"""
PC-BASIC - dos.py
Operating system shell and environment

(c) 2013--2018 Rob Hagemans
This file is released under the GNU GPL version 3 or later.
"""

import os
import sys
import logging
import threading
import time
from collections import deque
import subprocess
from subprocess import Popen, PIPE

from ..compat import SHELL_ENCODING, HIDE_WINDOW, split_quoted
from .codepage import CONTROL
from .base import error
from . import values


# get environment as bytes
getenvb = os.getenv


# command interpreter must support command.com convention
# to be able to use SHELL "dos-command"
# on linux, "wine cmd.exe" works OK
# dosemu can probably be made to work with a wrapper script
# sh doesn't work but makes little sense to use anyway as it's totally unlike MS-DOS
SHELL_COMMAND_SWITCH = u'/C'



##########################################
# calling shell environment

class Environment(object):
    """Handle environment changes."""

    def __init__(self, values):
        """Initialise."""
        self._values = values

    def environ_(self, args):
        """ENVIRON$: get environment string."""
        expr, = args
        if isinstance(expr, values.String):
            parm = expr.to_str()
            if not parm:
                raise error.BASICError(error.IFC)
            envstr = os.getenv(parm) or b''
        else:
            expr = values.to_int(expr)
            error.range_check(1, 255, expr)
            envlist = list(os.environ)
            if expr > len(envlist):
                envstr = b''
            else:
                envstr = b'%s=%s' % (envlist[expr-1], getenvb(envlist[expr-1]))
        return self._values.new_string().from_str(envstr)

    def environ_statement_(self, args):
        """ENVIRON: set environment string."""
        envstr = values.next_string(args)
        list(args)
        eqs = envstr.find(b'=')
        if eqs <= 0:
            raise error.BASICError(error.IFC)
        envvar = envstr[:eqs]
        os.environ[envvar] = envstr[eqs+1:]


#########################################
# shell

class Shell(object):
    """Launcher for command shell."""

    def __init__(self, queues, keyboard, screen, files, codepage, shell):
        """Initialise the shell."""
        self._shell = shell
        self._queues = queues
        self._keyboard = keyboard
        self._screen = screen
        self._files = files
        self._codepage = codepage
        self._last_command = deque()
        self._encoding = None

    def _process_stdout(self, stream, output):
        """Retrieve SHELL output and write to console."""
        while True:
            # blocking read
            c = stream.read(1)
            # stream ends if process closes
            if not c:
                return
            # don't access screen in this thread
            # the other thread already does
            output.append(c)

    def launch(self, command):
        """Run a SHELL subprocess."""
        logging.debug('Executing SHELL command %r', command)
        if not self._shell:
            logging.warning('SHELL statement not enabled: no command interpreter specified.')
            raise error.BASICError(error.IFC)
        cmd = split_quoted(self._shell)
        if command:
            cmd += [SHELL_COMMAND_SWITCH, self._codepage.str_to_unicode(command)]
        # get working directory; also raises IFC if current_device is CAS1
        work_dir = self._files.get_native_cwd()
        try:
            p = Popen(
                cmd, shell=False, cwd=work_dir,
                stdin=PIPE, stdout=PIPE, stderr=PIPE, startupinfo=HIDE_WINDOW
            )
        except (EnvironmentError, UnicodeEncodeError) as e:
            logging.warning(u'SHELL: command interpreter `%s` not accessible: %s', self._shell, e)
            raise error.BASICError(error.IFC)
        shell_output = self._launch_reader_thread(p.stdout)
        shell_cerr = self._launch_reader_thread(p.stderr)
        try:
            self._communicate(p, shell_output, shell_cerr)
        except EnvironmentError as e:
            logging.warning(e)
        finally:
            # ensure the process is terminated on exit
            if p.poll() is None:
                p.kill()

    def _launch_reader_thread(self, stream):
        """Launch output reader."""
        shell_output = deque()
        outp = threading.Thread(target=self._process_stdout, args=(stream, shell_output))
        # daemonise or join later? if we join, a shell that doesn't close will hang us on exit
        outp.daemon = True
        outp.start()
        return shell_output

