cache.js

class Cache {
    constructor(size) {
        this._cached = {}
        this.size = size // disabled
        this.enabled = size > 0
        this.hits = 0
        this.misses = 0
        this.recentKeys = []
    }

    _generateKey(params) {
        return params.map(obj => JSON.stringify(obj)).join('_')
    }

    flush() {
        this._cached = {}
    }

    _updateRecentKey(keyName) {
        const index = this.recentKeys.indexOf(keyName)
        if (index !== -1) {
            this.recentKeys.splice(index, 1)
        }
        this.recentKeys.splice(0, 0, keyName)
    }

    _updateCache() {
        if (this.recentKeys.length < this.size) {
            return false
        }
        const recentKey = this.recentKeys.pop()
        delete this._cached[recentKey]
        return true
    }

    get(params, promise) {
        if (!this.enabled) {
            return promise()
        }
        const cacheKey = this._generateKey(params)
        this._updateRecentKey(cacheKey)
        if (this._cached[cacheKey] !== undefined) {
            this.hits++
            return Promise.resolve(this._cached[cacheKey])
        }
        return promise().then((value) => {
            this.misses++
            this._cached[cacheKey] = value
            this._updateCache()
            return value
        })
    }
}

module.exports = Cache