# NixOS module: automatic nushell completion generation from manpages
#
# Modeled on nixpkgs' programs/fish.nix completion generator.
# For each package in environment.systemPackages, a small derivation runs
# `inshellah manpage-dir` against its share/man directory. Results are merged
# into a single directory and placed in nushell's vendor autoload path.
#
# Usage in your NixOS configuration:
#
#   { pkgs, ... }: {
#     imports = [ ./path/to/inshellah/nix/module.nix ];
#     programs.inshellah.enable = true;
#     # Optionally add packages not in systemPackages:
#     # programs.inshellah.extraPackages = [ pkgs.kubectl ];
#   }

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

let
  cfg = config.programs.inshellah;

  # The inshellah binary — override this if you build from the local flake
  inshellahPkg = cfg.package;

  # Per-package derivation: run inshellah manpage-dir against a package's manpages
  generateCompletions = package:
    pkgs.runCommandLocal
      (let
        inherit (lib.strings) stringLength substring storeDir;
        storeLength = stringLength storeDir + 34;
        pathName = substring storeLength (stringLength package - storeLength) package;
      in
        (package.name or pathName) + "_nu-completions"
      )
      ({
        inherit package;
        nativeBuildInputs = [ inshellahPkg ];
      } // lib.optionalAttrs (package ? meta.priority) {
        meta.priority = package.meta.priority;
      })
      ''
        mkdir -p $out
        if [ -d "$package/share/man" ]; then
          inshellah manpage-dir "$package/share/man" > "$out/completions.nu" 2>/dev/null || true
          # Remove empty files
          find $out -empty -delete
        fi
      '';

in {
  options.programs.inshellah = {
    enable = lib.mkEnableOption "nushell completion generation from manpages via inshellah";

    package = lib.mkOption {
      type = lib.types.package;
      description = "The inshellah package to use for generating completions.";
    };

    extraPackages = lib.mkOption {
      type = lib.types.listOf lib.types.package;
      default = [];
      description = ''
        Additional packages to generate nushell completions from, beyond
        those in {option}`environment.systemPackages`.
      '';
    };

    generatedCompletionsPath = lib.mkOption {
      type = lib.types.str;
      default = "/share/nushell/vendor/autoload";
      description = ''
        Subdirectory within the merged environment where completion files
        are placed. The default matches nushell's vendor autoload convention
        (discovered via XDG_DATA_DIRS).
      '';
    };
  };

  config = lib.mkIf cfg.enable {
    # Merge all per-package completions into a single directory.
    # This path ends up in the system profile, and nushell discovers it
    # via XDG_DATA_DIRS -> $prefix/share/nushell/vendor/autoload/
    environment.pathsToLink = [ cfg.generatedCompletionsPath ];

    environment.systemPackages = [
      (pkgs.buildEnv {
        name = "nushell-generated-completions";
        ignoreCollisions = true;
        paths = map generateCompletions (
          config.environment.systemPackages ++ cfg.extraPackages
        );
        pathsToLink = [ "/" ];
        # Nest everything under the vendor autoload path
        postBuild = ''
          if [ -d "$out" ]; then
            tmp=$(mktemp -d)
            cp -r "$out/"* "$tmp/" 2>/dev/null || true
            rm -rf "$out/"*
            mkdir -p "$out${cfg.generatedCompletionsPath}"
            for f in "$tmp"/*.nu; do
              [ -f "$f" ] && cp "$f" "$out${cfg.generatedCompletionsPath}/"
            done
            rm -rf "$tmp"
          fi
        '';
      })
    ];
  };
}