package app

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

	"github.com/golang-jwt/jwt/v5"
	"github.com/google/uuid"
	"golang.org/x/crypto/bcrypt"

	"github.com/geo-platform/tenant-api/internal/ops/domain"
	"github.com/geo-platform/tenant-api/internal/ops/repository"
	sharedauth "github.com/geo-platform/tenant-api/internal/shared/auth"
	"github.com/geo-platform/tenant-api/internal/shared/response"
)

type OperatorClaims struct {
	OperatorID  int64  `json:"operator_id"`
	Username    string `json:"username"`
	DisplayName string `json:"display_name"`
	Role        string `json:"role"`
	jwt.RegisteredClaims
}

type TokenIssuer struct {
	secret    []byte
	accessTTL time.Duration
}

func NewTokenIssuer(secret string, accessTTL time.Duration) *TokenIssuer {
	return &TokenIssuer{secret: []byte(secret), accessTTL: accessTTL}
}

func (t *TokenIssuer) AccessTTL() time.Duration { return t.accessTTL }

type IssuedToken struct {
	AccessToken string
	ExpiresAt   int64
}

func (t *TokenIssuer) Issue(operator *domain.OperatorAccount) (*IssuedToken, error) {
	now := time.Now()
	exp := now.Add(t.accessTTL)
	claims := OperatorClaims{
		OperatorID:  operator.ID,
		Username:    operator.Username,
		DisplayName: operator.DisplayName,
		Role:        operator.Role,
		RegisteredClaims: jwt.RegisteredClaims{
			ID:        uuid.New().String(),
			Subject:   "ops-access",
			IssuedAt:  jwt.NewNumericDate(now),
			ExpiresAt: jwt.NewNumericDate(exp),
		},
	}
	signed, err := jwt.NewWithClaims(jwt.SigningMethodHS256, claims).SignedString(t.secret)
	if err != nil {
		return nil, fmt.Errorf("sign ops token: %w", err)
	}
	return &IssuedToken{AccessToken: signed, ExpiresAt: exp.Unix()}, nil
}

func (t *TokenIssuer) Parse(raw string) (*OperatorClaims, error) {
	token, err := jwt.ParseWithClaims(raw, &OperatorClaims{}, func(tok *jwt.Token) (any, error) {
		if _, ok := tok.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, fmt.Errorf("unexpected signing method: %v", tok.Header["alg"])
		}
		return t.secret, nil
	})
	if err != nil {
		return nil, err
	}
	claims, ok := token.Claims.(*OperatorClaims)
	if !ok || !token.Valid {
		return nil, errors.New("invalid ops token")
	}
	if claims.Subject != "ops-access" {
		return nil, errors.New("wrong token subject")
	}
	return claims, nil
}

type AuthService struct {
	accounts *repository.AccountRepository
	audits   *AuditService
	issuer   *TokenIssuer
	guard    *sharedauth.LoginGuard
}

func NewAuthService(
	accounts *repository.AccountRepository,
	audits *AuditService,
	issuer *TokenIssuer,
	guards ...*sharedauth.LoginGuard,
) *AuthService {
	var guard *sharedauth.LoginGuard
	if len(guards) > 0 {
		guard = guards[0]
	}
	return &AuthService{accounts: accounts, audits: audits, issuer: issuer, guard: guard}
}

type LoginInput struct {
	Username  string
	Password  string
	IP        string
	UserAgent string
	RequestID string
}

type LoginResult struct {
	AccessToken string
	ExpiresAt   int64
	Operator    OperatorView
}

type OperatorView struct {
	ID          int64   `json:"id"`
	Username    string  `json:"username"`
	DisplayName string  `json:"display_name"`
	Email       *string `json:"email"`
	Role        string  `json:"role"`
	Status      string  `json:"status"`
}

func ToOperatorView(a *domain.OperatorAccount) OperatorView {
	return OperatorView{
		ID:          a.ID,
		Username:    a.Username,
		DisplayName: a.DisplayName,
		Email:       a.Email,
		Role:        a.Role,
		Status:      a.Status,
	}
}

