pub const Tag = enum {
    freestanding,
    other,

    contiki,
    elfiamcu,
    fuchsia,
    hermit,

    aix,
    haiku,
    hurd,
    linux,
    plan9,
    rtems,
    serenity,
    zos,

    dragonfly,
    freebsd,
    netbsd,
    openbsd,

    driverkit,
    ios,
    macos,
    tvos,
    visionos,
    watchos,

    illumos,
    solaris,

    windows,
    uefi,

    ps3,
    ps4,
    ps5,

    emscripten,
    wasi,

    amdhsa,
    amdpal,
    cuda,
    mesa3d,
    nvcl,
    opencl,
    opengl,
    vulkan,

    // LLVM tags deliberately omitted:
    // - bridgeos
    // - darwin
    // - kfreebsd
    // - nacl
    // - shadermodel

    pub inline fn isDarwin(tag: Tag) bool {
        return switch (tag) {
            .driverkit,
            .ios,
            .macos,
            .tvos,
            .visionos,
            .watchos,
            => true,
            else => false,
        };
    }

    pub inline fn isBSD(tag: Tag) bool {
        return tag.isDarwin() or switch (tag) {
            .freebsd, .openbsd, .netbsd, .dragonfly => true,
            else => false,
        };
    }

    pub inline fn isSolarish(tag: Tag) bool {
        return tag == .solaris or tag == .illumos;
    }

    pub fn exeFileExt(tag: Tag, arch: Cpu.Arch) [:0]const u8 {
        return switch (tag) {
            .windows => ".exe",
            .uefi => ".efi",
            .plan9 => arch.plan9Ext(),
            else => switch (arch) {
                .wasm32, .wasm64 => ".wasm",
                else => "",
            },
        };
    }

    pub fn staticLibSuffix(tag: Tag, abi: Abi) [:0]const u8 {
        return switch (abi) {
            .msvc, .itanium => ".lib",
            else => switch (tag) {
                .windows, .uefi => ".lib",
                else => ".a",
            },
        };
    }

    pub fn dynamicLibSuffix(tag: Tag) [:0]const u8 {
        return switch (tag) {
            .windows, .uefi => ".dll",
            .driverkit,
            .ios,
            .macos,
            .tvos,
            .visionos,
            .watchos,
            => ".dylib",
            else => ".so",
        };
    }

    pub fn libPrefix(tag: Os.Tag, abi: Abi) [:0]const u8 {
        return switch (abi) {
            .msvc, .itanium => "",
            else => switch (tag) {
                .windows, .uefi => "",
                else => "lib",
            },
        };
    }

    pub fn defaultVersionRange(tag: Tag, arch: Cpu.Arch, abi: Abi) Os {
        return .{
            .tag = tag,
            .version_range = .default(arch, tag, abi),
        };
    }

    pub inline fn versionRangeTag(tag: Tag) @typeInfo(TaggedVersionRange).@"union".tag_type.? {
        return switch (tag) {
            .freestanding,
            .other,

            .elfiamcu,

            .haiku,
            .plan9,
            .serenity,

            .illumos,

            .ps3,
            .ps4,
            .ps5,

            .emscripten,

            .mesa3d,
            => .none,

            .contiki,
            .fuchsia,
            .hermit,

            .aix,
            .rtems,
            .zos,

            .dragonfly,
            .freebsd,
            .netbsd,
            .openbsd,

            .driverkit,
            .macos,
            .ios,
            .tvos,
            .visionos,
            .watchos,

            .solaris,

            .uefi,

            .wasi,

            .amdhsa,
            .amdpal,
            .cuda,
            .nvcl,
            .opencl,
            .opengl,
            .vulkan,
            => .semver,

            .hurd => .hurd,
            .linux => .linux,

            .windows => .windows,
        };
    }
}