chore: refactor the input component (#165)

* refactor the input component

* fix clippy

* clean up

crates/ui/src/input/cursor.rs

@@ -0,0 +1,46 @@
+use std::ops::Range;
+
+/// A selection in the text, represented by start and end byte indices.
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Default)]
+pub struct Selection {
+    pub start: usize,
+    pub end: usize,
+}
+
+impl Selection {
+    pub fn new(start: usize, end: usize) -> Self {
+        Self { start, end }
+    }
+
+    pub fn len(&self) -> usize {
+        self.end.saturating_sub(self.start)
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.start == self.end
+    }
+
+    /// Clears the selection, setting start and end to 0.
+    pub fn clear(&mut self) {
+        self.start = 0;
+        self.end = 0;
+    }
+
+    /// Checks if the given offset is within the selection range.
+    pub fn contains(&self, offset: usize) -> bool {
+        offset >= self.start && offset < self.end
+    }
+}
+
+impl From<Range<usize>> for Selection {
+    fn from(value: Range<usize>) -> Self {
+        Self::new(value.start, value.end)
+    }
+}
+impl From<Selection> for Range<usize> {
+    fn from(value: Selection) -> Self {
+        value.start..value.end
+    }
+}
+
+pub type Position = lsp_types::Position;