.segment "CODE"

.scope Driver
    ;; Timer for the player to be able to pick up the joypad upon entering the
    ;; game.
    ;;
    ;; NOTE: this memory address is shared with `zp_title_timer`, as they can
    ;; never conflict with each other.
    zp_player_timer = $30
    PLAYER_TIMER_VALUE = HZ * 2

    .ifdef PAL
        ;; Frame counter which resets every 5 frames.
        zp_pal_counter = $31
    .endif

    ;; Timer for the pause/unpause workflow.
    PAUSE_TIMER_VALUE = (HZ / 3)
    zp_pause_timer = $32

    ;; Switch from the title screen to the main street. Note that this function
    ;; is to be called with the PPU disabled. If that's not the case, then it
    ;; will set the proper values to disable it on the next `nmi` call and set
    ;; the `title over` flag. With that, call again this function so the
    ;; switching is actually performed.
    .proc switch
        ;; Some things from here require the PPU to be disabled. Hence, if
        ;; that's not the case, disable it now. The `ppu` and the `title over`
        ;; flags are set as well.
        lda PPU::zp_mask
        beq @do_switch
        lda #%01000100
        ora Globals::zp_flags
        sta Globals::zp_flags
        lda #$00
        sta PPU::zp_mask
        rts

    @do_switch:
        ;; Get the assets ready for the main screen. That is, make sure that the
        ;; palettes and such are as desired since the title screen needed
        ;; another setup.
        jsr Assets::prepare_for_main_screen

        ;; Switch to the other base nametable.
        lda #%10001010
        sta PPU::zp_control

        ;; Enable back the PPU.
        lda #%00011110
        sta PPU::zp_mask

        ;; Setup the player timer.
        .ifdef PARTIAL
            lda #1
        .else
            lda #PLAYER_TIMER_VALUE
        .endif
        sta zp_player_timer

        ;; Mark the state of the game as "game". That is, the player has
        ;; started. Also set the `ppu` flag and unset the `title over` one.
        lda #%01000001
        ora Globals::zp_flags
        and #%11111011
        sta Globals::zp_flags

        rts
    .endproc

    .proc update
        lda zp_player_timer
        beq @game

        dec zp_player_timer
        beq @load_player

        ;; TODO: blinking of the selected player (every HZ count?).
        rts

    @load_player:
        jsr Player::init

        ;; Initialize pause timer.
        lda #0
        sta zp_pause_timer

    @game:
        ;; Check if the player is toggling the `pause` state.
        lda #(Joypad::BUTTON_START | Joypad::BUTTON_SELECT)
        and Joypad::zp_buttons1
        beq @skip_pause_handling

        ;; What does the timer say, is the player allowed to do it?
        lda zp_pause_timer
        bne @skip_pause_handling

        ;; The timer is zero and the player asked to pause, let's reset the
        ;; timer.
        lda #PAUSE_TIMER_VALUE
        sta zp_pause_timer

        ;; Pause vs unpause.
        lda #%00001000
        and Globals::zp_flags
        bne @unpause

        ;; Pause: set the flag and skip the update.
        lda #%00001000
        ora Globals::zp_flags
        sta Globals::zp_flags
        rts

    @unpause:
        ;; Unset the flag and go to update.
        lda #%11110111
        and Globals::zp_flags
        sta Globals::zp_flags
        bne @do_update

    @skip_pause_handling:
        ;; Decrement the pause timer if it's not in a zero value.
        lda zp_pause_timer
        beq @pause_check
        dec zp_pause_timer

    @pause_check:
        ;; Are we paused? If so return before updating.
        lda #%00001000
        and Globals::zp_flags
        beq @do_update
        rts

    @do_update:
        JAL Player::update
    .endproc

    .ifdef PAL
        ;; All the code that is needed to fix some values for PAL machines.
        .proc pal_handler
            ;; Check if 5 frames have passed since last counter reset.
            lda Driver::zp_pal_counter
            cmp #4
            beq @do_handle

            ;; Nope! Reset the player's step on PAL and increase the counter.
            lda #1
            sta Player::zp_step_on_pal
            inc Driver::zp_pal_counter
            bne @end

        @do_handle:
            ;; Increase the step just for this frame and reset the counter.
            lda Player::zp_step_on_pal
            clc
            adc #2
            sta Player::zp_step_on_pal
            lda #0
            sta Driver::zp_pal_counter
        @end:
            rts
        .endproc
    .endif
.endscope