Change containment check to overlap

Due to scenarios wherein a formatted link ended up as part of a larger
raw link after parsing, change the containment check to an overlap check
and add appropriate tests for these edge cases.

osu.Game.Tests/Chat/MessageFormatterTests.cs

@@ -333,6 +333,36 @@ public void TestMarkdownFormatLinkWithMisleadingUrlInText()
             Assert.AreEqual(18, result.Links[0].Length);
         }
 
+        [Test]
+        public void TestMarkdownFormatLinkThatContractsIntoLargerLink()
+        {
+            Message result = MessageFormatter.FormatMessage(new Message { Content = "super broken https://[osu.ppy](https://reddit.com).sh/" });
+
+            Assert.AreEqual("super broken https://osu.ppy.sh/", result.DisplayContent);
+            Assert.AreEqual(1, result.Links.Count);
+            Assert.AreEqual("https://reddit.com", result.Links[0].Url);
+            Assert.AreEqual(21, result.Links[0].Index);
+            Assert.AreEqual(7, result.Links[0].Length);
+        }
+
+        [Test]
+        public void TestMarkdownFormatLinkDirectlyNextToRawLink()
+        {
+            // the raw link has a port at the end of it, so that the raw link regex terminates at the port and doesn't consume display text from the formatted one
+            Message result = MessageFormatter.FormatMessage(new Message { Content = "https://localhost:8080[https://osu.ppy.sh](https://osu.ppy.sh) should be two links" });
+
+            Assert.AreEqual("https://localhost:8080https://osu.ppy.sh should be two links", result.DisplayContent);
+            Assert.AreEqual(2, result.Links.Count);
+
+            Assert.AreEqual("https://localhost:8080", result.Links[0].Url);
+            Assert.AreEqual(0, result.Links[0].Index);
+            Assert.AreEqual(22, result.Links[0].Length);
+
+            Assert.AreEqual("https://osu.ppy.sh", result.Links[1].Url);
+            Assert.AreEqual(22, result.Links[1].Index);
+            Assert.AreEqual(18, result.Links[1].Length);
+        }
+
         [Test]
         public void TestChannelLink()
         {

osu.Game/Online/Chat/MessageFormatter.cs

@@ -104,7 +104,7 @@ private static void handleAdvanced(Regex regex, MessageFormatterResult result, i
                 // sometimes an already-processed formatted link can reduce to a simple URL, too
                 // (example: [mean example - https://osu.ppy.sh](https://osu.ppy.sh))
                 // therefore we need to check if any of the pre-existing links contains the raw one we found
-                if (result.Links.All(existingLink => !existingLink.Contains(link)))
+                if (result.Links.All(existingLink => !existingLink.Overlaps(link)))
                     result.Links.Add(link);
             }
         }
@@ -298,7 +298,7 @@ public Link(string url, int startIndex, int length, LinkAction action, string ar
             Argument = argument;
         }
 
-        public bool Contains(Link otherLink) => otherLink.Index >= Index && otherLink.Index + otherLink.Length <= Index + Length;
+        public bool Overlaps(Link otherLink) => Index < otherLink.Index + otherLink.Length && otherLink.Index < Index + Length;
 
         public int CompareTo(Link otherLink) => Index > otherLink.Index ? 1 : -1;
     }