const std = @import("std");
const common = @import("../common.zig");
const Mirroring = common.Mirroring;

pub const Nrom = @This();

mirroring_mode: Mirroring,

pub fn init(initial_mirroring: Mirroring) Nrom {
    return .{ .mirroring_mode = initial_mirroring };
}

pub fn cpuRead(_: *const Nrom, address: u16, prg_rom: []const u8, prg_ram: []const u8) ?u8 {
    if (address >= 0x6000 and address <= 0x7fff) {
        const offset = address - 0x6000;
        if (offset < prg_ram.len) return prg_ram[offset];
        return 0;
    }
    if (address >= 0x8000 and address <= 0xffff) {
        const mask: usize = if (prg_rom.len <= 0x4000) 0x3fff else 0x7fff;
        const offset = (address - 0x8000) & mask;
        if (offset < prg_rom.len) return prg_rom[offset];
        return 0;
    }
    return null;
}

pub fn cpuWrite(_: *Nrom, address: u16, value: u8, prg_ram: []u8) bool {
    if (address >= 0x6000 and address <= 0x7fff) {
        const offset = address - 0x6000;
        if (offset < prg_ram.len) {
            prg_ram[offset] = value;
            return true;
        }
    }
    return false;
}

pub fn ppuRead(_: *const Nrom, address: u16, chr_rom: []const u8, chr_ram: []const u8, chr_is_ram: bool) ?u8 {
    if (address < 0x2000) {
        if (chr_is_ram) {
            if (address < chr_ram.len) return chr_ram[address];
        } else {
            if (chr_rom.len > 0) return chr_rom[address & (chr_rom.len - 1)];
        }
        return 0;
    }
    return null;
}

pub fn ppuWrite(_: *Nrom, address: u16, value: u8, chr_ram: []u8, chr_is_ram: bool) bool {
    if (address < 0x2000 and chr_is_ram) {
        if (address < chr_ram.len) {
            chr_ram[address] = value;
            return true;
        }
    }
    return false;
}

pub fn mirroring(self: *const Nrom) Mirroring {
    return self.mirroring_mode;
}

pub fn irqLine(_: *const Nrom) bool {
    return false;
}

pub fn notifyPpuAddress(_: *Nrom, _: u16) void {}

test "nrom prg mirroring" {
    var nrom = Nrom.init(.horizontal);
    var prg_16k: [0x4000]u8 = undefined;
    @memset(&prg_16k, 0x42);
    prg_16k[0] = 0x11;

    var ram: [0x2000]u8 = undefined;
    @memset(&ram, 0);

    // 16K PRG is mirrored at $8000 and $C000
    try std.testing.expectEqual(@as(?u8, 0x11), nrom.cpuRead(0x8000, &prg_16k, &ram));
    try std.testing.expectEqual(@as(?u8, 0x11), nrom.cpuRead(0xc000, &prg_16k, &ram));
}