Lewerow/Zurvan

var TypeChecks = require('./utils/TypeChecks');

var dependencyOK = 'OK';
var lineBreak = '\n';
var reasonSeparator = ';';

function dependencyExistsAsFunction(f) {
  if (f === undefined) {
    return 'does not exist';
  }
  if (!TypeChecks.isFunction(f)) {
    return 'is not a function';
  }
  return dependencyOK;
}

function contextualFunctionDependency(functionName) {
  return {
    status: function(context) {
      var obj = {};
      obj[functionName] = TypeChecks.isObject(context)
        ? dependencyExistsAsFunction(context[functionName])
        : 'does not exist (not even its object context)';
      return obj;
    }
  };
}

var deps = {
  atIntercept: {
    Promise: {
      status: function(context) {
        var dependencyStatuses = contextualFunctionDependency(
          'promiseScheduler'
        ).status(context);
        if (dependencyStatuses.promiseScheduler === dependencyOK) {
          var promiseScheduler = context.promiseScheduler;
          dependencyStatuses[
            'promiseScheduler.resolve'
          ] = dependencyExistsAsFunction(promiseScheduler.resolve);
          dependencyStatuses[
            'promiseScheduler.reject'
          ] = dependencyExistsAsFunction(promiseScheduler.reject);
          dependencyStatuses[
            'promiseScheduler.prototype.then'
          ] = dependencyExistsAsFunction(promiseScheduler.prototype.then);
          dependencyStatuses[
            'promiseScheduler.prototype.catch'
          ] = dependencyExistsAsFunction(promiseScheduler.prototype.catch);
        }
        return dependencyStatuses;
      }
    }
  },
  atStartup: {
    setImmediate: contextualFunctionDependency('setImmediate'),
    clearImmediate: contextualFunctionDependency('clearImmediate')
  }
};

function missingDependencies(deps, context) {
  return Object.keys(deps)
    .map(function(key) {
      return { name: key, statuses: deps[key].status(context) };
    })
    .map(function(dependency) {
      return {
        name: dependency.name,
        statuses: Object.keys(dependency.statuses)
          .filter(function(statusName) {
            return dependency.statuses[statusName] !== dependencyOK;
          })
          .map(function(statusName) {
            return statusName + ' ' + dependency.statuses[statusName];
          })
      };
    })
    .filter(function(dependency) {
      return dependency.statuses.length > 0;
    })
    .map(function(dependency) {
      return (
        'Missing dependency: ' +
        dependency.name +
        '. Reason(s): ' +
        dependency.statuses.join(reasonSeparator)
      );
    })
    .join(lineBreak);
}

module.exports = {
  missingAtStartup: function() {
    return missingDependencies(deps.atStartup, global);
  },

  missingAtIntercept: function(config) {
    return missingDependencies(deps.atIntercept, config);
  }
};