package usecase

import (
	"context"
	"errors"
	"strings"
	"time"

	"golang.org/x/crypto/bcrypt"

	"gateway/internal/library/crypto"
	memberconfig "gateway/internal/model/member/config"
	member "gateway/internal/model/member/domain"
	domrepo "gateway/internal/model/member/domain/repository"
	domusecase "gateway/internal/model/member/domain/usecase"
	"gateway/internal/model/member/totp"
)

// TOTPUseCaseParam wires TOTPUseCase dependencies. Cipher is mandatory; the
// factory rejects construction when the KEK is missing or invalid.
type TOTPUseCaseParam struct {
	Profile domrepo.TOTPProfileRepository
	Enroll  domrepo.TOTPEnrollStore
	Replay  domrepo.TOTPReplayStore
	Cipher  *crypto.Cipher
	Config  memberconfig.Config
	Now     func() time.Time
}

// MustTOTPUseCase constructs a TOTPUseCase. All collaborators must be non-nil
// (the wiring layer is responsible for validating SecretKEK before calling).
func MustTOTPUseCase(param TOTPUseCaseParam) domusecase.TOTPUseCase {
	if param.Profile == nil {
		panic("member: totp profile repository is required")
	}
	if param.Enroll == nil {
		panic("member: totp enroll store is required")
	}
	if param.Replay == nil {
		panic("member: totp replay store is required")
	}
	if param.Cipher == nil {
		panic("member: totp cipher is required")
	}
	now := param.Now
	if now == nil {
		now = time.Now
	}
	return &totpUseCase{
		profile: param.Profile,
		enroll:  param.Enroll,
		replay:  param.Replay,
		cipher:  param.Cipher,
		config:  param.Config.Defaults(),
		now:     now,
	}
}

type totpUseCase struct {
	profile domrepo.TOTPProfileRepository
	enroll  domrepo.TOTPEnrollStore
	replay  domrepo.TOTPReplayStore
	cipher  *crypto.Cipher
	config  memberconfig.Config
	now     func() time.Time
}

func (uc *totpUseCase) StartEnroll(ctx context.Context, tenantID, uid, account string) (*domusecase.EnrollStartDTO, error) {
	if tenantID == "" || uid == "" {
		return nil, errb.InputMissingRequired("tenant_id and uid are required")
	}
	rec, err := uc.profile.Get(ctx, tenantID, uid)
	if err != nil {
		return nil, errb.SysInternal("read totp profile failed").WithCause(err)
	}
	if rec != nil && rec.Enrolled {
		return nil, errb.ResAlreadyExist("totp already enrolled").WithCause(member.ErrTOTPAlreadyEnroll)
	}

	secret, err := totp.GenerateSecret()
	if err != nil {
		return nil, errb.SysInternal("totp secret generation failed").WithCause(err)
	}
	cipherBlob, err := uc.cipher.Encrypt(secret)
	if err != nil {
		return nil, errb.SysInternal("totp secret encrypt failed").WithCause(err)
	}
	ttl := time.Duration(uc.config.TOTP.EnrollTTLSeconds) * time.Second
	if err := uc.enroll.Save(ctx, tenantID, uid, cipherBlob, ttl); err != nil {
		return nil, errb.SysInternal("totp enroll persist failed").WithCause(err)
	}

	accountLabel := account
	if accountLabel == "" {
		accountLabel = uid
	}
	otpURL, err := totp.BuildOtpauthURL(totp.OtpauthURLInput{
		Issuer:    uc.config.TOTP.Issuer,
		Account:   accountLabel,
		Secret:    secret,
		Algorithm: uc.config.TOTP.Algorithm,
		Digits:    uc.config.TOTP.Digits,
		Period:    time.Duration(uc.config.TOTP.PeriodSeconds) * time.Second,
	})
	if err != nil {
		return nil, errb.SysInternal("totp otpauth url build failed").WithCause(err)
	}

