/* $Id$ */

/*
 * This file is part of OpenTTD.
 * OpenTTD 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, version 2.
 * OpenTTD 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 OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/** @file widget_type.h Definitions about widgets. */

#ifndef WIDGET_TYPE_H
#define WIDGET_TYPE_H

#include "core/bitmath_func.hpp"
#include "strings_type.h"
#include "gfx_type.h"

/* How the resize system works:
    First, you need to add a WWT_RESIZEBOX to the widgets, and you need
     to add the flag WDF_RESIZABLE to the window. Now the window is ready
     to resize itself.
    As you may have noticed, all widgets have a RESIZE_XXX in their line.
     This lines controls how the widgets behave on resize. RESIZE_NONE means
     it doesn't do anything. Any other option let's one of the borders
     move with the changed width/height. So if a widget has
     RESIZE_RIGHT, and the window is made 5 pixels wider by the user,
     the right of the window will also be made 5 pixels wider.
    Now, what if you want to clamp a widget to the bottom? Give it the flag
     RESIZE_TB. This is RESIZE_TOP + RESIZE_BOTTOM. Now if the window gets
     5 pixels bigger, both the top and bottom gets 5 bigger, so the whole
     widgets moves downwards without resizing, and appears to be clamped
     to the bottom. Nice aint it?
   You should know one more thing about this system. Most windows can't
    handle an increase of 1 pixel. So there is a step function, which
    let the windowsize only be changed by X pixels. You configure this
    after making the window, like this:
      w->resize.step_height = 10;
    Now the window will only change in height in steps of 10.
   You can also give a minimum width and height. The default value is
    the default height/width of the window itself. You can change this
    AFTER window - creation, with:
     w->resize.width or w->resize.height.
   That was all.. good luck, and enjoy :) -- TrueLight */

enum DisplayFlags {
	RESIZE_NONE   = 0,  ///< no resize required

	RESIZE_LEFT   = 1,  ///< left resize flag
	RESIZE_RIGHT  = 2,  ///< rigth resize flag
	RESIZE_TOP    = 4,  ///< top resize flag
	RESIZE_BOTTOM = 8,  ///< bottom resize flag

	RESIZE_LR     = RESIZE_LEFT  | RESIZE_RIGHT,   ///<  combination of left and right resize flags
	RESIZE_RB     = RESIZE_RIGHT | RESIZE_BOTTOM,  ///<  combination of right and bottom resize flags
	RESIZE_TB     = RESIZE_TOP   | RESIZE_BOTTOM,  ///<  combination of top and bottom resize flags
	RESIZE_LRB    = RESIZE_LEFT  | RESIZE_RIGHT  | RESIZE_BOTTOM, ///< combination of left, right and bottom resize flags
	RESIZE_LRTB   = RESIZE_LEFT  | RESIZE_RIGHT  | RESIZE_TOP | RESIZE_BOTTOM,  ///<  combination of all resize flags
	RESIZE_RTB    = RESIZE_RIGHT | RESIZE_TOP    | RESIZE_BOTTOM, ///<  combination of right, top and bottom resize flag

	/* The following flags are used by the system to specify what is disabled, hidden, or clicked
	 * They are used in the same place as the above RESIZE_x flags, Widget visual_flags.
	 * These states are used in exceptions. If nothing is specified, they will indicate
	 * Enabled, visible or unclicked widgets*/
	WIDG_DISABLED = 4,  ///< widget is greyed out, not available
	WIDG_HIDDEN   = 5,  ///< widget is made invisible
	WIDG_LOWERED  = 6,  ///< widget is paint lowered, a pressed button in fact
};
DECLARE_ENUM_AS_BIT_SET(DisplayFlags);

enum {
	WIDGET_LIST_END = -1, ///< indicate the end of widgets' list for vararg functions
};

/** Bits of the #WWT_MATRIX widget data. */
enum MatrixWidgetValues {
	/* Number of column bits of the WWT_MATRIX widget data. */
	MAT_COL_START = 0, ///< Lowest bit of the number of columns.
	MAT_COL_BITS  = 8, ///< Number of bits for the number of columns in the matrix.

