{ lib, stdenv, resholve, binlore, writeTextFile }:

rec {
  /* These functions break up the work of partially validating the
    'solutions' attrset and massaging it into env/cli args.

    Note: some of the left-most args do not *have* to be passed as
    deep as they are, but I've done so to provide more error context
  */

  # for brevity / line length
  spaces = l: builtins.concatStringsSep " " l;
  colons = l: builtins.concatStringsSep ":" l;
  semicolons = l: builtins.concatStringsSep ";" l;

  /* Throw a fit with dotted attr path context */
  nope = path: msg:
    throw "${builtins.concatStringsSep "." path}: ${msg}";

  /* Special-case directive value representations by type */
  phraseDirective = solution: env: name: val:
    if builtins.isInt val then builtins.toString val
    else if builtins.isString val then name
    else if true == val then name
    else if false == val then "" # omit!
    else if null == val then "" # omit!
    else if builtins.isList val then "${name}:${semicolons (map lib.escapeShellArg val)}"
    else nope [ solution env name ] "unexpected type: ${builtins.typeOf val}";

  /* Build fake/fix/keep directives from Nix types */
  phraseDirectives = solution: env: val:
    lib.mapAttrsToList (phraseDirective solution env) val;

  /* Custom ~search-path routine to handle relative path strings */
  relSafeBinPath = input:
    if lib.isDerivation input then ((lib.getOutput "bin" input) + "/bin")
    else if builtins.isString input then input
    else throw "unexpected type for input: ${builtins.typeOf input}";

  /* Special-case value representation by type/name */
  phraseEnvVal = solution: env: val:
    if env == "inputs" then (colons (map relSafeBinPath val))
    else if builtins.isString val then val
    else if builtins.isList val then spaces val
    else if builtins.isAttrs val then spaces (phraseDirectives solution env val)
    else nope [ solution env ] "unexpected type: ${builtins.typeOf val}";

  /* Shell-format each env value */
  shellEnv = solution: env: value:
    lib.escapeShellArg (phraseEnvVal solution env value);

  /* Build a single ENV=val pair */
  phraseEnv = solution: env: value:
    "RESHOLVE_${lib.toUpper env}=${shellEnv solution env value}";

  /* Discard attrs:
  - claimed by phraseArgs
  - only needed for binlore.collect
  */
  removeUnneededArgs = value:
    removeAttrs value [ "scripts" "flags" "unresholved" ];

  /* Verify required arguments are present */
  validateSolution = { scripts, inputs, interpreter, ... }: true;

  /* Pull out specific solution keys to build ENV=val pairs */
  phraseEnvs = solution: value:
    spaces (lib.mapAttrsToList (phraseEnv solution) (removeUnneededArgs value));

  /* Pull out specific solution keys to build CLI argstring */
  phraseArgs = { flags ? [ ], scripts, ... }:
    spaces (flags ++ scripts);

  phraseBinloreArgs = value:
    let
      hasUnresholved = builtins.hasAttr "unresholved" value;
    in {
      drvs = value.inputs ++
        lib.optionals hasUnresholved [ value.unresholved ];
      strip = if hasUnresholved then [ value.unresholved ] else [ ];
    };

  /* Build a single resholve invocation */
  phraseInvocation = solution: value:
    if validateSolution value then
    # we pass resholve a directory
      "RESHOLVE_LORE=${binlore.collect (phraseBinloreArgs value) } ${phraseEnvs solution value} ${resholve}/bin/resholve --overwrite ${phraseArgs value}"
    else throw "invalid solution"; # shouldn't trigger for now

  injectUnresholved = solutions: unresholved: (builtins.mapAttrs (name: value: value // { inherit unresholved; } ) solutions);

  /* Build resholve invocation for each solution. */
  phraseCommands = solutions: unresholved:
    builtins.concatStringsSep "\n" (
      lib.mapAttrsToList phraseInvocation (injectUnresholved solutions unresholved)
    );

  /*
    subshell/PS4/set -x and : command to output resholve envs
    and invocation. Extra context makes it clearer what the
    Nix API is doing, makes nix-shell debugging easier, etc.
  */
  phraseContext = { invokable, prep ? ''cd "$out"'' }: ''
    (
      ${prep}
      PS4=$'\x1f'"\033[33m[resholve context]\033[0m "
      set -x
      : invoking resholve with PWD=$PWD
      ${invokable}
    )
  '';
  phraseContextForPWD = invokable: phraseContext { inherit invokable; prep = ""; };
  phraseContextForOut = invokable: phraseContext { inherit invokable; };

  phraseSolution = name: solution: (phraseContextForOut (phraseInvocation name solution));
  phraseSolutions = solutions: unresholved:
    phraseContextForOut (phraseCommands solutions unresholved);

  writeScript = name: partialSolution: text:
    writeTextFile {
      inherit name text;
      executable = true;
      checkPhase = ''
         ${(phraseContextForPWD (
             phraseInvocation name (
               partialSolution // {
                 scripts = [ "${placeholder "out"}" ];
               }
             )
           )
         )}
      '' + lib.optionalString (partialSolution.interpreter != "none") ''
        ${partialSolution.interpreter} -n $out
      '';
    };
  writeScriptBin = name: partialSolution: text:
    writeTextFile rec {
      inherit name text;
      executable = true;
      destination = "/bin/${name}";
      checkPhase = ''
        ${phraseContextForOut (
            phraseInvocation name (
              partialSolution // {
                scripts = [ "bin/${name}" ];
              }
            )
          )
        }
      '' + lib.optionalString (partialSolution.interpreter != "none") ''
        ${partialSolution.interpreter} -n $out/bin/${name}
      '';
    };
  mkDerivation = { pname
    , src
    , version
    , passthru ? { }
    , solutions
    , ...
    }@attrs:
    let
      inherit stdenv;

      /*
      Knock out our special solutions arg, but otherwise
      just build what the caller is giving us. We'll
      actually resholve it separately below (after we
      generate binlore for it).
      */
      unresholved = (stdenv.mkDerivation ((removeAttrs attrs [ "solutions" ])
        // {
        inherit version src;
        pname = "${pname}-unresholved";
      }));
    in
    /*
    resholve in a separate derivation; some concerns:
    - we aren't keeping many of the user's args, so they
      can't readily set LOGLEVEL and such...
    - not sure how this affects multiple outputs
    */
    lib.extendDerivation true passthru (stdenv.mkDerivation {
      src = unresholved;
      inherit version pname;
      buildInputs = [ resholve ];
      disallowedReferences = [ resholve ];

      # retain a reference to the base
      passthru = unresholved.passthru // {
        unresholved = unresholved;
        # fallback attr for update bot to query our src
        originalSrc = unresholved.src;
      };

      # do these imply that we should use NoCC or something?
      dontConfigure = true;
      dontBuild = true;

      installPhase = ''
        cp -R $src $out
      '';

      # enable below for verbose debug info if needed
      # supports default python.logging levels
      # LOGLEVEL="INFO";
      preFixup = phraseSolutions solutions unresholved;

      # don't break the metadata...
      meta = unresholved.meta;
    });
}