diff --git a/source/app.d b/source/app.d
index e3b76eb..4865685 100644
--- a/source/app.d
+++ b/source/app.d
@@ -1,45 +1,12 @@
-import std.algorithm : filter, map, startsWith;
-import std.array : array, empty, front, replace;
-import std.conv : to;
-import std.datetime : dur, TimeOfDay, Clock;
 import std.getopt : defaultGetoptPrinter, getopt;
-import std.json : JSONValue;
-import std.regex : ctRegex, matchAll;
 import std.stdio : File, stdout, writeln;
-import std.string : strip;
-import std.typecons : tuple;
-import std.format : format;
-
-import kxml.xml : readDocument, XmlNode;
 
 import requests : postContent;
 
+import fahrplanparser;
+
 import substitution;
 
-auto parseTime(in string input)
-{
-    auto matches = matchAll(input, ctRegex!(`(?P<hours>\d+):(?P<minutes>\d+)`));
-    auto actualTime = TimeOfDay(matches.front["hours"].to!int, matches.front["minutes"].to!int);
-    matches.popFront;
-    if (!matches.empty)
-    {
-        auto expectedTime = TimeOfDay(matches.front["hours"].to!int,
-                matches.front["minutes"].to!int);
-        return tuple(expectedTime, actualTime - expectedTime);
-
-    }
-    return tuple(actualTime, dur!"minutes"(0));
-}
-
-auto getRowContents(XmlNode[] rows)
-{
-    return rows.map!(row => row.parseXPath("//td")[1 .. $ - 1].map!((column) {
-            auto link = column.parseXPath("//a");
-            if (!link.empty)
-                return link.front.getCData.replace("...", "");
-            return column.getCData;}));
-}
-
 void main(string[] args)
 {
     string fileName;
@@ -63,28 +30,18 @@ void main(string[] args)
              "type_dm" : "any",
              "itdLPxx_bcl" : "true"]);
 
-    auto currentTime = Clock.currTime;
     loadSubstitutionFile(substitutionFileName);
-    JSONValue j = ["time" : "%02s:%02s".format(currentTime.hour, currentTime.minute)];
-    j.object["departures"] = readDocument(cast(string) content.data)
-            .parseXPath(`//table[@id="departureMonitor"]/tbody/tr`)[1 .. $]
-            .getRowContents
-            .filter!(row => !row.empty)
-            .map!(a => ["departure" : a[0].parseTime[0].to!string[0 .. $ - 3],
-                        "delay" : a[0].parseTime[1].total!"minutes".to!string,
-                        "line" : a[1],
-                        "direction" : a[2].substitute])
-            .array.JSONValue;
 
+    auto output = (cast(string) content.data).parseFahrplan;
     if (fileName !is null)
     {
-        auto output = File(fileName, "w");
-        scope(exit) output.close;
-        output.writeln(j.toPrettyString.replace("\\/", "/"));
+        auto outfile = File(fileName, "w");
+        scope(exit) outfile.close;
+        outfile.writeln(output);
     }
     else
     {
-        j.toPrettyString.replace("\\/", "/").writeln;
+        output.writeln;
     }
 
 }
diff --git a/source/fahrplanparser.d b/source/fahrplanparser.d
new file mode 100644
index 0000000..258e39f
--- /dev/null
+++ b/source/fahrplanparser.d
@@ -0,0 +1,100 @@
+module fahrplanparser;
+
+import std.algorithm : filter, map, startsWith;
+import std.array : array, empty, front, replace;
+import std.conv : to;
+import std.datetime : dur, TimeOfDay, Clock;
+import std.format : format;
+import std.json : JSONValue;
+import std.regex : ctRegex, matchAll;
+import std.string : strip;
+import std.typecons : tuple;
+
+import kxml.xml : readDocument, XmlNode;
+
+import substitution;
+
+public:
+
+auto parseFahrplan(in string data)
+{
+    auto currentTime = Clock.currTime;
+    JSONValue j = ["time" : "%02s:%02s".format(currentTime.hour, currentTime.minute)];
+    j.object["departures"] = data.readDocument
+            .parseXPath(`//table[@id="departureMonitor"]/tbody/tr`)[1 .. $]
+            .getRowContents
+            .filter!(row => !row.empty)
+            .map!(a => ["departure" : a[0].parseTime[0].to!string[0 .. $ - 3],
+                        "delay" : a[0].parseTime[1].total!"minutes".to!string,
+                        "line" : a[1],
+                        "direction" : a[2].substitute])
+            .array.JSONValue;
+    return j.toPrettyString.replace("\\/", "/");
+}
+
+private:
+
+class BadTimeInputException : Exception
+{
+    this(string msg) @safe pure nothrow @nogc
+    {
+        super(msg);
+    }
+
+    this() @safe pure nothrow @nogc
+    {
+        this("");
+    }
+}
+
+auto parseTime(in string input) @safe
+{
+    auto matches = matchAll(input, ctRegex!(`(?P<hours>\d{1,2}):(?P<minutes>\d{2})`));
+    if (matches.empty)
+        throw new BadTimeInputException();
+    auto actualTime = TimeOfDay(matches.front["hours"].to!int, matches.front["minutes"].to!int);
+    matches.popFront;
+    if (!matches.empty)
+    {
+        auto expectedTime = TimeOfDay(matches.front["hours"].to!int,
+                matches.front["minutes"].to!int);
+        auto timeDiff = actualTime - expectedTime;
+
+        if(timeDiff < dur!"minutes"(0))
+            timeDiff = dur!"hours"(24) + timeDiff;
+
+        return tuple(expectedTime, timeDiff);
+    }
+    return tuple(actualTime, dur!"minutes"(0));
+}
+
+@safe unittest
+{
+    import std.exception : assertThrown;
+    assertThrown(parseTime(""));
+    assertThrown(parseTime("lkeqf"));
+    assertThrown(parseTime(":"));
+    assertThrown(parseTime("00:0"));
+
+    assert("00:00".parseTime == tuple(TimeOfDay(0, 0), dur!"minutes"(0)));
+    assert("0:00".parseTime == tuple(TimeOfDay(0, 0), dur!"minutes"(0)));
+
+    assert("00:00 00:00".parseTime == tuple(TimeOfDay(0, 0), dur!"minutes"(0)));
+
+    assert("12:3412:34".parseTime == tuple(TimeOfDay(12, 34), dur!"minutes"(0)));
+
+    assert("ölqjfo12:34oieqf12:31ölqjf".parseTime == tuple(TimeOfDay(12, 31), dur!"minutes"(3)));
+
+    assert("17:53 (planmäßig 17:51 Uhr)".parseTime == tuple(TimeOfDay(17, 51), dur!"minutes"(2)));
+
+    assert("00:00 23:59".parseTime == tuple(TimeOfDay(23,59), dur!"minutes"(1)));
+}
+
+auto getRowContents(XmlNode[] rows)
+{
+    return rows.map!(row => row.parseXPath("//td")[1 .. $ - 1].map!((column) {
+            auto link = column.parseXPath("//a");
+            if (!link.empty)
+                return link.front.getCData.replace("...", "");
+            return column.getCData;}));
+}