	/* Number of row bits of the WWT_MATRIX widget data. */
	MAT_ROW_START = 8, ///< Lowest bit of the number of rows.
	MAT_ROW_BITS  = 8, ///< Number of bits for the number of rows in the matrix.
};

/**
 * Window widget types, nested widget types, and nested widget part types.
 */
enum WidgetType {
	/* Window widget types. */
	WWT_EMPTY,      ///< Empty widget, place holder to reserve space in widget array

	WWT_PANEL,      ///< Simple depressed panel
	WWT_INSET,      ///< Pressed (inset) panel, most commonly used as combo box _text_ area
	WWT_IMGBTN,     ///< Button with image
	WWT_IMGBTN_2,   ///< Button with diff image when clicked

	WWT_TEXTBTN,    ///< Button with text
	WWT_TEXTBTN_2,  ///< Button with diff text when clicked
	WWT_LABEL,      ///< Centered label
	WWT_TEXT,       ///< Pure simple text
	WWT_MATRIX,     ///< Grid of rows and columns. @see MatrixWidgetValues
	WWT_SCROLLBAR,  ///< Vertical scrollbar
	WWT_FRAME,      ///< Frame
	WWT_CAPTION,    ///< Window caption (window title between closebox and stickybox)

	WWT_HSCROLLBAR, ///< Horizontal scrollbar
	WWT_STICKYBOX,  ///< Sticky box (normally at top-right of a window)
	WWT_SCROLL2BAR, ///< 2nd vertical scrollbar
	WWT_RESIZEBOX,  ///< Resize box (normally at bottom-right of a window)
	WWT_CLOSEBOX,   ///< Close box (at top-left of a window)
	WWT_DROPDOWN,   ///< Drop down list
	WWT_EDITBOX,    ///< a textbox for typing
	WWT_LAST,       ///< Last Item. use WIDGETS_END to fill up padding!!

	/* Nested widget types. */
	NWID_HORIZONTAL,     ///< Horizontal container.
	NWID_HORIZONTAL_LTR, ///< Horizontal container that doesn't change the order of the widgets for RTL languages.
	NWID_VERTICAL,       ///< Vertical container.
	NWID_SPACER,         ///< Invisible widget that takes some space.
	NWID_SELECTION,      ///< Stacked widgets, only one visible at a time (eg in a panel with tabs).
	NWID_LAYERED,        ///< Widgets layered on top of each other, all visible at the same time.
	NWID_VIEWPORT,       ///< Nested widget containing a viewport.

	/* Nested widget part types. */
	WPT_RESIZE,       ///< Widget part for specifying resizing.
	WPT_RESIZE_PTR,   ///< Widget part for specifying resizing via a pointer.
	WPT_MINSIZE,      ///< Widget part for specifying minimal size.
	WPT_MINSIZE_PTR,  ///< Widget part for specifying minimal size via a pointer.
	WPT_FILL,         ///< Widget part for specifying fill.
	WPT_DATATIP,      ///< Widget part for specifying data and tooltip.
	WPT_DATATIP_PTR,  ///< Widget part for specifying data and tooltip via a pointer.
	WPT_PADDING,      ///< Widget part for specifying a padding.
	WPT_PIPSPACE,     ///< Widget part for specifying pre/inter/post space for containers.
	WPT_ENDCONTAINER, ///< Widget part to denote end of a container.
	WPT_FUNCTION,     ///< Widget part for calling a user function.

	/* Pushable window widget types. */
	WWT_MASK = 0x7F,

	WWB_PUSHBUTTON  = 1 << 7,

	WWT_PUSHBTN     = WWT_PANEL   | WWB_PUSHBUTTON,
	WWT_PUSHTXTBTN  = WWT_TEXTBTN | WWB_PUSHBUTTON,
	WWT_PUSHIMGBTN  = WWT_IMGBTN  | WWB_PUSHBUTTON,
};

/** Marker for the "end of widgets" in a Window(Desc) widget table. */
#define WIDGETS_END WWT_LAST, RESIZE_NONE, INVALID_COLOUR, 0, 0, 0, 0, 0, STR_NULL

/**
 * Window widget data structure
 */
struct Widget {
	WidgetType type;                  ///< Widget type
	DisplayFlags display_flags;       ///< Resize direction, alignment, etc. during resizing
	Colours colour;                   ///< Widget colour, see docs/ottd-colourtext-palette.png
	int16 left;                       ///< The left edge of the widget
	int16 right;                      ///< The right edge of the widget
	int16 top;                        ///< The top edge of the widget
	int16 bottom;                     ///< The bottom edge of the widget
	uint16 data;                      ///< The String/Image or special code (list-matrixes) of a widget
	StringID tooltips;                ///< Tooltips that are shown when rightclicking on a widget
};

