import: Add 'elpa' importer.

* guix/import/elpa.scm: New file.
* guix/scripts/import.scm: Add "elpa" to 'importers'.
* guix/scripts/import/elpa.scm: New file.
* Makefile.am (MODULES): Add 'guix/import/elpa.scm' and
  'guix/scripts/import/elpa.scm'.
  (SCM_TESTS): Add 'tests/elpa.scm'.
* doc/guix.texi (Invoking guix import): Document it.
* tests/elpa.scm: New file.
* po/guix/POTFILES.in: Add 'guix/scripts/import/elpa.scm'.

7 files changed, 470 insertions, 1 deletions

diff --git a/Makefile.am b/Makefile.am
index 44d3b09a82..63be2228a4 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -97,6 +97,7 @@ MODULES =					\
   guix/import/snix.scm				\
   guix/import/cabal.scm				\
   guix/import/hackage.scm			\
+  guix/import/elpa.scm   			\
   guix/scripts/download.scm			\
   guix/scripts/build.scm			\
   guix/scripts/archive.scm			\
@@ -113,6 +114,7 @@ MODULES =					\
   guix/scripts/import/gnu.scm			\
   guix/scripts/import/nix.scm			\
   guix/scripts/import/hackage.scm		\
+  guix/scripts/import/elpa.scm  		\
   guix/scripts/environment.scm			\
   guix/scripts/publish.scm			\
   guix/scripts/edit.scm				\
@@ -187,6 +189,7 @@ SCM_TESTS =					\
   tests/packages.scm				\
   tests/snix.scm				\
   tests/hackage.scm				\
+  tests/elpa.scm				\
   tests/store.scm				\
   tests/monads.scm				\
   tests/gexp.scm				\
diff --git a/doc/guix.texi b/doc/guix.texi
index 284d667f34..d10279e992 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -3856,6 +3856,34 @@ package name by a hyphen and a version number as in the following example:
 @example
 guix import hackage mtl-2.1.3.1
 @end example
+
+@item elpa
+@cindex elpa
+Import meta-data from an Emacs Lisp Package Archive (ELPA) package
+repository (@pxref{Packages,,, emacs, The GNU Emacs Manual}).
+
+Specific command-line options are:
+
+@table @code
+@item --archive=@var{repo}
+@itemx -a @var{repo}
+@var{repo} identifies the archive repository from which to retrieve the
+information.  Currently the supported repositories and their identifiers
+are:
+@itemize -
+@item
+@uref{"http://elpa.gnu.org/packages", GNU}, selected by the @code{gnu}
+identifier.  This is the default.
+
+@item
+@uref{"http://stable.melpa.org/packages", MELPA-Stable}, selected by the
+@code{melpa-stable} identifier.
+
+@item
+@uref{"http://melpa.org/packages", MELPA}, selected by the @code{melpa}
+identifier.
+@end itemize
+@end table
 @end table
 
 The structure of the @command{guix import} code is modular.  It would be
diff --git a/guix/import/elpa.scm b/guix/import/elpa.scm
new file mode 100644
index 0000000000..3b3dc1f91a
--- /dev/null
+++ b/guix/import/elpa.scm
@@ -0,0 +1,230 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2015 Federico Beffa <beffa@fbengineering.ch>
+;;;
+;;; 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/>.
+
+(define-module (guix import elpa)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 rdelim)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-9)
+  #:use-module (srfi srfi-9 gnu)
+  #:use-module (srfi srfi-11)
+  #:use-module (srfi srfi-26)
+  #:use-module ((guix download) #:select (download-to-store))
+  #:use-module (guix import utils)
+  #:use-module (guix store)
+  #:use-module (guix ui)
+  #:use-module (guix hash)
+  #:use-module (guix base32)
+  #:use-module ((guix utils) #:select (call-with-temporary-output-file
+                                       memoize))
+  #:export (elpa->guix-package))
+
+(define (elpa-dependencies->names deps)
+  "Convert DEPS, a list of symbol/version pairs à la ELPA, to a list of
+package names as strings"
+  (match deps
+    (((names _ ...) ...)
+     (map symbol->string names))))
+
+(define emacs-standard-library?
+  (let ((libs '("emacs" "cl-lib")))
+    (lambda (lib)
+      "Return true if LIB is part of Emacs itself.  The check is not
+exhaustive and only attempts to recognize a subset of packages which in the
+past were distributed separately from Emacs."
+      (member lib libs))))
+
+(define (filter-dependencies names)
+  "Remove the package names included with Emacs from the list of
+NAMES (strings)."
+  (filter emacs-standard-library? names))
+
+(define (elpa-name->package-name name)
+  "Given the NAME of an Emacs package, return the corresponding Guix name."
