"""Build an Amiga Copper list that displays a static 320x200 low-res screen.

The Copper runs every frame and re-loads the bitplane pointers + registers, so
the picture stays stable.  Each instruction is a MOVE (register offset, value);
the list ends with WAIT $FFFF,$FFFE.
"""
from __future__ import annotations

import struct

DIWSTRT, DIWSTOP, DDFSTRT, DDFSTOP = 0x08E, 0x090, 0x092, 0x094
BPLCON0, BPLCON1, BPLCON2 = 0x100, 0x102, 0x104
BPL1MOD, BPL2MOD = 0x108, 0x10A
BPLPT = 0x0E0                          # BPL1PTH; +4 per plane
COLOR0 = 0x180


def list_len(nplanes, ncolors) -> int:
    pairs = 9 + nplanes * 2 + ncolors  # DIW*2, DDF*2, BPLCON0/1/2, BPLMOD*2 = 9
    return pairs * 4 + 4               # + end WAIT


def build(nplanes, ham, plane_addrs, colors) -> bytes:
    bplcon0 = (nplanes << 12) | (0x0800 if ham else 0) | 0x0200
    moves = [
        (DIWSTRT, 0x2C81), (DIWSTOP, 0xF4C1),
        (DDFSTRT, 0x0038), (DDFSTOP, 0x00D0),
        (BPLCON0, bplcon0), (BPLCON1, 0x0000), (BPLCON2, 0x0024),
        (BPL1MOD, 0x0000), (BPL2MOD, 0x0000),
    ]
    for p, addr in enumerate(plane_addrs):
        moves.append((BPLPT + p * 4, (addr >> 16) & 0xFFFF))
        moves.append((BPLPT + p * 4 + 2, addr & 0xFFFF))
    for i, c in enumerate(colors):
        moves.append((COLOR0 + i * 2, c & 0x0FFF))

    out = bytearray()
    for reg, val in moves:
        out += struct.pack(">HH", reg & 0x1FE, val & 0xFFFF)
    out += struct.pack(">HH", 0xFFFF, 0xFFFE)      # end of copper list
    return bytes(out)