//
// Copyright(C) 2005-2014 Simon Howard
//
// 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
// of the License, 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.
//

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#include "txt_scrollpane.h"
#include "txt_gui.h"
#include "txt_io.h"
#include "txt_main.h"
#include "txt_table.h"

#include "doomkeys.h"

#define SCROLLBAR_VERTICAL   (1 << 0)
#define SCROLLBAR_HORIZONTAL (1 << 1)

static int FullWidth(txt_scrollpane_t *scrollpane)
{
    if (scrollpane->child != NULL)
    {
        return scrollpane->child->w;
    }
    else
    {
        return 0;
    }
}

static int FullHeight(txt_scrollpane_t *scrollpane)
{
    if (scrollpane->child != NULL)
    {
        return scrollpane->child->h;
    }
    else
    {
        return 0;
    }
}

// Calculate which scroll bars the pane needs.

static int NeedsScrollbars(txt_scrollpane_t *scrollpane)
{
    int result;

    result = 0;

    if (FullWidth(scrollpane) > scrollpane->w)
    {
        result |= SCROLLBAR_HORIZONTAL;
    }
    if (FullHeight(scrollpane) > scrollpane->h)
    {
        result |= SCROLLBAR_VERTICAL;
    }

    return result;
}

// If a scrollbar isn't needed, the scroll position is reset.

static void SanityCheckScrollbars(txt_scrollpane_t *scrollpane)
{
    int scrollbars;
    int max_x, max_y;

    scrollbars = NeedsScrollbars(scrollpane);

    if ((scrollbars & SCROLLBAR_HORIZONTAL) == 0)
    {
        scrollpane->x = 0;
    }
    if ((scrollbars & SCROLLBAR_VERTICAL) == 0)
    {
        scrollpane->y = 0;
    }

    max_x = FullWidth(scrollpane) - scrollpane->w;
    max_y = FullHeight(scrollpane) - scrollpane->h;

    if (scrollpane->x < 0)
    {
        scrollpane->x = 0;
    }
    else if (scrollpane->x > max_x)
    {
        scrollpane->x = max_x;
    }

    if (scrollpane->y < 0)
    {
        scrollpane->y = 0;
    }
    else if (scrollpane->y > max_y)
    {
        scrollpane->y = max_y;
    }
}

static void TXT_ScrollPaneSizeCalc(TXT_UNCAST_ARG(scrollpane))
{
    TXT_CAST_ARG(txt_scrollpane_t, scrollpane);
    int scrollbars;

    if (scrollpane->child != NULL)
    {
        TXT_CalcWidgetSize(scrollpane->child);
    }

    // Expand as necessary (to ensure that no scrollbars are needed)?

    if (scrollpane->expand_w)
    {
        scrollpane->w = FullWidth(scrollpane);
    }
    if (scrollpane->expand_h)
    {
        scrollpane->h = FullHeight(scrollpane);
    }

    scrollpane->widget.w = scrollpane->w;
    scrollpane->widget.h = scrollpane->h;

    // If we have scroll bars, we need to expand slightly to
    // accomodate them. Eg. if we have a vertical scrollbar, we
    // need to be an extra character wide.

    scrollbars = NeedsScrollbars(scrollpane);

    if (scrollbars & SCROLLBAR_HORIZONTAL)
    {
        ++scrollpane->widget.h;
    }
    if (scrollbars & SCROLLBAR_VERTICAL)
    {
        ++scrollpane->widget.w;
    }

    if (scrollpane->child != NULL)
    {
        if (scrollpane->child->w < scrollpane->w)
        {
            scrollpane->child->w = scrollpane->w;
        }
        if (scrollpane->child->h < scrollpane->h)
        {
            scrollpane->child->h = scrollpane->h;
        }
    }
}

static void TXT_ScrollPaneDrawer(TXT_UNCAST_ARG(scrollpane))
{
    TXT_CAST_ARG(txt_scrollpane_t, scrollpane);
    int x1, y1, x2, y2;
    int scrollbars;

    // We set a clipping area of the scroll pane.

    x1 = scrollpane->widget.x,
    y1 = scrollpane->widget.y,
    x2 = x1 + scrollpane->w,
    y2 = y1 + scrollpane->h;

    scrollbars = NeedsScrollbars(scrollpane);

    if (scrollbars & SCROLLBAR_HORIZONTAL)
    {
        TXT_DrawHorizScrollbar(x1,
                               y1 + scrollpane->h,
                               scrollpane->w,
                               scrollpane->x,
                               FullWidth(scrollpane) - scrollpane->w);
    }

    if (scrollbars & SCROLLBAR_VERTICAL)
    {
        TXT_DrawVertScrollbar(x1 + scrollpane->w,
                              y1,
                              scrollpane->h,
                              scrollpane->y,
                              FullHeight(scrollpane) - scrollpane->h);
    }

    TXT_PushClipArea(x1, x2, y1, y2);

    // Draw the child widget

    if (scrollpane->child != NULL)
    {
        TXT_DrawWidget(scrollpane->child);
    }

    // Restore old clipping area.

