Puzzle 22: Create an abstraction for "map"

This will help with some future changes

1 files changed, 99 insertions, 45 deletions

diff --git a/22.c b/22.c
index a4a687f..a021510 100644
--- a/22.c
+++ b/22.c
@@ -39,6 +39,85 @@ direction_name(enum direction dir)
 }
 
 
+struct map {
+	char * _buf;
+	int cols;
+	int rows;
+	enum map_type type;
+};
+
+
+// Initialise a map from a buffer.
+//
+// The map takes ownership of the buffer from when it's called, whether
+// or not the initialisation is successful
+struct map *
+map_init(struct map * map, char * buf, size_t buflen, enum map_type type)
+{
+	char * beg, * end;
+	long pos;
+
+	map->_buf = NULL;
+	map->cols = 0;
+	map->rows = 0;
+	map->type = type;
+
+	// Work out max lines and longest line.
+	for (beg = buf; beg < buf + buflen; beg = end + 1, ++map->rows) {
+		end = memchr(beg, '\n', buf + buflen - beg);
+		if (end - beg > map->cols)
+			map->cols = end - beg;
+	}
+	if (map->cols == 0 || map->rows == 0) {
+		fprintf(stderr, "Unexpected map size (%d,%d)\n", map->cols, map->rows);
+		free(buf);
+		return NULL;
+	}
+	++map->cols; // Also count the newline on the end of each line.
+
+	// Resize the map data buffer to hold a full grid of data
+	if ((map->_buf = realloc(buf, map->cols * map->rows)) == NULL) {
+		fprintf(stderr, "Bad realloc(%d)\n", map->cols * map->rows);
+		free(buf);
+		return NULL;
+	}
+	memset(map->_buf + buflen, ' ', map->cols * map->rows - buflen);
+
+	// Move the map data so that it fits the grid properly
+	for (end = map->_buf + buflen, pos = map->rows - 1; pos >= 0; end = beg, --pos) {
+		beg = memrchr(map->_buf, '\n', (end - map->_buf) - 1);
+		beg = beg ? beg + 1 : map->_buf;
+		memmove(map->_buf + pos * map->cols, beg, (end - beg));
+		memset(map->_buf + (pos * map->cols) + (end - beg) - 1, ' ', map->cols - (end - beg) + 1);
+		map->_buf[pos * map->cols + map->cols - 1] = '\n';
+	}
+
+	return map;
+}
+
+
+void
+map_tidy(struct map * map)
+{
+	if (!map)
+		return;
+
+	free(map->_buf);
+	return;
+}
+
+
+int
+map_elem(struct map const * map, int x, int y)
+{
+	if (x < 0 || x >= map->cols - 1
+			|| y < 0 || y >= map->rows)
+		return ' ';
+
+	return map->_buf[x + y * map->cols];
+}
+
+
 struct elf {
 	int x;
 	int y;
@@ -84,7 +163,7 @@ elf_turn(struct elf * elf, char turn)
 
 
 int
-elf_move(struct elf * elf, char const * map, int cols, int rows, enum map_type mtype, int distance)
+elf_move(struct elf * elf, struct map const * map, int distance)
 {
 	while (distance > 0) {
 		int dx = 0, dy = 0, elem;
@@ -100,18 +179,18 @@ elf_move(struct elf * elf, char const * map, int cols, int rows, enum map_type m
 			return -1;
 		}
 
-		switch (mtype) {
+		switch (map->type) {
 		case M_FLAT:
-			newelf.x = modulo(elf->x + dx, cols);
-			newelf.y = modulo(elf->y + dy, rows);
+			newelf.x = modulo(elf->x + dx, map->cols);
+			newelf.y = modulo(elf->y + dy, map->rows);
 			newelf.dir = elf->dir;
-			elem = map[newelf.x + newelf.y * cols];
+			elem = map_elem(map, newelf.x, newelf.y);
 
 			// Just keep going until we wrap around to a non-blank position
 			while (elem == ' ' || elem == '\n') {
-				newelf.x = modulo(newelf.x + dx, cols);
-				newelf.y = modulo(newelf.y + dy, rows);
-				elem = map[newelf.x + newelf.y * cols];
+				newelf.x = modulo(newelf.x + dx, map->cols);
+				newelf.y = modulo(newelf.y + dy, map->rows);
+				elem = map_elem(map, newelf.x, newelf.y);
 			}
 			break;
 
