"""
This module implements Git's wildmatch pattern matching which itself is derived
from Rsync's wildmatch. Git uses wildmatch for its ".gitignore" files.
"""

import re
import warnings
from typing import (
	AnyStr,
	Optional,  # Replaced by `X | None` in 3.10.
	Tuple)  # Replaced by `tuple` in 3.9.

from .. import util
from ..pattern import RegexPattern

_BYTES_ENCODING = 'latin1'
"""
The encoding to use when parsing a byte string pattern.
"""

_DIR_MARK = 'ps_d'
"""
The regex group name for the directory marker. This is only used by
:class:`GitIgnoreSpec`.
"""


class GitWildMatchPatternError(ValueError):
	"""
	The :class:`GitWildMatchPatternError` indicates an invalid git wild match
	pattern.
	"""
	pass


class GitWildMatchPattern(RegexPattern):
	"""
	The :class:`GitWildMatchPattern` class represents a compiled Git wildmatch
	pattern.
	"""

	# Keep the dict-less class hierarchy.
	__slots__ = ()

	@classmethod
	def pattern_to_regex(
		cls,
		pattern: AnyStr,
	) -> Tuple[Optional[AnyStr], Optional[bool]]:
		"""
		Convert the pattern into a regular expression.

		*pattern* (:class:`str` or :class:`bytes`) is the pattern to convert into a
		regular expression.

		Returns the uncompiled regular expression (:class:`str`, :class:`bytes`, or
		:data:`None`); and whether matched files should be included (:data:`True`),
		excluded (:data:`False`), or if it is a null-operation (:data:`None`).
		"""
		if isinstance(pattern, str):
			return_type = str
		elif isinstance(pattern, bytes):
			return_type = bytes
			pattern = pattern.decode(_BYTES_ENCODING)
		else:
			raise TypeError(f"pattern:{pattern!r} is not a unicode or byte string.")

		original_pattern = pattern

		if pattern.endswith('\\ '):
			# EDGE CASE: Spaces can be escaped with backslash. If a pattern that ends
			# with backslash followed by a space, only strip from left.
			pattern = pattern.lstrip()
		else:
			pattern = pattern.strip()

		if pattern.startswith('#'):
			# A pattern starting with a hash ('#') serves as a comment (neither
			# includes nor excludes files). Escape the hash with a back-slash to match
			# a literal hash (i.e., '\#').
			regex = None
			include = None

		elif pattern == '/':
			# EDGE CASE: According to `git check-ignore` (v2.4.1), a single '/' does
			# not match any file.
			regex = None
			include = None

		elif pattern:
			if pattern.startswith('!'):
				# A pattern starting with an exclamation mark ('!') negates the pattern
				# (exclude instead of include). Escape the exclamation mark with a
				# back-slash to match a literal exclamation mark (i.e., '\!').
				include = False
				# Remove leading exclamation mark.
				pattern = pattern[1:]
			else:
				include = True

			# Allow a regex override for edge cases that cannot be handled through
			# normalization.
			override_regex = None

			# Split pattern into segments.
			pattern_segs = pattern.split('/')

			# Check whether the pattern is specifically a directory pattern before
			# normalization.
			is_dir_pattern = not pattern_segs[-1]

			# Normalize pattern to make processing easier.

			# EDGE CASE: Deal with duplicate double-asterisk sequences. Collapse each
			# sequence down to one double-asterisk. Iterate over the segments in
			# reverse and remove the duplicate double asterisks as we go.
			for i in range(len(pattern_segs) - 1, 0, -1):
				prev = pattern_segs[i-1]
				seg = pattern_segs[i]
				if prev == '**' and seg == '**':
					del pattern_segs[i]

			if len(pattern_segs) == 2 and pattern_segs[0] == '**' and not pattern_segs[1]:
				# EDGE CASE: The '**/' pattern should match everything except individual
				# files in the root directory. This case cannot be adequately handled
				# through normalization. Use the override.
				override_regex = f'^.+(?P<{_DIR_MARK}>/).*$'

			if not pattern_segs[0]:
				# A pattern beginning with a slash ('/') will only match paths directly
				# on the root directory instead of any descendant paths. So, remove
				# empty first segment to make pattern relative to root.
				del pattern_segs[0]

