package repository

import (
	"context"
	"crypto/sha256"
	"database/sql"
	"encoding/binary"
	"fmt"
	"path/filepath"
	"sort"
	"strings"
	"time"
)

// SQLiteMigrationSummary 只包含表名和数量，可以安全写入终端或工单。
type SQLiteMigrationSummary struct {
	DryRun bool
	Tables []SQLiteMigrationTable
}

type SQLiteMigrationTable struct {
	Name  string
	Count int64
}

// SQLiteMigrationError 隐藏可能带业务主键的数据库原始错误。
// Cause 只供 errors.Is/As 和测试使用，不应直接输出。
type SQLiteMigrationError struct {
	Stage string
	Table string
	Cause error
}

func (e *SQLiteMigrationError) Error() string {
	if e.Table == "" {
		return "SQLite 到 MySQL 迁移失败：" + e.Stage
	}
	return fmt.Sprintf("SQLite 到 MySQL 迁移失败：%s（表 %s）", e.Stage, e.Table)
}

func (e *SQLiteMigrationError) Unwrap() error { return e.Cause }

type sqliteMigrationTableSpec struct {
	name       string
	columns    []string
	primaryKey []string
}

// 顺序同时满足 MySQL 外键依赖；列清单故意不含 MySQL 生成列 current_client_id。
var sqliteMigrationTables = []sqliteMigrationTableSpec{
	{name: "users", columns: []string{"user_id", "username", "password_hash", "role", "status", "last_login_at", "password_changed_at", "created_at", "updated_at"}, primaryKey: []string{"user_id"}},
	{name: "clients", columns: []string{"client_id", "name", "device_address", "platform", "pdd_package", "capabilities", "last_seen_at", "created_at", "updated_at"}, primaryKey: []string{"client_id"}},
	{name: "shopee_products", columns: []string{"goods_id", "title", "shopee_status", "main_sku_code", "pdd_goods_url", "pdd_goods_id", "created_at", "updated_at"}, primaryKey: []string{"goods_id"}},
	{name: "pdd_products", columns: []string{"id", "goods_id", "url", "title", "shop_name", "skus_json", "collect_status", "collect_msg", "artifact_ref", "collected_at", "deleted_at", "created_at", "updated_at"}, primaryKey: []string{"id"}},
	{name: "shopee_skus", columns: []string{"sku_id", "goods_id", "spec_raw", "color", "size", "advice", "parse_ok", "sku_code", "is_manual", "created_at", "updated_at"}, primaryKey: []string{"sku_id"}},
	{name: "syb_orders", columns: []string{"syb_id", "order_no", "title", "shopee_goods_id", "shopee_sku_id", "product_spec", "quantity", "price_twd_cent", "image_url", "syb_data", "created_at", "updated_at"}, primaryKey: []string{"syb_id"}},
	{name: "sku_mappings", columns: []string{"shopee_sku_id", "pdd_goods_id", "pdd_option_key", "pdd_options", "goods_id", "mapped_at", "mapped_by"}, primaryKey: []string{"shopee_sku_id", "pdd_goods_id"}},
	{name: "tasks", columns: []string{"task_id", "task_type", "status", "version", "priority", "assigned_client", "claimed_at", "syb_id", "order_no", "goods_id", "shopee_sku_id", "pdd_goods_url", "pdd_goods_id", "pdd_options", "quantity", "max_price_cent", "result_data", "error_code", "error_message", "finished_at", "created_at", "updated_at"}, primaryKey: []string{"task_id"}},
	{name: "task_claims", columns: []string{"task_id", "client_id", "claimed_at"}, primaryKey: []string{"task_id", "client_id"}},
	{name: "idempotency_keys", columns: []string{"key", "request_hash", "response_body", "created_at"}, primaryKey: []string{"key"}},
	{name: "syb_session", columns: []string{"username", "cookies", "expires_at", "updated_at"}, primaryKey: []string{"username"}},
	{name: "syb_sync_state", columns: []string{"id", "last_synced_at", "updated_at"}, primaryKey: []string{"id"}},
	{name: "web_sessions", columns: []string{"session_hash", "user_id", "expires_at", "created_at", "last_seen_at"}, primaryKey: []string{"session_hash"}},
	{name: "client_user_assignments", columns: []string{"assignment_id", "client_id", "user_id", "started_at", "ended_at", "assigned_by_user_id", "ended_by_user_id", "end_reason"}, primaryKey: []string{"assignment_id"}},
	{name: "syb_sync_runs", columns: []string{"run_id", "user_id", "date_from", "date_to", "status", "stock_count", "detail_count", "created_count", "updated_count", "skipped_count", "error_message", "cursor_advanced", "started_at", "finished_at"}, primaryKey: []string{"run_id"}},
}

