// Package lexer provides basic helpers to implement parsers
package lexer

import "io"

// Lexer adds Accept and AcceptAll support to a
// [io.RuneScanner]
type Lexer struct {
	io.RuneScanner
}

// Accept consumes a rune from the source if it meets the condition.
// it returns true if the condition was met and false if it wasn't.
func (p Lexer) Accept(cond func(rune) bool) bool {
	return Accept(p, cond)
}

// AcceptAll consumes runes from the source as long as they meet the
// condition. it returns true if the condition was met for at least one rune,
// and false if it wasn't.
func (p Lexer) AcceptAll(cond func(rune) bool) bool {
	return AcceptAll(p, cond)
}

// NewLexer extends a [io.RuneScanner] with Accept()/AcceptAll()
// functionality
func NewLexer(src io.RuneScanner) *Lexer {
	if src == nil {
		return nil
	}

	return &Lexer{src}
}

// StateFn is a State Function of the parser
type StateFn func() (StateFn, error)

// Run runs a state machine until the state function either
// returns nil or an error
func Run(fn StateFn) error {
	var err error

	for fn != nil && err == nil {
		fn, err = fn()
	}

	return err
}

// Accept consumes a rune from the source if it meets the condition.
// it returns true if the condition was met and false if it wasn't.
func Accept(src io.RuneScanner, cond func(r rune) bool) bool {
	r, _, err := src.ReadRune()
	switch {
	case err != nil:
		return false
	case cond(r):
		return true
	default:
		_ = src.UnreadRune()
		return false
	}
}

// AcceptAll consumes runes from the source as long as they meet the
// condition. it returns true if the condition was met for at least one rune,
// and false if it wasn't.
func AcceptAll(src io.RuneScanner, cond func(r rune) bool) bool {
	var accepted bool

	for {
		r, _, err := src.ReadRune()
		switch {
		case err != nil:
			return accepted
		case cond(r):
			accepted = true
		default:
			_ = src.UnreadRune()
			return accepted
		}
	}
}