package jsh

import (
	"math"
	"unicode"
	"os"
	"os/exec"
)

// FieldsN slices s into substrings after each instance of a whitespace
// character (according to unicode.IsSpace) and returns a slice of those
// substrings. The slice's length is guaranteed to be at most maxN, and
// all leftover fields are put into the last substring.
func FieldsN(s string, maxN int) []string {
	// First count the fields.
	n := 0
	inField := false
	for _, rune := range s {
		wasInField := inField
		inField = !unicode.IsSpace(rune)
		if inField && !wasInField {
			n++
		}
	}
	n = int(math.Min(float64(n), float64(maxN)))

	// Now create them.
	a := make([]string, n)
	na := 0
	fieldStart := -1 // Set to -1 when looking for start of field.
	for i, rune := range s {
		if unicode.IsSpace(rune) && na+1 < maxN {
			if fieldStart >= 0 {
				a[na] = s[fieldStart:i]
				na++
				fieldStart = -1
			}
		} else if fieldStart == -1 {
			fieldStart = i
		}
	}
	if fieldStart >= 0 { // Last field might end at EOF.
		a[na] = s[fieldStart:]
	}
	return a
}

// Falls back to procps-ng passing the space-separated arguments in the given
// args slice. If args is nil, we default to the arguments passed to the command
// line using os.Args
func FallbackWithArgs(program string, args []string) *[]byte {
	if args == nil {
		args = os.Args[1:]
	}
	out, err := exec.Command(program, args...).Output()
	if err != nil {
		panic(err)
	}
	return &out	
}

func Fallback(program string) *[]byte {
	return FallbackWithArgs(program, nil)
}