+  (let ((package-name-prefix "emacs-"))
+    (if (string-prefix? package-name-prefix name)
+        (string-downcase name)
+        (string-append package-name-prefix (string-downcase name)))))
+
+(define* (elpa-url #:optional (repo 'gnu))
+  "Retrun the URL of REPO."
+  (let ((elpa-archives
+         '((gnu . "http://elpa.gnu.org/packages")
+           (melpa-stable . "http://stable.melpa.org/packages")
+           (melpa . "http://melpa.org/packages"))))
+    (assq-ref elpa-archives repo)))
+
+(define* (elpa-fetch-archive #:optional (repo 'gnu))
+  "Retrive the archive with the list of packages available from REPO."
+  (let ((url (and=> (elpa-url repo)
+                    (cut string-append <> "/archive-contents"))))
+    (if url
+        (call-with-downloaded-file url read)
+        (leave (_ "~A: currently not supported~%") repo))))
+
+(define (call-with-downloaded-file url proc)
+  "Fetch URL, store the content in a temporary file and call PROC with that
+file.  Returns the value returned by PROC."
+  (call-with-temporary-output-file
+   (lambda (temp port)
+     (or (and (url-fetch url temp)
+              (call-with-input-file temp proc))
+         (error "download failed" url)))))
+
+(define (is-elpa-package? name elpa-pkg-spec)
+  "Return true if the string NAME corresponds to the name of the package
+defined by ELPA-PKG-SPEC, a package specification as in an archive
+'archive-contents' file."
+  (eq? (first elpa-pkg-spec) (string->symbol name)))
+
+(define* (elpa-package-info name #:optional (repo 'gnu))
+  "Extract the information about the package NAME from the package archieve of
+REPO."
+  (let* ((archive (elpa-fetch-archive repo))
+         (pkgs (match archive ((version pkg-spec ...) pkg-spec)))
+         (info (filter (cut is-elpa-package? name <>) pkgs)))
+    (if (pair? info) (first info) #f)))
+
+;; Object to store information about an ELPA package.
+(define-record-type <elpa-package>
+  (make-elpa-package name version inputs synopsis kind home-page description
+                     source-url)
+  elpa-package?
+  (name elpa-package-name)
+  (version elpa-package-version)
+  (inputs elpa-package-inputs)
+  (synopsis elpa-package-synopsis)
+  (kind elpa-package-kind)
+  (home-page elpa-package-home-page)
+  (description elpa-package-description)
+  (source-url elpa-package-source-url))
+
+(set-record-type-printer! <elpa-package>
+                          (lambda (package port)
+                            (format port "#<elpa-package ~a-~a>"
+                                      (elpa-package-name package)
+                                      (elpa-package-version package))))
+
+(define (elpa-version->string elpa-version)
+  "Convert the package version as used in Emacs package files into a string."
+  (if (pair? elpa-version)
+      (let-values (((ms rest) (match elpa-version
+                                ((ms . rest)
+                                 (values ms rest)))))
+        (fold (lambda (n s) (string-append s "." (number->string n)))
+              (number->string ms) rest))
+      #f))
+
+(define (package-home-page alist)
+  "Extract the package home-page from ALIST."
+  (or (assq-ref alist ':url) "unspecified"))
+
+(define (ensure-list alist)
+  "If ALIST is the symbol 'nil return the empty list.  Otherwise, return ALIST."
+  (if (eq? alist 'nil)
+      '()
+      alist))
+
+(define (package-source-url kind name version repo)
+  "Return the source URL of the package described the the strings NAME and
+VERSION at REPO.  KIND is either the symbol 'single or 'tar."
+  (case kind
+    ((single) (full-url repo name ".el" version))
+    ((tar) (full-url repo name ".tar" version))
+    (else
+     #f)))
+
+(define* (full-url repo name suffix #:optional (version #f))
+  "Return the full URL of the package NAME at REPO and the SUFFIX.  Maybe
+include VERSION."
+  (if version
+      (string-append (elpa-url repo) "/" name "-" version suffix)
+      (string-append (elpa-url repo) "/" name suffix)))
+
+(define (fetch-package-description kind name repo)
+  "Fetch the description of package NAME of type KIND from REPO."
+  (let ((url (full-url repo name "-readme.txt")))
+    (call-with-downloaded-file url read-string)))
+
+(define* (fetch-elpa-package name #:optional (repo 'gnu))
+  "Fetch package NAME from REPO."
