"""
Agent 调度器服务
实现多种调度策略
"""
from typing import List, Optional
from app.models import Agent


class BaseScheduler:
    """调度器基类"""
    
    def select_agent(self, agents: List[Agent], context: dict = None) -> Optional[Agent]:
        """选择 Agent，子类实现"""
        raise NotImplementedError


class RoundRobinScheduler(BaseScheduler):
    """轮询调度器"""
    
    def __init__(self):
        self._index = 0
    
    def select_agent(self, agents: List[Agent], context: dict = None) -> Optional[Agent]:
        if not agents:
            return None
        
        # 只选择在线的 Agent
        online_agents = [a for a in agents if a.status == 'online']
        if not online_agents:
            return None
        
        # 轮询选择
        agent = online_agents[self._index % len(online_agents)]
        self._index += 1
        return agent


class WeightedRoundRobinScheduler(BaseScheduler):
    """加权轮询调度器（默认）"""
    
    def __init__(self):
        self._index = 0
        self._weights = {}
    
    def select_agent(self, agents: List[Agent], context: dict = None) -> Optional[Agent]:
        if not agents:
            return None
        
        # 只选择在线的 Agent
        online_agents = [a for a in agents if a.status == 'online']
        if not online_agents:
            return None
        
        # 计算总权重
        total_weight = sum(a.weight for a in online_agents)
        if total_weight == 0:
            return online_agents[0] if online_agents else None
        
        # 加权轮询
        current_weight = self._index % total_weight
        cumulative = 0
        
        for agent in online_agents:
            cumulative += agent.weight
            if current_weight < cumulative:
                self._index += 1
                return agent
        
        return online_agents[-1]


class LeastConnectionsScheduler(BaseScheduler):
    """最少连接调度器"""
    
    def select_agent(self, agents: List[Agent], context: dict = None) -> Optional[Agent]:
        if not agents:
            return None
        
        # 只选择在线且未达连接上限的 Agent
        available_agents = [
            a for a in agents 
            if a.status == 'online' and a.current_sessions < a.connection_limit
        ]
        
        if not available_agents:
            return None
        
        # 选择连接数最少的
        return min(available_agents, key=lambda a: a.current_sessions)


class LeastResponseTimeScheduler(BaseScheduler):
    """最快响应调度器（基于最后心跳时间）"""
    
    def select_agent(self, agents: List[Agent], context: dict = None) -> Optional[Agent]:
        if not agents:
            return None
        
        # 只选择在线的 Agent
        online_agents = [a for a in agents if a.status == 'online']
        if not online_agents:
            return None
        
        # 选择最近有心跳的（响应快的）
        from datetime import datetime
        now = datetime.utcnow()
        
        def response_score(agent):
            if not agent.last_heartbeat:
                return float('inf')
            # 最近心跳 = 分数低 = 优先选择
            return (now - agent.last_heartbeat).total_seconds()
        
        return min(online_agents, key=response_score)


class CapabilityMatchScheduler(BaseScheduler):
    """能力匹配调度器"""
    
    def select_agent(self, agents: List[Agent], context: dict = None) -> Optional[Agent]:
        if not agents or not context:
            return None
        
        required_capabilities = context.get('capabilities', [])
        if not required_capabilities:
            # 没有特殊要求，使用加权轮询
            return WeightedRoundRobinScheduler().select_agent(agents, context)
        
        # 只选择在线且有对应能力的 Agent
        matching_agents = []
        for agent in agents:
            if agent.status != 'online':
                continue
            
            agent_caps = agent.capabilities or []
            # 检查是否具备所有必需能力
            if all(cap in agent_caps for cap in required_capabilities):
                matching_agents.append(agent)
        
        if not matching_agents:
            # 没有匹配的，回退到加权轮询
            return WeightedRoundRobinScheduler().select_agent(agents, context)
        
        # 在匹配的 Agent 中使用加权轮询
        return WeightedRoundRobinScheduler().select_agent(matching_agents, context)


class AgentScheduler:
    """Agent 调度器工厂"""
    
    STRATEGIES = {
        'round_robin': RoundRobinScheduler,
        'weighted_round_robin': WeightedRoundRobinScheduler,
        'least_connections': LeastConnectionsScheduler,
        'least_response_time': LeastResponseTimeScheduler,
        'capability_match': CapabilityMatchScheduler,
    }
    
    def __init__(self, strategy: str = 'weighted_round_robin'):
        self._strategy_name = strategy
        self._scheduler = self.STRATEGIES.get(strategy, WeightedRoundRobinScheduler)()
    
    def select_agent(self, agents: List[Agent], context: dict = None) -> Optional[Agent]:
        """选择 Agent"""
        return self._scheduler.select_agent(agents, context)
    
    def get_strategy(self) -> str:
        """获取当前策略"""
        return self._strategy_name
    
    @classmethod
    def get_available_strategies(cls) -> list:
        """获取可用策略列表"""
        return list(cls.STRATEGIES.keys())