//! 9proc: the demo 9P2000 server, built on the 9proc library.
//!
//!   /README, /build/*, /comptime/{types,decls}, /runtime/{pid,ppid,uptime,argv,cwd,env,clients},
//!   /runtime/fn/{fib30,hostname,now,random,uname}, /runtime/ctl (echo|fib|sleep-ms|add|trap|panic),
//!   /scratch (in-memory tree), /vars/state (the worker's exposed state),
//!   /threads, /addr, /mem, /hex, /breakpoints, /panic (the Linux debug layer).
//!
//! A worker thread ("worker") runs `workerLoop`, incrementing `state.ticks`
//! every ~10 ms; `trap` makes it execute `@breakpoint()` on its next tick and
//! `panic` makes it panic from inside `workerLoop`. Panics go through the
//! library's hook, so the message and stack are published under /panic and
//! the process is held there until /panic/ctl says "continue" (`--no-hold`
//! disables the hold).
//!
//! Static memory: every buffer is a global; the only heap user is /scratch
//! (init.gpa, 512 MiB budget). With `max_clients` = 16 and msize = 1 MiB the
//! per-client core Storage is 3 MiB + 8 x 64 KiB snapshots and the Conn's fid
//! table ~1.88 MiB (32768 fids plus their hash index, needed for the 20000-fid
//! adversarial test), so `probe_storage` is ~86 MiB of BSS; untouched pages
//! cost nothing (an idle server has an RSS of ~7 MiB).
const std = @import("std");
const builtin = @import("builtin");
const cloud9 = @import("cloud9");
const build_options = @import("build_options");
const proc9 = @import("9proc");
const linux = std.os.linux;
const Writer = std.Io.Writer;
const plinux = proc9.linux;
const runtime = plinux.runtime;

pub const panic = std.debug.FullPanic(plinux.debug.panicHook);

/// Simultaneous 9P clients; further connections are closed (see probe.zig for
/// the idle-eviction rule).
pub const max_clients = 16;
pub const max_msize: u32 = 1 << 20;

pub const State = struct {
    ticks: u64,
    phase: enum { idle, working, trapped },
    last_job: struct { id: u32, cost: f32 },
};

const Build = struct {
    pub const zig_version: []const u8 = builtin.zig_version_string;
    pub const target: []const u8 = build_options.target;
    pub const optimize: []const u8 = build_options.optimize;
    pub const time: []const u8 = build_options.build_time;
    pub const change: []const u8 = build_options.change_id;
};

/// What every generator and the ctl handler see (`Shared.ctx`).
const App = struct {
    info: runtime.Info,
    probe: *ProbeT,
    shared: *S.Shared,
};

/// /runtime/fn/<name>: reading the file calls the function.
pub const Fns = struct {
    pub fn hostname(_: *anyopaque, w: *Writer) anyerror!void {
        var u: linux.utsname = undefined;
        if (linux.errno(linux.uname(&u)) != .SUCCESS) return error.Uname;
        try w.writeAll(std.mem.sliceTo(&u.nodename, 0));
    }

    pub fn now(_: *anyopaque, w: *Writer) anyerror!void {
        try w.print("{d}", .{runtime.realtimeSecs()});
    }

    pub fn random(_: *anyopaque, w: *Writer) anyerror!void {
        var b: [8]u8 = undefined;
        var got: usize = 0;
        while (got < b.len) {
            const rc = linux.getrandom(b[got..].ptr, b.len - got, 0);
            switch (linux.errno(rc)) {
                .SUCCESS => got += rc,
                .INTR => continue,
                else => return error.Random,
            }
        }
        try w.print("{x:0>16}", .{std.mem.readInt(u64, &b, .little)});
    }

    pub fn uname(_: *anyopaque, w: *Writer) anyerror!void {
        var u: linux.utsname = undefined;
        if (linux.errno(linux.uname(&u)) != .SUCCESS) return error.Uname;
        try w.writeAll(std.mem.sliceTo(&u.release, 0));
    }