+  (let ((pkg (elpa-package-info name repo)))
+    (match pkg
+      ((name version reqs synopsis kind . rest)
+       (let* ((name (symbol->string name))
+             (ver (elpa-version->string version))
+             (url (package-source-url kind name ver repo)))
+         (make-elpa-package name ver
+                            (ensure-list reqs) synopsis kind
+                            (package-home-page (first rest))
+                            (fetch-package-description kind name repo)
+                            url)))
+      (_ #f))))
+
+(define* (elpa-package->sexp pkg)
+  "Return the `package' S-expression for the Emacs package PKG, a record of
+type '<elpa-package>'."
+
+  (define name (elpa-package-name pkg))
+
+  (define version (elpa-package-version pkg))
+
+  (define source-url (elpa-package-source-url pkg))
+
+  (define dependencies
+    (let* ((deps (elpa-package-inputs pkg))
+           (names (filter-dependencies (elpa-dependencies->names deps))))
+      (map (lambda (n)
+             (let ((new-n (elpa-name->package-name n)))
+               (list new-n (list 'unquote (string->symbol new-n)))))
+           names)))
+
+  (define (maybe-inputs input-type inputs)
+    (match inputs
+      (()
+       '())
+      ((inputs ...)
+       (list (list input-type
+                   (list 'quasiquote inputs))))))
+
+  (let ((tarball (with-store store
+                   (download-to-store store source-url))))
+    `(package
+       (name ,(elpa-name->package-name name))
+       (version ,version)
+       (source (origin
+                 (method url-fetch)
+                 (uri (string-append ,@(factorize-uri source-url version)))
+                 (sha256
+                  (base32
+                   ,(if tarball
+                        (bytevector->nix-base32-string (file-sha256 tarball))
+                        "failed to download package")))))
+       (build-system emacs-build-system)
+       ,@(maybe-inputs 'inputs dependencies)
+       (home-page ,(elpa-package-home-page pkg))
+       (synopsis ,(elpa-package-synopsis pkg))
+       (description ,(elpa-package-description pkg))
+       (license license:gpl3+))))
+
+(define* (elpa->guix-package name #:optional (repo 'gnu))
+  "Fetch the package NAME from REPO and produce a Guix package S-expression."
+  (let ((pkg (fetch-elpa-package name repo)))
+    (and=> pkg elpa-package->sexp)))
+
+;;; elpa.scm ends here
diff --git a/guix/scripts/import.scm b/guix/scripts/import.scm
index 45ce092f13..d0bdec133d 100644
--- a/guix/scripts/import.scm
+++ b/guix/scripts/import.scm
@@ -73,7 +73,7 @@ rather than \\n."
 ;;; Entry point.
 ;;;
 
-(define importers '("gnu" "nix" "pypi" "cpan" "hackage"))
+(define importers '("gnu" "nix" "pypi" "cpan" "hackage" "elpa"))
 
 (define (resolve-importer name)
   (let ((module (resolve-interface
diff --git a/guix/scripts/import/elpa.scm b/guix/scripts/import/elpa.scm
new file mode 100644
index 0000000000..9034eb74e7
--- /dev/null
+++ b/guix/scripts/import/elpa.scm
@@ -0,0 +1,98 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2015 Federico Beffa <beffa@fbengineering.ch>
+;;;
+;;; 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/>.
+
+(define-module (guix scripts import elpa)
+  #:use-module (guix ui)
+  #:use-module (guix utils)
+  #:use-module (guix import elpa)
+  #:use-module (guix scripts import)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-11)
+  #:use-module (srfi srfi-37)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 format)
+  #:export (guix-import-elpa))
+
+
+;;;
+;;; Command-line options.
+;;;
+
+(define %default-options
+  '((repo . 'gnu)))
+
+(define (show-help)
+  (display (_ "Usage: guix import elpa PACKAGE-NAME
+Import the latest package named PACKAGE-NAME from an ELPA repository.\n"))
+  (display (_ "
+  -a, --archive=ARCHIVE          specify the archive repository"))
+  (display (_ "
+  -h, --help                     display this help and exit"))
+  (display (_ "
+  -V, --version                  display version information and exit"))
+  (newline)
+  (show-bug-report-information))
+
+(define %options
+  ;; Specification of the command-line options.
+  (cons* (option '(#\h "help") #f #f
+                 (lambda args
+                   (show-help)
+                   (exit 0)))
+         (option '(#\V "version") #f #f
+                 (lambda args
+                   (show-version-and-exit "guix import elpa")))
+         (option '(#\a "archive") #t #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'repo (string->symbol arg)
+                               (alist-delete 'repo result))))
+         %standard-import-options))
+
+
+;;;
+;;; Entry point.
+;;;
+
+(define (guix-import-elpa . args)
+  (define (parse-options)
+    ;; Return the alist of option values.
