From a5f17e298a1d7500ff6c3c53950b2af086948cff Mon Sep 17 00:00:00 2001
From: Clyne Sullivan <clyne@bitgloo.com>
Date: Wed, 7 Dec 2022 21:47:54 -0500
Subject: [PATCH] day7: add annotations

---
 day7/both.bas | 73 ++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 67 insertions(+), 6 deletions(-)

diff --git a/day7/both.bas b/day7/both.bas
index efe35a8..0041b66 100644
--- a/day7/both.bas
+++ b/day7/both.bas
@@ -1,44 +1,76 @@
 REM Advent of Code 2022: Day 7, part 1 and 2
 REM Written in Applesoft BASIC
 
+REM Usual initialization. SPEED= sets the text speed; I play with it
+REM and some empty FOR loops during the program for artistic effect.
+
  10  ONERR  GOTO 700
  20  PRINT  CHR$ (4),"OPEN INPUT"
  30  PRINT  CHR$ (4),"READ INPUT"
  40  HOME 
  50  SPEED= 170
+
+REM DN$ and DS are a index-matched "map" of paths and sizes. A size of
+REM 200 accommodated my input.
+REM W$ stores the current working directory.
+
  100  DIM DN$(200)
  110  DIM DS(200)
  120  FOR I = 0 TO 199:DN$(I) = "": NEXT I
  130  FOR I = 0 TO 199:DS(I) = 0: NEXT I
  140 W$ = "/"
+
+REM Main loop: consume a line of input, display it, and then handle
+REM either the "ls" or "cd" that it is.
+
  200  GOSUB 4000
  210  PRINT "$";
  215  FOR I = 0 TO 1000: NEXT I
  218  SPEED= 70: PRINT  RIGHT$ (S$, LEN (S$) - 1): SPEED= 170
  220  IF  LEFT$ (S$,4) = "$ cd" GOTO 300
  230  GOTO 500
+
+REM "cd" routine. If the path starts with '/', then clear the working
+REM directory so we return to root.
+REM If starting with a '.', GOTO 350 to handle backing up a level.
+REM Otherwise, append to the working directory.
+
  300 C$ =  MID$ (S$,6,1)
  305  IF  ASC (C$) = 47 THEN W$ = ""
  310  IF  ASC (C$) = 46 GOTO 350
  320 W$ = W$ +  MID$ (S$,6, LEN (S$) - 5)
  330  IF  ASC ( RIGHT$ (W$,1)) <  > 47 THEN W$ = W$ + "/"
  340  GOTO 400
+
  350 W$ =  LEFT$ (W$, LEN (W$) - 1)
  360  IF  RIGHT$ (W$,1) <  > "/" GOTO 350
  370  GOTO 200
+
+REM Call 2000 to create a size entry for this directory if it does not
+REM exist.
+
  400 S$ = W$
  410  GOSUB 2000
  420  GOTO 200
+
+ REM "ls" routine. Leave the loop if we reach the next command; skip dirs.
+
  500 V = 0
  510  GOSUB 4000
- 515  IF  LEFT$ (S$,1) = "$" GOTO 600
+ 515  IF  LEFT$ (S$,1) = "$" GOTO 210
  520  PRINT S$
  530  IF  LEFT$ (S$,3) = "dir" GOTO 510
+
+REM Call 3000 to add file's size to relevant directorys' totals.
+
  540 V =  VAL (S$)
  550 S$ = W$
  560  GOSUB 3000
  570  GOTO 510
- 600  GOTO 210
+
+REM We will land here once the file has been completely read. Do the
+REM search for part 1, summing into T.
+
  700 T = 0
  710  FOR I = 0 TO 199
  720  IF  LEN (DN$(I)) = 0 THEN I = 199: GOTO 740
@@ -46,21 +78,33 @@ REM Written in Applesoft BASIC
  740  NEXT I
  745  PRINT 
  750  PRINT "part 1: ";T;" bytes"
+
+REM Part 2 is at 5000. It will come back to 900 to exit.
+
  760  GOTO 5000
+
  900  PRINT  CHR$ (4),"CLOSE"
  910  SPEED= 255
  920  END 
+
+REM Subroutine: Fetches the size of directory S$, putting it in V.
+
  1000 V = 0
  1010  FOR I = 0 TO 199
  1020  IF DN$(I) = S$ THEN V = DS(I):I = 199
  1030  NEXT I
  1040  RETURN 
- 2000 V = 0
- 2005  FOR I = 0 TO 199
+
+REM Subroutine: Initializes new entry for directory S$.
+
+ 2000  FOR I = 0 TO 199
  2010  IF DN$(I) = S$ THEN  PRINT "ERROR": END 
- 2020  IF  LEN (DN$(I)) = 0 THEN DN$(I) = S$:DS(I) = V:I = 199
+ 2020  IF  LEN (DN$(I)) = 0 THEN DN$(I) = S$:DS(I) = 0:I = 199
  2030  NEXT I
  2040  RETURN 
+
+REM Subroutine: Adds size V to entry for directory S$ and its parents.
+
  3000  FOR I = 0 TO 199
  3010 L =  LEN (S$)
  3015 M =  LEN (DN$(I))
@@ -70,19 +114,27 @@ REM Written in Applesoft BASIC
  3050  RETURN 
  3060 DS(I) = DS(I) + V
  3080  GOTO 3040
+
+REM Subroutine: Reads next line of input from the file.
+
  4000 S$ = ""
  4010  GET C$
  4020  IF  ASC (C$) < 32 GOTO 4050
  4030 S$ = S$ + C$
  4040  GOTO 4010
  4050  RETURN 
+
+REM Part 2. Start by printing total filesystem size.
+
  5000  PRINT "$ ";
  5002  SPEED= 70: PRINT "df -h": SPEED= 170
  5004  FOR I = 0 TO 1000: NEXT I
  5006 S$ = "/"
- 5008  GOSUB 1000
  5010  GOSUB 1000
  5015  PRINT V
+
+REM Calculate free memory requirements.
+
  5020 UN = 70000000 - V
  5030 RE = 30000000 - UN
  5040 DE = 99999999
@@ -90,12 +142,21 @@ REM Written in Applesoft BASIC
  5110  SPEED= 70: PRINT " cleanup": SPEED= 170
  5120  FOR I = 0 TO 1000: NEXT I
  5130  PRINT "NEED TO FREE ";RE;" BYTES..."
+
+REM The actual work: iterate for smallest entry that is at least RE bytes.
+
  5200  FOR I = 0 TO 199
  5210  IF  LEN (DN$(I)) = 0 THEN I = 199: GOTO 5230
  5220  IF DS(I) > RE AND DS(I) < DE THEN DE = DS(I)
  5230  NEXT I
+
+REM All done!
+
  5240  PRINT "FREED ";DE;" BYTES."
  5250  GOTO 900
+
+REM Debug subroutine: print all contents of directory/size map.
+
  6000  FOR I = 0 TO 199
  6010  IF  LEN (DN$(I)) = 0 THEN I = 199: GOTO 6030
  6020  PRINT DN$(I),DS(I)