nesemu/src/native_core/mapper/mappers/mmc3.rs

use super::*;

pub(crate) struct Mmc3 {
    prg_rom: Vec<u8>,
    chr_data: Vec<u8>,
    chr_is_ram: bool,
    prg_ram: Vec<u8>,
    prg_ram_enabled: bool,
    prg_ram_write_protect: bool,
    mirroring: Mirroring,
    bank_regs: [u8; 8],
    bank_select: u8,
    irq_latch: u8,
    irq_counter: u8,
    irq_reload: bool,
    irq_enabled: bool,
    irq_pending: bool,
}

impl Mmc3 {
    pub(crate) fn new(rom: InesRom) -> Self {
        Self {
            prg_rom: rom.prg_rom,
            chr_data: rom.chr_data,
            chr_is_ram: rom.chr_is_ram,
            prg_ram: vec![0; 0x2000],
            prg_ram_enabled: true,
            prg_ram_write_protect: false,
            mirroring: rom.header.mirroring,
            bank_regs: [0; 8],
            bank_select: 0,
            irq_latch: 0,
            irq_counter: 0,
            irq_reload: false,
            irq_enabled: false,
            irq_pending: false,
        }
    }

    fn prg_bank_count_8k(&self) -> usize {
        (self.prg_rom.len() / 0x2000).max(1)
    }

    fn prg_mode(&self) -> bool {
        (self.bank_select & 0x40) != 0
    }

    fn chr_invert(&self) -> bool {
        (self.bank_select & 0x80) != 0
    }

    fn prg_bank_for_slot(&self, slot: usize) -> usize {
        let last = self.prg_bank_count_8k() - 1;
        let second_last = last.saturating_sub(1);
        match (self.prg_mode(), slot) {
            (false, 0) => self.bank_regs[6] as usize,
            (false, 1) => self.bank_regs[7] as usize,
            (false, 2) => second_last,
            (false, 3) => last,
            (true, 0) => second_last,
            (true, 1) => self.bank_regs[7] as usize,
            (true, 2) => self.bank_regs[6] as usize,
            (true, 3) => last,
            _ => 0,
        }
    }

    pub(super) fn chr_bank_for_1k_page(&self, page: usize) -> usize {
        let regs = &self.bank_regs;
        let mut layout = [0usize; 8];

        layout[0] = (regs[0] as usize) & !1;
        layout[1] = layout[0] + 1;
        layout[2] = (regs[1] as usize) & !1;
        layout[3] = layout[2] + 1;
        layout[4] = regs[2] as usize;
        layout[5] = regs[3] as usize;
        layout[6] = regs[4] as usize;
        layout[7] = regs[5] as usize;

        if self.chr_invert() {
            layout.rotate_left(4);
        }
        layout[page]
    }

    fn clock_irq_scanline(&mut self) {
        if self.irq_reload || self.irq_counter == 0 {
            self.irq_counter = self.irq_latch;
            self.irq_reload = false;
        } else {
            self.irq_counter = self.irq_counter.wrapping_sub(1);
        }
        if self.irq_enabled && self.irq_counter == 0 {
            self.irq_pending = true;
        }
    }
}

impl Mapper for Mmc3 {
    fn cpu_read(&self, addr: u16) -> u8 {
        if addr < 0x8000 {
            return 0;
        }
        let slot = ((addr - 0x8000) / 0x2000) as usize;
        let bank = self.prg_bank_for_slot(slot);
        read_bank(
            &self.prg_rom,
            0x2000,
            bank,
            ((addr as usize) - 0x8000) & 0x1FFF,
        )
    }

    fn cpu_write(&mut self, addr: u16, value: u8) {
        match addr {
            0x8000..=0x9FFF if (addr & 1) == 0 => self.bank_select = value,
            0x8000..=0x9FFF => {
                let reg = (self.bank_select & 0x07) as usize;
                self.bank_regs[reg] = value;
            }
            0xA000..=0xBFFF if (addr & 1) == 0 => {
                self.mirroring = if (value & 1) == 0 {
                    Mirroring::Vertical
                } else {
                    Mirroring::Horizontal
                };
            }
            0xA000..=0xBFFF => {
                self.prg_ram_enabled = (value & 0x80) != 0;
                self.prg_ram_write_protect = (value & 0x40) != 0;
            }
            0xC000..=0xDFFF if (addr & 1) == 0 => self.irq_latch = value,
            0xC000..=0xDFFF => {
                self.irq_counter = 0;
                self.irq_reload = true;
            }
            0xE000..=0xFFFF if (addr & 1) == 0 => {
                self.irq_enabled = false;
                self.irq_pending = false;
            }
            0xE000..=0xFFFF => self.irq_enabled = true,
            _ => {}
        }
    }

