YACSWA/frontend/www/elm-local-storage-ports.js

const ElmLocalStoragePorts = function () {}
const localStorage = window.localStorage

ElmLocalStoragePorts.prototype.subscribe =
    function (app, getPortName, setPortName, clearPortName, responsePortName, listKeysPortName) {
      if (!getPortName) getPortName = 'getItem'
      if (!setPortName) setPortName = 'setItem'
      if (!clearPortName) clearPortName = 'clear'
      if (!listKeysPortName) listKeysPortName = 'listKeys'
      if (!responsePortName) responsePortName = 'response'

      if (app.ports[responsePortName]) {
        const responsePort = app.ports[responsePortName]

        if (app.ports[getPortName]) {
          app.ports[getPortName].subscribe(function (key) {
            let val = null
            try {
              val = JSON.parse(localStorage.getItem(key))
            } catch (e) {}
            responsePort.send({
              key,
              value: val
            })
          })
        } else {
          console.warn(getPortName + ': This port is not connected.')
        }

        if (app.ports[setPortName]) {
          app.ports[setPortName].subscribe(function (kv) {
            const key = kv[0]
            const json = kv[1]
            if (json === null) {
              localStorage.removeItem(key)
            } else {
              localStorage.setItem(key, JSON.stringify(json))
            }
          })
        } else {
          console.warn(setPortName + ': This port is not connected.')
        }

        if (app.ports[clearPortName]) {
          app.ports[clearPortName].subscribe(function (prefix) {
            if (prefix) {
              const cnt = localStorage.length
              for (let i = cnt - 1; i >= 0; --i) {
                const key = localStorage.key(i)
                if (key && key.startsWith(prefix)) {
                  localStorage.removeItem(key)
                }
              }
            } else {
              localStorage.clear()
            }
          })
        } else {
          console.warn(clearPortName + ': This port is not connected.')
        }

        if (app.ports[listKeysPortName]) {
          app.ports[listKeysPortName].subscribe(function (prefix) {
            const cnt = localStorage.length
            const keys = []
            for (let i = 0; i < cnt; i++) {
              const key = localStorage.key(i)
              if (key && key.startsWith(prefix)) {
                keys.push(key)
              }
            }
            responsePort.send(keys)
          })
        } else {
          console.warn(listKeysPortName + ': This port is not connected.')
        }
      } else {
        console.warn(responsePortName + ': This port is not connected.')
      }
    }