# buildLisp provides Nix functions to build Common Lisp packages,
# targeting SBCL.
#
# buildLisp is designed to enforce conventions and do away with the
# free-for-all of existing Lisp build systems.

{ pkgs ? import <nixpkgs> {}, ... }:

let
  inherit (builtins) map elemAt match filter;
  inherit (pkgs) lib runCommandNoCC makeWrapper writeText writeShellScriptBin sbcl;

  #
  # Internal helper definitions
  #

  # 'genLoadLisp' generates Lisp code that instructs SBCL to load all
  # the provided Lisp libraries.
  genLoadLisp = deps: lib.concatStringsSep "\n"
    (map (lib: "(load \"${lib}/${lib.lispName}.fasl\")") (allDeps deps));

  # 'genCompileLisp' generates a Lisp file that instructs SBCL to
  # compile the provided list of Lisp source files to $out.
  genCompileLisp = srcs: deps: writeText "compile.lisp" ''
    ;; This file compiles the specified sources into the Nix build
    ;; directory, creating one FASL file for each source.
    (require 'sb-posix)

    ${genLoadLisp deps}

    (defun nix-compile-lisp (file srcfile)
      (let ((outfile (make-pathname :type "fasl"
                                    :directory (or (sb-posix:getenv "NIX_BUILD_TOP")
                                                   (error "not running in a Nix build"))
                                    :name (substitute #\- #\/ srcfile))))
        (multiple-value-bind (_outfile _warnings-p failure-p)
            (compile-file srcfile :output-file outfile)
          (if failure-p (sb-posix:exit 1)
              (progn
                ;; For the case of multiple files belonging to the same
                ;; library being compiled, load them in order:
                (load outfile)

                ;; Write them to the FASL list in the same order:
                (format file "cat ~a~%" (namestring outfile)))))))

    (let ((*compile-verbose* t)
          ;; FASL files are compiled into the working directory of the
          ;; build and *then* moved to the correct out location.
          (pwd (sb-posix:getcwd)))

      (with-open-file (file "cat_fasls"
                            :direction :output
                            :if-does-not-exist :create)

        ;; These forms were inserted by the Nix build:
        ${
          lib.concatStringsSep "\n" (map (src: "(nix-compile-lisp file \"${src}\")") srcs)
        }
        ))
  '';

  # 'genTestLisp' generates a Lisp file that loads all sources and deps and
  # executes expression
  genTestLisp = name: srcs: deps: expression: writeText "${name}.lisp" ''
    ;; Dependencies
    ${genLoadLisp deps}

    ;; Sources
    ${lib.concatStringsSep "\n" (map (src: "(load \"${src}\")") srcs)}

    ;; Test expression
    (unless ${expression}
      (exit :code 1))
  '';

  # 'dependsOn' determines whether Lisp library 'b' depends on 'a'.
  dependsOn = a: b: builtins.elem a b.lispDeps;

  # 'allDeps' flattens the list of dependencies (and their
  # dependencies) into one ordered list of unique deps.
  allDeps = deps: (lib.toposort dependsOn (lib.unique (
    lib.flatten (deps ++ (map (d: d.lispDeps) deps))
  ))).result;

  # 'allNative' extracts all native dependencies of a dependency list
  # to ensure that library load paths are set correctly during all
  # compilations and program assembly.
  allNative = native: deps: lib.unique (
    lib.flatten (native ++ (map (d: d.lispNativeDeps) deps))
  );

  # 'genDumpLisp' generates a Lisp file that instructs SBCL to dump
  # the currently loaded image as an executable to $out/bin/$name.
  #
  # TODO(tazjin): Compression is currently unsupported because the
  # SBCL in nixpkgs is, by default, not compiled with zlib support.
  genDumpLisp = name: main: deps: writeText "dump.lisp" ''
    (require 'sb-posix)

    ${genLoadLisp deps}

    (let* ((bindir (concatenate 'string (sb-posix:getenv "out") "/bin"))
           (outpath (make-pathname :name "${name}"
                                   :directory bindir)))
      (save-lisp-and-die outpath
                         :executable t
                         :toplevel (function ${main})
                         :purify t))
    ;;
  '';

  # Add an `overrideLisp` attribute to a function result that works
  # similar to `overrideAttrs`, but is used specifically for the
  # arguments passed to Lisp builders.
  makeOverridable = f: orig: (f orig) // {
    overrideLisp = new: makeOverridable f (orig // (new orig));
  };

