rhodecode/lib/diffs.py

# -*- coding: utf-8 -*-

# Copyright (C) 2011-2016  RhodeCode GmbH
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License, version 3
# (only), as published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# This program is dual-licensed. If you wish to learn more about the
# RhodeCode Enterprise Edition, including its added features, Support services,
# and proprietary license terms, please see https://rhodecode.com/licenses/


"""
Set of diffing helpers, previously part of vcs
"""

import collections
import re
import difflib
import logging

from itertools import tee, imap

from pylons.i18n.translation import _

from rhodecode.lib.vcs.exceptions import VCSError
from rhodecode.lib.vcs.nodes import FileNode, SubModuleNode
from rhodecode.lib.vcs.backends.base import EmptyCommit
from rhodecode.lib.helpers import escape
from rhodecode.lib.utils2 import safe_unicode

log = logging.getLogger(__name__)

# define max context, a file with more than this numbers of lines is unusable
# in browser anyway
MAX_CONTEXT = 1024 * 1014


class OPS(object):
    ADD = 'A'
    MOD = 'M'
    DEL = 'D'


def wrap_to_table(str_):
    return '''<table class="code-difftable">
                <tr class="line no-comment">
                <td class="add-comment-line tooltip" title="%s"><span class="add-comment-content"></span></td>
                <td></td>
                <td class="lineno new"></td>
                <td class="code no-comment"><pre>%s</pre></td>
                </tr>
              </table>''' % (_('Click to comment'), str_)


def wrapped_diff(filenode_old, filenode_new, diff_limit=None, file_limit=None,
                 show_full_diff=False, ignore_whitespace=True, line_context=3,
                 enable_comments=False):
    """
    returns a wrapped diff into a table, checks for cut_off_limit for file and
    whole diff and presents proper message
    """

    if filenode_old is None:
        filenode_old = FileNode(filenode_new.path, '', EmptyCommit())

    if filenode_old.is_binary or filenode_new.is_binary:
        diff = wrap_to_table(_('Binary file'))
        stats = None
        size = 0
        data = None

    elif diff_limit != -1 and (diff_limit is None or
        (filenode_old.size < diff_limit and filenode_new.size < diff_limit)):

        f_gitdiff = get_gitdiff(filenode_old, filenode_new,
                                ignore_whitespace=ignore_whitespace,
                                context=line_context)
        diff_processor = DiffProcessor(
            f_gitdiff, format='gitdiff', diff_limit=diff_limit,
            file_limit=file_limit, show_full_diff=show_full_diff)
        _parsed = diff_processor.prepare()

        diff = diff_processor.as_html(enable_comments=enable_comments)
        stats = _parsed[0]['stats'] if _parsed else None
        size = len(diff or '')
        data = _parsed[0] if _parsed else None
    else:
        diff = wrap_to_table(_('Changeset was too big and was cut off, use '
                               'diff menu to display this diff'))
        stats = None
        size = 0
        data = None
    if not diff:
        submodules = filter(lambda o: isinstance(o, SubModuleNode),
                            [filenode_new, filenode_old])
        if submodules:
            diff = wrap_to_table(escape('Submodule %r' % submodules[0]))
        else:
            diff = wrap_to_table(_('No changes detected'))

    cs1 = filenode_old.commit.raw_id
    cs2 = filenode_new.commit.raw_id

    return size, cs1, cs2, diff, stats, data


def get_gitdiff(filenode_old, filenode_new, ignore_whitespace=True, context=3):
    """
    Returns git style diff between given ``filenode_old`` and ``filenode_new``.

