var Q = require('q');

/**
 * OKQuery!
 * Takes a query spec for a resource and maps it the proper read
 * methods of that resource. This is simply to separate the notions
 * of queries and resources.
 */
function OKQuery(options) {
  if (!(this instanceof OKQuery)) return new OKQuery(options);
  options = options || {};
  if (!options.resource)
    throw new Error('No resource provided to query');
  var resource = options.resource;
  var type = resource.type;
  var query = options.query || '*';
  Object.defineProperty(this, 'resource', {
    value: resource,
    writable: false
  });
  Object.defineProperty(this, 'type', {
    value: resource.type,
    writable: false
  });
  this.get = createQuery(resource, query, {
    default: options.default
  });
}

function createQuery(resource, query, options) {
  options = options || {};
  var query;
  if (isDynamic(query)) {
    query = queryDynamic(resource);
  } else if (isSet(query)) {
    query = queryAll(resource);
  } else {
    query = querySingle(resource, query);
  }
  if (options.default)
    query = withDefault(query, options.default);
  return query;
}

function queryDynamic(resource) {
  return function(id) {
    return resource.get(id);
  }
}

function queryAll(resource) {
  return function() {
    return resource.all();
  }
}

function querySingle(resource, id) {
  return function() {
    return resource.get(id);
  }
}

function withDefault(queryFn, resultDefault) {
  return function() {
    return Q.Promise(function(resolve, reject) {
      queryFn().then(function(data) {
        data = data || resultDefault;
        resolve(data);
      }, reject);
    });
  };
}

function isDynamic(query) {
  return query && query.charAt(0) === ':';
}

function isSet(query) {
  return query && query === '*';
}

module.exports = OKQuery;