%include "ponydos.inc"
cpu 8086
bits 16

%ifdef BLINKY
TITLEBAR_ATTRIBUTE equ 0x07
WINDOW_ATTRIBUTE equ 0x70
%else
TITLEBAR_ATTRIBUTE equ 0x0f
WINDOW_ATTRIBUTE equ 0xf0
%endif

WINDOW_STATUS_NORMAL equ 0
WINDOW_STATUS_MOVE equ 1

; 0x0000
jmp near process_event

; 0x0003 PROC_INITIALIZE_ENTRYPOINT
; initialize needs to preserve ds
initialize:
	push ds

	; On entry, ds and es will not be set correctly for us
	mov bp, cs
	mov ds, bp
	mov es, bp

	call hook_self_onto_window_chain

	; We must explicitly request redraw from the compositor
	call request_redraw

	pop ds
	retf

; process_event needs to preserve all registers other than ax
; in:
;  al = event
;  bx = window ID
;  cx, dx = event-specific
; out:
;  ax = event-specific
process_event:
	push bx
	push cx
	push dx
	push si
	push di
	push bp
	push ds
	push es

	; On entry, ds and es will not be set correctly for us
	mov bp, cs
	mov ds, bp
	mov es, bp

	cmp al, WM_PAINT
	jne .not_paint
	call event_paint
	jmp .end
	.not_paint:

	cmp al, WM_MOUSE
	jne .not_mouse
	call event_mouse
	jmp .end
	.not_mouse:

	cmp al, WM_KEYBOARD
	jne .not_keyboard
	call event_keyboard
	jmp .end
	.not_keyboard:

	cmp al, WM_UNHOOK
	jne .not_unhook
	call event_unhook
	jmp .end
	.not_unhook:

	cmp al, WM_OPEN_FILE
	jne .not_open_file
	call event_open_file
	jmp .end
	.not_open_file:

	.end:
	cmp byte [exiting], 0
	je .not_exiting
	; Once we have deallocated our own memory, we may not call any
	; external functions that might allocate. Safest place to do the
	; deallocation is just before returning control to our caller
	call deallocate_own_memory
	.not_exiting:

	pop es
	pop ds
	pop bp
	pop di
	pop si
	pop dx
	pop cx
	pop bx
	retf

; ------------------------------------------------------------------
; Event handlers
; ------------------------------------------------------------------

; in:
;  al = WM_PAINT
;  bx = window ID
; out:
;  clobbers everything
event_paint:
	; Forward the paint event to the next window in the chain
	; We must do this before we paint ourselves, because painting must
	; happen from the back to the front
	; Because we only have one window, we don't need to save our own ID
	mov bx, [window_next]
	call send_event

	call update_usage_display

	mov bx, [window_width] ; Buffer width, usually same as window width
	mov cx, [window_width]
	mov dx, [window_height]
	mov si, window_data
	mov di, [window_x]
	mov bp, [window_y]

	cmp di, 0
	jge .not_clip_left
	.clip_left:
		; Adjust the start of buffer to point to the first cell
		; that is on screen
		sub si, di
		sub si, di
		; Adjust window width to account for non-rendered area
		; that is off screen
		add cx, di
		; Set X to 0
		xor di, di
	.not_clip_left:

	mov ax, di
	add ax, cx
	cmp ax, COLUMNS
	jle .not_clip_right
	.clip_right:
		; Adjust the width to only go as far as the right edge
		sub ax, COLUMNS
		sub cx, ax
	.not_clip_right:

	mov ax, bp
	add ax, dx
	cmp ax, ROWS
	jle .not_clip_bottom
	.clip_bottom:
		; Adjust the height to only go as far as the bottom edge
		sub ax, ROWS
		sub dx, ax
	.not_clip_bottom:

	call PONYDOS_SEG:SYS_DRAW_RECT

	ret

; in:
;  al = WM_MOUSE
;  bx = window ID
;  cl = X
;  ch = Y
;  dl = mouse buttons held down
; out:
;  clobbers everything
event_mouse:
	test dl, MOUSE_PRIMARY | MOUSE_SECONDARY
	jnz .not_end_window_change
	; If we were moving the window, releasing the button signals the
	; end of the action
	mov byte [window_status], WINDOW_STATUS_NORMAL
	.not_end_window_change:

	; Expand X and Y to 16 bits for easier calculations
	; Because we only have one window, we don't need to save our own ID
	xor bx, bx
	mov bl, ch
	xor ch, ch

	; Are we moving the window at the moment?
	cmp byte [window_status], WINDOW_STATUS_MOVE
	jne .not_moving
	call move_window
	.not_moving:

