package dbsync

import (
	"fmt"
	"path/filepath"
	"strings"
)

// DefaultChannelOpts 创建公司默认同步通道（Z12c）。
type DefaultChannelOpts struct {
	TenantID     int64
	AgentID      int64
	Name         string
	RemoteDriver Driver
	RemoteDSN    string
	OnlineDBID   string // 空则用 channel id
	DatabaseName string
}

// FindSystemDefaultChannel 返回该公司 IsSystemDefault 通道（若有多条取最新启用的）。
func (s *FileStore) FindSystemDefaultChannel(tenantID int64) (*Channel, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	list, err := s.readChannels()
	if err != nil {
		return nil, err
	}
	var best *Channel
	for i := range list {
		ch := list[i]
		if ch.TenantID != tenantID || !ch.IsSystemDefault {
			continue
		}
		cp := ch
		if best == nil || cp.UpdatedAt.After(best.UpdatedAt) {
			best = &cp
		}
	}
	return best, nil
}

// EnsureSystemDefaultChannel 若无默认同步通道则创建；返回通道（已存在则复用）。
func (s *FileStore) EnsureSystemDefaultChannel(opts DefaultChannelOpts) (Channel, error) {
	if opts.TenantID <= 0 {
		return Channel{}, fmt.Errorf("tenant_id required")
	}
	if existing, err := s.FindSystemDefaultChannel(opts.TenantID); err == nil && existing != nil {
		ch := *existing
		if opts.AgentID > 0 && ch.AgentID == 0 {
			ch.AgentID = opts.AgentID
			saved, err := s.SaveChannel(ch)
			if err != nil {
				return Channel{}, err
			}
			return saved, nil
		}
		return ch, nil
	}
	driver := opts.RemoteDriver
	if driver == "" {
		driver = DriverPostgres
	}
	dsn := strings.TrimSpace(opts.RemoteDSN)
	if dsn == "" {
		driver = DriverSQLite
		dsn = filepath.ToSlash(filepath.Join(".", "data", "dbsync", fmt.Sprintf("tenant_%d_online.db", opts.TenantID)))
		dsn = "file:" + dsn + "?_pragma=busy_timeout(5000)"
	}
	name := strings.TrimSpace(opts.Name)
	if name == "" {
		name = fmt.Sprintf("公司默认同步 #%d", opts.TenantID)
	}
	ch := Channel{
		TenantID:        opts.TenantID,
		Name:            name,
		Enabled:         false, // 默认同步通道供 agent push 落点；不启本地 outbox 轮询
		Direction:       DirLocalToRemote,
		ConflictPolicy:  PolicyLWWSource,
		IsSystemDefault: true,
		AgentID:         opts.AgentID,
		Local: Endpoint{
			Driver: DriverSQLite,
			DSN:    "file:./data/dbsync/local_placeholder.db?_pragma=busy_timeout(5000)",
			Tables: nil,
		},
		Remote: Endpoint{
			Driver: driver,
			DSN:    dsn,
			Tables: nil,
		},
		PKColumns: map[string]string{},
	}
	if err := ValidateChannelConfig(&ch); err != nil {
		return Channel{}, err
	}
	saved, err := s.SaveChannel(ch)
	if err != nil {
		return Channel{}, err
	}
	return saved, nil
}

// ResolveOnlineDBID 默认 online_db_id：优先显式值，否则通道 id。
func ResolveOnlineDBID(explicit, channelID string) string {
	if s := strings.TrimSpace(explicit); s != "" {
		return s
	}
	return strings.TrimSpace(channelID)
}