package classes

import (
	"context"
	"crypto/rand"
	"crypto/subtle"
	"encoding/hex"
	"errors"
	"time"

	"git.golem15.com/golem15/fonoteka/plugins/golem15/user/models"
	"gorm.io/gorm"
)

type resetTTLKey struct{}
type activationTTLKey struct{}

// ContextWithCodeTTL stores the reset and activation lifetimes used by Verify.
// A missing value falls back to 60 minutes and 72 hours.
func ContextWithCodeTTL(ctx context.Context, reset, activation time.Duration) context.Context {
	if ctx == nil {
		ctx = context.Background()
	}
	ctx = context.WithValue(ctx, resetTTLKey{}, reset)
	return context.WithValue(ctx, activationTTLKey{}, activation)
}

func resetTTL(ctx context.Context) time.Duration {
	if ctx != nil {
		if d, ok := ctx.Value(resetTTLKey{}).(time.Duration); ok && d > 0 {
			return d
		}
	}
	return 60 * time.Minute
}

func activationTTL(ctx context.Context) time.Duration {
	if ctx != nil {
		if d, ok := ctx.Value(activationTTLKey{}).(time.Duration); ok && d > 0 {
			return d
		}
	}
	return 72 * time.Hour
}

func newCode() (string, error) {
	buf := make([]byte, 32)
	if _, err := rand.Read(buf); err != nil {
		return "", err
	}
	return hex.EncodeToString(buf), nil
}

// IssueResetCode stores a fresh plain-text reset code and returns it.
func IssueResetCode(ctx context.Context, db *gorm.DB, user *models.User) (string, error) {
	return issueCode(ctx, db, user, "reset_password_code", "reset_password_code_issued_at")
}

// IssueActivationCode stores a fresh plain-text activation code and returns it.
func IssueActivationCode(ctx context.Context, db *gorm.DB, user *models.User) (string, error) {
	return issueCode(ctx, db, user, "activation_code", "activation_code_issued_at")
}

func issueCode(ctx context.Context, db *gorm.DB, user *models.User, codeCol, issuedCol string) (string, error) {
	if user == nil || user.ID == 0 || db == nil {
		return "", errors.New("golem15.user: cannot issue a code without a saved user")
	}
	code, err := newCode()
	if err != nil {
		return "", err
	}
	now := time.Now()
	err = db.WithContext(ctx).Model(&models.User{}).Where("id = ?", user.ID).UpdateColumns(map[string]any{
		codeCol:   code,
		issuedCol: now,
	}).Error
	if err != nil {
		return "", err
	}
	switch codeCol {
	case "reset_password_code":
		user.ResetPasswordCode = &code
		user.ResetPasswordCodeIssuedAt = &now
	default:
		user.ActivationCode = &code
		user.ActivationCodeIssuedAt = &now
	}
	return code, nil
}

// VerifyResetCode accepts the stored code inside the reset TTL.
// A NULL issued-at is treated as issued now. Success clears the code and
// marks the password as self-set. The caller stores the new password.
func VerifyResetCode(ctx context.Context, db *gorm.DB, userID uint, code string) (*models.User, bool) {
	user, err := takeUser(ctx, db, userID, false)
	if err != nil || user == nil || user.ResetPasswordCode == nil {
		return nil, false
	}
	if !codeFresh(user.ResetPasswordCodeIssuedAt, resetTTL(ctx)) || !codesEqual(code, *user.ResetPasswordCode) {
		return nil, false
	}
	if err := db.WithContext(ctx).Model(&models.User{}).Where("id = ?", user.ID).UpdateColumns(map[string]any{
		"reset_password_code":           nil,
		"reset_password_code_issued_at": nil,
		"has_self_set_password":         true,
	}).Error; err != nil {
		return nil, false
	}
	user.ResetPasswordCode = nil
	user.ResetPasswordCodeIssuedAt = nil
	user.HasSelfSetPassword = true
	return user, true
}

// VerifyActivationCode accepts the stored code inside the activation TTL.
// A soft-deleted row is visible and is restored on success.
func VerifyActivationCode(ctx context.Context, db *gorm.DB, userID uint, code string) (*models.User, bool) {
	user, err := takeUser(ctx, db, userID, true)
	if err != nil || user == nil || user.IsActivated || user.ActivationCode == nil {
		return nil, false
	}
	if !codeFresh(user.ActivationCodeIssuedAt, activationTTL(ctx)) || !codesEqual(code, *user.ActivationCode) {
		return nil, false
	}
	if user.DeletedAt.Valid {
		if err := db.WithContext(ctx).Unscoped().Model(&models.User{}).Where("id = ?", user.ID).Update("deleted_at", nil).Error; err != nil {
			return nil, false
		}
		user.DeletedAt = gorm.DeletedAt{}
	}
	now := time.Now()
	if err := db.WithContext(ctx).Model(&models.User{}).Where("id = ?", user.ID).UpdateColumns(map[string]any{
		"is_activated":              true,
		"activated_at":              now,
		"activation_code":           nil,
		"activation_code_issued_at": nil,
	}).Error; err != nil {
		return nil, false
	}
	user.IsActivated = true
	user.ActivatedAt = &now
	user.ActivationCode = nil
	user.ActivationCodeIssuedAt = nil
	return user, true
}

func takeUser(ctx context.Context, db *gorm.DB, id uint, unscoped bool) (*models.User, error) {
	if db == nil || id == 0 {
		return nil, nil
	}
	q := db.WithContext(ctx)
	if unscoped {
		q = q.Unscoped()
	}
	var user models.User
	err := q.Where("id = ?", id).Take(&user).Error
	if errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	return &user, nil
}

func codeFresh(issued *time.Time, ttl time.Duration) bool {
	at := time.Now()
	if issued != nil && !issued.IsZero() {
		at = *issued
	}
	return !time.Now().After(at.Add(ttl))
}

func codesEqual(got, stored string) bool {
	if len(got) != len(stored) {
		return false
	}
	return subtle.ConstantTimeCompare([]byte(got), []byte(stored)) == 1
}