    :param ignore_whitespace: ignore whitespaces in diff
    """
    # make sure we pass in default context
    context = context or 3
    # protect against IntOverflow when passing HUGE context
    if context > MAX_CONTEXT:
        context = MAX_CONTEXT

    submodules = filter(lambda o: isinstance(o, SubModuleNode),
                        [filenode_new, filenode_old])
    if submodules:
        return ''

    for filenode in (filenode_old, filenode_new):
        if not isinstance(filenode, FileNode):
            raise VCSError(
                "Given object should be FileNode object, not %s"
                % filenode.__class__)

    repo = filenode_new.commit.repository
    old_commit = filenode_old.commit or repo.EMPTY_COMMIT
    new_commit = filenode_new.commit

    vcs_gitdiff = repo.get_diff(
        old_commit, new_commit, filenode_new.path,
        ignore_whitespace, context, path1=filenode_old.path)
    return vcs_gitdiff

NEW_FILENODE = 1
DEL_FILENODE = 2
MOD_FILENODE = 3
RENAMED_FILENODE = 4
COPIED_FILENODE = 5
CHMOD_FILENODE = 6
BIN_FILENODE = 7


class LimitedDiffContainer(object):

    def __init__(self, diff_limit, cur_diff_size, diff):
        self.diff = diff
        self.diff_limit = diff_limit
        self.cur_diff_size = cur_diff_size

    def __getitem__(self, key):
        return self.diff.__getitem__(key)

    def __iter__(self):
        for l in self.diff:
            yield l


class Action(object):
    """
    Contains constants for the action value of the lines in a parsed diff.
    """

    ADD = 'add'
    DELETE = 'del'
    UNMODIFIED = 'unmod'

    CONTEXT = 'context'


class DiffProcessor(object):
    """
    Give it a unified or git diff and it returns a list of the files that were
    mentioned in the diff together with a dict of meta information that
    can be used to render it in a HTML template.

    .. note:: Unicode handling

       The original diffs are a byte sequence and can contain filenames
       in mixed encodings. This class generally returns `unicode` objects
       since the result is intended for presentation to the user.

    """
    _chunk_re = re.compile(r'^@@ -(\d+)(?:,(\d+))? \+(\d+)(?:,(\d+))? @@(.*)')
    _newline_marker = re.compile(r'^\\ No newline at end of file')

    # used for inline highlighter word split
    _token_re = re.compile(r'()(&gt;|&lt;|&amp;|\W+?)')

    def __init__(self, diff, format='gitdiff', diff_limit=None,
                 file_limit=None, show_full_diff=True):
        """
        :param diff: A `Diff` object representing a diff from a vcs backend
        :param format: format of diff passed, `udiff` or `gitdiff`
        :param diff_limit: define the size of diff that is considered "big"
            based on that parameter cut off will be triggered, set to None
            to show full diff
        """
        self._diff = diff
        self._format = format
        self.adds = 0
        self.removes = 0
        # calculate diff size
        self.diff_limit = diff_limit
        self.file_limit = file_limit
        self.show_full_diff = show_full_diff
        self.cur_diff_size = 0
        self.parsed = False
        self.parsed_diff = []

        if format == 'gitdiff':
            self.differ = self._highlight_line_difflib
            self._parser = self._parse_gitdiff
        else:
            self.differ = self._highlight_line_udiff
            self._parser = self._parse_udiff

    def _copy_iterator(self):
        """
        make a fresh copy of generator, we should not iterate thru
        an original as it's needed for repeating operations on
        this instance of DiffProcessor
        """
        self.__udiff, iterator_copy = tee(self.__udiff)
        return iterator_copy

    def _escaper(self, string):
        """
        Escaper for diff escapes special chars and checks the diff limit

        :param string:
        """

        self.cur_diff_size += len(string)

        if not self.show_full_diff and (self.cur_diff_size > self.diff_limit):
            raise DiffLimitExceeded('Diff Limit Exceeded')

        return safe_unicode(string)\
            .replace('&', '&amp;')\
            .replace('<', '&lt;')\
            .replace('>', '&gt;')

    def _line_counter(self, l):
        """
        Checks each line and bumps total adds/removes for this diff

