1 files changed, 81 insertions, 4 deletions

diff --git a/src/rope.rs b/src/rope.rs
index 320cd14..b1b5831 100644
--- a/src/rope.rs
+++ b/src/rope.rs
@@ -1,6 +1,6 @@
-use std::fmt::{Display, Error, Formatter};
+use std::fmt::{Display, Formatter};
 use std::fs::File;
-use std::io::{ErrorKind, Read};
+use std::io::{ErrorKind, Read, Write};
 use std::path::Path;
 use std::rc::Rc;
 
@@ -10,6 +10,8 @@ const MAX_NODE_SIZE: usize = 4;
 struct Branch {
     left: Rc<Node>,
     right: Rc<Node>,
+    // Number of newline characters under this branch.
+    lines: usize,
 }
 
 enum Node {
@@ -36,10 +38,73 @@ impl Node {
             _ => false,
         };
     }
+
+    fn lines(&self) -> usize {
+        match self {
+            Node::Leaf(v) => {
+                let mut count = 0;
+                for &c in v {
+                    if c == b'\n' {
+                        count += 1;
+                    }
+                }
+                return count;
+            }
+            Node::Branch(b) => {
+                return b.lines;
+            }
+        }
+    }
+
+    fn print_lines(
+        &self,
+        out: &mut dyn Write,
+        start: usize,
+        end: usize,
+    ) -> Result<(), std::io::Error> {
+        match self {
+            Node::Leaf(v) => {
+                let mut nl_count = 0;
+                let mut start_pos = 0;
+                let mut end_pos = v.len();
+                for (i, &c) in v.iter().enumerate() {
+                    if c != b'\n' {
+                        continue;
+                    }
+                    nl_count += 1;
+                    if nl_count == start {
+                        start_pos = i;
+                    }
+                    if nl_count == end {
+                        end_pos = i + 1;
+                    }
+                }
+                if let Err(err) = out.write(&v[start_pos..end_pos]) {
+                    return Err(err);
+                }
+                return Ok(());
+            }
+            Node::Branch(b) => {
+                let right_start;
+                if start <= b.left.lines() {
+                    if let Err(err) = b.left.print_lines(out, start, end) {
+                        return Err(err);
+                    }
+                    right_start = 0;
+                } else {
+                    right_start = start - b.left.lines();
+                }
+                if end <= b.left.lines() {
+                    return Ok(());
+                }
+                return b.right.print_lines(out, right_start, end - b.left.lines());
+            }
+        }
+    }
 }
 
 impl Display for Node {
-    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), std::fmt::Error> {
         let mut buf = Vec::new();
         self.write(&mut buf);
         return write!(f, "{}", String::from_utf8_lossy(&buf));
@@ -57,9 +122,11 @@ impl Rope {
         if other.empty() {
             return Rope(me);
         }
+        let lines = me.lines() + other.lines();
         return Rope(Rc::new(Node::Branch(Branch {
             left: me,
             right: other,
+            lines: lines,
         })));
     }
 
@@ -89,10 +156,20 @@ impl Rope {
         }
         return Ok(rope);
     }
+
+    pub fn print_lines(
+        &self,
+        out: &mut dyn Write,
+        start: usize,
+        end: usize,
+    ) -> Result<(), std::io::Error> {
+        let Rope(me) = self;
+        return me.print_lines(out, start, end);
+    }
 }
 
 impl Display for Rope {
-    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), std::fmt::Error> {
         let Rope(n) = self;
         return write!(f, "{}", n);
     }