package parsekit

import "fmt"

// Cursor represents the position of a cursor in various ways.
type Cursor struct {
	Byte   int // The cursor offset in bytes, relative to start of file
	Rune   int // The cursor offset in UTF8 runes, relative to start of file
	Column int // The column at which the cursor is (0-indexed)
	Line   int // The line at which the cursor is (0-indexed)
}

// String produces a string representation of the cursor position.
func (c Cursor) String() string {
	if c.Line == 0 && c.Column == 0 {
		return fmt.Sprintf("start of file")
	}
	return fmt.Sprintf("line %d, column %d", c.Line+1, c.Column+1)
}

// Move updates the position of the cursor, based on the provided input string.
// The input string represents the runes that has been skipped over. This
// method will take newlines into account to keep track of line numbers and
// column positions automatically.
//
// Note: when you are writing a parser using parsekit, it's unlikely
// that you will use this method directly. The parsekit package takes care
// of calling it at the correct time.
func (c *Cursor) Move(input string) *Cursor {
	c.Byte += len(input)
	for _, r := range input {
		c.Rune++
		if r == '\n' {
			c.Column = 0
			c.Line++
		} else {
			c.Column++
		}
	}
	return c
}