package random

import (
	"math/rand"
	"strings"
)

// Standard character set.
const (
	CharsetAlpha        string = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
	CharsetAlphanumeric string = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	CharsetAlphaLower   string = "abcdefghijklmnopqrstuvwxyz"
	CharsetAlphaUpper   string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
	CharsetNumeric      string = "0123456789"
	CharsetSymbols      string = "!@#$%^&*()-=_+[]{};:,.<>/?"
)

// Alpha generates a random string of the specified length using a mixed-case alphabetical character set.
var Alpha = String([]rune(CharsetAlpha))

// Alphanumeric generates a random string of the specified length using an alphanumeric character set.
var Alphanumeric = String([]rune(CharsetAlphanumeric))

// AlphaLower generates a random string of the specified length using a lowercase alphabetical character set.
var AlphaLower = String([]rune(CharsetAlphaLower))

// AlphaUpper generates a random string of the specified length using an uppercase alphabetical character set.
var AlphaUpper = String([]rune(CharsetAlphaUpper))

// Numeric generates a random string of the specified length containing numbers only.
var Numeric = String([]rune(CharsetNumeric))

// Password generates a random string of the specified length, including the specified counts of numbers and symbols.
func Password(length, numbers, symbols int) string {
	parts := []string{
		Alpha(length - numbers - symbols),
		Numeric(numbers),
		Symbols(symbols),
	}

	str := strings.Join(parts, "")
	m := map[int]rune{}
	for i, c := range str {
		m[i] = c
	}

	jumbled := []rune{}
	for _, c := range m {
		jumbled = append(jumbled, c)
	}

	return string(jumbled)
}

// String returns a function that can be used to generate a random string of the specified length using the given character set.
func String(chars []rune) func(length int) string {
	max := len(chars)
	return func(length int) string {
		s := make([]rune, length)
		for i := range s {
			s[i] = chars[rand.Intn(max)]
		}
		return string(s)
	}
}

// Symbols generates a random string of the specified length using a limited selection of symbols.
var Symbols = String([]rune(CharsetSymbols))