        :param l:
        """
        if l.startswith('+') and not l.startswith('+++'):
            self.adds += 1
        elif l.startswith('-') and not l.startswith('---'):
            self.removes += 1
        return safe_unicode(l)

    def _highlight_line_difflib(self, line, next_):
        """
        Highlight inline changes in both lines.
        """

        if line['action'] == Action.DELETE:
            old, new = line, next_
        else:
            old, new = next_, line

        oldwords = self._token_re.split(old['line'])
        newwords = self._token_re.split(new['line'])
        sequence = difflib.SequenceMatcher(None, oldwords, newwords)

        oldfragments, newfragments = [], []
        for tag, i1, i2, j1, j2 in sequence.get_opcodes():
            oldfrag = ''.join(oldwords[i1:i2])
            newfrag = ''.join(newwords[j1:j2])
            if tag != 'equal':
                if oldfrag:
                    oldfrag = '<del>%s</del>' % oldfrag
                if newfrag:
                    newfrag = '<ins>%s</ins>' % newfrag
            oldfragments.append(oldfrag)
            newfragments.append(newfrag)

        old['line'] = "".join(oldfragments)
        new['line'] = "".join(newfragments)

    def _highlight_line_udiff(self, line, next_):
        """
        Highlight inline changes in both lines.
        """
        start = 0
        limit = min(len(line['line']), len(next_['line']))
        while start < limit and line['line'][start] == next_['line'][start]:
            start += 1
        end = -1
        limit -= start
        while -end <= limit and line['line'][end] == next_['line'][end]:
            end -= 1
        end += 1
        if start or end:
            def do(l):
                last = end + len(l['line'])
                if l['action'] == Action.ADD:
                    tag = 'ins'
                else:
                    tag = 'del'
                l['line'] = '%s<%s>%s</%s>%s' % (
                    l['line'][:start],
                    tag,
                    l['line'][start:last],
                    tag,
                    l['line'][last:]
                )
            do(line)
            do(next_)

    def _clean_line(self, line, command):
        if command in ['+', '-', ' ']:
            # only modify the line if it's actually a diff thing
            line = line[1:]
        return line

    def _parse_gitdiff(self, inline_diff=True):
        _files = []
        diff_container = lambda arg: arg

        for chunk in self._diff.chunks():
            head = chunk.header

            diff = imap(self._escaper, chunk.diff.splitlines(1))
            raw_diff = chunk.raw
            limited_diff = False
            exceeds_limit = False

            op = None
            stats = {
                'added': 0,
                'deleted': 0,
                'binary': False,
                'ops': {},
            }

            if head['deleted_file_mode']:
                op = OPS.DEL
                stats['binary'] = True
                stats['ops'][DEL_FILENODE] = 'deleted file'

            elif head['new_file_mode']:
                op = OPS.ADD
                stats['binary'] = True
                stats['ops'][NEW_FILENODE] = 'new file %s' % head['new_file_mode']
            else:  # modify operation, can be copy, rename or chmod

                # CHMOD
                if head['new_mode'] and head['old_mode']:
                    op = OPS.MOD
                    stats['binary'] = True
                    stats['ops'][CHMOD_FILENODE] = (
                        'modified file chmod %s => %s' % (
                            head['old_mode'], head['new_mode']))
                # RENAME
                if head['rename_from'] != head['rename_to']:
                    op = OPS.MOD
                    stats['binary'] = True
                    stats['ops'][RENAMED_FILENODE] = (
                        'file renamed from %s to %s' % (
                            head['rename_from'], head['rename_to']))
                # COPY
                if head.get('copy_from') and head.get('copy_to'):
                    op = OPS.MOD
                    stats['binary'] = True
                    stats['ops'][COPIED_FILENODE] = (
                        'file copied from %s to %s' % (
                            head['copy_from'], head['copy_to']))

