package ai

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

	"gorm.io/gorm"
	"senlinai-agent/backend/internal/logic/projects"
	"senlinai-agent/backend/internal/models"
)

const (
	aiSessionCreateAction = "ai_session_create"
	aiSessionCreateLimit  = 20
	defaultSessionStatus  = "ready"
)

var (
	ErrInvalidSession = errors.New("invalid ai session")
	ErrExpertNotFound = errors.New("ai expert not found")
)

type sessionGateway interface {
	ReserveRateLimit(userID uint, action string, limit int, window time.Duration) error
	SelectKey(userID uint) (SelectedKey, error)
	RecordCall(database *gorm.DB, userID uint, provider string, usedKeyType string, action string, status string, errText string) error
}

// SessionService 只管理项目内普通 AI 会话；它不会把上下文自动转换为任务、笔记或资料。
type SessionService struct {
	gateway sessionGateway
}

func NewSessionService(gateway sessionGateway) *SessionService {
	return &SessionService{gateway: gateway}
}

// List 在项目 owner 校验后返回该项目的会话，内部自增 ID 不离开服务边界。
func (s *SessionService) List(userID uint, projectIdentity string) ([]models.SaAISession, error) {
	project, err := projects.FindOwnedProject(userID, projectIdentity)
	if err != nil {
		return nil, err
	}
	var sessions []models.SaAISession
	if err := models.DBService.Preload("Expert").Where("project_id = ?", project.ID).Order("updated_at desc, id desc").Find(&sessions).Error; err != nil {
		return nil, err
	}
	if sessions == nil {
		sessions = []models.SaAISession{}
	}
	return sessions, nil
}

// Create 先校验项目，再限流，最后才选择 provider/key；会话创建不会生成任何正式业务对象。
func (s *SessionService) Create(userID uint, projectIdentity, title, context string) (*models.SaAISession, error) {
	return s.CreateWithExpert(userID, projectIdentity, title, context, "")
}

// CreateWithExpert 创建带本地专家角色的项目会话。
func (s *SessionService) CreateWithExpert(userID uint, projectIdentity, title, context, expertIdentity string) (*models.SaAISession, error) {
	title = strings.TrimSpace(title)
	context = strings.TrimSpace(context)
	if title == "" {
		return nil, ErrInvalidSession
	}
	project, err := projects.FindOwnedProject(userID, projectIdentity)
	if err != nil {
		return nil, err
	}
	if s.gateway == nil {
		return nil, errors.New("ai gateway is required")
	}
	expert, err := findExpertByIdentity(models.DBService, expertIdentity)
	if err != nil {
		return nil, err
	}

	if err := s.gateway.ReserveRateLimit(userID, aiSessionCreateAction, aiSessionCreateLimit, time.Hour); err != nil {
		if errors.Is(err, ErrAIRateLimited) {
			if auditErr := s.gateway.RecordCall(models.DBService, userID, "none", "none", aiSessionCreateAction, "failed", "ai_rate_limited"); auditErr != nil {
				return nil, fmt.Errorf("record ai rate limit failure: %w", auditErr)
			}
			return nil, ErrAIRateLimited
		}
		if auditErr := s.gateway.RecordCall(models.DBService, userID, "none", "none", aiSessionCreateAction, "failed", "rate_limit_reservation_failed"); auditErr != nil {
			return nil, fmt.Errorf("check rate limit: %v; record failure: %w", err, auditErr)
		}
		return nil, err
	}

	selected, err := s.gateway.SelectKey(userID)
	if err != nil {
		code := "provider_selection_failed"
		if errors.Is(err, ErrAIKeyMissing) {
			code = "ai_key_missing"
		}
		provider, keyType := selectedAuditMetadata(selected)
		if auditErr := s.gateway.RecordCall(models.DBService, userID, provider, keyType, aiSessionCreateAction, "failed", code); auditErr != nil {
			return nil, fmt.Errorf("select ai key: %v; record failure: %w", err, auditErr)
		}
		return nil, err
	}

	session := models.SaAISession{
		ProjectID: project.ID,
		CreatedBy: userID,
		Title:     title,
		Context:   context,
		Status:    defaultSessionStatus,
	}
	if expert != nil {
		session.ExpertID = &expert.ID
		session.ExpertIdentity = &expert.Identity
	}
	failureCode := "session_create_failed"
	err = models.DBService.Transaction(func(tx *gorm.DB) error {
		if err := tx.Create(&session).Error; err != nil {
			return err
		}
		// ready 只表示会话入口已建立，不表示 provider 已回复或任何业务对象已创建。
		failureCode = "audit_write_failed"
		if err := s.gateway.RecordCall(tx, userID, selected.Provider, selected.KeyType, aiSessionCreateAction, defaultSessionStatus, ""); err != nil {
			return err
		}
		failureCode = "session_transaction_failed"
		return nil
	})
	if err != nil {
		if auditErr := s.gateway.RecordCall(models.DBService, userID, selected.Provider, selected.KeyType, aiSessionCreateAction, "failed", failureCode); auditErr != nil {
			return nil, fmt.Errorf("create ai session transaction: %v; record failure: %w", err, auditErr)
		}
		return nil, err
	}
	session.Expert = expert
	return &session, nil
}

func selectedAuditMetadata(selected SelectedKey) (string, string) {
	provider := strings.TrimSpace(selected.Provider)
	keyType := strings.TrimSpace(selected.KeyType)
	if provider == "" {
		provider = "none"
	}
	if keyType == "" {
		keyType = "none"
	}
	return provider, keyType
}

func aiSessionStatus(session models.SaAISession) string {
	if status := strings.TrimSpace(session.Status); status != "" {
		return status
	}
	return defaultSessionStatus
}