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package spectre

import (
	"crypto/hmac"
	"crypto/sha256"
	"golang.org/x/crypto/scrypt"
	"strings"
)

// Spectre is a spectre client
type Spectre struct {
	name   string
	secret string
	scoper Scoper

	key []byte
}

// New returns a Spectre client
func New(name, secret string, opts ...Option) (s *Spectre, err error) {
	s = &Spectre{
		name:   name,
		secret: secret,
		scoper: DefaultScoper,
	}
	for _, opt := range opts {
		opt(s)
	}
	s.key, err = s.userKey()
	return
}

// Option is a Spectre option
type Option func(*Spectre)

// WithScoper assigns a scoper to Spectre
func WithScoper(scoper Scoper) Option {
	return func(s *Spectre) {
		s.scoper = scoper
	}
}

func (s *Spectre) userKey() ([]byte, error) {
	nameBytes := []byte(s.name)
	secretBytes := []byte(s.secret)
	keyScope := []byte(s.scoper.Scope(Authentication))

	nameBytesLen := len(nameBytes)
	keySalt := append(keyScope,
		byte(nameBytesLen>>24),
		byte(nameBytesLen>>16),
		byte(nameBytesLen>>8),
		byte(nameBytesLen),
	)
	keySalt = append(keySalt, nameBytes...)

	return scrypt.Key(secretBytes, keySalt, 32768, 8, 2, 64)
}

func (s *Spectre) siteKey(name string, counter int, scope Scope) []byte {
	nameBytes := []byte(name)
	scopeBytes := []byte(s.scoper.Scope(scope))

	nameBytesLen := len(nameBytes)
	keySalt := append(scopeBytes,
		byte(nameBytesLen>>24),
		byte(nameBytesLen>>16),
		byte(nameBytesLen>>8),
		byte(nameBytesLen),
	)
	keySalt = append(keySalt, nameBytes...)
	keySalt = append(keySalt,
		byte(counter>>24),
		byte(counter>>16),
		byte(counter>>8),
		byte(counter),
	)

	sign := hmac.New(sha256.New, s.key)
	sign.Write(keySalt)

	return sign.Sum(nil)
}

// Site returns a site password based on Options
func (s *Spectre) Site(siteName string, opts ...SiteOption) string {
	siteOpts := &options{
		template: "",
		counter:  1,
		scope:    Authentication,
	}
	for _, opt := range opts {
		opt(siteOpts)
	}

	if siteOpts.template == "" {
		siteOpts.template = siteOpts.scope.DefaultTemplate()
	}

	siteKey := s.siteKey(siteName, siteOpts.counter, siteOpts.scope)

	templateSet := templates[siteOpts.template]
	template := templateSet[int(siteKey[0])%len(templateSet)]

	var out strings.Builder
	for idx, b := range template {
		chars := characters[string(b)]
		char := chars[int(siteKey[idx+1])%len(chars)]
		out.WriteByte(char)
	}
	return out.String()
}

type options struct {
	template Template
	counter  int
	scope    Scope
}

// SiteOption is an option for Spectre.Site
type SiteOption func(*options)

// WithTemplate specifies a Template
func WithTemplate(t Template) SiteOption {
	return func(opts *options) {
		opts.template = t
	}
}

// WithCounter specifies a counter
func WithCounter(c int) SiteOption {
	return func(opts *options) {
		opts.counter = c
	}
}

// WithScope specifies a Scope
func WithScope(s Scope) SiteOption {
	return func(opts *options) {
		opts.scope = s
	}
}