From 3fb7cb82cda854839b3d97c2cd25ae8182aca387 Mon Sep 17 00:00:00 2001
From: Tom Alexander <tom@fizz.buzz>
Date: Wed, 1 Nov 2023 01:07:54 -0400
Subject: [PATCH] Implement get_contents for document.

---
 src/types/document.rs        | 27 +++++++++++++----
 src/types/remove_trailing.rs | 56 ++++++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+), 5 deletions(-)
 create mode 100644 src/types/remove_trailing.rs

diff --git a/src/types/document.rs b/src/types/document.rs
index a6e8217..157e929 100644
--- a/src/types/document.rs
+++ b/src/types/document.rs
@@ -1,12 +1,12 @@
 use std::path::PathBuf;
 
+use super::remove_trailing::RemoveTrailing;
 use super::Element;
 use super::NodeProperty;
 use super::Object;
 use super::PostBlank;
 use super::StandardProperties;
 use super::Timestamp;
-use crate::types::remove_trailing::RemoveTrailing;
 
 pub type PriorityCookie = u8;
 pub type HeadlineLevel = u16;
@@ -64,10 +64,27 @@ impl<'s> StandardProperties<'s> for Document<'s> {
 
     fn get_contents<'b>(&'b self) -> Option<&'s str> {
         let post_blank = self.get_post_blank();
-        let foo: RemoveTrailing<_, post_blank> =
-            RemoveTrailing::new(self.source.split_inclusive("\n"));
-        // self.source.split_inclusive("\n")
-        todo!()
+        let mut content_lines = self
+            .source
+            .split_inclusive('\n')
+            .remove_trailing(post_blank);
+        let first_line = content_lines.next();
+        let last_line = content_lines.last().or(first_line);
+        match (first_line, last_line) {
+            (None, None) => None,
+            (None, Some(_)) | (Some(_), None) => unreachable!(),
+            (Some(first_line), Some(last_line)) => {
+                let first_line_offset = first_line.as_ptr() as usize;
+                let last_line_offset = last_line.as_ptr() as usize + last_line.len();
+                let source_offset = self.source.as_ptr() as usize;
+                debug_assert!(super::lesser_element::is_slice_of(self.source, first_line));
+                debug_assert!(super::lesser_element::is_slice_of(self.source, last_line));
+                Some(
+                    &self.source[(first_line_offset - source_offset)
+                        ..(last_line_offset - first_line_offset)],
+                )
+            }
+        }
     }
 
     fn get_post_blank(&self) -> PostBlank {
diff --git a/src/types/remove_trailing.rs b/src/types/remove_trailing.rs
new file mode 100644
index 0000000..822c64c
--- /dev/null
+++ b/src/types/remove_trailing.rs
@@ -0,0 +1,56 @@
+pub(crate) trait RemoveTrailing: Iterator + Sized {
+    fn remove_trailing<R: Into<usize>>(self, amount_to_remove: R) -> RemoveTrailingIter<Self>;
+}
+
+impl<I> RemoveTrailing for I
+where
+    I: Iterator,
+{
+    fn remove_trailing<R: Into<usize>>(self, amount_to_remove: R) -> RemoveTrailingIter<Self> {
+        RemoveTrailingIter {
+            inner: self,
+            buffer: Vec::new(),
+            next_to_pop: 0,
+            amount_to_remove: amount_to_remove.into(),
+        }
+    }
+}
+
+pub(crate) struct RemoveTrailingIter<I: Iterator> {
+    inner: I,
+    buffer: Vec<I::Item>,
+    next_to_pop: usize,
+    amount_to_remove: usize,
+}
+
+impl<I: Iterator> Iterator for RemoveTrailingIter<I> {
+    type Item = I::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.buffer.len() < self.amount_to_remove {
+            self.buffer.reserve_exact(self.amount_to_remove);
+        }
+        while self.buffer.len() < self.amount_to_remove {
+            if let Some(elem) = self.inner.next() {
+                self.buffer.push(elem);
+            } else {
+                // The inner was smaller than amount_to_remove, so never return anything.
+                return None;
+            }
+        }
+
+        let new_value = self.inner.next();
+        if self.amount_to_remove == 0 {
+            return new_value;
+        }
+
+        if let Some(new_value) = new_value {
+            let ret = std::mem::replace(&mut self.buffer[self.next_to_pop], new_value);
+            self.next_to_pop = (self.next_to_pop + 1) % self.amount_to_remove;
+            Some(ret)
+        } else {
+            // We have exactly the amount in the buffer than we wanted to cut off, so stop returning values.
+            None
+        }
+    }
+}