package imtenant

import (
	"context"
	"fmt"
	"os"
	"strconv"
	"sync"

	"github.com/gogf/gf/v2/frame/g"
	sf "github.com/tinode/snowflake"
)

const defaultSnowflakeWorkerID = 1023

var (
	snowflakeOnce sync.Once
	snowflakeGen  *sf.SnowFlake
	snowflakeErr  error
)

// NextSnowflakeID returns an unencrypted Snowflake ID suitable for IM BIGINT keys.
func NextSnowflakeID(ctx context.Context) (int64, error) {
	snowflakeOnce.Do(func() {
		workerID := g.Cfg().MustGet(ctx, "imDirectDb.snowflakeWorkerId", defaultSnowflakeWorkerID).Int()
		if value := os.Getenv("IM_DIRECT_DB_SNOWFLAKE_WORKER_ID"); value != "" {
			workerID, snowflakeErr = strconv.Atoi(value)
			if snowflakeErr != nil {
				snowflakeErr = fmt.Errorf("invalid IM_DIRECT_DB_SNOWFLAKE_WORKER_ID: %w", snowflakeErr)
				return
			}
		}
		if workerID < 0 || workerID > 1023 {
			snowflakeErr = fmt.Errorf("IM Snowflake worker ID must be between 0 and 1023")
			return
		}
		snowflakeGen, snowflakeErr = sf.NewSnowFlake(uint32(workerID))
	})
	if snowflakeErr != nil {
		return 0, snowflakeErr
	}
	id, err := snowflakeGen.Next()
	if err != nil {
		return 0, err
	}
	if id == 0 || id > uint64(^uint64(0)>>1) {
		return 0, fmt.Errorf("generated invalid IM Snowflake ID")
	}
	return int64(id), nil
}