package parser

// Parser holds the internal state of the Parser.
type Parser struct {
	state        StateFn      // a function that handles the current state
	stack        []StateFn    // state function stack, for nested parsing
	input        string       // the scanned input
	len          int          // the total length of the input in bytes
	pos          int          // current byte scanning position in the input
	newline      bool         // keep track of when we have scanned a newline
	cursorRow    int          // current row number in the input
	cursorColumn int          // current column position in the input
	buffer       StringBuffer // an efficient buffer, used to build string values
	items        chan Item    // channel of resulting Parser items
	item         Item         // the current item as reached by Next() and retrieved by Get()
	err          *Error       // an error when lexing failed, retrieved by Error()
}

// StateFn represents the state of the parser as a function
// that returns the next state.
type StateFn func(*Parser) StateFn

// ItemType represents the type of a parser Item.
type ItemType int

// ItemEOF is a built-in parser item type that is used for flagging that the
// end of the input was reached.
const ItemEOF ItemType = -1

// ItemError is a built-in parser item type that is used for flagging that
// an error has occurred during parsing.
const ItemError ItemType = -2

// Item represents an item returned from the parser.
type Item struct {
	Type  ItemType
	Value string
}

// Error is used as the error type when parsing errors occur.
// The error includes some extra meta information to allow for useful
// error messages to the user.
type Error struct {
	Message string
	Row     int
	Column  int
}

func (err *Error) Error() string {
	return err.Message
}