/** Different forms of sizing nested widgets, using NWidgetBase::AssignSizePosition() */
enum SizingType {
	ST_ARRAY,    ///< Initialize nested widget tree to generate a #Widget * array.
	ST_SMALLEST, ///< Initialize nested widget tree to smallest size. Also updates \e current_x and \e current_y.
	ST_RESIZE,   ///< Resize the nested widget tree.
};

/* Forward declarations. */
class NWidgetCore;
struct Scrollbar;

/**
 * Baseclass for nested widgets.
 * @invariant After initialization, \f$current\_x = smallest\_x + n * resize\_x, for n \geq 0\f$.
 * @invariant After initialization, \f$current\_y = smallest\_y + m * resize\_y, for m \geq 0\f$.
 * @ingroup NestedWidgets
 */
class NWidgetBase : public ZeroedMemoryAllocator {
public:
	NWidgetBase(WidgetType tp);

	virtual void SetupSmallestSize(Window *w, bool init_array) = 0;
	virtual void AssignSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool allow_resize_x, bool allow_resize_y, bool rtl) = 0;

	virtual void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl) = 0;
	virtual void FillNestedArray(NWidgetCore **array, uint length) = 0;

	virtual NWidgetCore *GetWidgetFromPos(int x, int y) = 0;
	virtual NWidgetBase *GetWidgetOfType(WidgetType tp);

	/**
	 * Set additional space (padding) around the widget.
	 * @param top    Amount of additional space above the widget.
	 * @param right  Amount of additional space right of the widget.
	 * @param bottom Amount of additional space below the widget.
	 * @param left   Amount of additional space left of the widget.
	 */
	inline void SetPadding(uint8 top, uint8 right, uint8 bottom, uint8 left)
	{
		this->padding_top = top;
		this->padding_right = right;
		this->padding_bottom = bottom;
		this->padding_left = left;
	};

	inline uint GetHorizontalStepSize(SizingType sizing) const;
	inline uint GetVerticalStepSize(SizingType sizing) const;

	virtual void Draw(const Window *w) = 0;
	virtual void Invalidate(const Window *w) const;

	WidgetType type;      ///< Type of the widget / nested widget.
	bool fill_x;          ///< Allow horizontal filling from initial size.
	bool fill_y;          ///< Allow vertical filling from initial size.
	uint resize_x;        ///< Horizontal resize step (\c 0 means not resizable).
	uint resize_y;        ///< Vertical resize step (\c 0 means not resizable).
	/* Size of the widget in the smallest window possible.
	 * Computed by #SetupSmallestSize() followed by #AssignSizePosition().
	 */
	uint smallest_x;      ///< Smallest horizontal size of the widget in a filled window.
	uint smallest_y;      ///< Smallest vertical size of the widget in a filled window.
	/* Current widget size (that is, after resizing). */
	uint current_x;       ///< Current horizontal size (after resizing).
	uint current_y;       ///< Current vertical size (after resizing).

	uint pos_x;           ///< Horizontal position of top-left corner of the widget in the window.
	uint pos_y;           ///< Vertical position of top-left corner of the widget in the window.

	NWidgetBase *next;    ///< Pointer to next widget in container. Managed by parent container widget.
	NWidgetBase *prev;    ///< Pointer to previous widget in container. Managed by parent container widget.

	uint8 padding_top;    ///< Paddings added to the top of the widget. Managed by parent container widget.
	uint8 padding_right;  ///< Paddings added to the right of the widget. Managed by parent container widget.
	uint8 padding_bottom; ///< Paddings added to the bottom of the widget. Managed by parent container widget.
	uint8 padding_left;   ///< Paddings added to the left of the widget. Managed by parent container widget.

protected:
	inline void StoreSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool allow_resize_x, bool allow_resize_y);
};

/**
 * Get the horizontal sizing step.
 * @param sizing Type of resize being performed.
 */
inline uint NWidgetBase::GetHorizontalStepSize(SizingType sizing) const
{
	if (sizing == ST_RESIZE) return this->resize_x;
	return this->fill_x ? 1 : 0;
}