    fn cpu_read_low(&self, addr: u16) -> Option<u8> {
        if (0x6000..=0x7FFF).contains(&addr) {
            if self.prg_ram_enabled {
                Some(self.prg_ram[(addr as usize) - 0x6000])
            } else {
                Some(0)
            }
        } else {
            None
        }
    }

    fn cpu_write_low(&mut self, addr: u16, value: u8) -> bool {
        if (0x6000..=0x7FFF).contains(&addr) {
            if self.prg_ram_enabled && !self.prg_ram_write_protect {
                self.prg_ram[(addr as usize) - 0x6000] = value;
            }
            true
        } else {
            false
        }
    }

    fn ppu_read(&self, addr: u16) -> u8 {
        if addr > 0x1FFF {
            return 0;
        }
        let page = (addr / 0x0400) as usize;
        let bank = self.chr_bank_for_1k_page(page);
        read_bank(&self.chr_data, 0x0400, bank, (addr as usize) & 0x03FF)
    }

    fn ppu_write(&mut self, addr: u16, value: u8) {
        if !self.chr_is_ram || addr > 0x1FFF {
            return;
        }
        let page = (addr / 0x0400) as usize;
        let bank = self.chr_bank_for_1k_page(page);
        let total_banks = (self.chr_data.len() / 0x0400).max(1);
        let bank_idx = safe_mod(bank, total_banks);
        let idx = bank_idx * 0x0400 + ((addr as usize) & 0x03FF);
        if let Some(cell) = self.chr_data.get_mut(idx) {
            *cell = value;
        }
    }

    fn mirroring(&self) -> Mirroring {
        self.mirroring
    }

    fn clock_scanline(&mut self) {
        self.clock_irq_scanline();
    }

    fn needs_ppu_a12_clock(&self) -> bool {
        true
    }

    fn poll_irq(&mut self) -> bool {
        let out = self.irq_pending;
        self.irq_pending = false;
        out
    }

    fn save_state(&self, out: &mut Vec<u8>) {
        out.extend_from_slice(&self.bank_regs);
        out.push(self.bank_select);
        out.push(encode_mirroring(self.mirroring));
        out.push(self.irq_latch);
        out.push(self.irq_counter);
        out.push(u8::from(self.irq_reload));
        out.push(u8::from(self.irq_enabled));
        out.push(u8::from(self.irq_pending));
        out.push(u8::from(self.prg_ram_enabled));
        out.push(u8::from(self.prg_ram_write_protect));
        write_state_bytes(out, &self.prg_ram);
        write_chr_state(out, &self.chr_data);
    }

    fn load_state(&mut self, data: &[u8]) -> Result<(), String> {
        if data.len() < 17 {
            return Err("mapper state is truncated".to_string());
        }
        self.bank_regs.copy_from_slice(&data[0..8]);
        self.bank_select = data[8];
        self.mirroring = decode_mirroring(data[9]);
        self.irq_latch = data[10];
        self.irq_counter = data[11];
        self.irq_reload = data[12] != 0;
        self.irq_enabled = data[13] != 0;
        self.irq_pending = data[14] != 0;
        let mut cursor = 15usize;
        self.prg_ram_enabled = data[cursor] != 0;
        cursor += 1;
        self.prg_ram_write_protect = data[cursor] != 0;
        cursor += 1;
        let prg_ram = read_state_bytes(data, &mut cursor)?;
        if prg_ram.len() != self.prg_ram.len() {
            return Err("mapper state does not match loaded ROM".to_string());
        }
        self.prg_ram.copy_from_slice(prg_ram);
        load_chr_state(&mut self.chr_data, &data[cursor..])
    }
}