                # If our new parsed headers didn't match anything fallback to
                # old style detection
                if op is None:
                    if not head['a_file'] and head['b_file']:
                        op = OPS.ADD
                        stats['binary'] = True
                        stats['ops'][NEW_FILENODE] = 'new file'

                    elif head['a_file'] and not head['b_file']:
                        op = OPS.DEL
                        stats['binary'] = True
                        stats['ops'][DEL_FILENODE] = 'deleted file'

                # it's not ADD not DELETE
                if op is None:
                    op = OPS.MOD
                    stats['binary'] = True
                    stats['ops'][MOD_FILENODE] = 'modified file'

            # a real non-binary diff
            if head['a_file'] or head['b_file']:
                try:
                    raw_diff, chunks, _stats = self._parse_lines(diff)
                    stats['binary'] = False
                    stats['added'] = _stats[0]
                    stats['deleted'] = _stats[1]
                    # explicit mark that it's a modified file
                    if op == OPS.MOD:
                        stats['ops'][MOD_FILENODE] = 'modified file'
                    exceeds_limit = len(raw_diff) > self.file_limit

                    # changed from _escaper function so we validate size of
                    # each file instead of the whole diff
                    # diff will hide big files but still show small ones
                    # from my tests, big files are fairly safe to be parsed
                    # but the browser is the bottleneck
                    if not self.show_full_diff and exceeds_limit:
                        raise DiffLimitExceeded('File Limit Exceeded')

                except DiffLimitExceeded:
                    diff_container = lambda _diff: \
                        LimitedDiffContainer(
                            self.diff_limit, self.cur_diff_size, _diff)

                    exceeds_limit = len(raw_diff) > self.file_limit
                    limited_diff = True
                    chunks = []

            else:  # GIT format binary patch, or possibly empty diff
                if head['bin_patch']:
                    # we have operation already extracted, but we mark simply
                    # it's a diff we wont show for binary files
                    stats['ops'][BIN_FILENODE] = 'binary diff hidden'
                chunks = []

            if chunks and not self.show_full_diff and op == OPS.DEL:
                # if not full diff mode show deleted file contents
                # TODO: anderson: if the view is not too big, there is no way
                # to see the content of the file
                chunks = []

            chunks.insert(0, [{
                                  'old_lineno': '',
                                  'new_lineno': '',
                                  'action': Action.CONTEXT,
                                  'line': msg,
                              } for _op, msg in stats['ops'].iteritems()
                              if _op not in [MOD_FILENODE]])

            _files.append({
                'filename': safe_unicode(head['b_path']),
                'old_revision': head['a_blob_id'],
                'new_revision': head['b_blob_id'],
                'chunks': chunks,
                'raw_diff': safe_unicode(raw_diff),
                'operation': op,
                'stats': stats,
                'exceeds_limit': exceeds_limit,
                'is_limited_diff': limited_diff,
            })

        sorter = lambda info: {OPS.ADD: 0, OPS.MOD: 1,
                               OPS.DEL: 2}.get(info['operation'])

        if not inline_diff:
            return diff_container(sorted(_files, key=sorter))

        # highlight inline changes
        for diff_data in _files:
            for chunk in diff_data['chunks']:
                lineiter = iter(chunk)
                try:
                    while 1:
                        line = lineiter.next()
                        if line['action'] not in (
                                Action.UNMODIFIED, Action.CONTEXT):
                            nextline = lineiter.next()
                            if nextline['action'] in ['unmod', 'context'] or \
                               nextline['action'] == line['action']:
                                continue
                            self.differ(line, nextline)
                except StopIteration:
                    pass

        return diff_container(sorted(_files, key=sorter))

    def _parse_udiff(self, inline_diff=True):
        raise NotImplementedError()

    def _parse_lines(self, diff):
        """
        Parse the diff an return data for the template.
        """

        lineiter = iter(diff)
        stats = [0, 0]
        chunks = []
        raw_diff = []

        try:
            line = lineiter.next()