			elif len(pattern_segs) == 1 or (len(pattern_segs) == 2 and not pattern_segs[1]):
				# A single pattern without a beginning slash ('/') will match any
				# descendant path. This is equivalent to "**/{pattern}". So, prepend
				# with double-asterisks to make pattern relative to root.
				# - EDGE CASE: This also holds for a single pattern with a trailing
				#   slash (e.g. dir/).
				if pattern_segs[0] != '**':
					pattern_segs.insert(0, '**')

			else:
				# EDGE CASE: A pattern without a beginning slash ('/') but contains at
				# least one prepended directory (e.g. "dir/{pattern}") should not match
				# "**/dir/{pattern}", according to `git check-ignore` (v2.4.1).
				pass

			if not pattern_segs:
				# After resolving the edge cases, we end up with no pattern at all. This
				# must be because the pattern is invalid.
				raise GitWildMatchPatternError(f"Invalid git pattern: {original_pattern!r}")

			if not pattern_segs[-1] and len(pattern_segs) > 1:
				# A pattern ending with a slash ('/') will match all descendant paths if
				# it is a directory but not if it is a regular file. This is equivalent
				# to "{pattern}/**". So, set last segment to a double-asterisk to
				# include all descendants.
				pattern_segs[-1] = '**'

			if override_regex is None:
				# Build regular expression from pattern.
				output = ['^']
				need_slash = False
				end = len(pattern_segs) - 1
				for i, seg in enumerate(pattern_segs):
					if seg == '**':
						if i == 0 and i == end:
							# A pattern consisting solely of double-asterisks ('**') will
							# match every path.
							output.append(f'[^/]+(?:/.*)?')

						elif i == 0:
							# A normalized pattern beginning with double-asterisks
							# ('**') will match any leading path segments.
							output.append('(?:.+/)?')
							need_slash = False

						elif i == end:
							# A normalized pattern ending with double-asterisks ('**') will
							# match any trailing path segments.
							if is_dir_pattern:
								output.append(f'(?P<{_DIR_MARK}>/).*')
							else:
								output.append(f'/.*')

						else:
							# A pattern with inner double-asterisks ('**') will match multiple
							# (or zero) inner path segments.
							output.append('(?:/.+)?')
							need_slash = True

					elif seg == '*':
						# Match single path segment.
						if need_slash:
							output.append('/')

						output.append('[^/]+')

						if i == end:
							# A pattern ending without a slash ('/') will match a file or a
							# directory (with paths underneath it). E.g., "foo" matches "foo",
							# "foo/bar", "foo/bar/baz", etc.
							output.append(f'(?:(?P<{_DIR_MARK}>/).*)?')

						need_slash = True

					else:
						# Match segment glob pattern.
						if need_slash:
							output.append('/')

						try:
							output.append(cls._translate_segment_glob(seg))
						except ValueError as e:
							raise GitWildMatchPatternError(f"Invalid git pattern: {original_pattern!r}") from e

						if i == end:
							# A pattern ending without a slash ('/') will match a file or a
							# directory (with paths underneath it). E.g., "foo" matches "foo",
							# "foo/bar", "foo/bar/baz", etc.
							output.append(f'(?:(?P<{_DIR_MARK}>/).*)?')

						need_slash = True

				output.append('$')
				regex = ''.join(output)

			else:
				# Use regex override.
				regex = override_regex

		else:
			# A blank pattern is a null-operation (neither includes nor excludes
			# files).
			regex = None
			include = None

		if regex is not None and return_type is bytes:
			regex = regex.encode(_BYTES_ENCODING)

		return regex, include

	@staticmethod
	def _translate_segment_glob(pattern: str) -> str:
		"""
		Translates the glob pattern to a regular expression. This is used in the
		constructor to translate a path segment glob pattern to its corresponding
		regular expression.

		*pattern* (:class:`str`) is the glob pattern.

