package authservice

import (
	"strings"

	"github.com/google/shlex"
)

// Used to find the name of the command to be executed from a command string which
// can be passed to bash. Ignores all arguments passed to the command and any parameters
// defined in the command string
func extractCommandName(command string) (string, error) {
	words, err := shlex.Split(command)
	if err != nil {
		return "", err
	}
	for _, word := range words {
		if isParameter(word) {
			continue
		}

		return word, nil
	}
	return "", nil
}

// Reports whether word is a valid name for a parameter in bash
// Valid names are composed of letters, numbers or an underscore, and must start
// with a letter or an underscore
func isParameter(word string) bool {
	// Parameter must have a name and value separated by an '='
	if !strings.Contains(word, "=") {
		return false
	}

	// Verify name of parameter follows the rules
	name := strings.SplitN(word, "=", 2)[0]
	// All characters must be either letter, number or underscore
	for _, char := range name {
		if isNumber(char) || isLetter(char) || char == '_' {
			continue
		}
		return false
	}

	// First character must be a letter or underscore
	var firstRune rune
	// Extract first char of parameter name
	for _, char := range name {
		firstRune = char
		break
	}
	if isLetter(firstRune) || firstRune == '_' {
		return true
	}

	return false
}

func isLetter(char rune) bool {
	return ('a' <= char && char <= 'z') || ('A' <= char && char <= 'Z')
}

func isNumber(char rune) bool {
	return ('0' <= char && char <= '9')
}