	; Check if the mouse is outside our window
	cmp cx, [window_x]
	jl .outside ; x < window_x
	cmp bx, [window_y]
	jl .outside ; y < window_y
	mov ax, [window_x]
	add ax, [window_width]
	cmp ax, cx
	jle .outside ; window_x + window_width <= x
	mov ax, [window_y]
	add ax, [window_height]
	cmp ax, bx
	jle .outside ; window_y + window_height <= y

	.inside:
		cmp byte [window_mouse_released_inside], 0
		je .not_click
		test dl, MOUSE_PRIMARY | MOUSE_SECONDARY
		jz .not_click
		.click:
			call event_click
		.not_click:

		; We need to keep track of if the mouse has been inside our
		; window without the buttons held, in order to avoid
		; generating click events in cases where the cursor is
		; dragged into our window while buttons are held
		test dl, MOUSE_PRIMARY | MOUSE_SECONDARY
		jz .buttons_not_held
		.buttons_held:
			mov byte [window_mouse_released_inside], 0
			jmp .buttons_end
		.buttons_not_held:
			mov byte [window_mouse_released_inside], 1
		.buttons_end:

		; We must forward the event even if it was inside our
		; window, to make sure other windows know when the mouse
		; leaves them
		; Set x and y to 255 so that windows below ours don't think
		; the cursor is inside them
		; Also clear the mouse buttons – not absolutely necessary
		; but it's cleaner if other windows don't get any
		; information about the mouse
		mov al, WM_MOUSE
		mov bx, [window_next]
		mov cx, 0xffff
		xor dl, dl
		call send_event
		ret

	.outside:
		mov byte [window_mouse_released_inside], 0

		; Not our window, forward the event
		mov al, WM_MOUSE
		mov ch, bl ; Pack the X and Y back into cx
		mov bx, [window_next]
		call send_event
		ret
	ret

; in:
;  bx = Y
;  cx = X
;  dl = mouse buttons
event_click:
	push ax
	; This is not a true event passed into our event handler, but
	; rather one we've synthetized from the mouse event
	; The reason we synthetize this event is because most interface
	; elements react to clicks specifically, so having this event
	; making implementing them easier

	; Raising a window is done by first unhooking, then rehooking it to
	; the window chain
	call unhook_self_from_window_chain
	call hook_self_onto_window_chain
	call request_redraw

	; Did the user click the title bar?
	cmp [window_y], bx
	jne .not_title_bar
	.title_bar:
		; Did the user click the window close button?
		mov ax, [window_x]
		add ax, [window_width]
		dec ax
		cmp ax, cx
		jne .not_close
		.close:
			call unhook_self_from_window_chain
			mov byte [exiting], 1
			; We don't need to call request_redraw here, since
			; it will be called unconditionally above
			jmp .title_bar_end
		.not_close:

		; Clicking on the title bar signals beginning of a window
		; move
		mov byte [window_status], WINDOW_STATUS_MOVE
		mov ax, [window_x]
		sub ax, cx
		mov [window_move_x_offset], ax
	.title_bar_end:
	.not_title_bar:

	.end:
	pop ax
	ret

; in:
;  al = WM_KEYBOARD
;  bx = window ID
;  cl = typed character
;  ch = pressed key
; out:
;  clobbers everything
event_keyboard:
	; Unlike most other events, keyboard events are not forwarded
	; Since we do not care about the keyboard for this app, we just
	; swallow the event
	ret

; in:
;  al = WM_UNHOOK
;  bx = window ID
;  cx = window ID of the window to unhook from the window chain
; out:
;  ax = own window ID if we did not unhook
;       next window ID if we did
;  clobbers everything else
event_unhook:
	cmp bx, cx
	je .unhook_self

	; Save our own ID
	push bx

	; Propagate the event
	mov bx, [window_next]
	call send_event

	; Update window_next in case the next one unhooked
	mov [window_next], ax

	; Return our own ID
	pop ax
	ret

	.unhook_self:
		; Return window_next to the caller, unhooking us from the
		; chain
		mov ax, [window_next]
		ret

; in:
;  al = WM_OPEN_FILE
;  ds:cx = filename
;  ds ≠ cs
; out:
;  ds = cs
;  clobbers everything
event_open_file:
	; File open events are sent specifically to a process, so we don't
	; need to forward it
	; Unlike other event handlers, event_open_file is called with ds
	; still set to calling process's segment, so that it can read the
	; passed-in filename. For simplicity of code running after the,
	; event handlers, we set ds to point to our own segment on return
	push cs
	pop ds
	ret

; ------------------------------------------------------------------
; Event handler subroutines
; ------------------------------------------------------------------

; in:
;  bx = Y
;  cx = X
move_window:
	push ax

	; Offset the X coördinate so that the apparent drag position
	; remains the same
	mov ax, cx
	add ax, [window_move_x_offset]

	; Only do an update if something has changed. Reduces flicker
	cmp [window_x], ax
	jne .update_location
	cmp [window_y], bx
	jne .update_location
	jmp .end

