Implement slice, take, and compare.

src/main.rs

@@ -1,4 +1,6 @@
-use nom::bytes::complete::tag;
+use std::ops::RangeBounds;
+
+use nom::{bytes::complete::tag, Compare, InputTake, Slice};
 
 fn main() {
     let input = "this is my test input".to_owned();
@@ -11,11 +13,86 @@ fn main() {
 
 #[derive(Debug)]
 struct WrappedInput<'s> {
-    contents: &'s str,
+    full_source: &'s str,
+    start: usize,
+    end: usize, //exclusive
+    preceding_line_break: Option<usize>,
 }
 
 impl<'s> WrappedInput<'s> {
+    /// Returns a wrapped string that keeps track of values we need for parsing org-mode.
+    ///
+    /// Only call this on the full original string. Calling this on a substring can result in invalid values.
     pub fn new(input: &'s str) -> Self {
-        WrappedInput { contents: input }
+        WrappedInput {
+            full_source: input,
+            start: 0,
+            end: input.len(),
+            preceding_line_break: None,
+        }
+    }
+}
+
+impl<'s> InputTake for WrappedInput<'s> {
+    fn take(&self, count: usize) -> Self {
+        self.slice(..count)
+    }
+
+    fn take_split(&self, count: usize) -> (Self, Self) {
+        (self.slice(count..), self.slice(..count))
+    }
+}
+
+impl<'s, O: Into<&'s str>> Compare<O> for WrappedInput<'s> {
+    fn compare(&self, t: O) -> nom::CompareResult {
+        (&self.full_source[self.start..self.end]).compare(t.into())
+    }
+
+    fn compare_no_case(&self, t: O) -> nom::CompareResult {
+        (&self.full_source[self.start..self.end]).compare_no_case(t.into())
+    }
+}
+
+impl<'s> From<&'s str> for WrappedInput<'s> {
+    fn from(value: &'s str) -> Self {
+        WrappedInput::new(value)
+    }
+}
+
+impl<'s> From<&WrappedInput<'s>> for &'s str {
+    fn from(value: &WrappedInput<'s>) -> Self {
+        &value.full_source[value.start..value.end]
+    }
+}
+
+impl<'s, R> Slice<R> for WrappedInput<'s>
+where
+    R: RangeBounds<usize>,
+{
+    fn slice(&self, range: R) -> Self {
+        let new_start = match range.start_bound() {
+            std::ops::Bound::Included(idx) => self.start + idx,
+            std::ops::Bound::Excluded(idx) => self.start + idx - 1,
+            std::ops::Bound::Unbounded => self.start,
+        };
+        let new_end = match range.end_bound() {
+            std::ops::Bound::Included(idx) => self.start + idx,
+            std::ops::Bound::Excluded(idx) => self.start + idx - 1,
+            std::ops::Bound::Unbounded => self.start,
+        };
+
+        // TODO: calculate updated values for WrappedInput
+        WrappedInput {
+            full_source: self.full_source,
+            start: new_start,
+            end: new_end,
+            preceding_line_break: None,
+        }
+    }
+}
+
+impl<'s> std::fmt::Display for WrappedInput<'s> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        Into::<&str>::into(self).fmt(f)
     }
 }