package cache

import (
	"context"
	"crypto/rand"
	"encoding/json"
	"errors"
	"fmt"
	"math/big"
	"time"

	"github.com/redis/go-redis/v9"
)

const (
	shareCodeKeyPrefix  = "share:"
	sharePendingSet        = "share:pending"
	shareImportPendingHash = "share:import:pending"
	shareFlushLockPref     = "share:flush:lock:"
	shareImportFlushLockPref = "share:import:flush:lock:"
	shareCodeLength     = 5
	shareCodeTTL        = 30 * time.Minute
	shareCodeCharset    = "23456789ABCDEFGHJKLMNPQRSTUVWXYZ"
	shareCodeMaxRetries = 20

	fieldMacAddr   = "mac_addr"
	fieldIPAddr    = "ip_addr"
	fieldEqData    = "eq_data"
	fieldExpireAt  = "expire_at"
	fieldPersisted = "persisted"
)

var shareCreateScript = redis.NewScript(`
if redis.call('EXISTS', KEYS[1]) == 1 then
  return 0
end
redis.call('HSET', KEYS[1],
  'mac_addr', ARGV[1],
  'ip_addr', ARGV[2],
  'eq_data', ARGV[3],
  'expire_at', ARGV[4],
  'persisted', '0'
)
redis.call('EXPIRE', KEYS[1], tonumber(ARGV[5]))
redis.call('SADD', KEYS[2], ARGV[6])
return 1
`)

type ShareImportPendingLog struct {
	MacAddr   string `json:"mac_addr"`
	ShareCode string `json:"share_code"`
	IpAddr    string `json:"ip_addr"`
	EqData    string `json:"eq_data"`
	ExpireAt  string `json:"expire_at"`
}

type ShareCodeData struct {
	ShareCode string
	MacAddr   string
	IpAddr    string
	EqData    string
	ExpireAt  time.Time
	Persisted bool
}

type ShareCodeCache struct {
	rdb *redis.Client
}

func NewShareCodeCache(rdb *redis.Client) *ShareCodeCache {
	return &ShareCodeCache{rdb: rdb}
}

func ShareCodeTTL() time.Duration {
	return shareCodeTTL
}

func (c *ShareCodeCache) Create(ctx context.Context, macAddr, ipAddr string, eqData []byte) (*ShareCodeData, error) {
	expireAt := time.Now().Add(shareCodeTTL)
	eqJSON := string(eqData)

	for i := 0; i < shareCodeMaxRetries; i++ {
		code, err := randomShareCode()
		if err != nil {
			return nil, err
		}

		key := shareCodeKey(code)
		ok, err := shareCreateScript.Run(ctx, c.rdb, []string{key, sharePendingSet},
			macAddr, ipAddr, eqJSON, expireAt.Format(time.RFC3339), int(shareCodeTTL.Seconds()), code,
		).Int()
		if err != nil {
			return nil, fmt.Errorf("create share code in redis: %w", err)
		}
		if ok == 1 {
			return &ShareCodeData{
				ShareCode: code,
				MacAddr:   macAddr,
				IpAddr:    ipAddr,
				EqData:    eqJSON,
				ExpireAt:  expireAt,
				Persisted: false,
			}, nil
		}
	}

	return nil, errors.New("failed to allocate unique share code")
}

func (c *ShareCodeCache) Get(ctx context.Context, shareCode string) (*ShareCodeData, error) {
	key := shareCodeKey(shareCode)
	values, err := c.rdb.HGetAll(ctx, key).Result()
	if err != nil {
		return nil, fmt.Errorf("hgetall share code: %w", err)
	}
	if len(values) == 0 {
		return nil, nil
	}

	expireAt, err := time.Parse(time.RFC3339, values[fieldExpireAt])
	if err != nil {
		return nil, fmt.Errorf("parse share code expire_at: %w", err)
	}

	return &ShareCodeData{
		ShareCode: shareCode,
		MacAddr:   values[fieldMacAddr],
		IpAddr:    values[fieldIPAddr],
		EqData:    values[fieldEqData],
		ExpireAt:  expireAt,
		Persisted: values[fieldPersisted] == "1",
	}, nil
}

func (c *ShareCodeCache) ListPending(ctx context.Context) ([]string, error) {
	codes, err := c.rdb.SMembers(ctx, sharePendingSet).Result()
	if err != nil {
		return nil, fmt.Errorf("smembers share pending: %w", err)
	}
	return codes, nil
}

func (c *ShareCodeCache) AcquireFlushLock(ctx context.Context, shareCode string) (bool, error) {
	lockKey := shareFlushLockPref + shareCode
	return c.rdb.SetNX(ctx, lockKey, "1", 30*time.Second).Result()
}

func (c *ShareCodeCache) ReleaseFlushLock(ctx context.Context, shareCode string) error {
	return c.rdb.Del(ctx, shareFlushLockPref+shareCode).Err()
}

func (c *ShareCodeCache) MarkPersisted(ctx context.Context, shareCode string) error {
	key := shareCodeKey(shareCode)
	if err := c.rdb.HSet(ctx, key, fieldPersisted, "1").Err(); err != nil {
		return fmt.Errorf("mark share code persisted: %w", err)
	}
	return c.rdb.SRem(ctx, sharePendingSet, shareCode).Err()
}

func (c *ShareCodeCache) EnqueueImportLog(ctx context.Context, macAddr, shareCode, ipAddr, eqData string, expireAt time.Time) error {
	field := fmt.Sprintf("%s:%s:%d", macAddr, shareCode, time.Now().UnixNano())
	payload, err := json.Marshal(ShareImportPendingLog{
		MacAddr:   macAddr,
		ShareCode: shareCode,
		IpAddr:    ipAddr,
		EqData:    eqData,
		ExpireAt:  expireAt.Format(time.RFC3339),
	})
	if err != nil {
		return fmt.Errorf("marshal import pending log: %w", err)
	}
	if err := c.rdb.HSet(ctx, shareImportPendingHash, field, payload).Err(); err != nil {
		return fmt.Errorf("enqueue import log: %w", err)
	}
	return nil
}

func (c *ShareCodeCache) ListPendingImports(ctx context.Context) (map[string]string, error) {
	logs, err := c.rdb.HGetAll(ctx, shareImportPendingHash).Result()
	if err != nil {
		return nil, fmt.Errorf("hgetall import pending: %w", err)
	}
	return logs, nil
}

func (c *ShareCodeCache) RemovePendingImport(ctx context.Context, field string) error {
	return c.rdb.HDel(ctx, shareImportPendingHash, field).Err()
}

func (c *ShareCodeCache) AcquireImportFlushLock(ctx context.Context, field string) (bool, error) {
	return c.rdb.SetNX(ctx, shareImportFlushLockPref+field, "1", 30*time.Second).Result()
}

func (c *ShareCodeCache) ReleaseImportFlushLock(ctx context.Context, field string) error {
	return c.rdb.Del(ctx, shareImportFlushLockPref+field).Err()
}

func shareCodeKey(code string) string {
	return shareCodeKeyPrefix + code
}

func randomShareCode() (string, error) {
	b := make([]byte, shareCodeLength)
	max := big.NewInt(int64(len(shareCodeCharset)))
	for i := range b {
		n, err := rand.Int(rand.Reader, max)
		if err != nil {
			return "", err
		}
		b[i] = shareCodeCharset[n.Int64()]
	}
	return string(b), nil
}