(defvar *forward-index* (make-string-hash-table))
(defvar *inverse-index* (make-string-hash-table))

(defun make-string-hash-table ()
	"helper function to create a hash table that works with multiple types of keys"
	(make-hash-table :test #'equal))

; index a site into *forward-index*
(defun index-site (html doc-id)
    (let ((words (split-sequence #\Space html))
          (index (make-string-hash-table)))
         (dolist (word words) (if (gethash word index)
                       (incf (gethash word index))
                       (setf (gethash word index) 1)))

; generate the inverse index from *forward-index* into *inverse-index*
(defun generate-inverse-index ()
 (maphash (lambda (doc-id word-map)
       (maphash (lambda (word hits)
             (let ((doc-hit-list (list doc-id hits)))
             (if (gethash word *inverse-index*)
             (push doc-hit-list (gethash word *inverse-index*))
             (setf (gethash word *inverse-index*) (list doc-hit-list))))) word-map)) *forward-index*)
	(setf *forward-index* (make-string-hash-table))