# this module is heavily inspired by a home-manager module
# created by @piousdeer, although improved and slightly simplified.
# see: https://gist.github.com/piousdeer/b29c272eaeba398b864da6abf6cb5daa
{ config, lib, ... }:

let
  inherit (lib)
    hm
    types
    assertMsg
    mkOption
    escapeShellArg
    splitString
    recursiveUpdate
    setAttrByPath
    concatLines
    ;

  optionPathsToExtend = [
    "home.file"
    "xdg.configFile"
    "xdg.dataFile"
    "xdg.stateFile"
  ];
in
{
  options =
    let
      # like `mergeAttrsList`, but doesn't overwrite deep paths,
      # adding to the inner attrsets instead.
      recursiveMergeAttrsList = builtins.foldl' recursiveUpdate { };

      path = p: splitString "." p;

      mutableOption = mkOption {
        type = types.attrsOf (
          types.submodule {
            options.mutable = mkOption {
              type = types.bool;
              default = false;
              description = ''
                Instead of linking from this file to the nix store,
                copy the contents to the path directly, thus making
                the file writable to programs.
                Requires the `force` option to be true.
              '';
            };
          }
        );
      };
    in
    recursiveMergeAttrsList (map (p: setAttrByPath (path p) mutableOption) optionPathsToExtend);

  config = {
    home.activation.overwriteMutableFiles = hm.dag.entryAfter [ "linkGeneration" ] (
      let
        # all xdg files end up inside the normal `home.file`
        # list either way, we don't have to look into the others.
        cfg = config.home.file // config.xdg.configFile;
        allFiles = builtins.attrValues cfg;
        mutableFiles = builtins.filter (
          f: (f.mutable or false) && assertMsg f.force "`mutable` also requires `force` to be set to true"
        ) allFiles;

        copyFileCommand =
          { source, target, ... }:
          ''
            run cp $VERBOSE_ARG --remove-destination --no-preserve=mode \
              ${escapeShellArg source} ${escapeShellArg target} \
              || errorEcho "Overwriting mutable file '${escapeShellArg target}' failed!"
          '';
      in
      ''
        ${config.lib.bash.initHomeManagerLib}

        verboseEcho "Overwriting symlinks with mutable files"
        ${concatLines (map copyFileCommand mutableFiles)}
      ''
    );
  };
}