;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2014 Ludovic Courtès <ludo@gnu.org>
;;;
;;; 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 gexp)
  #:use-module ((guix store)
                #:select (direct-store-path?))
  #:use-module (guix monads)
  #:use-module ((guix derivations)
                #:select (derivation? derivation->output-path
                          %guile-for-build derivation))
  #:use-module (guix packages)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-26)
  #:use-module (ice-9 match)
  #:export (gexp
            gexp?
            gexp->derivation
            gexp->file
            gexp->script))

;;; Commentary:
;;;
;;; This module implements "G-expressions", or "gexps".  Gexps are like
;;; S-expressions (sexps), with two differences:
;;;
;;;   1. References (un-quotations) to derivations or packages in a gexp are
;;;      replaced by the corresponding output file name;
;;;
;;;   2. Gexps embed information about the derivations they refer to.
;;;
;;; Gexps make it easy to write to files Scheme code that refers to store
;;; items, or to write Scheme code to build derivations.
;;;
;;; Code:

;; "G expressions".
(define-record-type <gexp>
  (make-gexp references proc)
  gexp?
  (references gexp-references)                    ; ((DRV-OR-PKG OUTPUT) ...)
  (proc       gexp-proc))                         ; procedure

;; Reference to one of the derivation's outputs, for gexps used in
;; derivations.
(define-record-type <output-ref>
  (output-ref name)
  output-ref?
  (name output-ref-name))

(define raw-derivation
  (store-lift derivation))

(define (lower-inputs inputs)
  "Turn any package from INPUTS into a derivation; return the corresponding
input list as a monadic value."
  (with-monad %store-monad
    (sequence %store-monad
              (map (match-lambda
                    (((? package? package) sub-drv ...)
                     (mlet %store-monad ((drv (package->derivation package)))
                       (return `(,drv ,@sub-drv))))
                    (input
                     (return input)))
                   inputs))))

(define* (gexp->derivation name exp
                           #:key
                           (system (%current-system))
                           hash hash-algo recursive?
                           (env-vars '())
                           (modules '())
                           (guile-for-build (%guile-for-build))
                           references-graphs
                           local-build?)
  "Return a derivation NAME that runs EXP (a gexp) with GUILE-FOR-BUILD (a
derivation) on SYSTEM.

Make MODULES available in the evaluation context of EXP; MODULES is a list of
names of Guile modules from the current search path to be copied in the store,
compiled, and made available in the load path during the execution of
EXP---e.g., '((guix build utils) (guix build gnu-build-system)).

The other arguments are as for 'derivation'."
  (define %modules modules)
  (define outputs (gexp-outputs exp))

  (mlet* %store-monad ((inputs   (lower-inputs (gexp-inputs exp)))
                       (sexp     (gexp->sexp exp))
                       (builder  (text-file (string-append name "-builder")
                                            (object->string sexp)))
                       (modules  (if (pair? %modules)
                                     (imported-modules %modules
                                                       #:system system
                                                       #:guile guile-for-build)
                                     (return #f)))
                       (compiled (if (pair? %modules)
                                     (compiled-modules %modules
                                                       #:system system
                                                       #:guile guile-for-build)
                                     (return #f)))
                       (guile    (if guile-for-build
                                     (return guile-for-build)
                                     (package->derivation
                                      (@ (gnu packages base) guile-final)
                                      system))))
    (raw-derivation name
                    (string-append (derivation->output-path guile)
                                   "/bin/guile")
                    `("--no-auto-compile"
                      ,@(if (pair? %modules)
                            `("-L" ,(derivation->output-path modules)
                              "-C" ,(derivation->output-path compiled))
                            '())
                      ,builder)
                    #:outputs outputs
                    #:env-vars env-vars
                    #:system system
                    #:inputs `((,guile)
                               (,builder)
                               ,@(if modules
                                     `((,modules) (,compiled) ,@inputs)
                                     inputs))
                    #:hash hash #:hash-algo hash-algo #:recursive? recursive?
                    #:references-graphs references-graphs
                    #:local-build? local-build?)))

