ribbon.js

import {slice} from "./array";
import constant from "./constant";
import {cos, halfPi, sin} from "./math";
import {path} from "d3-path";

function defaultSource(d) {
  return d.source;
}

function defaultTarget(d) {
  return d.target;
}

function defaultRadius(d) {
  return d.radius;
}

function defaultStartAngle(d) {
  return d.startAngle;
}

function defaultEndAngle(d) {
  return d.endAngle;
}

export default function() {
  var source = defaultSource,
      target = defaultTarget,
      radius = defaultRadius,
      startAngle = defaultStartAngle,
      endAngle = defaultEndAngle,
      context = null;

  function ribbon() {
    var buffer,
        argv = slice.call(arguments),
        s = source.apply(this, argv),
        t = target.apply(this, argv),
        sr = +radius.apply(this, (argv[0] = s, argv)),
        sa0 = startAngle.apply(this, argv) - halfPi,
        sa1 = endAngle.apply(this, argv) - halfPi,
        sx0 = sr * cos(sa0),
        sy0 = sr * sin(sa0),
        tr = +radius.apply(this, (argv[0] = t, argv)),
        ta0 = startAngle.apply(this, argv) - halfPi,
        ta1 = endAngle.apply(this, argv) - halfPi;

    if (!context) context = buffer = path();

    context.moveTo(sx0, sy0);
    context.arc(0, 0, sr, sa0, sa1);
    if (sa0 !== ta0 || sa1 !== ta1) { // TODO sr !== tr?
      context.quadraticCurveTo(0, 0, tr * cos(ta0), tr * sin(ta0));
      context.arc(0, 0, tr, ta0, ta1);
    }
    context.quadraticCurveTo(0, 0, sx0, sy0);
    context.closePath();

    if (buffer) return context = null, buffer + "" || null;
  }

  ribbon.radius = function(_) {
    return arguments.length ? (radius = typeof _ === "function" ? _ : constant(+_), ribbon) : radius;
  };

  ribbon.startAngle = function(_) {
    return arguments.length ? (startAngle = typeof _ === "function" ? _ : constant(+_), ribbon) : startAngle;
  };

  ribbon.endAngle = function(_) {
    return arguments.length ? (endAngle = typeof _ === "function" ? _ : constant(+_), ribbon) : endAngle;
  };

  ribbon.source = function(_) {
    return arguments.length ? (source = _, ribbon) : source;
  };

  ribbon.target = function(_) {
    return arguments.length ? (target = _, ribbon) : target;
  };

  ribbon.context = function(_) {
    return arguments.length ? ((context = _ == null ? null : _), ribbon) : context;
  };

  return ribbon;
}