/**
 * Get the vertical sizing step.
 * @param sizing Type of resize being performed.
 */
inline uint NWidgetBase::GetVerticalStepSize(SizingType sizing) const
{
	if (sizing == ST_RESIZE) return this->resize_y;
	return this->fill_y ? 1 : 0;
}

/** Base class for a resizable nested widget.
 * @ingroup NestedWidgets */
class NWidgetResizeBase : public NWidgetBase {
public:
	NWidgetResizeBase(WidgetType tp, bool fill_x, bool fill_y);

	void SetMinimalSize(uint min_x, uint min_y);
	void SetFill(bool fill_x, bool fill_y);
	void SetResize(uint resize_x, uint resize_y);

	void AssignSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool allow_resize_x, bool allow_resize_y, bool rtl);

	uint min_x; ///< Minimal horizontal size of only this widget.
	uint min_y; ///< Minimal vertical size of only this widget.
};

/** Nested widget flags that affect display and interaction withe 'real' widgets. */
enum NWidgetDisplay {
	NDB_LOWERED  = 0, ///< Widget is lowered (pressed down) bit.
	NDB_DISABLED = 1, ///< Widget is disabled (greyed out) bit.

	ND_LOWERED  = 1 << NDB_LOWERED,  ///< Bit value of the lowered flag.
	ND_DISABLED = 1 << NDB_DISABLED, ///< Bit value of the disabled flag.
};
DECLARE_ENUM_AS_BIT_SET(NWidgetDisplay);

/** Base class for a 'real' widget.
 * @ingroup NestedWidgets */
class NWidgetCore : public NWidgetResizeBase {
public:
	NWidgetCore(WidgetType tp, Colours colour, bool def_fill_x, bool def_fill_y, uint16 widget_data, StringID tool_tip);

	void SetIndex(int index);
	void SetDataTip(uint16 widget_data, StringID tool_tip);

	inline void SetLowered(bool lowered);
	inline bool IsLowered();
	inline void SetDisabled(bool disabled);
	inline bool IsDisabled();

	void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);
	/* virtual */ void FillNestedArray(NWidgetCore **array, uint length);
	/* virtual */ NWidgetCore *GetWidgetFromPos(int x, int y);

	virtual Scrollbar *FindScrollbar(Window *w, bool allow_next = true) = 0;

	NWidgetDisplay disp_flags; ///< Flags that affect display and interaction with the widget.
	Colours colour;            ///< Colour of this widget.
	int index;                 ///< Index of the nested widget in the widget array of the window (\c -1 means 'not used').
	uint16 widget_data;        ///< Data of the widget. @see Widget::data
	StringID tool_tip;         ///< Tooltip of the widget. @see Widget::tootips
};

/**
 * Lower or raise the widget.
 * @param lowered Widget must be lowered (drawn pressed down).
 */
inline void NWidgetCore::SetLowered(bool lowered)
{
	this->disp_flags = lowered ? SETBITS(this->disp_flags, ND_LOWERED) : CLRBITS(this->disp_flags, ND_LOWERED);
}

/** Return whether the widget is lowered. */
inline bool NWidgetCore::IsLowered()
{
	return HasBit(this->disp_flags, NDB_LOWERED);
}

/**
 * Disable (grey-out) or enable the widget.
 * @param disabled Widget must be disabled.
 */
inline void NWidgetCore::SetDisabled(bool disabled)
{
	this->disp_flags = disabled ? SETBITS(this->disp_flags, ND_DISABLED) : CLRBITS(this->disp_flags, ND_DISABLED);
}

/** Return whether the widget is disabled. */
inline bool NWidgetCore::IsDisabled()
{
	return HasBit(this->disp_flags, NDB_DISABLED);
}


/** Baseclass for container widgets.
 * @ingroup NestedWidgets */
class NWidgetContainer : public NWidgetBase {
public:
	NWidgetContainer(WidgetType tp);
	~NWidgetContainer();

	void Add(NWidgetBase *wid);
	/* virtual */ void FillNestedArray(NWidgetCore **array, uint length);

	/** Return whether the container is empty. */
	inline bool IsEmpty() { return head == NULL; };

	/* virtual */ NWidgetBase *GetWidgetOfType(WidgetType tp);

protected:
	NWidgetBase *head; ///< Pointer to first widget in container.
	NWidgetBase *tail; ///< Pointer to last widget in container.
};

