package pwgen

import (
	"errors"
)

const (
	DefaultLength           = 20
	DefaultSpecialsAlphabet = `!?~@#$%^&*()-+={}[]\/{}|<>`
)

var ErrLengthOverflow = errors.New("length overflow")

type generationOptionFunc func(options *options)

func (f generationOptionFunc) ApplyToOptions(options *options) {
	f(options)
}

func WithLength(length uint) GenerationOption {
	return generationOptionFunc(func(options *options) {
		options.Length = length
	})
}

func WithLetters(letters uint) GenerationOption {
	return generationOptionFunc(func(options *options) {
		options.Letters = letters
	})
}

func WithUppercase(uppercase uint) GenerationOption {
	return generationOptionFunc(func(options *options) {
		options.Uppercase = uppercase
	})
}

func WithLowercase(lowercase uint) GenerationOption {
	return generationOptionFunc(func(options *options) {
		options.Lowercase = lowercase
	})
}

func WithDigits(digits uint) GenerationOption {
	return generationOptionFunc(func(options *options) {
		options.Digits = digits
	})
}

func WithSpecials(specials uint) GenerationOption {
	return generationOptionFunc(func(options *options) {
		options.Specials = specials
	})
}

func WithSpecialsAlphabet(specialsAlphabet string) GenerationOption {
	return generationOptionFunc(func(options *options) {
		if specialsAlphabet == "" {
			specialsAlphabet = DefaultSpecialsAlphabet
		}
		options.SpecialsAlphabet = specialsAlphabet
	})
}

func defaultOptions(opts ...GenerationOption) *options {
	o := &options{
		Length:           DefaultLength,
		Letters:          0,
		Digits:           3,
		Uppercase:        3,
		Lowercase:        3,
		Specials:         3,
		SpecialsAlphabet: DefaultSpecialsAlphabet,
	}

	for i := range opts {
		opts[i].ApplyToOptions(o)
	}

	return o
}

type options struct {
	Length           uint
	Letters          uint
	Digits           uint
	Uppercase        uint
	Lowercase        uint
	Specials         uint
	SpecialsAlphabet string
}

func (o options) effectiveLength() (uint, error) {
	var length uint

	for _, i := range []uint{o.Digits, o.Lowercase, o.Uppercase, o.Specials} {
		if length+i < length {
			return 0, ErrLengthOverflow
		}
		length += i
	}

	if upperAndLower := o.Lowercase + o.Uppercase; upperAndLower < o.Letters {
		length += o.Letters - upperAndLower
	}

	if length > o.Length {
		return length, nil
	}

	return o.Length, nil
}