package batchimport

import (
	"context"
	"crypto/rand"
	"fmt"
	"strings"
	"time"

	"github.com/gogf/gf/v2/errors/gerror"
	"github.com/gogf/gf/v2/frame/g"
)

const (
	batchNoPrefixLength        = 3
	batchNoSequenceLength      = 3
	batchNoSequenceMax         = 999
	batchNoSequenceTTL         = 48 * time.Hour
	batchNoSequenceRedisPrefix = "iotlcm:batch:no:seq:"
	randomNoSuffixLength       = 8
	randomNoAlphabet           = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789"
)

func NextBatchNo(prefix string) (string, error) {
	return NextBatchNoContext(context.Background(), prefix)
}

func NextBatchNoContext(ctx context.Context, prefix string) (string, error) {
	prefix, err := normalizeBatchNoPrefix(prefix)
	if err != nil {
		return "", err
	}
	if ctx == nil {
		ctx = context.Background()
	}
	now := time.Now()
	seq, err := nextDailyBatchSequence(ctx, now)
	if err != nil {
		return "", err
	}
	return formatBatchNo(prefix, now, seq)
}

func NextRandomNo(prefix string) (string, error) {
	prefix = strings.TrimSpace(strings.ToUpper(prefix))
	if prefix == "" {
		return "", gerror.New("编号前缀不能为空")
	}

	random, err := randomNoSuffix(randomNoSuffixLength)
	if err != nil {
		return "", err
	}
	return fmt.Sprintf("%s%s%s", prefix, time.Now().Format("20060102150405"), random), nil
}

func normalizeBatchNoPrefix(prefix string) (string, error) {
	prefix = strings.TrimSpace(strings.ToUpper(prefix))
	if prefix == "" {
		return "", gerror.New("批次号前缀不能为空")
	}
	if len(prefix) != batchNoPrefixLength {
		return "", gerror.Newf("批次号前缀必须为%d位", batchNoPrefixLength)
	}
	return prefix, nil
}

func nextDailyBatchSequence(ctx context.Context, now time.Time) (int64, error) {
	key := batchNoSequenceKey(now)
	script := `
local v = redis.call("INCR", KEYS[1])
if v == 1 then
  redis.call("EXPIRE", KEYS[1], ARGV[1])
end
return v`
	res, err := g.Redis().Do(ctx, "EVAL", script, 1, key, int(batchNoSequenceTTL.Seconds()))
	if err != nil {
		return 0, gerror.Wrap(err, "生成批次号序号失败")
	}
	seq := res.Int64()
	if seq <= 0 {
		return 0, gerror.New("生成批次号序号失败")
	}
	if seq > batchNoSequenceMax {
		return 0, gerror.Newf("当日批次号序号超过%03d", batchNoSequenceMax)
	}
	return seq, nil
}

func batchNoSequenceKey(now time.Time) string {
	return batchNoSequenceRedisPrefix + now.Format("20060102")
}

func formatBatchNo(prefix string, now time.Time, seq int64) (string, error) {
	if seq <= 0 || seq > batchNoSequenceMax {
		return "", gerror.Newf("批次号序号必须在1-%03d之间", batchNoSequenceMax)
	}
	return fmt.Sprintf("%s%s%0*d", prefix, now.Format("20060102150405"), batchNoSequenceLength, seq), nil
}

func randomNoSuffix(length int) (string, error) {
	if length <= 0 {
		return "", gerror.New("随机码长度必须大于0")
	}

	buf := make([]byte, length)
	randomBytes := make([]byte, length)
	if _, err := rand.Read(randomBytes); err != nil {
		return "", gerror.Wrap(err, "生成随机码失败")
	}

	alphabetLen := byte(len(randomNoAlphabet))
	for i, b := range randomBytes {
		buf[i] = randomNoAlphabet[b%alphabetLen]
	}
	return string(buf), nil
}