#lang typed/racket

(require (for-syntax syntax/parse racket/list))

(provide Symbol VariableMapping
         eval-with eval1-with
         ;; Syntax
         auto-hash-ref/explicit auto-hash-ref/:)

(module+ test
  (require typed/rackunit))

;;; ===================
;;; HashTable injection
;;; ===================

(define-type Variable Symbol)
(define-type (VariableMapping A) (Immutable-HashTable Variable A))

(: eval-with (-> (VariableMapping Any) Any AnyValues))
(define (eval-with ht expr)
  (parameterize ([current-namespace (make-base-namespace)])
    (for ([(x val) (in-hash ht)]) (namespace-set-variable-value! x val))
    (eval expr)))

(: eval1-with (-> (VariableMapping Any) Any Any))
(define (eval1-with ht expr)
  (call-with-values (λ () (eval-with ht expr))
                    (λ args (car args))))

(module+ test
  (test-case "eval-with"
    (check-equal? (eval1-with (hash 'a 1 'b 2) '(+ a b 1))
                  4)
    (define ht : (VariableMapping Integer) (hash 'a 1 'b 2))
    (define expr : Any '(+ a b 1))
    (check-equal? (eval1-with ht expr)
                  4)))

(define-syntax (auto-hash-ref/explicit stx)
  (syntax-parse stx
    [(_ (ht:id xs:id ...) body:expr)
     #`(let #,(for/list ([x (syntax->list #'(xs ...))])
                #`[#,x (hash-ref ht '#,x)])
         body)]))

(module+ test
  (test-case "auto-hash-ref/explicit"
    (define mytable #hash((a . 3) (b . 4)))
    (check-equal? (auto-hash-ref/explicit (mytable b a)
                                          (* a b))
                  12)
    (define ht #hash((a . #t) (b . #f)))
    (check-equal? (auto-hash-ref/explicit (ht a b)
                                          (and (not a) b))
                  #f)))

(define-syntax (auto-hash-ref/: stx)
  (syntax-parse stx
    [(_ ht:id body)
     (let* ([names/: (collect-colons (syntax->datum #'body))])
       #`(let #,(for/list ([x names/:])
                  ;; put x in the same context as body
                  #`[#,(datum->syntax #'body x)
                     (hash-ref ht '#,(strip-colon x))])
           body))]))

;;; The helper functions for auto-hash-ref/:.
(begin-for-syntax
  ;; Collect all the symbols starting with a colon in datum.
  (define (collect-colons datum)
    (remove-duplicates
     (flatten
      (for/list ([token datum])
        (cond
          [(symbol? token)
           (let ([name (symbol->string token)])
             (if (eq? #\: (string-ref name 0))
                 token
                 '()))]
          [(list? token)
           (collect-colons token)]
          [else '()])))))

  ;; Strip the leading colon off x.
  (define (strip-colon x)
    (let ([x-str (symbol->string x)])
      (if (eq? #\: (string-ref x-str 0))
          (string->symbol (substring x-str 1))
          x))))

(module+ test
  (test-case "auto-hash-ref/:"
    (define ht1 #hash((x . #t) (y . #t) (t . #f)))
    (define z #t)
    (check-equal? (auto-hash-ref/: ht1
                                   (and :x (not :y) z (or (and :t) :x)))
                  #f)
    (define ht2 #hash((a . 1) (b . 2)))
    (check-equal? (auto-hash-ref/: ht2 (+ :a (* 2 :b)))
                  5)))