package jettison

// isValidNumber returns whether s is a valid JSON
// number literal. Taken from encoding/json.
func isValidNumber(s string) bool {
	// This function implements the JSON numbers grammar.
	// See https://tools.ietf.org/html/rfc7159#section-6
	// and https://www.json.org/img/number.png.
	if s == "" {
		return false
	}
	// Optional minus sign.
	if s[0] == '-' {
		s = s[1:]
		if s == "" {
			return false
		}
	}
	// Digits.
	switch {
	default:
		return false
	case s[0] == '0':
		s = s[1:]
	case '1' <= s[0] && s[0] <= '9':
		s = s[1:]
		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
			s = s[1:]
		}
	}
	// Dot followed by one or more digits.
	if len(s) >= 2 && s[0] == '.' && '0' <= s[1] && s[1] <= '9' {
		s = s[2:]
		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
			s = s[1:]
		}
	}
	// e or E followed by an optional - or + sign
	// and one or more digits.
	if len(s) >= 2 && (s[0] == 'e' || s[0] == 'E') {
		s = s[1:]
		if s[0] == '+' || s[0] == '-' {
			s = s[1:]
			if s == "" {
				return false
			}
		}
		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
			s = s[1:]
		}
	}
	// Make sure we are at the end.
	return s == ""
}