"""Generates the ColecoVision/Adam cartridge viewer (Z80 machine code).

Sets the TMS9918A to Graphics Mode 2, builds the name table, copies the
6144-byte pattern from cartridge ROM to VRAM >0000, and expands the 768 per-cell
colour bytes x8 into the 6144-byte colour table at VRAM >2000 -- the same picture
the TI-99 viewer makes, but in Z80 with the ColecoVision VDP ports.

display: forever (hold), key (poll the controller's fire button then reset),
seconds (count VDP frame flags then reset).  A cartridge has no OS to return to,
so key/seconds reset the machine (JP 0), which re-runs the cart and re-displays.
"""

from __future__ import annotations

from .z80 import Asm

VDP_DATA = 0xBE          # data port (VRAM, auto-increment)
VDP_CTRL = 0xBF          # control port (address / register / status)
VDP_REGS = [0x02, 0xC0, 0x0E, 0xFF, 0x03, 0x36, 0x07, 0x01]   # Graphics Mode 2
PATTERN_BYTES = 6144
NCELLS = 768
RATE = 60               # NTSC frames/second
JOY_SEG = 0xC0          # OUT (>C0) selects the joystick / left-fire segment
JOY_PORT = 0xFC         # IN (>FC) reads controller 1
SOUND_PORT = 0xFF       # SN76489 sound chip
# SN76489 "attenuation = 15 (off)" latch byte for each of the 4 channels.
SOUND_OFF = [0x9F, 0xBF, 0xDF, 0xFF]


def _set_write_addr(a: Asm, addr: int):
    a.ld_a(addr & 0xFF);                 a.out_n_a(VDP_CTRL)
    a.ld_a(((addr >> 8) & 0x3F) | 0x40); a.out_n_a(VDP_CTRL)


def build(code_base: int, data_addr: int, display: str = "forever",
          seconds: int = 0) -> bytes:
    a = Asm(code_base)
    a.di()

    # ---- silence the SN76489 (our >55AA header skips the BIOS sound init, so the
    #      chip powers up holding a tone); set all 4 channels to attenuation off ----
    for v in SOUND_OFF:
        a.ld_a(v)
        a.out_n_a(SOUND_PORT)

    # ---- programme the 8 VDP registers ----
    for reg, val in enumerate(VDP_REGS):
        a.ld_a(val);        a.out_n_a(VDP_CTRL)
        a.ld_a(0x80 | reg); a.out_n_a(VDP_CTRL)

    # ---- name table >3800 = 0,1,...,255 repeated 3 times (768 bytes) ----
    _set_write_addr(a, 0x3800)
    a.ld_a(0)
    a.ld_c(3)
    a.label("name_o")
    a.ld_b(0)                            # B=0 -> DJNZ runs 256 times
    a.label("name_i")
    a.out_n_a(VDP_DATA)
    a.inc_a()
    a.djnz("name_i")
    a.dec_c()
    a.jr_nz("name_o")

    # ---- pattern table >0000 = 6144 bytes from ROM (24 * 256) ----
    _set_write_addr(a, 0x0000)
    a.ld_hl(data_addr)
    a.ld_c(PATTERN_BYTES // 256)
    a.label("pat_o")
    a.ld_b(0)
    a.label("pat_i")
    a.ld_a_hl()
    a.out_n_a(VDP_DATA)
    a.inc_hl()
    a.djnz("pat_i")
    a.dec_c()
    a.jr_nz("pat_o")

    # ---- colour table >2000 = each cell colour written 8x (768 -> 6144) ----
    _set_write_addr(a, 0x2000)
    a.ld_hl(data_addr + PATTERN_BYTES)
    a.ld_c(NCELLS // 256)
    a.label("col_o")
    a.ld_b(0)
    a.label("col_i")
    a.ld_a_hl()
    for _ in range(8):
        a.out_n_a(VDP_DATA)
    a.inc_hl()
    a.djnz("col_i")
    a.dec_c()
    a.jr_nz("col_o")

    # ---- hold the picture ----
    if display == "key":
        a.label("kwait")
        a.ld_a(0); a.out_n_a(JOY_SEG)    # select joystick / left-fire segment
        a.in_a_n(JOY_PORT)
        a.and_n(0x40)                    # bit 6 = fire button (active low)
        a.jr_nz("kwait")                 # still high -> not pressed
        a.jp(0x0000)                     # reset -> re-display
    elif display == "seconds":
        a.ld_de(max(1, min(0xFFFF, int(seconds) * RATE)))
        a.label("swait")
        a.in_a_n(VDP_CTRL)               # read VDP status (clears frame flag)
        a.and_n(0x80)
        a.jr_z("swait")                  # no new frame yet
        a.dec_de()
        a.ld_a_d(); a.or_e()
        a.jr_nz("swait")
        a.jp(0x0000)                     # reset -> re-display
    else:                                # forever
        a.label("hang")
        a.jr("hang")
    return a.resolve()