		Returns the regular expression (:class:`str`).
		"""
		# NOTE: This is derived from `fnmatch.translate()` and is similar to the
		# POSIX function `fnmatch()` with the `FNM_PATHNAME` flag set.

		escape = False
		regex = ''
		i, end = 0, len(pattern)
		while i < end:
			# Get next character.
			char = pattern[i]
			i += 1

			if escape:
				# Escape the character.
				escape = False
				regex += re.escape(char)

			elif char == '\\':
				# Escape character, escape next character.
				escape = True

			elif char == '*':
				# Multi-character wildcard. Match any string (except slashes), including
				# an empty string.
				regex += '[^/]*'

			elif char == '?':
				# Single-character wildcard. Match any single character (except a
				# slash).
				regex += '[^/]'

			elif char == '[':
				# Bracket expression wildcard. Except for the beginning exclamation
				# mark, the whole bracket expression can be used directly as regex, but
				# we have to find where the expression ends.
				# - "[][!]" matches ']', '[' and '!'.
				# - "[]-]" matches ']' and '-'.
				# - "[!]a-]" matches any character except ']', 'a' and '-'.
				j = i

				# Pass bracket expression negation.
				if j < end and (pattern[j] == '!' or pattern[j] == '^'):
					j += 1

				# Pass first closing bracket if it is at the beginning of the
				# expression.
				if j < end and pattern[j] == ']':
					j += 1

				# Find closing bracket. Stop once we reach the end or find it.
				while j < end and pattern[j] != ']':
					j += 1

				if j < end:
					# Found end of bracket expression. Increment j to be one past the
					# closing bracket:
					#
					#  [...]
					#   ^   ^
					#   i   j
					#
					j += 1
					expr = '['

					if pattern[i] == '!':
						# Bracket expression needs to be negated.
						expr += '^'
						i += 1
					elif pattern[i] == '^':
						# POSIX declares that the regex bracket expression negation "[^...]"
						# is undefined in a glob pattern. Python's `fnmatch.translate()`
						# escapes the caret ('^') as a literal. Git supports the using a
						# caret for negation. Maintain consistency with Git because that is
						# the expected behavior.
						expr += '^'
						i += 1

					# Build regex bracket expression. Escape slashes so they are treated
					# as literal slashes by regex as defined by POSIX.
					expr += pattern[i:j].replace('\\', '\\\\')

					# Add regex bracket expression to regex result.
					regex += expr

					# Set i to one past the closing bracket.
					i = j

				else:
					# Failed to find closing bracket, treat opening bracket as a bracket
					# literal instead of as an expression.
					regex += '\\['

			else:
				# Regular character, escape it for regex.
				regex += re.escape(char)

		if escape:
			raise ValueError(f"Escape character found with no next character to escape: {pattern!r}")

		return regex

	@staticmethod
	def escape(s: AnyStr) -> AnyStr:
		"""
		Escape special characters in the given string.

		*s* (:class:`str` or :class:`bytes`) a filename or a string that you want to
		escape, usually before adding it to a ".gitignore".

		Returns the escaped string (:class:`str` or :class:`bytes`).
		"""
		if isinstance(s, str):
			return_type = str
			string = s
		elif isinstance(s, bytes):
			return_type = bytes
			string = s.decode(_BYTES_ENCODING)
		else:
			raise TypeError(f"s:{s!r} is not a unicode or byte string.")

		# Reference: https://git-scm.com/docs/gitignore#_pattern_format
		meta_characters = r"[]!*#?"

		out_string = "".join("\\" + x if x in meta_characters else x for x in string)

		if return_type is bytes:
			return out_string.encode(_BYTES_ENCODING)
		else:
			return out_string

util.register_pattern('gitwildmatch', GitWildMatchPattern)


class GitIgnorePattern(GitWildMatchPattern):
	"""
	The :class:`GitIgnorePattern` class is deprecated by :class:`GitWildMatchPattern`.
	This class only exists to maintain compatibility with v0.4.
	"""

	def __init__(self, *args, **kw) -> None:
		"""
		Warn about deprecation.
		"""
		self._deprecated()
		super(GitIgnorePattern, self).__init__(*args, **kw)

	@staticmethod
	def _deprecated() -> None:
		"""
		Warn about deprecation.
		"""
		warnings.warn((
			"GitIgnorePattern ('gitignore') is deprecated. Use GitWildMatchPattern "
			"('gitwildmatch') instead."
		), DeprecationWarning, stacklevel=3)

	@classmethod
	def pattern_to_regex(cls, *args, **kw):
		"""
		Warn about deprecation.
		"""
		cls._deprecated()
		return super(GitIgnorePattern, cls).pattern_to_regex(*args, **kw)

# Register `GitIgnorePattern` as "gitignore" for backward compatibility with
# v0.4.
util.register_pattern('gitignore', GitIgnorePattern)