//! system/services/fat/fat-test — a client that proves the FAT mount end to end:
//! it waits for the fat server to mount the USB volume at /mnt/usb, lists the
//! root directory through the VFS (which routes /mnt/usb to the fat backend), and
//! reads a known file off it. Shipped in the initial_ramdisk; the `fat-mount`
//! kernel test spawns it alongside init.

const std = @import("std");
const runtime = @import("runtime");
const fs = runtime.fs;

fn writeLine(comptime fmt: []const u8, arguments: anytype) void {
    var line: [128]u8 = undefined;
    _ = runtime.system.write(std.fmt.bufPrint(&line, fmt, arguments) catch return);
}

pub fn main(init: runtime.process.Init) void {
    _ = init;

    // Wait for /mnt/usb to be mounted — the fat server races us at boot (it must
    // bring up the whole USB storage chain first).
    var opened: ?fs.Directory = null;
    var tries: u32 = 0;
    while (opened == null and tries < 1400) : (tries += 1) {
        opened = fs.openDirectory("/mnt/usb");
        if (opened == null) runtime.system.sleep(50);
    }
    var dir = opened orelse {
        _ = runtime.system.write("fat-test: /mnt/usb never became available\n");
        return;
    };

    var count: u32 = 0;
    var entry: fs.Entry = .{};
    while (dir.next(&entry)) {
        writeLine("fat-test: entry '{s}' kind={d} size={d}\n", .{ entry.name(), @intFromEnum(entry.kind), entry.size });
        count += 1;
        if (count > 32) break;
    }
    dir.close();
    writeLine("fat-test: listed {d} entries\n", .{count});

    // Read a known file off the boot volume through the mount (best effort): the
    // kernel image is an ELF, so its first bytes are the ELF magic.
    if (fs.open("/mnt/usb/system/kernel", .{})) |opened_file| {
        var file = opened_file;
        var magic: [4]u8 = undefined;
        const n = file.read(&magic) orelse 0;
        file.close();
        if (n == 4 and magic[0] == 0x7F and magic[1] == 'E' and magic[2] == 'L' and magic[3] == 'F') {
            _ = runtime.system.write("fat-test: read /mnt/usb/system/kernel ELF magic ok\n");
        } else {
            writeLine("fat-test: /mnt/usb/system/kernel read {d} bytes (not ELF magic)\n", .{n});
        }
    }

    // Exercise directory + file mutation through the mount: mkdir, create a file
    // inside it, read it back, then remove it — proof mkdir/unlink reach the engine.
    if (fs.makeDirectory("/mnt/usb/TESTDIR")) {
        var wrote = false;
        if (fs.open("/mnt/usb/TESTDIR/HELLO.TXT", .{ .create = true, .truncate = true })) |created| {
            var f = created;
            wrote = (f.writeAll("mutation-ok") orelse 0) == "mutation-ok".len;
            f.close();
        }
        // The created file carries a real modification time (stamped from the RTC).
        var mtime_ok = false;
        if (fs.attributes("/mnt/usb/TESTDIR/HELLO.TXT")) |attrs| {
            writeLine("fat-test: mtime {d}\n", .{attrs.mtime});
            mtime_ok = attrs.mtime > 1_577_836_800; // after 2020-01-01
        }
        if (mtime_ok) _ = runtime.system.write("fat-test: mtime ok\n");

        // Rename it, then read from the new name and confirm the old name is gone.
        const renamed = fs.rename("/mnt/usb/TESTDIR/HELLO.TXT", "/mnt/usb/TESTDIR/RENAMED.TXT");
        const old_gone = !fs.exists("/mnt/usb/TESTDIR/HELLO.TXT");
        if (renamed and old_gone) _ = runtime.system.write("fat-test: rename ok\n");
        var readback = false;
        if (fs.open("/mnt/usb/TESTDIR/RENAMED.TXT", .{})) |reopened| {
            var f = reopened;
            var buf: [16]u8 = undefined;
            const got = f.read(&buf) orelse 0;
            f.close();
            readback = std.mem.eql(u8, buf[0..got], "mutation-ok");
        }
        const removed = fs.remove("/mnt/usb/TESTDIR/RENAMED.TXT");
        const gone = !fs.exists("/mnt/usb/TESTDIR/RENAMED.TXT");
        if (wrote and mtime_ok and renamed and old_gone and readback and removed and gone) {
            _ = runtime.system.write("fat-test: mutations ok\n");
        } else {
            writeLine("fat-test: mutations FAILED (wrote={} mtime={} renamed={} oldgone={} read={} removed={} gone={})\n", .{ wrote, mtime_ok, renamed, old_gone, readback, removed, gone });
        }
    } else {
        _ = runtime.system.write("fat-test: mkdir /mnt/usb/TESTDIR failed\n");
    }

    if (count > 0) {
        while (true) {
            _ = runtime.system.write("fat-test: ok\n");
            runtime.system.sleep(1000);
        }
    }
    _ = runtime.system.write("fat-test: root listing was empty\n");
}
