;;; suffiex-tree.el --- Ukkonen algorithm for building a suffix tree -*- lexical-binding: t; -*-

;;; Author: Durand
;;; Version: 0.0.1

;;; Commentary:

;; Our node is represented as a list of the following elements:

;; start      , which is the starting index of the edge going from its parent
;;              node to this node
;; end        , the index of the end of the above edge
;; suffix-link, the index of the node this node's suffix-link points to
;; children   , a hash-table of pairs of integers and indices of its
;;              children

;; To compute the length of the edge going into NODE we use:
;; (- (min end (1+ position)) start)
;; which is actually how far the position is on that edge,
;; if it is on that edge.

;;; Code:

;;;###autoload
(defun st-min (&rest args)
  "Return the minimum among ARGS.
If an argument is 'infty, then it is considered greater than
every number."
  (apply #'min (delq nil
                     (mapcar
                      (lambda (arg)
                        (cond
                         ((number-or-marker-p arg) arg)
                         ((eq arg 'infty) nil)))
                      args))))

;;;###autoload
(defun st-edge-length (node position)
  "Return the length of the edge into NODE.
See the comment above this function for the reason
POSITION is here."
  (- (st-min (car (cdr node)) (1+ position))
     (car node)))

;;;###autoload
(defun st-new-node (tree last-added start &optional end)
  "Make a new node with START and END as the coming edge.
Then add the new node to TREE.
LAST-ADDED is the number of elements already in the TREE."
  (let* ((end (or end 'infty) ;; 'infty represents the index of a leaf
              )
         (suffix-link 0) ;; The suffix link is initially 0
         (new-node
          (list start end
                suffix-link
                (make-hash-table))))
    (puthash (1+ last-added) new-node tree)
    (1+ last-added)))

;;;###autoload
(defun st-add-suffix-link (tree need-sl node)
  "If NEED-SL is positive, then add the suffix link.
In particular, the node corresponding to NEED-SL in TREE
gets a suffix link pointing to NODE.

This always returns NODE."
  (cond
   ((and (> need-sl 1) (/= need-sl node))
    (setcar (cdr (cdr (gethash need-sl tree))) node)))
  node)

;;;###autoload
(defun st-canonize (tree node position active-edge-index active-length active-node)
  "Walk down TREE to find the correct active point."
  (let ((node-edge-length (st-edge-length (gethash node tree) position)))
    (cond
     ((>= active-length node-edge-length)
      (list t
            (+ active-edge-index
               node-edge-length)
            (- active-length
               node-edge-length)
            node))
     (t
      (list nil
            active-edge-index
            active-length
            active-node)))))

;;;###autoload
(defun st-extend-tree (tree last-added position remain
                       active-node active-edge-index
                       active-length character str)
  "Extend a tree by CHARACTER.
The return value is
(tree last-added remain active-node
 active-edge-index active-length)"
  (let* ((need-sl 0)
         (remain (1+ remain))
         continue-p breakp)
    (while (and (not breakp) (> remain 0))
      (setq continue-p nil breakp nil)
      (cond
       ((= active-length 0)
        (setq active-edge-index position)))
      (let* ((actual-node (gethash active-node tree))
             (nxt (cond
                   (actual-node
                    (gethash (aref str active-edge-index)
                             (cadr (cdr (cdr actual-node))))))))
        (cond
         ((null nxt)
          (let ((leaf (st-new-node tree last-added position)))
            (setq last-added leaf)
            (puthash (aref str active-edge-index)
                     leaf
                     (cadr (cdr (cdr (gethash active-node tree)))))
            (setq need-sl (st-add-suffix-link tree need-sl active-node)))
            ;; rule 2
            )
         (t
          (let* ((result (st-canonize
                          tree nxt position active-edge-index
                          active-length active-node)))
            (cond
             ((car result)
              ;; observation 2
              (setq active-edge-index (cadr result))
              (setq active-length (caddr result))
              (setq active-node (cadr (cddr result)))
              (setq continue-p t))
             (t
              (cond
               ((eq (aref str (+ active-length
                                 (car (gethash nxt tree))))
                    character)
                ;; observation 1
                (setq active-length (1+ active-length))
                (setq need-sl (st-add-suffix-link tree need-sl active-node))
                (setq breakp t)))
              (cond
               (breakp)
               (t ;; splitting
                (let ((split (st-new-node
                              tree last-added (car (gethash nxt tree))
                              (+ (car (gethash nxt tree)) active-length))))
                  (setq last-added split)
                  (puthash
                   (aref str active-edge-index)
                   split (cadr (cdr (cdr (gethash active-node tree)))))
                  (let ((leaf (st-new-node tree last-added position)))
                    (setq last-added leaf)
                    (puthash character leaf
                             (cadddr (gethash split tree)))
                    (setcar (gethash nxt tree)
                            (+ (car (gethash nxt tree))
                               active-length))
                    (puthash (aref str (car (gethash nxt tree))) nxt
                             (cadddr (gethash split tree)))
                    ;; rule 2
                    (setq need-sl
                          (st-add-suffix-link tree need-sl split)))))))))))
            (cond
             ((or continue-p breakp))
             (t
              (setq remain (1- remain))
              (cond
               ((and (eq active-node 1) ; root
                     (> active-length 0))
                (setq active-length (1- active-length))
                (setq active-edge-index
                      (1+ (- position remain))))
               (t
                (setq active-node
                      (let ((slink (caddr (gethash active-node tree))))
                        (cond
                         ((> slink 1) slink)
                                        ; or root
                         (t 1))))))))))
    (list tree last-added remain active-node
          active-edge-index active-length)))

