const std = @import("std");

pub const screen_width: u16 = 256;
pub const screen_height: u16 = 240;

pub const Region = enum {
    ntsc,
    pal,

    /// Native CPU clock frequency in Hz.
    pub fn cpuClockRate(self: Region) u32 {
        return switch (self) {
            .ntsc => 1_789_773,
            .pal => 1_662_607,
        };
    }

    /// Total scanlines per frame (262 for NTSC, 312 for PAL).
    pub fn totalScanlines(self: Region) u16 {
        return switch (self) {
            .ntsc => 262,
            .pal => 312,
        };
    }

    /// Scanline index of the pre-render scanline (261 for NTSC, 311 for PAL).
    pub fn preRenderScanline(self: Region) u16 {
        return switch (self) {
            .ntsc => 261,
            .pal => 311,
        };
    }

    /// Number of VBlank scanlines.
    pub fn vblankScanlines(self: Region) u16 {
        return switch (self) {
            .ntsc => 20,
            .pal => 70,
        };
    }

    /// CPU cycles to suppress PPU register writes after power/reset (~1 frame).
    pub fn powerUpSuppressionCycles(self: Region) u32 {
        return switch (self) {
            .ntsc => 29_658,
            .pal => 33_132,
        };
    }
};

/// Nametable mirroring mode used by PPU CIRAM and Cartridge mappers.
pub const Mirroring = enum {
    horizontal,
    vertical,
    single_screen_lower,
    single_screen_upper,
    four_screen,
};

/// Standard 8-button NES controller layout.
pub const Button = enum(u8) {
    a = 1 << 0,
    b = 1 << 1,
    select = 1 << 2,
    start = 1 << 3,
    up = 1 << 4,
    down = 1 << 5,
    left = 1 << 6,
    right = 1 << 7,
};

test "region properties" {
    const ntsc: Region = .ntsc;
    try std.testing.expectEqual(@as(u32, 1_789_773), ntsc.cpuClockRate());
    try std.testing.expectEqual(@as(u16, 262), ntsc.totalScanlines());
    try std.testing.expectEqual(@as(u16, 261), ntsc.preRenderScanline());
    try std.testing.expectEqual(@as(u32, 29_658), ntsc.powerUpSuppressionCycles());

    const pal: Region = .pal;
    try std.testing.expectEqual(@as(u32, 1_662_607), pal.cpuClockRate());
    try std.testing.expectEqual(@as(u16, 312), pal.totalScanlines());
    try std.testing.expectEqual(@as(u16, 311), pal.preRenderScanline());
    try std.testing.expectEqual(@as(u32, 33_132), pal.powerUpSuppressionCycles());
}