import os
import socket
from typing import Optional
from typing import TypeVar
from typing import Union
from urllib.parse import urlparse

from ddtrace.internal.constants import DEFAULT_TIMEOUT
from ddtrace.internal.settings._core import DDConfig


DEFAULT_HOSTNAME = "localhost"
DEFAULT_TRACE_PORT = 8126
DEFAULT_UNIX_TRACE_PATH = "/var/run/datadog/apm.socket"
DEFAULT_UNIX_DSD_PATH = "/var/run/datadog/dsd.socket"
DEFAULT_STATS_PORT = 8125

T = TypeVar("T")


# This method returns if a hostname is an IPv6 address
def is_ipv6_hostname(hostname: Union[T, str]) -> bool:
    if not isinstance(hostname, str):
        return False
    try:
        socket.inet_pton(socket.AF_INET6, hostname)
        return True
    except socket.error:  # not a valid address
        return False


def _derive_trace_url(config: "AgentConfig") -> str:
    user_supplied_host = config._trace_agent_hostname or config._agent_host
    user_supplied_port = config._trace_agent_port or config._agent_port

    url = config._trace_agent_url
    if not url:
        if user_supplied_host is not None or user_supplied_port is not None:
            host = user_supplied_host or DEFAULT_HOSTNAME
            port = user_supplied_port or DEFAULT_TRACE_PORT
            if is_ipv6_hostname(host):
                host = f"[{host}]"
            url = "http://%s:%s" % (host, port)
        elif os.path.exists("/var/run/datadog/apm.socket"):
            url = "unix://%s" % (DEFAULT_UNIX_TRACE_PATH)
        else:
            url = f"http://{DEFAULT_HOSTNAME}:{DEFAULT_TRACE_PORT}"

    return url


def _derive_stats_url(config: "AgentConfig") -> str:
    user_supplied_host = config._dogstatsd_host or config._agent_host
    user_supplied_port = config._dogstatsd_port or config._agent_port
    url = config._dogstatsd_url

    if not url:
        if user_supplied_host is not None or user_supplied_port is not None:
            port = user_supplied_port or DEFAULT_STATS_PORT
            host = user_supplied_host or DEFAULT_HOSTNAME
            if is_ipv6_hostname(host):
                host = f"[{host}]"
            url = f"udp://{host}:{port}"
        elif os.path.exists("/var/run/datadog/dsd.socket"):
            url = "unix://%s" % (DEFAULT_UNIX_DSD_PATH)
        else:
            url = f"udp://{DEFAULT_HOSTNAME}:{DEFAULT_STATS_PORT}"
    return url


class AgentConfig(DDConfig):
    __prefix__ = "dd"

    _trace_agent_hostname = DDConfig.v(
        Optional[str],
        "trace_agent_hostname",
        default=None,
        help_type="String",
        help="Legacy configuration, stores the hostname of the trace agent",
    )

    _trace_agent_port = DDConfig.v(
        Optional[int],
        "trace_agent_port",
        default=None,
        help_type="Int",
        help="Legacy configuration, stores the port of the trace agent",
    )

    _trace_agent_url = DDConfig.v(
        Optional[str],
        "trace_agent_url",
        default=None,
        help_type="String",
        help="Stores the URL of the trace agent",
    )

    trace_agent_timeout_seconds = DDConfig.v(
        float,
        "trace_agent_timeout_seconds",
        default=DEFAULT_TIMEOUT,
        help_type="Float",
        help="Stores the timeout in seconds for the trace agent",
    )

    _dogstatsd_host = DDConfig.v(
        Optional[str],
        "dogstatsd_host",
        default=None,
        help_type="String",
        help="Stores the hostname of the agent receiving DogStatsD metrics",
    )

    _dogstatsd_port = DDConfig.v(
        Optional[int],
        "dogstatsd_port",
        default=None,
        help_type="Int",
        help="Stores the port of the agent receiving DogStatsD metrics",
    )

    _dogstatsd_url = DDConfig.v(
        Optional[str],
        "dogstatsd_url",
        default=None,
        help_type="String",
        help="Stores the URL of the DogStatsD agent",
    )

    _agent_host = DDConfig.v(
        Optional[str],
        "agent_host",
        default=None,
        help_type="String",
        help="Stores the hostname of the agent",
    )

    _agent_port = DDConfig.v(
        Optional[int],
        "agent_port",
        default=None,
        help_type="Int",
        help="Stores the port of the agent",
    )

    trace_native_span_events = DDConfig.v(
        bool,
        "trace_native_span_events",
        default=False,
        help_type="Boolean",
        help="Stores whether native span events are enabled",
    )
    # Effective trace agent URL (this is the one that will be used)
    trace_agent_url = DDConfig.d(str, _derive_trace_url)
    # Effective DogStatsD URL (this is the one that will be used)
    dogstatsd_url = DDConfig.d(str, _derive_stats_url)


config = AgentConfig()


def get_agent_hostname() -> str:
    """
    Returns the hostname of the agent using the resolved trace_agent_url.
    """
    url = urlparse(config.trace_agent_url)
    if url.hostname:
        return url.hostname
    return DEFAULT_HOSTNAME


def get_agent_port() -> int:
    """
    Returns the port of the agent using the resolved trace_agent_url.
    """
    url = urlparse(config.trace_agent_url)
    if url.port:
        return url.port
    return DEFAULT_TRACE_PORT