile: "${lib.strings.concatStringsSep "| " (subsitutePasswordFile passwordFile)} < ${passwordFile.template}";
            installPasswordFile = passwordFile: ''
              install -C -o ${passwordFile.owner} -g ${passwordFile.group} -m ${passwordFile.mode} -d ${builtins.dirOf passwordFile.path}
              temp="$(mktemp)"
              trap 'rm "$temp"' ERR
              ${renderPasswordFile passwordFile} > "$temp"
              install -C -o ${passwordFile.owner} -g ${passwordFile.group} -m ${passwordFile.mode} -T "$temp" ${passwordFile.path}
              rm "$temp"
              trap - ERR
            '';
            installPasswordFileApp = passwordFile: pkgs.writeShellApplication {
              name = builtins.replaceStrings ["/"] ["_"] passwordFile.path;
              runtimeInputs = with pkgs; [ gawk ];
              text = installPasswordFile passwordFile;
            };
            installPasswordFileSandboxed = passwordFile:
              ''${lib.getExe (installPasswordFileApp passwordFile)} || echo Failed to install ${lib.strings.escapeShellArg passwordFile.path}'';
          in
          ''
            echo Installing secrets...
            ${lib.strings.concatLines (builtins.map installPasswordFileSandboxed passwordFiles)}
          '';
      };
      extraSystemBuilderCmds =
        let
          passwords = builtins.attrValues config.vivarium.passwords;
          readPasswordClear = password: "pass show ${lib.strings.escapeShellArg password.path}" + (
            if password.selector == null
            then " | head -n1"
            else
              (if password.selector == "@"
              then ""
              else " | tail -n +2 | yq -r '.${password.selector}'")
          );
          readPassword = password: (readPasswordClear password) + (lib.strings.optionalString (password.transform != null) " | ${password.transform}");
          gitPath = password: ''"$PASSWORD_STORE_DIR"/${lib.strings.escapeShellArg password.path}.gpg'';
          isGeneratedPassword = password: ''test -f ${gitPath password}'';
          dateGit = password: " " + ''(cd "$(dirname ${gitPath password})"; git log -n1 --format='format:%ct' "$(basename ${gitPath password})")'' + " ";
          dateStore = password: ''sudo stat -c '%Y' ${passwordStorePath password}'';
          isInStore = password: ''sudo test -f ${passwordStorePath password}'';
          testCanGenerate = password: lib.asserts.assertMsg (builtins.elem password.selector [ "@" null ]) "Unimplemented: generator + selector ${describePassword password}";
          generatePassword = password: assert testCanGenerate password; ''${password.generator} | pass insert -m ${lib.strings.escapeShellArg password.path}'';
          raiseCantGenerate = password: ''echo "Error: no generator" ; exit 1'';
          syncPasswordStore = password: ''
            # ${describePassword password}
            write=false
            if ${isInStore password}
            then
              if ${isGeneratedPassword password}
              then
                date_store="$(${dateStore password})"
                date_git="$(${dateGit password})"
                if [ "$date_git" -eq "$date_store" ]
                then
                  echo ${lib.strings.escapeShellArg (describePassword password)}: up-to-date
                elif [ "$date_git" -gt "$date_store" ]
                then
                  echo ${lib.strings.escapeShellArg (describePassword password)}: updating
                  write=true
                else
                  echo ERROR ${lib.strings.escapeShellArg (describePassword password)}: store is more recent than git
                  exit 1
                fi
              else
                echo ERROR ${lib.strings.escapeShellArg (describePassword password)}: exists in store but not in git
                exit 1
              fi
            else
              if ${isGeneratedPassword password}
              then
                echo ${lib.strings.escapeShellArg (describePassword password)}: installing
              else
                echo ${lib.strings.escapeShellArg (describePassword password)}: generating
                ${(if password.generator != null then generatePassword else raiseCantGenerate) password}
              fi
              write=true
            fi
            if [ "$write" = true ]
            then
              temp="$(mktemp)"
              trap 'rm "$temp"' ERR
              ${readPassword password} > "$temp"
              touch -d @"$(${dateGit password})" "$temp"
              sudo install -o root -g root -m u=rw -p -T "$temp" ${lib.strings.escapeShellArg (passwordStorePath password)}
              rm "$temp"
              trap - ERR
            fi
