Restructure markdown highlighter

src/markdown/span.rs

@@ -0,0 +1,83 @@
+use std::{
+    fmt,
+    ops::{Deref, Range},
+};
+
+#[derive(Clone, Eq, PartialEq)]
+pub struct Span<'a> {
+    complete_str: &'a str,
+    range: Range<usize>,
+}
+
+impl<'a> Span<'a> {
+    pub fn new(complete_str: &'a str) -> Self {
+        Self {
+            complete_str,
+            range: 0..complete_str.len(),
+        }
+    }
+
+    pub fn get(&self, slice: Range<usize>) -> Option<Self> {
+        let start = self.range.start.checked_add(slice.start)?;
+        let end = self.range.start.checked_add(slice.end)?;
+
+        if end > self.range.end || end < start {
+            return None;
+        }
+
+        Some(Self {
+            complete_str: self.complete_str,
+            range: Range { start, end },
+        })
+    }
+
+    pub fn complete_str(&self) -> Self {
+        Self::new(self.complete_str)
+    }
+
+    pub fn split_at(&self, i: usize) -> Option<(Self, Self)> {
+        let head = self.get(0..i)?;
+        let tail = self.get(i..self.range.len())?;
+        Some((head, tail))
+    }
+
+    /// Try to merge the spans.
+    ///
+    /// This only works if spans are pointing into the same backing buffer, and are adjacent.
+    pub fn try_merge(&self, other: &Self) -> Option<Self> {
+        if self.complete_str.as_ptr() != other.complete_str.as_ptr() {
+            return None;
+        }
+
+        if self.range.end == other.range.start {
+            Some(Self {
+                range: self.range.start..other.range.end,
+                ..*self
+            })
+        } else if self.range.start == other.range.end {
+            Some(Self {
+                range: other.range.start..self.range.end,
+                ..*self
+            })
+        } else {
+            None
+        }
+    }
+}
+
+impl Deref for Span<'_> {
+    type Target = str;
+
+    fn deref(&self) -> &Self::Target {
+        &self.complete_str[self.range.clone()]
+    }
+}
+
+impl<'a> fmt::Debug for Span<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("Span")
+            .field(&self.range)
+            .field(&self.deref())
+            .finish()
+    }
+}