const (
	ActionLoginSuccess = "auth.login.success"
	ActionLoginFailed  = "auth.login.failure"
)

func (s *AuthService) Login(ctx context.Context, in LoginInput) (*LoginResult, error) {
	in.Username = strings.TrimSpace(in.Username)
	if in.Username == "" {
		return nil, response.ErrBadRequest(40000, "invalid_payload", "username is required")
	}

	permit, err := s.acquireLoginPermit(ctx, in)
	if err != nil {
		return nil, err
	}
	credentialsVerified := false
	defer func() {
		if credentialsVerified {
			permit.RecordSuccess(ctx)
			return
		}
		permit.Release(ctx)
	}()

	account, err := s.accounts.GetByUsername(ctx, in.Username)
	if err != nil {
		permit.RecordFailure(ctx)
		s.recordLoginFailure(ctx, in, "account_not_found")
		return nil, response.ErrUnauthorized(40110, "invalid_credentials", "账号或密码错误")
	}

	if !account.IsActive() {
		permit.RecordFailure(ctx)
		s.recordLoginFailure(ctx, in, "account_disabled")
		return nil, response.ErrForbidden(40310, "account_disabled", "账号已停用")
	}

	if err := bcrypt.CompareHashAndPassword([]byte(account.PasswordHash), []byte(in.Password)); err != nil {
		permit.RecordFailure(ctx)
		s.recordLoginFailure(ctx, in, "wrong_password")
		return nil, response.ErrUnauthorized(40110, "invalid_credentials", "账号或密码错误")
	}
	credentialsVerified = true

	token, err := s.issuer.Issue(account)
	if err != nil {
		return nil, fmt.Errorf("issue token: %w", err)
	}

	if err := s.accounts.MarkLogin(ctx, account.ID); err != nil {
		// non-fatal — login already succeeded
		_ = err
	}

	id := account.ID
	_ = s.audits.Append(ctx, domain.AuditEvent{
		OperatorID:   &id,
		OperatorName: account.DisplayName,
		Action:       ActionLoginSuccess,
		IP:           in.IP,
		UserAgent:    in.UserAgent,
		RequestID:    in.RequestID,
	})

	return &LoginResult{
		AccessToken: token.AccessToken,
		ExpiresAt:   token.ExpiresAt,
		Operator:    ToOperatorView(account),
	}, nil
}

func (s *AuthService) acquireLoginPermit(ctx context.Context, in LoginInput) (*sharedauth.LoginPermit, error) {
	if s.guard == nil {
		return nil, nil
	}
	permit, err := s.guard.Acquire(ctx, sharedauth.LoginGuardSubject{
		Identifier: in.Username,
		IP:         in.IP,
	})
	if err == nil {
		return permit, nil
	}

	var blocked *sharedauth.LoginGuardBlockedError
	if errors.As(err, &blocked) {
		detail := fmt.Sprintf("请 %d 秒后重试", blocked.RetryAfterSeconds())
		switch blocked.Reason {
		case sharedauth.LoginGuardBlockedInProgress:
			return nil, response.ErrTooManyRequests(42912, "login_in_progress", detail)
		case sharedauth.LoginGuardBlockedLocked:
			return nil, response.ErrTooManyRequests(42911, "login_locked", detail)
		default:
			return nil, response.ErrTooManyRequests(42910, "login_rate_limited", detail)
		}
	}
	if errors.Is(err, sharedauth.ErrLoginGuardUnavailable) {
		return nil, response.ErrServiceUnavailable(50305, "login_guard_unavailable", "login protection is temporarily unavailable")
	}
	return nil, err
}

func (s *AuthService) recordLoginFailure(ctx context.Context, in LoginInput, reason string) {
	_ = s.audits.Append(ctx, domain.AuditEvent{
		Action:    ActionLoginFailed,
		IP:        in.IP,
		UserAgent: in.UserAgent,
		RequestID: in.RequestID,
		Metadata: map[string]any{
			"username": in.Username,
			"reason":   reason,
		},
	})
}