            while line:
                raw_diff.append(line)
                lines = []
                chunks.append(lines)

                match = self._chunk_re.match(line)

                if not match:
                    break

                gr = match.groups()
                (old_line, old_end,
                 new_line, new_end) = [int(x or 1) for x in gr[:-1]]
                old_line -= 1
                new_line -= 1

                context = len(gr) == 5
                old_end += old_line
                new_end += new_line

                if context:
                    # skip context only if it's first line
                    if int(gr[0]) > 1:
                        lines.append({
                            'old_lineno': '...',
                            'new_lineno': '...',
                            'action':     Action.CONTEXT,
                            'line':       line,
                        })

                line = lineiter.next()

                while old_line < old_end or new_line < new_end:
                    command = ' '
                    if line:
                        command = line[0]

                    affects_old = affects_new = False

                    # ignore those if we don't expect them
                    if command in '#@':
                        continue
                    elif command == '+':
                        affects_new = True
                        action = Action.ADD
                        stats[0] += 1
                    elif command == '-':
                        affects_old = True
                        action = Action.DELETE
                        stats[1] += 1
                    else:
                        affects_old = affects_new = True
                        action = Action.UNMODIFIED

                    if not self._newline_marker.match(line):
                        old_line += affects_old
                        new_line += affects_new
                        lines.append({
                            'old_lineno':   affects_old and old_line or '',
                            'new_lineno':   affects_new and new_line or '',
                            'action':       action,
                            'line':         self._clean_line(line, command)
                        })
                        raw_diff.append(line)

                    line = lineiter.next()

                    if self._newline_marker.match(line):
                        # we need to append to lines, since this is not
                        # counted in the line specs of diff
                        lines.append({
                            'old_lineno':   '...',
                            'new_lineno':   '...',
                            'action':       Action.CONTEXT,
                            'line':         self._clean_line(line, command)
                        })

        except StopIteration:
            pass
        return ''.join(raw_diff), chunks, stats

    def _safe_id(self, idstring):
        """Make a string safe for including in an id attribute.

        The HTML spec says that id attributes 'must begin with
        a letter ([A-Za-z]) and may be followed by any number
        of letters, digits ([0-9]), hyphens ("-"), underscores
        ("_"), colons (":"), and periods (".")'. These regexps
        are slightly over-zealous, in that they remove colons
        and periods unnecessarily.

        Whitespace is transformed into underscores, and then
        anything which is not a hyphen or a character that
        matches \w (alphanumerics and underscore) is removed.

        """
        # Transform all whitespace to underscore
        idstring = re.sub(r'\s', "_", '%s' % idstring)
        # Remove everything that is not a hyphen or a member of \w
        idstring = re.sub(r'(?!-)\W', "", idstring).lower()
        return idstring

    def prepare(self, inline_diff=True):
        """
        Prepare the passed udiff for HTML rendering.

        :return: A list of dicts with diff information.
        """
        parsed = self._parser(inline_diff=inline_diff)
        self.parsed = True
        self.parsed_diff = parsed
        return parsed

    def as_raw(self, diff_lines=None):
        """
        Returns raw diff as a byte string
        """
        return self._diff.raw

    def as_html(self, table_class='code-difftable', line_class='line',
                old_lineno_class='lineno old', new_lineno_class='lineno new',
                code_class='code', enable_comments=False, parsed_lines=None):
        """
        Return given diff as html table with customized css classes
        """
        def _link_to_if(condition, label, url):
            """
            Generates a link if condition is meet or just the label if not.
            """

            if condition:
                return '''<a href="%(url)s" class="tooltip"
                title="%(title)s">%(label)s</a>''' % {
                    'title': _('Click to select line'),
                    'url': url,
                    'label': label
                }
            else:
                return label
        if not self.parsed:
            self.prepare()

        diff_lines = self.parsed_diff
        if parsed_lines:
            diff_lines = parsed_lines