  # 'testSuite' builds a Common Lisp test suite that loads all of srcs and deps,
  # and then executes expression to check its result
  testSuite = { name, expression, srcs, deps ? [], native ? [] }:
    let
      lispNativeDeps = allNative native deps;
      lispDeps = allDeps deps;
    in runCommandNoCC name {
      LD_LIBRARY_PATH = lib.makeLibraryPath lispNativeDeps;
      LANG = "C.UTF-8";
    } ''
      echo "Running test suite ${name}"

      ${sbcl}/bin/sbcl --script ${genTestLisp name srcs deps expression} \
        | tee $out

      echo "Test suite ${name} succeeded"
    '';

  #
  # Public API functions
  #

  # 'library' builds a list of Common Lisp files into a single FASL
  # which can then be loaded into SBCL.
  library =
    { name
    , srcs
    , deps ? []
    , native ? []
    , tests ? null
    }:
    let
      lispNativeDeps = (allNative native deps);
      lispDeps = allDeps deps;
      testDrv = if ! isNull tests
        then testSuite {
          name = tests.name or "${name}-test";
          srcs = srcs ++ (tests.srcs or []);
          deps = deps ++ (tests.deps or []);
          expression = tests.expression;
        }
        else null;
    in lib.fix (self: runCommandNoCC "${name}-cllib" {
      LD_LIBRARY_PATH = lib.makeLibraryPath lispNativeDeps;
      LANG = "C.UTF-8";
      passthru = {
        inherit lispNativeDeps lispDeps;
        lispName = name;
        lispBinary = false;
        tests = testDrv;
        sbcl = sbclWith [ self ];
      };
    } ''
      ${if ! isNull testDrv
        then "echo 'Test ${testDrv} succeeded'"
        else "echo 'No tests run'"}
      ${sbcl}/bin/sbcl --script ${genCompileLisp srcs lispDeps}

      echo "Compilation finished, assembling FASL files"

      # FASL files can be combined by simply concatenating them
      # together, but it needs to be in the compilation order.
      mkdir $out

      chmod +x cat_fasls
      ./cat_fasls > $out/${name}.fasl
    '');

  # 'program' creates an executable containing a dumped image of the
  # specified sources and dependencies.
  program =
    { name
    , main ? "${name}:main"
    , srcs
    , deps ? []
    , native ? []
    , tests ? null
    }:
    let
      lispDeps = allDeps deps;
      libPath = lib.makeLibraryPath (allNative native lispDeps);
      selfLib = library {
        inherit name srcs native;
        deps = lispDeps;
      };
      testDrv = if ! isNull tests
        then testSuite {
          name = tests.name or "${name}-test";
          srcs =
            (
              srcs ++ (tests.srcs or []));
          deps = deps ++ (tests.deps or []);
          expression = tests.expression;
        }
        else null;
    in lib.fix (self: runCommandNoCC "${name}" {
      nativeBuildInputs = [ makeWrapper ];
      LD_LIBRARY_PATH = libPath;
      LANG = "C.UTF-8";
      passthru = {
        lispName = name;
        lispDeps = [ selfLib ] ++ (tests.deps or []);
        lispNativeDeps = native;
        lispBinary = true;
        tests = testDrv;
        sbcl = sbclWith [ self ];
      };
    } ''
      ${if ! isNull testDrv
        then "echo 'Test ${testDrv} succeeded'"
        else ""}
      mkdir -p $out/bin

      ${sbcl}/bin/sbcl --script ${
        genDumpLisp name main ([ selfLib ] ++ lispDeps)
      }

      wrapProgram $out/bin/${name} --prefix LD_LIBRARY_PATH : "${libPath}"
    '');

  # 'bundled' creates a "library" that calls 'require' on a built-in
  # package, such as any of SBCL's sb-* packages.
  bundled = name: (makeOverridable library) {
    inherit name;
    srcs = lib.singleton (builtins.toFile "${name}.lisp" "(require '${name})");
  };

  # 'sbclWith' creates an image with the specified libraries /
  # programs loaded.
  sbclWith = deps:
  let lispDeps = filter (d: !d.lispBinary) (allDeps deps);
  in writeShellScriptBin "sbcl" ''
    export LD_LIBRARY_PATH="${lib.makeLibraryPath (allNative [] lispDeps)}"
    export LANG="C.UTF-8"
    exec ${sbcl}/bin/sbcl ${lib.optionalString (deps != []) "--load ${writeText "load.lisp" (genLoadLisp lispDeps)}"} $@
  '';
in {
  library = makeOverridable library;
  program = makeOverridable program;
  sbclWith = makeOverridable sbclWith;
  bundled = makeOverridable bundled;
}