from dataclasses import dataclass, field
from enum import Enum
from typing import List, Optional, Type, Union

import pybreaker

from redis import ConnectionPool, Redis, RedisCluster
from redis.asyncio.multidb.healthcheck import (
    DEFAULT_HEALTH_CHECK_DELAY,
    DEFAULT_HEALTH_CHECK_INTERVAL,
    DEFAULT_HEALTH_CHECK_POLICY,
    DEFAULT_HEALTH_CHECK_PROBES,
    DEFAULT_HEALTH_CHECK_TIMEOUT,
    HealthCheck,
    HealthCheckPolicies,
    PingHealthCheck,
)
from redis.backoff import ExponentialWithJitterBackoff, NoBackoff
from redis.data_structure import WeightedList
from redis.event import EventDispatcher, EventDispatcherInterface
from redis.maint_notifications import MaintNotificationsConfig
from redis.multidb.circuit import (
    DEFAULT_GRACE_PERIOD,
    CircuitBreaker,
    PBCircuitBreakerAdapter,
)
from redis.multidb.database import Database, Databases
from redis.multidb.failover import (
    DEFAULT_FAILOVER_ATTEMPTS,
    DEFAULT_FAILOVER_DELAY,
    FailoverStrategy,
    WeightBasedFailoverStrategy,
)
from redis.multidb.failure_detector import (
    DEFAULT_FAILURE_RATE_THRESHOLD,
    DEFAULT_FAILURES_DETECTION_WINDOW,
    DEFAULT_MIN_NUM_FAILURES,
    CommandFailureDetector,
    FailureDetector,
)
from redis.retry import Retry

DEFAULT_AUTO_FALLBACK_INTERVAL = 120


class InitialHealthCheck(Enum):
    ALL_AVAILABLE = "all_available"
    MAJORITY_AVAILABLE = "majority_available"
    ONE_AVAILABLE = "one_available"


def default_event_dispatcher() -> EventDispatcherInterface:
    return EventDispatcher()


@dataclass
class DatabaseConfig:
    """
    Dataclass representing the configuration for a database connection.

    This class is used to store configuration settings for a database connection,
    including client options, connection sourcing details, circuit breaker settings,
    and cluster-specific properties. It provides a structure for defining these
    attributes and allows for the creation of customized configurations for various
    database setups.

    Attributes:
        weight (float): Weight of the database to define the active one.
        client_kwargs (dict): Additional parameters for the database client connection.
        from_url (Optional[str]): Redis URL way of connecting to the database.
        from_pool (Optional[ConnectionPool]): A pre-configured connection pool to use.
        circuit (Optional[CircuitBreaker]): Custom circuit breaker implementation.
        grace_period (float): Grace period after which we need to check if the circuit could be closed again.
        health_check_url (Optional[str]): URL for health checks. Cluster FQDN is typically used
            on public Redis Enterprise endpoints.

    Methods:
        default_circuit_breaker:
            Generates and returns a default CircuitBreaker instance adapted for use.
    """

    weight: float = 1.0
    client_kwargs: dict = field(default_factory=dict)
    from_url: Optional[str] = None
    from_pool: Optional[ConnectionPool] = None
    circuit: Optional[CircuitBreaker] = None
    grace_period: float = DEFAULT_GRACE_PERIOD
    health_check_url: Optional[str] = None

    def default_circuit_breaker(self) -> CircuitBreaker:
        circuit_breaker = pybreaker.CircuitBreaker(reset_timeout=self.grace_period)
        return PBCircuitBreakerAdapter(circuit_breaker)


@dataclass
class MultiDbConfig:
    """
    Configuration class for managing multiple database connections in a resilient and fail-safe manner.

    Attributes:
        databases_config: A list of database configurations.
        client_class: The client class used to manage database connections.
        command_retry: Retry strategy for executing database commands.
        failure_detectors: Optional list of additional failure detectors for monitoring database failures.
        min_num_failures: Minimal count of failures required for failover
        failure_rate_threshold: Percentage of failures required for failover
        failures_detection_window: Time interval for tracking database failures.
        health_checks: Optional list of additional health checks performed on databases.
        health_check_interval: Time interval for executing health checks.
        health_check_probes: Number of attempts to evaluate the health of a database.
        health_check_delay: Delay between health check attempts.
        health_check_timeout: Timeout for the full health check operation (including all probes).
        health_check_policy: Policy for determining database health based on health checks.
        failover_strategy: Optional strategy for handling database failover scenarios.
        failover_attempts: Number of retries allowed for failover operations.
        failover_delay: Delay between failover attempts.
        auto_fallback_interval: Time interval to trigger automatic fallback.
        event_dispatcher: Interface for dispatching events related to database operations.
        initial_health_check_policy: Defines the policy used to determine whether the databases setup is
                                     healthy during the initial health check.

