{ depot, pkgs, lib, ... }:

let
  bins = depot.nix.getBins pkgs.s6-portable-utils [ "s6-ln" "s6-ls" "s6-touch" ]
    ;

  linkTo = name: path: depot.nix.runExecline.local name {} [
    "importas" "out" "out"
    bins.s6-ln "-s" path "$out"
  ];

  # Build a rust executable, $out is the executable.
  rustSimple = args@{name, ...}: src:
    linkTo name "${rustSimpleBin args src}/bin/${name}";

  # Like `rustSimple`, but put the binary in `$out/bin/`.
  rustSimpleBin = {
    name,
    dependencies ? [],
    doCheck ? true,
  }: src:
    (if doCheck then testRustSimple else pkgs.lib.id)
    (pkgs.buildRustCrate ({
      pname = name;
      version = "1.0.0";
      crateName = name;
      crateBin = [ name ];
      dependencies = dependencies;
      src = pkgs.runCommandLocal "write-main.rs" {
        src = src;
        passAsFile = [ "src" ];
      } ''
        mkdir -p $out/src/bin
        cp "$srcPath" $out/src/bin/${name}.rs
        find $out
      '';
    }));

  # Build a rust library, that can be used as dependency to `rustSimple`.
  # Wrapper around `pkgs.buildRustCrate`, takes all its arguments.
  rustSimpleLib = {
    name,
    dependencies ? [],
    doCheck ? true,
  }: src:
    (if doCheck then testRustSimple else pkgs.lib.id)
    (pkgs.buildRustCrate ({
      pname = name;
      version = "1.0.0";
      crateName = name;
      dependencies = dependencies;
      src = pkgs.runCommandLocal "write-lib.rs" {
        src = src;
        passAsFile = [ "src" ];
      } ''
        mkdir -p $out/src
        cp "$srcPath" $out/src/lib.rs
        find $out
      '';
    }));

  /* Takes a `buildRustCrate` derivation as an input,
    * builds it with `{ buildTests = true; }` and runs
    * all tests found in its `tests` dir. If they are
    * all successful, `$out` will point to the crate
    * built with `{ buildTests = false; }`, otherwise
    * it will fail to build.
    *
    * See also `nix.drvSeqL` which is used to implement
    * this behavior.
    */
  testRustSimple = rustDrv:
    let
      crate = buildTests: rustDrv.override { inherit buildTests; };
      tests = depot.nix.runExecline.local "${rustDrv.name}-tests-run" {} [
        "importas" "out" "out"
        "if" [
          "pipeline" [ bins.s6-ls "${crate true}/tests" ]
          "forstdin" "-o0" "test"
          "importas" "test" "test"
          "${crate true}/tests/$test"
        ]
        bins.s6-touch "$out"
      ];
    in depot.nix.drvSeqL [ tests ] (crate false);

in {
  inherit
    rustSimple
    rustSimpleBin
    rustSimpleLib
    ;
}