package transaction

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"strings"
	"time"
)

// backendService backend 容器部署事务使用的服务名常量。
//
// 该常量同时用于部署表相关事务的归属判定与历史查询的条件过滤。
const backendService = "backend"

// BackendContainerDeployment is the last container slot committed for backend.
// Runtime inspection remains authoritative for the current external state; this
// record distinguishes a fresh installation from loss or drift after deployment.
//
// BackendContainerDeployment backend 最近一次提交使用的容器槽位持久化记录。
// 它只保留单行（singleton_id=1），用于区分全新安装与部署后丢失/漂移：运行时 inspect
// 始终是当前外部状态的权威来源，而本记录提供“机器是否曾成功部署”的持久化证据。
type BackendContainerDeployment struct {
	ActivePort    int       // 当前对外服务的端口，只能是 8080 或 8081。
	ContainerName string    // 生效容器的名称。
	ImageDigest   string    // 生效容器镜像的摘要。
	ContainerID   string    // 生效容器的 ID。
	TransactionID string    // 提交本次部署的事务 ID。
	UpdatedAt     time.Time // 记录最近一次更新（提交）时间（UTC）。
}

// BackendContainerDeployment returns the single committed backend container state.
//
// BackendContainerDeployment 返回当前唯一已提交的 backend 容器部署记录。参数 ctx
// 用于取消查询。若尚无部署记录则返回 ErrNotFound。
func (s *Store) BackendContainerDeployment(ctx context.Context) (BackendContainerDeployment, error) {
	return scanBackendContainerDeployment(s.db.QueryRowContext(ctx, `
        SELECT active_port, container_name, image_digest, container_id,
               transaction_id, updated_at
          FROM backend_container_deployment
         WHERE singleton_id = 1`))
}

// HasCommittedBackendContainerTransactionHistory reports whether this store
// contains a committed container backend transaction. This is the legacy
// deployment evidence used when a database predates the deployment table.
// Failed and rolled-back first-install attempts do not mark a machine deployed.
//
// HasCommittedBackendContainerTransactionHistory 报告当前存储中是否存在已提交的
// backend 容器事务历史。当数据库版本早于部署表（缺少 backend_container_deployment
// 单例记录）时，它作为历史部署证据使用：只要存在 service 为 backend 且幂等键匹配
// backend:container:* 且状态为 COMMITTED 的事务，即视为该机器已部署。失败或回滚的
// 首次安装尝试不会把机器标记为已部署。参数 ctx 用于取消查询，返回是否已部署的布尔值
// 及可能的错误。
func (s *Store) HasCommittedBackendContainerTransactionHistory(ctx context.Context) (bool, error) {
	var found int
	if err := s.db.QueryRowContext(ctx, `
        SELECT EXISTS (
            SELECT 1
              FROM transactions
             WHERE service = ?
               AND idempotency_key GLOB 'backend:container:*'
               AND state = ?
        )`, backendService, StateCommitted).Scan(&found); err != nil {
		return false, fmt.Errorf("query committed backend container transaction history: %w", err)
	}
	return found == 1, nil
}

// CommitBackendContainerDeployment atomically records the active container and
// commits its transaction. A crash cannot leave COMMITTED without the matching
// deployment row, or publish a deployment row for an unfinished transaction.
//
// CommitBackendContainerDeployment 原子地记录生效容器并把其事务提交为 COMMITTED。
// 参数 ctx 用于取消操作；transactionID 为待提交的事务 ID，必须与 backend 服务匹配
// 且当前状态为 DRAINING；deployment 为要写入的容器部署信息；message 为随状态事件
// 记录的信息。返回值为更新后的最新事务快照。由于部署行写入与事务状态提交在同一个
// Serializable 事务内完成，崩溃不可能留下“已 COMMITTED 却没有对应部署行”或“未完成
// 事务却已发布部署行”的中间状态。
func (s *Store) CommitBackendContainerDeployment(
	ctx context.Context,
	transactionID string,
	deployment BackendContainerDeployment,
	message string,
) (Transaction, error) {
	if transactionID == "" || strings.TrimSpace(transactionID) != transactionID {
		return Transaction{}, errors.New("exact transaction ID is required")
	}
	if err := validateBackendContainerDeployment(deployment); err != nil {
		return Transaction{}, err
	}

	tx, err := s.db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelSerializable})
	if err != nil {
		return Transaction{}, fmt.Errorf("begin backend container deployment commit: %w", err)
	}
	defer tx.Rollback()