    pub fn fib30(_: *anyopaque, w: *Writer) anyerror!void {
        try w.print("{d}", .{fib(30)});
    }
};

const cfg: proc9.Config = .{
    .name = "9proc-demo",
    .build = Build,
    .types = &.{ cloud9.Qid, cloud9.Stat, cloud9.Msg, proc9.core.Node, linux.Statx },
    .decls_of = @This(),
    .fns = Fns,
    .runtime = runtime.Fns(App, "info"),
    .ctl = &ctl,
    .ctl_dir = .runtime,
    .ctl_bytes = 64 * 1024,
    .msize = max_msize,
    .max_fids = 32768,
    .max_providers = 8,
    .snapshot_slots = 8,
    .snapshot_bytes = 64 * 1024,
};
const S = proc9.Server(cfg);
const ProbeT = plinux.Probe(S);
const ProbeStorage = ProbeT.Storage(max_clients);

// -- static state -------------------------------------------------------------

pub var state: State = .{ .ticks = 0, .phase = .idle, .last_job = .{ .id = 0, .cost = 0 } };
var trap_requested: std.atomic.Value(bool) = .init(false);
var panic_requested: std.atomic.Value(bool) = .init(false);

/// Zero-filled static memory for `T`. (An `= undefined` global is emitted as
/// 0xAA-filled .data in Debug builds, which would make the binary 120 MiB;
/// zeros go to .bss and cost nothing until touched.)
fn Bss(comptime T: type) type {
    return struct {
        bytes: [@sizeOf(T)]u8 align(@alignOf(T)) = @splat(0),
        fn get(b: *@This()) *T {
            return @ptrCast(&b.bytes);
        }
    };
}
var app_mem: Bss(App) = .{};
var shared_mem: Bss(S.Shared) = .{};
var probe_storage_mem: Bss(ProbeStorage) = .{};
var probe_mem: Bss(ProbeT) = .{};
var scratch_mem: Bss(proc9.Scratch) = .{};

/// Sizes of the static pieces, for the report and `--help`.
pub const static_bytes = @sizeOf(ProbeStorage) + @sizeOf(S.Shared) + @sizeOf(ProbeT);

// -- the worker ---------------------------------------------------------------

/// Ticks every ~10 ms; honours `trap` and `panic` requests from /runtime/ctl.
pub noinline fn workerLoop() void {
    plinux.setThreadName("worker");
    var job: u32 = 0;
    while (true) {
        napMs(10);
        state.ticks +%= 1;
        if (panic_requested.swap(false, .acq_rel)) {
            state.phase = .working;
            @panic("demo panic requested over 9p");
        }
        if (trap_requested.swap(false, .acq_rel)) {
            state.phase = .trapped;
            @breakpoint();
            state.phase = .idle;
        }
        if (state.ticks % 100 == 0) {
            job +%= 1;
            state.phase = .working;
            state.last_job = .{ .id = job, .cost = @as(f32, @floatFromInt(job % 7)) * 0.5 };
            state.phase = .idle;
        }
    }
}

/// The worker's sleep, issued as a raw syscall from this file so that the
/// thread's innermost frame (the first line of /threads/<tid>/stack, which
/// 9proc/test/debug.sh resolves through /addr) is in demo/main.zig rather than in std.
/// EINTR (a capture signal) just ends the nap early.
inline fn napMs(ms: u64) void {
    var req: linux.timespec = .{ .sec = @intCast(ms / 1000), .nsec = @intCast((ms % 1000) * 1_000_000) };
    switch (builtin.cpu.arch) {
        .x86_64 => _ = asm volatile ("syscall"
            : [ret] "={rax}" (-> usize),
            : [number] "{rax}" (@intFromEnum(linux.SYS.nanosleep)),
              [arg1] "{rdi}" (@intFromPtr(&req)),
              [arg2] "{rsi}" (@as(usize, 0)),
            : .{ .rcx = true, .r11 = true, .memory = true }),
        .aarch64 => _ = asm volatile ("svc #0"
            : [ret] "={x0}" (-> usize),
            : [number] "{x8}" (@intFromEnum(linux.SYS.nanosleep)),
              [arg1] "{x0}" (@intFromPtr(&req)),
              [arg2] "{x1}" (@as(usize, 0)),
            : .{ .memory = true }),
        else => plinux.sleepMs(ms),
    }
}

