{
  description                  = "spine (sisu like parser & document generator) made available to process markup samples";
  inputs = {
    nixpkgs.url                = "github:NixOS/nixpkgs/nixpkgs-unstable"; # "github:nixos/nixpkgs";
    flake-utils.url            = "github:numtide/flake-utils";
    spine.url                  = "git+file:///home/ralph/grotto/repo/git.repo/projects/doc-reform/code/software/spine";
    spine.inputs.nixpkgs.follows = "nixpkgs";
    spine.flake                = true;
  };
  outputs = { self, nixpkgs, flake-utils, spine } @inputs:
    let
      version                  = "0.12.0";
      shell                    = ./shell.nix; # ./default.nix;
      devEnv                   = ./.envrc; # ./shell.nix; # ./default.nix;
      supportedSystems         = [ "x86_64-linux" ]; # [ "x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin" ];
      forAllSystems            = nixpkgs.lib.genAttrs supportedSystems;
      nixpkgsFor               = forAllSystems (system: import nixpkgs { inherit system;  }); # nixpkgs instantiated for supported system types.
    in {
      packages = forAllSystems (system:
        let pkgs               = nixpkgsFor.${system};
        in {
          default              = spine.packages.${system}.default;
          spine-dmd            = spine.packages.${system}.spine-dmd;
          spine-ldc            = spine.packages.${system}.spine-ldc;
          #spine-gdc            = spine.packages.${system}.spine-gdc;
          #vendorSha256         = "sha256-0Q00000000000000000000000000000000000000000=";
      });
      apps = forAllSystems (system: {
        default = {
          type                 = "app";
          program              = "${self.packages.${system}.default}/bin/spine";
        };
      });
      devShells = forAllSystems (system:
        let
          pkgs = nixpkgsFor.${system};
          shellHook = ''
            export DFLAGS="-O2 -inline -boundscheck=on -color=on"
            export Date=`date "+%Y%m%d"`
            ### set local values in .envrc-local (or modify here if you must)
            # export SpinePROJ=~/grotto/repo/git.repo/projects/doc-reform/code/software/spine
            # export SpineDOC=~/grotto/repo/git.repo/projects/project-spine/doc-reform-markup/spine-markup-samples
            # export SpineOUT=/srv/www/spine
            export SpineDBpath=/var/www/sqlite
            # export SpineDBpath=/srv/www/spine/sqlite
            export SpineSRC=$SpinePROJ/src
            export SpineBIN=$SpinePROJ/result/bin
            export SpinePOD=$SpineDOC/markup/pod
            export SpineSearchActionLocal='http://localhost/spine_search'
            export SpineSearchActionRemote='https://sisudoc.org/spine_search'
            export SpineCGIform='spine_search'
            export SpineSQLdb='spine.search.db'
            export spineNixHelp="cat ./.env/nix-commands"
            export spineTest="nix shell .#default --print-build-logs --command spine --very-verbose --epub --html --html-link-search --html-link-curate --curate --output=\"\$SpineOUT\" $SpinePOD/*"
            export spineHtml="spine --very-verbose --html --html-link-search --html-link-curate --curate --sqlite-update --sqlite-db-filename=\"spine.search.db\" --cgi-sqlite-search-filename=\"spine_search\" --sqlite-db-path=\"\$SpineDBpath\" --output=\"\$SpineOUT\" $SpinePOD/*"
            export spineEpub="spine --very-verbose --epub --output=\"\$SpineOUT\" $SpinePOD/*"
            export spineLatex="spine --very-verbose --latex --output=\"\$SpineOUT\" $SpinePOD/*"
            export spinePdf="spine --very-verbose --pdf --output=\"\$SpineOUT\" $SpinePOD/*"
            export spineSqliteCreateDB="spine --very-verbose --sqlite-db-recreate --sqlite-db-path=\"$SpineDBpath\" --sqlite-db-filename=\"spine.search.db\""
            export spineSqlite="spine --very-verbose --sqlite-discrete --sqlite-db-path=\"$SpineDBpath\" --sqlite-db-filename=\"spine.search.db\" --output=\"\$SpineOUT\" $SpinePOD/*"
            #export spineSqlite="spine --very-verbose --sqlite-update --sqlite-db-path=\"$SpineDBpath\" --sqlite-db-filename=\"spine.search.db\" --output=\"\$SpineOUT\" $SpinePOD/*"
          '';
        in with pkgs; {
          devShell = mkShell {
            name               = "spine base dev shell";
            inherit shell;
            inherit devEnv;
            #buildInputs        = [ sqlite ];
            #nativeBuildInputs  = [ dub dmd ldc gdc gnumake ];
            packages     = [
              sqlite
              dub dmd ldc gnumake
            ];
            inherit shellHook;
          };
          devShell-epub = mkShell {
            name               = "spine dev shell for epub output";
            inherit shell;
            inherit devEnv;
            packages = [
              dub dmd ldc gnumake
              sqlite
              libxml2
              html-tidy
              xmlstarlet
              epubcheck
              ebook_tools
              libxml2
              html-tidy
              xmlstarlet
              epubcheck
              ebook_tools
              epr
              sigil
              calibre #(suite includes: ebook-viewer)
              foliate
            ];
            inherit shellHook;
          };
          devShell-html = mkShell {
            name               = "spine dev shell for latex & pdf output";
            inherit shell;
            inherit devEnv;
            packages = [
              dub dmd ldc gnumake
              sqlite
            ];
            inherit shellHook;
          };
          devShell-latex-pdf = mkShell {
            name               = "spine dev shell for latex & pdf output";
            inherit shell;
            inherit devEnv;
            packages = [
              dub dmd ldc gnumake
              sqlite
              source-sans-pro
              source-serif-pro
              source-code-pro
              texlive.combined.scheme-full
            ];
            inherit shellHook;
          };
          devShell-sqlite = mkShell {
            name               = "spine dev shell for latex & pdf output";
            inherit shell;
            inherit devEnv;
            packages = [
              dub dmd ldc gnumake
              sqlite
            ];
            inherit shellHook;
          };
          devShell-i18n = mkShell {
            name               = "spine dev shell internationalization, po4a";
            inherit shell;
            inherit devEnv;
            packages = [
              dub dmd ldc gnumake
              sqlite
              perl534Packages.Po4a
            ];
            inherit shellHook;
          };
          default = import ./shell.nix { inherit pkgs; };
      });
  };
}