"""Helpers for image tests using an attached client on a PTY."""

import contextlib
import colorsys
import errno
import fcntl
import itertools
import os
import re
import select
import signal
import struct
import subprocess
import sys
import termios
import time


class Client:
    """An attached client and the bytes written to its terminal."""

    def __init__(self, pid, fd):
        self.pid = pid
        self.fd = fd
        self.data = bytearray()

    def read(self, duration=0.1):
        """Read terminal output for a bounded time."""
        end = time.monotonic() + duration
        while time.monotonic() < end:
            if not select.select([self.fd], [], [], 0.01)[0]:
                continue
            try:
                data = os.read(self.fd, 65536)
            except OSError as e:
                if e.errno == errno.EIO:
                    raise RuntimeError("attached client exited") from e
                raise
            if not data:
                raise RuntimeError("attached client exited")
            self.data.extend(data)

    def clear(self):
        """Finish reading earlier output before starting a new check."""
        self.read()
        self.data.clear()

    def images(self):
        """Decode complete SIXEL sequences from the terminal output."""
        images = []
        for params, body in re.findall(
                rb"\033P([0-9;]*)q(.*?)\033\\", self.data, re.S):
            params = params.split(b";")
            p2 = int(params[1] or b"0") if len(params) > 1 else 0
            images.append(decode_sixel(body, p2))
        return images


class ImageTest:
    """A server with one pane which copies input directly to its output."""

    serial = itertools.count()

    def __init__(self, tmux, sx=40, sy=16):
        # Short, unique socket labels also fit macOS's socket path limit.
        self.server = [tmux, "-Lis%d-%d" % (os.getpid(), next(self.serial)),
            "-f/dev/null"]
        self.sx = sx
        self.sy = sy
        self.clients = []
        self.marker = 0

    def run(self, *args, check=True, input=None):
        """Run a command on this server."""
        p = subprocess.run(self.server + list(args), capture_output=True,
            input=input, timeout=10)
        if check and p.returncode != 0:
            raise RuntimeError("%r: %s" % (args, p.stderr.decode()))
        return p.stdout.decode().strip()

    def wait(self, predicate):
        """Read client output while waiting for a server state change."""
        end = time.monotonic() + 10
        while True:
            for client in self.clients:
                client.read(0.01)
            if predicate():
                return
            if time.monotonic() >= end:
                raise RuntimeError("timed out waiting for server state")
            time.sleep(0.01)

    def start(self):
        """Start the pane and skip when the server has no image support."""
        self.run("new-session", "-d", "-s", "image", "-x", str(self.sx),
            "-y", str(self.sy), "stty raw -echo; "
            "printf '\033]2;READY\007'; exec cat")
        support = self.run("display-message", "-p", "#{image_support}")
        if support == "0":
            sys.exit(101)
        assert support == "1", ("unexpected image_support", support)
        self.run("set-option", "-g", "status", "off")
        self.wait(lambda: self.run("display-message", "-p",
            "#{pane_title}") == "READY")

    def attach(self, graphical=True, utf8=True, cw=8, ch=16, term=None):
        """Attach a client with a known cell pixel size and image feature."""
        if term is None:
            term = "xterm-256color" if graphical else "screen-256color"
        features = term + (":sixel" if graphical else ":sixel@")
        self.run("set-option", "-as", "terminal-features", features)
        pid, fd = os.forkpty()
        if pid == 0:
            try:
                os.environ.pop("TMUX", None)
                os.environ["TERM"] = term
                os.environ["LC_ALL"] = "C.UTF-8" if utf8 else "C"
                fcntl.ioctl(0, termios.TIOCSWINSZ, struct.pack("HHHH",
                    self.sy, self.sx, self.sx * cw, self.sy * ch))
                args = self.server + (["-u"] if utf8 else [])
                os.execv(self.server[0], args +
                    ["attach-session", "-t", "image"])
            finally:
                os._exit(1)
        client = Client(pid, fd)
        self.clients.append(client)
        self.wait(lambda: any(line.startswith(str(pid) + ":") for line in
            self.run("list-clients", "-F", "#{client_pid}:").splitlines()))
        # Answer DA so the startup timeout cannot schedule a later redraw.
        os.write(fd, b"\033[?65;4c" if graphical else b"\033[?65c")
        self.wait(lambda: self.client_size(client) ==
            "%dx%d:%dx%d" % (self.sx, self.sy, cw, ch))
        if len(self.clients) == 1 and cw != 0 and ch != 0:
            self.wait(lambda: self.run("display-message", "-p",
                "#{window_cell_width}x#{window_cell_height}") ==
                "%dx%d" % (cw, ch))
        client.name = next(line.split(":", 1)[1] for line in
            self.run("list-clients", "-F",
                "#{client_pid}:#{client_name}").splitlines()
            if line.startswith(str(pid) + ":"))
        client.read(0.2)
        client.clear()
        return client

    def client_size(self, client):
        """Get the character and cell pixel size of one client."""
        prefix = str(client.pid) + ":"
        return next((line[len(prefix):] for line in self.run("list-clients",
            "-F", "#{client_pid}:#{client_width}x#{client_height}:"
            "#{client_cell_width}x#{client_cell_height}").splitlines()
            if line.startswith(prefix)), None)

    def send(self, data):
        """Send literal bytes to the pane."""
        if len(data) > 512:
            self.run("load-buffer", "-b", "image", "-", input=data)
            self.run("paste-buffer", "-b", "image", "-S", "-r", "-d")
        else:
            self.run("send-keys", "-H", *["%02x" % ch for ch in data])

