Factor out code for enumerating the tiles in a directory

dirtiles.hpp

@@ -1,12 +1,46 @@
 #include <string>
+#include <vector>
 
 #ifndef DIRTILES_HPP
 #define DIRTILES_HPP
 
-std::string dir_read_tile(std::string pbfPath);
-
 void dir_write_tile(const char *outdir, int z, int tx, int ty, std::string const &pbf);
 
 void check_dir(const char *d, bool force, bool forcetable);
 
+struct zxy {
+	long long z;
+	long long x;
+	long long y;
+
+	zxy(int _z, int _x, int _y)
+	    : z(_z), x(_x), y(_y) {
+	}
+
+	bool operator<(const zxy &other) const {
+		if (z < other.z) {
+			return true;
+		}
+		if (z == other.z) {
+			if (x < other.x) {
+				return true;
+			}
+			if (x == other.x) {
+				if (y > other.y) {
+					return true;  // reversed for TMS
+				}
+			}
+		}
+
+		return false;
+	}
+
+	std::string path() {
+		return std::to_string(z) + "/" + std::to_string(x) + "/" + std::to_string(y) + ".pbf";
+	}
+};
+
+std::vector<zxy> enumerate_dirtiles(const char *fname);
+std::string dir_read_tile(std::string pbfPath, struct zxy tile);
+
 #endif