#lang racket/base
(require (for-syntax racket/base
                     syntax/kerncase
                     syntax/struct
                     racket/struct-info)
         racket/undefined)

(provide (protect-out (for-syntax shared-body)))

(define-for-syntax (shared-body stx cons-id code-insp make-check-cdr)
  (syntax-case stx ()
    [(_ ([name expr] ...) body1 body ...)
     (let ([names (syntax->list (syntax (name ...)))]
           [exprs (syntax->list (syntax (expr ...)))])
       (for-each (lambda (name)
                   (unless (identifier? name)
                     (raise-syntax-error
                      'shared
                      "not an identifier"
                      stx
                      name)))
                 names)
       (let ([dup (check-duplicate-identifier names)])
         (when dup
           (raise-syntax-error
            'shared
            "duplicate identifier"
            stx
            dup)))
       (let ([exprs (map (lambda (expr)
                           (let ([e (local-expand
                                     expr
                                     'expression
                                     (append
                                      (kernel-form-identifier-list)
                                      names))])
                             ;; Remove #%app if present...
                             (syntax-case (syntax-disarm e code-insp) (#%plain-app)
                               [(#%plain-app a ...)
                                (syntax/loc e (a ...))]
                               [_else e])))
                         exprs)]
             [temp-ids (generate-temporaries names)]
             [placeholder-ids (generate-temporaries names)]
             [ph-used?s (map (lambda (x) (box #f)) names)]
             [struct-decl-for (lambda (id)
                                (and (identifier? id)
                                     (let ([get-struct
                                            (lambda (id)
                                              (let ([v (syntax-local-value id (lambda () #f))])
                                                (and v
                                                     (struct-declaration-info? v)
                                                     (let ([decl (extract-struct-info v)])
                                                       (and (cadr decl)
                                                            (andmap values (list-ref decl 4))
                                                            (append decl
                                                                    (list
                                                                     (if (struct-auto-info? v)
                                                                         (struct-auto-info-lists v)
                                                                         (list null null)))))))))])
                                       (or (get-struct id)
                                           (let ([s (syntax-property id 'constructor-for)])
                                             (and s
                                                  (identifier? s)
                                                  (get-struct s)))
                                           (let* ([s (symbol->string (syntax-e id))]
                                                  [m (regexp-match-positions "make-" s)])
                                             (and m
                                                  (let ([name (datum->syntax
                                                               id
                                                               (string->symbol (string-append (substring s 0 (caar m))
                                                                                              (substring s (cdar m) (string-length s))))
                                                               id)])
                                                    (get-struct name))))))))]
             [append-ids null]
             [same-special-id? (lambda (a b)
                                 ;; Almost module-or-top-identifier=?,
                                 ;; but handle `the-cons' specially
                                 (or (free-identifier=?
                                      a
                                      (if (eq? 'the-cons (syntax-e b))
                                          cons-id
                                          b))
                                     (free-identifier=? 
                                      a 
                                      (datum->syntax
                                       #f
                                       (if (eq? 'the-cons (syntax-e b))
                                           'cons
                                           (syntax-e b))))))]
             [remove-all (lambda (lst rmv-lst)
                           (define (remove e l)
                             (cond
                              [(free-identifier=? e (car l)) (cdr l)]
                              [else (cons (car l) (remove e (cdr l)))]))
                           (let loop ([lst lst] [rmv-lst rmv-lst])
                             (if (null? rmv-lst)
                                 lst
                                 (loop (remove (car rmv-lst) lst)
                                       (cdr rmv-lst)))))]
             [disarm (lambda (stx) (syntax-disarm stx code-insp))])
         (with-syntax ([(graph-expr ...)
                        (map (lambda (expr)
                               (let loop ([expr expr])
                                 (define (bad n)
                                   (raise-syntax-error
                                    'shared
                                    (format "illegal use of ~a" n)
                                    stx
                                    expr))
                                 (define (cons-elem expr)
                                   (or (and (identifier? expr)
                                            (ormap (lambda (i ph ph-used?) 
                                                     (and (free-identifier=? i expr)
                                                          (set-box! ph-used? #t)
                                                          ph))
                                                   names placeholder-ids ph-used?s))
                                       (loop expr)))
                                 (syntax-case* (disarm expr) (the-cons mcons append box box-immutable vector vector-immutable) same-special-id?
