theprogrammablemind/src/project.js

const project = (object, filter) => {
  if (!object) {
    return
  }

  const projection = {}
  const set = (property, value) => {
    if (value === null || value === undefined) {
      return
    }
    projection[property] = value
  }
  if (Array.isArray(filter)) {
    if (Array.isArray(object)) {
      return object.map(element => project(element, filter))
    } else {
      for (let properties of filter) {
        if (typeof properties === 'function') {
          properties = properties(object)
        }
        if (typeof properties === 'object') {
          if (properties.propertyLists) {
            for (const propertyList in properties.propertyLists) {
              if (object[propertyList]) {
                for (const property of object[propertyList]) {
                  set(property, project(object[property], properties.propertyLists[propertyList]))
                }
              }
            }
          }
          if (properties.valueLists) {
            for (const listProperty in properties.valueLists) {
              const old = object[listProperty]
              if (Array.isArray(old)) {
                set(listProperty, old.map((element) => project(element, properties.valueLists[listProperty])))
              } else {
                set(listProperty, project(old, properties.valueLists[listProperty]))
              }
            }
          }
          if (properties.properties) {
            for (const property in properties.properties) {
              const old = object[property]
              set(property, project(old, properties.properties[property]))
            }
          }
          if (properties.property) {
            const property = properties.property
            if (properties.isPropertyList) {
              if (!Array.isArray(object[property])) {
                continue
              }
              for (const propertyRef of object[property]) {
                const old = object[propertyRef]
                set(propertyRef, project(old, properties.filter))
              }
            } else {
              const old = object[property]
              set(property, project(old, properties.filter))
            }
          }
        } else {
          if (!Array.isArray(properties)) {
            properties = [properties]
          }
          for (const property of properties) {
            set(property, object[property])
          }
        }
      }
    }
  } else if (typeof filter === 'object') {
    for (const property of Object.keys(filter)) {
      set(property, project(object[property], filter[property]))
    }
  }
  return projection
}

module.exports = { project }