package store

import (
	"database/sql"
	"fmt"
	"strings"
)

// dialect 收敛 SQLite / PostgreSQL 差异。全部查询以 ? 占位符书写，PG 执行前 rebind。
type dialect interface {
	name() string
	rebind(query string) string
	// lockConversation 在事务内锁定会话的事件序列分配（跨实例安全）。
	// PG：事务级咨询锁；SQLite：单写连接天然串行，无需额外锁。
	lockConversation(tx *sql.Tx, conversationID string) error
	// lockScope 锁定设置 scope 的读改写（owner+scope）。
	lockScope(tx *sql.Tx, owner, scope string) error
	// lockAdmission 锁定执行许可账本的清点与登记（U3 admission）。
	lockAdmission(tx *sql.Tx) error
	// lockBootstrap 锁定首次管理员引导的「核验无用户→建号→激活 Key」串行段
	//（KTD12：防两个进程并发引导出双管理员）。
	lockBootstrap(tx *sql.Tx) error
	// lockAccount serializes credential and session admission for one owner.
	lockAccount(tx *sql.Tx, owner string) error
}

// ---- SQLite（嵌入式档）----

type sqliteDialect struct{}

func (sqliteDialect) name() string                            { return "sqlite" }
func (sqliteDialect) rebind(q string) string                  { return q }
func (sqliteDialect) lockConversation(*sql.Tx, string) error  { return nil }
func (sqliteDialect) lockScope(*sql.Tx, string, string) error { return nil }
func (sqliteDialect) lockAdmission(*sql.Tx) error             { return nil }
func (sqliteDialect) lockBootstrap(*sql.Tx) error             { return nil }
func (sqliteDialect) lockAccount(*sql.Tx, string) error       { return nil }

// ---- PostgreSQL（多用户/多实例档）----

type postgresDialect struct{}

func (postgresDialect) name() string { return "postgres" }

func (postgresDialect) rebind(q string) string {
	var b strings.Builder
	n := 0
	for i := 0; i < len(q); i++ {
		if q[i] == '?' {
			n++
			fmt.Fprintf(&b, "$%d", n)
			continue
		}
		b.WriteByte(q[i])
	}
	return b.String()
}

func (postgresDialect) lockConversation(tx *sql.Tx, conversationID string) error {
	_, err := tx.Exec(`SELECT pg_advisory_xact_lock(hashtext($1))`, "conv:"+conversationID)
	return err
}

func (postgresDialect) lockScope(tx *sql.Tx, owner, scope string) error {
	_, err := tx.Exec(`SELECT pg_advisory_xact_lock(hashtext($1))`, "scope:"+owner+"/"+scope)
	return err
}

func (postgresDialect) lockAdmission(tx *sql.Tx) error {
	_, err := tx.Exec(`SELECT pg_advisory_xact_lock(hashtext($1))`, "admission:exec-slots")
	return err
}

func (postgresDialect) lockBootstrap(tx *sql.Tx) error {
	_, err := tx.Exec(`SELECT pg_advisory_xact_lock(hashtext($1))`, "bootstrap:first-admin")
	return err
}

func (postgresDialect) lockAccount(tx *sql.Tx, owner string) error {
	_, err := tx.Exec(`SELECT pg_advisory_xact_lock(hashtext($1))`, "account:"+owner)
	return err
}