// OpenLegacySQLiteReadOnly 以操作系统只读模式打开历史 admin.db。
func OpenLegacySQLiteReadOnly(path string) (*sql.DB, error) {
	absPath, err := filepath.Abs(path)
	if err != nil {
		return nil, &SQLiteMigrationError{Stage: "无法解析 SQLite 路径", Cause: err}
	}
	dsn := "file:" + filepath.ToSlash(absPath) + "?mode=ro&_pragma=query_only(1)&_pragma=foreign_keys(1)"
	db, err := sql.Open("sqlite", dsn)
	if err != nil {
		return nil, &SQLiteMigrationError{Stage: "无法准备只读 SQLite", Cause: err}
	}
	db.SetMaxOpenConns(1)
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	if err := db.PingContext(ctx); err != nil {
		db.Close()
		return nil, &SQLiteMigrationError{Stage: "无法打开只读 SQLite", Cause: err}
	}
	var queryOnly int
	if err := db.QueryRow(`PRAGMA query_only`).Scan(&queryOnly); err != nil || queryOnly != 1 {
		db.Close()
		return nil, &SQLiteMigrationError{Stage: "SQLite 未进入只读模式", Cause: err}
	}
	return db, nil
}

// MigrateSQLiteToMySQL 只允许把 SQLite v8 导入空的 MySQL 目标库。
func MigrateSQLiteToMySQL(source, target *sql.DB, dryRun bool) (*SQLiteMigrationSummary, error) {
	if err := validateLegacySQLite(source); err != nil {
		return nil, err
	}
	if err := validateEmptyMySQLTarget(target); err != nil {
		return nil, err
	}
	summary, err := migrationSummary(source, dryRun)
	if err != nil {
		return nil, err
	}
	if dryRun {
		return summary, nil
	}

	tx, err := target.BeginTx(context.Background(), &sql.TxOptions{Isolation: sql.LevelReadCommitted})
	if err != nil {
		return nil, &SQLiteMigrationError{Stage: "无法开始 MySQL 导入事务", Cause: err}
	}
	defer tx.Rollback()
	for _, spec := range sqliteMigrationTables {
		if err := copySQLiteTable(source, tx, spec); err != nil {
			return nil, err
		}
	}
	if err := tx.Commit(); err != nil {
		return nil, &SQLiteMigrationError{Stage: "无法提交 MySQL 导入事务", Cause: err}
	}
	if _, err := VerifySQLiteToMySQL(source, target); err != nil {
		return nil, err
	}
	return summary, nil
}

// VerifySQLiteToMySQL 比较逐表数量和全部迁移列的确定性摘要，不输出业务内容。
func VerifySQLiteToMySQL(source, target *sql.DB) (*SQLiteMigrationSummary, error) {
	if err := validateLegacySQLite(source); err != nil {
		return nil, err
	}
	if err := CheckMySQLSchema(target); err != nil {
		return nil, &SQLiteMigrationError{Stage: "MySQL schema 不完整", Cause: err}
	}
	summary, err := migrationSummary(source, false)
	if err != nil {
		return nil, err
	}
	for _, spec := range sqliteMigrationTables {
		sourceCount, sourceDigest, err := tableDigest(source, spec, false)
		if err != nil {
			return nil, &SQLiteMigrationError{Stage: "无法核对 SQLite 数据", Table: spec.name, Cause: err}
		}
		targetCount, targetDigest, err := tableDigest(target, spec, true)
		if err != nil {
			return nil, &SQLiteMigrationError{Stage: "无法核对 MySQL 数据", Table: spec.name, Cause: err}
		}
		if sourceCount != targetCount || sourceDigest != targetDigest {
			return nil, &SQLiteMigrationError{Stage: "数量或内容摘要不一致", Table: spec.name}
		}
	}
	if err := verifyMySQLRelations(target); err != nil {
		return nil, err
	}
	return summary, nil
}

