use super::Mapper;
use crate::cartridge::Mirroring;
use crate::savestate::{SaveStateError, StateReader, StateWriter};
const PRG_BANK_8K: usize = 0x2000;
const WRAM_LEN: usize = 8192;
const CHR_BANK_1K: usize = 0x0400;
enum ChrMemory {
Rom(Vec<u8>),
Ram(Vec<u8>),
}
pub(super) struct IremG101 {
prg_rom: Vec<u8>,
chr: ChrMemory,
wram: Vec<u8>,
prg_banks: [u8; 2],
chr_banks: [u8; 8],
mirror_ctrl: u8,
}
impl IremG101 {
pub(super) fn new(prg_rom: Vec<u8>, chr_rom: Vec<u8>, mirroring: Mirroring) -> Self {
let chr = if chr_rom.is_empty() {
ChrMemory::Ram(vec![0; 0x2000])
} else {
ChrMemory::Rom(chr_rom)
};
Self {
prg_rom,
chr,
wram: vec![0; WRAM_LEN],
prg_banks: [0, 1],
chr_banks: [0; 8],
mirror_ctrl: ((mirroring as u8) & 1) ^ 1,
}
}
fn prg_bank_count_8k(&self) -> usize {
self.prg_rom.len() / PRG_BANK_8K
}
fn chr_bank_count_1k(&self) -> usize {
match &self.chr {
ChrMemory::Rom(r) => (r.len() / CHR_BANK_1K).max(1),
ChrMemory::Ram(r) => (r.len() / CHR_BANK_1K).max(1),
}
}
fn get_mirroring(&self) -> Mirroring {
if self.mirror_ctrl & 1 != 0 {
Mirroring::Horizontal
} else {
Mirroring::Vertical
}
}
fn is_swapped(&self) -> bool {
self.mirror_ctrl & 2 != 0
}
}
impl Mapper for IremG101 {
fn cpu_read(&mut self, addr: u16) -> Option<u8> {
match addr {
0x6000..=0x7FFF => Some(self.wram[(addr & 0x1FFF) as usize]),
0x8000..=0x9FFF | 0xC000..=0xDFFF => {
let is_8000 = self.is_swapped() ^ ((addr & 0x4000) == 0);
let (bank, base_addr) = if is_8000 {
(
self.prg_banks[0] as usize % self.prg_bank_count_8k(),
0x8000,
)
} else {
(self.prg_bank_count_8k().saturating_sub(2), 0xC000)
};
let offset = bank * PRG_BANK_8K + (addr as usize - base_addr);
Some(self.prg_rom[offset % self.prg_rom.len()])
}
0xA000..=0xBFFF => {
let bank = self.prg_banks[1] as usize % self.prg_bank_count_8k();
let offset = bank * PRG_BANK_8K + (addr as usize - 0xA000);
Some(self.prg_rom[offset % self.prg_rom.len()])
}
0xE000..=0xFFFF => {
let last = self.prg_bank_count_8k().saturating_sub(1);
let offset = last * PRG_BANK_8K + (addr as usize - 0xE000);
Some(self.prg_rom[offset % self.prg_rom.len()])
}
_ => None,
}
}
fn cpu_write(&mut self, addr: u16, data: u8) -> bool {
match addr {
0x6000..=0x7FFF => {
self.wram[(addr & 0x1FFF) as usize] = data;
true
}
0x8000..=0x8FFF => {
self.prg_banks[0] = data;
true
}
0x9000..=0x9FFF => {
self.mirror_ctrl = data;
true
}
0xA000..=0xAFFF => {
self.prg_banks[1] = data;
true
}
0xB000..=0xBFFF => {
self.chr_banks[(addr & 0x07) as usize] = data;
true
}
_ => false,
}
}
fn ppu_read(&mut self, addr: u16) -> Option<u8> {
if !matches!(addr, 0x0000..=0x1FFF) {
return None;
}
let slot = addr as usize / CHR_BANK_1K;
let bank = self.chr_banks[slot] as usize % self.chr_bank_count_1k();
let offset = bank * CHR_BANK_1K + (addr as usize & 0x03FF);
match &mut self.chr {
ChrMemory::Rom(chr_rom) => Some(chr_rom[offset % chr_rom.len()]),
ChrMemory::Ram(chr_ram) => Some(chr_ram[offset % chr_ram.len()]),
}
}
fn ppu_write(&mut self, addr: u16, data: u8) -> bool {
if !matches!(addr, 0x0000..=0x1FFF) {
return false;
}
let slot = addr as usize / CHR_BANK_1K;
let bank = self.chr_banks[slot] as usize % self.chr_bank_count_1k();
let offset = bank * CHR_BANK_1K + (addr as usize & 0x03FF);
if let ChrMemory::Ram(chr_ram) = &mut self.chr {
let len = chr_ram.len();
chr_ram[offset % len] = data;
}
true
}
fn mirroring(&self) -> Mirroring {
self.get_mirroring()
}
fn save_state(&self, writer: &mut StateWriter) {
writer.write_bytes(&self.prg_banks);
writer.write_bytes(&self.chr_banks);
writer.write_u8(self.mirror_ctrl);
writer.write_bytes(&self.wram);
match &self.chr {
ChrMemory::Rom(_) => writer.write_bool(false),
ChrMemory::Ram(chr_ram) => {
writer.write_bool(true);
writer.write_bytes(chr_ram);
}
}
}
fn load_state(&mut self, reader: &mut StateReader<'_>) -> Result<(), SaveStateError> {
reader.read_bytes_into(&mut self.prg_banks)?;
reader.read_bytes_into(&mut self.chr_banks)?;
self.mirror_ctrl = reader.read_u8()?;
reader.read_bytes_into(&mut self.wram)?;
let has_chr_ram = reader.read_bool()?;
match (&mut self.chr, has_chr_ram) {
(ChrMemory::Ram(chr_ram), true) => reader.read_bytes_into(chr_ram)?,
(ChrMemory::Rom(_), false) => {}
_ => {
return Err(SaveStateError::InvalidData(
"CHR RAM mismatch for Irem G-101 save state",
));
}
}
Ok(())
}
}