shelf

shelf.ts

type Item = null | string | number | boolean | Item[] | {[k: string]: Item};

// Must match the shape of the data
type Version = number | [number, Version[]] | [number, {[k: string]: Version}];

type Path = (string | number)[]

interface Doc {
  data: Item,
  versions: Version,
  nextSeq: number,
}

const isObject = (x: any): x is {[k: string]: Item} => (typeof x === 'object' && !Array.isArray(x) && x != null)
const isVObj = (v: Version): v is [number, {[k: string]: Version}] => !(typeof v === 'number') && isObject(v[1])
const isVArr = (v: Version): v is [number, Version[]] => !(typeof v === 'number') && Array.isArray(v[1])

const setInner = (data: Item, versions: Version, nextSeq: number, path: Path, newVal: Item): Doc => {
  if (path.length === 0) {
    return {
      data: newVal,
      versions: isObject(newVal) ? [nextSeq, {}]
      : Array.isArray(newVal) ? [nextSeq, []]
      : nextSeq,
      nextSeq: nextSeq + 1,
    }
  } else {
    let p = path[0]
    if (typeof p === 'string') {
      if (!isObject(data)) throw Error('invalid path component for data')
      if (!isVObj(versions)) throw Error('invalid versions data')

      let inner = setInner(data[p], versions[1][p], nextSeq, path.slice(1), newVal)
      inner.data = {
        ...(data.data as any),
        [p]: inner.data
      }
      inner.versions = [versions[0], {
        ...versions[1],
        [p]: inner.versions
      }]
      return inner
    } else {
      if (typeof p !== 'number') throw Error('invalid path component')
      if (!Array.isArray(data)) throw Error('invalid path component for data')
      if (!isVArr(versions)) throw Error('invalid versions data')

      let inner = setInner(data[p], versions[1][p], nextSeq, path.slice(1), newVal)

      let d = data.slice()
      d[p] = inner.data
      inner.data = d

      let v: [number, Version[]] = [versions[0], versions[1].slice()]
      v[1][p] = inner.versions
      inner.versions = v

      return inner
    }
  }
}

export const set = (doc: Doc, path: Path, newVal: Item): Doc => {
  return setInner(doc.data, doc.versions, doc.nextSeq, path, newVal)
}


;(() => {
  // ****************** Usage example
  let doc: Doc = {
    data: null,
    versions: 0,
    nextSeq: 1,
  }

  doc = set(doc, [], {})
  console.log(doc)

  doc = set(doc, ['x'], 'hi there')
  console.log(doc)

  doc = set(doc, [], [])
  console.log(doc)

  doc = set(doc, [0], 123)
  console.log(doc)
})()