discourse/app/assets/javascripts/discourse-common/addon/utils/handle-descriptor.js

import { computed, get } from "@ember/object";
import extractValue from "./extract-value";

export default function handleDescriptor(target, key, desc, params = []) {
  return {
    enumerable: desc.enumerable,
    configurable: desc.configurable,
    writeable: desc.writeable,
    initializer: function() {
      let computedDescriptor;

      if (desc.writable) {
        var val = extractValue(desc);
        if (typeof val === "object") {
          let value = {};
          if (val.get) {
            value.get = callUserSuppliedGet(params, val.get);
          }
          if (val.set) {
            value.set = callUserSuppliedSet(params, val.set);
          }
          computedDescriptor = value;
        } else {
          computedDescriptor = callUserSuppliedGet(params, val);
        }
      } else {
        throw new Error(
          "ember-computed-decorators does not support using getters and setters"
        );
      }

      return computed.apply(null, params.concat(computedDescriptor));
    }
  };
}

function niceAttr(attr) {
  const parts = attr.split(".");
  let i;

  for (i = 0; i < parts.length; i++) {
    if (
      parts[i] === "@each" ||
      parts[i] === "[]" ||
      parts[i].indexOf("{") !== -1
    ) {
      break;
    }
  }

  return parts.slice(0, i).join(".");
}

function callUserSuppliedGet(params, func) {
  params = params.map(niceAttr);
  return function() {
    let paramValues = params.map(p => get(this, p));

    return func.apply(this, paramValues);
  };
}

function callUserSuppliedSet(params, func) {
  params = params.map(niceAttr);
  return function(key, value) {
    let paramValues = params.map(p => get(this, p));
    paramValues.unshift(value);

    return func.apply(this, paramValues);
  };
}