use super::Mapper;
use crate::cartridge::{CHR_BANK_LEN, Mirroring};
use crate::savestate::{SaveStateError, StateReader, StateWriter};
const PRG_RAM_LEN: usize = 0x2000;
const PRG_BANK_LEN: usize = 0x8000;
enum ChrMemory {
Rom(Vec<u8>),
Ram(Vec<u8>),
}
pub(super) struct Anrom {
prg_rom: Vec<u8>,
prg_ram: Vec<u8>,
chr: ChrMemory,
selected_prg_bank: usize,
mirroring: Mirroring,
}
impl Anrom {
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; CHR_BANK_LEN])
} else {
ChrMemory::Rom(chr_rom)
};
Self {
prg_rom,
prg_ram: vec![0; PRG_RAM_LEN],
chr,
selected_prg_bank: 0,
mirroring: Mirroring::SPAGE0,
}
}
fn prg_bank_count(&self) -> usize {
(self.prg_rom.len() / PRG_BANK_LEN).max(1)
}
fn prg_rom_index(&self, addr: u16) -> usize {
let bank = self.selected_prg_bank % self.prg_bank_count();
let offset = addr as usize - 0x8000;
(bank * PRG_BANK_LEN + offset) % self.prg_rom.len()
}
}
impl Mapper for Anrom {
fn cpu_read(&mut self, addr: u16) -> Option<u8> {
match addr {
0x6000..=0x7FFF => Some(self.prg_ram[(addr - 0x6000) as usize]),
0x8000..=0xFFFF => Some(self.prg_rom[self.prg_rom_index(addr)]),
_ => None,
}
}
fn cpu_write(&mut self, addr: u16, data: u8) -> bool {
match addr {
0x6000..=0x7FFF => {
self.prg_ram[(addr - 0x6000) as usize] = data;
true
}
0x8000..=0xFFFF => {
self.selected_prg_bank = (data & 0x0F) as usize;
self.mirroring = if data & 0x10 == 0 {
Mirroring::SPAGE0
} else {
Mirroring::SPAGE1
};
true
}
_ => false,
}
}
fn ppu_read(&mut self, addr: u16) -> Option<u8> {
match (&mut self.chr, addr) {
(ChrMemory::Rom(chr_rom), 0x0000..=0x1FFF) => Some(chr_rom[addr as usize]),
(ChrMemory::Ram(chr_ram), 0x0000..=0x1FFF) => Some(chr_ram[addr as usize]),
_ => None,
}
}
fn ppu_write(&mut self, addr: u16, data: u8) -> bool {
match (&mut self.chr, addr) {
(ChrMemory::Ram(chr_ram), 0x0000..=0x1FFF) => {
chr_ram[addr as usize] = data;
true
}
(ChrMemory::Rom(_), 0x0000..=0x1FFF) => true,
_ => false,
}
}
fn mirroring(&self) -> Mirroring {
self.mirroring
}
fn save_state(&self, writer: &mut StateWriter) {
writer.write_bytes(&self.prg_ram);
writer.write_u64(self.selected_prg_bank as u64);
writer.write_u8(match self.mirroring {
Mirroring::SPAGE0 => 0,
Mirroring::SPAGE1 => 1,
_ => 0,
});
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_ram)?;
self.selected_prg_bank = reader.read_u64()? as usize;
self.mirroring = match reader.read_u8()? {
0 => Mirroring::SPAGE0,
1 => Mirroring::SPAGE1,
_ => {
return Err(SaveStateError::InvalidData(
"invalid mirroring mode for ANROM save state",
));
}
};
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 presence mismatch for ANROM save state",
));
}
}
Ok(())
}
}