/** Stacked widgets, widgets all occupying the same space in the window.
 * @note the semantics difference between #NWID_SELECTION and #NWID_LAYERED is currently not used.
 */
class NWidgetStacked : public NWidgetContainer {
public:
	NWidgetStacked(WidgetType tp);

	void SetupSmallestSize(Window *w, bool init_array);
	void AssignSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool allow_resize_x, bool allow_resize_y, bool rtl);
	void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);

	/* virtual */ void Draw(const Window *w);
	/* virtual */ NWidgetCore *GetWidgetFromPos(int x, int y);
};

/** Nested widget container flags, */
enum NWidContainerFlags {
	NCB_EQUALSIZE = 0, ///< Containers should keep all their (resizing) children equally large.

	NC_NONE = 0,                       ///< All flags cleared.
	NC_EQUALSIZE = 1 << NCB_EQUALSIZE, ///< Value of the #NCB_EQUALSIZE flag.
};
DECLARE_ENUM_AS_BIT_SET(NWidContainerFlags);

/** Container with pre/inter/post child space. */
class NWidgetPIPContainer : public NWidgetContainer {
public:
	NWidgetPIPContainer(WidgetType tp, NWidContainerFlags flags = NC_NONE);

	void SetPIP(uint8 pip_pre, uint8 pip_inter, uint8 pip_post);

	/* virtual */ void Draw(const Window *w);
	/* virtual */ NWidgetCore *GetWidgetFromPos(int x, int y);

protected:
	NWidContainerFlags flags; ///< Flags of the container.
	uint8 pip_pre;            ///< Amount of space before first widget.
	uint8 pip_inter;          ///< Amount of space between widgets.
	uint8 pip_post;           ///< Amount of space after last widget.
};

/** Horizontal container.
 * @ingroup NestedWidgets */
class NWidgetHorizontal : public NWidgetPIPContainer {
public:
	NWidgetHorizontal(NWidContainerFlags flags = NC_NONE);

	void SetupSmallestSize(Window *w, bool init_array);
	void AssignSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool allow_resize_x, bool allow_resize_y, bool rtl);

	void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);
};

/** Horizontal container that doesn't change the direction of the widgets for RTL languages.
 * @ingroup NestedWidgets */
class NWidgetHorizontalLTR : public NWidgetHorizontal {
public:
	NWidgetHorizontalLTR(NWidContainerFlags flags = NC_NONE);

	void AssignSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool allow_resize_x, bool allow_resize_y, bool rtl);

	void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);
};

/** Vertical container.
 * @ingroup NestedWidgets */
class NWidgetVertical : public NWidgetPIPContainer {
public:
	NWidgetVertical(NWidContainerFlags flags = NC_NONE);

	void SetupSmallestSize(Window *w, bool init_array);
	void AssignSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool allow_resize_x, bool allow_resize_y, bool rtl);

	void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);
};


/** Spacer widget.
 * @ingroup NestedWidgets */
class NWidgetSpacer : public NWidgetResizeBase {
public:
	NWidgetSpacer(int length, int height);

	void SetupSmallestSize(Window *w, bool init_array);
	void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);
	/* virtual */ void FillNestedArray(NWidgetCore **array, uint length);

	/* virtual */ void Draw(const Window *w);
	/* virtual */ void Invalidate(const Window *w) const;
	/* virtual */ NWidgetCore *GetWidgetFromPos(int x, int y);
};

/** Nested widget with a child.
 * @ingroup NestedWidgets */
class NWidgetBackground : public NWidgetCore {
public:
	NWidgetBackground(WidgetType tp, Colours colour, int index, NWidgetPIPContainer *child = NULL);
	~NWidgetBackground();

	void Add(NWidgetBase *nwid);
	void SetPIP(uint8 pip_pre, uint8 pip_inter, uint8 pip_post);

	void SetupSmallestSize(Window *w, bool init_array);
	void AssignSizePosition(SizingType sizing, uint x, uint y, uint given_width, uint given_height, bool allow_resize_x, bool allow_resize_y, bool rtl);

	void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);
	/* virtual */ void FillNestedArray(NWidgetCore **array, uint length);

