from . import coap_macros as macros
from .coap_option import CoapOption


class CoapPacket:
    def __init__(self):
        self.version = macros.COAP_VERSION.COAP_VERSION_UNSUPPORTED
        self.type = macros.COAP_TYPE.COAP_CON
        self.method = macros.COAP_METHOD.COAP_GET
        self.token = bytearray()
        self.payload = bytearray()
        self.messageid = 0
        self.content_format = macros.COAP_CONTENT_FORMAT.COAP_NONE
        self.query = bytearray()
        self.options = []

    def addOption(self, number, opt_payload):
        if len(self.options) >= macros._MAX_OPTION_NUM:
            return
        self.options.append(CoapOption(number, opt_payload))

    def setUriHost(self, address):
        self.addOption(macros.COAP_OPTION_NUMBER.COAP_URI_HOST, address)

    def setUriPath(self, url):
        for subPath in url.split('/'):
            self.addOption(macros.COAP_OPTION_NUMBER.COAP_URI_PATH, subPath)

    def setObserve(self, value):
        """Set the Observe option (RFC 7641).

        For requests:
            value=0: register as observer
            value=1: deregister

        For notifications:
            value=sequence number (24-bit, 0-16777215)
        """
        if value < 256:
            buf = bytearray([value & 0xFF])
        elif value < 65536:
            buf = bytearray([(value >> 8) & 0xFF, value & 0xFF])
        else:
            buf = bytearray([(value >> 16) & 0xFF, (value >> 8) & 0xFF, value & 0xFF])
        self.addOption(macros.COAP_OPTION_NUMBER.COAP_OBSERVE, buf)

    def setMaxAge(self, seconds):
        """Set the Max-Age option (seconds until resource is considered stale)."""
        if seconds < 256:
            buf = bytearray([seconds & 0xFF])
        elif seconds < 65536:
            buf = bytearray([(seconds >> 8) & 0xFF, seconds & 0xFF])
        else:
            buf = bytearray([
                (seconds >> 24) & 0xFF, (seconds >> 16) & 0xFF,
                (seconds >> 8) & 0xFF, seconds & 0xFF
            ])
        self.addOption(macros.COAP_OPTION_NUMBER.COAP_MAX_AGE, buf)

    def getObserveValue(self):
        """Extract the Observe option value from the packet, or None if absent."""
        for opt in self.options:
            if opt.number == macros.COAP_OPTION_NUMBER.COAP_OBSERVE:
                val = 0
                for b in opt.buffer:
                    val = (val << 8) | b
                return val
        return None

    def getUriPath(self):
        """Reconstruct the URI path from URI_PATH options."""
        parts = []
        for opt in self.options:
            if opt.number == macros.COAP_OPTION_NUMBER.COAP_URI_PATH and len(opt.buffer) > 0:
                parts.append(opt.buffer.decode("utf-8"))
        return "/".join(parts)

    def toString(self):
        class_, detail = macros.CoapResponseCode.decode(self.method)
        return "type: {}, method: {}.{:02d}, messageid: {}, payload: {}".format(
            macros.coapTypeToString(self.type), class_, detail,
            self.messageid, self.payload
        )