	.update_location:
		mov [window_x], ax
		mov [window_y], bx
		call request_redraw

	.end:
	pop ax
	ret

update_usage_display:
	push ax
	push cx
	push si
	push di
	push ds

	mov cx, PONYDOS_SEG
	mov ds, cx

	mov si, GLOBAL_MEMORY_ALLOCATION_MAP
	mov di, window_data.indicators
	mov cx, MEM_ALLOCATION_MAP_SIZE
	.loop:
		lodsb
		test al, al
		jz .unused
		.used:
			mov al, 0xfe
			jmp .loop_bottom
		.unused:
			xor al, al

		.loop_bottom:
		stosb
		inc di
		loop .loop

	.end:
	pop ds
	pop di
	pop si
	pop cx
	pop ax
	ret

; ------------------------------------------------------------------
; Window chain
; ------------------------------------------------------------------

; in:
;  al = event
;  bx = window to send the event to
;  cx, dx = event-specific
; out:
;  ax = event-specific, 0 if bx=0
send_event:
	test bx, bx
	jnz .non_zero_id

	; Returning 0 if the window ID is 0 makes window unhooking simpler
	xor ax, ax
	ret

	.non_zero_id:
	push bp

	; Push the return address
	push cs
	mov bp, .end
	push bp

	; Push the address we're doing a far-call to
	mov bp, bx
	and bp, 0xf000 ; Highest nybble of window ID marks the segment
	push bp
	xor bp, bp ; Event handler is always at address 0
	push bp

	retf

	.end:
	pop bp
	ret

hook_self_onto_window_chain:
	push ax
	push es

	mov ax, PONYDOS_SEG
	mov es, ax

	; Window ID is made of the segment (top nybble) and an arbitrary
	; process-specific part (lower three nybbles). Since we only have
	; one window, we can leave the process-specific part as zero
	mov ax, cs

	xchg [es:GLOBAL_WINDOW_CHAIN_HEAD], ax

	; Save the old head of the chain, so that we can propagate events
	; down to it
	mov [window_next], ax

	pop es
	pop ax
	ret

unhook_self_from_window_chain:
	push bx
	push cx
	push es

	mov ax, PONYDOS_SEG
	mov es, ax

	mov al, WM_UNHOOK
	mov bx, [es:GLOBAL_WINDOW_CHAIN_HEAD]
	; Our window ID is just our segment, see the comment in
	; hook_self_onto_window_chain
	mov cx, cs
	call send_event

	; Update the head of the chain, in case we were at the head
	mov [es:GLOBAL_WINDOW_CHAIN_HEAD], ax

	pop es
	pop cx
	pop bx
	ret

; ------------------------------------------------------------------
; Memory management
; ------------------------------------------------------------------

deallocate_own_memory:
	push bx
	push cx
	push es

	mov bx, PONYDOS_SEG
	mov es, bx

	; Segment 0xn000 corresponds to slot n in the allocation table
	mov bx, cs
	mov cl, 12
	shr bx, cl

	mov byte [es:GLOBAL_MEMORY_ALLOCATION_MAP + bx], 0

	pop es
	pop cx
	pop bx
	ret

; ------------------------------------------------------------------
; Painting
; ------------------------------------------------------------------

request_redraw:
	push ax
	push es

	mov ax, PONYDOS_SEG
	mov es, ax

	mov byte [es:GLOBAL_REDRAW], 1

	pop es
	pop ax
	ret

; ------------------------------------------------------------------
; Variables
; ------------------------------------------------------------------

exiting db 0

window_next dw 0xffff
window_x dw 65
window_y dw 3
window_width dw 10
window_height dw 3

window_mouse_released_inside db 0
window_status db WINDOW_STATUS_NORMAL
window_move_x_offset dw 0

window_data:
	db 'U', TITLEBAR_ATTRIBUTE, 's', TITLEBAR_ATTRIBUTE, 'a', TITLEBAR_ATTRIBUTE, 'g', TITLEBAR_ATTRIBUTE, 'e', TITLEBAR_ATTRIBUTE
	times 10-5-1 db 0x00, TITLEBAR_ATTRIBUTE
	db 'x', TITLEBAR_ATTRIBUTE
	db '0', WINDOW_ATTRIBUTE, '1', WINDOW_ATTRIBUTE, '2', WINDOW_ATTRIBUTE, '3', WINDOW_ATTRIBUTE, '4', WINDOW_ATTRIBUTE, '5'
	db WINDOW_ATTRIBUTE, '6', WINDOW_ATTRIBUTE, '7', WINDOW_ATTRIBUTE, '8', WINDOW_ATTRIBUTE, '9', WINDOW_ATTRIBUTE
	.indicators: times 10 db 0x00, WINDOW_ATTRIBUTE