//! The QEMU run steps (docs/build-packages-plan.md, phase 3): `run-x86-64`
//! boots the serial-enabled FAT image via UEFI/OVMF; `run-x86-64-gpu` adds a
//! virtio-gpu adapter for the native-present display path. OVMF firmware is
//! probed across distro/OS layouts (-Dovmf-code / -Dovmf-vars override).

const std = @import("std");

/// Wire up the `run-x86-64` and `run-x86-64-gpu` steps around the given
/// serial-enabled boot image (the guest boots that self-contained image
/// attached as USB storage, not the installed FHS zig-out).
pub fn addRunSteps(b: *std.Build, fat_image_serial: std.Build.LazyPath) void {
    // Firmware lives in different places per OS/distro, so probe the known
    // layouts (Architecture, Debian/Ubuntu, Fedora, macOS Homebrew) and use the first
    // that exists. Override with -Dovmf-code / -Dovmf-vars if yours is elsewhere.
    const ovmf_code = b.option(
        []const u8,
        "ovmf-code",
        "Path to the OVMF_CODE firmware image",
    ) orelse firstExisting(b.graph.io, &.{
        "/usr/share/edk2/x64/OVMF_CODE.4m.fd", // Architecture
        "/usr/share/OVMF/OVMF_CODE_4M.fd", // Debian/Ubuntu
        "/usr/share/OVMF/OVMF_CODE.fd", // older Debian/Ubuntu
        "/usr/share/edk2-ovmf/x64/OVMF_CODE.fd", // Fedora
        "/opt/homebrew/share/qemu/edk2-x86_64-code.fd", // macOS Homebrew (Apple Silicon)
        "/usr/local/share/qemu/edk2-x86_64-code.fd", // macOS Homebrew (Intel)
    });
    const ovmf_vars = b.option(
        []const u8,
        "ovmf-vars",
        "Path to the OVMF_VARS firmware image (a writable copy is made)",
    ) orelse firstExisting(b.graph.io, &.{
        "/usr/share/edk2/x64/OVMF_VARS.4m.fd", // Architecture
        "/usr/share/OVMF/OVMF_VARS_4M.fd", // Debian/Ubuntu
        "/usr/share/OVMF/OVMF_VARS.fd", // older Debian/Ubuntu
        "/usr/share/edk2-ovmf/x64/OVMF_VARS.fd", // Fedora
        "/opt/homebrew/share/qemu/edk2-i386-vars.fd", // macOS Homebrew (Apple Silicon)
        "/usr/local/share/qemu/edk2-i386-vars.fd", // macOS Homebrew (Intel)
    });

    // The firmware needs to write NVRAM, so give it a writable copy of the vars.
    const vars_copy = b.addSystemCommand(&.{ "cp", "-f", ovmf_vars });
    const vars_out = vars_copy.addOutputFileArg("OVMF_VARS.4m.fd");

    // Capture the guest's serial0 (danos's machine-readable log) to the qemu-test
    // scratch area — a dev/host artifact, kept out of the boot volume we mount.
    // (/system/logs on the volume belongs to the guest's own logger.) One
    // timestamped file per run.
    const log_dir = b.fmt("{s}/qemu-test", .{b.install_path});
    const make_log_dir = b.addSystemCommand(&.{ "mkdir", "-p", log_dir });

    // --- run-x86-64: boot the x86-64 kernel in QEMU via UEFI/OVMF ---
    const run_efi = b.addSystemCommand(&.{
        "qemu-system-x86_64",
        "-device",
        "qemu-xhci,id=xhci",
        "-device",
        "usb-mouse,bus=xhci.0",
        "-device",
        "usb-kbd,bus=xhci.0",
        "-machine",
        "q35",
        "-m",
        "128M",
        "-drive",
        b.fmt("if=pflash,format=raw,readonly=on,file={s}", .{ovmf_code}),
    });
    run_efi.addArg("-drive");
    run_efi.addPrefixedFileArg("if=pflash,format=raw,file=", vars_out);
    // Boot off the FAT32 USB image: a mass-storage device on the same xHCI bus as
    // the keyboard and mouse. OVMF finds \EFI\BOOT\BOOTX64.efi on it and boots.
    // The serial-enabled variant, so serial0 carries the log for this dev boot.
    run_efi.addArg("-drive");
    run_efi.addPrefixedFileArg("if=none,id=bootusb,format=raw,file=", fat_image_serial);
    run_efi.addArgs(&.{
        "-device",
        "usb-storage,bus=xhci.0,drive=bootusb,removable=on,bootindex=0",
        "-net",
        "none",
        // Emulated display advertising 1280x720 as its native (EDID preferred)
        // resolution, so the kernel's native-resolution switch has something to
        // find. `-vga none` avoids a second, default adapter.
        "-vga",
        "none",
        "-device",
        "VGA,edid=on,xres=1280,yres=720",
    });
    const serial_log = b.fmt("{s}/run-x86-64-serial0-{s}.log", .{ log_dir, timestamp(b) });
    run_efi.addArgs(&.{ "-serial", b.fmt("file:{s}", .{serial_log}) });
    // We boot the self-contained `fat_image_serial` (added as a file arg above, so
    // it's already a dependency) — not the installed FHS zig-out — so `run-x86-64`
    // builds only the serial kernel, never the flashable one. Just make the serial
    // scratch dir first.
    run_efi.step.dependOn(&make_log_dir.step);