	/* virtual */ void Draw(const Window *w);
	/* virtual */ NWidgetCore *GetWidgetFromPos(int x, int y);
	/* virtual */ NWidgetBase *GetWidgetOfType(WidgetType tp);
	/* virtual */ Scrollbar *FindScrollbar(Window *w, bool allow_next = true);

private:
	NWidgetPIPContainer *child; ///< Child widget.
};

/**
 * Nested widget to display a viewport in a window.
 * After initializing the nested widget tree, call #InitializeViewport(). After changing the window size,
 * call #UpdateViewportCoordinates() eg from Window::OnResize().
 * @todo Class derives from #NWidgetCore, but does not use #colour, #widget_data, or #tool_tip.
 * @ingroup NestedWidgets */
class NWidgetViewport : public NWidgetCore {
public:
	NWidgetViewport(int index);

	/* virtual */ void SetupSmallestSize(Window *w, bool init_array);
	/* virtual */ void StoreWidgets(Widget *widgets, int length, bool left_moving, bool top_moving, bool rtl);
	/* virtual */ void Draw(const Window *w);
	/* virtual */ Scrollbar *FindScrollbar(Window *w, bool allow_next = true);

	void InitializeViewport(Window *w, uint32 follow_flags, ZoomLevel zoom);
	void UpdateViewportCoordinates(Window *w);
};

/** Leaf widget.
 * @ingroup NestedWidgets */
class NWidgetLeaf : public NWidgetCore {
public:
	NWidgetLeaf(WidgetType tp, Colours colour, int index, uint16 data, StringID tip);

	/* virtual */ void SetupSmallestSize(Window *w, bool init_array);
	/* virtual */ void Draw(const Window *w);
	/* virtual */ void Invalidate(const Window *w) const;
	/* virtual */ Scrollbar *FindScrollbar(Window *w, bool allow_next = true);

	static void InvalidateDimensionCache();
private:
	static Dimension stickybox_dimension; ///< Cached size of a stickybox widget.
	static Dimension resizebox_dimension; ///< Cached size of a resizebox widget.
	static Dimension closebox_dimension;  ///< Cached size of a closebox widget.
};

Widget *InitializeNWidgets(NWidgetBase *nwid, bool rtl = false);
bool CompareWidgetArrays(const Widget *orig, const Widget *gen, bool report = true);

/**
 * @defgroup NestedWidgetParts Hierarchical widget parts
 * To make nested widgets easier to enter, nested widget parts have been created. They allow the tree to be defined in a flat array of parts.
 *
 * - Leaf widgets start with a #NWidget(WidgetType tp, Colours col, int16 idx) part.
 *   Next, specify its properties with one or more of
 *   - #SetMinimalSize Define the minimal size of the widget.
 *   - #SetFill Define how the widget may grow to make it nicely.
 *   - #SetDataTip Define the data and the tooltip of the widget.
 *   - #SetResize Define how the widget may resize.
 *   - #SetPadding Create additional space around the widget.
 *
 * - To insert a nested widget tree from an external source, nested widget part #NWidgetFunction exists.
 *   For further customization, the #SetPadding part may be used.
 *
 * - Space widgets (#NWidgetSpacer) start with a #NWidget(WidgetType tp), followed by one or more of
 *   - #SetMinimalSize Define the minimal size of the widget.
 *   - #SetFill Define how the widget may grow to make it nicely.
 *   - #SetResize Define how the widget may resize.
 *   - #SetPadding Create additional space around the widget.
 *
 * - Container widgets #NWidgetHorizontal, #NWidgetHorizontalLTR, and #NWidgetVertical, start with a #NWidget(WidgetType tp) part.
 *   Their properties are derived from the child widgets so they cannot be specified.
 *   You can however use
 *   - #SetPadding Define additional padding around the container.
 *   - #SetPIP Set additional pre/inter/post child widget space.
 *   .
 *   Underneath these properties, all child widgets of the container must be defined. To denote that they are childs, add an indent before the nested widget parts of
 *   the child widgets (it has no meaning for the compiler but it makes the widget parts easier to read).
 *   Below the last child widget, use an #EndContainer part. This part should be aligned with the #NWidget part that started the container.
 *
 * - Stacked widgets #NWidgetStacked map each of their childs onto the same space. It behaves like a container, except there is no pre/inter/post space,
 *   so the widget does not support #SetPIP. #SetPadding is allowed though.
 *   Like the other container widgets, below the last child widgets, a #EndContainer part should be used to denote the end of the stacked widget.
 *
 * - Background widgets #NWidgetBackground start with a #NWidget(WidgetType tp, Colours col, int16 idx) part.
 *   What follows depends on how the widget is used.
 *   - If the widget is used as a leaf widget, that is, to create some space in the window to display a viewport or some text, use the properties of the
 *     leaf widgets to define how it behaves.
 *   - If the widget is used a background behind other widgets, it is considered to be a container widgets. Use the properties listed there to define its
 *     behaviour.
 *   .
 *   In both cases, the background widget \b MUST end with a #EndContainer widget part.
 *
 * @see NestedWidgets
 */

