Eating my way through Web APIs

const recipe = writable({
  id: 'JdjtOympO6yuhGytoNBHv',
  image: '/images/JdjtOympO6yuhGytoNBHv',
  title: 'Pancakes',
  description: 'With bananas and honey',
  prepTime: 25,
  portions: 2,
  ingredients: ['3 eggs', '60gr flour'...],
  instructions: ['Mix wet ingredients'...],
})

const persist = debounce(() => {
  localStorage.setItem(
    'recipes',
    JSON.stringify(get(recipes).map((item) => get(item))),
  )
}, 500)

export const recipes = writable([])
let suscriptions = []

// Listens for changes in the top level recipes array
recipes.subscribe(() => {
  // Unsubscribe from every previous individual recipe subscription
  suscriptions.forEach((unsubscribe) => {
    unsubscribe()
  })

  // Create new subscriptions for every recipe object in the recipes list
  suscriptions = get(recipes).map((store) => store.subscribe(persist))
  persist()
})

let items = []

export const restore = () => {
  try {
    items = JSON.parse(localStorage.getItem('recipes'))
    if (!Array.isArray(items)) {
      items = []
    }
  } catch {
    items = []
  }

  recipes.set(items.map((item) => writable(item)))
}

<input
  class="add-photo-input"
  type="file"
  accept="image/*"
  on:change={(event) => {
    let file = event.target.files[0]
    $recipe.image = await saveImage(file, $recipe.id)
  }}
/>

const imageDB = new Promise((resolve) => {
  let db
  let dbReady = false
  let dbVersion = 2

  const request = indexedDB.open('files', dbVersion)

  request.onsuccess = (event) => {
    db = event.target.result
  }

  request.onupgradeneeded = (event) => {
    let db = event.target.result
    db.createObjectStore('images', { keyPath: 'id', autoIncrement: true })
    dbReady = true
    resolve(db)
  }
})

export const saveImage = async (file) => {
  const reader = new FileReader()

  reader.readAsBinaryString(file)

  return new Promise((resolve, reject) => {
    reader.onload = (event) => {
      const bits = event.target.result
      const ob = {
        created: new Date(),
        data: bits,
      }
      const trans = (await imageDB).transaction(['images'], 'readwrite')
      const addReq = trans.objectStore('images').add(ob)
      addReq.onerror = (event) => {
        reject(new Error('Error storing data'))
      }
      addReq.onsuccess = (event) => {
        resolve(event.target.result)
      }
    }
  })
}

export const saveImage = async (file, id = nanoid()) => {
  let newCache = await caches.open('images-cache')

  const request = `/images/${id}`

  await newCache.put(request, new Response(file))

  return request
}

export const getImage = async (request) => {
  let newCache = await caches.open('images-cache')

  const response = await newCache.match(request)

  if (!response) return null

  return URL.createObjectURL(await response.blob())
}

new File(bits, name, options)

new Blob(array, options)

export const pack = (files) => {
  const dir = []
  let start = 0
  for (const item of files) {
    dir.push([item.name, start, item.size, item.type])
    start += item.size
  }

  const dirJSON = JSON.stringify(dir)

  const dirSize = new Uint32Array([dirJSON.length])

  return new File([...files, dirJSON, dirSize], 'myfiles.archive')
}

export const compress = async (file) => {
  const readableStream = file.stream()

  const compressedStream = readableStream.pipeThrough(
    new CompressionStream('gzip'),
  )

  return streamToBlob(compressedStream)
}

export const download = (blob, name) => {
  const url = URL.createObjectURL(blob)
  const link = document.createElement('a')
  link.href = url
  link.download = name
  link.click()
  URL.revokeObjectURL(url)
}

const handleDownload = async () => {
  download(
    new File([exportBlob], 'monchi.export.gz', { type: 'application/gzip' }),
    'monchi.export.gz',
  )
}

export const decompress = async (file) => {
  const readableStream = file.stream()

  const decompressedStream = readableStream.pipeThrough(
    new DecompressionStream('gzip'),
  )

  return streamToBlob(decompressedStream)
}

export const readCentralDir = async (blob) => {
  const last4 = await blob.slice(-4).arrayBuffer()
  
  const size = new DataView(last4).getUint32(0,true)

  const jsonPart = blob.slice(blob.size - size - 4, blob.size - 4)

  return new Response(jsonPart).json()
}

export const unpack = (file, centralDir) =>
  centralDir.map((item) => {
    const [name, start, size, type] = item
    return new File([file.slice(start, start + size)], name, {
      type: type,
    })
  })

const importRecipes = async (files) => {
  const file = files[0]
  const blob = await decompress(file)

  const centralDir = await readCentralDir(blob)

  const fileList = unpack(blob, centralDir)

  for (const file of fileList) {
    if (file.name === 'recipes.json') {
      const text = await file.text()
      localStorage.setItem('recipes', text)
    } else {
      await saveImage(file, file.name)
    }
  }

  restore()
}