less.go

package command

import (
	"bytes"
	"strconv"
)

// lessFunc reports whether key a sorts before key b.
type lessFunc func(a, b []byte) bool

// chooseLess selects the ordering for the active comparison flag. At most one
// of -n, -h, -M, -V applies; lexical byte order is the default.
func chooseLess(f flags) lessFunc {
	switch {
	case bool(f.numericEnabled):
		return numericLess
	case bool(f.humanNumericEnabled):
		return humanLess
	case bool(f.monthSortEnabled):
		return monthLess
	case bool(f.versionSortEnabled):
		return versionLess
	default:
		return lexicalLess
	}
}

// lexicalLess compares keys as raw bytes.
func lexicalLess(a, b []byte) bool {
	return bytes.Compare(a, b) < 0
}

// numericLess compares the leading numeric value of each key (-n), falling back
// to lexical order when either key is not a number.
func numericLess(a, b []byte) bool {
	na, oka := parseFloat(a)
	nb, okb := parseFloat(b)
	if oka && okb {
		return na < nb
	}
	return lexicalLess(a, b)
}

// parseFloat parses a trimmed key as a float, reporting success.
func parseFloat(key []byte) (float64, bool) {
	n, err := strconv.ParseFloat(string(bytes.TrimSpace(key)), 64)
	return n, err == nil
}