#lang racket/base

(require (for-syntax racket/base racket/list))
(provide (rename-out [kaitai:module-begin #%module-begin])
         (except-out (all-from-out racket/base) #%module-begin))

;; meow

;; makes a syntax error raiser
(define-for-syntax (rse msg)
  (lambda () (raise-syntax-error #f msg)))

;; converts a ksy id to a racket id
;; maps _ to -
(define-for-syntax (kaitai-str->sym str)
  (string->symbol (regexp-replace* #px"_" str "-")))

;; generates struct definitions
(define-for-syntax (gen-struct top [given-id #f])
  (define id (or given-id (hash-ref (hash-ref top "meta" (hash)) "id"
                                    (rse "type has no meta.id and none was provided"))))
  (define id-sym (kaitai-str->sym id))
  (define seq (hash-ref top "seq" (rse "form must have a seq element")))
  (define instances (hash-ref top "instances" (hash)))
  #`((provide [struct-out #,id-sym])
     (struct #,id-sym
      [#,@(map (lambda (a) (kaitai-str->sym (hash-ref a "id" (rse "seq element has no id"))))
               seq)] #:transparent)))

;; language infrastructure

(define-syntax (kaitai:module-begin stx)
  (define body (second (syntax-e stx)))
  (define top-struct (gen-struct (syntax->datum body)))
  ; (displayln top-struct)
  #`(#%module-begin
     #,@top-struct))

(module reader syntax/module-reader
  #:read kaitai-read
  #:read-syntax kaitai-read
  #:language 'kaitai

  (require yaml)

  (define (kaitai-read path port)
    (or (read-yaml port) eof))

  (define (kaitai-read-syntax path port)
    (datum->syntax #f (kaitai-read path port))))