bullseye.js

'use strict';

var crossvent = require('crossvent');
var throttle = require('./throttle');
var tailormade = require('./tailormade');

function bullseye (el, target, options) {
  var o = options;
  var domTarget = target && target.tagName;

  if (!domTarget && arguments.length === 2) {
    o = target;
  }
  if (!domTarget) {
    target = el;
  }
  if (!o) { o = {}; }

  var destroyed = false;
  var throttledWrite = throttle(write, 30);
  var tailorOptions = { update: o.autoupdateToCaret !== false && update };
  var tailor = o.caret && tailormade(target, tailorOptions);

  write();

  if (o.tracking !== false) {
    crossvent.add(window, 'resize', throttledWrite);
  }

  return {
    read: readNull,
    refresh: write,
    destroy: destroy,
    sleep: sleep
  };

  function sleep () {
    tailorOptions.sleeping = true;
  }

  function readNull () { return read(); }

  function read (readings) {
    var bounds = target.getBoundingClientRect();
    var scrollTop = document.body.scrollTop || document.documentElement.scrollTop;
    if (tailor) {
      readings = tailor.read();
      return {
        x: (readings.absolute ? 0 : bounds.left) + readings.x,
        y: (readings.absolute ? 0 : bounds.top) + scrollTop + readings.y + 20
      };
    }
    return {
      x: bounds.left,
      y: bounds.top + scrollTop
    };
  }

  function update (readings) {
    write(readings);
  }

  function write (readings) {
    if (destroyed) {
      throw new Error('Bullseye can\'t refresh after being destroyed. Create another instance instead.');
    }
    if (tailor && !readings) {
      tailorOptions.sleeping = false;
      tailor.refresh(); return;
    }
    var p = read(readings);
    if (!tailor && target !== el) {
      p.y += target.offsetHeight;
    }
    var context = o.context;
    el.style.left = p.x + 'px';
    el.style.top = (context ? context.offsetHeight : p.y) + 'px';
  }

  function destroy () {
    if (tailor) { tailor.destroy(); }
    crossvent.remove(window, 'resize', throttledWrite);
    destroyed = true;
  }
}

module.exports = bullseye;