/// @file
/// @brief TriangleMesh: class definition and member function declarations

#pragma once

// hpp
#include <array>      // std::array
#include <tuple>      // std::tuple
#include <vector>     // std::vector
#include <unordered_set> // std::unordered_set
#include <filesystem>    // std::filesystem

namespace ex5 {

///@brief Two-dimensional triangle mesh
class TriangleMesh {

public:
  ///@brief Vertex coordinate
  using Vec2d = std::array<double, 2>;

  ///@brief Index triplet
  using Vec3i = std::array<size_t, 3>;

  ///@brief Axis-aligned bounding box described using the bottom left and upper right coordinate
  using BBox = std::tuple<Vec2d, Vec2d>;

private:
  std::vector<Vec2d> vertices;  ///< sequence of vertices
  std::vector<Vec3i> triangles; ///< sequence of index triplets each indexing the three corner vertices of a triangle

public:
  /// @brief Generates a regular triangular mesh pattern inside an axis-aligned bounding box
  /// @param box Axis-aligned bounding box of the generated mesh
  /// @param h Lower bound for the edge length of the generate triangles
  TriangleMesh(BBox box, double h);

  /// @brief Calculates the current axis-aligned bounding box
  /// @return Bounding box of all triangles/vertices in the mesh
  BBox bbox() const;

  /// @brief Read-only access to the vertices of the mesh
  /// @return Reference to the underlying sequence of vertices
  const std::vector<Vec2d>& getVertices() const;

  /// @brief Read-only access to triangles of the mesh
  /// @return Reference to the underlying sequence of triangles
  const std::vector<Vec3i>& getTriangles() const;

  /// @brief Prints the sequences of vertices and triangles to the console
  void print() const;

  /// @brief Generate SVG image
  /// @param filepath Filename for the generated output
  BBox save(std::filesystem::path filepath) const;

  /// @brief Evaluates the invariants of the class
  /// @return false, if any of the invariants is violated, true otherwise
  /// Invariants:
  ///   - each triangle references valid indices
  ///   - each triangle references three distinct corners
  ///   - edges are not occupied more than twice (no hidden edges)
  ///   - no unreferenced vertices are present
  bool check_invariants() const;

  /// @brief Removes a set of vertices from the mesh:
  ///   - all triangles connected to the removed vertices are removed
  ///   - all unused vertices potentially originating from the triangle removal are removed 
  /// @param indices Vertex indices to be removed
  /// @return Total number of removed vertices and total number of removed triangles
  std::tuple<size_t, size_t> remove_vertices(std::unordered_set<size_t> indices);
};

} // namespace mesh