1 files changed, 69 insertions, 0 deletions
diff --git a/src/estd/cursor.zig b/src/estd/cursor.zig
new file mode 100644
index 0000000..c0a4a32
--- /dev/null
+++ b/src/estd/cursor.zig
@@ -0,0 +1,69 @@
+const std = @import("std");
+
+pub const ReadError = error {
+    EndOfBuffer
+};
+
+pub fn Cursor(comptime T: type) type {
+    return struct {
+        const Self = @This();
+
+        buffer: []const T,
+        index: usize,
+        touched_index: usize,
+
+        pub fn init(buffer: []const T) Self {
+            return .{
+                .buffer = buffer,
+                .index = 0,
+                .touched_index = 0,
+            };
+        }
+
+        pub fn peek(self: Self, amount: usize) ReadError![]const T {
+            if (self.index + amount > self.buffer.len) {
+                return ReadError.EndOfBuffer;
+            }
+
+            return self.buffer[self.index..self.index + amount];
+        }
+
+        pub fn consume(self: *Self, amount: usize) ReadError![]const T {
+            const slice = try self.peek(amount);
+            self.index += amount;
+            self.touched_index = self.index;
+            return slice;
+        }
+
+        pub fn snapshot(self: Self) usize {
+            return self.index;
+        }
+
+        pub fn rollback(self: *Self, index: usize) void {
+            self.index = index;
+        }
+
+        pub fn touched_slice(self: Self) []const T {
+            return self.buffer[0..self.touched_index];
+        }
+    };
+}
+
+test "peek" {
+    const buffer = "1234";
+    const cursor = Cursor(u8).init(buffer);
+    try std.testing.expectEqualSlices(u8, "1", try cursor.peek(1));
+    try std.testing.expectEqualSlices(u8, "12", try cursor.peek(2));
+    try std.testing.expectEqualSlices(u8, "123", try cursor.peek(3));
+    try std.testing.expectEqualSlices(u8, "1234", try cursor.peek(4));
+    try std.testing.expectError(ReadError.EndOfBuffer, cursor.peek(5));
+}
+
+test "consume" {
+    const buffer = "12345678";
+    var cursor = Cursor(u8).init(buffer);
+    try std.testing.expectEqualSlices(u8, "1", try cursor.consume(1));
+    try std.testing.expectEqualSlices(u8, "23", try cursor.consume(2));
+    try std.testing.expectEqualSlices(u8, "456", try cursor.consume(3));
+    try std.testing.expectError(ReadError.EndOfBuffer, cursor.consume(4));
+}