const std = @import("std");
const posix = std.posix;
const linux = std.os.linux;

extern "c" fn forkpty(
    amaster: *c_int,
    name: ?[*:0]u8,
    termp: ?*const anyopaque,
    winp: ?*const posix.winsize,
) c_int;
extern "c" fn execvp(file: [*:0]const u8, argv: [*:null]const ?[*:0]const u8) c_int;
extern "c" fn _exit(status: c_int) noreturn;

fn writeAll(fd: c_int, bytes: []const u8) !void {
    var off: usize = 0;
    while (off < bytes.len) {
        const rc = linux.write(fd, bytes[off..].ptr, bytes.len - off);
        switch (posix.errno(rc)) {
            .SUCCESS => off += @intCast(rc),
            .INTR => {},
            else => |err| {
                std.debug.print("write failed: {}\n", .{err});
                return error.WriteFailed;
            },
        }
    }
}

fn waitNoHang(pid: c_int) bool {
    var status: u32 = 0;
    const rc = linux.waitpid(pid, &status, linux.W.NOHANG);
    return posix.errno(rc) == .SUCCESS and rc == @as(usize, @intCast(pid));
}

pub fn main(init: std.process.Init) !void {
    const gpa = init.gpa;
    const args = try init.minimal.args.toSlice(init.arena.allocator());
    if (args.len != 2) {
        std.debug.print("usage: {s} <pardes-exe>\n", .{args[0]});
        return error.BadArgs;
    }

    const exe = args[1];
    const marker = "PARDES_E2E";
    const command = "echo " ++ marker ++ "\r";

    var master: c_int = undefined;
    const ws = posix.winsize{ .row = 24, .col = 80, .xpixel = 0, .ypixel = 0 };
    const pid = forkpty(&master, null, null, &ws);
    if (pid == 0) {
        const child_argv = [_:null]?[*:0]const u8{ exe.ptr, null };
        _ = execvp(exe.ptr, &child_argv);
        _exit(127);
    }
    defer _ = linux.close(master);
    defer posix.kill(pid, posix.SIG.KILL) catch {};

    var output: std.ArrayList(u8) = .empty;
    defer output.deinit(gpa);

    var buf: [4096]u8 = undefined;
    for (0..20) |_| {
        var fds = [_]posix.pollfd{.{
            .fd = master,
            .events = posix.POLL.IN,
            .revents = 0,
        }};
        _ = try posix.poll(&fds, 100);
        if ((fds[0].revents & posix.POLL.IN) != 0) {
            const n = posix.read(master, &buf) catch break;
            if (n == 0) break;
            try output.appendSlice(gpa, buf[0..n]);
            break;
        }
    }

    try writeAll(master, command);

    var saw_marker = false;
    for (0..80) |_| {
        var fds = [_]posix.pollfd{.{
            .fd = master,
            .events = posix.POLL.IN,
            .revents = 0,
        }};
        _ = try posix.poll(&fds, 100);
        if ((fds[0].revents & (posix.POLL.IN | posix.POLL.HUP | posix.POLL.ERR)) != 0) {
            const n = posix.read(master, &buf) catch break;
            if (n == 0) break;
            try output.appendSlice(gpa, buf[0..n]);
            if (std.mem.containsAtLeast(u8, output.items, 1, marker)) {
                saw_marker = true;
                break;
            }
        }
        if (waitNoHang(pid)) break;
    }

    try writeAll(master, "\x03");
    for (0..20) |_| {
        if (waitNoHang(pid)) break;
        var fds = [_]posix.pollfd{.{
            .fd = master,
            .events = posix.POLL.IN,
            .revents = 0,
        }};
        _ = posix.poll(&fds, 50) catch {};
        if ((fds[0].revents & posix.POLL.IN) != 0) {
            _ = posix.read(master, &buf) catch 0;
        }
    }

    if (!saw_marker) {
        std.debug.print("app did not render marker; captured {d} bytes:\n{s}\n", .{
            output.items.len,
            output.items[0..@min(output.items.len, 4096)],
        });
        return error.MarkerNotRendered;
    }
}