1"""Generic wrapper for read-eval-print-loops, a.k.a. interactive shells
2"""
3import os.path
4import signal
5import sys
6
7import pexpect
8
9PY3 = (sys.version_info[0] >= 3)
10
11if PY3:
12    basestring = str
13
14PEXPECT_PROMPT = u'[PEXPECT_PROMPT>'
15PEXPECT_CONTINUATION_PROMPT = u'[PEXPECT_PROMPT+'
16
17class REPLWrapper(object):
18    """Wrapper for a REPL.
19
20    :param cmd_or_spawn: This can either be an instance of :class:`pexpect.spawn`
21      in which a REPL has already been started, or a str command to start a new
22      REPL process.
23    :param str orig_prompt: The prompt to expect at first.
24    :param str prompt_change: A command to change the prompt to something more
25      unique. If this is ``None``, the prompt will not be changed. This will
26      be formatted with the new and continuation prompts as positional
27      parameters, so you can use ``{}`` style formatting to insert them into
28      the command.
29    :param str new_prompt: The more unique prompt to expect after the change.
30    :param str extra_init_cmd: Commands to do extra initialisation, such as
31      disabling pagers.
32    """
33    def __init__(self, cmd_or_spawn, orig_prompt, prompt_change,
34                 new_prompt=PEXPECT_PROMPT,
35                 continuation_prompt=PEXPECT_CONTINUATION_PROMPT,
36                 extra_init_cmd=None):
37        if isinstance(cmd_or_spawn, basestring):
38            self.child = pexpect.spawn(cmd_or_spawn, echo=False, encoding='utf-8')
39        else:
40            self.child = cmd_or_spawn
41        if self.child.echo:
42            # Existing spawn instance has echo enabled, disable it
43            # to prevent our input from being repeated to output.
44            self.child.setecho(False)
45            self.child.waitnoecho()
46
47        if prompt_change is None:
48            self.prompt = orig_prompt
49        else:
50            self.set_prompt(orig_prompt,
51                        prompt_change.format(new_prompt, continuation_prompt))
52            self.prompt = new_prompt
53        self.continuation_prompt = continuation_prompt
54
55        self._expect_prompt()
56
57        if extra_init_cmd is not None:
58            self.run_command(extra_init_cmd)
59
60    def set_prompt(self, orig_prompt, prompt_change):
61        self.child.expect(orig_prompt)
62        self.child.sendline(prompt_change)
63
64    def _expect_prompt(self, timeout=-1):
65        return self.child.expect_exact([self.prompt, self.continuation_prompt],
66                                       timeout=timeout)
67
68    def run_command(self, command, timeout=-1):
69        """Send a command to the REPL, wait for and return output.
70
71        :param str command: The command to send. Trailing newlines are not needed.
72          This should be a complete block of input that will trigger execution;
73          if a continuation prompt is found after sending input, :exc:`ValueError`
74          will be raised.
75        :param int timeout: How long to wait for the next prompt. -1 means the
76          default from the :class:`pexpect.spawn` object (default 30 seconds).
77          None means to wait indefinitely.
78        """
79        # Split up multiline commands and feed them in bit-by-bit
80        cmdlines = command.splitlines()
81        # splitlines ignores trailing newlines - add it back in manually
82        if command.endswith('\n'):
83            cmdlines.append('')
84        if not cmdlines:
85            raise ValueError("No command was given")
86
87        res = []
88        self.child.sendline(cmdlines[0])
89        for line in cmdlines[1:]:
90            self._expect_prompt(timeout=timeout)
91            res.append(self.child.before)
92            self.child.sendline(line)
93
94        # Command was fully submitted, now wait for the next prompt
95        if self._expect_prompt(timeout=timeout) == 1:
96            # We got the continuation prompt - command was incomplete
97            self.child.kill(signal.SIGINT)
98            self._expect_prompt(timeout=1)
99            raise ValueError("Continuation prompt found - input was incomplete:\n"
100                             + command)
101        return u''.join(res + [self.child.before])
102
103def python(command="python"):
104    """Start a Python shell and return a :class:`REPLWrapper` object."""
105    return REPLWrapper(command, u">>> ", u"import sys; sys.ps1={0!r}; sys.ps2={1!r}")
106
107def bash(command="bash"):
108    """Start a bash shell and return a :class:`REPLWrapper` object."""
109    bashrc = os.path.join(os.path.dirname(__file__), 'bashrc.sh')
110    child = pexpect.spawn(command, ['--rcfile', bashrc], echo=False,
111                          encoding='utf-8')
112
113    # If the user runs 'env', the value of PS1 will be in the output. To avoid
114    # replwrap seeing that as the next prompt, we'll embed the marker characters
115    # for invisible characters in the prompt; these show up when inspecting the
116    # environment variable, but not when bash displays the prompt.
117    ps1 = PEXPECT_PROMPT[:5] + u'\\[\\]' + PEXPECT_PROMPT[5:]
118    ps2 = PEXPECT_CONTINUATION_PROMPT[:5] + u'\\[\\]' + PEXPECT_CONTINUATION_PROMPT[5:]
119    prompt_change = u"PS1='{0}' PS2='{1}' PROMPT_COMMAND=''".format(ps1, ps2)
120
121    return REPLWrapper(child, u'\\$', prompt_change,
122                       extra_init_cmd="export PAGER=cat")
123