A POC of a JS patch applier for Automerge.

automerge-patch-materializer

    const putPatch = (obj: any, p: A.PutPatch) => {
      const { path, value } = p
      const tail = path.pop()
      const local = path.reduce((acc, next) => acc[next], obj)
      local[tail] = value
      return obj
    }

    const splicePatch = (obj: any, p: A.SpliceTextPatch) => {
      const { path, value } = p
      
      const pos = path.pop() as number
      const tail = path.pop()
      const local = path.reduce((acc, next) => acc[next], obj)

      const prefix = local[tail].substring(0, pos)
      const suffix = local[tail].slice(pos)
      local[tail] = prefix + value + suffix
      return obj
    }

    const delPatch = (obj: any, p: A.DelPatch) => {
      const { path, length } = p
      const tail = path.pop()
      const local = path.reduce((acc, next) => acc[next], obj)
      // TODO: support length
      delete local[tail]
      return obj
    }

    const insertPatch = (obj: any, p: A.InsertPatch) => {
      const { path, values } = p
      const pos = path.pop()
      const tail = path.pop()
      const local = path.reduce((acc, next) => acc[next], obj)
      local[tail].splice(pos, 0, ...values)
      return obj
    }

    const applyPatches = (obj: any, ps: A.Patch[]) => {
      return ps.reduce((acc, p) => applyPatch(acc, p), obj)
    }
    
    const applyPatch = (obj: any, p: A.Patch) => {
      console.log('ptch', obj, p)
      switch (p.action) {
        case "put":
          return putPatch(obj, p);
        case "splice":
          return splicePatch(obj, p);
        case "del":
          return delPatch(obj, p);
        case "insert":
          return insertPatch(obj, p);
        case "inc":
        case "mark":
        case "unmark":
        case "conflict":
          throw new Error(`Patch action not implemented.\n${JSON.stringify(p, undefined, 2)}`)
      }
    }
    const pojo = {}

    handle.on("change", ({ handle, doc, patches }) => {
      applyPatches(pojo, patches)
    })