    TXT_PopClipArea();
}

static void TXT_ScrollPaneDestructor(TXT_UNCAST_ARG(scrollpane))
{
    TXT_CAST_ARG(txt_scrollpane_t, scrollpane);

    if (scrollpane->child != NULL)
    {
        TXT_DestroyWidget(scrollpane->child);
    }
}

static void TXT_ScrollPaneFocused(TXT_UNCAST_ARG(scrollpane), int focused)
{
    TXT_CAST_ARG(txt_scrollpane_t, scrollpane);

    // Whether the child is focused depends only on whether the scroll pane
    // itself is focused. Pass through focus to the child.

    if (scrollpane->child != NULL)
    {
        TXT_SetWidgetFocus(scrollpane->child, focused);
    }
}

// Hack for tables - when browsing a table inside a scroll pane,
// automatically scroll the window to show the newly-selected
// item.

static void ShowSelectedWidget(txt_scrollpane_t *scrollpane)
{
    txt_widget_t *selected;

    selected = TXT_GetSelectedWidget(scrollpane->child);

    // Scroll up or down?

    if (selected->y <= scrollpane->widget.y)
    {
        scrollpane->y -= scrollpane->widget.y - selected->y;
    }
    else if ((signed) (selected->y + selected->h) >
             (signed) (scrollpane->widget.y + scrollpane->h))
    {
        scrollpane->y += (selected->y + selected->h)
                       - (scrollpane->widget.y + scrollpane->h);
    }

    // Scroll left or right?

    if (selected->x <= scrollpane->widget.x)
    {
        scrollpane->x -= scrollpane->widget.x - selected->x;
    }
    else if ((signed) (selected->x + selected->w) >
             (signed) (scrollpane->widget.x + scrollpane->w))
    {
        scrollpane->x += (selected->x + selected->w)
                       - (scrollpane->widget.x + scrollpane->w);
    }
}

// Another hack for tables - when scrolling in 'pages', the normal key press
// event does not provide children with enough information to know how far
// to move their selection to reach a new page. This function does so.
// Note that it *only* affects scrolling in pages, not with arrows!
// A side-effect of this, rather than 'pulling' the selection to fit within
// the new page, is that we will jump straight over ranges of unselectable
// items longer than a page, but that is also true of arrow-key scrolling.
// The other unfortunate effect of doing things this way is that page keys
// have no effect on tables _not_ in scrollpanes: not even home/end.

static int PageSelectedWidget(txt_scrollpane_t *scrollpane, int key)
{
    int pagex = 0; // No page left/right yet, but some keyboards have them
    int pagey = 0;

    // Subtract one from the absolute page distance as this is slightly more
    // intuitive: a page down first jumps to the bottom of the current page,
    // then proceeds to scroll onwards.

    switch (key)
    {
        case KEY_PGUP:
            pagey = 1 - scrollpane->h;
            break;

        case KEY_PGDN:
            pagey = scrollpane->h - 1;
            break;

        default: // We shouldn't even be in this function
            return 0;
    }

    if (scrollpane->child->widget_class == &txt_table_class)
    {
        return TXT_PageTable(scrollpane->child, pagex, pagey);
    }

    return 0;
}

// Interpret arrow key presses as scroll commands

static int InterpretScrollKey(txt_scrollpane_t *scrollpane, int key)
{
    int maxy;

    switch (key)
    {
        case KEY_UPARROW:
            if (scrollpane->y > 0)
            {
                --scrollpane->y;
                return 1;
            }
            break;

        case KEY_DOWNARROW:
            if (scrollpane->y < FullHeight(scrollpane) - scrollpane->h)
            {
                ++scrollpane->y;
                return 1;
            }
            break;

        case KEY_LEFTARROW:
            if (scrollpane->x > 0)
            {
                --scrollpane->x;
                return 1;
            }
            break;

        case KEY_RIGHTARROW:
            if (scrollpane->x < FullWidth(scrollpane) - scrollpane->w)
            {
                ++scrollpane->x;
                return 1;
            }
            break;

        case KEY_PGUP:
            if (scrollpane->y > 0)
            {
                scrollpane->y -= scrollpane->h;
                if (scrollpane->y < 0)
                {
                    scrollpane->y = 0;
                }
                return 1;
            }
            break;

        case KEY_PGDN:
            maxy = FullHeight(scrollpane) - scrollpane->h;
            if (scrollpane->y < maxy)
            {
                scrollpane->y += scrollpane->h;
                if (scrollpane->y > maxy)
                {
                    scrollpane->y = maxy;
                }
                return 1;
            }
            break;

        default:
            break;
    }

    return 0;
}

static int TXT_ScrollPaneKeyPress(TXT_UNCAST_ARG(scrollpane), int key)
{
    TXT_CAST_ARG(txt_scrollpane_t, scrollpane);
    int result;

    result = 0;

    if (scrollpane->child != NULL)
    {
        result = TXT_WidgetKeyPress(scrollpane->child, key);

        // Gross hack - if we're scrolling in a menu with the keyboard,
        // automatically move the scroll pane to show the new
        // selected item.