/** Widget part for storing data and tooltip information.
 * @ingroup NestedWidgetParts */
struct NWidgetPartDataTip {
	uint16 data;      ///< Data value of the widget.
	StringID tooltip; ///< Tooltip of the widget.
};

/** Widget part for storing basic widget information.
 * @ingroup NestedWidgetParts */
struct NWidgetPartWidget {
	Colours colour; ///< Widget colour.
	int16 index;    ///< Widget index in the widget array.
};

/** Widget part for storing padding.
 * @ingroup NestedWidgetParts */
struct NWidgetPartPaddings {
	uint8 top, right, bottom, left; ///< Paddings for all directions.
};

/** Widget part for storing pre/inter/post spaces.
 * @ingroup NestedWidgetParts */
struct NWidgetPartPIP {
	uint8 pre, inter, post; ///< Amount of space before/between/after child widgets.
};

/** Pointer to function returning a nested widget.
 * @param biggest_index Pointer to storage for collecting the biggest index used in the nested widget.
 * @return Nested widget (tree).
 * @postcond \c *biggest_index must contain the value of the biggest index in the returned tree.
 */
typedef NWidgetBase *NWidgetFunctionType(int *biggest_index);

/** Partial widget specification to allow NWidgets to be written nested.
 * @ingroup NestedWidgetParts */
struct NWidgetPart {
	WidgetType type;                         ///< Type of the part. @see NWidgetPartType.
	union {
		Point xy;                        ///< Part with an x/y size.
		Point *xy_ptr;                   ///< Part with a pointer to an x/y size.
		NWidgetPartDataTip data_tip;     ///< Part with a data/tooltip.
		NWidgetPartDataTip *datatip_ptr; ///< Part with a pointer to data/tooltip.
		NWidgetPartWidget widget;        ///< Part with a start of a widget.
		NWidgetPartPaddings padding;     ///< Part with paddings.
		NWidgetPartPIP pip;              ///< Part with pre/inter/post spaces.
		NWidgetFunctionType *func_ptr;   ///< Part with a function call.
		NWidContainerFlags cont_flags;   ///< Part with container flags.
	} u;
};

/**
 * Widget part function for setting the resize step.
 * @param dx Horizontal resize step. 0 means no horizontal resizing.
 * @param dy Vertical resize step. 0 means no vertical resizing.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart SetResize(int16 dx, int16 dy)
{
	NWidgetPart part;

	part.type = WPT_RESIZE;
	part.u.xy.x = dx;
	part.u.xy.y = dy;

	return part;
}

/**
 * Widget part function for using a pointer to set the resize step.
 * @param ptr Pointer to horizontal and vertical resize step.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart SetResize(Point *ptr)
{
	NWidgetPart part;

	part.type = WPT_RESIZE_PTR;
	part.u.xy_ptr = ptr;

	return part;
}

/**
 * Widget part function for setting the minimal size.
 * @param dx Horizontal minimal size.
 * @param dy Vertical minimal size.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart SetMinimalSize(int16 x, int16 y)
{
	NWidgetPart part;

	part.type = WPT_MINSIZE;
	part.u.xy.x = x;
	part.u.xy.y = y;

	return part;
}

/**
 * Widget part function for using a pointer to set the minimal size.
 * @param ptr Pointer to horizontal and vertical minimal size.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart SetMinimalSize(Point *ptr)
{
	NWidgetPart part;

	part.type = WPT_MINSIZE_PTR;
	part.u.xy_ptr = ptr;

	return part;
}

/**
 * Widget part function for setting filling.
 * @param x_fill Allow horizontal filling from minimal size.
 * @param y_fill Allow vertical filling from minimal size.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart SetFill(bool x_fill, bool y_fill)
{
	NWidgetPart part;

