;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2023 Pierre-Henry Fröhring <contact@phfrohring.com>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

;; Commentary:
;;
;; Code:

(define-module (guix build mix-build-system)
  #:use-module ((guix build gnu-build-system) #:prefix gnu:)
  #:use-module (guix build utils)
  #:use-module (ice-9 ftw)
  #:use-module (ice-9 match)
  #:use-module (ice-9 regex)
  #:use-module (ice-9 string-fun)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-71)
  #:export (mix-build
            %standard-phases))

;; The Elixir version is constant as soon as it is computable from the current
;; execution.  It is a X.Y string where X and Y are respectively the major and
;; minor version number of the Elixir used in the build.
(define %elixir-version (make-parameter "X.Y"))

(define* (elixir-libdir path #:optional (version (%elixir-version)))
  "Return the path where all libraries under PATH for a specified Elixir
VERSION are installed."
  (string-append path "/lib/elixir/" version))

(define* (strip-prefix name #:optional (prefix "elixir-"))
  "Return NAME without the prefix PREFIX."
  (if (string-prefix? prefix name)
      (string-drop name (string-length prefix))
      name))

(define (mix-build-dir mix-build-root mix-env)
  "Return the directory where build artifacts are to be installed according to
en environment MIX-ENV in the current directory.  MIX-BUILD-ROOT depends on the
package arguments.  See: https://hexdocs.pm/mix/1.15/Mix.html#module-environment-variables"
  (string-append mix-build-root "/" mix-env "/lib"))

(define (elixir-version inputs)
  "Return an X.Y string where X and Y are respectively the major and minor version number of PACKAGE.
Example: /gnu/store/…-elixir-1.14.0 → 1.14"
  ((compose
    (cute string-join <> ".")
    (cute take <> 2)
    (cute string-split <> #\.)
    strip-prefix
    strip-store-file-name)
   (assoc-ref inputs "elixir")))

(define* (unpack #:key source mix-path #:allow-other-keys)
  "Unpack SOURCE in the working directory, and change directory within the
source.  When SOURCE is a directory, copy it in a sub-directory of the current
working directory."
  (let ((gnu-unpack (assoc-ref gnu:%standard-phases 'unpack)))
    (gnu-unpack #:source source)
    (when (file-exists? "contents.tar.gz")
      (invoke "tar" "xvf" "contents.tar.gz"))))

(define (list-directories dir)
  "List absolute paths of directories directly under the directory DIR."
  (map (cute string-append dir "/" <>)
       (scandir dir (lambda (filename)
                      (and (not (member filename '("." "..")))
                           (directory-exists? (string-append dir "/" filename)))))))

(define* (set-mix-env #:key inputs mix-path mix-exs #:allow-other-keys)
  "Set environment variables.
See: https://hexdocs.pm/mix/1.15.7/Mix.html#module-environment-variables"
  (setenv "MIX_ARCHIVES" "archives")
  (setenv "MIX_BUILD_ROOT" "_build")
  (setenv "MIX_DEPS_PATH" "deps")
  (setenv "MIX_EXS" mix-exs)
  (setenv "MIX_HOME" (getcwd))
  (setenv "MIX_PATH" (or mix-path ""))
  (setenv "MIX_REBAR3" (string-append (assoc-ref inputs "rebar3") "/bin/rebar3")))

(define* (set-elixir-version #:key inputs #:allow-other-keys)
  "Store the version number of the Elixir input in a parameter."
  (%elixir-version (elixir-version inputs))
  (format #t "Elixir version: ~a~%" (%elixir-version)))

(define* (build #:key mix-environments #:allow-other-keys)
  "Builds the Mix project."
  (for-each (lambda (mix-env)
              (setenv "MIX_ENV" mix-env)
              (invoke "mix" "compile" "--no-deps-check"))
            mix-environments))

(define* (check #:key (tests? #t) #:allow-other-keys)
  "Test the Mix project."
  (if tests?
      (invoke "mix" "test" "--no-deps-check")
      (format #t "tests? = ~a~%" tests?)))

(define* (remove-mix-dirs . _)
  "Remove all .mix/ directories.
We do not want to copy them to the installation directory."
  (for-each delete-file-recursively
            (find-files "." (file-name-predicate "\\.mix$") #:directories? #t)))

(define (package-name->elixir-name name+ver)
  "Convert the Guix package NAME-VER to the corresponding Elixir name-version
format.  Example: elixir-a-pkg-1.2.3 -> a_pkg"
  ((compose
    (cute string-join <> "_")
    (cute drop-right <> 1)
    (cute string-split <> #\-))
   (strip-prefix name+ver)))

(define* (install #:key
                  inputs
                  outputs
                  name
                  build-per-environment
                  #:allow-other-keys)
  "Install build artifacts in the store."
  (let* ((lib-name (package-name->elixir-name name))
         (lib-dir (string-append (elixir-libdir (assoc-ref outputs "out")) "/" lib-name))
         (root (getenv "MIX_BUILD_ROOT"))
         (env (if build-per-environment "prod" "shared")))
    (mkdir-p lib-dir)
    (copy-recursively (string-append (mix-build-dir root env) "/" lib-name) lib-dir
                      #:follow-symlinks? #t)))

(define %standard-phases
  (modify-phases gnu:%standard-phases
    (delete 'bootstrap)
    (delete 'configure)
    (add-after 'install-locale 'set-mix-env set-mix-env)
    (add-after 'set-mix-env 'set-elixir-version set-elixir-version)
    (replace 'unpack unpack)
    (replace 'build build)
    (replace 'check check)
    (add-before 'install 'remove-mix-dirs remove-mix-dirs)
    (replace 'install install)))

(define* (mix-build #:key inputs (phases %standard-phases)
                    #:allow-other-keys #:rest args)
  "Build the given Mix package, applying all of PHASES in order."
  (apply gnu:gnu-build #:inputs inputs #:phases phases args))

;;; mix-build-system.scm ends here