module-options.nix

{ config
, lib
, pkgs
, ...
}:
let
  inherit (lib) mkOption mkPackageOption types;

  # A new kind of option type that calls lib.getExe on derivations
  exeType = lib.mkOptionType {
    name = "exe";
    description = "Path to executable";
    check = x: lib.isString x || builtins.isPath x || lib.isDerivation x;
    merge = loc: defs:
      let
        res = lib.mergeOneOption loc defs;
      in
      if lib.isString res || builtins.isPath res
      then "${res}"
      else lib.getExe res;
  };

  # The schema of the treefmt.toml data structure.
  configSchema = {
    global = {
      excludes = mkOption {
        description = "A global list of paths to exclude. Supports glob.";
        type = types.listOf types.str;
        default = [ ];
        example = [ "./node_modules/**" ];
      };
    };

    formatter = mkOption {
      type = types.attrsOf (types.submodule [
        {
          options = {
            command = mkOption {
              description = "Executable obeying the treefmt formatter spec";
              type = exeType;
            };

            options = mkOption {
              description = "List of arguments to pass to the command";
              type = types.listOf types.str;
              default = [ ];
            };

            includes = mkOption {
              description = "List of files to include for formatting. Supports globbing.";
              type = types.listOf types.str;
            };

            excludes = mkOption {
              description = "List of files to exclude for formatting. Supports globbing. Takes precedence over the includes.";
              type = types.listOf types.str;
              default = [ ];
            };
          };
        }
      ]);
      default = { };
      description = "Set of formatters to use";
    };
  };

  configFormat = pkgs.formats.toml { };
in
{
  # Schema
  options = {
    # Represents the treefmt.toml config
    settings = configSchema;

    package = mkPackageOption pkgs "treefmt" { };

    projectRootFile = mkOption {
      description = ''
        File to look for to determine the root of the project in the
        build.wrapper.
      '';
      example = "flake.nix";
    };

    # Outputs
    build = {
      devShell = mkOption {
        description = "The development shell with treefmt and its underlying programs";
        type = types.package;
        readOnly = true;
      };
      configFile = mkOption {
        description = ''
          Contains the generated config file derived from the settings.
        '';
        type = types.path;
      };
      wrapper = mkOption {
        description = ''
          The treefmt package, wrapped with the config file.
        '';
        type = types.package;
        defaultText = lib.literalMD "wrapped `treefmt` command";
        default =
          let
            x = pkgs.writeShellScriptBin "treefmt" ''
              set -euo pipefail
              find_up() {
                ancestors=()
                while true; do
                  if [[ -f $1 ]]; then
                    echo "$PWD"
                    exit 0
                  fi
                  ancestors+=("$PWD")
                  if [[ $PWD == / ]] || [[ $PWD == // ]]; then
                    echo "ERROR: Unable to locate the projectRootFile ($1) in any of: ''${ancestors[*]@Q}" >&2
                    exit 1
                  fi
                  cd ..
                done
              }
              tree_root=$(find_up "${config.projectRootFile}")
              exec ${config.package}/bin/treefmt --config-file ${config.build.configFile} "$@" --tree-root "$tree_root"
            '';
          in
          (x // { meta = config.package.meta // x.meta; });
      };
      programs = mkOption {
        type = types.attrsOf types.package;
        description = ''
          Attrset of formatter programs enabled in treefmt configuration.

          The key of the attrset is the formatter name, with the value being the
          package used to do the formatting.
        '';
        defaultText = lib.literalMD "Programs used in configuration";
        default =
          pkgs.lib.concatMapAttrs
            (k: v:
              if v.enable
              then { "${k}" = v.package; }
              else { })
            config.programs;
      };
      check = mkOption {
        description = ''
          Create a flake check to test that the given project tree is already
          formatted.

          Input argument is the path to the project tree (usually 'self').
        '';
        type = types.functionTo types.package;
        defaultText = lib.literalMD "Default check implementation";
        default = self:
          pkgs.runCommandLocal "treefmt-check"
            {
              buildInputs = [ pkgs.git config.build.wrapper ];
              meta.description = "Check that the project tree is formatted";
            }
            ''
              set -e
              # `treefmt --fail-on-change` is broken for purs-tidy; So we must rely
              # on git to detect changes. An unintended advantage of this approach
              # is that when the check fails, it will print a helpful diff at the end.
              PRJ=$TMP/project
              cp -r ${self} $PRJ
              chmod -R a+w $PRJ
              cd $PRJ
              export HOME=$TMPDIR
              cat > $HOME/.gitconfig <<EOF
              [user]
                name = Nix
                email = nix@localhost
              [init]
                defaultBranch = main
              EOF
              git init
              git add .
              git commit -m init --quiet
              export LANG=C.UTF-8
              export LC_ALL=C.UTF-8
              treefmt --version
              treefmt --no-cache
              git status
              git --no-pager diff --exit-code
              touch $out
            '';
      };
    };
  };

  # Config
  config.build = {
    configFile = configFormat.generate "treefmt.toml" config.settings;
    devShell = pkgs.mkShell {
      nativeBuildInputs = [ config.build.wrapper ] ++ (lib.attrValues config.build.programs);
    };
  };
}