brub

src/reader.rs

@@ -1,5 +1,8 @@
 use std::fs::File;
-use std::io::{self, Read, Seek, SeekFrom};
+use std::io::{self, Read, Seek, SeekFrom, Write};
+use std::slice;
+
+type BytesRead = usize;
 
 pub struct Reader {
 	file: File,
@@ -14,22 +17,26 @@ impl Reader {
 		}
 	}
 
-	pub fn prev_line(&mut self) -> std::io::Result<Option<String>> {
+	pub fn prev_line(&mut self, their_buf: &mut impl Write) -> std::io::Result<BytesRead> {
 		let file = &mut self.file;
 		if self.last_line_start == 0 {
-			return Ok(None);
+			Ok(0)
 		} else {
+			let mut temp = vec![];
 			for sub in 1..self.last_line_start {
 				file.seek(SeekFrom::Start(self.last_line_start - sub))?;
-				let mut buf = [0u8];
-				file.read_exact(&mut buf)?;
-				if buf[0] == b'\n' {
-					let mut buf = vec![0u8; (sub - 1) as usize];
-					file.read_exact(&mut buf)?;
-					self.last_line_start -= sub;
+				let mut byte = 0u8;
+				file.read_exact(slice::from_mut(&mut byte))?;
+				if byte == b'\n' || sub == self.last_line_start {
+					their_buf.write_all(&[byte])?;
+					temp.reverse();
+					their_buf.write_all(&temp)?;
+					return Ok(sub as usize);
+				} else {
+					temp.push(byte);
 				}
 			}
+			Ok(0)
 		}
-		Ok(None)
 	}
 }