	return &domusecase.EnrollStartDTO{
		OtpauthURL: otpURL,
		Issuer:     uc.config.TOTP.Issuer,
		Account:    accountLabel,
		Digits:     uc.config.TOTP.Digits,
		PeriodSec:  uc.config.TOTP.PeriodSeconds,
		ExpiresIn:  uc.config.TOTP.EnrollTTLSeconds,
	}, nil
}

func (uc *totpUseCase) ConfirmEnroll(ctx context.Context, tenantID, uid, code string) ([]string, error) {
	if tenantID == "" || uid == "" || code == "" {
		return nil, errb.InputMissingRequired("tenant_id, uid and code are required")
	}
	rec, err := uc.profile.Get(ctx, tenantID, uid)
	if err != nil {
		return nil, errb.SysInternal("read totp profile failed").WithCause(err)
	}
	if rec != nil && rec.Enrolled {
		return nil, errb.ResAlreadyExist("totp already enrolled").WithCause(member.ErrTOTPAlreadyEnroll)
	}

	cipherBlob, err := uc.enroll.Get(ctx, tenantID, uid)
	if err != nil {
		if errors.Is(err, member.ErrTOTPEnrollMissing) {
			return nil, errb.ResNotFound("totp enroll", uid).WithCause(err)
		}
		return nil, errb.SysInternal("read totp enroll failed").WithCause(err)
	}
	secret, err := uc.cipher.Decrypt(cipherBlob)
	if err != nil {
		return nil, errb.SysInternal("totp secret decrypt failed").WithCause(err)
	}

	if _, ok := totp.Verify(secret, code, uc.now(), uc.period(), uc.config.TOTP.Digits, uc.config.TOTP.Window); !ok {
		return nil, errb.AuthForbidden("invalid totp code").WithCause(member.ErrTOTPInvalidCode)
	}

	plainCodes, hashes, err := uc.generateBackupCodes()
	if err != nil {
		return nil, err
	}

	if err := uc.profile.Save(ctx, tenantID, uid, &domrepo.TOTPProfileRecord{
		Enrolled:        true,
		SecretCipher:    cipherBlob,
		BackupCodesHash: hashes,
		EnrolledAt:      uc.now().UnixMilli(),
	}); err != nil {
		return nil, errb.SysInternal("persist totp profile failed").WithCause(err)
	}
	if delErr := uc.enroll.Delete(ctx, tenantID, uid); delErr != nil {
		return nil, errb.SysInternal("clear totp enroll failed").WithCause(delErr)
	}
	return plainCodes, nil
}

func (uc *totpUseCase) VerifyCode(ctx context.Context, tenantID, uid, code string) error {
	if tenantID == "" || uid == "" || code == "" {
		return errb.InputMissingRequired("tenant_id, uid and code are required")
	}
	rec, err := uc.profile.Get(ctx, tenantID, uid)
	if err != nil {
		return errb.SysInternal("read totp profile failed").WithCause(err)
	}
	if rec == nil || !rec.Enrolled {
		return errb.ResInvalidState("totp not enrolled").WithCause(member.ErrTOTPNotEnrolled)
	}
	secret, err := uc.cipher.Decrypt(rec.SecretCipher)
	if err != nil {
		return errb.SysInternal("totp secret decrypt failed").WithCause(err)
	}

	now := uc.now()
	cleanCode := strings.TrimSpace(code)
	digits := uc.config.TOTP.Digits
	if len(cleanCode) == digits {
		if step, ok := totp.Verify(secret, cleanCode, now, uc.period(), digits, uc.config.TOTP.Window); ok {
			ttl := time.Duration(uc.config.TOTP.ReplayTTLSeconds) * time.Second
			fresh, markErr := uc.replay.MarkUsed(ctx, tenantID, uid, step, ttl)
			if markErr != nil {
				return errb.SysInternal("totp replay mark failed").WithCause(markErr)
			}
			if !fresh {
				return errb.AuthForbidden("totp code already used").WithCause(member.ErrTOTPCodeReplay)
			}
			return nil
		}
	}