;;;###autoload
(defun st-build-for-str (str)
  "Build the suffix tree for STR."
  (let* ((position 0)
         (character (ignore-error 'error (aref str position)))
         (tree (make-hash-table))
         (last-added 0)
         (remain 0)
         (active-node (st-new-node tree last-added -1 -1))
         (active-edge-index 0)
         (active-length 0)
         result)
    (setq last-added active-node)
    (while character
      (setq result (st-extend-tree tree last-added position remain
                                   active-node active-edge-index
                                   active-length character str))
      (setq tree (pop result))
      (setq last-added (pop result))
      (setq remain (pop result))
      (setq active-node (pop result))
      (setq active-edge-index (pop result))
      (setq active-length (pop result))
      (setq position (1+ position))
      (setq character (ignore-error 'error (aref str position))))
    tree))

;;; Some printing functions

(require 'hierarchy)

;;;###autoload
(defun st-print-str (str)
  "Print generalized string"
  (mapc (lambda (char)
          (cond ((characterp char) (insert char))
                (t (insert ", "))))
        str))

;;;###autoload
(defun st-print-tree-for-str (str)
  "Print the suffix tree for STR."
  (let* ((symbol (make-symbol "test")))
    (set symbol (st-build-for-str str))
    (insert "suffix tree for strings: ")
    (st-print-str str)
    (insert "\n")
    (st-print-tree (symbol-value symbol) str)))

;;;###autoload
(defun st-reduce-index (node strs)
  "Reduce the second element of the NODE."
  (let* ((lengths (mapcar #'length strs))
         (start (car node))
         (end (cadr node))
         (first-greater-than-start
          (let ((sum -1) (index 0) done result)
            (while (and (not done) (< index (length strs)))
              (cond
               ((<= (+ sum (nth index lengths)) start)
                (setq index (1+ index))
                (setq sum (+ sum (nth index lengths))))
               (t (setq result (+ sum (nth index lengths)))
                  (setq done t))))
            (cond ((null result) (setq result (1- (apply #'+ lengths)))))
            result)))
    (st-min end first-greater-than-start))
  ;; (let* ((start (car node))
  ;;        (end (cadr node))
  ;;        (index start)
  ;;        result stop)
  ;;   (while (and (not stop) (or (eq end 'infty) (<= index end)))
  ;;     (cond
  ;;      ((and (< index (length str)) (characterp (aref str index))) (setq index (1+ index)))
  ;;      (t (setq stop t)
  ;;         (setq result index))))
  ;;   (cond ((and (numberp end) (= index (1+ end))) (setq result end)))
  ;;   (cond ((<= result start) (setq result 'end)))
  ;;   result)
  )

;; ;;;###autoload
;; (defun st-build-generalized-tree (strs)
;;   (let* ((copy strs)
;;          (long-str
;;           (let ((index 1) result)
;;             (while (consp copy)
;;               (setq result (vconcat result
;;                                     (car copy)
;;                                     (vector (- index))))
;;               (setq index (1+ index))
;;               (setq copy (cdr copy)))
;;             result))
;;          (tree (make-symbol "tree")))
;;     (set tree (st-build-for-str long-str))))