    Methods:
        databases:
            Retrieves a collection of database clients managed by weighted configurations.
            Initializes database clients based on the provided configuration and removes
            redundant retry objects for lower-level clients to rely on global retry logic.

        default_failure_detectors:
            Returns the default list of failure detectors used to monitor database failures.

        default_health_checks:
            Returns the default list of health checks used to monitor database health
            with specific retry and backoff strategies.

        default_failover_strategy:
            Provides the default failover strategy used for handling failover scenarios
            with defined retry and backoff configurations.
    """

    databases_config: List[DatabaseConfig]
    client_class: Type[Union[Redis, RedisCluster]] = Redis
    command_retry: Retry = Retry(
        backoff=ExponentialWithJitterBackoff(base=1, cap=10), retries=3
    )
    failure_detectors: Optional[List[FailureDetector]] = None
    min_num_failures: int = DEFAULT_MIN_NUM_FAILURES
    failure_rate_threshold: float = DEFAULT_FAILURE_RATE_THRESHOLD
    failures_detection_window: float = DEFAULT_FAILURES_DETECTION_WINDOW
    health_checks: Optional[List[HealthCheck]] = None
    health_check_interval: float = DEFAULT_HEALTH_CHECK_INTERVAL
    health_check_probes: int = DEFAULT_HEALTH_CHECK_PROBES
    health_check_delay: float = DEFAULT_HEALTH_CHECK_DELAY
    health_check_timeout: float = DEFAULT_HEALTH_CHECK_TIMEOUT
    health_check_policy: HealthCheckPolicies = DEFAULT_HEALTH_CHECK_POLICY
    failover_strategy: Optional[FailoverStrategy] = None
    failover_attempts: int = DEFAULT_FAILOVER_ATTEMPTS
    failover_delay: float = DEFAULT_FAILOVER_DELAY
    auto_fallback_interval: float = DEFAULT_AUTO_FALLBACK_INTERVAL
    event_dispatcher: EventDispatcherInterface = field(
        default_factory=default_event_dispatcher
    )
    initial_health_check_policy: InitialHealthCheck = InitialHealthCheck.ALL_AVAILABLE

    def databases(self) -> Databases:
        databases = WeightedList()

        for database_config in self.databases_config:
            # The retry object is not used in the lower level clients, so we can safely remove it.
            # We rely on command_retry in terms of global retries.
            database_config.client_kwargs["retry"] = Retry(
                retries=0, backoff=NoBackoff()
            )

            # Maintenance notifications are disabled by default in underlying clients,
            # but user can override this by providing their own config.
            if "maint_notifications_config" not in database_config.client_kwargs:
                database_config.client_kwargs["maint_notifications_config"] = (
                    MaintNotificationsConfig(enabled=False)
                )

            if database_config.from_url:
                client = self.client_class.from_url(
                    database_config.from_url, **database_config.client_kwargs
                )
            elif database_config.from_pool:
                database_config.from_pool.set_retry(
                    Retry(retries=0, backoff=NoBackoff())
                )
                client = self.client_class.from_pool(
                    connection_pool=database_config.from_pool
                )
            else:
                client = self.client_class(**database_config.client_kwargs)

            circuit = (
                database_config.default_circuit_breaker()
                if database_config.circuit is None
                else database_config.circuit
            )
            databases.add(
                Database(
                    client=client,
                    circuit=circuit,
                    weight=database_config.weight,
                    health_check_url=database_config.health_check_url,
                ),
                database_config.weight,
            )

        return databases

    def default_failure_detectors(self) -> List[FailureDetector]:
        return [
            CommandFailureDetector(
                min_num_failures=self.min_num_failures,
                failure_rate_threshold=self.failure_rate_threshold,
                failure_detection_window=self.failures_detection_window,
            ),
        ]

    def default_health_checks(self) -> List[HealthCheck]:
        return [
            PingHealthCheck(
                health_check_probes=self.health_check_probes,
                health_check_delay=self.health_check_delay,
                health_check_timeout=self.health_check_timeout,
            ),
        ]

    def default_failover_strategy(self) -> FailoverStrategy:
        return WeightBasedFailoverStrategy()