                                   [(the-cons a d)
                                    (with-syntax ([a (cons-elem #'a)]
                                                  [d (cons-elem #'d)])
                                      (syntax/loc expr (cons a d)))]
                                   [(the-cons . _)
                                    (bad "cons")]
                                   [(mcons a d)
                                    (syntax (mcons undefined undefined))]
                                   [(mcons . _)
                                    (bad "mcons")]
                                   [(lst e ...)
                                    (ormap (lambda (x) (same-special-id? #'lst x))
                                           (syntax->list #'(list list*)))
                                    (with-syntax ([(e ...)
                                                   (map (lambda (x) (cons-elem x))
                                                        (syntax->list (syntax (e ...))))])
                                      (syntax/loc expr (lst e ...)))]
                                   [(lst . _)
                                    (ormap (lambda (x) (same-special-id? #'lst x))
                                           (syntax->list #'(list list*)))
                                    (bad (syntax-e #'lst))]
                                   [(append e0 ... e)
                                    (let ([len-id (car (generate-temporaries '(len)))])
                                      (set! append-ids (cons len-id append-ids))
                                      (with-syntax ([e (cons-elem #'e)]
                                                    [len-id len-id])
                                        (syntax/loc expr (let ([ph (make-placeholder e)]
                                                               [others (append e0 ... null)])
                                                           (set! len-id (length others))
                                                           (append others ph)))))]
                                   [(append . _)
                                    (bad "append")]
                                   [(box v)
                                    (syntax (box undefined))]
                                   [(box . _)
                                    (bad "box")]
                                   [(box-immutable v)
                                    (with-syntax ([v (cons-elem #'v)])
                                      (syntax/loc expr (box-immutable v)))]
                                   [(vector e ...)
                                    (with-syntax ([(e ...)
                                                   (map (lambda (x) (syntax undefined))
                                                        (syntax->list (syntax (e ...))))])
                                      (syntax (vector e ...)))]
                                   [(vector . _)
                                    (bad "vector")]
                                   [(vector-immutable e ...)
                                    (with-syntax ([(e ...)
                                                   (map (lambda (x) (cons-elem x))
                                                        (syntax->list (syntax (e ...))))])
                                      (syntax/loc expr (vector-immutable e ...)))]
                                   [(vector-immutable . _)
                                    (bad "vector-immutable")]
                                   [(make-x . args)
                                    (struct-decl-for (syntax make-x))
                                    (let ([decl (struct-decl-for (syntax make-x))]
                                          [args (syntax->list (syntax args))])
                                      (unless args
                                        (bad "structure constructor"))
                                      (let ([expected (- (length (list-ref decl 4))
                                                         (length (car (list-ref decl 6))))])
                                        (unless (= expected (length args))
                                          (raise-syntax-error
                                           'shared
                                           (format "wrong argument count for structure constructor; expected ~a, found ~a"
                                                   expected (length args))
                                           stx
                                           expr)))
                                      (with-syntax ([undefineds (map (lambda (x) (syntax undefined)) args)])
                                        (syntax (make-x . undefineds))))]
                                   [_else expr])))
                             exprs)]
                       [(init-expr ...)
                        (map (lambda (expr temp-id used?)
                               (let ([init-id
                                      (syntax-case* expr (the-cons mcons list list* append box box-immutable vector vector-immutable) same-special-id?
                                        [(the-cons . _)
                                         temp-id]
                                        [(mcons . _) temp-id]
                                        [(list . _) temp-id]
                                        [(list* . _) temp-id]
                                        [(append . _) temp-id]
                                        [(box . _) temp-id]
                                        [(box-immutable . _) temp-id]
                                        [(vector . _) temp-id]
                                        [(vector-immutable . _) temp-id]
                                        [(make-x . _)
                                         (syntax-case (syntax-disarm expr code-insp) ()
                                           [(make-x . _)
                                            (struct-decl-for (syntax make-x))])
                                         temp-id]
                                        [else #f])])
                                 (cond
                                  [init-id
                                   (set-box! used? #t)
                                   init-id]
                                  [(unbox used?)
                                   temp-id]
                                  [else
                                   expr])))
                             exprs temp-ids ph-used?s)]
                       [(finish-expr ...)
