vega-runtime/src/parameters.js

Runtime support for Vega dataflows.

import {tupleid} from 'vega-dataflow';
import {
  accessor, array, compare, error, field,
  hasOwnProperty, isArray, isObject, key
} from 'vega-util';

/**
 * Parse a set of operator parameters.
 */
export default function parseParameters(spec, params) {
  params = params || {};
  const ctx = this;

  for (const key in spec) {
    const value = spec[key];
    params[key] = isArray(value)
      ? value.map(v => parseParameter(v, ctx, params))
      : parseParameter(value, ctx, params);
  }

  return params;
}

/**
 * Parse a single parameter.
 */
function parseParameter(spec, ctx, params) {
  if (!spec || !isObject(spec)) return spec;

  for (let i=0, n=PARSERS.length, p; i<n; ++i) {
    p = PARSERS[i];
    if (hasOwnProperty(spec, p.key)) {
      return p.parse(spec, ctx, params);
    }
  }

  return spec;
}

/** Reference parsers. */
var PARSERS = [
  {key: '$ref',      parse: getOperator},
  {key: '$key',      parse: getKey},
  {key: '$expr',     parse: getExpression},
  {key: '$field',    parse: getField},
  {key: '$encode',   parse: getEncode},
  {key: '$compare',  parse: getCompare},
  {key: '$context',  parse: getContext},
  {key: '$subflow',  parse: getSubflow},
  {key: '$tupleid',  parse: getTupleId}
];

/**
 * Resolve an operator reference.
 */
function getOperator(_, ctx) {
  return ctx.get(_.$ref) || error('Operator not defined: ' + _.$ref);
}

/**
 * Resolve an expression reference.
 */
function getExpression(_, ctx, params) {
  if (_.$params) { // parse expression parameters
    ctx.parseParameters(_.$params, params);
  }
  const k = 'e:' + _.$expr.code;
  return ctx.fn[k] || (ctx.fn[k] = accessor(
    ctx.parameterExpression(_.$expr),
    _.$fields
  ));
}

/**
 * Resolve a key accessor reference.
 */
function getKey(_, ctx) {
  const k = 'k:' + _.$key + '_' + (!!_.$flat);
  return ctx.fn[k] || (ctx.fn[k] = key(_.$key, _.$flat, ctx.expr.codegen));
}

/**
 * Resolve a field accessor reference.
 */
function getField(_, ctx) {
  if (!_.$field) return null;
  const k = 'f:' + _.$field + '_' + _.$name;
  return ctx.fn[k] || (ctx.fn[k] = field(_.$field, _.$name, ctx.expr.codegen));
}

/**
 * Resolve a comparator function reference.
 */
function getCompare(_, ctx) {
  // As of Vega 5.5.3, $tupleid sort is no longer used.
  // Keep here for now for backwards compatibility.
  const k = 'c:' + _.$compare + '_' + _.$order,
        c = array(_.$compare).map(_ => (_ && _.$tupleid) ? tupleid : _);
  return ctx.fn[k] || (ctx.fn[k] = compare(c, _.$order, ctx.expr.codegen));
}

/**
 * Resolve an encode operator reference.
 */
function getEncode(_, ctx) {
  const spec = _.$encode,
        encode = {};

  for (const name in spec) {
    const enc = spec[name];
    encode[name] = accessor(ctx.encodeExpression(enc.$expr), enc.$fields);
    encode[name].output = enc.$output;
  }
  return encode;
}

/**
 * Resolve a context reference.
 */
function getContext(_, ctx) {
  return ctx;
}

/**
 * Resolve a recursive subflow specification.
 */
function getSubflow(_, ctx) {
  const spec = _.$subflow;
  return function(dataflow, key, parent) {
    const subctx = ctx.fork().parse(spec),
          op = subctx.get(spec.operators[0].id),
          p = subctx.signals.parent;
    if (p) p.set(parent);
    op.detachSubflow = () => ctx.detach(subctx);
    return op;
  };
}

/**
 * Resolve a tuple id reference.
 */
function getTupleId() {
  return tupleid;
}