#include "Player.hpp"
#include "../Input.hpp"
#include <unordered_set>

namespace MC::Entities {

void Player::update(Time const& time, Input const& input, GFX::Camera& camera, World::World& world) {
    auto const input_direction = directional_input(input);

    auto destination = movement(time, input_direction);

    if (can_collide()) {
        if (m_velocity.y() < 0.0)
            destination = rescue_from_void_on_new_chunk(time, world, destination);

        auto const [position, blocked_axes] = process_collisions(world, m_transform.position(), destination);

        destination = position;
        m_on_ground = blocked_axes.y().negative;

        for (UInt axis = 0; axis < 3; axis++) {
            if (blocked_axes[axis].positive) m_velocity[axis] = std::min(m_velocity[axis], 0.0);
            if (blocked_axes[axis].negative) m_velocity[axis] = std::max(m_velocity[axis], 0.0);
        }
    }

    move_to(destination);
    rotate(rotational_input(input));

    update_camera_position(camera);

    update_targeted_block(world);
    actions(input, world);
}

void Player::render(GFX::Actions& actions) {
    if (m_targeted_block.has_value()) {
        auto position = Vec3(m_targeted_block->position);
        actions.add({
            .mesh = &m_outline_mesh,
            .program = GFX::Resources::Program::BlockOutline,
            .transform = Transform{position},
            // TODO: These are very thin lines, do we have any better easy options?
            .draw_mode = GFX::DrawMode::Lines,
        });
    }
}

void Player::move(Position::WorldOffset by) {
    m_transform.position() += by;
}

void Player::rotate(Rotation by) {
    m_transform.rotation() += by;
    m_transform.rotation().pitch() = std::clamp(m_transform.rotation().pitch(), -89.0, 89.0);
}

void Player::move_to(Position::World to) {
    m_transform.position() = to;
}

void Player::rotate_to(Rotation to) {
    m_transform.rotation() = to;
}

AABB Player::bounds() const {
    return bounding_box_for_position(m_transform.position());
}

Bool Player::can_collide() const {
    // Collisions are always on, except when in noclip mode.
    return m_movement != MovementMode::NoClip;
}

Position::World Player::movement(Time const& time, Vec3 input_direction) {
    switch (m_movement) {
        case MovementMode::Walking: m_velocity = walking_velocity(time, input_direction); break;
        case MovementMode::Flying: m_velocity = flying_velocity(time, input_direction); break;
        case MovementMode::NoClip: m_velocity = noclip_velocity(time, input_direction); break;
    }

    return m_transform.position() + m_velocity;
}

Vec3 Player::walking_velocity(Time const& time, Vec3 input_direction) {
    constexpr auto base_move_speed = 8.0;
    constexpr auto initial_jump_velocity = 0.16;
    constexpr auto gravity = 0.6;

    auto walking_direction = m_transform.right() * input_direction.x() + m_transform.forward() * input_direction.z();
    walking_direction.y() = 0;
    if (!walking_direction.is_zero()) walking_direction = walking_direction.normalize();

    auto const walking_velocity = walking_direction * base_move_speed * time.delta();

    auto vertical_velocity = 0.0;
    if (m_on_ground && input_direction.y() > 0.5) {
        vertical_velocity = initial_jump_velocity;
        m_on_ground = false;
    } else {
        // TODO: This integration depends on frame delta.
        vertical_velocity = m_velocity.y() - gravity * time.delta();
    }

    return {
        walking_velocity.x(),
        vertical_velocity,
        walking_velocity.z(),
    };
}

Vec3 Player::flying_velocity(Time const& time, Vec3 input_direction) const {
    constexpr auto base_move_speed = 10.0;

    auto flying_direction = m_transform.right() * input_direction.x() + m_transform.forward() * input_direction.z();
    flying_direction.y() = 0;
    if (!flying_direction.is_zero()) flying_direction = flying_direction.normalize();

    auto const flying_velocity = flying_direction * base_move_speed * time.delta();
    auto vertical_velocity = input_direction.y() * base_move_speed * time.delta();

    return {
        flying_velocity.x(),
        vertical_velocity,
        flying_velocity.z(),
    };
}

