package service

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"errors"
	"fmt"
	"regexp"
	"strings"
	"time"
	"unicode/utf8"

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

	"git.sundynix.cn/Blizzard/Veyra/internal/apperror"
	"git.sundynix.cn/Blizzard/Veyra/internal/model"
)

type AuthRepository interface {
	CreateUser(context.Context, model.User, model.Credential) (model.User, error)
	FindCredential(context.Context, string) (model.User, model.Credential, error)
	CreateSession(context.Context, model.Session, string) error
	FindSessionUser(context.Context, string, string, time.Time) (model.User, error)
	RevokeSession(context.Context, string, string, time.Time) error
	ListUsers(context.Context, int) ([]model.User, error)
}

type AuthService struct {
	repo      AuthRepository
	now       func() time.Time
	dummyHash []byte
}

func NewAuthService(repo AuthRepository) (*AuthService, error) {
	hash, err := bcrypt.GenerateFromPassword([]byte("invalid-user-timing-placeholder"), bcrypt.DefaultCost)
	if err != nil {
		return nil, fmt.Errorf("initialize password verifier: %w", err)
	}
	return &AuthService{repo: repo, now: time.Now, dummyHash: hash}, nil
}

var loginPattern = regexp.MustCompile(`^[a-z0-9_]{3,64}$`)

// ProvisionUser is called by a local CLI. Public registration cannot choose ADMIN.
func (s *AuthService) ProvisionUser(ctx context.Context, login, password, name, role string) (model.User, error) {
	login = strings.ToLower(strings.TrimSpace(login))
	name = strings.TrimSpace(name)
	minimumPasswordLength := 12
	if role == "ADMIN" {
		minimumPasswordLength = 8
	}
	if !loginPattern.MatchString(login) || len(password) < minimumPasswordLength || len(password) > 72 || utf8.RuneCountInString(name) > 80 || name == "" || (role != "USER" && role != "ADMIN") {
		return model.User{}, apperror.ErrInvalidInput
	}
	if s.repo == nil {
		return model.User{}, apperror.ErrUnavailable
	}
	hash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
	if err != nil {
		return model.User{}, fmt.Errorf("hash password: %w", err)
	}
	user := model.User{ID: uuid.NewString(), DisplayName: name, Status: "ACTIVE", Role: role}
	credential := model.Credential{ID: uuid.NewString(), UserID: user.ID, LoginName: login, PasswordHash: string(hash)}
	return s.repo.CreateUser(ctx, user, credential)
}

type LoginResult struct {
	User      model.User
	Token     string
	ExpiresAt time.Time
}

func (s *AuthService) Login(ctx context.Context, login, password, audience string) (LoginResult, error) {
	if audience != "admin" && audience != "app" {
		return LoginResult{}, apperror.ErrInvalidInput
	}
	if s.repo == nil {
		return LoginResult{}, apperror.ErrUnavailable
	}
	login = strings.ToLower(strings.TrimSpace(login))
	if !loginPattern.MatchString(login) || len(password) > 72 || password == "" {
		return LoginResult{}, apperror.ErrUnauthenticated
	}
	user, credential, err := s.repo.FindCredential(ctx, login)
	if err != nil {
		if errors.Is(err, apperror.ErrNotFound) {
			_ = bcrypt.CompareHashAndPassword(s.dummyHash, []byte(password))
			return LoginResult{}, apperror.ErrUnauthenticated
		}
		return LoginResult{}, err
	}
	if bcrypt.CompareHashAndPassword([]byte(credential.PasswordHash), []byte(password)) != nil || user.Status != "ACTIVE" || (audience == "admin" && user.Role != "ADMIN") || (audience == "app" && user.Role != "USER") {
		return LoginResult{}, apperror.ErrUnauthenticated
	}
	raw := make([]byte, 32)
	if _, err := rand.Read(raw); err != nil {
		return LoginResult{}, fmt.Errorf("generate session token: %w", err)
	}
	token := base64.RawURLEncoding.EncodeToString(raw)
	expires := s.now().UTC().Add(8 * time.Hour)
	session := model.Session{ID: uuid.NewString(), UserID: user.ID, TokenHash: TokenHash(token), Audience: audience, ExpiresAt: expires}
	if err := s.repo.CreateSession(ctx, session, credential.PasswordHash); err != nil {
		return LoginResult{}, err
	}
	return LoginResult{User: user, Token: token, ExpiresAt: expires}, nil
}

func (s *AuthService) Authenticate(ctx context.Context, token, audience string) (model.User, error) {
	if s.repo == nil {
		return model.User{}, apperror.ErrUnavailable
	}
	if len(token) != 43 {
		return model.User{}, apperror.ErrUnauthenticated
	}
	if audience != "admin" && audience != "app" {
		return model.User{}, apperror.ErrUnauthenticated
	}
	user, err := s.repo.FindSessionUser(ctx, TokenHash(token), audience, s.now().UTC())
	if err != nil {
		return model.User{}, err
	}
	if user.Status != "ACTIVE" || audience == "admin" && user.Role != "ADMIN" || audience == "app" && user.Role != "USER" {
		return model.User{}, apperror.ErrUnauthenticated
	}
	return user, nil
}

func (s *AuthService) Logout(ctx context.Context, token, audience string) error {
	if s.repo == nil {
		return apperror.ErrUnavailable
	}
	return s.repo.RevokeSession(ctx, TokenHash(token), audience, s.now().UTC())
}

func (s *AuthService) ListUsers(ctx context.Context) ([]model.User, error) {
	if s.repo == nil {
		return nil, apperror.ErrUnavailable
	}
	return s.repo.ListUsers(ctx, 100)
}

func TokenHash(token string) string {
	sum := sha256.Sum256([]byte(token))
	return hex.EncodeToString(sum[:])
}