nesemu/src/native_core/mapper/mappers/mapper155.rs

use super::*;

pub(crate) struct InesMapper155 {
    prg_rom: Vec<u8>,
    chr_data: Vec<u8>,
    chr_is_ram: bool,
    prg_ram: Vec<u8>,
    shift_reg: u8,
    shift_count: u8,
    control: u8,
    chr_bank0: u8,
    chr_bank1: u8,
    prg_bank: u8,
    mirroring_default: Mirroring,
}

impl InesMapper155 {
    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],
            shift_reg: 0,
            shift_count: 0,
            control: 0x0C,
            chr_bank0: 0,
            chr_bank1: 0,
            prg_bank: 0,
            mirroring_default: rom.header.mirroring,
        }
    }

    fn prg_mode(&self) -> u8 {
        (self.control >> 2) & 0x03
    }

    fn chr_mode(&self) -> u8 {
        (self.control >> 4) & 1
    }

    fn prg_bank_count_16k(&self) -> usize {
        (self.prg_rom.len() / 0x4000).max(1)
    }

    fn outer_a17_override_enabled(&self) -> bool {
        (self.prg_bank & 0x10) != 0
    }

    fn outer_bank_half(&self) -> usize {
        ((self.prg_bank >> 3) & 1) as usize
    }

    fn map_bank_16k_with_outer(&self, inner_bank: usize) -> usize {
        let total = self.prg_bank_count_16k();
        if !self.outer_a17_override_enabled() || total <= 8 {
            return safe_mod(inner_bank, total);
        }
        let half = (total / 2).max(1);
        let base = safe_mod(self.outer_bank_half(), 2) * half;
        base + safe_mod(inner_bank, half)
    }

    fn write_serial(&mut self, addr: u16, value: u8) {
        if (value & 0x80) != 0 {
            self.shift_reg = 0;
            self.shift_count = 0;
            self.control |= 0x0C;
            return;
        }

        self.shift_reg |= (value & 1) << self.shift_count;
        self.shift_count = self.shift_count.wrapping_add(1);
        if self.shift_count < 5 {
            return;
        }

        let reg = (addr >> 13) & 0x03;
        match reg {
            0 => self.control = self.shift_reg & 0x1F,
            1 => self.chr_bank0 = self.shift_reg & 0x1F,
            2 => self.chr_bank1 = self.shift_reg & 0x1F,
            _ => self.prg_bank = self.shift_reg & 0x1F, // MMC1A uses bit 4 for A17 behavior
        }
        self.shift_reg = 0;
        self.shift_count = 0;
    }
}

impl Mapper for InesMapper155 {
    fn cpu_read(&self, addr: u16) -> u8 {
        if addr < 0x8000 {
            return 0;
        }

        let prg_mode = self.prg_mode();
        if prg_mode <= 1 {
            let bank32 = (self.prg_bank as usize) >> 1;
            let bank16 = bank32 * 2 + usize::from(addr >= 0xC000);
            read_bank(
                &self.prg_rom,
                0x4000,
                self.map_bank_16k_with_outer(bank16),
                (addr as usize) & 0x3FFF,
            )
        } else if prg_mode == 2 {
            if addr < 0xC000 {
                read_bank(
                    &self.prg_rom,
                    0x4000,
                    self.map_bank_16k_with_outer(0),
                    (addr as usize) - 0x8000,
                )
            } else {
                read_bank(
                    &self.prg_rom,
                    0x4000,
                    self.map_bank_16k_with_outer((self.prg_bank & 0x0F) as usize),
                    (addr as usize) - 0xC000,
                )
            }
        } else if addr < 0xC000 {
            read_bank(
                &self.prg_rom,
                0x4000,
                self.map_bank_16k_with_outer((self.prg_bank & 0x0F) as usize),
                (addr as usize) - 0x8000,
            )
        } else {
            let fixed_last = if self.outer_a17_override_enabled() && self.prg_bank_count_16k() > 8 {
                self.prg_bank_count_16k() / 2 - 1
            } else {
                self.prg_bank_count_16k().saturating_sub(1)
            };
            read_bank(
                &self.prg_rom,
                0x4000,
                self.map_bank_16k_with_outer(fixed_last),
                (addr as usize) - 0xC000,
            )
        }
    }

    fn cpu_write(&mut self, addr: u16, value: u8) {
        if addr >= 0x8000 {
            self.write_serial(addr, value);
        }
    }

    fn cpu_read_low(&self, addr: u16) -> Option<u8> {
        if (0x6000..=0x7FFF).contains(&addr) {
            return self.prg_ram.get((addr as usize) & 0x1FFF).copied();
        }
        None
    }

    fn cpu_write_low(&mut self, addr: u16, value: u8) -> bool {
        if (0x6000..=0x7FFF).contains(&addr) {
            if let Some(cell) = self.prg_ram.get_mut((addr as usize) & 0x1FFF) {
                *cell = value;
            }
            return true;
        }
        false
    }

    fn ppu_read(&self, addr: u16) -> u8 {
        if addr > 0x1FFF {
            return 0;
        }
        if self.chr_mode() == 0 {
            let bank = (self.chr_bank0 as usize) >> 1;
            read_bank(&self.chr_data, 0x2000, bank, addr as usize)
        } else if addr < 0x1000 {
            read_bank(
                &self.chr_data,
                0x1000,
                self.chr_bank0 as usize,
                addr as usize,
            )
        } else {
            read_bank(
                &self.chr_data,
                0x1000,
                self.chr_bank1 as usize,
                (addr as usize) - 0x1000,
            )
        }
    }

    fn ppu_write(&mut self, addr: u16, value: u8) {
        if !self.chr_is_ram || addr > 0x1FFF {
            return;
        }
        let idx = if self.chr_mode() == 0 {
            let total_banks = (self.chr_data.len() / 0x2000).max(1);
            let bank = safe_mod((self.chr_bank0 as usize) >> 1, total_banks);
            bank * 0x2000 + ((addr as usize) & 0x1FFF)
        } else {
            let total_banks = (self.chr_data.len() / 0x1000).max(1);
            let bank = if addr < 0x1000 {
                self.chr_bank0 as usize
            } else {
                self.chr_bank1 as usize
            };
            safe_mod(bank, total_banks) * 0x1000 + ((addr as usize) & 0x0FFF)
        };
        if let Some(cell) = self.chr_data.get_mut(idx) {
            *cell = value;
        }
    }

    fn mirroring(&self) -> Mirroring {
        match self.control & 0x03 {
            0 => Mirroring::OneScreenLow,
            1 => Mirroring::OneScreenHigh,
            2 => Mirroring::Vertical,
            3 => Mirroring::Horizontal,
            _ => self.mirroring_default,
        }
    }

    fn save_state(&self, out: &mut Vec<u8>) {
        out.push(self.shift_reg);
        out.push(self.shift_count);
        out.push(self.control);
        out.push(self.chr_bank0);
        out.push(self.chr_bank1);
        out.push(self.prg_bank);
        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() < 6 {
            return Err("mapper state is truncated".to_string());
        }
        self.shift_reg = data[0];
        self.shift_count = data[1];
        self.control = data[2];
        self.chr_bank0 = data[3];
        self.chr_bank1 = data[4];
        self.prg_bank = data[5];

        let mut cursor = 6usize;
        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..])
    }
}