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Bebop/bebop/command_line.py

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"""Integrated command-line implementation."""
import curses
import curses.ascii
import curses.textpad
import os
import tempfile
from typing import Optional
from bebop.external import open_external_program
from bebop.links import Links
class CommandLine:
"""Basic and flaky command-line à la Vim, using curses module's Textbox.
I don't understand how to get proper pad-like behaviour, e.g. to scroll past
the window's right border when writing more content than the width allows.
Therefore I just added the M-e keybind to call an external editor and use
its content as result.
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Attributes:
- window: curses window to use for the command line and Textbox.
- editor_command: external command to use to edit content externally.
- textbox: Textbox object handling user input.
"""
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CHAR_COMMAND = ":"
CHAR_DIGIT = "&"
CHAR_TEXT = ">"
def __init__(self, window, editor_command):
self.window = window
self.editor_command = editor_command
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self.textbox = curses.textpad.Textbox(self.window)
def clear(self):
"""Clear command-line contents."""
self.window.clear()
self.window.refresh()
def gather(self) -> str:
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"""Return the string currently written by the user in command line.
This doesn't count the command char used, but it includes then prefix.
Trailing whitespace is trimmed.
"""
return self.textbox.gather()[1:].rstrip()
def focus(
self,
command_char,
validator=None,
prefix="",
escape_to_none=False
) -> Optional[str]:
"""Give user focus to the command bar.
Show the command char and give focus to the command textbox. The
validator function is passed to the textbox.
Arguments:
- command_char: char to display before the command line; it must be an
str of length 1, else the return value of `gather` might be wrong.
- validator: function to use to validate the input chars; if omitted,
`validate_common_input` is used.
- prefix: string to insert before the cursor in the command line.
- escape_to_none: if True, an escape interruption returns None instead
of an empty string.
Returns:
User input as string. The string will be empty if the validator raised
an EscapeInterrupt, unless `escape_to_none` is True.
"""
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validator = validator or self._validate_common_input
self.window.clear()
self.window.refresh()
self.window.addstr(command_char + prefix)
curses.curs_set(1)
try:
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command = self.textbox.edit(validator)
except EscapeCommandInterrupt:
command = "" if not escape_to_none else None
except TerminateCommandInterrupt as exc:
command = exc.command
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else:
command = command[1:].rstrip()
curses.curs_set(0)
self.clear()
return command
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def _validate_common_input(self, ch: int):
"""Generic input validator, handles a few more cases than default.
This validator can be used as a default validator as it handles, on top
of the Textbox defaults:
- Erasing the first command char, i.e. clearing the line, cancels the
command input.
- Pressing ESC also cancels the input.
This validator can be safely called at the beginning of other validators
to handle the keys above.
"""
if ch == curses.KEY_BACKSPACE: # Cancel input if all line is cleaned.
text = self.gather()
if len(text) == 0:
raise EscapeCommandInterrupt()
elif ch == curses.ascii.ESC: # Could be ESC or ALT
self.window.nodelay(True)
ch = self.window.getch()
if ch == -1:
raise EscapeCommandInterrupt()
else: # ALT keybinds.
if ch == ord("e"):
self.open_editor(self.gather())
self.window.nodelay(False)
return ch
def focus_for_link_navigation(self, init_char: int, links: Links):
"""Handle a initial digit input by the user.
When a digit key is pressed, the user intents to visit a link (or
dropped something on the numpad). To reduce the number of key types
needed, Bebop uses the following algorithm:
- If the current user input identifies a link without ambiguity, it is
used directly.
- If it is ambiguous, the user either inputs as many digits required
to disambiguate the link ID, or press enter to validate her input.
Examples:
- I have 3 links. Pressing "2" takes me to link 2.
- I have 15 links. Pressing "3" takes me to link 3 (no ambiguity).
- I have 15 links. Pressing "1" and "2" takes me to link 12.
- I have 456 links. Pressing "1", "2" and Enter takes me to link 12.
- I have 456 links. Pressing "1", "2" and "6" takes me to link 126.
Arguments:
- init_char: the first char (code) being pressed.
- links: accessible Links.
Returns:
The tuple (error, value); if error is 0, value is the link ID to use; if
error is 1, discard value and do nothing; if error is 2, value is an
error than can be showed to the user.
"""
digit = init_char & 0xf
num_links = len(links)
# If there are less than 10 links, just open it now.
if num_links < 10:
return 0, digit
# Else check if the digit alone is sufficient.
digit = chr(init_char)
max_digits = 0
while num_links:
max_digits += 1
num_links //= 10
candidates = links.disambiguate(digit, max_digits)
if len(candidates) == 1:
return 0, candidates[0]
# Else, focus the command line to let the user input more digits.
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validator = lambda ch: self._validate_link_digit(ch, links, max_digits)
link_input = self.focus(CommandLine.CHAR_DIGIT, validator, digit)
if not link_input:
return 1, None
try:
link_id = int(link_input)
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except ValueError:
return 2, f"Invalid link ID {link_input}."
return 0, link_id
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def _validate_link_digit(self, ch: int, links: Links, max_digits: int):
"""Handle input chars to be used as link ID."""
# Handle common chars.
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ch = self._validate_common_input(ch)
# Only accept digits. If we reach the amount of required digits, open
# link now and leave command line. Else just process it.
if curses.ascii.isdigit(ch):
digits = self.gather() + chr(ch)
candidates = links.disambiguate(digits, max_digits)
if len(candidates) == 1:
raise TerminateCommandInterrupt(candidates[0])
return ch
# If not a digit but a printable character, ignore it.
if curses.ascii.isprint(ch):
return 0
# Everything else could be a control character and should be processed.
return ch
def open_editor(self, existing_content=None):
"""Open an external editor and raise termination interrupt."""
try:
with tempfile.NamedTemporaryFile("w+t", delete=False) as temp_file:
if existing_content:
temp_file.write(existing_content)
temp_filepath = temp_file.name
except OSError:
return
command = self.editor_command + [temp_filepath]
open_external_program(command)
try:
with open(temp_filepath, "rt") as temp_file:
content = temp_file.read().rstrip("\r\n")
os.unlink(temp_filepath)
except OSError:
return
raise TerminateCommandInterrupt(content)
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def prompt_key(self, keys):
"""Focus the command line and wait for the user """
validator = lambda ch: self._validate_prompt(ch, keys)
key = self.focus(CommandLine.CHAR_TEXT, validator)
return key if key in keys else ""
def _validate_prompt(self, ch: int, keys):
"""Handle input chars and raise a terminate interrupt on a valid key."""
# Handle common keys.
ch = self._validate_common_input(ch)
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try:
char = chr(ch)
except ValueError:
pass
else:
if char in keys:
raise TerminateCommandInterrupt(char)
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return 0
class EscapeCommandInterrupt(Exception):
"""Signal that ESC has been pressed during command line."""
pass
class TerminateCommandInterrupt(Exception):
"""Signal that validation ended command line input early.
The value to use is stored in the command attribute. This value can be of
any type: str for common commands but also int for ID input, etc.
"""
def __init__(self, command, *args, **kwargs):
super().__init__(*args, **kwargs)
self.command = command