1import * as _ from 'lodash-es'
2import { PtErr } from '../../sharedF/throwErrorF/sharedErrF.mts'
3
4type CacheEntry<T> = { expAtMs: number, cacheVal: T }
5
6const memCacheH: Record<string, CacheEntry<unknown>> = {}
7const keysSortedByExp: string[] = []
8
9type CacheFetchOpts<T> = {
10  cacheKey: string
11  ttlMs: number
12  cacheMissFn: () => Promise<T>
13}
14
15export const cacheFetch = async <T,>({cacheKey, ttlMs, cacheMissFn}: CacheFetchOpts<T>): Promise<T> => {
16  let now = _.now()
17
18  const nowIdx = _.sortedIndexBy(keysSortedByExp, 'nowidx', (ckey) => {
19    if (ckey == 'nowidx') return now
20    if (!memCacheH[ckey]) {
21      throw new PtErr('!memCacheH[ckey]', {ckey, cacheKey, memCacheH, keysSortedByExp})
22    }
23    return memCacheH[ckey].expAtMs
24  })
25
26  const delCount = nowIdx
27  const expiredKeys = keysSortedByExp.splice(0, delCount)
28  // console.log({delCount, expiredKeys}, _.map(keysSortedByExp, (ckey) => memCacheH[ckey].expAtMs))
29  if (expiredKeys.length > 0) {
30    console.log(delCount, 'expired: ', expiredKeys.join(' '))
31    _.each(expiredKeys, (ckey) => {
32      delete memCacheH[ckey]
33    })  
34  }
35
36  const existingEntry = memCacheH[cacheKey]
37  if (existingEntry) {
38    return existingEntry.cacheVal as T
39  }
40
41  const cacheVal = await cacheMissFn()
42
43  const newEntry = {
44    expAtMs: now + ttlMs,
45    cacheVal
46  }
47  memCacheH[cacheKey] = newEntry
48
49  const sortedIdx = _.sortedIndexBy(keysSortedByExp, cacheKey, (ckey) => {
50    if (!memCacheH[ckey]) {
51      console.log('!memCacheH[ckey]', {ckey, cacheKey, memCacheH, keysSortedByExp})
52    }
53    return memCacheH[ckey].expAtMs
54  })
55  keysSortedByExp.splice(sortedIdx, 0, cacheKey)
56
57  return cacheVal
58}