func validateLegacySQLite(db *sql.DB) error {
	var version int
	if err := db.QueryRow(`PRAGMA user_version`).Scan(&version); err != nil || version != schemaVersion {
		return &SQLiteMigrationError{Stage: "SQLite schema 必须是 v8", Cause: err}
	}
	var quickCheck string
	if err := db.QueryRow(`PRAGMA quick_check`).Scan(&quickCheck); err != nil || quickCheck != "ok" {
		return &SQLiteMigrationError{Stage: "SQLite 一致性检查失败", Cause: err}
	}
	rows, err := db.Query(`PRAGMA foreign_key_check`)
	if err != nil {
		return &SQLiteMigrationError{Stage: "SQLite 外键检查失败", Cause: err}
	}
	defer rows.Close()
	if rows.Next() {
		return &SQLiteMigrationError{Stage: "SQLite 存在外键异常"}
	}
	if err := rows.Err(); err != nil {
		return &SQLiteMigrationError{Stage: "SQLite 外键检查失败", Cause: err}
	}
	if err := CheckSchema(db); err != nil {
		return &SQLiteMigrationError{Stage: "SQLite schema 不完整", Cause: err}
	}
	return nil
}

func validateEmptyMySQLTarget(db *sql.DB) error {
	if err := CheckMySQLSchema(db); err != nil {
		return &SQLiteMigrationError{Stage: "MySQL schema 不完整", Cause: err}
	}
	for _, spec := range sqliteMigrationTables {
		var count int64
		if err := db.QueryRow("SELECT COUNT(*) FROM " + quoteMySQLIdentifier(spec.name)).Scan(&count); err != nil {
			return &SQLiteMigrationError{Stage: "无法检查 MySQL 目标", Table: spec.name, Cause: err}
		}
		if count != 0 {
			return &SQLiteMigrationError{Stage: "MySQL 目标不是空库", Table: spec.name}
		}
	}
	return nil
}

func migrationSummary(db *sql.DB, dryRun bool) (*SQLiteMigrationSummary, error) {
	summary := &SQLiteMigrationSummary{DryRun: dryRun, Tables: make([]SQLiteMigrationTable, 0, len(sqliteMigrationTables))}
	for _, spec := range sqliteMigrationTables {
		var count int64
		if err := db.QueryRow("SELECT COUNT(*) FROM " + quoteSQLiteIdentifier(spec.name)).Scan(&count); err != nil {
			return nil, &SQLiteMigrationError{Stage: "无法统计 SQLite 数据", Table: spec.name, Cause: err}
		}
		summary.Tables = append(summary.Tables, SQLiteMigrationTable{Name: spec.name, Count: count})
	}
	return summary, nil
}

func copySQLiteTable(source *sql.DB, target *sql.Tx, spec sqliteMigrationTableSpec) error {
	selectSQL := "SELECT " + joinQuoted(spec.columns, quoteSQLiteIdentifier) + " FROM " + quoteSQLiteIdentifier(spec.name) +
		" ORDER BY " + joinQuoted(spec.primaryKey, quoteSQLiteIdentifier)
	rows, err := source.Query(selectSQL)
	if err != nil {
		return &SQLiteMigrationError{Stage: "无法读取 SQLite", Table: spec.name, Cause: err}
	}
	defer rows.Close()
	placeholders := strings.TrimSuffix(strings.Repeat("?,", len(spec.columns)), ",")
	insertSQL := "INSERT INTO " + quoteMySQLIdentifier(spec.name) + " (" +
		joinQuoted(spec.columns, quoteMySQLIdentifier) + ") VALUES (" + placeholders + ")"
	stmt, err := target.Prepare(insertSQL)
	if err != nil {
		return &SQLiteMigrationError{Stage: "无法准备 MySQL 导入", Table: spec.name, Cause: err}
	}
	defer stmt.Close()
	for rows.Next() {
		values, pointers := scanBuffers(len(spec.columns))
		if err := rows.Scan(pointers...); err != nil {
			return &SQLiteMigrationError{Stage: "无法读取 SQLite 行", Table: spec.name, Cause: err}
		}
		if _, err := stmt.Exec(values...); err != nil {
			return &SQLiteMigrationError{Stage: "无法写入 MySQL", Table: spec.name, Cause: err}
		}
	}
	if err := rows.Err(); err != nil {
		return &SQLiteMigrationError{Stage: "无法遍历 SQLite", Table: spec.name, Cause: err}
	}
	return nil
}

