;;; Ikarus Scheme -- A compiler for R6RS Scheme.
;;; Copyright (C) 2006,2007  Abdulaziz Ghuloum
;;; 
;;; This program is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License version 3 as
;;; published by the Free Software Foundation.
;;; 
;;; 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
;;; General Public License for more details.
;;; 
;;; You should have received a copy of the GNU General Public License
;;; along with this program.  If not, see <http://www.gnu.org/licenses/>.


(library (ikarus.sort)
  (export list-sort vector-sort vector-sort!)
  (import 
    (ikarus system $fx)
    (except (ikarus) list-sort vector-sort vector-sort!))
  
  (module (sort-tail)
    (define (merge1 <? a1 ls1 ls2) 
      (cond
        [(null? ls2) ls1]
        [else
         (let ([a2 (car ls2)])
           (cond
             [(<? a2 a1) 
              (cons a2 (merge1 <? a1 ls1 (cdr ls2)))]
             [else
              (cons a1 (merge2 <? a2 (cdr ls1) ls2))]))]))
    
    (define (merge2 <? a2 ls1 ls2) 
      (cond
        [(null? ls1) ls2]
        [else
         (let ([a1 (car ls1)])
           (cond
             [(<? a2 a1) 
              (cons a2 (merge1 <? a1 ls1 (cdr ls2)))]
             [else
              (cons a1 (merge2 <? a2 (cdr ls1) ls2))]))]))
  
    (define (merge <? ls1 ls2) 
      (cond
        [(null? ls2) ls1]
        [else 
         (let ([a1 (car ls1)] [a2 (car ls2)])
           (cond
             [(<? a2 a1) 
              (cons a2 (merge1 <? a1 ls1 (cdr ls2)))]
             [else
              (cons a1 (merge2 <? a2 (cdr ls1) ls2))]))]))
  
    (define (sort-head <? ls n)
      (cond
        [($fx= n 0) (values '() ls)]
        [($fx= n 1)
         (values (cons (car ls) '()) (cdr ls))]
        [else
         (let-values ([(sorted-head tail) 
                       (sort-head <? ls ($fxsra n 1))])
           (let-values ([(sorted-tail tail) 
                         (sort-head <? tail ($fx- n ($fxsra n 1)))])
             (values (merge <? sorted-head sorted-tail) tail)))]))
  
    (define (sort-tail <? ls n) 
      (cond
        [($fx<= n 1) ls]
        [else
         (let-values ([(sorted-head tail) 
                       (sort-head <? ls ($fxsra n 1))])
            (merge <? sorted-head 
              (sort-tail <? tail ($fx- n ($fxsra n 1)))))])))

  (define (list-sort <? ls) 
    (unless (procedure? <?)
      (die 'list-sort "not a procedure" <?))
    (sort-tail <? ls (length ls)))



  (define (vector-sort <? v)
    ;;; FIXME: improve
    (unless (procedure? <?)
      (die 'vector-sort "not a procedure" <?))
    (unless (vector? v)
      (die 'vector-sort "not a vector" v))
    (list->vector 
      (sort-tail <? (vector->list v) (vector-length v))))

  (define (vector-sort! <? v) 
    (import (ikarus system $vectors))
    (import (ikarus system $pairs))
    (unless (procedure? <?)
      (die 'vector-sort! "not a procedure" <?))
    (unless (vector? v)
      (die 'vector-sort! "not a vector" v))
    (let f ([i 0] [v v] 
            [ls (sort-tail <? (vector->list v) (vector-length v))])
      (unless (null? ls) 
        ($vector-set! v i ($car ls))
        (f ($fx+ i 1) v ($cdr ls)))))
    
  )