require'nes'

-- Press A to switch between the two PRG banks.

-- fixed 16kB for prgrom0, 3 other banks of 16kB each mappable at 0x8000
mappers.UxROM{ prgsize=(16+16*3)*1024 }

location(chrrom0)

local font = section("font")
    dc.b 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00 -- <SPC>
    dc.b 0x38,0x38,0x2c,0x64,0x7e,0x46,0xce,0x00,0x38,0x38,0x2c,0x64,0x7e,0x46,0xce,0x00 -- A
    dc.b 0xfc,0x62,0x66,0x7c,0x62,0x66,0xfc,0x00,0xfc,0x62,0x66,0x7c,0x62,0x66,0xfc,0x00 -- B
    dc.b 0x7c,0xe6,0xc2,0xc0,0xc0,0xe6,0x7c,0x00,0x7c,0xe6,0xc2,0xc0,0xc0,0xe6,0x7c,0x00 -- C
    dc.b 0xfc,0x4e,0x46,0x46,0x46,0xce,0xfc,0x00,0xfc,0x4e,0x46,0x46,0x46,0xce,0xfc,0x00 -- D
    dc.b 0xfe,0x66,0x60,0x7c,0x60,0x66,0xfe,0x00,0xfe,0x66,0x60,0x7c,0x60,0x66,0xfe,0x00 -- E
    dc.b 0xfe,0x66,0x60,0x7c,0x60,0x60,0xf0,0x00,0xfe,0x66,0x60,0x7c,0x60,0x60,0xf0,0x00 -- F
    dc.b 0x7c,0xe6,0xc0,0xce,0xc6,0xe6,0x7c,0x00,0x7c,0xe6,0xc0,0xce,0xc6,0xe6,0x7c,0x00 -- G
    dc.b 0xee,0x66,0x66,0x7e,0x66,0x66,0xee,0x00,0xee,0x66,0x66,0x7e,0x66,0x66,0xee,0x00 -- H
    dc.b 0x3c,0x18,0x18,0x18,0x18,0x18,0x3c,0x00,0x3c,0x18,0x18,0x18,0x18,0x18,0x3c,0x00 -- I
    dc.b 0x0e,0x06,0x06,0xc6,0xc6,0xce,0x7c,0x00,0x0e,0x06,0x06,0xc6,0xc6,0xce,0x7c,0x00 -- J
    dc.b 0xce,0xdc,0xf8,0xf0,0xf8,0xdc,0xce,0x00,0xce,0xdc,0xf8,0xf0,0xf8,0xdc,0xce,0x00 -- K
    dc.b 0xc0,0xc0,0xc0,0xc0,0xc6,0xc6,0xfe,0x00,0xc0,0xc0,0xc0,0xc0,0xc6,0xc6,0xfe,0x00 -- L
    dc.b 0xc6,0xee,0xfe,0xd6,0xc6,0xc6,0xc6,0x00,0xc6,0xee,0xfe,0xd6,0xc6,0xc6,0xc6,0x00 -- M
    dc.b 0xc6,0xe6,0xf6,0xde,0xce,0xc6,0xc6,0x00,0xc6,0xe6,0xf6,0xde,0xce,0xc6,0xc6,0x00 -- N
    dc.b 0x7c,0xee,0xc6,0xc6,0xc6,0xee,0x7c,0x00,0x7c,0xee,0xc6,0xc6,0xc6,0xee,0x7c,0x00 -- O
    dc.b 0xfc,0xc6,0xc6,0xc6,0xfc,0xc0,0xc0,0x00,0xfc,0xc6,0xc6,0xc6,0xfc,0xc0,0xc0,0x00 -- P
    dc.b 0x7c,0xce,0xc6,0xc6,0xde,0xec,0x7e,0x00,0x7c,0xce,0xc6,0xc6,0xde,0xec,0x7e,0x00 -- Q
    dc.b 0xfc,0x66,0x66,0x7c,0x58,0x6c,0xe6,0x00,0xfc,0x66,0x66,0x7c,0x58,0x6c,0xe6,0x00 -- R
    dc.b 0x7c,0xc6,0xc0,0x7c,0x06,0xc6,0x7c,0x00,0x7c,0xc6,0xc0,0x7c,0x06,0xc6,0x7c,0x00 -- S
    dc.b 0xfe,0x92,0x10,0x10,0x10,0x10,0x38,0x00,0xfe,0x92,0x10,0x10,0x10,0x10,0x38,0x00 -- T
    dc.b 0xe6,0xe6,0xc2,0xc2,0xc2,0xe6,0x7c,0x00,0xe6,0xe6,0xc2,0xc2,0xc2,0xe6,0x7c,0x00 -- U
    dc.b 0xc6,0xc6,0xc6,0x6c,0x6c,0x38,0x38,0x00,0xc6,0xc6,0xc6,0x6c,0x6c,0x38,0x38,0x00 -- V
    dc.b 0xc6,0xc6,0xd6,0xfe,0xee,0xc6,0x82,0x00,0xc6,0xc6,0xd6,0xfe,0xee,0xc6,0x82,0x00 -- W
    dc.b 0x86,0xcc,0x78,0x30,0x78,0xcc,0x86,0x00,0x86,0xcc,0x78,0x30,0x78,0xcc,0x86,0x00 -- X
    dc.b 0xc6,0xc6,0x6c,0x38,0x18,0x18,0x38,0x00,0xc6,0xc6,0x6c,0x38,0x18,0x18,0x38,0x00 -- Y
    dc.b 0x7e,0xce,0x98,0x30,0x62,0xe6,0xfc,0x00,0x7e,0xce,0x98,0x30,0x62,0xe6,0xfc,0x00 -- Z
charset(" abcdefghijklmnopqrstuvwxyz", \x(x + (font.org - font.location.start) // 16))

-- define some text of same length in both swappable PRG banks 1 and 2
location(prgrom1)
local text1 = "bank one"
local sec_text1 = section("text1") byte(text1)

location(prgrom2)
local text2 = "bank two"
local sec_text2 = section("text2") byte(text2)
-- force sec_text2 to have same offset in prgrom2 than sec_text1 in prgrom1,
-- so we can use either address to reference the custom bank data
relate(sec_text1, sec_text2)

-- fixed bank, last 16kB
location(prgrom)
@@nmi @irq rti

joya = 1
curbank = 0
@@switchbank
    lda #3
    eor curbank
    sta curbank
    switchprgrom()
    -- load screen text in PPU RAM 0x21CA
    ppu_addr(0x21ca)
    ldy #0 @_loadtxt lda sec_text1,y sta PPUDATA iny cpy ##text1 bne _loadtxt
    -- reset scroll position
    ppu_addr(0) sta BGSCROL sta BGSCROL
    rts

@@main
    init()
    vblank_waitbegin()
    -- load BG palette in PPU RAM
    ppu_addr(BGPAL)
    for _,v in ipairs{ 0x1f, 0x00, 0x10, 0x20 } do lda #v sta PPUDATA end
    -- switch between the two banks
    lda #2 sta curbank
    jsr switchbank
    -- show BG
    lda #0x0a sta PPUMASK
    -- idle
@_loop
    vblank_waitbegin()
    read_joy_a(1) bcc _noswitch
    lda joya bne _switch
    jsr switchbank lda #1 sta joya bne _switch
@_noswitch
    lda #0 sta joya
@_switch
    jmp _loop

writebin(filename..'.nes')
writesym(filename..'.mlb', 'mesen')
writesym(filename..'.nes', 'fceux')
print(stats)