#!/usr/bin/env python

from __future__ import print_function
import argparse
import socket
import random
import capnp

import calculator_capnp


def read_value(value):
    '''Helper function to asynchronously call read() on a Calculator::Value and
    return a promise for the result.  (In the future, the generated code might
    include something like this automatically.)'''

    return value.read().then(lambda result: result.value)


def evaluate_impl(expression, params=None):
    '''Implementation of CalculatorImpl::evaluate(), also shared by
    FunctionImpl::call().  In the latter case, `params` are the parameter
    values passed to the function; in the former case, `params` is just an
    empty list.'''

    which = expression.which()

    if which == 'literal':
        return capnp.Promise(expression.literal)
    elif which == 'previousResult':
        return read_value(expression.previousResult)
    elif which == 'parameter':
        assert expression.parameter < len(params)
        return capnp.Promise(params[expression.parameter])
    elif which == 'call':
        call = expression.call
        func = call.function

        # Evaluate each parameter.
        paramPromises = [evaluate_impl(param, params) for param in call.params]

        joinedParams = capnp.join_promises(paramPromises)
        # When the parameters are complete, call the function.
        ret = (joinedParams
               .then(lambda vals: func.call(vals))
               .then(lambda result: result.value))

        return ret
    else:
        raise ValueError("Unknown expression type: " + which)


class ValueImpl(calculator_capnp.Calculator.Value.Server):

    "Simple implementation of the Calculator.Value Cap'n Proto interface."

    def __init__(self, value):
        self.value = value

    def read(self, **kwargs):
        return self.value


class FunctionImpl(calculator_capnp.Calculator.Function.Server):

    '''Implementation of the Calculator.Function Cap'n Proto interface, where the
    function is defined by a Calculator.Expression.'''

    def __init__(self, paramCount, body):
        self.paramCount = paramCount
        self.body = body.as_builder()

    def call(self, params, _context, **kwargs):
        '''Note that we're returning a Promise object here, and bypassing the
        helper functionality that normally sets the results struct from the
        returned object. Instead, we set _context.results directly inside of
        another promise'''

        assert len(params) == self.paramCount
        # using setattr because '=' is not allowed inside of lambdas
        return evaluate_impl(self.body, params).then(lambda value: setattr(_context.results, 'value', value))


class OperatorImpl(calculator_capnp.Calculator.Function.Server):

    '''Implementation of the Calculator.Function Cap'n Proto interface, wrapping
    basic binary arithmetic operators.'''

    def __init__(self, op):
        self.op = op

    def call(self, params, **kwargs):
        assert len(params) == 2

        op = self.op

        if op == 'add':
            return params[0] + params[1]
        elif op == 'subtract':
            return params[0] - params[1]
        elif op == 'multiply':
            return params[0] * params[1]
        elif op == 'divide':
            return params[0] / params[1]
        else:
            raise ValueError('Unknown operator')


class CalculatorImpl(calculator_capnp.Calculator.Server):

    "Implementation of the Calculator Cap'n Proto interface."

    def evaluate(self, expression, _context, **kwargs):
        return evaluate_impl(expression).then(lambda value: setattr(_context.results, 'value', ValueImpl(value)))

    def defFunction(self, paramCount, body, _context, **kwargs):
        return FunctionImpl(paramCount, body)

    def getOperator(self, op, **kwargs):
        return OperatorImpl(op)


def parse_args():
    parser = argparse.ArgumentParser(usage='''Runs the server bound to the\
given address/port ADDRESS may be '*' to bind to all local addresses.\
:PORT may be omitted to choose a port automatically. ''')

    parser.add_argument("address", help="ADDRESS[:PORT]")

    return parser.parse_args()


def restore(ref):
    assert ref.as_text() == 'calculator'
    return CalculatorImpl()


def main():
    address = parse_args().address

    if ':' in address:
        address, port = address.split(':')
        port = int(port)
    else:
        port = random.randint(60000, 61000)

    if address == '*':
        address = ''

    print("Listening on port: {}".format(port))

    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

    # Set TCP_NODELAY on socket to disable Nagle's algorithm. This is not
    # neccessary, but it speeds things up.
    s.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)

    s.bind((address, port))
    s.listen(1)  # service only 1 client at a time

    while True:
        try:
            (clientsocket, address) = s.accept()
            server = capnp.TwoPartyServer(clientsocket, restore)

            server.run_forever()
            print("client disconnected")
        except KeyboardInterrupt:
            break

if __name__ == '__main__':
    main()