{
  description                  = "a sisu like parser & document generator";
  inputs.nixpkgs.url           = "github:NixOS/nixpkgs/nixpkgs-unstable"; # "github:nixos/nixpkgs"; "github:NixOS/nixpkgs/nixpkgs-unstable"; "nixpkgs/nixos-unstable"; "nixpkgs/nixos-21.11";
  inputs.flake-utils.url       = "github:numtide/flake-utils";
  outputs = { self, nixpkgs, flake-utils } @inputs:
    let
      pname                    = "spine";
      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.
      checkPhase = ''
        runHook preCheck
        dub test --combined --skip-registry=all
        runHook postCheck
      '';
      installPhase = ''
        runHook preInstall
        mkdir -p $out/bin
        install -m755 ./bin/spine $out/bin/spine
        runHook postInstall
      '';
      postInstall = ''
        echo `ls -la $out/bin/spine`
        $out/bin/spine -v
      '';
    in {
      packages = forAllSystems (system:
        let pkgs               = nixpkgsFor.${system};
        in with pkgs; {
          default = stdenv.mkDerivation {
            inherit pname;
            inherit version;
            meta.mainProgram   = "spine";
            executable         = true;
            src                = self;
            inherit shell;
            inherit devEnv;
            buildInputs        = [ sqlite ];
            nativeBuildInputs  = [ dub dmd ldc gdc gnumake ]; # [ dub dmd ]; [ dub ldc ]; [ dub gdc ];
            buildPhase = ''
              runHook preBuild
              for DC_ in dmd ldmd2 ldc2 gdc gdmd; do
                echo "- check for D compiler $DC_"
                DC=$(type -P $DC_ || echo "")
                if [ ! "$DC" == "" ]; then break; fi
              done
              if [ "$DC" == "" ]; then exit "Error: could not find D compiler"; fi
              echo "$DC_ used as D compiler to build $pname"
              dub build --compiler=$DC --build=$DC_ --combined --skip-registry=all
              runHook postBuild
            '';
            inherit checkPhase;
            inherit installPhase;
            inherit postInstall;
          };
          spine-dmd = stdenv.mkDerivation {
            inherit pname;
            inherit version;
            meta.mainProgram   = "spine-dmd";
            executable         = true;
            src                = self;
            inherit shell;
            inherit devEnv;
            buildInputs        = [ sqlite ];
            nativeBuildInputs  = [ dub dmd gnumake ];
            buildPhase = ''
              runHook preBuild
              dub build --compiler=$(type -P dmd) --build=dmd --combined --skip-registry=all
              runHook postBuild
            '';
            inherit checkPhase;
            inherit installPhase;
            inherit postInstall;
          };
          spine-ldc = stdenv.mkDerivation {
            inherit pname;
            inherit version;
            meta.mainProgram   = "spine-ldc";
            executable         = true;
            src                = self;
            inherit shell;
            inherit devEnv;
            buildInputs        = [ sqlite ];
            nativeBuildInputs  = [ dub ldc gnumake ];
            buildPhase = ''
              runHook preBuild
              dub build --compiler=$(type -P ldc2) --build=ldc2 --combined --skip-registry=all
              runHook postBuild
            '';
            inherit checkPhase;
            inherit installPhase;
            inherit postInstall;
          };
          spine-gdc = stdenv.mkDerivation {
            inherit pname;
            inherit version;
            meta.mainProgram   = "spine-gdc";
            executable         = true;
            src                = self;
            inherit shell;
            inherit devEnv;
            buildInputs        = [ sqlite ];
            nativeBuildInputs  = [ dub gdc gnumake ];
            buildPhase = ''
              runHook preBuild
              dub build --compiler=$(type -P gdc) --build=gdc --combined --skip-registry=all
              runHook postBuild
            '';
            inherit checkPhase;
            inherit installPhase;
            inherit postInstall;
          };
          #vendorSha256 = "sha256-0Q00000000000000000000000000000000000000000=";
      });
      apps = forAllSystems (system: {
        default = {
          type                 = "app";
          program              = "${self.packages.${system}.default}/bin/spine";
        };
      });
      devShells = forAllSystems (system:
        let
          pkgs = nixpkgsFor.${system};
          shellHook = ''
            export DFLAGS="-O2 -inline -boundscheck=on -color=on"
            export Date=`date "+%Y%m%d"`
            export SpineVER=$(git describe --long --tags | sed 's/^[ a-z_-]\+\([0-9.]\+\)/\1/;s/\([^-]*-g\)/r\1/;s/-/./g')
            ### 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=$SpineDOC/markup/pod
            export SpineOUTversioned=$SpineOUT/$SpineVER
            export SpineSearchActionLocal='http://localhost/spine_search'
            # export SpineSearchActionRemote='https://sisudoc.org/spine_search'
            export SpineCGIform='spine_search'
            export SpineSQLdb='spine.search.db'
            export PROG_VER_GIT="`git describe --long --tags | sed -e 's/^[ a-z_-]\+\([0-9.]\+\)/\1/;s/\([^-]*-g\)/r\1/;s/-/./g'`"
            export PROG_VER_DECLARED="`cat ./views/version.txt | grep --color=never "enum" | sed 's/.\+(\([0-9]\+\),[ \t]\+\([0-9]\+\),[ \t]\+\([0-9]\+\)[ \t]*).\+/\1.\2.\3/g'`"
            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 rec {
            name = "spine dev shell default";
            inherit shell;
            inherit devEnv;
            #buildInputs        = [ sqlite ];
            #nativeBuildInputs  = [ dub dmd ldc gdc gnumake ];
            packages     = [
              sqlite
              dub dmd ldc gdc gnumake
            ];
            inherit shellHook;
          };
          devShell-epub = mkShell rec {
            name = "spine dev shell for epub output";
            inherit shell;
            inherit devEnv;
            packages     = [
              dub dmd ldc gdc 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 rec {
            name = "spine dev shell for latex & pdf output";
            inherit shell;
            inherit devEnv;
            packages     = [
              dub dmd ldc gdc gnumake
              sqlite
            ];
            inherit shellHook;
          };
          devShell-latex-pdf = mkShell rec {
            name = "spine dev shell for latex & pdf output";
            inherit shell;
            inherit devEnv;
            packages     = [
              dub dmd ldc gdc gnumake
              sqlite
              source-sans-pro
              source-serif-pro
              source-code-pro
              texlive.combined.scheme-full
            ];
            inherit shellHook;
          };
          devShell-sqlite = mkShell rec {
            name = "spine dev shell for latex & pdf output";
            inherit shell;
            inherit devEnv;
            packages     = [
              dub dmd ldc gdc gnumake
              sqlite
            ];
            inherit shellHook;
          };
          devShell-i18n = mkShell {
            inherit shell;
            inherit devEnv;
            packages     = [
              dub dmd ldc gdc gnumake
              sqlite
              perl534Packages.Po4a
            ];
            inherit shellHook;
          };
      });
  };
}