// -- /runtime/ctl -------------------------------------------------------------

/// The /runtime/ctl handler. The core stages the output and commits it only
/// on success, so a failed command leaves the previous result in place
/// (test/adv_9proc_hostile.py checks that).
fn ctl(ctx: *anyopaque, cmd: []const u8, out: *Writer) anyerror!void {
    const a: *App = @ptrCast(@alignCast(ctx));
    const line = std.mem.trim(u8, cmd, " \t\r\n\x00");
    var it = std.mem.tokenizeScalar(u8, line, ' ');
    const verb = it.next() orelse return error.BadCommand;
    if (std.mem.eql(u8, verb, "echo")) {
        try out.writeAll(std.mem.trimStart(u8, line[verb.len..], " \t"));
    } else if (std.mem.eql(u8, verb, "fib")) {
        const n = std.fmt.parseInt(u32, it.next() orelse return error.BadCommand, 10) catch return error.BadCommand;
        if (n > 93) return error.BadCommand; // fib(94) overflows u64
        try out.print("{d}", .{fib(n)});
    } else if (std.mem.eql(u8, verb, "sleep-ms")) {
        const n = std.fmt.parseInt(u64, it.next() orelse return error.BadCommand, 10) catch return error.BadCommand;
        const ms = @min(n, 10_000);
        a.probe.sleepServing(ms);
        try out.print("slept {d} ms", .{ms});
    } else if (std.mem.eql(u8, verb, "add")) {
        const x = std.fmt.parseInt(i64, it.next() orelse return error.BadCommand, 10) catch return error.BadCommand;
        const y = std.fmt.parseInt(i64, it.next() orelse return error.BadCommand, 10) catch return error.BadCommand;
        try out.print("{d}", .{x +% y});
    } else if (std.mem.eql(u8, verb, "trap")) {
        trap_requested.store(true, .release);
        try out.writeAll("trap armed: the worker stops in @breakpoint() on its next tick");
    } else if (std.mem.eql(u8, verb, "panic")) {
        panic_requested.store(true, .release);
        try out.writeAll("panic armed: the worker panics on its next tick");
    } else return error.BadCommand;
}

/// fib(n) for n <= 93 (fib(93) is the largest that fits u64).
fn fib(n: u32) u64 {
    std.debug.assert(n <= 93);
    if (n == 0) return 0;
    var a: u64 = 0;
    var b: u64 = 1;
    for (1..n) |_| {
        const c = a + b;
        a = b;
        b = c;
    }
    return b;
}

// -- main ---------------------------------------------------------------------

const usage_text =
    \\usage: 9proc-demo [--unix PATH | --tcp IP:PORT | --stdio] [--no-hold]
    \\
    \\A demo 9P2000 file server exposing this binary's build-time, comptime and
    \\runtime facts, plus a debugger-shaped view of the process (threads, stacks,
    \\memory, breakpoints, panics). Default is --stdio (9P on fd 0/1).
    \\--no-hold lets a panic abort at once instead of waiting for /panic/ctl.
    \\
;

pub fn main(init: std.process.Init) !void {
    run(init) catch |e| switch (e) {
        // Already reported on stderr; no stack trace wanted.
        error.Usage, error.Syscall => std.process.exit(1),
        else => return e,
    };
}