	if uc.tryBackupCode(ctx, tenantID, uid, rec, cleanCode) {
		return nil
	}
	return errb.AuthForbidden("invalid totp code").WithCause(member.ErrTOTPInvalidCode)
}

func (uc *totpUseCase) tryBackupCode(ctx context.Context, tenantID, uid string, rec *domrepo.TOTPProfileRecord, code string) bool {
	for _, hash := range rec.BackupCodesHash {
		if err := bcrypt.CompareHashAndPassword([]byte(hash), []byte(code)); err == nil {
			if _, err := uc.profile.ConsumeBackupCode(ctx, tenantID, uid, hash); err != nil {
				return false
			}
			return true
		}
	}
	return false
}

func (uc *totpUseCase) Disable(ctx context.Context, tenantID, uid string) error {
	if tenantID == "" || uid == "" {
		return errb.InputMissingRequired("tenant_id and uid are required")
	}
	if err := uc.profile.Clear(ctx, tenantID, uid); err != nil {
		return errb.SysInternal("clear totp profile failed").WithCause(err)
	}
	if err := uc.enroll.Delete(ctx, tenantID, uid); err != nil {
		return errb.SysInternal("clear totp enroll failed").WithCause(err)
	}
	return nil
}

func (uc *totpUseCase) RegenerateBackupCodes(ctx context.Context, tenantID, uid string) ([]string, error) {
	if tenantID == "" || uid == "" {
		return nil, errb.InputMissingRequired("tenant_id and uid are required")
	}
	rec, err := uc.profile.Get(ctx, tenantID, uid)
	if err != nil {
		return nil, errb.SysInternal("read totp profile failed").WithCause(err)
	}
	if rec == nil || !rec.Enrolled {
		return nil, errb.ResInvalidState("totp not enrolled").WithCause(member.ErrTOTPNotEnrolled)
	}
	plain, hashes, err := uc.generateBackupCodes()
	if err != nil {
		return nil, err
	}
	if err := uc.profile.ReplaceBackupCodes(ctx, tenantID, uid, hashes); err != nil {
		return nil, errb.SysInternal("replace backup codes failed").WithCause(err)
	}
	return plain, nil
}

func (uc *totpUseCase) Status(ctx context.Context, tenantID, uid string) (*domusecase.TOTPStatusDTO, error) {
	if tenantID == "" || uid == "" {
		return nil, errb.InputMissingRequired("tenant_id and uid are required")
	}
	rec, err := uc.profile.Get(ctx, tenantID, uid)
	if err != nil {
		return nil, errb.SysInternal("read totp profile failed").WithCause(err)
	}
	dto := &domusecase.TOTPStatusDTO{}
	if rec == nil {
		return dto, nil
	}
	dto.Enrolled = rec.Enrolled
	dto.EnrolledAt = rec.EnrolledAt
	dto.BackupCodesRemaining = len(rec.BackupCodesHash)
	return dto, nil
}

func (uc *totpUseCase) period() time.Duration {
	return time.Duration(uc.config.TOTP.PeriodSeconds) * time.Second
}

// generateBackupCodes returns the plaintext codes alongside their bcrypt
// hashes ready for persistence.
func (uc *totpUseCase) generateBackupCodes() (plain, hashes []string, err error) {
	codes, err := totp.GenerateBackupCodes(uc.config.TOTP.BackupCodeCount, uc.config.TOTP.BackupCodeLength)
	if err != nil {
		return nil, nil, errb.SysInternal("backup code generation failed").WithCause(err)
	}
	hashes = make([]string, 0, len(codes))
	for _, c := range codes {
		h, hashErr := bcrypt.GenerateFromPassword([]byte(c), bcrypt.DefaultCost)
		if hashErr != nil {
			return nil, nil, errb.SysInternal("backup code hash failed").WithCause(hashErr)
		}
		hashes = append(hashes, string(h))
	}
	return codes, hashes, nil
}