Center images when they are the only contents in a paragraph.

src/intermediate/paragraph.rs

@@ -1,3 +1,5 @@
+use std::any::Any;
+
 use super::macros::intermediate;
 use super::IObject;
 use crate::error::CustomError;
@@ -41,4 +43,32 @@ impl IParagraph {
             post_blank,
         })
     }
+
+    /// Checks if the paragraph contains nothing but a single image.
+    ///
+    /// When this happens, we want to center the image.
+    pub(crate) fn is_single_image(&self) -> bool {
+        let num_images = self
+            .children
+            .iter()
+            .filter(|c| match c {
+                IObject::RegularLink(iregular_link) => match &iregular_link.target {
+                    super::LinkTarget::Image { src, alt } => true,
+                    _ => false,
+                },
+                _ => false,
+            })
+            .count();
+        num_images == 1
+            && self.children.iter().all(|c| match c {
+                IObject::RegularLink(iregular_link) => match &iregular_link.target {
+                    super::LinkTarget::Image { src, alt } => true,
+                    _ => false,
+                },
+                IObject::PlainText(iplain_text) => {
+                    iplain_text.source.chars().all(|c| c.is_ascii_whitespace())
+                }
+                _ => false,
+            })
+    }
 }