func tableDigest(db *sql.DB, spec sqliteMigrationTableSpec, mysql bool) (int64, [32]byte, error) {
	quote := quoteSQLiteIdentifier
	if mysql {
		quote = quoteMySQLIdentifier
	}
	query := "SELECT " + joinQuoted(spec.columns, quote) + " FROM " + quote(spec.name) +
		" ORDER BY " + joinQuoted(spec.primaryKey, quote)
	rows, err := db.Query(query)
	if err != nil {
		return 0, [32]byte{}, err
	}
	defer rows.Close()
	hash := sha256.New()
	var count int64
	for rows.Next() {
		values, pointers := scanBuffers(len(spec.columns))
		if err := rows.Scan(pointers...); err != nil {
			return 0, [32]byte{}, err
		}
		for _, value := range values {
			writeDigestValue(hash, value)
		}
		count++
	}
	if err := rows.Err(); err != nil {
		return 0, [32]byte{}, err
	}
	var digest [32]byte
	copy(digest[:], hash.Sum(nil))
	return count, digest, nil
}

func verifyMySQLRelations(db *sql.DB) error {
	checks := []struct {
		name  string
		query string
	}{
		{"SKU 商品关系", `SELECT COUNT(*) FROM shopee_skus s LEFT JOIN shopee_products p ON p.goods_id=s.goods_id WHERE p.goods_id IS NULL`},
		{"规格映射关系", `SELECT COUNT(*) FROM sku_mappings m LEFT JOIN shopee_skus s ON s.sku_id=m.shopee_sku_id WHERE s.sku_id IS NULL`},
		{"网页登录会话关系", `SELECT COUNT(*) FROM web_sessions s LEFT JOIN users u ON u.user_id=s.user_id WHERE u.user_id IS NULL`},
		{"客户端归属用户关系", `SELECT COUNT(*) FROM client_user_assignments a LEFT JOIN users u ON u.user_id=a.user_id WHERE u.user_id IS NULL`},
		{"同步记录用户关系", `SELECT COUNT(*) FROM syb_sync_runs r LEFT JOIN users u ON u.user_id=r.user_id WHERE u.user_id IS NULL`},
		{"当前客户端归属唯一", `SELECT COUNT(*) FROM (SELECT client_id FROM client_user_assignments WHERE ended_at IS NULL GROUP BY client_id HAVING COUNT(*) > 1) duplicate_assignments`},
	}
	for _, check := range checks {
		var count int64
		if err := db.QueryRow(check.query).Scan(&count); err != nil {
			return &SQLiteMigrationError{Stage: "无法核对" + check.name, Cause: err}
		}
		if count != 0 {
			return &SQLiteMigrationError{Stage: check.name + "不一致"}
		}
	}
	return nil
}

func scanBuffers(count int) ([]any, []any) {
	values := make([]any, count)
	pointers := make([]any, count)
	for i := range values {
		pointers[i] = &values[i]
	}
	return values, pointers
}

func writeDigestValue(hash interface{ Write([]byte) (int, error) }, value any) {
	if value == nil {
		hash.Write([]byte{0})
		return
	}
	var bytes []byte
	switch typed := value.(type) {
	case []byte:
		bytes = typed
	case string:
		bytes = []byte(typed)
	case time.Time:
		bytes = []byte(typed.UTC().Format(time.RFC3339Nano))
	default:
		bytes = []byte(fmt.Sprint(typed))
	}
	hash.Write([]byte{1})
	var length [8]byte
	binary.BigEndian.PutUint64(length[:], uint64(len(bytes)))
	hash.Write(length[:])
	hash.Write(bytes)
}

func joinQuoted(names []string, quote func(string) string) string {
	quoted := make([]string, len(names))
	for i, name := range names {
		quoted[i] = quote(name)
	}
	return strings.Join(quoted, ",")
}

func quoteSQLiteIdentifier(name string) string {
	return `"` + strings.ReplaceAll(name, `"`, `""`) + `"`
}

func quoteMySQLIdentifier(name string) string {
	return "`" + strings.ReplaceAll(name, "`", "``") + "`"
}

// SortedMigrationSummary 供命令稳定输出，避免依赖内部外键导入顺序。
func SortedMigrationSummary(summary *SQLiteMigrationSummary) []SQLiteMigrationTable {
	tables := append([]SQLiteMigrationTable(nil), summary.Tables...)
	sort.Slice(tables, func(i, j int) bool { return tables[i].Name < tables[j].Name })
	return tables
}