"""Generates the TI-99/4A cartridge viewer (TMS9900 machine code).

Sets the TMS9918A to Graphics Mode 2 (256x192 bitmap), 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.
"""

from __future__ import annotations

from .tms9900 import Asm

VDP_DATA = 0x8C00     # write VRAM data
VDP_CTRL = 0x8C02     # write address / register
VDP_STATUS = 0x8802   # read VDP status (bit 7 = frame flag, cleared on read)
WORKSPACE = 0x8300    # scratchpad RAM

# VDP register values for Graphics Mode 2.
VDP_REGS = [
    0x02,   # R0  M3=1 (bitmap)
    0xC0,   # R1  16K + display on, interrupts off
    0x0E,   # R2  name table   >3800
    0xFF,   # R3  colour table >2000 (full 768 rows)
    0x03,   # R4  pattern table >0000 (full 768 rows)
    0x36,   # R5  sprite attr   >1B00 (parked)
    0x07,   # R6  sprite patt   >3800 (parked)
    0x01,   # R7  backdrop = black
]

PATTERN_BYTES = 6144
NCELLS = 768


def _set_write_addr(a: Asm, addr: int):
    """Point the VDP write address at VRAM `addr` (low byte then high|>40)."""
    a.li(0, (addr & 0xFF) << 8);          a.movb_r_sym(0, VDP_CTRL)
    a.li(0, (((addr >> 8) | 0x40) & 0xFF) << 8); a.movb_r_sym(0, VDP_CTRL)


def build(code_base: int, data_addr: int, display: str = "forever",
          seconds: int = 0, video: str = "ntsc") -> bytes:
    """Emit the viewer. `data_addr` = ROM address of the 6912-byte image data.

    `display` (forever/key/seconds) chooses how long the picture is held; on
    key/seconds the console is reset (BLWP @>0000) back to the TI title screen.
    """
    a = Asm(code_base)
    a.limi(0x0000)              # interrupts off
    a.lwpi(WORKSPACE)           # our register file in scratchpad

    # ---- programme the 8 VDP registers ----
    for reg, val in enumerate(VDP_REGS):
        a.li(0, val << 8)
        a.movb_r_sym(0, VDP_CTRL)
        a.li(0, (0x80 | reg) << 8)
        a.movb_r_sym(0, VDP_CTRL)

    # ---- name table >3800 = 0,1,...,255 repeated three times (768 bytes) ----
    _set_write_addr(a, 0x3800)
    a.clr(3)                    # R3 high byte = current value
    a.li(2, NCELLS)             # 768 entries
    a.label("nameloop")
    a.movb_r_sym(3, VDP_DATA)
    a.ai(3, 0x0100)             # value += 1 (in high byte, wraps mod 256)
    a.dec(2)
    a.jne("nameloop")

    # ---- pattern table >0000 = 6144 bytes copied from ROM ----
    _set_write_addr(a, 0x0000)
    a.li(1, data_addr)
    a.li(2, PATTERN_BYTES)
    a.label("patloop")
    a.movb_sinc_sym(1, VDP_DATA)
    a.dec(2)
    a.jne("patloop")

    # ---- colour table >2000 = each cell colour written 8x (768 -> 6144) ----
    _set_write_addr(a, 0x2000)
    a.li(1, data_addr + PATTERN_BYTES)
    a.li(2, NCELLS)
    a.label("colloop")
    a.movb_sinc_r(1, 4)         # R4 high byte = colour byte, advance ROM ptr
    for _ in range(8):
        a.movb_r_sym(4, VDP_DATA)
    a.dec(2)
    a.jne("colloop")

    # ---- how long to hold the picture ----
    if display == "seconds":
        rate = 50 if video == "pal" else 60
        frames = max(1, min(0xFFFF, int(seconds) * rate))
        a.li(2, frames)             # R2 = frames to wait
        a.label("fwait")
        a.movb_sym_r(VDP_STATUS, 1)  # read status (clears frame flag)
        a.andi(1, 0x8000)            # bit 7 = a new frame elapsed
        a.jeq("fwait")
        a.dec(2)
        a.jne("fwait")
        a.blwp_sym(0x0000)           # reset -> TI title screen
    elif display == "key":
        # scan keyboard columns 0..5; any pressed key (a row reads 0) -> reset.
        a.label("kscan")
        for col in range(6):
            a.li(12, 0x0024)         # CRU base for the column select
            a.li(5, col << 8)        # column in the low 3 bits of the high byte
            a.ldcr(5, 3)             # drive the 3 column-select lines
            a.li(12, 0x0006)         # CRU base for the 8 row inputs
            a.stcr(6, 8)             # read rows into R6 high byte (idle = >FF)
            a.ci(6, 0xFF00)          # any key down makes a row 0
            a.jne("kdone")
        a.jmp("kscan")
        a.label("kdone")
        a.blwp_sym(0x0000)           # reset -> TI title screen
    else:                            # forever
        a.label("halt")
        a.jmp("halt")
    return a.resolve()