;;;###autoload
(defun st-print-tree (tree str)
  "Print TREE with the aid of STR."
  (let* ((symbol-tree (make-symbol "test-tree")))
    (set symbol-tree (hierarchy-new))
    (maphash
     (lambda (key value)
       (hierarchy-add-tree
        (symbol-value symbol-tree) key nil
        (lambda (item)
          (hash-table-values (cadr (cdr (cdr (gethash item tree))))))))
     tree)
    (hierarchy-print (symbol-value symbol-tree)
                     (lambda (item)
                       (cond ((= item 1) "root")
                             (t (let* ((node (gethash item tree))
                                       ;; (reduced (st-reduce-index node str))
                                       )
                                  (substring str (car node)
                                             (cond ((integerp (cadr node)) (cadr node))))
                                  ;; (cond ((eq reduced 'end) "$")
                                  ;;       (t (apply #'string
                                  ;;                 (append
                                  ;;                  (seq-subseq str (car node)
                                  ;;                              reduced
                                  ;;                              ;; (cond ((integerp (cadr node)) (cadr node)))
                                  ;;                              )
                                  ;;                  nil))))
                                  
                                  ;; (format "%d): (%S, %S): (%d): \"%s\""
                                  ;;         item
                                  ;;         (car node)
                                  ;;         (cadr node)
                                  ;;         (caddr node)
                                  ;;         (substring str (car node) (cond ((integerp (cadr node)) (cadr node))))
                                  ;;         )
                                  )))))))

(provide 'suffix-tree)
;;; suffiex-tree.el ends here

;;; archive

;; ;;;###autoload
;; (defvar st-root nil
;;   "The root of the suffix tree.")

;; ;;;###autoload
;; (defvar st-position nil
;;   "The current position in the string.")

;; ;;;###autoload
;; (defvar st-wait-for-link nil
;;   "The node that is waiting to have a suffix link.")

;; ;;;###autoload
;; (defvar st-remain nil
;;   "The number of remaining suffixes to insert.")

;; ;;;###autoload
;; (defvar st-active-node nil
;;   "Where to insert a new suffix.")

;; ;;;###autoload
;; (defvar st-active-edge-index nil
;;   "The index of the active edge.")

;; ;;;###autoload
;; (defvar st-active-length nil
;;   "How far down is the active point down the active edge.")

;; (insert (format "after character %c, the tree becomes\n" character))
;; (insert (format "string is %s\n" (substring str 0 (1+ position))))
;; (insert (format "active-node: %d\n" active-node))
;; (insert (format "active-edge: %c\n" (aref str active-edge-index)))
;; (insert (format "active-length: %d\n" active-length))
;; (cond ((eq last-added 11)
;;        (insert (format "slink: %d\n" (caddr (gethash active-node tree))))
;;        (insert (format "con: %S" continue-p))
;;        (insert (format "breakp: %S\n" breakp))))
;; (st-print-tree tree (substring str 0 (1+ position)))
;; (insert "\n\n")


;; ;;;###autoload
;; (defvar st-output-buffer-name "*suffix-tree*"
;;   "The name of the buffer that contains the output.")

;; ;;;###autoload
;; (defun st-print-tree (tree node str prefix)
;;   "Print TREE in the dedicated output buffer starting at NODE.
;; PREFIX is used to recursively call this function.

;; We need STR since the information we stored in the tree
;; only contains the index into STR,
;; for the sake of optimizations."
;;   (with-temp-buffer-window st-output-buffer-name '((display-buffer-at-bottom)) nil
;;     (st-print-tree-internal tree node str prefix)))

;; ;;;###autoload
;; (defun st-print-tree-internal (tree node str prefix)
;;   "The function that really prints out the data."
;;   (let* ((node-data (gethash node tree))
;;          (start (car node-data))
;;          (end (cadr node-data))
;;          (edges (cdddr node-data))
;;          (node-num (format "(%d)" node))
;;          (node-label (format "%s-%s-%s"
;;                              prefix node-num
;;                              (substring str start end))))
;;     (prin1 node-label)
;;     ;; print the first edge
;;     (let* ((prefix-base (concat
;;                          prefix
;;                          (make-string (length node-label) 32)))
;;            ;; TODO
;;            ))))