package pwgen

import (
	"math/rand"
	"time"
)

var (
	_         Generator = (*DefaultGenerator)(nil)
	Default             = NewDefaultGenerator(nil)
	lowerCase           = alphabet('a', 'z')
	upperCase           = alphabet('A', 'Z')
	letters             = merge(lowerCase, upperCase)
	digits              = alphabet('0', '9')
)

func Generate(opts ...GenerationOption) (string, error) {
	return Default.Generate(opts...)
}

func NewDefaultGenerator(prng Int32n) DefaultGenerator {
	if prng == nil {
		prng = rand.New(rand.NewSource(time.Now().UnixNano()))
	}

	return DefaultGenerator{
		PRNG: prng,
	}
}

type DefaultGenerator struct {
	PRNG Int32n
}

func (d DefaultGenerator) Generate(opts ...GenerationOption) (string, error) {
	compiledOptions := defaultOptions(opts...)
	fullAlphabet := merge(lowerCase, upperCase, digits, []rune(compiledOptions.SpecialsAlphabet))

	effectiveLength, err := compiledOptions.effectiveLength()
	if err != nil {
		return "", err
	}

	generated := make([]rune, 0, effectiveLength)

	for i := uint(0); i < compiledOptions.Lowercase; i++ {
		generated = append(generated, runeFor(lowerCase, d.PRNG))
	}

	for i := uint(0); i < compiledOptions.Uppercase; i++ {
		generated = append(generated, runeFor(upperCase, d.PRNG))
	}

	for i := uint(0); i < compiledOptions.Digits; i++ {
		generated = append(generated, runeFor(digits, d.PRNG))
	}

	for i := uint(0); i < compiledOptions.Specials; i++ {
		generated = append(generated, runeFor([]rune(compiledOptions.SpecialsAlphabet), d.PRNG))
	}

	for i := compiledOptions.Lowercase + compiledOptions.Uppercase; i < compiledOptions.Letters; i++ {
		generated = append(generated, runeFor(letters, d.PRNG))
	}

	for i := uint(len(generated)); i < effectiveLength; i++ {
		generated = append(generated, runeFor(fullAlphabet, d.PRNG))
	}

	return string(shuffle(generated, d.PRNG)), nil
}