nixpkgs/lib/strings-with-deps.nix

{ lib }:
/*
  Usage:

    You define you custom builder script by adding all build steps to a list.
    for example:
         builder = writeScript "fsg-4.4-builder"
                 (textClosure [doUnpack addInputs preBuild doMake installPhase doForceShare]);

    a step is defined by noDepEntry, fullDepEntry or packEntry.
    To ensure that prerequisite are met those are added before the task itself by
    textClosureDupList. Duplicated items are removed again.

    See trace/nixpkgs/trunk/pkgs/top-level/builder-defs.nix for some predefined build steps

    Attention:

    let
      pkgs = (import <nixpkgs>) {};
    in let
      inherit (pkgs.stringsWithDeps) fullDepEntry packEntry noDepEntry textClosureMap;
      inherit (pkgs.lib) id;

      nameA = noDepEntry "Text a";
      nameB = fullDepEntry "Text b" ["nameA"];
      nameC = fullDepEntry "Text c" ["nameA"];

      stages = {
        nameHeader = noDepEntry "#! /bin/sh \n";
        inherit nameA nameB nameC;
      };
    in
      textClosureMap id stages
      [ "nameHeader" "nameA" "nameB" "nameC"
        nameC # <- added twice. add a dep entry if you know that it will be added once only [1]
        "nameB" # <- this will not be added again because the attr name (reference) is used
      ]

    # result: Str("#! /bin/sh \n\nText a\nText b\nText c\nText c",[])

    [1] maybe this behaviour should be removed to keep things simple (?)
*/

let
  inherit (lib)
    concatStringsSep
    head
    isAttrs
    listToAttrs
    tail
    ;
in
rec {

  /*
    !!! The interface of this function is kind of messed up, since
    it's way too overloaded and almost but not quite computes a
    topological sort of the depstrings.
  */

  textClosureList =
    predefined: arg:
    let
      f =
        done: todo:
        if todo == [ ] then
          {
            result = [ ];
            inherit done;
          }
        else
          let
            entry = head todo;
          in
          if isAttrs entry then
            let
              x = f done entry.deps;
              y = f x.done (tail todo);
            in
            {
              result = x.result ++ [ entry.text ] ++ y.result;
              done = y.done;
            }
          else if done ? ${entry} then
            f done (tail todo)
          else
            f (
              done
              // listToAttrs [
                {
                  name = entry;
                  value = 1;
                }
              ]
            ) ([ predefined.${entry} ] ++ tail todo);
    in
    (f { } arg).result;

  textClosureMap =
    f: predefined: names:
    concatStringsSep "\n" (map f (textClosureList predefined names));

  noDepEntry = text: {
    inherit text;
    deps = [ ];
  };
  fullDepEntry = text: deps: { inherit text deps; };
  packEntry = deps: {
    inherit deps;
    text = "";
  };

  stringAfter = deps: text: { inherit text deps; };

}