import * as Collections from "../utils/collections";
import Util from "../util";
import TransportManager from '../transports/transport_manager';
import * as Errors from '../errors';
import Strategy from './strategy';
import TransportStrategy from './transport_strategy';
import SequentialStrategy from './sequential_strategy';
import BestConnectedEverStrategy from './best_connected_ever_strategy';
import CachedStrategy from './cached_strategy';
import DelayedStrategy from './delayed_strategy';
import IfStrategy from './if_strategy';
import FirstConnectedStrategy from './first_connected_strategy';
import Runtime from "runtime";

const {Transports} = Runtime;
/** Transforms a JSON scheme to a strategy tree.
 *
 * @param {Array} scheme JSON strategy scheme
 * @param {Object} options a hash of symbols to be included in the scheme
 * @returns {Strategy} strategy tree that's represented by the scheme
 */
export var build = function(scheme, options) {
  var context = Collections.extend({}, globalContext, options);
  return evaluate(scheme, context)[1].strategy;
}

var UnsupportedStrategy : Strategy = {
  isSupported: function() {
    return false;
  },
  connect: function(_, callback) {
    var deferred = Util.defer(function() {
      callback(new Errors.UnsupportedStrategy());
    });
    return {
      abort: function() {
        deferred.ensureAborted();
      },
      forceMinPriority: function() {}
    };
  }
};

// DSL bindings

function returnWithOriginalContext(f) {
  return function(context) {
    return [f.apply(this, arguments), context];
  };
}

var globalContext = {
  extend: function(context, first, second) {
    return [Collections.extend({}, first, second), context];
  },

  def: function(context, name, value) {
    if (context[name] !== undefined) {
      throw "Redefining symbol " + name;
    }
    context[name] = value;
    return [undefined, context];
  },

  def_transport: function(context, name, type, priority, options, manager) {
    var transportClass = Transports[type];
    if (!transportClass) {
      throw new Errors.UnsupportedTransport(type);
    }

    var enabled =
      (!context.enabledTransports ||
        Collections.arrayIndexOf(context.enabledTransports, name) !== -1) &&
      (!context.disabledTransports ||
        Collections.arrayIndexOf(context.disabledTransports, name) === -1);

    var transport;
    if (enabled) {
      transport = new TransportStrategy(
        name,
        priority,
        manager ? manager.getAssistant(transportClass) : transportClass,
        Collections.extend({
          key: context.key,
          useTLS: context.useTLS,
          timeline: context.timeline,
          ignoreNullOrigin: context.ignoreNullOrigin
        }, options)
      );
    } else {
      transport = UnsupportedStrategy;
    }

    var newContext = context.def(context, name, transport)[1];
    newContext.Transports = context.Transports || {};
    newContext.Transports[name] = transport;
    return [undefined, newContext];
  },

  transport_manager: returnWithOriginalContext(function(_, options) {
    return new TransportManager(options);
  }),

  sequential: returnWithOriginalContext(function(_, options) {
    var strategies = Array.prototype.slice.call(arguments, 2);
    return new SequentialStrategy(strategies, options);
  }),

  cached: returnWithOriginalContext(function(context, ttl, strategy){
    return new CachedStrategy(strategy, context.Transports, {
      ttl: ttl,
      timeline: context.timeline,
      useTLS: context.useTLS
    });
  }),

  first_connected: returnWithOriginalContext(function(_, strategy) {
    return new FirstConnectedStrategy(strategy);
  }),

  best_connected_ever: returnWithOriginalContext(function() {
    var strategies = Array.prototype.slice.call(arguments, 1);
    return new BestConnectedEverStrategy(strategies);
  }),

  delayed: returnWithOriginalContext(function(_, delay, strategy) {
    return new DelayedStrategy(strategy, { delay: delay });
  }),

  "if": returnWithOriginalContext(function(_, test, trueBranch, falseBranch) {
    return new IfStrategy(test, trueBranch, falseBranch);
  }),

  is_supported: returnWithOriginalContext(function(_, strategy) {
    return function() {
      return strategy.isSupported();
    };
  })
};

// DSL interpreter

function isSymbol(expression) {
  return (typeof expression === "string") && expression.charAt(0) === ":";
}

function getSymbolValue(expression, context) {
  return context[expression.slice(1)];
}

function evaluateListOfExpressions(expressions, context) {
  if (expressions.length === 0) {
    return [[], context];
  }
  var head = evaluate(expressions[0], context);
  var tail = evaluateListOfExpressions(expressions.slice(1), head[1]);
  return [[head[0]].concat(tail[0]), tail[1]];
}

function evaluateString(expression, context) {
  if (!isSymbol(expression)) {
    return [expression, context];
  }
  var value = getSymbolValue(expression, context);
  if (value === undefined) {
    throw "Undefined symbol " + expression;
  }
  return [value, context];
}

function evaluateArray(expression, context) {
  if (isSymbol(expression[0])) {
    var f = getSymbolValue(expression[0], context);
    if (expression.length > 1) {
      if (typeof f !== "function") {
        throw "Calling non-function " + expression[0];
      }
      var args = [Collections.extend({}, context)].concat(
        Collections.map(expression.slice(1), function(arg) {
          return evaluate(arg, Collections.extend({}, context))[0];
        })
      );
      return f.apply(this, args);
    } else {
      return [f, context];
    }
  } else {
    return evaluateListOfExpressions(expression, context);
  }
}

function evaluate(expression, context) {
  if (typeof expression === "string") {
    return evaluateString(expression, context);
  } else if (typeof expression === "object") {
    if (expression instanceof Array && expression.length > 0) {
      return evaluateArray(expression, context);
    }
  }
  return [expression, context];
}