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;;; read-text-outline --- Read a text outline and display it as a sexp

;; 	Copyright (C) 2002, 2006, 2011 Free Software Foundation, Inc.
;;
;; This program is free software; you can redistribute it and/or
;; modify it under the terms of the GNU Lesser General Public License
;; as published by the Free Software Foundation; either version 3, or
;; (at your option) any later version.
;;
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;; Lesser General Public License for more details.
;;
;; You should have received a copy of the GNU Lesser General Public
;; License along with this software; see the file COPYING.LESSER.  If
;; not, write to the Free Software Foundation, Inc., 51 Franklin
;; Street, Fifth Floor, Boston, MA 02110-1301 USA

;;; Author: Thien-Thi Nguyen <ttn@gnu.org>

;;; Commentary:

;; Usage: read-text-outline OUTLINE
;;
;; Scan OUTLINE file and display a list of trees, the structure of
;; each reflecting the "levels" in OUTLINE.  The recognized outline
;; format (used to indicate outline headings) is zero or more pairs of
;; leading spaces followed by "-".  Something like:
;;
;;    - a                  0
;;      - b                1
;;        - c              2
;;      - d                1
;;    - e                  0
;;      - f                1
;;        - g              2
;;      - h                1
;;
;; In this example the levels are shown to the right.  The output for
;; such a file would be the single line:
;;
;;   (("a" ("b" "c") "d") ("e" ("f" "g") "h"))
;;
;; Basically, anything at the beginning of a list is a parent, and the
;; remaining elements of that list are its children.
;;
;;
;; Usage from a Scheme program: These two procs are exported:
;;
;;   (read-text-outline . args)           ; only first arg is used
;;   (read-text-outline-silently port)
;;   (make-text-outline-reader re specs)
;;
;; `make-text-outline-reader' returns a proc that reads from PORT and
;; returns a list of trees (similar to `read-text-outline-silently').
;;
;; RE is a regular expression (string) that is used to identify a header
;; line of the outline (as opposed to a whitespace line or intervening
;; text).  RE must begin w/ a sub-expression to match the "level prefix"
;; of the line.  You can use `level-submatch-number' in SPECS (explained
;; below) to specify a number other than 1, the default.
;;
;; Normally, the level of the line is taken directly as the length of
;; its level prefix.  This often results in adjacent levels not mapping
;; to adjacent numbers, which confuses the tree-building portion of the
;; program, which expects top-level to be 0, first sub-level to be 1,
;; etc.  You can use `level-substring-divisor' or `compute-level' in
;; SPECS to specify a constant scaling factor or specify a completely
;; alternative procedure, respectively.
;;
;; SPECS is an alist which may contain the following key/value pairs:
;;
;; - level-submatch-number NUMBER
;; - level-substring-divisor NUMBER
;; - compute-level PROC
;; - body-submatch-number NUMBER
;; - extra-fields ((FIELD-1 . SUBMATCH-1) (FIELD-2 . SUBMATCH-2) ...)
;;
;; The PROC value associated with key `compute-level' should take a
;; Scheme match structure (as returned by `regexp-exec') and return a
;; number, the normalized level for that line.  If this is specified,
;; it takes precedence over other level-computation methods.
;;
;; Use `body-submatch-number' if RE specifies the whole body, or if you
;; want to make use of the extra fields parsing.  The `extra-fields'
;; value is a sub-alist, whose keys name additional fields that are to
;; be recognized.  These fields along with `level' are set as object
;; properties of the final string ("body") that is consed into the tree.
;; If a field name ends in "?" the field value is set to be #t if there
;; is a match and the result is not an empty string, and #f otherwise.
;;
;;
;; Bugs and caveats:
;;
;; (1) Only the first file specified on the command line is scanned.
;; (2) TAB characters at the beginnings of lines are not recognized.
;; (3) Outlines that "skip" levels signal an error.  In other words,
;;     this will fail:
;;
;;            - a               0
;;              - b             1
;;                  - c         3       <-- skipped 2 -- error!
;;              - d             1
;;
;;
;; TODO: Determine what's the right thing to do for skips.
;;       Handle TABs.
;;       Make line format customizable via longopts.

;;; Code:

(define-module (scripts read-text-outline)
  :export (read-text-outline
           read-text-outline-silently
           make-text-outline-reader)
  :use-module (ice-9 regex)
  :autoload (ice-9 rdelim) (read-line)
  :autoload (ice-9 getopt-long) (getopt-long))

(define %include-in-guild-list #f)
(define %summary "Convert textual outlines to s-expressions.")