+    (args-fold* args %options
+                (lambda (opt name arg result)
+                  (leave (_ "~A: unrecognized option~%") name))
+                (lambda (arg result)
+                  (alist-cons 'argument arg result))
+                %default-options))
+
+  (let* ((opts (parse-options))
+         (args (filter-map (match-lambda
+                            (('argument . value)
+                             value)
+                            (_ #f))
+                           (reverse opts))))
+    (match args
+      ((package-name)
+       (let ((sexp (elpa->guix-package package-name (assoc-ref opts 'repo))))
+         (unless sexp
+           (leave (_ "failed to download package '~a'~%") package-name))
+         sexp))
+      (()
+       (leave (_ "too few arguments~%")))
+      ((many ...)
+       (leave (_ "too many arguments~%"))))))
+
+;;; elpa.scm ends here
diff --git a/po/guix/POTFILES.in b/po/guix/POTFILES.in
index 247fe2cf6a..ed8cc7f1cd 100644
--- a/po/guix/POTFILES.in
+++ b/po/guix/POTFILES.in
@@ -10,6 +10,7 @@ guix/scripts/package.scm
 guix/scripts/gc.scm
 guix/scripts/hash.scm
 guix/scripts/import.scm
+guix/scripts/import/elpa.scm
 guix/scripts/pull.scm
 guix/scripts/substitute.scm
 guix/scripts/authenticate.scm
diff --git a/tests/elpa.scm b/tests/elpa.scm
new file mode 100644
index 0000000000..5d2914b8df
--- /dev/null
+++ b/tests/elpa.scm
@@ -0,0 +1,109 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2015 Federico Beffa <beffa@fbengineering.ch>
+;;;
+;;; 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/>.
+
+(define-module (test-elpa)
+  #:use-module (guix import elpa)
+  #:use-module (guix tests)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-64)
+  #:use-module (ice-9 match))
+
+(define elpa-mock-archive
+  '(1
+    (ace-window .
+                [(0 9 0)
+                 ((avy
+                   (0 2 0)))
+                 "Quickly switch windows." single
+                 ((:url . "https://github.com/abo-abo/ace-window")
+                  (:keywords "window" "location"))])
+    (auctex .
+            [(11 88 6)
+             nil "Integrated environment for *TeX*" tar
+             ((:url . "http://www.gnu.org/software/auctex/"))])))
+
+(define auctex-readme-mock "This is the AUCTeX description.")
+
+(define* (elpa-package-info-mock name #:optional (repo "gnu"))
+  "Simulate retrieval of 'archive-contents' file from REPO and extraction of
+information about package NAME. (Function 'elpa-package-info'.)"
+  (let* ((archive elpa-mock-archive)
+         (info (filter (lambda (p) (eq? (first p) (string->symbol name)))
+                       (cdr archive))))
+    (if (pair? info) (first info) #f)))
+
+(define elpa-version->string
+  (@@ (guix import elpa) elpa-version->string))
+
+(define package-source-url
+  (@@ (guix import elpa) package-source-url))
+
+(define nil->empty
+  (@@ (guix import elpa) nil->empty))
+
+(define package-home-page
+  (@@ (guix import elpa) package-home-page))
+
+(define make-elpa-package
+  (@@ (guix import elpa) make-elpa-package))
+
+(test-begin "elpa")
+
+(define (eval-test-with-elpa pkg)
+  (mock
+   ;; replace the two fetching functions
+   ((guix import elpa) fetch-elpa-package
+    (lambda* (name #:optional (repo "gnu"))
+      (let ((pkg (elpa-package-info-mock name repo)))
+        (match pkg
+          ((name version reqs synopsis kind . rest)
+           (let* ((name (symbol->string name))
+                  (ver (elpa-version->string version))
+                  (url (package-source-url kind name ver repo)))
+             (make-elpa-package name ver
+                                (nil->empty reqs) synopsis kind
+                                (package-home-page (first rest))
+                                auctex-readme-mock
+                                url)))
+          (_ #f)))))
+   (match (elpa->guix-package pkg)
+     (('package
+        ('name "emacs-auctex")
+        ('version "11.88.6")
+        ('source
+         ('origin
+           ('method 'url-fetch)
+           ('uri ('string-append
+                  "http://elpa.gnu.org/packages/auctex-" 'version ".tar"))
+           ('sha256 ('base32 (? string? hash)))))
+        ('build-system 'emacs-build-system)
+        ('home-page "http://www.gnu.org/software/auctex/")
+        ('synopsis "Integrated environment for *TeX*")
+        ('description (? string?))
+        ('license 'license:gpl3+))
+      #t)
+     (x
+      (pk 'fail x #f)))))
+
+(test-assert "elpa->guix-package test 1"
+  (eval-test-with-elpa "auctex"))
+
+(test-end "elpa")
+
+
+(exit (= (test-runner-fail-count (test-runner-current)) 0))