fn run(init: std.process.Init) !void {
    // Transparent huge pages would back the first touched page of every
    // client buffer with 2 MiB. Best effort: ignore failure.
    _ = linux.prctl(@intFromEnum(linux.PR.SET_THP_DISABLE), 1, 0, 0, 0);
    const arena = init.arena.allocator();
    const args = try init.minimal.args.toSlice(arena);

    const Mode = enum { stdio, unix, tcp };
    var mode: Mode = .stdio;
    var address: []const u8 = "";
    var hold = true;
    var i: usize = 1;
    while (i < args.len) : (i += 1) {
        const a = args[i];
        if (std.mem.eql(u8, a, "--stdio")) {
            mode = .stdio;
        } else if (std.mem.eql(u8, a, "--unix") or std.mem.eql(u8, a, "--tcp")) {
            i += 1;
            if (i >= args.len) {
                std.debug.print("9proc-demo: {s} needs an argument\n{s}", .{ a, usage_text });
                return error.Usage;
            }
            mode = if (a[2] == 'u') .unix else .tcp;
            address = args[i];
        } else if (std.mem.eql(u8, a, "--no-hold")) {
            hold = false;
        } else if (std.mem.eql(u8, a, "--help") or std.mem.eql(u8, a, "-h")) {
            std.debug.print("{s}\nstatic memory: {d} bytes ({d} clients, msize {d})\n", .{ usage_text, static_bytes, max_clients, max_msize });
            return;
        } else {
            std.debug.print("9proc-demo: unknown argument {s}\n{s}", .{ a, usage_text });
            return error.Usage;
        }
    }

    // argv, env and cwd are gathered once, into the arena.
    var argv_text: std.ArrayList(u8) = .empty;
    for (args) |a| {
        try argv_text.appendSlice(arena, a);
        try argv_text.append(arena, '\n');
    }
    var env_text: std.ArrayList(u8) = .empty;
    for (init.minimal.environ.block.view().slice) |entry| {
        try env_text.appendSlice(arena, std.mem.span(entry));
        try env_text.append(arena, '\n');
    }
    var cwd_buf: [4096]u8 = undefined;
    const cwd_rc = linux.getcwd(&cwd_buf, cwd_buf.len);
    const cwd_text: []const u8 = if (linux.errno(cwd_rc) == .SUCCESS)
        try arena.dupe(u8, std.mem.sliceTo(cwd_buf[0..cwd_rc], 0))
    else
        "";

    const app = app_mem.get();
    const shared = shared_mem.get();
    const probe = probe_mem.get();
    const scratch = scratch_mem.get();
    app.* = .{
        .info = .{ .argv = argv_text.items, .env = env_text.items, .cwd = cwd_text, .start_mono = runtime.monotonicSecs() },
        .probe = probe,
        .shared = shared,
    };
    shared.* = .init(app);
    try shared.expose("state", &state);
    scratch.* = try proc9.Scratch.init(init.gpa, 512 << 20);
    // Freed on the way out so a Debug build's allocator does not report the
    // tree as leaked (with a stack trace on stderr) after a clean --stdio EOF.
    defer scratch.deinit();
    scratch.max_file = 64 << 20;
    scratch.now = &runtime.realtimeSecs;
    try shared.addProvider(scratch.provider("scratch"));

    const listen: plinux.Listen = switch (mode) {
        .stdio => .{ .client = .{ .in = 0, .out = 1 } },
        .unix => .{ .unix = address },
        .tcp => .{ .tcp = address },
    };
    probe.init(shared, probe_storage_mem.get(), .{ .io = init.io, .listen = listen, .msize = max_msize, .hold_on_panic = hold }) catch |e| {
        switch (e) {
            error.PathTooLong => std.debug.print("9proc-demo: unix socket path too long\n", .{}),
            error.BadAddress => std.debug.print("9proc-demo: --tcp wants an IPv4 literal a.b.c.d:port\n", .{}),
            error.Syscall => std.debug.print("9proc-demo: {t} ({t})\n", .{ e, probe.last_errno }),
            else => std.debug.print("9proc-demo: {t}\n", .{e}),
        }
        return if (e == error.PathTooLong or e == error.BadAddress) error.Usage else error.Syscall;
    };
    // Failure past this point (thread spawn) still closes the listener and
    // restores the signal dispositions.
    errdefer probe.stop();
    app.info.clients = probe.clientCounter();

