Add position to scanner

1 files changed, 33 insertions, 7 deletions

diff --git a/src/scanner.rs b/src/scanner.rs
index 83f68e3..e007f2f 100644
--- a/src/scanner.rs
+++ b/src/scanner.rs
@@ -1,11 +1,37 @@
-use std::io::Read;
-
-pub struct Scanner<Source: Read> {
-	source: Source,
+pub struct Scanner {
+	source: Box<[char]>,
+	position: usize,
 }
 
-impl<Source: Read> Scanner<Source> {
-	pub fn new(source: Source) -> Self {
-		Self { source }
+impl Scanner {
+	pub fn new(source: impl AsRef<str>) -> Self {
+		Self {
+			source: source.as_ref().chars().collect(),
+			position: 0,
+		}
+	}
+
+	pub fn position(&self) -> usize {
+		self.position
+	}
+
+	pub fn goto(&mut self, position: usize) -> Option<String> {
+		// allow reverse ranges
+		let production = if self.position < position {
+			self.source.get(self.position..position)?.iter().collect()
+		} else {
+			self.source
+				.get(position..self.position)?
+				.iter()
+				.rev()
+				.collect()
+		};
+
+		self.position = position;
+		Some(production)
+	}
+
+	pub fn advance(&mut self, amount: usize) -> Option<String> {
+		self.goto(self.position + amount)
 	}
 }