        if ((key == KEY_UPARROW || key == KEY_DOWNARROW
          || key == KEY_LEFTARROW || key == KEY_RIGHTARROW
          || key == KEY_PGUP || key == KEY_PGDN)
         && scrollpane->child->widget_class == &txt_table_class)
        {
            if (PageSelectedWidget(scrollpane, key))
            {
                result = 1;
            }

            ShowSelectedWidget(scrollpane);
        }

        // If the child widget didn't use the keypress, we can see 
        // if it can be interpreted as a scrolling command.

        if (result == 0)
        {
            result = InterpretScrollKey(scrollpane, key);
        }
    }

    return result;
}

static void TXT_ScrollPaneMousePress(TXT_UNCAST_ARG(scrollpane),
                                     int x, int y, int b)
{
    TXT_CAST_ARG(txt_scrollpane_t, scrollpane);
    int scrollbars;
    int rel_x, rel_y;

    scrollbars = NeedsScrollbars(scrollpane);

    if (b == TXT_MOUSE_SCROLLUP)
    {
        if (scrollbars & SCROLLBAR_VERTICAL)
        {
            scrollpane->y -= 3;
        }
        else if (scrollbars & SCROLLBAR_HORIZONTAL)
        {
            scrollpane->x -= 3;
        }

        return;
    }
    else if (b == TXT_MOUSE_SCROLLDOWN)
    {
        if (scrollbars & SCROLLBAR_VERTICAL)
        {
            scrollpane->y += 3;
        }
        else if (scrollbars & SCROLLBAR_HORIZONTAL)
        {
            scrollpane->x += 3;
        }

        return;
    }

    rel_x = x - scrollpane->widget.x;
    rel_y = y - scrollpane->widget.y;

    // Click on the horizontal scrollbar?
    if ((scrollbars & SCROLLBAR_HORIZONTAL) && rel_y == scrollpane->h)
    {
        if (rel_x == 0)
        {
            --scrollpane->x;
        }
        else if (rel_x == scrollpane->w - 1)
        {
            ++scrollpane->x;
        }
        else
        {
            int range = FullWidth(scrollpane) - scrollpane->w;
            int bar_max = scrollpane->w - 3;

            scrollpane->x = ((rel_x - 1) * range + bar_max - 1) / bar_max;
        }

        return;
    }

    // Click on the vertical scrollbar?
    if ((scrollbars & SCROLLBAR_VERTICAL) && rel_x == scrollpane->w)
    {
        if (rel_y == 0)
        {
            --scrollpane->y;
        }
        else if (rel_y == scrollpane->h - 1)
        {
            ++scrollpane->y;
        }
        else
        {
            int range = FullHeight(scrollpane) - scrollpane->h;
            int bar_max = scrollpane->h - 3;

            scrollpane->y = ((rel_y - 1) * range + bar_max - 1) / bar_max;
        }

        return;
    }

    if (scrollpane->child != NULL)
    {
        TXT_WidgetMousePress(scrollpane->child, x, y, b);
    }
}

static void TXT_ScrollPaneLayout(TXT_UNCAST_ARG(scrollpane))
{
    TXT_CAST_ARG(txt_scrollpane_t, scrollpane);

    SanityCheckScrollbars(scrollpane);

    // The child widget takes the same position as the scroll pane
    // itself, but is offset by the scroll position.

    if (scrollpane->child != NULL)
    {
        scrollpane->child->x = scrollpane->widget.x - scrollpane->x;
        scrollpane->child->y = scrollpane->widget.y - scrollpane->y;

        TXT_LayoutWidget(scrollpane->child);
    }
}

static int TXT_ScrollPaneSelectable(TXT_UNCAST_ARG(scrollpane))
{
    TXT_CAST_ARG(txt_scrollpane_t, scrollpane);

    // If scroll bars are displayed, the scroll pane must be selectable
    // so that we can use the arrow keys to scroll around.

    if (NeedsScrollbars(scrollpane))
    {
        return 1;
    }

    // Otherwise, whether this is selectable depends on the child widget.

    return TXT_SelectableWidget(scrollpane->child);
}

txt_widget_class_t txt_scrollpane_class =
{
    TXT_ScrollPaneSelectable,
    TXT_ScrollPaneSizeCalc,
    TXT_ScrollPaneDrawer,
    TXT_ScrollPaneKeyPress,
    TXT_ScrollPaneDestructor,
    TXT_ScrollPaneMousePress,
    TXT_ScrollPaneLayout,
    TXT_ScrollPaneFocused,
};

txt_scrollpane_t *TXT_NewScrollPane(int w, int h, TXT_UNCAST_ARG(target))
{
    TXT_CAST_ARG(txt_widget_t, target);
    txt_scrollpane_t *scrollpane;

    scrollpane = malloc(sizeof(txt_scrollpane_t));
    TXT_InitWidget(scrollpane, &txt_scrollpane_class);
    scrollpane->w = w;
    scrollpane->h = h;
    scrollpane->x = 0;
    scrollpane->y = 0;
    scrollpane->child = target;
    scrollpane->expand_w = w <= 0;
    scrollpane->expand_h = h <= 0;

    // Set parent pointer for inner widget.

    target->parent = &scrollpane->widget;

    return scrollpane;
}