(define (gexp-inputs exp)
  "Return the input list for EXP."
  (define (add-reference-inputs ref result)
    (match ref
      (((? derivation?) (? string?))
       (cons ref result))
      (((? package?) (? string?))
       (cons ref result))
      ((? gexp? exp)
       (append (gexp-inputs exp) result))
      (((? string? file))
       (if (direct-store-path? file)
           (cons ref result)
           result))
      ((refs ...)
       (fold-right add-reference-inputs result refs))
      (_
       ;; Ignore references to other kinds of objects.
       result)))

  (fold-right add-reference-inputs
              '()
              (gexp-references exp)))

(define (gexp-outputs exp)
  "Return the outputs referred to by EXP as a list of strings."
  (define (add-reference-output ref result)
    (match ref
      (($ <output-ref> name)
       (cons name result))
      ((? gexp? exp)
       (append (gexp-outputs exp) result))
      (_
       result)))

  (fold-right add-reference-output
              '()
              (gexp-references exp)))

(define* (gexp->sexp exp)
  "Return (monadically) the sexp corresponding to EXP for the given OUTPUT,
and in the current monad setting (system type, etc.)"
  (define (reference->sexp ref)
    (with-monad %store-monad
      (match ref
        (((? derivation? drv) (? string? output))
         (return (derivation->output-path drv output)))
        (((? package? p) (? string? output))
         (package-file p #:output output))
        (($ <output-ref> output)
         ;; Output file names are not known in advance but the daemon defines
         ;; an environment variable for each of them at build time, so use
         ;; that trick.
         (return `((@ (guile) getenv) ,output)))
        ((? gexp? exp)
         (gexp->sexp exp))
        (((? string? str))
         (return (if (direct-store-path? str) str ref)))
        ((refs ...)
         (sequence %store-monad (map reference->sexp refs)))
        (x
         (return x)))))

  (mlet %store-monad
      ((args (sequence %store-monad
                       (map reference->sexp (gexp-references exp)))))
    (return (apply (gexp-proc exp) args))))

(define (canonicalize-reference ref)
  "Return a canonical variant of REF, which adds any missing output part in
package/derivation references."
  (match ref
    ((? package? p)
     `(,p "out"))
    ((? derivation? d)
     `(,d "out"))
    (((? package?) (? string?))
     ref)
    (((? derivation?) (? string?))
     ref)
    ((? string? s)
     (if (direct-store-path? s) `(,s) s))
    ((refs ...)
     (map canonicalize-reference refs))
    (x x)))

(define (syntax-location-string s)
  "Return a string representing the source code location of S."
  (let ((props (syntax-source s)))
    (if props
        (let ((file   (assoc-ref props 'filename))
              (line   (and=> (assoc-ref props 'line) 1+))
              (column (assoc-ref props 'column)))
          (if file
              (simple-format #f "~a:~a:~a"
                             file line column)
              (simple-format #f "~a:~a" line column)))
        "<unknown location>")))

(define-syntax gexp
  (lambda (s)
    (define (collect-escapes exp)
      ;; Return all the 'ungexp' present in EXP.
      (let loop ((exp    exp)
                 (result '()))
        (syntax-case exp (ungexp ungexp-splicing)
          ((ungexp _)
           (cons exp result))
          ((ungexp _ _)
           (cons exp result))
          ((ungexp-splicing _ ...)
           (cons exp result))
          ((exp0 exp ...)
           (let ((result (loop #'exp0 result)))
             (fold loop result #'(exp ...))))
          (_
           result))))