(define (?? symbol)
  (let ((name (symbol->string symbol)))
    (string=? "?" (substring name (1- (string-length name))))))

(define (msub n)
  (lambda (m)
    (match:substring m n)))

(define (??-predicates pair)
  (cons (car pair)
        (if (?? (car pair))
            (lambda (m)
              (not (string=? "" (match:substring m (cdr pair)))))
            (msub (cdr pair)))))

(define (make-line-parser re specs)
  (let* ((rx (let ((fc (substring re 0 1)))
               (make-regexp (if (string=? "^" fc)
                                re
                                (string-append "^" re)))))
         (check (lambda (key)
                  (assq-ref specs key)))
         (level-substring (msub (or (check 'level-submatch-number) 1)))
         (extract-level (cond ((check 'compute-level)
                               => (lambda (proc)
                                    (lambda (m)
                                      (proc m))))
                              ((check 'level-substring-divisor)
                               => (lambda (n)
                                    (lambda (m)
                                      (/ (string-length (level-substring m))
                                         n))))
                              (else
                               (lambda (m)
                                 (string-length (level-substring m))))))
         (extract-body (cond ((check 'body-submatch-number)
                              => msub)
                             (else
                              (lambda (m) (match:suffix m)))))
         (misc-props! (cond ((check 'extra-fields)
                             => (lambda (alist)
                                  (let ((new (map ??-predicates alist)))
                                    (lambda (obj m)
                                      (for-each
                                       (lambda (pair)
                                         (set-object-property!
                                          obj (car pair)
                                          ((cdr pair) m)))
                                       new)))))
                            (else
                             (lambda (obj m) #t)))))
    ;; retval
    (lambda (line)
      (cond ((regexp-exec rx line)
             => (lambda (m)
                  (let ((level (extract-level m))
                        (body  (extract-body m)))
                    (set-object-property! body 'level level)
                    (misc-props! body m)
                    body)))
            (else #f)))))

(define (make-text-outline-reader re specs)
  (let ((parse-line (make-line-parser re specs)))
    ;; retval
    (lambda (port)
      (let* ((all '(start))
             (pchain (list)))           ; parents chain
        (let loop ((line (read-line port))
                   (prev-level -1)      ; how this relates to the first input
                                        ; level determines whether or not we
                                        ; start in "sibling" or "child" mode.
                                        ; in the end, `start' is ignored and
                                        ; it's much easier to ignore parents
                                        ; than siblings (sometimes).  this is
                                        ; not to encourage ignorance, however.
                   (tp all))            ; tail pointer
          (or (eof-object? line)
              (cond ((parse-line line)
                     => (lambda (w)
                          (let* ((words (list w))
                                 (level (object-property w 'level))
                                 (diff (- level prev-level)))
                            (cond

                             ;; sibling
                             ((zero? diff)
                              ;; just extend the chain
                              (set-cdr! tp words))

                             ;; child
                             ((positive? diff)
                              (or (= 1 diff)
                                  (error "unhandled diff not 1:" diff line))
                              ;; parent may be contacted by uncle later (kids
                              ;; these days!) so save its level
                              (set-object-property! tp 'level prev-level)
                              (set! pchain (cons tp pchain))
                              ;; "push down" car into hierarchy
                              (set-car! tp (cons (car tp) words)))

                             ;; uncle
                             ((negative? diff)
                              ;; prune back to where levels match
                              (do ((p pchain (cdr p)))
                                  ((= level (object-property (car p) 'level))
                                   (set! pchain p)))
                              ;; resume at this level
                              (set-cdr! (car pchain) words)
                              (set! pchain (cdr pchain))))

                            (loop (read-line port) level words))))
                    (else (loop (read-line port) prev-level tp)))))
        (set! all (car all))
        (if (eq? 'start all)
            '()                         ; wasteland
            (cdr all))))))

(define read-text-outline-silently
  (make-text-outline-reader "(([ ][ ])*)- *"
                            '((level-substring-divisor . 2))))

(define (read-text-outline . args)
  (write (read-text-outline-silently (open-file (car args) "r")))
  (newline)
  #t)                                   ; exit val

(define main read-text-outline)

;;; read-text-outline ends here