;;; Environment manipulation
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;; (var . val) / "var=val" rep conversion:

 

(define (split-env-string var=val)
  (let ((i (string-index var=val #\=)))
    (if i (values (substring var=val 0 i)
		  (substring var=val (+ i 1) (string-length var=val)))
	(error "No \"=\" in environment string" var=val))))

(define (env-list->alist env-list)
  (map (lambda (var=val)
	 (call-with-values (lambda () (split-env-string var=val))
			   cons))
       env-list))

(define (alist->env-vec alist)
  (list->vector (map (lambda (var.val)
		       (string-append (car var.val) "="
				      (let ((val (cdr var.val)))
					(if (string? val) val
					    (string-join val ":")))))
		     alist)))

;;; ENV->ALIST

(import-os-error-syscall %load-env () "scm_envvec")

(define (environ-env->alist) 
  (let ((env-list.envvec (%load-env)))
    (cons (env-list->alist (car env-list.envvec)) 
	  (cdr env-list.envvec))))

	   
;;; ALIST->ENV

;;; (%create-env ((vector 'X) -> address))
(import-os-error-syscall %create-env (envvec) "create_env")

;;; assumes aligned env
(define (envvec-alist->env alist)
  (%create-env (alist->env-vec alist)))

(import-os-error-syscall %align-env (envvec) "align_env")

(import-os-error-syscall %free-env (envvec) "free_envvec")

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Environment per thread
(define *env-cache* 'uninitialized)
(define env-lock (make-lock))

(define (install-env)
  (set! *env-cache* (environ**-read))
  (set! $env ;;; TODO The old thread-fluid will remain
	(make-preserved-thread-fluid
	 (env-cache))))
;  (set! env-lock (make-lock)))

(define (env-cache)
  *env-cache*)

;; Actually do the syscall and update the cache
;; assumes the env lock obtained
(define (change-and-cache-env env)
  (environ**-set env)
  (set! *env-cache* env))

;; The thread-specific env: A thread fluid

(define $env 'empty-env-value)

(define (thread-read-env) (thread-fluid $env))
(define (thread-set-env! res) (set-thread-fluid! $env res))
(define (let-env res thunk)
  (let-thread-fluid $env res thunk))

(define (really-with-env* env thunk)
  (with-lock env-lock
    (lambda ()
      (change-and-cache-env env)))
  (let-env env thunk))

(define (align-env!)
  (let ((res (thread-read-env)))
    (if (not (env=? res (env-cache)))
	(change-and-cache-env res))))

(define (thread-change-env res)
  (with-lock env-lock
    (lambda ()
      (change-and-cache-env res)
      (thread-set-env! (env-cache)))))

(define environ-resource (make-resource align-env! env-lock))

(define env-reinitializer
  (make-reinitializer install-env))

(define-record env
      envvec
      alist)	; Corresponding alist

(define-record-resumer type/env
  (lambda (env)
    (set-env:envvec env #f)))

(define (env=? e1 e2)
  (and (env:envvec e1)
       (eq? (env:envvec e1) 
	    (env:envvec e2))))

(define-record envvec 
  environ ;; char**
  )

(define (add-envvec-finalizer! envvec)
  (add-finalizer! envvec envvec-finalizer))

(define-exported-binding "envvec-record-type" type/envvec)
(define-exported-binding "add-envvec-finalizer!" add-envvec-finalizer!)

(define (envvec-finalizer envvec)
  (%free-env envvec))

(define (environ**-read)
  (let ((alist.envvec (environ-env->alist)))
    (make-env (cdr alist.envvec) (car alist.envvec))))

(define (environ**-set env)
   (if (env:envvec env)
       (%align-env (env:envvec env))
       (set-env:envvec env (envvec-alist->env (env:alist env)))))

(define (getenv var)
  (let* ((env (thread-read-env))
	 (res (assoc var (env:alist env))))
    (if res (cdr res) res)))

(define (env->alist)
  (env:alist (thread-read-env)))

(define (setenv var val)
  (let* ((env (thread-read-env))
	 (alist (if val
		    (alist-update 
		     var 
		     val 
		    (env:alist env))
		    (alist-delete
		     var
		     (env:alist env)))))
    (thread-set-env! 
     (make-env 
      #f
      alist))))

(define (alist->env alist)
  (thread-set-env!
   (make-env
    #f
    alist)))

(define (with-env* alist-delta thunk)
  (let ((new-env (fold (lambda (key/val alist)
			  (alist-update (car key/val) (cdr key/val) alist))
			(env->alist)
			alist-delta)))
    (with-total-env* new-env thunk)))

(define (with-total-env* alist thunk)
  (really-with-env* (make-env #f alist) thunk))

(define (alist-delete key alist)
  (filter (lambda (key/val) (not (equal? key (car key/val)))) alist))

(define (alist-update key val alist)
  (cons (cons key val)
	(alist-delete key alist)))

;;; Remove shadowed entries from ALIST. Preserves element order.
;;; (This version shares no structure.)

(define (alist-compress alist) 
  (reverse (let compress ((alist alist) (ans '()))
	     (if (pair? alist)
		 (let ((key/val (car alist))
		       (alist (cdr alist)))
		   (compress alist (if (assoc (car key/val) ans) ans
				       (cons key/val ans))))
		 ans))))

(define (add-before elt before list)
  (let rec ((list list))
    (if (pair? list)
	(let ((x (car list)))
	  (if (equal? x before)
	      (cons elt list)
	      (cons x (rec (cdr list)))))
	(cons elt list))))

;;; In ADD-AFTER, the labelled LET adds ELT after the last occurrence of AFTER
;;; in LIST, and returns the list. However, if the LET finds no occurrence 
;;; of AFTER in LIST, it returns #F instead.

(define (add-after elt after list)
  (or (let rec ((list list))
	(if (pair? list)
	    (let* ((x (car list))
		   (tail (cdr list))
		   (ans (rec tail))) ; #f if AFTER wasn't encountered.
	      (cond (ans (cons x ans))
		    ((equal? x after)
		     (cons x (cons elt tail)))
		    (else #f)))		; AFTER doesn't appear in LIST.
	    #f))			; AFTER doesn't appear in LIST.
      (cons elt list)))

(define-simple-syntax (with-env delta . body)
  (with-env* `delta (lambda () . body)))

(define-simple-syntax (with-total-env env . body)
  (with-total-env* `env (lambda () . body)))

(install-env)