Vec3 Player::noclip_velocity(Time const& time, Vec3 input_direction) const {
    constexpr auto base_move_speed = 10.0;

    auto const [x, y, z] = input_direction.elements;
    auto const direction = m_transform.right() * x + Vec3(0, y, 0) + m_transform.forward() * z;

    return direction * base_move_speed * time.delta();
}

void Player::update_targeted_block(World::World& world) {
    auto constexpr max_block_reach = 4.0;

    auto const look_transform = camera_transform();
    Ray const ray{look_transform.position(), -look_transform.forward()};
    auto const traversal = world.traverse(
        ray,
        [](auto b) { return b.type.is_solid(); },
        max_block_reach
    );

    if (traversal.hit) m_targeted_block = {traversal.block, traversal.normal};
    else m_targeted_block = {};
}

void Player::actions(Input const& input, World::World& world) {
    // Breaking and placing blocks.
    auto left_click = input.pressed(Mouse::Left);
    auto right_click = input.pressed(Mouse::Right);
    if (left_click || right_click) {
        if (m_targeted_block.has_value()) {
            auto targeted_block = m_targeted_block.value();
            if (left_click) {
                world.break_block(targeted_block.position);
            } else {
                auto const new_block = Position::BlockWorld(targeted_block.position + targeted_block.normal);
                auto const current_box = bounding_box_for_position(m_transform.position());
                auto const block_box = World::Chunk::block_bounds(new_block);

                if (!current_box.collides(block_box)) // Don't place blocks inside the player.
                    world.set_block(new_block, World::BlockType::Stone);
            }
        }
    }

    // Toggle movement modes.
    if (input.double_pressed(Key::Space)) {
        if (m_movement == MovementMode::Walking) m_movement = MovementMode::Flying;
        else if (m_movement == MovementMode::Flying) m_movement = MovementMode::Walking;
    }

    if (input.pressed(Key::N)) {
        if (m_movement == MovementMode::NoClip) m_movement = MovementMode::Walking;
        else m_movement = MovementMode::NoClip;
    }
}

#define STUCK_THRESHOLD 100

Player::ProcessCollisionsResult Player::process_collisions(World::World& world, Position::World from, Position::World to) {
    if (from.mostly_equal(to)) return {to, {}};

    auto const current_box = bounding_box_for_position(from);

    // All the blocks we could theoretically collide with.
    // NOTE: It isn't updated as new responses are applied,
    // as that would be (currently) too expensive.
    // At very high speeds, this may lead to phasing through blocks.
    auto const collision_domain = terrain_collision_domain(from, to, world);

    // Sort the responses first by the magnitude of the velocity until the collision,
    // and then by the distance from the entity, so that we slide along the closest block.
    // If we apply a response, we need to check again for collisions,
    // since we might have slid into another block. (up to STUCK_THRESHOLD times)
    // If there are no more responses, we have no collisions,
    // and the player can move freely to the proposed position.

    Vector<3, BlockedAxis> blocked_axes;

    struct Response {
        AABB::CollisionResponse response;
        Real distance_from_entity_squared;
        Real magnitude_squared;
    };
    std::vector<Response> responses;
    for (UInt stuck = 0; stuck < STUCK_THRESHOLD; stuck++) {
        auto const v = to - from;

        for (auto possible_collision : collision_domain) {
            auto const response = current_box.collision_response(v, possible_collision);
            auto const total_velocity = response.v_to_collision + response.v_slide;
            if (!total_velocity.mostly_equal(v) && !total_velocity.is_nan()) {
                responses.push_back({
                    response,
                    possible_collision.center().distance_squared(from),
                    response.v_to_collision.magnitude_squared(),
                });
            }
        }

        if (responses.empty()) return {to, blocked_axes};

        std::sort(responses.begin(), responses.end(), [=](const Response& a, const Response& b) -> bool {
            return std::tie(a.magnitude_squared, a.distance_from_entity_squared) < std::tie(b.magnitude_squared, b.distance_from_entity_squared);
        });

