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;
            },
        }
    }
}

// TIOCSWINSZ on the pty master: changes the size and makes the kernel raise
// SIGWINCH in the slave's foreground process group (i.e. the app under test).
fn setWinsize(fd: c_int, rows: u16, cols: u16) !void {
    const ws = posix.winsize{ .row = rows, .col = cols, .xpixel = 0, .ypixel = 0 };
    const rc = linux.ioctl(fd, linux.T.IOCSWINSZ, @intFromPtr(&ws));
    if (posix.errno(rc) != .SUCCESS) return error.IoctlFailed;
}

// Poll the pty for up to `iters` * 100ms, appending everything read into
// `output`. Returns true as soon as `needle` is present in the accumulated
// output (the app renders to the alt screen, so we just scan the byte stream).
fn pollFor(
    gpa: std.mem.Allocator,
    master: c_int,
    output: *std.ArrayList(u8),
    needle: []const u8,
    iters: usize,
) !bool {
    if (std.mem.indexOf(u8, output.items, needle) != null) return true;
    var buf: [4096]u8 = undefined;
    for (0..iters) |_| {
        var fds = [_]posix.pollfd{.{ .fd = master, .events = posix.POLL.IN, .revents = 0 }};
        _ = posix.poll(&fds, 100) catch {};
        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.indexOf(u8, output.items, needle) != null) return true;
        }
    }
    return std.mem.indexOf(u8, output.items, needle) != null;
}

fn dump(items: []const u8, msg: []const u8) void {
    std.debug.print("E2E FAIL: {s}\ncaptured {d} bytes:\n{s}\n", .{
        msg,
        items.len,
        items[0..@min(items.len, 8192)],
    });
}

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];

    // Boot the app in a small pty.
    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);

    // 1. The app posts an initial winsize on startup. Its winsize handler bumps
    //    the resize counter to 1 and calls vx.resize, which forces a full
    //    repaint, so "resizes 1" shows up in the rendered stream. This just
    //    confirms the app is up and handled its first size.
    if (!try pollFor(gpa, master, &output, "resizes=1", 60)) {
        dump(output.items, "app never handled its initial winsize (no 'resizes=1')");
        return error.InitialResizeMissing;
    }

    // 2. Regression check for "resizes aren't happening": grow the outer pty.
    //    This delivers SIGWINCH to the app. Only if the app installed its
    //    resize handler will it post a new winsize event, bump the counter to
    //    2, and repaint -> "resizes 2". If the handler is missing the counter
    //    stays at 1 forever and this times out.
    try setWinsize(master, 50, 200);
    if (!try pollFor(gpa, master, &output, "resizes=2", 80)) {
        dump(output.items, "SIGWINCH was not turned into a resize (counter stuck at 1)");
        return error.ResizeNotDelivered;
    }

    // 3. Sym mode (default): keystrokes are forwarded to the embedded shell.
    //    The tag shows the "sy" mode indicator and the marker echoes back.
    const marker = "PARDES_E2E";
    try writeAll(master, "echo " ++ marker ++ "\r");
    if (!try pollFor(gpa, master, &output, marker, 80)) {
        dump(output.items, "app did not render echoed marker");
        return error.MarkerNotRendered;
    }
    if (!try pollFor(gpa, master, &output, "sy ", 20)) {
        dump(output.items, "no 'sy' mode indicator on the tag in sym mode");
        return error.ModeIndicatorMissing;
    }

    // NOTE on the polls below: vaxis diff-renders, and char-mode text is built
    // one keystroke per frame, so the inserted chars are emitted across frames
    // and never appear as a contiguous byte run. We therefore `settle` (drain so
    // the input is fully processed, which also avoids racing the resize), force a
    // full repaint with setWinsize (which re-emits whole rows contiguously), and
    // only then poll. Command *output* (e.g. R42Q) lands in one frame already, so
    // it needs no repaint.

    // 4. A left-click enters char mode and typed text is inserted as an overlay.
    //    SGR mouse: press+release of button 0 at a body cell (col 6, row 3).
    try writeAll(master, "\x1b[<0;6;3M\x1b[<0;6;3m");
    try writeAll(master, "EDITZZ1");
    _ = try pollFor(gpa, master, &output, "ZZNEVERZZ", 6); // settle
    try setWinsize(master, 50, 201); // force a full repaint
    if (!try pollFor(gpa, master, &output, "EDITZZ1", 80)) {
        dump(output.items, "char-mode insertion did not render");
        return error.EditNotRendered;
    }

    // 5. The same repaint confirms the mode flipped sy -> ch on the tag. If char
    //    mode never engaged, the marker went to the shell and the tag reads "sy".
    if (!try pollFor(gpa, master, &output, "ch /", 80)) {
        dump(output.items, "left-click did not switch the tag to 'ch' (char mode)");
        return error.CharModeNotEntered;
    }

    // 6. A second click anchors a second independent insertion run.
    try writeAll(master, "\x1b[<0;6;5M\x1b[<0;6;5m");
    try writeAll(master, "EDITZZ2");
    _ = try pollFor(gpa, master, &output, "ZZNEVERZZ", 6); // settle
    try setWinsize(master, 50, 202); // force a full repaint
    if (!try pollFor(gpa, master, &output, "EDITZZ2", 80)) {
        dump(output.items, "second anchored insertion did not render");
        return error.SecondEditNotRendered;
    }

    // 6b. Middle-click executes the typed text read off the rendered screen.
    //     Char-click a blank body row, type a computed echo as an insertion, then
    //     middle-select exactly those 15 cells (text col 0 -> screen cols 2..16)
    //     and release. The result "Q7Z" appears only if the SELECTED inserted
    //     text ran — proving selection sees typed text, not the tty beneath it.
    try writeAll(master, "\x1b[<0;3;14M\x1b[<0;3;14m"); // char-click blank row 13
    try writeAll(master, "echo Q$((3+4))Z");
    _ = try pollFor(gpa, master, &output, "ZZNEVERZZ", 6); // settle (build the run)
    try writeAll(master, "\x1b[<1;3;14M\x1b[<33;17;14M\x1b[<1;17;14m"); // middle-select it
    if (!try pollFor(gpa, master, &output, "Q7Z", 80)) {
        dump(output.items, "middle-click did not execute the selected typed text");
        return error.MiddleExecFailed;
    }

    // 7. Esc leaves char mode (tag back to sy) and input resumes going to the
    //    pty: a computed echo's result only appears if the shell executed it.
    //    (In char mode the literal "$((20+22))" would render but never "R42Q".)
    //    The settle after Esc lets vaxis emit a *standalone* Escape — a lone ESC
    //    immediately followed by text is otherwise parsed as Alt+<char>.
    try writeAll(master, "\x1b");
    _ = try pollFor(gpa, master, &output, "ZZNEVERZZ", 6); // settle
    try writeAll(master, "echo R$((20+22))Q\r");
    if (!try pollFor(gpa, master, &output, "R42Q", 80)) {
        dump(output.items, "Esc did not return to sym mode (computed echo never ran)");
        return error.SymModeNotRestored;
    }

    // Tell the app to quit (ctrl-c is the app's own exit key).
    try writeAll(master, "\x03");
}