chore: initial commit of ai site platform

Co-authored-by: Cursor <cursoragent@cursor.com>

platform/internal/crud/pool.go

@@ -0,0 +1,50 @@
+package crud
+
+import (
+	"database/sql"
+	"fmt"
+	"sync"
+
+	"aijianzhan/platform/internal/meta"
+	"aijianzhan/platform/internal/schema"
+)
+
+// DBPool 按 database_per_app 缓存连接。
+type DBPool struct {
+	mu      sync.Mutex
+	baseDSN string
+	primary *sql.DB
+	dbs     map[string]*sql.DB
+}
+
+func NewDBPool(defaultDB *sql.DB, baseDSN string) *DBPool {
+	return &DBPool{primary: defaultDB, baseDSN: baseDSN, dbs: map[string]*sql.DB{}}
+}
+
+func (p *DBPool) ForApp(app *meta.AppRecord) (*sql.DB, error) {
+	if p == nil {
+		return nil, fmt.Errorf("db pool nil")
+	}
+	if app == nil || app.DatabaseName == "" {
+		return p.primary, nil
+	}
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	if db, ok := p.dbs[app.DatabaseName]; ok {
+		return db, nil
+	}
+	dsn, err := schema.DSNForDatabase(p.baseDSN, app.DatabaseName)
+	if err != nil {
+		return nil, err
+	}
+	db, err := sql.Open("postgres", dsn)
+	if err != nil {
+		return nil, err
+	}
+	if err := db.Ping(); err != nil {
+		_ = db.Close()
+		return nil, fmt.Errorf("ping app db %s: %w", app.DatabaseName, err)
+	}
+	p.dbs[app.DatabaseName] = db
+	return db, nil
+}