import time
import krpc
import math

# ================= 配置参数 =================
TARGET_LANDING_VELOCITY = -2.0  # 目标着陆速度 (m/s)
SAFETY_MARGIN = 80.0            # 安全余量 (m)
MIN_TWR_FOR_BURN = 1.1          # 开始减速的最小TWR

# PID 控制器参数
SPEED_KP = 0.15
SPEED_KI = 0.05
SPEED_KD = 0.1
INTEGRAL_LIMIT = 0.5

# 节流阀滤波
ALPHA = 0.3  # 平滑系数

DT = 0.1     # 控制周期

# 预测参数
PREDICTION_STEPS = 50  # 预测步数
# ===========================================

conn = krpc.connect(name='Dynamic Landing V2')
if not conn.space_center:
    print("No active vessel found.")
    exit()
vessel = conn.space_center.active_vessel

class PID:
    def __init__(self, kp, ki, kd, integral_limit=1.0):
        self.kp, self.ki, self.kd = kp, ki, kd
        self.prev_error = 0
        self.integral = 0
        self.integral_limit = integral_limit

    def update(self, error, dt):
        self.integral += error * dt
        self.integral = max(-self.integral_limit, min(self.integral_limit, self.integral))
        derivative = (error - self.prev_error) / dt
        self.prev_error = error
        return (self.kp * error) + (self.ki * self.integral) + (self.kd * derivative)

class AdvancedRocketPerformance:
    """高级火箭性能计算器 - 考虑燃料消耗和TWR变化"""
    
    def __init__(self, vessel):
        self.vessel = vessel
        self.body = vessel.orbit.body
        self.g = self.body.surface_gravity  # 重力加速度 (m/s²)
        
        # 获取发动机参数
        self.engines = vessel.parts.engines
        self.max_thrust = sum(e.max_thrust for e in self.engines if e.active)
        
        # 计算燃料消耗率 (kg/s) - 假设所有发动机都激活
        self.fuel_flow_rate = 0.0
        for engine in self.engines:
            if engine.active:
                # 获取发动机的比冲和推力
                # fuel_flow = thrust / (Isp * g0)
                # g0 = 9.80665 m/s²
                isp = engine.vacuum_specific_impulse
                self.fuel_flow_rate += engine.max_thrust / (isp * 9.80665)
        
    def get_mass(self):
        """获取当前质量 (kg)"""
        return self.vessel.mass
    
    def get_fuel_mass(self):
        """获取燃料质量 (kg)"""
        fuel_mass = 0.0
        for part in self.vessel.parts.all:
            for resource in part.resources:
                if resource.name in ['LiquidFuel', 'Oxidizer', 'MonoPropellant']:
                    fuel_mass += resource.amount * resource.density
        return fuel_mass
    
    def get_dry_mass(self):
        """获取干重 (kg)"""
        return self.get_mass() - self.get_fuel_mass()
    
    def get_twr(self, mass=None):
        """
        计算推重比 (Thrust-to-Weight Ratio)
        
        Args:
            mass: 可选，指定质量计算TWR。如果为None，使用当前质量
        """
        if mass is None:
            mass = self.get_mass()
        if mass == 0:
            return 0.0
        return self.max_thrust / (mass * self.g)
    
    def get_max_deceleration(self, mass=None):
        """
        计算最大减速度 (m/s²)
        
        Args:
            mass: 可选，指定质量计算减速度。如果为None，使用当前质量
        """
        twr = self.get_twr(mass)
        # 有效减速度 = 推重比 * g - g = g * (TWR - 1)
        return self.g * (twr - 1) if twr > 1 else 0.0
    
    def predict_mass_after_burn(self, burn_time, throttle=1.0):
        """
        预测燃烧指定时间后的质量
        
        Args:
            burn_time: 燃烧时间 (s)
            throttle: 节流阀 (0-1)
            
        Returns:
            预测的质量 (kg)
        """
        fuel_consumed = self.fuel_flow_rate * throttle * burn_time
        current_fuel = self.get_fuel_mass()
        remaining_fuel = max(0, current_fuel - fuel_consumed)
        return self.get_dry_mass() + remaining_fuel
    
    def calculate_deceleration_distance_advanced(self, current_velocity, target_velocity):
        """
        计算从当前速度减速到目标速度需要的距离（考虑TWR变化）
        
        使用数值积分方法，考虑燃料消耗导致的TWR增加
        
        Args:
            current_velocity: 当前垂直速度 (m/s, 负值表示下降)
            target_velocity: 目标速度 (m/s, 负值表示下降)
            
        Returns:
            需要的减速距离 (m)
        """
        # 检查当前是否能够减速
        current_twr = self.get_twr()
        if current_twr <= MIN_TWR_FOR_BURN:
            return float('inf')  # 无法减速
        
        # 使用数值积分计算减速距离
        # 将减速过程分成多个小段，每段使用该段的平均TWR
        
        total_distance = 0.0
        v = current_velocity
        dt = 0.1  # 时间步长 (s)
        
        while v < target_velocity:
            # 预测当前速度下燃烧dt时间后的质量
            # 假设平均节流阀为0.8（保守估计）
            predicted_mass = self.predict_mass_after_burn(dt, throttle=0.8)
            
