Add LastLineSpacingSpan

markwon-core/src/main/java/io/noties/markwon/core/spans/LastLineSpacingSpan.java

@@ -0,0 +1,43 @@
+package io.noties.markwon.core.spans;
+
+import android.graphics.Paint;
+import android.text.Spanned;
+import android.text.style.LineHeightSpan;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Px;
+
+/**
+ * @since 4.0.0-SNAPSHOT
+ */
+public class LastLineSpacingSpan implements LineHeightSpan {
+
+    @NonNull
+    public static LastLineSpacingSpan create(@Px int spacing) {
+        return new LastLineSpacingSpan(spacing);
+    }
+
+    private final int spacing;
+
+    public LastLineSpacingSpan(@Px int spacing) {
+        this.spacing = spacing;
+    }
+
+    @Override
+    public void chooseHeight(CharSequence text, int start, int end, int spanstartv, int v, Paint.FontMetricsInt fm) {
+        if (selfEnd(end, text, this)) {
+            // let's just add what we want
+            fm.descent += spacing;
+            fm.bottom += spacing;
+        }
+    }
+
+    private static boolean selfEnd(int end, CharSequence text, Object span) {
+        // this is some kind of interesting magic here... only the last
+        // span will receive correct _end_ argument, but previous spans
+        // receive it tilted by one (1). Most likely it's just a new-line character... and
+        // if needed we could check for that
+        final int spanEnd = ((Spanned) text).getSpanEnd(span);
+        return spanEnd == end || spanEnd == end - 1;
+    }
+}