                        (let ([gen-n (lambda (l)
                                       (let loop ([l l][n 0])
                                         (if (null? l)
                                             null
                                             (cons (datum->syntax (quote-syntax here) n #f)
                                                   (loop (cdr l) (add1 n))))))]
                              [append-ids (reverse append-ids)])
                          (map (lambda (name expr)
                                 (let loop ([name name] [expr expr])
                                   (with-syntax ([name name])
                                     (syntax-case* (disarm expr) (the-cons mcons list list* append box box-immutable vector vector-immutable) 
                                                   same-special-id?
                                       [(the-cons a d)
                                        #`(begin #,(loop #`(car name) #'a)
                                                 #,(loop #`(cdr name) #'d))]
                                       [(mcons a d)
                                        (syntax (begin 
                                                  (set-mcar! name a)
                                                  (set-mcdr! name d)))]
                                       [(list e ...)
                                        (let ([es (syntax->list #'(e ...))])
                                          #`(begin
                                              #,@(map (lambda (n e)
                                                        (loop #`(list-ref name #,n) e))
                                                      (gen-n es)
                                                      es)))]
                                       [(list* e ...)
                                        (let* ([es (syntax->list #'(e ...))]
                                               [last-n (sub1 (length es))])
                                          #`(begin
                                              #,@(map (lambda (n e)
                                                        (loop #`(#,(if (= (syntax-e n) last-n)
                                                                       #'list-tail
                                                                       #'list-ref)
                                                                 name 
                                                                 #,n) 
                                                              e))
                                                      (gen-n es)
                                                      es)))]
                                       [(append e0 ... e)
                                        (with-syntax ([len-id (car append-ids)])
                                          (set! append-ids (cdr append-ids))
                                          (loop #`(list-tail name len-id) #'e))]
                                       [(box v)
                                        (syntax (set-box! name v))]
                                       [(box-immutable v)
                                        (loop #'(unbox name) #'v)]
                                       [(vector e ...)
                                        (with-syntax ([(n ...) (gen-n (syntax->list (syntax (e ...))))])
                                          (syntax (let ([vec name])
                                                    (vector-set! vec n e)
                                                    ...)))]
                                       [(vector-immutable e ...)
                                        (let ([es (syntax->list #'(e ...))])
                                          #`(begin
                                              #,@(map (lambda (n e)
                                                        (loop #`(vector-ref name #,n) e))
                                                      (gen-n es)
                                                      es)))]
                                       [(make-x e ...)
                                        (struct-decl-for (syntax make-x))
                                        (let ([decl (struct-decl-for (syntax make-x))])
                                          (syntax-case (remove-all (reverse (list-ref decl 4)) (cadr (list-ref decl 6))) ()
                                            [() 
                                             (syntax (void))]
                                            [(setter ...) 
                                             (syntax (begin (setter name e) ...))]))]
                                       [_else (syntax (void))]))))
                               names exprs))]
                       [(check-expr ...)
                        (if make-check-cdr
                            (map (lambda (name expr)
                                   (syntax-case* expr (the-cons) same-special-id?
                                     [(the-cons a d)
                                      (make-check-cdr name)]
                                     [_else (syntax #t)]))
                                 names exprs)
                            null)]
                       [(temp-id ...) temp-ids]
                       [(placeholder-id ...) placeholder-ids]
                       [(ph-used? ...)  (map unbox ph-used?s)]
                       [(used-ph-id ...) (filter values
                                                 (map (lambda (ph ph-used?)
                                                        (and (unbox ph-used?)
                                                             ph))
                                                      placeholder-ids ph-used?s))]
                       [(maybe-ph-id ...) (map (lambda (ph ph-used?)
                                                 (and (unbox ph-used?)
                                                      ph))
                                               placeholder-ids ph-used?s)])
           (with-syntax ([(ph-init ...) (filter values
                                                (map (lambda (ph ph-used? graph-expr)
                                                       (and (unbox ph-used?)
                                                            #`(placeholder-set! #,ph #,graph-expr)))
                                                     placeholder-ids ph-used?s
                                                     (syntax->list #'(graph-expr ...))))]
                         [(append-id ...) append-ids])
             (syntax/loc stx
               (letrec-values ([(used-ph-id) (make-placeholder #f)] ...
                               [(append-id) #f] ...
                               [(temp-id ...)
                                (begin
                                  ph-init ...
                                  (apply values (make-reader-graph
                                                 (list maybe-ph-id ...))))]
                               [(name) init-expr] ...)
                 finish-expr
                 ...
                 check-expr
                 ...
                 body1
                 body
                 ...))))))]))