        // TODO: This applies the entire response, even though ideally we'd apply it in two parts,
        // since technically the total velocity is a diagonal of the two components.
        // This should only be a marginal issue, though.
        auto const response = responses[0].response;
        to = from + response.v_to_collision + response.v_slide;

        auto check_axis = [&](Real axis_normal, BlockedAxis& axis) -> Bool {
            if (axis_normal < -0.5) { axis.negative = true; return true; }
            if (axis_normal > 0.5) { axis.positive = true; return true; }
            return false;
        };

        check_axis(response.normal.x(), blocked_axes.x()) ||
            check_axis(response.normal.y(), blocked_axes.y()) ||
            check_axis(response.normal.z(), blocked_axes.z());

        responses.clear();
    }

    // We got stuck, don't move.
    // Also, if we're stuck, we're also presumably touching the ground on any axis.
    return {from, {BlockedAxis{true, true}, BlockedAxis{true, true}, BlockedAxis{true, true}}};
}

std::vector<AABB> Player::terrain_collision_domain(
    Position::World from, Position::World to,
    World::World& world
) {
    // Make the box a bit bigger so we don't clip through blocks.
    auto domain_box = bounding_box_for_position(from)
        .unite(bounding_box_for_position(to))
        .sum(AABB{{1, 1, 1}});

    std::vector<AABB> colliding_blocks;

    // TODO: Unbind from chunks and loop through all the
    // blocks individually inside domain.
    // This will be more efficient and actually accurate,
    // since right now if you're fast enough you can clip
    // through whole chunks.

    std::unordered_set<World::ChunkIndex> chunks_to_check;
    for (auto corner : domain_box.corners()) {
        chunks_to_check.insert(World::ChunkIndex::from_position(corner));
    }

    for (auto chunk_index : chunks_to_check) {
        auto& chunk = world.chunks().get(chunk_index);
        if (!chunk.chunk.has_value()) continue;
        auto chunk_position = chunk.chunk.value().position();
        chunk.chunk->for_each([&](auto p, auto b) {
            if (!b.type.is_solid()) return Iteration::Continue;
            auto block_bounds = World::Chunk::block_bounds(p).offset(chunk_position);
            if (domain_box.collides(block_bounds)) colliding_blocks.push_back(block_bounds);
            return Iteration::Continue;
        });
    }

    return colliding_blocks;
}

Position::World Player::rescue_from_void_on_new_chunk(Time const& time, World::World& world, Position::World position) {
    auto& chunk = world.chunks().get(World::ChunkIndex::from_position(position));
    // If the chunk was generated at the previous tick, we
    // can rescue the player by moving them to the top of the chunk.
    if (chunk.generated() && chunk.generated_at_tick == time.tick() - 1){
        // TODO: Move to first solid block.
        position.y() = World::Chunk::Height / 2.0;
        m_transform.position() = position;
        m_velocity.y() = 0;
    }
    return position;
}

Transform Player::camera_transform() const {
    auto position = m_transform.position();
    position.y() += 1.5;
    return {
        position,
        m_transform.rotation(),
        m_transform.scale(),
    };
}

void Player::update_camera_position(GFX::Camera& camera) const {
    auto cam_transform = camera_transform();

    camera.set_position(cam_transform.position());
    camera.set_angles(cam_transform.rotation());
}

Vec3 Player::directional_input(Input const& input) {
    Real x = input.held(Key::D) - input.held(Key::A);
    Real y = input.held(Key::Space) - input.held(Key::LeftShift);
    Real z = input.held(Key::S) - input.held(Key::W);

    return {x, y, z};
}

Rotation Player::rotational_input(Input const& input) {
    constexpr auto base_rotation_speed = 0.1f;

    auto r = input.mouse_movement();
    return {r.y() * base_rotation_speed, r.x() * base_rotation_speed, 0.0f};
}

AABB Player::bounding_box_for_position(Position::World position) {
    Vec3 box_start = {
        position.x() - s_bounds.max.x() / 2,
        position.y(),
        position.z() - s_bounds.max.z() / 2,
    };

    return s_bounds.offset(box_start);
}

Position::World Player::position_for_bounding_box(AABB box) {
    auto center = box.center();
    return {center.x(), box.min.y(), center.z()};
}

GFX::Mesh Player::create_outline_cube_mesh() {
    GFX::Util::MeshBuilder<Vector<3, F32>> builder{};
    auto slightly_bigger_block_bounds = AABB{{1, 1, 1}}.sum(AABB{{0.01, 0.01, 0.01}});
    builder.primitive(GFX::Util::Primitives::line_box(slightly_bigger_block_bounds));
    return builder.mesh();
}

}