From a56b3551c19e4fb3a860d86bc2bf3e18a68080d9 Mon Sep 17 00:00:00 2001
From: Adam Spragg <adam@spra.gg>
Date: Mon, 2 Jan 2023 11:30:27 +0000
Subject: Puzzle 22: Create "elf" type to hold position and orientation

This will help when just moving around can change the orientation, as
you move over an edge
---
 22.c | 74 ++++++++++++++++++++++++++++++++++++++++----------------------------
 1 file changed, 44 insertions(+), 30 deletions(-)

diff --git a/22.c b/22.c
index 706d62a..f29f78e 100644
--- a/22.c
+++ b/22.c
@@ -32,42 +32,55 @@ direction_name(enum direction dir)
 }
 
 
-enum direction
-direction_turn(enum direction dir, char turn)
+struct elf {
+	long pos;
+	enum direction dir;
+};
+
+
+int
+elf_turn(struct elf * elf, char turn)
 {
 #define direction_go(d, t) (1000 * (d) + (t))
 
-	switch (direction_go(dir, turn)) {
+	switch (direction_go(elf->dir, turn)) {
 	case direction_go(D_NORTH, 'R'):
 	case direction_go(D_SOUTH, 'L'):
-		return D_EAST;
+		elf->dir = D_EAST;
+		break;
 
 	case direction_go(D_NORTH, 'L'):
 	case direction_go(D_SOUTH, 'R'):
-		return D_WEST;
+		elf->dir = D_WEST;
+		break;
 
 	case direction_go(D_EAST, 'L'):
 	case direction_go(D_WEST, 'R'):
-		return D_NORTH;
+		elf->dir = D_NORTH;
+		break;
 
 	case direction_go(D_EAST, 'R'):
 	case direction_go(D_WEST, 'L'):
-		return D_SOUTH;
+		elf->dir = D_SOUTH;
+		break;
+
+	default:
+		fprintf(stderr, "Unexpected elf_turn(%d, %c)\n", elf->dir, turn);
+		return -1;
 	}
 
-	fprintf(stderr, "Unexpected direction_turn(%d, %c)\n", dir, turn);
-	return D_NORTH;
+	return 0;
 
 #undef direction_go
 }
 
 
 int
-map_move(char * map, int cols, int rows, int pos, enum direction dir, int distance)
+elf_move(struct elf * elf, char const * map, int cols, int rows, int distance)
 {
 	int skip, wrap, base;
 
-	switch (dir) {
+	switch (elf->dir) {
 	case D_NORTH:
 		skip = -cols;
 		wrap = cols * rows;
@@ -89,21 +102,21 @@ map_move(char * map, int cols, int rows, int pos, enum direction dir, int distan
 		break;
 
 	default:
-		fprintf(stderr, "Unexpected direction %d\n", dir);
+		fprintf(stderr, "Unexpected direction %d\n", elf->dir);
 		return -1;
 	}
 
-	base = (pos / wrap) * wrap;
+	base = (elf->pos / wrap) * wrap;
 
 	while (distance > 0) {
-		int newpos = base + modulo(pos + skip, wrap);
+		int newpos = base + modulo(elf->pos + skip, wrap);
 
 		while (map[newpos] == ' ' || map[newpos] == '\n')
 			newpos = base + modulo(newpos + skip, wrap);
 
 		switch (map[newpos]) {
 		case '.':
-			pos = newpos;
+			elf->pos = newpos;
 			--distance;
 			break;
 
@@ -117,7 +130,7 @@ map_move(char * map, int cols, int rows, int pos, enum direction dir, int distan
 		}
 	}
 
-	return pos;
+	return 0;
 }
 
 
@@ -127,11 +140,10 @@ main()
 	char * buf = NULL, * beg, * end;
 	long bufsiz = 0, buflen = 0, maxline = 0, lines = 0;
 	long pos;
-	enum direction dir;
+	struct elf elf;
 	char distance[8], c;
 	int dlen = 0;
 
-
 	// Read map data
 	// Don't try and figure out lines yet, in case we get a line longer than
 	// our read buffer, which could make things awkward.
@@ -190,29 +202,31 @@ main()
 	}
 
 	// Set initial position
-	pos = 0;
-	dir = D_EAST;
-	while (buf[pos] != '.') {
-		++pos;
-	}
+	elf.pos = 0;
+	elf.dir = D_EAST;
+	while (buf[elf.pos] != '.')
+		++elf.pos;
 
 	// Read and follow the movement instructions.
-	while (pos >= 0 && (c = fgetc(stdin)) != EOF) {
+	while (elf.pos >= 0 && (c = fgetc(stdin)) != EOF) {
 		if (isdigit(c)) {
 			distance[dlen++] = c;
 		}
 		else if (c == 'L' || c == 'R') {
 			distance[dlen] = '\0';
 
-			pos = map_move(buf, maxline, lines, pos, dir, atoi(distance));
+			if (elf_move(&elf, buf, maxline, lines, atoi(distance)) != 0)
+				elf.pos = -1;
+			if (elf_turn(&elf, c) != 0)
+				elf.pos = -1;
 
-			dir = direction_turn(dir, c);
 			dlen = 0;
 		}
 		else if (c == '\n') {
 			// Cover last bit of distance, if any
 			distance[dlen] = '\0';
-			pos = map_move(buf, maxline, lines, pos, dir, atoi(distance));
+			if (elf_move(&elf, buf, maxline, lines, atoi(distance)) != 0)
+				elf.pos = -1;
 			break;
 		}
 		else {
@@ -221,15 +235,15 @@ main()
 			return -1;
 		}
 	}
-	if (pos < 0) {
+	if (elf.pos < 0) {
 		free(buf);
 		return -1;
 	}
 
 	// Done.
 	printf("Password is %ld (%ld,%ld,%d)\n",
-			1000 * (1 + pos / maxline) + 4 * (1 + pos % maxline) + dir,
-			(1 + pos % maxline), (1 + pos / maxline), dir);
+			1000 * (1 + elf.pos / maxline) + 4 * (1 + elf.pos % maxline) + elf.dir,
+			(1 + elf.pos % maxline), (1 + elf.pos / maxline), elf.dir);
 
 	// Tidy and exit.
 	free(buf);
-- 
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