#!/usr/bin/python3

import http.client
import json
import urllib

address, port = 'localhost', 3030

class PrologEngine(object):
    def __init__(self, address=address, port=port, code=''):
        self.id = None
        self.conn = http.client.HTTPConnection(address, port, timeout=10)

        hdrs = {'Content-Type': 'application/json; charset=utf-8'}
        opts = json.dumps({'destroy': False, 'src_text': code, 'format': 'json'})
        self.conn.request('POST', '/pengine/create', body=opts, headers=hdrs)

        response = self.conn.getresponse()
        data = response.read()
        reply = json.loads(str(data, encoding='utf-8'))
        if reply['event'] == 'create':
            self.id = reply['id']
        else:
            raise Exception('could not create engine: ' + reply['code'])

    def send(self, event, fmt='json'):
        params = urllib.parse.urlencode({
            'id': self.id,
            'event': event,
            'format': fmt})
        self.conn.request('GET', '/pengine/send?' + params)

        response = self.conn.getresponse()
        data = str(response.read(), encoding='utf-8')
        if response.status == http.client.OK:
            return json.loads(data) if fmt == 'json' else data
        return None

    def ask(self, query, template='', fmt='json'):
        event = 'ask(({}),[template({})])'.format(query, template)
        reply = self.send(event, fmt=fmt)
        return reply

    def next(self, n=1):
        event = 'next({})'.format(n)
        reply = self.send(event)
        return reply

    def stop(self):
        return self.send('stop')

    def destroy(self):
        reply = self.send('destroy')
        self.id = None
        self.conn.close()
        self.conn = None

# Basic sanity check.
if __name__ == '__main__':
    engine = PrologEngine(code='dup([],[]). dup([H|T],[H,H|TT]) :- dup(T,TT).')
    print('engine id is ' + engine.id)
    print(engine.ask("run_tests({},'{}',Result)".format('dup/2', engine.id)))
    engine.destroy()