/*
 * Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
 * Copyright (C) 2016 Furrtek
 *
 * This file is part of PortaPack.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include "ui_focus.hpp"
#include "ui_widget.hpp"

#include <cstdint>

#include <algorithm>
#include <functional>
#include <utility>
#include <vector>

#define pow2(x) ((x) * (x))

namespace ui {

Widget* FocusManager::focus_widget() const {
    return focus_widget_;
}

void FocusManager::set_focus_widget(Widget* const new_focus_widget) {
    // Widget already has focus.
    if (new_focus_widget == focus_widget()) {
        return;
    }

    if (new_focus_widget) {
        if (!new_focus_widget->focusable())
            return;
    }

    // Blur old widget.
    // NB: This will crash if the focus_widget is a destroyed instance.
    if (focus_widget()) {
        focus_widget()->on_blur();
        focus_widget()->set_dirty();
    }

    focus_widget_ = new_focus_widget;

    if (focus_widget()) {
        focus_widget()->on_focus();
        focus_widget()->set_dirty();
    }
}

using test_result_t = std::pair<Widget* const, const uint32_t>;
using test_fn = std::function<test_result_t(Widget* const)>;
using test_collection_t = std::vector<test_result_t>;

/* Walk all visible widgets in hierarchy, collecting those that pass test */
template <typename TestFn>
static void widget_collect_visible(Widget* const w, TestFn test, test_collection_t& collection) {
    for (auto child : w->children()) {
        if (!child->hidden()) {
            const auto result = test(child);
            if (result.first) {
                collection.push_back(result);
            }
            widget_collect_visible(child, test, collection);
        }
    }
}

static int32_t rect_distances(
    const KeyEvent direction,
    const Rect& rect_start,
    const Rect& rect_end) {
    Coord on_axis_max, on_axis_min;

    switch (direction) {
        case KeyEvent::Right:
            on_axis_max = rect_end.left();
            on_axis_min = rect_start.right();
            break;

        case KeyEvent::Left:
            on_axis_max = rect_start.left();
            on_axis_min = rect_end.right();
            break;

        case KeyEvent::Down:
            on_axis_max = rect_end.top();
            on_axis_min = rect_start.bottom();
            break;

        case KeyEvent::Up:
            on_axis_max = rect_start.top();
            on_axis_min = rect_end.bottom();
            break;

        default:
            return -1;
    }

    Coord on_axis_distance = on_axis_max - on_axis_min;
    if (on_axis_distance < 0) {
        return -1;
    }

    Coord perpendicular_axis_start, perpendicular_axis_end;

    switch (direction) {
        case KeyEvent::Right:
        case KeyEvent::Left:
            perpendicular_axis_start = rect_start.center().y();
            perpendicular_axis_end = rect_end.center().y();
            break;

        case KeyEvent::Up:
        case KeyEvent::Down:
            perpendicular_axis_start = rect_start.center().x();
            perpendicular_axis_end = rect_end.center().x();
            break;

        default:
            return -1;
    }

    switch (direction) {
        case KeyEvent::Right:
        case KeyEvent::Left:
            return pow2(std::abs(perpendicular_axis_end - perpendicular_axis_start) + 1) * (on_axis_distance + 1);
            break;

        case KeyEvent::Up:
        case KeyEvent::Down:
            return (std::abs(perpendicular_axis_end - perpendicular_axis_start) + 1) * pow2(on_axis_distance + 1);
            break;

        default:
            return 0;
    }
}

void FocusManager::update(
    Widget* const top_widget,
    const KeyEvent event) {
    if (focus_widget()) {
        const auto focus_screen_rect = focus_widget()->screen_rect();

        const auto test_fn = [&focus_screen_rect, event](ui::Widget* const w) -> test_result_t {
            // if( w->visible() && w->focusable() ) {
            if (w->focusable()) {
                const auto distance = rect_distances(event, focus_screen_rect, w->screen_rect());
                if (distance >= 0) {
                    return {w, distance};
                }
            }

            return {nullptr, 0};
        };

        const auto find_back_fn = [](ui::Widget* const w) -> test_result_t {
            if (w->focusable() && (w->id == -1))
                return {w, 0};
            else
                return {nullptr, 0};
        };

        test_collection_t collection;
        widget_collect_visible(top_widget, test_fn, collection);

        const auto compare_fn = [](const test_result_t& a, const test_result_t& b) {
            return a.second < b.second;
        };

        const auto nearest = std::min_element(collection.cbegin(), collection.cend(), compare_fn);
        // Up and left to indicate back
        if (event == KeyEvent::Back) {
            collection.clear();
            widget_collect_visible(top_widget, find_back_fn, collection);
            if (!collection.empty())
                set_focus_widget(collection[0].first);
        } else if (nearest != collection.cend()) {
            // focus->blur();
            const auto new_focus = (*nearest).first;
            set_focus_widget(new_focus);
        } else {
            if ((focus_widget()->id >= 0) && (event == KeyEvent::Left)) {
                // Stuck left, move to back button
                collection.clear();
                widget_collect_visible(top_widget, find_back_fn, collection);
                if (!collection.empty())
                    set_focus_widget(collection[0].first);
            }
        }
    }
}

} /* namespace ui */