package nns01

import (
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"time"

	"github.com/go-acme/lego/v4/acme"
	"github.com/go-acme/lego/v4/acme/api"
	"github.com/go-acme/lego/v4/challenge"
	"github.com/go-acme/lego/v4/log"
)

type ValidateFunc func(core *api.Core, domain string, chlng acme.Challenge) error

// Challenge implements the nns-01 challenge.
type Challenge struct {
	core     *api.Core
	validate ValidateFunc
	provider challenge.Provider
}

func NewChallenge(core *api.Core, validate ValidateFunc, provider challenge.Provider) *Challenge {
	chlg := &Challenge{
		core:     core,
		validate: validate,
		provider: provider,
	}

	return chlg
}

// PreSolve submits the txt record to the nns provider.
func (c *Challenge) PreSolve(authz acme.Authorization) error {
	domain := challenge.GetTargetedDomain(authz)
	log.Infof("[%s] acme: Preparing to solve NNS-01", domain)

	chlng, keyAuth, err := c.getChallengeInfo(authz)
	if err != nil {
		return err
	}

	err = c.provider.Present(authz.Identifier.Value, chlng.Token, keyAuth)
	if err != nil {
		return fmt.Errorf("[%s] acme: error presenting token: %w", domain, err)
	}

	return nil
}

func (c *Challenge) Solve(authz acme.Authorization) error {
	domain := challenge.GetTargetedDomain(authz)
	log.Infof("[%s] acme: Trying to solve NNS-01", domain)

	chlng, keyAuth, err := c.getChallengeInfo(authz)
	if err != nil {
		return err
	}

	chlng.KeyAuthorization = keyAuth
	return c.validate(c.core, domain, chlng)
}

// CleanUp cleans the challenge.
func (c *Challenge) CleanUp(authz acme.Authorization) error {
	log.Infof("[%s] acme: Cleaning NNS-01 challenge", challenge.GetTargetedDomain(authz))

	chlng, keyAuth, err := c.getChallengeInfo(authz)
	if err != nil {
		return err
	}

	return c.provider.CleanUp(authz.Identifier.Value, chlng.Token, keyAuth)
}

func (c *Challenge) Sequential() (bool, time.Duration) {
	if p, ok := c.provider.(sequential); ok {
		return ok, p.Sequential()
	}
	return false, 0
}

type sequential interface {
	Sequential() time.Duration
}

// RecordInfo contains the information use to create the TXT record.
type RecordInfo struct {
	// FQDN is the full-qualified challenge domain (`acme-challenge.[domain]`)
	FQDN string
	// Value contains the value for the TXT record
	Value string
}

// GetRecordInfo returns information used to create a TXT record which will fulfill the `nns-01` challenge.
func GetRecordInfo(domain, keyAuth string) RecordInfo {
	keyAuthShaBytes := sha256.Sum256([]byte(keyAuth))
	// base64URL encoding without padding
	value := base64.RawURLEncoding.EncodeToString(keyAuthShaBytes[:sha256.Size])

	return RecordInfo{
		Value: value,
		FQDN:  getRecordFQDN(domain),
	}
}

func getRecordFQDN(domain string) string {
	return fmt.Sprintf("acme-challenge.%s", domain)
}

func (c *Challenge) getChallengeInfo(authz acme.Authorization) (acme.Challenge, string, error) {
	chlng, err := challenge.FindChallenge(challenge.NNS01, authz)
	if err != nil {
		return acme.Challenge{}, "", err
	}

	// Generate the Key Authorization for the challenge
	keyAuth, err := c.core.GetKeyAuthorization(chlng.Token)
	if err != nil {
		return acme.Challenge{}, "", err
	}

	return chlng, keyAuth, nil
}