    const worker = std.Thread.spawn(.{}, workerLoop, .{}) catch |e| {
        std.debug.print("9proc-demo: worker thread: {t}\n", .{e});
        return error.Syscall;
    };
    worker.detach();

    switch (mode) {
        .unix => std.debug.print("9proc-demo: listening on unix!{s}\n", .{address}),
        .tcp => std.debug.print("9proc-demo: listening on tcp!{s}\n", .{address}),
        .stdio => {},
    }
    probe.start() catch |e| {
        std.debug.print("9proc-demo: thread spawn failed: {t}\n", .{e});
        return error.Syscall;
    };
    // SIGTERM/SIGINT end the loop cleanly: the socket file is unlinked, the
    // signal dispositions restored and the scratch tree freed.
    // A disposition of SIG_IGN inherited from the parent is left alone (Unix
    // convention): 9ns runs a --spawn server with SIGINT ignored so that
    // Ctrl-C on the terminal reaches only the program, not its file server.
    const term: linux.Sigaction = .{ .handler = .{ .handler = onTerm }, .mask = linux.sigemptyset(), .flags = 0 };
    for ([_]linux.SIG{ .TERM, .INT }) |sig| {
        var old: linux.Sigaction = undefined;
        _ = linux.sigaction(sig, null, &old);
        if (old.handler.handler != linux.SIG.IGN) _ = linux.sigaction(sig, &term, null);
    }
    probe.wait();
    probe.stop();
}

/// Async-signal-safe: an atomic store and one eventfd write.
fn onTerm(_: linux.SIG) callconv(.c) void {
    probe_mem.get().requestStop();
}

// -- tests --------------------------------------------------------------------

test "ctl commands" {
    const probe = probe_mem.get();
    const shared = shared_mem.get();
    var a: App = .{ .info = .{}, .probe = probe, .shared = shared };
    probe.thread_tid = .init(0);
    probe.serving = .initEmpty();
    probe.nested = 0;
    var buf: [128]u8 = undefined;
    var w: Writer = .fixed(&buf);
    try ctl(&a, "add 2 3\n", &w);
    try std.testing.expectEqualStrings("5", w.buffered());
    try std.testing.expectError(error.BadCommand, ctl(&a, "nope", &w));
    w = .fixed(&buf);
    try ctl(&a, "fib 93", &w);
    try std.testing.expectEqualStrings("12200160415121876738", w.buffered());
    w = .fixed(&buf);
    try std.testing.expectError(error.BadCommand, ctl(&a, "fib 94", &w));
    try std.testing.expectError(error.BadCommand, ctl(&a, "frobnicate", &w));
    w = .fixed(&buf);
    try ctl(&a, "echo  hi there ", &w);
    try std.testing.expectEqualStrings("hi there", w.buffered());
    w = .fixed(&buf);
    try ctl(&a, "sleep-ms 1", &w);
    try std.testing.expectEqualStrings("slept 1 ms", w.buffered());
    w = .fixed(&buf);
    try ctl(&a, "trap", &w);
    try std.testing.expect(trap_requested.swap(false, .acq_rel));
    w = .fixed(&buf);
    try ctl(&a, "panic", &w);
    try std.testing.expect(panic_requested.swap(false, .acq_rel));
}

test "static footprint is what the file comment says" {
    try std.testing.expect(@sizeOf(ProbeStorage) > 16 * (3 << 20));
    try std.testing.expect(@sizeOf(ProbeStorage) < 100 << 20);
}