package store

import (
	"database/sql"
	"fmt"
	"io/fs"
	"log/slog"
	"sort"

	"git.yeij.top/AskaEth/Scoreboard/server/migrations"
)

const createMigrationsTable = `CREATE TABLE IF NOT EXISTS schema_migrations (
	name       TEXT PRIMARY KEY,
	applied_at TEXT NOT NULL DEFAULT (datetime('now'))
)`

// Migrate 按文件名顺序迁移系统库（data/system.db）。
func (s *Store) Migrate() error {
	fsys, err := fs.Sub(migrations.SystemFS, "system")
	if err != nil {
		return fmt.Errorf("定位系统库迁移目录: %w", err)
	}
	return migrate(s.db, fsys, "system")
}

// MigrateEvent 迁移赛事库（event.db）。赛事库由调用方自行打开，
// 本函数只负责执行 event/ 下的迁移，不持有连接。
func MigrateEvent(db *sql.DB) error {
	fsys, err := fs.Sub(migrations.EventFS, "event")
	if err != nil {
		return fmt.Errorf("定位赛事库迁移目录: %w", err)
	}
	return migrate(db, fsys, "event")
}

// migrate 执行 fsys 中尚未应用的迁移，每个迁移在独立事务中完成。
func migrate(db *sql.DB, fsys fs.FS, label string) error {
	if _, err := db.Exec(createMigrationsTable); err != nil {
		return fmt.Errorf("创建 schema_migrations: %w", err)
	}

	applied, err := appliedMigrations(db)
	if err != nil {
		return err
	}

	names, err := fs.Glob(fsys, "*.sql")
	if err != nil {
		return err
	}
	sort.Strings(names)

	for _, name := range names {
		if applied[name] {
			continue
		}
		body, err := fs.ReadFile(fsys, name)
		if err != nil {
			return fmt.Errorf("读取迁移 %s: %w", name, err)
		}
		if err := applyMigration(db, name, string(body)); err != nil {
			return err
		}
		slog.Info("已应用迁移", "db", label, "name", name)
	}
	return nil
}

func appliedMigrations(db *sql.DB) (map[string]bool, error) {
	rows, err := db.Query(`SELECT name FROM schema_migrations`)
	if err != nil {
		return nil, fmt.Errorf("查询迁移记录: %w", err)
	}
	defer func() { _ = rows.Close() }()

	applied := make(map[string]bool)
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return nil, err
		}
		applied[name] = true
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}
	return applied, nil
}

func applyMigration(db *sql.DB, name, body string) error {
	tx, err := db.Begin()
	if err != nil {
		return fmt.Errorf("开启事务: %w", err)
	}
	defer func() { _ = tx.Rollback() }()

	if _, err := tx.Exec(body); err != nil {
		return fmt.Errorf("执行迁移 %s: %w", name, err)
	}
	if _, err := tx.Exec(`INSERT INTO schema_migrations(name) VALUES (?)`, name); err != nil {
		return fmt.Errorf("记录迁移 %s: %w", name, err)
	}
	return tx.Commit()
}