#| Copyright 2024 Peter McGoron
 |
 | Licensed under the Apache License, Version 2.0 (the "License");
 | you may not use this file except in compliance with the License.
 | You may obtain a copy of the License at
 |
 |     http://www.apache.org/licenses/LICENSE-2.0
 |
 | Unless required by applicable law or agreed to in writing, software
 | distributed under the License is distributed on an "AS IS" BASIS,
 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 | See the License for the specific language governing permissions and
 | limitations under the License.
 |#

(define-record-type <iterator>
  (make-iterator-container closure capabilities type)
  iterator?
  (closure iterator-closure)
  (capabilities iterator-capabilities)
  (type iterator-type))

(define (iterator-invoke itr field . args)
  ((iterator-closure itr) field args))

(define-syntax define-invocation
  (syntax-rules ()
    ((define-invocation name args ...)
     (define (name itr args ...)
       (iterator-invoke itr (quote name) args ...)))))

(define-syntax define-iterator-implementation
  (syntax-rules (else)
    ((_ (cstr cstr-args ...) self ((name . formal) body ...) ...)
     (define (cstr cstr-args ...)
       (letrec ((self
                 (make-iterator-container
                  (lambda (type args)
                    (case type
                      ((name) (apply (lambda formal body ...) args))
                      ...
                      (else (raise (not-implemented-exception self
                                                              type
                                                              args)))))
                  '(name ...)
                  (quote cstr))))
         self)))))

(define-invocation iterator-at-start?)
(define-invocation iterator-at-end?)
(define-invocation iterator-advance spaces)
(define-invocation iterator-ref)
(define-invocation iterator-set! val)
(define-invocation iterator->index)

(define (iterator-next itr)
  (iterator-advance itr 1))
(define (iterator-prev itr)
  (iterator-advance itr -1))