using System;

namespace XP.Common.Controls
{
    /// <summary>
    /// 虚拟摇杆核心计算逻辑（纯函数，无副作用）| Virtual joystick core calculation logic (pure functions, no side effects)
    /// </summary>
    public static class JoystickCalculator
    {
        /// <summary>
        /// 将位移限制在圆形区域内 | Clamp displacement within circular radius
        /// </summary>
        /// <param name="dx">X 轴偏移量 | X axis displacement</param>
        /// <param name="dy">Y 轴偏移量 | Y axis displacement</param>
        /// <param name="radius">最大半径（必须大于 0）| Maximum radius (must be greater than 0)</param>
        /// <returns>限制后的 (clampedDx, clampedDy) 元组 | Clamped (clampedDx, clampedDy) tuple</returns>
        public static (double clampedDx, double clampedDy) ClampToRadius(double dx, double dy, double radius)
        {
            if (radius <= 0)
                throw new ArgumentOutOfRangeException(nameof(radius), "半径必须大于 0 | Radius must be greater than 0");

            var distance = Math.Sqrt(dx * dx + dy * dy);

            // 如果距离在半径内，直接返回原值 | If within radius, return original values
            if (distance <= radius)
                return (dx, dy);

            // 归一化到半径上 | Normalize to radius boundary
            var scale = radius / distance;
            return (dx * scale, dy * scale);
        }

        /// <summary>
        /// 计算归一化输出，包含死区映射 | Calculate normalized output with dead zone mapping
        /// </summary>
        /// <param name="dx">X 轴偏移量 | X axis displacement</param>
        /// <param name="dy">Y 轴偏移量 | Y axis displacement</param>
        /// <param name="radius">最大半径（必须大于 0）| Maximum radius (must be greater than 0)</param>
        /// <param name="deadZone">死区比例，范围 [0.0, 1.0) | Dead zone ratio, range [0.0, 1.0)</param>
        /// <param name="mode">摇杆模式 | Joystick mode</param>
        /// <returns>归一化输出 (outputX, outputY) 元组，范围 [-1.0, 1.0] | Normalized output tuple, range [-1.0, 1.0]</returns>
        public static (double outputX, double outputY) CalculateOutput(
            double dx, double dy, double radius, double deadZone, JoystickMode mode)
        {
            if (radius <= 0)
                throw new ArgumentOutOfRangeException(nameof(radius), "半径必须大于 0 | Radius must be greater than 0");

            if (deadZone < 0.0 || deadZone >= 1.0)
                throw new ArgumentOutOfRangeException(nameof(deadZone), "死区比例必须在 [0.0, 1.0) 范围内 | Dead zone must be in range [0.0, 1.0)");

            // 步骤 1-2：将位移限制在半径内 | Step 1-2: Clamp displacement within radius
            var (clampedDx, clampedDy) = ClampToRadius(dx, dy, radius);

            // 步骤 3：计算比例值 | Step 3: Calculate ratio
            var ratioX = clampedDx / radius;
            var ratioY = clampedDy / radius;

            // 步骤 4：对每个轴分别应用死区 | Step 4: Apply dead zone to each axis independently
            var outputX = ApplyDeadZone(ratioX, deadZone);
            var outputY = ApplyDeadZone(ratioY, deadZone);

            // 步骤 5：SingleAxisY 模式下强制 OutputX = 0 | Step 5: Force OutputX = 0 in SingleAxisY mode
            if (mode == JoystickMode.SingleAxisY)
                outputX = 0.0;

            return (outputX, outputY);
        }

        /// <summary>
        /// 对单轴比例值应用死区映射 | Apply dead zone mapping to a single axis ratio
        /// </summary>
        /// <param name="ratio">轴比例值，范围 [-1.0, 1.0] | Axis ratio, range [-1.0, 1.0]</param>
        /// <param name="deadZone">死区比例，范围 [0.0, 1.0) | Dead zone ratio, range [0.0, 1.0)</param>
        /// <returns>死区映射后的输出值 | Output value after dead zone mapping</returns>
        internal static double ApplyDeadZone(double ratio, double deadZone)
        {
            var absRatio = Math.Abs(ratio);

            // 在死区内，输出为 0 | Within dead zone, output is 0
            if (absRatio < deadZone)
                return 0.0;

            // 死区外线性映射：sign(ratio) × (absRatio - D) / (1 - D) | Linear mapping outside dead zone
            return Math.Sign(ratio) * (absRatio - deadZone) / (1.0 - deadZone);
        }
    }
}