Add tool to convert bson object id to time

Makefile

@@ -1,6 +1,6 @@
 CFLAGS=-std=c99 -Wpedantic
 
 %: %.d
-	dmd $@
+	dmd -release $@
 
-all: stderr stdout bigger graph i numnorm numsum randarg unixtime
+all: stderr stdout bigger graph i numnorm numsum randarg unixtime bsonobjectiddate

bsonobjectiddate.d

@@ -0,0 +1,52 @@
+import std.stdio;
+import std.string;
+import std.conv;
+import std.datetime;
+
+SysTime toTime(string objectId) {
+	immutable datepart = objectId[0 .. 8].to!ulong(16);
+	return SysTime(unixTimeToStdTime(datepart));
+}
+
+void prettyDate(const SysTime date) {
+	writeln(date.toISOExtString());
+}
+
+string toObjectId(const SysTime time) {
+	return format("%x", time.toUnixTime()) ~ "0000000000000000";
+}
+
+void fromArgs(string[] args) {
+	foreach (objectId; args[1 .. $]) {
+		prettyDate(toTime(objectId));
+	}
+}
+
+void fromStdin() {
+	while (!stdin.eof()) {
+		immutable line = chomp(readln());
+
+		if (line == "") {
+			continue;
+		}
+
+		prettyDate(toTime(line));
+	}
+}
+
+void main(string[] args) {
+	// If any arguments were given try to parse them as objectids.
+	// Otherwise we try to get object ids from stdin.
+	if (args.length > 1) {
+		fromArgs(args);
+	} else {
+		fromStdin();
+	}
+}
+
+unittest {
+	immutable now = Clock.currTime();
+	immutable objectId = "5460edbd0000000000000000";
+
+	assert(toObjectId(toTime(objectId)) == objectId);
+}