;; -*- mode: common-lisp -*-
#|
clasm-6502: An assembler for the 6502 written in Common Lisp.
Copyright (C) 2024  Aleksei Eaves

This library 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 2.1 of the License, or (at your option) any later version.

This library 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 library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
|#

(defun interpret-character (s x)
  "Interpret meanings of characters."
  (cond
	((>= x (length s))
	 'end-of-line)
	(t
	 ;; Have character, interpret
	 (let ((c (char s x)))
	   (cond
		 ((eq c #\;) ; Comment
		  'comment)
		 ((eq c #\ ) ; Space
		  'whitespace)
		 (t
		  'normal))))))

(defun extract-word (line-string index)
  "Extract a single word from line-string, starting at index."
  (cond
	((member (interpret-character line-string index)
			 `(end-of-line comment))
	 'end-of-line)
	((equal (interpret-character line-string index)
			'whitespace)
	 'whitespace)
	(t
	 (subseq
	  line-string
	  index
	  (do ((end index (incf end)))
		  ((not (equal 'normal
					   (interpret-character line-string end)))
		   end))))))

(defun extract-words (line-string &optional (index 0))
  "Return a list the constituent word strings of line-string."
  ;; Word Processing Logic
  (let ((word (extract-word line-string index)))
	(cond
	  ;; Terminate execution at end-of-line.
	  ((equal word 'end-of-line)
	   nil)
	  ;; If empty, continue on.
	  ((equal word 'whitespace)
	   (extract-words line-string (+ index 1)))
	  ;; Otherwise, extract word and move ahead.
	  (t
	   (cons word
			 (extract-words line-string
							(+ index
							   (length word))))))))

(defun program (source-filename)
  "Turns an assembly source file into a list, prepended with line numbers."
  (let ((source-file (open source-filename))
		(source-line-number 0))
	(labels
		((recurse ()
		   (let ((line (read-line source-file nil 'EOF)))
			 (if (equal line 'EOF)
				 nil
				 (let ((line-list (extract-words line)))
				   (if (equal line-list nil)
					   (progn
						 (incf source-line-number)
						 (recurse))
					   (cons
						(list (incf source-line-number)
							  (extract-words line))
						(recurse))))))))
	  (recurse))))