          '';
          allFilenames = builtins.map (password: "${passwordStoreDir}/${passwordHash password}") passwords;
        in
        ''
          ln -s ${lib.getExe (pkgs.writeShellApplication {
            name = "update-password-store";
            text = ''
              test -d "$PASSWORD_STORE_DIR"
              sudo install -C -o root -g root -m u=rwx -d "${passwordStoreDir}"

              ${lib.strings.concatLines (builtins.map syncPasswordStore passwords)}

              comm -23 <(sudo find ${passwordStoreDir} -type f | sort) <(echo ${lib.strings.escapeShellArg (lib.strings.concatLines allFilenames)} | sort) | while read -r file
              do
                echo Removing "$file" from password store
                sudo rm "$file"
              done
            '';
          })} $out/bin/
        '';
    };
    vivarium.passwords =
      let
        passwordsList = lib.lists.flatten (map (f: builtins.attrValues f.passwords) passwordFiles);
        passwordsAttrs = map (password: { ${passwordHash password} = password; }) passwordsList;
      in
      lib.attrsets.mergeAttrsList passwordsAttrs;
  };
  options = {
    # Using vivarium because that's where it's from, and we don't want it in home manager's frogeye
    # TODO Make this cleaner, merge the two, somehow
    vivarium =
      let
        defaultvar = "@PASSWORD@";
        passwordSubmodule = lib.types.submodule ({ ... }: {
          options = {
            path = lib.mkOption {
              type = lib.types.str;
              description = "Path to the password store entry";
            };
            selector = lib.mkOption {
              type = lib.types.nullOr lib.types.str;
              default = null;
              description = "If unset, selects the first line. If '@', select everything. If any other value, will parse the password metadata as YML and use selector (yq).";
            };
            generator = lib.mkOption {
              type = lib.types.nullOr lib.types.str;
              default = "${lib.getExe pkgs.pwgen} -s 32";
              description = "Command to generate the password. Won't work when selector is set to read metadata.";
            };
            transform = lib.mkOption {
              type = lib.types.nullOr lib.types.str;
              default = null;
              description = "Shell command to transform the password with before substitution";
            };
          };
        });
      in
      {
        passwords = lib.mkOption {
          default = { };
          type = lib.types.attrsOf passwordSubmodule;
        };
        passwordFiles =
          lib.mkOption {
            default = { };
            type = lib.types.attrsOf (lib.types.submodule ({ name, config, ... }: {
              options = {
                path = lib.mkOption {
                  type = lib.types.str;
                  default = name;
                  description = "Where to place the file.";
                };
                mode = lib.mkOption {
                  type = lib.types.str;
                  default = "0400";
                  description = "Unix permission";
                };
                owner = lib.mkOption {
                  type = lib.types.str;
                  default = "root";
                  description = "Owner of the secret file";
                };
                group = lib.mkOption {
                  type = lib.types.str;
                  default = "root";
                  description = "Group of the secret file";
                };
                text = lib.mkOption {
                  type = lib.types.str;
                  default = defaultvar;
                  description = "Content of the template used to make the file. Exclusive with `template`.";
                };
                template = lib.mkOption {
                  type = lib.types.path;
                  default = pkgs.writeText "password-template" config.text;
                  description = "Content of the template used to make the file. Exclusive with `text`.";
                };
                passwords = lib.mkOption {
                  default = lib.optionalAttrs (config.password != null) { ${defaultvar} = config.password; };
                  type = lib.types.attrsOf passwordSubmodule;
                  description = "Paths to passwords that will substitute the variables in the template. Exclusive with `password`";
                };
                password = lib.mkOption {
                  type = passwordSubmodule;
                  description = "Path to password that will substitute '@PASSWORD@' in the template. Exclusive with `passwords`.";
                };
              };
            }));
          };
      };
  };
}