import sys
import selectors
import json
import io
import struct

request_search = {
    'morpheus': 'Follow the white rabbit. \U0001f430',
    'ring': 'In the caves beneath the Misty Mountains. \U0001f48d',
    '\U0001f436': '\U0001f43e Playing ball! \U0001f3d0',
}


class Message:

    def __init__(self, selector, sock, addr):
        self.selector = selector
        self.sock = sock
        self.addr = addr
        self._recv_buffer = b''
        self._send_buffer = b''
        self._jsonheader_len = None
        self.jsonheader = None
        self.request = None
        self.response_created = False

    def _set_selector_events_mask(self, mode):
        """Set selector to listen for events: mode is 'r', 'w', or 'rw'."""
        if mode == 'r':
            events = selectors.EVENT_READ
        elif mode == 'w':
            events = selectors.EVENT_WRITE
        elif mode == 'rw':
            events = selectors.EVENT_READ | selectors.EVENT_WRITE
        else:
            raise ValueError(f'Invalid events mask mode {repr(mode)}.')
        self.selector.modify(self.sock, events, data=self)

    def _read(self):
        try:
            # Should be ready to read
            data = self.sock.recv(4096)
        except BlockingIOError:
            # Resource temporarily unavailable (errno EWOULDBLOCK)
            pass
        else:
            if data:
                self._recv_buffer += data
            else:
                raise RuntimeError('Peer closed.')

    def _write(self):
        if self._send_buffer:
            print('sending', repr(self._send_buffer), 'to', self.addr)
            try:
                # Should be ready to write
                sent = self.sock.send(self._send_buffer)
            except BlockingIOError:
                # Resource temporarily unavailable (errno EWOULDBLOCK)
                pass
            else:
                self._send_buffer = self._send_buffer[sent:]
                # Close when the buffer is drained. The response has been sent.
                if sent and not self._send_buffer:
                    self.close()

    def _json_encode(self, obj, encoding):
        return json.dumps(obj, ensure_ascii=False).encode(encoding)

    def _json_decode(self, json_bytes, encoding):
        tiow = io.TextIOWrapper(io.BytesIO(json_bytes), encoding=encoding,
                                newline='')
        obj = json.load(tiow)
        tiow.close()
        return obj

    def _create_message(self, *, content_bytes, content_type,
                        content_encoding):
        jsonheader = {
            'byteorder': sys.byteorder,
            'content-type': content_type,
            'content-encoding': content_encoding,
            'content-length': len(content_bytes)
        }
        jsonheader_bytes = self._json_encode(jsonheader, 'utf-8')
        message_hdr = struct.pack('>H', len(jsonheader_bytes))
        message = message_hdr + jsonheader_bytes + content_bytes
        return message

    def _create_response_json_content(self):
        action = self.request.get('action')
        if action == 'search':
            query = self.request.get('value')
            answer = request_search.get(query) or f'No match for "{query}".'
            content = {'result': answer}
        else:
            content = {'result': f'Error: invalid action "{action}".'}
        content_encoding = 'utf-8'
        response = {
            'content_bytes': self._json_encode(content, content_encoding),
            'content_type': 'text/json',
            'content_encoding': content_encoding
        }
        return response

    def _create_response_binary_content(self):
        response = {
            'content_bytes': b'First 10 bytes of request: ' +
                             self.request[:10],
            'content_type': 'binary/custom-server-binary-type',
            'content_encoding': 'binary'
        }
        return response

    def process_events(self, mask):
        if mask & selectors.EVENT_READ:
            self.read()
        if mask & selectors.EVENT_WRITE:
            self.write()

    def read(self):
        self._read()

        if self._jsonheader_len is None:
            self.process_protoheader()

        if self._jsonheader_len is not None:
            if self.jsonheader is None:
                self.process_jsonheader()

        if self.jsonheader:
            if self.request is None:
                self.process_request()

    def write(self):
        if self.request:
            if not self.response_created:
                self.create_response()

        self._write()

    def close(self):
        print('closing connection to', self.addr)
        try:
            self.selector.unregister(self.sock)
        except Exception as e:
            print(f'error: selector.unregister() exception for',
                  f'{self.addr}: {repr(e)}')

        try:
            self.sock.close()
        except OSError as e:
            print(f'error: socket.close() exception for',
                  f'{self.addr}: {repr(e)}')
        finally:
            # Delete reference to socket object for garbage collection
            self.sock = None

    def process_protoheader(self):
        hdrlen = 2
        if len(self._recv_buffer) >= hdrlen:
            self._jsonheader_len = struct.unpack('>H',
                                                 self._recv_buffer[:hdrlen])[0]
            self._recv_buffer = self._recv_buffer[hdrlen:]

    def process_jsonheader(self):
        hdrlen = self._jsonheader_len
        if len(self._recv_buffer) >= hdrlen:
            self.jsonheader = self._json_decode(self._recv_buffer[:hdrlen],
                                                'utf-8')
            self._recv_buffer = self._recv_buffer[hdrlen:]
            for reqhdr in ('byteorder', 'content-length', 'content-type',
                           'content-encoding'):
                if reqhdr not in self.jsonheader:
                    raise ValueError(f'Missing required header "{reqhdr}".')

    def process_request(self):
        content_len = self.jsonheader['content-length']
        if not len(self._recv_buffer) >= content_len:
            return
        data = self._recv_buffer[:content_len]
        self._recv_buffer = self._recv_buffer[content_len:]
        if self.jsonheader['content-type'] == 'text/json':
            encoding = self.jsonheader['content-encoding']
            self.request = self._json_decode(data, encoding)
            print('received request', repr(self.request), 'from', self.addr)
        else:
            # Binary or unknown content-type
            self.request = data
            print(f'received {self.jsonheader["content-type"]} request from',
                  self.addr)
        # Set selector to listen for write events, we're done reading.
        self._set_selector_events_mask('w')

    def create_response(self):
        if self.jsonheader['content-type'] == 'text/json':
            response = self._create_response_json_content()
        else:
            # Binary or unknown content-type
            response = self._create_response_binary_content()
        message = self._create_message(**response)
        self.response_created = True
        self._send_buffer += message