	record, err := getTransactionByID(ctx, tx, transactionID)
	if err != nil {
		return Transaction{}, err
	}
	if record.Service != backendService {
		return Transaction{}, fmt.Errorf("transaction %s service must be %s", transactionID, backendService)
	}
	if record.State != StateDraining {
		return Transaction{}, &TransitionError{From: record.State, To: StateCommitted}
	}

	now := s.now().UTC()
	_, err = tx.ExecContext(ctx, `
        INSERT INTO backend_container_deployment (
            singleton_id, active_port, container_name, image_digest,
            container_id, transaction_id, updated_at
        ) VALUES (1, ?, ?, ?, ?, ?, ?)
        ON CONFLICT(singleton_id) DO UPDATE SET
            active_port = excluded.active_port,
            container_name = excluded.container_name,
            image_digest = excluded.image_digest,
            container_id = excluded.container_id,
            transaction_id = excluded.transaction_id,
            updated_at = excluded.updated_at`,
		deployment.ActivePort,
		deployment.ContainerName,
		deployment.ImageDigest,
		deployment.ContainerID,
		transactionID,
		formatTime(now),
	)
	if err != nil {
		return Transaction{}, fmt.Errorf("write backend container deployment: %w", err)
	}

	result, err := tx.ExecContext(ctx, `
        UPDATE transactions
           SET state = ?, version = version + 1, updated_at = ?
         WHERE id = ? AND version = ? AND state = ?`,
		StateCommitted,
		formatTime(now),
		transactionID,
		record.Version,
		StateDraining,
	)
	if err != nil {
		return Transaction{}, fmt.Errorf("commit backend container transaction state: %w", err)
	}
	rows, err := result.RowsAffected()
	if err != nil {
		return Transaction{}, fmt.Errorf("read committed backend container transaction rows: %w", err)
	}
	if rows != 1 {
		return Transaction{}, errors.New("backend container transaction changed concurrently")
	}
	if err := insertEvent(ctx, tx, transactionID, "", "TRANSACTION_STATE_CHANGED", record.State, StateCommitted, message, now); err != nil {
		return Transaction{}, err
	}
	if err := tx.Commit(); err != nil {
		return Transaction{}, fmt.Errorf("commit backend container deployment: %w", err)
	}

	record.State = StateCommitted
	record.Version++
	record.UpdatedAt = now
	return record, nil
}

// validateBackendContainerDeployment 校验 backend 容器部署信息的合法性。
//
// ActivePort 必须是 8080 或 8081；ContainerName、ImageDigest、ContainerID 均不能
// 为空且不能含有首尾空白（即必须是精确值）。全部通过返回 nil，否则返回描述具体
// 问题的错误。
func validateBackendContainerDeployment(deployment BackendContainerDeployment) error {
	if deployment.ActivePort != 8080 && deployment.ActivePort != 8081 {
		return fmt.Errorf("backend container deployment port must be 8080 or 8081: %d", deployment.ActivePort)
	}
	for _, field := range []struct {
		name  string
		value string
	}{
		{"container name", deployment.ContainerName},
		{"image digest", deployment.ImageDigest},
		{"container ID", deployment.ContainerID},
	} {
		if field.value == "" || strings.TrimSpace(field.value) != field.value {
			return fmt.Errorf("exact backend container %s is required", field.name)
		}
	}
	return nil
}

// scanBackendContainerDeployment 从单行结果反序列化一条 backend 容器部署记录。
//
// 参数 row 提供扫描能力，返回反序列化后的 BackendContainerDeployment。将持久化的
// updated_at 文本解析为 time.Time。未命中返回 ErrNotFound，其他解析失败返回包装后
// 的错误。
func scanBackendContainerDeployment(row rowScanner) (BackendContainerDeployment, error) {
	var deployment BackendContainerDeployment
	var updatedAt string
	if err := row.Scan(
		&deployment.ActivePort,
		&deployment.ContainerName,
		&deployment.ImageDigest,
		&deployment.ContainerID,
		&deployment.TransactionID,
		&updatedAt,
	); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return BackendContainerDeployment{}, ErrNotFound
		}
		return BackendContainerDeployment{}, fmt.Errorf("scan backend container deployment: %w", err)
	}
	parsed, err := parseTime(updatedAt)
	if err != nil {
		return BackendContainerDeployment{}, fmt.Errorf("parse backend container deployment update time: %w", err)
	}
	deployment.UpdatedAt = parsed
	return deployment, nil
}