            # 计算该段的平均减速度
            avg_decel = self.get_max_deceleration(predicted_mass)
            
            if avg_decel <= 0:
                return float('inf')  # 无法继续减速
            
            # 计算该段的速度变化和距离
            dv = avg_decel * dt
            new_v = v + dv
            
            # 使用平均速度计算距离
            avg_v = (v + new_v) / 2
            distance = abs(avg_v * dt)
            
            total_distance += distance
            v = new_v
            
            # 防止无限循环
            if total_distance > 100000:  # 超过100km认为不合理
                return float('inf')
        
        return total_distance
    
    def should_start_deceleration(self, altitude, current_velocity, target_velocity):
        """
        判断是否应该开始减速（高级版）
        
        Args:
            altitude: 当前高度 (m)
            current_velocity: 当前垂直速度 (m/s)
            target_velocity: 目标速度 (m/s)
            
        Returns:
            (should_burn, required_distance, trigger_altitude, current_twr)
        """
        # 计算需要的减速距离（考虑TWR变化）
        required_distance = self.calculate_deceleration_distance_advanced(
            current_velocity, target_velocity
        )
        
        # 添加安全余量
        trigger_altitude = required_distance + SAFETY_MARGIN
        
        # 检查TWR是否足够
        current_twr = self.get_twr()
        
        should_burn = (altitude <= trigger_altitude) and (current_twr >= MIN_TWR_FOR_BURN)
        
        return should_burn, required_distance, trigger_altitude, current_twr

# 初始化控制器
speed_pid = PID(SPEED_KP, SPEED_KI, SPEED_KD, INTEGRAL_LIMIT)
performance = AdvancedRocketPerformance(vessel)

# 节流阀平滑处理
last_throttle = 0.0

# 姿态控制设置
vessel.auto_pilot.engage()
vessel.auto_pilot.reference_frame = vessel.surface_velocity_reference_frame
vessel.auto_pilot.target_direction = (0, -1, 0)  # 始终指向速度反方向

print("高级动态着陆程序启动...")
print(f"目标着陆速度: {TARGET_LANDING_VELOCITY} m/s")
print(f"安全余量: {SAFETY_MARGIN} m")
print(f"最大推力: {performance.max_thrust:.0f} N")
print(f"燃料消耗率: {performance.fuel_flow_rate:.2f} kg/s")

# 自检
vessel.control.throttle = 0.99
time.sleep(0.1)
vessel.control.throttle = 0

burn_started = False
last_status = ""

while True:
    # 1. 获取飞行数据
    flight = vessel.flight(vessel.orbit.body.reference_frame)
    alt = max(0, flight.surface_altitude - 9.50)  # 考虑雷达高度计偏移
    vel = flight.vertical_speed
    
    # 2. 获取火箭性能
    mass = performance.get_mass()
    fuel_mass = performance.get_fuel_mass()
    dry_mass = performance.get_dry_mass()
    thrust = performance.max_thrust
    twr = performance.get_twr()
    max_decel = performance.get_max_deceleration()
    
    # 3. 判断是否应该开始减速
    should_burn, required_dist, trigger_alt, current_twr = performance.should_start_deceleration(
        alt, vel, TARGET_LANDING_VELOCITY
    )
    
    # 4. 姿态控制逻辑
    if alt < 30 or abs(vel) < 0.5:
        # 离地很近或速度很慢时，强制垂直向上
        vessel.auto_pilot.reference_frame = vessel.surface_reference_frame
        vessel.auto_pilot.target_direction = (1, 0, 0)  # 向天
    else:
        # 正常减速阶段，锁定速度反方向
        vessel.auto_pilot.reference_frame = vessel.surface_velocity_reference_frame
        vessel.auto_pilot.target_direction = (0, -1, 0)
    
    # 5. 刹车控制
    if alt < 10000 and thrust > 0 and not vessel.control.brakes:
        vessel.control.brakes = True
    
    if alt < 30 and vessel.control.brakes:
        vessel.control.brakes = False
    
    # 6. 自动部署脚架
    if alt < 500:
        vessel.control.gear = True
    
    # 7. 动态速度规划
    if should_burn:
        burn_started = True
        target_vel = TARGET_LANDING_VELOCITY
    elif not burn_started:
        # 还没开始减速，使用自由落体或微调
        target_vel = -10000.0  # 允许快速下降
    else:
        # 已经开始减速，保持目标着陆速度
        target_vel = TARGET_LANDING_VELOCITY
    
    # 8. 触地检测
    if alt < 1.0 and abs(vel) < 0.5:
        vessel.control.throttle = 0
        vessel.control.sas = True
        print("已着陆！")
        break
    
    # 9. PID 计算
    error = target_vel - vel
    raw_throttle = speed_pid.update(error, DT)
    
    # 10. 节流阀滤波
    throttle = (ALPHA * raw_throttle) + ((1.0 - ALPHA) * last_throttle)
    throttle = max(0.0, min(1.0, throttle))
    last_throttle = throttle
    
    # 11. 执行控制
    vessel.control.throttle = throttle
    
    # 12. 信息输出
    if burn_started:
        status = f"减速中 | TWR: {twr:.2f} | 燃料: {fuel_mass:.0f}kg"
    else:
        status = f"自由落体 | 触发高度: {trigger_alt:.0f}m"
    
    print(f"高度: {alt:6.1f}m | 速度: {vel:6.1f}m/s | 目标速: {target_vel:6.1f}m/s | "
          f"节流阀: {throttle:.2f} | 质量: {mass:.0f}kg | 减速距离: {required_dist:6.1f}m | "
          f"{status}")
    
    time.sleep(DT)