# idea: provide a build environments for your developement of preference
/*
  #### examples of use: ####
  # Add this to your ~/.nixpkgs/config.nix:
  {
    packageOverrides = pkgs : with pkgs; {
      sdlEnv = pkgs.myEnvFun {
          name = "sdl";
          buildInputs = [ stdenv SDL SDL_image SDL_ttf SDL_gfx cmake SDL_net  pkgconfig];
      };
    };
  }

  # Then you can install it by:  
  #  $ nix-env -i env-sdl
  # And you can load it simply calling:  
  #  $ load-env-sdl
  # and this will update your env vars to have 'make' and 'gcc' finding the SDL
  # headers and libs.


  ##### Another example, more complicated but achieving more: #######
  # Make an environment to build nix from source and create ctags (tagfiles can
  # be extracted from TAG_FILES) from every source package. Here would be a
  # full ~/.nixpkgs/config.nix
  {
    packageOverrides = pkgs : with pkgs; with sourceAndTags;
    let complicatedMyEnv = { name, buildInputs ? [], cTags ? [], extraCmds ? ""}:
            pkgs.myEnvFun {
              inherit name;
            buildInputs = buildInputs 
                  ++ map (x : sourceWithTagsDerivation
                    ( (addCTaggingInfo x ).passthru.sourceWithTags ) ) cTags;
            extraCmds = ''
              ${extraCmds}
              HOME=${builtins.getEnv "HOME"}
              . ~/.bashrc
            '';
          };
    in rec {
      # this is the example we will be using
      nixEnv = complicatedMyEnv {
        name = "nix";
        buildInputs = [ libtool stdenv perl curl bzip2 openssl db45 autoconf automake zlib ];
      };
    };
  }

  # Now we should build our newly defined custom environment using this command on a shell, so type:
  #  $ nix-env -i env-nix

  # You can load the environment simply typing a "load-env-${name}" command.
  #  $ load-env-nix
  # The result using that command should be:
  #  env-nix loaded
  and show you a shell with a prefixed prompt.
*/

{ mkDerivation, substituteAll, pkgs }:
    { stdenv ? pkgs.stdenv, name, buildInputs ? []
    , propagatedBuildInputs ? [], gcc ? stdenv.gcc, cTags ? [], extraCmds ? ""
    , shell ? "${pkgs.bashInteractive}/bin/bash"}:

mkDerivation {
  # The setup.sh script from stdenv will expect the native build inputs in
  # the buildNativeInputs environment variable.
  buildNativeInputs = [ ] ++ buildInputs;
  # Trick to bypass the stdenv usual change of propagatedBuildInputs => propagatedNativeBuildInputs
  propagatedBuildInputs2 = propagatedBuildInputs;

  name = "env-${name}";
  phases = [ "buildPhase" "fixupPhase" ];
  setupNew = substituteAll {
    src = ../../stdenv/generic/setup.sh;
    initialPath= (import ../../stdenv/common-path.nix) { inherit pkgs; };
    inherit gcc;
  };

  buildPhase = ''
    set -x
    mkdir -p "$out/dev-envs" "$out/nix-support" "$out/bin"
    s="$out/nix-support/setup-new-modified"
    cp "$setupNew" "$s"
    # shut some warning up.., do not use set -e
    sed -e 's@set -e@@' \
        -e 's@assertEnvExists\s\+NIX_STORE@:@' \
        -e 's@trap.*@@' \
        -i "$s"
    cat >> "$out/dev-envs/''${name/env-/}" << EOF
      buildNativeInputs="$buildNativeInputs"
      propagatedBuildInputs="$propagatedBuildInputs2"
      # the setup-new script wants to write some data to a temp file.. so just let it do that and tidy up afterwards
      tmp="\$("${pkgs.coreutils}/bin/mktemp" -d)"
      NIX_BUILD_TOP="\$tmp"
      phases=
      # only do all the setup stuff in nix-support/*
      set +e
      # This prevents having -rpath /lib in NIX_LDFLAGS
      export NIX_NO_SELF_RPATH=1
      if [[ -z "\$ZSH_VERSION" ]]; then
        source "$s"
      else
        setopt interactivecomments
        # fix bash indirection
        # let's hope the bash arrays aren't used
        # substitute is using bash array, so skip it
        echo '
            setopt NO_BAD_PATTERN
            setopt NO_BANG_HIST
            setopt NO_BG_NICE
            setopt NO_EQUALS
            setopt NO_FUNCTION_ARGZERO
            setopt GLOB_SUBST
            setopt NO_HUP
            setopt INTERACTIVE_COMMENTS
            setopt KSH_ARRAYS
            setopt NO_MULTIOS
            setopt NO_NOMATCH
            setopt RM_STAR_SILENT
            setopt POSIX_BUILTINS
            setopt SH_FILE_EXPANSION
            setopt SH_GLOB
            setopt SH_OPTION_LETTERS
            setopt SH_WORD_SPLIT
          ' >> "\$tmp/script"
        sed -e 's/\''${!\([^}]*\)}/\''${(P)\1}/g' \
            -e 's/[[]\*\]//' \
            -e 's/substitute() {/ substitute() { return; /' \
            -e 's@PATH=\$@PATH=${pkgs.coreutils}/bin@' \
            "$s" >> "\$tmp/script"
        echo "\$tmp/script";
        source "\$tmp/script";
      fi
      rm -fr "\$tmp"
      ${extraCmds}
      export PATH
      echo $name loaded
    EOF

    mkdir -p $out/bin
    sed -e s,@shell@,${shell}, -e s,@myenvpath@,$out/dev-envs/${name}, \
      -e s,@name@,${name}, ${./loadenv.sh} > $out/bin/load-env-${name}
    chmod +x $out/bin/load-env-${name}
  '';
}