#pragma once

#include <cmath>

namespace extra2d {

// ---------------------------------------------------------------------------
// 常量
// ---------------------------------------------------------------------------
constexpr float PI_F = 3.14159265358979323846f;
constexpr float DEG_TO_RAD = PI_F / 180.0f;
constexpr float RAD_TO_DEG = 180.0f / PI_F;

// ---------------------------------------------------------------------------
// 2D 向量
// ---------------------------------------------------------------------------
struct Vec2 {
  float x = 0.0f;
  float y = 0.0f;

  constexpr Vec2() = default;
  constexpr Vec2(float x, float y) : x(x), y(y) {}

  // 基础运算
  Vec2 operator+(const Vec2 &v) const { return {x + v.x, y + v.y}; }
  Vec2 operator-(const Vec2 &v) const { return {x - v.x, y - v.y}; }
  Vec2 operator*(float s) const { return {x * s, y * s}; }
  Vec2 operator/(float s) const { return {x / s, y / s}; }
  Vec2 operator-() const { return {-x, -y}; }

  Vec2 &operator+=(const Vec2 &v) {
    x += v.x;
    y += v.y;
    return *this;
  }
  Vec2 &operator-=(const Vec2 &v) {
    x -= v.x;
    y -= v.y;
    return *this;
  }
  Vec2 &operator*=(float s) {
    x *= s;
    y *= s;
    return *this;
  }
  Vec2 &operator/=(float s) {
    x /= s;
    y /= s;
    return *this;
  }

  bool operator==(const Vec2 &v) const { return x == v.x && y == v.y; }
  bool operator!=(const Vec2 &v) const { return !(*this == v); }

  // 向量运算
  float length() const { return std::sqrt(x * x + y * y); }
  float lengthSquared() const { return x * x + y * y; }

  Vec2 normalized() const {
    float len = length();
    if (len > 0.0f)
      return {x / len, y / len};
    return {0.0f, 0.0f};
  }

  float dot(const Vec2 &v) const { return x * v.x + y * v.y; }
  float cross(const Vec2 &v) const { return x * v.y - y * v.x; }

  float distance(const Vec2 &v) const { return (*this - v).length(); }
  float angle() const { return std::atan2(y, x) * RAD_TO_DEG; }

  static Vec2 lerp(const Vec2 &a, const Vec2 &b, float t) {
    return a + (b - a) * t;
  }

  static constexpr Vec2 Zero() { return {0.0f, 0.0f}; }
  static constexpr Vec2 One() { return {1.0f, 1.0f}; }
  static constexpr Vec2 UnitX() { return {1.0f, 0.0f}; }
  static constexpr Vec2 UnitY() { return {0.0f, 1.0f}; }
};

inline Vec2 operator*(float s, const Vec2 &v) { return v * s; }

using Point = Vec2;

} // namespace extra2d