@@ -120,7 +199,7 @@ elf_move(struct elf * elf, char const * map, int cols, int rows, enum map_type m
 			return -1;
 
 		default:
-			fprintf(stderr, "Unknown map type %d\n", mtype);
+			fprintf(stderr, "Unknown map type %d\n", map->type);
 			return -1;
 		}
 
@@ -147,9 +226,10 @@ elf_move(struct elf * elf, char const * map, int cols, int rows, enum map_type m
 int
 main(int argc, char ** argv)
 {
-	char * buf = NULL, * beg, * end;
+	char * buf = NULL;
+	struct map map;
 	enum map_type mtype = M_FLAT;
-	long bufsiz = 0, buflen = 0, maxline = 0, lines = 0;
+	long bufsiz = 0, buflen = 0;
 	long pos;
 	struct elf elf;
 	char distance[8];
@@ -217,42 +297,16 @@ main(int argc, char ** argv)
 		buflen += strlen(buf + buflen);
 	}
 
-	// Work out max lines and longest line.
-	for (beg = buf, lines = 0; beg < buf + buflen; beg = end + 1, ++lines) {
-		end = memchr(beg, '\n', buf + buflen - beg);
-		if (end - beg > maxline)
-			maxline = end - beg;
-	}
-	if (maxline == 0 || lines == 0) {
-		fprintf(stderr, "Unexpected map size (%ld,%ld)\n", maxline, lines);
-		free(buf);
+	if (map_init(&map, buf, buflen, mtype) == NULL) {
+		fprintf(stderr, "Failed to initialise map\n");
 		return -1;
 	}
-	++maxline; // Also count the newline on the end of each line.
-
-	// Resize the map data buffer to hold a full grid of data
-	if ((beg = realloc(buf, lines * maxline)) == NULL) {
-		fprintf(stderr, "Bad realloc(%ld)\n", bufsiz);
-		free(buf);
-		return -1;
-	}
-	buf = beg;
-	memset(buf + buflen, ' ', lines * maxline - buflen);
-
-	// Move the map data so that it fits the grid properly
-	for (end = buf + buflen, pos = lines - 1; pos >= 0; end = beg, --pos) {
-		beg = memrchr(buf, '\n', (end - buf) - 1);
-		beg = beg ? beg + 1 : buf;
-		memmove(buf + pos * maxline, beg, (end - beg));
-		memset(buf + (pos * maxline) + (end - beg) - 1, ' ', maxline - (end - beg) + 1);
-		buf[pos * maxline + maxline - 1] = '\n';
-	}
 
 	// Set initial position
 	elf.x = 0;
 	elf.y = 0;
 	elf.dir = D_EAST;
-	while (elf.x < maxline && buf[elf.x] != '.')
+	while (elf.x < map.cols && map_elem(&map, elf.x, elf.y) != '.')
 		++elf.x;
 
 	// Read and follow the movement instructions.
@@ -263,7 +317,7 @@ main(int argc, char ** argv)
 		else if (c == 'L' || c == 'R') {
 			distance[dlen] = '\0';
 
-			if (elf_move(&elf, buf, maxline, lines, mtype, atoi(distance)) != 0)
+			if (elf_move(&elf, &map, atoi(distance)) != 0)
 				elf.x = -1;
 			if (elf_turn(&elf, c) != 0)
 				elf.x = -1;
@@ -273,18 +327,18 @@ main(int argc, char ** argv)
 		else if (c == '\n') {
 			// Cover last bit of distance, if any
 			distance[dlen] = '\0';
-			if (elf_move(&elf, buf, maxline, lines, mtype, atoi(distance)) != 0)
+			if (elf_move(&elf, &map, atoi(distance)) != 0)
 				elf.x = -1;
 			break;
 		}
 		else {
 			fprintf(stderr, "Unexpected movement instruction (%c)\n", c);
-			free(buf);
+			map_tidy(&map);
 			return -1;
 		}
 	}
 	if (elf.x < 0) {
-		free(buf);
+		map_tidy(&map);
 		return -1;
 	}
 
@@ -294,7 +348,7 @@ main(int argc, char ** argv)
 			1 + elf.x, 1 + elf.y, elf.dir);
 
 	// Tidy and exit.
-	free(buf);
+	map_tidy(&map);
 
 	return 0;
 }