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 nowMs() i64 {
    var ts: linux.timespec = undefined;
    _ = linux.clock_gettime(linux.CLOCK.MONOTONIC, &ts);
    return ts.sec * 1000 + @divFloor(@as(i64, ts.nsec), 1_000_000);
}

// Drain the pty for a fixed WALL-CLOCK duration (a real settle). pollFor's
// iter-count "settle" is unreliable for big bursts: reading caps at 4096/iter so
// all iters can be spent reading with no idle wait, making it finish too soon.
fn drainFor(gpa: std.mem.Allocator, master: c_int, output: *std.ArrayList(u8), ms: i64) !void {
    const deadline = nowMs() + ms;
    var buf: [4096]u8 = undefined;
    while (nowMs() < deadline) {
        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) {
            const n = posix.read(master, &buf) catch break;
            if (n == 0) break;
            try output.appendSlice(gpa, buf[0..n]);
        }
    }
}

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;
    }

    // NOTE on polls: vaxis diff-renders, and char-mode text is built one keystroke
    // per frame, so inserted chars are emitted across frames and never appear as a
    // contiguous byte run. We `settle` (drain so input is processed, also avoiding
    // a resize race), force a full repaint with setWinsize (re-emits whole rows
    // contiguously), then poll. Command *output* lands in one frame already.

    // 3. Default is TEXT mode: the tag shows "ch" and shell prompts are hidden.
    if (!try pollFor(gpa, master, &output, "ch /", 60)) {
        dump(output.items, "default tag is not 'ch' (text mode)");
        return error.TextModeNotDefault;
    }

    // 4. Esc switches to TTY mode and forwards keystrokes to the shell. The settle
    //    lets vaxis emit a *standalone* Escape (lone ESC + text would be Alt+char).
    const marker = "PARDES_E2E";
    try writeAll(master, "\x1b");
    _ = try pollFor(gpa, master, &output, "ZZNEVERZZ", 6); // settle
    try writeAll(master, "echo " ++ marker ++ "\r");
    if (!try pollFor(gpa, master, &output, marker, 80)) {
        dump(output.items, "tty mode did not forward the marker to the shell");
        return error.TtyModeNoForward;
    }
    try setWinsize(master, 50, 201); // repaint so the whole tag re-emits contiguously
    if (!try pollFor(gpa, master, &output, "sy /", 40)) {
        dump(output.items, "no 'sy' indicator after Esc (tty mode)");
        return error.TtyModeIndicatorMissing;
    }

    // 5. Prompt hiding. In tty mode a command line + its output are both visible.
    //    Switching back to text mode hides the prompt/command rows but keeps the
    //    output. We clear the capture, switch with a left-click, force a repaint,
    //    then check the fresh frame: output present, prompt + command absent.
    try writeAll(master, "echo CMDHIDEZZ\r");
    if (!try pollFor(gpa, master, &output, "CMDHIDEZZ", 80)) {
        dump(output.items, "tty mode did not run the command");
        return error.TtyCommandFailed;
    }
    _ = try pollFor(gpa, master, &output, "ZZNEVERZZ", 8); // drain all tty-mode frames
    output.clearRetainingCapacity(); // so the next poll only sees the text-mode repaint
    try writeAll(master, "\x1b[<0;6;3M\x1b[<0;6;3m"); // left-click body -> text mode
    _ = try pollFor(gpa, master, &output, "ZZNEVERZZ", 6); // settle
    try setWinsize(master, 50, 202); // force a full repaint (text mode, prompts hidden)
    if (!try pollFor(gpa, master, &output, "CMDHIDEZZ", 80)) {
        dump(output.items, "command output not shown in text mode");
        return error.OutputHiddenInTextMode;
    }
    if (std.mem.indexOf(u8, output.items, "goblin@") != null) {
        dump(output.items, "shell prompt still visible in text mode");
        return error.PromptNotHidden;
    }
    if (std.mem.indexOf(u8, output.items, "echo CMDHIDEZZ") != null) {
        dump(output.items, "command line still visible in text mode");
        return error.CommandNotHidden;
    }

    // 6. Text-mode editing + middle-click execute. Click a blank row to pin the
    //    cursor at text col 0, compose a computed echo, then middle-select those
    //    15 cells (screen cols 2..16) and release. "Q7Z" appears only if the
    //    SELECTED typed text ran — proving selection reads the rendered screen.
    try writeAll(master, "\x1b[<0;3;14M\x1b[<0;3;14m"); // click blank row 13, col 0
    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. Right-click a directory opens (acme "look") a terminal there and ls's
    //    it. Make a dir with a unique entry, then `clear` and echo its path so the
    //    path lands as contiguous output on body row 0 (screen row 1). Right-click
    //    (no drag) on it: the new terminal lists the dir, so the unique entry
    //    appears only if the directory was actually opened.
    try writeAll(master, "\x1b");
    try drainFor(gpa, master, &output, 700); // settle (standalone Esc -> tty)
    try writeAll(master, "rm -rf /tmp/pardesE2E; mkdir -p /tmp/pardesE2E/ZZUNIQDIR; clear; echo /tmp/pardesE2E\r");
    try drainFor(gpa, master, &output, 2000); // let it run + the screen fully settle
    try writeAll(master, "\x1b[<2;5;2M\x1b[<2;5;2m"); // right-click the path on screen row 1
    if (!try pollFor(gpa, master, &output, "ZZUNIQDIR", 120)) {
        dump(output.items, "right-click on a directory did not open+ls it");
        return error.RightClickDirFailed;
    }

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