define(['exports', 'module', '../utils', '../exception'], function (exports, module, _utils, _exception) {
  'use strict';

  // istanbul ignore next

  function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { 'default': obj }; }

  var _Exception = _interopRequireDefault(_exception);

  module.exports = function (instance) {
    instance.registerHelper('each', function (context, options) {
      if (!options) {
        throw new _Exception['default']('Must pass iterator to #each');
      }

      var fn = options.fn,
          inverse = options.inverse,
          i = 0,
          ret = '',
          data = undefined,
          contextPath = undefined;

      if (options.data && options.ids) {
        contextPath = _utils.appendContextPath(options.data.contextPath, options.ids[0]) + '.';
      }

      if (_utils.isFunction(context)) {
        context = context.call(this);
      }

      if (options.data) {
        data = _utils.createFrame(options.data);
      }

      function execIteration(field, index, last) {
        if (data) {
          data.key = field;
          data.index = index;
          data.first = index === 0;
          data.last = !!last;

          if (contextPath) {
            data.contextPath = contextPath + field;
          }
        }

        ret = ret + fn(context[field], {
          data: data,
          blockParams: _utils.blockParams([context[field], field], [contextPath + field, null])
        });
      }

      if (context && typeof context === 'object') {
        if (_utils.isArray(context)) {
          for (var j = context.length; i < j; i++) {
            if (i in context) {
              execIteration(i, i, i === context.length - 1);
            }
          }
        } else if (global.Symbol && context[global.Symbol.iterator]) {
          var newContext = [];
          var iterator = context[global.Symbol.iterator]();
          for (var it = iterator.next(); !it.done; it = iterator.next()) {
            newContext.push(it.value);
          }
          context = newContext;
          for (var j = context.length; i < j; i++) {
            execIteration(i, i, i === context.length - 1);
          }
        } else {
          (function () {
            var priorKey = undefined;

            Object.keys(context).forEach(function (key) {
              // We're running the iterations one step out of sync so we can detect
              // the last iteration without have to scan the object twice and create
              // an itermediate keys array.
              if (priorKey !== undefined) {
                execIteration(priorKey, i - 1);
              }
              priorKey = key;
              i++;
            });
            if (priorKey !== undefined) {
              execIteration(priorKey, i - 1, true);
            }
          })();
        }
      }

      if (i === 0) {
        ret = inverse(this);
      }

      return ret;
    });
  };
});
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