    def emit(self, data):
        """Send pane output and wait until its trailing title is parsed."""
        for client in self.clients:
            client.clear()
        self.marker += 1
        title = "image-%d" % self.marker
        self.send(data + b"\033]2;" + title.encode() + b"\007")
        self.wait(lambda: self.run("display-message", "-p",
            "#{pane_title}") == title)
        for client in self.clients:
            client.read(0.2)

    def redraw(self):
        """Request a full redraw and collect its terminal output."""
        for client in self.clients:
            client.clear()
        for client in self.clients:
            self.run("refresh-client", "-t", client.name)
        for client in self.clients:
            client.read(0.2)

    def resize(self, client, sx, sy, cw=8, ch=16):
        """Resize one client's terminal and wait for the window size."""
        client.clear()
        fcntl.ioctl(client.fd, termios.TIOCSWINSZ,
            struct.pack("HHHH", sy, sx, sx * cw, sy * ch))
        os.kill(client.pid, signal.SIGWINCH)
        self.wait(lambda: self.client_size(client) ==
            "%dx%d:%dx%d" % (sx, sy, cw, ch))
        self.wait(lambda: self.run("display-message", "-p",
            "#{window_width}x#{window_height}") == "%dx%d" % (sx, sy))
        client.read(0.2)

    def close(self):
        """Stop the server and reap every attached client."""
        self.run("kill-server", check=False)
        for client in self.clients:
            os.close(client.fd)
            if os.waitpid(client.pid, os.WNOHANG) == (0, 0):
                os.kill(client.pid, signal.SIGTERM)
                os.waitpid(client.pid, 0)


@contextlib.contextmanager
def image_test(tmux, sx=40, sy=16):
    """Clean up the server even when a test fails or skips."""
    test = ImageTest(tmux, sx, sy)
    try:
        test.start()
        yield test
    finally:
        test.close()


def sixel(w, h, palette, pixels, p2=1):
    """Build SIXEL input from a palette and row-major palette indexes."""
    assert len(pixels) == w * h
    out = ['\033P9;%dq"1;1;%d;%d' % (p2, w, h)]
    for c, rgb in enumerate(palette):
        out.append("#%d;2;%d;%d;%d" % (c, *rgb))
    for y in range(0, h, 6):
        planes = []
        for c in range(len(palette)):
            columns = []
            for x in range(w):
                bits = sum(1 << bit for bit in range(min(6, h - y))
                    if pixels[(y + bit) * w + x] == c)
                columns.append(chr(0x3f + bits))
            if all(ch == "?" for ch in columns):
                continue
            plane = "#%d" % c
            for ch, run in itertools.groupby(columns):
                n = len(list(run))
                plane += "!%d%s" % (n, ch) if n > 3 else ch * n
            planes.append(plane)
        out.append("$".join(planes))
        if y + 6 < h:
            out.append("-")
    out.append("\033\\")
    return "".join(out).encode()


def decode_sixel(body, p2=1):
    """Read RGB output pixels without using tmux's SIXEL decoder."""
    attributes = re.match(rb'"1;1;(\d+);(\d+)', body)
    assert attributes is not None, ("missing raster attributes", body[:80])
    w, h = map(int, attributes.groups())
    pixels = [None if p2 == 1 else (0, 0, 0)] * (w * h)
    palette = {}
    c = x = y = 0
    pos = attributes.end()
    while pos < len(body):
        ch = body[pos]
        pos += 1
        if ch == ord("#"):
            match = re.match(rb"(\d+)(?:;([12]);(\d+);(\d+);(\d+))?", body[pos:])
            assert match is not None, body[pos:pos + 80]
            c = int(match[1])
            if match[2] is not None:
                values = tuple(int(match[i]) for i in range(3, 6))
                if match[2] == b"1":
                    hue, lightness, saturation = values
                    rgb = colorsys.hls_to_rgb(((hue + 240) % 360) / 360,
                        lightness / 100, saturation / 100)
                    palette[c] = tuple(int(v * 255 + .5) for v in rgb)
                else:
                    assert all(v <= 100 for v in values), values
                    palette[c] = tuple((v * 255 + 50) // 100 for v in values)
            pos += match.end()
            continue
        if ch == ord("$"):
            x = 0
            continue
        if ch == ord("-"):
            x = 0
            y += 6
            continue
        n = 1
        if ch == ord("!"):
            match = re.match(rb"(\d+)(.)", body[pos:], re.S)
            assert match is not None
            n = int(match[1])
            ch = match[2][0]
            pos += match.end()
        assert 0x3f <= ch <= 0x7e, ch
        for bit in range(6):
            if not (ch - 0x3f) & (1 << bit):
                continue
            assert y + bit < h and x + n <= w, (x, y, n, bit, w, h)
            assert c in palette, ("undefined output colour", c)
            for xx in range(x, x + n):
                pixels[(y + bit) * w + xx] = palette[c]
        x += n
    return w, h, pixels


def check_image(image, w, h, expected):
    """Compare decoded output with expected RGB pixels and transparency."""
    assert image[:2] == (w, h), (image[:2], (w, h))
    assert len(expected) == w * h
    for i, (actual, wanted) in enumerate(zip(image[2], expected)):
        if wanted is None:
            assert actual is None, (i % w, i // w, actual, wanted)
        else:
            assert actual is not None, (i % w, i // w, actual, wanted)
            assert max(abs(a - b) for a, b in zip(actual, wanted)) <= 3, (
                i % w, i // w, actual, wanted)