neser 0.1.1

NESER - NES Emulator in Rust - is a NES emulator written in Rust. It aims to be a high-quality, hardware-accurate emulator that is also easy to use and extend. It supports a wide range of NES games and features, including various mappers, audio processing, and input handling. NESER is designed to be modular and extensible, allowing developers to easily add new features or support for additional hardware. It can be run using one of two frontends: a native desktop application using SDL2, or a web application using WebAssembly. The desktop application provides a high-performance, feature-rich experience with support for various input devices and display options, while the web application allows users to play NES games directly in their browsers without needing to install any software in a BYOR manner (Bring Your Own Roms).
Documentation 
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//! Mapper 342 - COOLGIRL multicart (minimal baseline)
//!
//! Specifications:
//! - Main: <https://www.nesdev.org/wiki/NES_2.0_Mapper_342>
//!
//! Known Limitations:
//! - This is a minimal baseline implementation that only supports fixed
//!   PRG/CHR mapping for mapper instantiation and basic execution.
//! - COOLGIRL mapper-code emulation modes, advanced banking, and flash behavior
//!   are not implemented yet.

use crate::cartridge::base_mapper::BaseMapper;
use crate::cartridge::mapper::{Mapper, MapperCapabilities};

const MAPPER_NUMBER: u16 = 342;
const PRG_BANK_SIZE_BYTES: usize = 32 * 1024;
const CHR_BANK_SIZE_BYTES: usize = 8 * 1024;
const MAX_PRG_RAM_KB: usize = 32;

/// Mapper 342 - COOLGIRL multicart.
///
/// This initial implementation provides only fixed mapping behavior so that
/// Mapper 342 ROMs can instantiate.
pub struct Mapper342 {
    base: BaseMapper,
}

impl Mapper342 {
    pub fn new(ctx: super::mapper::MapperContext) -> Self {
        let capabilities = MapperCapabilities {
            max_prg_ram_kb: MAX_PRG_RAM_KB,
            prg_bank_size_kb: 32,
            chr_bank_size_kb: 8,
            ..Default::default()
        };
        let mut base = BaseMapper::new(&ctx, capabilities);
        base.configure_prg_banking(PRG_BANK_SIZE_BYTES);
        base.configure_chr_banking(CHR_BANK_SIZE_BYTES);
        Self { base }
    }
}

impl Mapper for Mapper342 {
    fn base(&self) -> &BaseMapper {
        &self.base
    }

    fn base_mut(&mut self) -> &mut BaseMapper {
        &mut self.base
    }

    fn mapper_number(&self) -> u16 {
        MAPPER_NUMBER
    }

    fn write_prg(&mut self, addr: u16, value: u8) {
        // Delegate potential PRG-RAM writes ($6000-$7FFF) to the base mapper.
        self.base.try_write_prg_ram(addr, value);
        // No mapper-specific register handling in baseline implementation.
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::cartridge::NametableLayout;
    use crate::cartridge::mapper::{MapperContext, create_mapper};
    use crate::cartridge::test_helpers::banked_data;

    fn mapper_342_context(prg_bank_count: usize, chr_bank_count: usize) -> MapperContext {
        MapperContext::new_for_test(
            MAPPER_NUMBER,
            banked_data(PRG_BANK_SIZE_BYTES, prg_bank_count),
            banked_data(CHR_BANK_SIZE_BYTES, chr_bank_count),
            NametableLayout::Vertical,
        )
    }

    #[test]
    fn mapper_342_is_registered() {
        let result = create_mapper(mapper_342_context(4, 4));
        assert!(result.is_ok(), "Mapper 342 should be registered");
    }

    #[test]
    fn mapper_342_reports_mapper_number() {
        let mapper = Mapper342::new(mapper_342_context(2, 2));
        assert_eq!(mapper.mapper_number(), MAPPER_NUMBER);
    }
}