    const run_efi_step = b.step("run-x86-64", "Boot the x86-64 kernel in QEMU (UEFI/OVMF); serial0 is logged to zig-out/qemu-test/run-x86-64-serial0-<timestamp>.log");
    run_efi_step.dependOn(&run_efi.step);

    // --- run-x86-64-gpu: the same boot plus a virtio-gpu adapter ---
    // The VGA device still supplies the boot (GOP) framebuffer the compositor starts
    // on; the virtio-gpu function is discovered by the device-manager stack, its
    // driver announces a shared scanout, and the compositor upgrades off the GOP
    // floor to fenced, tear-free native presents (docs/display-v2.md).
    // This is the interactive twin of the `display-native` test case, and 512M
    // matches it (the whole driver stack + the compositor's surfaces at once).
    // QEMU shows one head per adapter: pick the virtio-gpu head in the View menu
    // to watch the native output.
    const run_gpu = b.addSystemCommand(&.{
        "qemu-system-x86_64",
        "-device",
        "qemu-xhci,id=xhci",
        "-device",
        "usb-mouse,bus=xhci.0",
        "-device",
        "usb-kbd,bus=xhci.0",
        "-machine",
        "q35",
        "-m",
        "512M",
        "-drive",
        b.fmt("if=pflash,format=raw,readonly=on,file={s}", .{ovmf_code}),
    });
    run_gpu.addArg("-drive");
    run_gpu.addPrefixedFileArg("if=pflash,format=raw,file=", vars_out);
    run_gpu.addArg("-drive");
    run_gpu.addPrefixedFileArg("if=none,id=bootusb,format=raw,file=", fat_image_serial);
    run_gpu.addArgs(&.{
        "-device",
        "usb-storage,bus=xhci.0,drive=bootusb,removable=on,bootindex=0",
        "-net",
        "none",
        "-vga",
        "none",
        "-device",
        "VGA,edid=on,xres=1280,yres=720",
        "-device",
        "virtio-gpu-pci",
    });
    const gpu_serial_log = b.fmt("{s}/run-x86-64-gpu-serial0-{s}.log", .{ log_dir, timestamp(b) });
    run_gpu.addArgs(&.{ "-serial", b.fmt("file:{s}", .{gpu_serial_log}) });
    run_gpu.step.dependOn(&make_log_dir.step);

    const run_gpu_step = b.step("run-x86-64-gpu", "Boot in QEMU with a virtio-gpu adapter: the compositor upgrades to fenced (tear-free) native presents; watch the virtio-gpu head in QEMU's View menu");
    run_gpu_step.dependOn(&run_gpu.step);
}

/// Return the first path in `candidates` that exists on the build host, else the
/// first candidate as a fallback so a missing-firmware error still names a
/// concrete (and, by convention, the primary) path. Used to locate OVMF firmware
/// across distro/OS layouts without configuration.
fn firstExisting(io: std.Io, candidates: []const []const u8) []const u8 {
    for (candidates) |path| {
        std.Io.Dir.accessAbsolute(io, path, .{}) catch continue;
        return path;
    }
    return candidates[0];
}

/// A UTC timestamp like "20260708-153045", for naming a per-run artifact so
/// repeated runs don't clobber each other's logs. Resolved when `zig build`
/// runs, which is moments before QEMU launches.
fn timestamp(b: *std.Build) []const u8 {
    const ns = std.Io.Clock.now(.real, b.graph.io).nanoseconds;
    const secs: u64 = @intCast(@divFloor(ns, std.time.ns_per_s));
    const es = std.time.epoch.EpochSeconds{ .secs = secs };
    const yd = es.getEpochDay().calculateYearDay();
    const md = yd.calculateMonthDay();
    const ds = es.getDaySeconds();
    return b.fmt("{d:0>4}{d:0>2}{d:0>2}-{d:0>2}{d:0>2}{d:0>2}", .{
        yd.year,
        md.month.numeric(),
        @as(u32, md.day_index) + 1,
        ds.getHoursIntoDay(),
        ds.getMinutesIntoHour(),
        ds.getSecondsIntoMinute(),
    });
}