	part.type = WPT_FILL;
	part.u.xy.x = x_fill;
	part.u.xy.y = y_fill;

	return part;
}

/**
 * Widget part function for denoting the end of a container
 * (horizontal, vertical, WWT_FRAME, WWT_INSET, or WWT_PANEL).
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart EndContainer()
{
	NWidgetPart part;

	part.type = WPT_ENDCONTAINER;

	return part;
}

/** Widget part function for setting the data and tooltip.
 * @param data Data of the widget.
 * @param tip  Tooltip of the widget.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart SetDataTip(uint16 data, StringID tip)
{
	NWidgetPart part;

	part.type = WPT_DATATIP;
	part.u.data_tip.data = data;
	part.u.data_tip.tooltip = tip;

	return part;
}

/**
 * Widget part function for setting the data and tooltip via a pointer.
 * @param ptr Pointer to the data and tooltip of the widget.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart SetDataTip(NWidgetPartDataTip *ptr)
{
	NWidgetPart part;

	part.type = WPT_DATATIP_PTR;
	part.u.datatip_ptr = ptr;

	return part;
}

/**
 * Widget part function for setting additional space around a widget.
 * Parameters start above the widget, and are specified in clock-wise direction.
 * @param top The padding above the widget.
 * @param right The padding right of the widget.
 * @param bottom The padding below the widget.
 * @param left The padding left of the widget.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart SetPadding(uint8 top, uint8 right, uint8 bottom, uint8 left)
{
	NWidgetPart part;

	part.type = WPT_PADDING;
	part.u.padding.top = top;
	part.u.padding.right = right;
	part.u.padding.bottom = bottom;
	part.u.padding.left = left;

	return part;
}

/**
 * Widget part function for setting a padding.
 * @param padding The padding to use for all directions.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart SetPadding(uint8 padding)
{
	return SetPadding(padding, padding, padding, padding);
}

/**
 * Widget part function for setting a pre/inter/post spaces.
 * @param pre The amount of space before the first widget.
 * @param inter The amount of space between widgets.
 * @param post The amount of space after the last widget.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart SetPIP(uint8 pre, uint8 inter, uint8 post)
{
	NWidgetPart part;

	part.type = WPT_PIPSPACE;
	part.u.pip.pre = pre;
	part.u.pip.inter = inter;
	part.u.pip.post = post;

	return part;
}

/**
 * Widget part function for starting a new 'real' widget.
 * @param tp  Type of the new nested widget.
 * @param col Colour of the new widget.
 * @param idx Index of the widget in the widget array.
 * @note with #WWT_PANEL, #WWT_FRAME, #WWT_INSET, a new container is started.
 *       Child widgets must have a index bigger than the parent index.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart NWidget(WidgetType tp, Colours col, int16 idx)
{
	NWidgetPart part;

	part.type = tp;
	part.u.widget.colour = col;
	part.u.widget.index = idx;

	return part;
}

/**
 * Widget part function for starting a new horizontal container, vertical container, or spacer widget.
 * @param tp         Type of the new nested widget, #NWID_HORIZONTAL(_LTR), #NWID_VERTICAL, #NWID_SPACER, #NWID_SELECTION, or #NWID_LAYERED.
 * @param cont_flags Flags for the containers (#NWID_HORIZONTAL(_LTR) and #NWID_VERTICAL).
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart NWidget(WidgetType tp, NWidContainerFlags cont_flags = NC_NONE)
{
	NWidgetPart part;

	part.type = tp;
	part.u.cont_flags = cont_flags;

	return part;
}

/**
 * Obtain a nested widget (sub)tree from an external source.
 * @param func_ptr Pointer to function that returns the tree.
 * @ingroup NestedWidgetParts
 */
static inline NWidgetPart NWidgetFunction(NWidgetFunctionType *func_ptr)
{
	NWidgetPart part;

	part.type = WPT_FUNCTION;
	part.u.func_ptr = func_ptr;

	return part;
}

NWidgetContainer *MakeNWidgets(const NWidgetPart *parts, int count, int *biggest_index);

const Widget *InitializeWidgetArrayFromNestedWidgets(const NWidgetPart *parts, int parts_length, const Widget *orig_wid, Widget **wid_cache);

#endif /* WIDGET_TYPE_H */