    def _drain_final(self, shell_output):
        """Drain final output from shell."""
        if not shell_output:
            return
        elif not self._detect_encoding(shell_output):
            # one-char output, must be rare...
            shell_output.append(b'\r')
        elif not shell_output[-1] in (self._enc(u'\r'), self._enc(u'\n')):
            shell_output.append(self._enc(u'\r'))
        self._show_output(shell_output)

    def _communicate(self, p, shell_output, shell_cerr):
        """Communicate with launched shell."""
        word = []
        while p.poll() is None:
            self._show_output(shell_output)
            self._show_output(shell_cerr)
            try:
                self._queues.wait()
                # expand=False suppresses key macros
                c = self._keyboard.get_fullchar(expand=False)
            except error.Break:
                pass
            if not c:
                continue
            elif c in (b'\r', b'\n'):
                # put sentinel on queue
                shell_output.append(b'')
                shell_cerr.append(b'')
                # send the command
                self._send_input(p.stdin, word)
                word = []
            elif c == b'\b':
                # handle backspace
                if word:
                    word.pop()
                    self._screen.write(b'\x1D \x1D')
            elif not c.startswith(b'\0'):
                # exclude e-ascii (arrow keys not implemented)
                word.append(c)
                self._screen.write(c)
        # drain final output
        self._drain_final(shell_output)
        self._drain_final(shell_cerr)

    def _send_input(self, pipe, word):
        """Write keyboard input to pipe."""
        # for shell input, send CRLF or LF depending on platform
        self._last_command.extend(word)
        bytes_word = b''.join(word) + b'\r\n'
        unicode_word = self._codepage.str_to_unicode(bytes_word, preserve=CONTROL)
        # cmd.exe /u outputs UTF-16 but does not accept it as input...
        pipe.write(unicode_word.encode(SHELL_ENCODING, errors='replace'))

    def _detect_encoding(self, shell_output):
        """Detect UTF-16LE output."""
        if self._encoding:
            return True
        elif len(shell_output) > 1:
            # detect UTF-16 output (assuming the first output char is ascii...)
            self._encoding = 'utf-16le' if shell_output[1] == b'\0' else SHELL_ENCODING
            return True
        return False

    def _enc(self, unitext):
        """Encode argument."""
        return unitext.encode(self._encoding, errors='replace')

    def _show_output(self, shell_output):
        """Write shell output to screen."""
        # detect sentinel for start of new command
        if shell_output and self._detect_encoding(shell_output):
            # detect sentinel for start of new command
            # wait for at least one LF
            if not shell_output[0]:
                if b'\n' not in shell_output:
                    return
            # can't do a comprehension as it will crash if the deque is accessed by the thread
            lines = deque()
            while shell_output:
                lines.append(shell_output.popleft())
            # push back last char if not aligned to encoding
            if self._encoding == 'utf-16le' and lines[-1] != b'\0':
                shell_output.appendleft(lines.pop())
            # detect echo
            while not lines[0]:
                lines.popleft()
                while lines:
                    reply = lines.popleft()
                    if self._encoding == 'utf-16le':
                        reply += lines.popleft()
                    try:
                        cmd = self._last_command.popleft()
                    except IndexError:
                        cmd = b''
                    if self._enc(cmd) != reply:
                        lines.appendleft(reply)
                        if reply not in (self._enc(u'\r'), self._enc(u'\n')):
                            # two CRs, for some reason
                            lines.appendleft(self._enc(u'\r'))
                        break
            outstr = b''.join(lines)
            # accept CRLF or LF in output
            outstr = outstr.replace(self._enc(u'\r\n'), self._enc(u'\r'))
            # remove BELs (dosemu uses these a lot)
            outstr = outstr.replace(self._enc(u'\x07'), b'')
            outstr = outstr.decode(self._encoding, errors='replace')
            outstr = self._codepage.str_from_unicode(outstr, errors='replace')
            self._screen.write(outstr)
