;;; Guix QA Frontpage
;;;
;;; Copyright © 2023 Christopher Baines <mail@cbaines.net>
;;;
;;; This program is free software: you can redistribute it and/or
;;; modify it under the terms of the GNU Affero General Public License
;;; as published by the Free Software Foundation, either version 3 of
;;; the License, or (at your option) any later version.
;;;
;;; This program 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
;;; Affero General Public License for more details.
;;;
;;; You should have received a copy of the GNU Affero General Public
;;; License along with this program.  If not, see
;;; <http://www.gnu.org/licenses/>.

(define-module (guix-qa-frontpage utils)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-71)
  #:use-module (ice-9 match)
  #:use-module (fibers)
  #:use-module (fibers channels)
  #:use-module (guix-build-coordinator utils fibers)
  #:export (fiberize
            fibers-map
            fibers-for-each)
  #:re-export (with-fibers-port-timeouts))

(define* (fiberize proc #:key (parallelism 1))
  (let ((channel (make-channel)))
    (for-each
     (lambda _
       (spawn-fiber
        (lambda ()
          (while #t
            (let ((reply-channel args (car+cdr
                                       (get-message channel))))
              (put-message
               reply-channel
               (with-exception-handler
                   (lambda (exn)
                     (cons 'exception exn))
                 (lambda ()
                   (with-throw-handler #t
                     (lambda ()
                       (call-with-values
                           (lambda ()
                             (apply proc args))
                         (lambda vals
                           (cons 'result vals))))
                     (lambda _
                       (backtrace))))
                 #:unwind? #t)))))
        #:parallel? #t))
     (iota parallelism))

    (lambda args
      (let ((reply-channel (make-channel)))
        (put-message channel (cons reply-channel args))
        (match (get-message reply-channel)
          (('result . vals) (apply values vals))
          (('exception . exn) (raise-exception exn)))))))

(define (fibers-map proc . lists)
  (let ((channels
         (apply
          map
          (lambda args
            (let ((channel (make-channel)))
              (spawn-fiber
               (lambda ()
                 (put-message
                  channel
                  (with-exception-handler
                      (lambda (exn)
                        (cons 'exception exn))
                    (lambda ()
                      (with-throw-handler #t
                        (lambda ()
                          (call-with-values
                              (lambda ()
                                (apply proc args))
                            (lambda val
                              (cons 'result val))))
                        (lambda _
                          (backtrace))))
                    #:unwind? #t))))
              channel))
          lists)))
    (map
     (match-lambda
       (('result . val) val)
       (('exception . exn) (raise-exception exn)))
     (map get-message channels))))

(define (fibers-for-each proc . lists)
  ;; Like split-at, but don't care about the order of the resulting lists, and
  ;; don't error if the list is shorter than i elements
  (define (split-at* lst i)
    (let lp ((l lst) (n i) (acc '()))
      (if (or (<= n 0) (null? l))
          (values (reverse! acc) l)
          (lp (cdr l) (- n 1) (cons (car l) acc)))))

  ;; As this can be called with lists with tens of thousands of items in them,
  ;; batch the
  (define batch-size 20)
  (define (get-batch lists)
    (let ((split-lists
           (map (lambda (lst)
                  (let ((batch rest (split-at* lst batch-size)))
                    (cons batch rest)))
                lists)))
      (values (map car split-lists)
              (map cdr split-lists))))

  (let loop ((lists lists))
    (call-with-values
        (lambda ()
          (get-batch lists))
      (lambda (batch rest)
        (apply fibers-map proc batch)
        (unless (null? (car rest))
          (loop  rest)))))
  *unspecified*)