    (define (escape->ref exp)
      ;; Turn 'ungexp' form EXP into a "reference".
      (syntax-case exp (ungexp ungexp-splicing output)
        ((ungexp output)
         #'(output-ref "out"))
        ((ungexp output name)
         #'(output-ref name))
        ((ungexp thing)
         #'thing)
        ((ungexp drv-or-pkg out)
         #'(list drv-or-pkg out))
        ((ungexp-splicing lst)
         #'lst)))

    (define (substitute-references exp substs)
      ;; Return a variant of EXP where all the cars of SUBSTS have been
      ;; replaced by the corresponding cdr.
      (syntax-case exp (ungexp ungexp-splicing)
        ((ungexp _ ...)
         (match (assoc exp substs)
           ((_ id)
            id)
           (_
            #'(syntax-error "error: no 'ungexp' substitution"
                            #'ref))))
        (((ungexp-splicing _ ...) rest ...)
         (syntax-case exp ()
           ((exp rest ...)
            (match (assoc #'exp substs)
              ((_ id)
               (with-syntax ((id id))
                 #`(append id
                           #,(substitute-references #'(rest ...) substs))))
              (_
               #'(syntax-error "error: no 'ungexp-splicing' substitution"
                               #'ref))))))
        ((exp0 exp ...)
         #`(cons #,(substitute-references #'exp0 substs)
                 #,(substitute-references #'(exp ...) substs)))
        (x #''x)))

    (syntax-case s (ungexp output)
      ((_ exp)
       (let* ((escapes (delete-duplicates (collect-escapes #'exp)))
              (formals (generate-temporaries escapes))
              (sexp    (substitute-references #'exp (zip escapes formals)))
              (refs    (map escape->ref escapes)))
         #`(make-gexp (map canonicalize-reference (list #,@refs))
                      (lambda #,formals
                        #,sexp)))))))


;;;
;;; Convenience procedures.
;;;

(define* (gexp->script name exp
                       #:key (modules '())
                       (guile (@ (gnu packages base) guile-final)))
  "Return an executable script NAME that runs EXP using GUILE with MODULES in
its search path."
  (mlet %store-monad ((modules  (imported-modules modules))
                      (compiled (compiled-modules modules)))
    (gexp->derivation name
                      (gexp
                       (call-with-output-file (ungexp output)
                         (lambda (port)
                           (format port
                                   "#!~a/bin/guile --no-auto-compile~%!#~%"
                                   (ungexp guile))
                           (write
                            '(set! %load-path
                                   (cons (ungexp modules) %load-path))
                            port)
                           (write
                            '(set! %load-compiled-path
                                   (cons (ungexp compiled)
                                         %load-compiled-path))
                            port)
                           (write '(ungexp exp) port)
                           (chmod port #o555)))))))

(define (gexp->file name exp)
  "Return a derivation that builds a file NAME containing EXP."
  (gexp->derivation name
                    (gexp
                     (call-with-output-file (ungexp output)
                       (lambda (port)
                         (write '(ungexp exp) port))))))



;;;
;;; Syntactic sugar.
;;;

(eval-when (expand load eval)
  (define (read-ungexp chr port)
    "Read an 'ungexp' or 'ungexp-splicing' form from PORT."
    (define unquote-symbol
      (match (peek-char port)
        (#\@
         (read-char port)
         'ungexp-splicing)
        (_
         'ungexp)))

    (match (read port)
      ((? symbol? symbol)
       (let ((str (symbol->string symbol)))
         (match (string-index-right str #\:)
           (#f
            `(,unquote-symbol ,symbol))
           (colon
            (let ((name   (string->symbol (substring str 0 colon)))
                  (output (substring str (+ colon 1))))
              `(,unquote-symbol ,name ,output))))))
      (x
       `(,unquote-symbol ,x))))

  (define (read-gexp chr port)
    "Read a 'gexp' form from PORT."
    `(gexp ,(read port)))

  ;; Extend the reader
  (read-hash-extend #\~ read-gexp)
  (read-hash-extend #\$ read-ungexp))

;;; gexp.scm ends here