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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018 Mathieu Othacehe <m.othacehe@gmail.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/>.
+
+(define-module (gnu installer steps)
+ #:use-module (guix records)
+ #:use-module (ice-9 match)
+ #:use-module (srfi srfi-1)
+ #:use-module (srfi srfi-34)
+ #:use-module (srfi srfi-35)
+ #:export (&installer-step-abort
+ installer-step-abort?
+
+ &installer-step-break
+ installer-step-break?
+
+ <installer-step>
+ installer-step
+ make-installer-step
+ installer-step?
+ installer-step-id
+ installer-step-description
+ installer-step-compute
+ installer-step-configuration-proc
+
+ run-installer-steps
+ find-step-by-id
+ result->step-ids
+ result-step
+ result-step-done?))
+
+;; This condition may be raised to abort the current step.
+(define-condition-type &installer-step-abort &condition
+ installer-step-abort?)
+
+;; This condition may be raised to break out from the steps execution.
+(define-condition-type &installer-step-break &condition
+ installer-step-break?)
+
+;; An installer-step record is basically an id associated to a compute
+;; procedure. The COMPUTE procedure takes exactly one argument, an association
+;; list containing the results of previously executed installer-steps (see
+;; RUN-INSTALLER-STEPS description). The value returned by the COMPUTE
+;; procedure will be stored in the results list passed to the next
+;; installer-step and so on.
+(define-record-type* <installer-step>
+ installer-step make-installer-step
+ installer-step?
+ (id installer-step-id) ;symbol
+ (description installer-step-description ;string
+ (default #f))
+ (compute installer-step-compute) ;procedure
+ (configuration-format-proc installer-step-configuration-proc ;procedure
+ (default #f)))
+
+(define* (run-installer-steps #:key
+ steps
+ (rewind-strategy 'previous)
+ (menu-proc (const #f)))
+ "Run the COMPUTE procedure of all <installer-step> records in STEPS
+sequencially. If the &installer-step-abort condition is raised, fallback to a
+previous install-step, accordingly to the specified REWIND-STRATEGY.
+
+REWIND-STRATEGY possible values are 'previous, 'menu and 'start. If 'previous
+is selected, the execution will resume at the previous installer-step. If
+'menu is selected, the MENU-PROC procedure will be called. Its return value
+has to be an installer-step ID to jump to. The ID has to be the one of a
+previously executed step. It is impossible to jump forward. Finally if 'start
+is selected, the execution will resume at the first installer-step.
+
+The result of every COMPUTE procedures is stored in an association list, under
+the form:
+
+ '((STEP-ID . COMPUTE-RESULT) ...)
+
+where STEP-ID is the ID field of the installer-step and COMPUTE-RESULT the
+result of the associated COMPUTE procedure. This result association list is
+passed as argument of every COMPUTE procedure. It is finally returned when the
+computation is over.
+
+If the &installer-step-break condition is raised, stop the computation and
+return the accumalated result so far."
+ (define (pop-result list)
+ (cdr list))
+
+ (define (first-step? steps step)
+ (match steps
+ ((first-step . rest-steps)
+ (equal? first-step step))))
+
+ (define* (skip-to-step step result
+ #:key todo-steps done-steps)
+ (match (list todo-steps done-steps)
+ (((todo . rest-todo) (prev-done ... last-done))
+ (if (eq? (installer-step-id todo)
+ (installer-step-id step))
+ (run result
+ #:todo-steps todo-steps
+ #:done-steps done-steps)
+ (skip-to-step step (pop-result result)
+ #:todo-steps (cons last-done todo-steps)
+ #:done-steps prev-done)))))
+
+ (define* (run result #:key todo-steps done-steps)
+ (match todo-steps
+ (() (reverse result))
+ ((step . rest-steps)
+ (guard (c ((installer-step-abort? c)
+ (case rewind-strategy
+ ((previous)
+ (match done-steps
+ (()
+ ;; We cannot go previous the first step. So re-raise
+ ;; the exception. It might be useful in the case of
+ ;; nested run-installer-steps. Abort to 'raise-above
+ ;; prompt to prevent the condition from being catched
+ ;; by one of the previously installed guard.
+ (abort-to-prompt 'raise-above c))
+ ((prev-done ... last-done)
+ (run (pop-result result)
+ #:todo-steps (cons last-done todo-steps)
+ #:done-steps prev-done))))
+ ((menu)
+ (let ((goto-step (menu-proc
+ (append done-steps (list step)))))
+ (if (eq? goto-step step)
+ (run result
+ #:todo-steps todo-steps
+ #:done-steps done-steps)
+ (skip-to-step goto-step result
+ #:todo-steps todo-steps
+ #:done-steps done-steps))))
+ ((start)
+ (if (null? done-steps)
+ ;; Same as above, it makes no sense to jump to start
+ ;; when we are at the first installer-step. Abort to
+ ;; 'raise-above prompt to re-raise the condition.
+ (abort-to-prompt 'raise-above c)
+ (run '()
+ #:todo-steps steps
+ #:done-steps '())))))
+ ((installer-step-break? c)
+ (reverse result)))
+ (let* ((id (installer-step-id step))
+ (compute (installer-step-compute step))
+ (res (compute result)))
+ (run (alist-cons id res result)
+ #:todo-steps rest-steps
+ #:done-steps (append done-steps (list step))))))))
+
+ (call-with-prompt 'raise-above
+ (lambda ()
+ (run '()
+ #:todo-steps steps
+ #:done-steps '()))
+ (lambda (k condition)
+ (raise condition))))
+
+(define (find-step-by-id steps id)
+ "Find and return the step in STEPS whose id is equal to ID."
+ (find (lambda (step)
+ (eq? (installer-step-id step) id))
+ steps))
+
+(define (result-step results step-id)
+ "Return the result of the installer-step specified by STEP-ID in
+RESULTS."
+ (assoc-ref results step-id))
+
+(define (result-step-done? results step-id)
+ "Return #t if the installer-step specified by STEP-ID has a COMPUTE value
+stored in RESULTS. Return #f otherwise."
+ (and (assoc step-id results) #t))