        _html_empty = True
        _html = []
        _html.append('''<table class="%(table_class)s">\n''' % {
            'table_class': table_class
        })

        for diff in diff_lines:
            for line in diff['chunks']:
                _html_empty = False
                for change in line:
                    _html.append('''<tr class="%(lc)s %(action)s">\n''' % {
                        'lc': line_class,
                        'action': change['action']
                    })
                    anchor_old_id = ''
                    anchor_new_id = ''
                    anchor_old = "%(filename)s_o%(oldline_no)s" % {
                        'filename': self._safe_id(diff['filename']),
                        'oldline_no': change['old_lineno']
                    }
                    anchor_new = "%(filename)s_n%(oldline_no)s" % {
                        'filename': self._safe_id(diff['filename']),
                        'oldline_no': change['new_lineno']
                    }
                    cond_old = (change['old_lineno'] != '...' and
                                change['old_lineno'])
                    cond_new = (change['new_lineno'] != '...' and
                                change['new_lineno'])
                    if cond_old:
                        anchor_old_id = 'id="%s"' % anchor_old
                    if cond_new:
                        anchor_new_id = 'id="%s"' % anchor_new

                    if change['action'] != Action.CONTEXT:
                        anchor_link = True
                    else:
                        anchor_link = False

                    ###########################################################
                    # COMMENT ICONS
                    ###########################################################
                    _html.append('''\t<td class="add-comment-line"><span class="add-comment-content">''')

                    if enable_comments and change['action'] != Action.CONTEXT:
                        _html.append('''<a href="#"><span class="icon-comment-add"></span></a>''')

                    _html.append('''</span></td><td class="comment-toggle tooltip" title="Toggle Comments"><i class="icon-comment"></i></td>\n''')

                    ###########################################################
                    # OLD LINE NUMBER
                    ###########################################################
                    _html.append('''\t<td %(a_id)s class="%(olc)s">''' % {
                        'a_id': anchor_old_id,
                        'olc': old_lineno_class
                    })

                    _html.append('''%(link)s''' % {
                        'link': _link_to_if(anchor_link, change['old_lineno'],
                                            '#%s' % anchor_old)
                    })
                    _html.append('''</td>\n''')
                    ###########################################################
                    # NEW LINE NUMBER
                    ###########################################################

                    _html.append('''\t<td %(a_id)s class="%(nlc)s">''' % {
                        'a_id': anchor_new_id,
                        'nlc': new_lineno_class
                    })

                    _html.append('''%(link)s''' % {
                        'link': _link_to_if(anchor_link, change['new_lineno'],
                                            '#%s' % anchor_new)
                    })
                    _html.append('''</td>\n''')
                    ###########################################################
                    # CODE
                    ###########################################################
                    code_classes = [code_class]
                    if (not enable_comments or
                            change['action'] == Action.CONTEXT):
                        code_classes.append('no-comment')
                    _html.append('\t<td class="%s">' % ' '.join(code_classes))
                    _html.append('''\n\t\t<pre>%(code)s</pre>\n''' % {
                        'code': change['line']
                    })

                    _html.append('''\t</td>''')
                    _html.append('''\n</tr>\n''')
        _html.append('''</table>''')
        if _html_empty:
            return None
        return ''.join(_html)

    def stat(self):
        """
        Returns tuple of added, and removed lines for this instance
        """
        return self.adds, self.removes

    def get_context_of_line(
            self, path, diff_line=None, context_before=3, context_after=3):
        """
        Returns the context lines for the specified diff line.

        :type diff_line: :class:`DiffLineNumber`
        """
        assert self.parsed, "DiffProcessor is not initialized."

        if None not in diff_line:
            raise ValueError(
                "Cannot specify both line numbers: {}".format(diff_line))

        file_diff = self._get_file_diff(path)
        chunk, idx = self._find_chunk_line_index(file_diff, diff_line)

        first_line_to_include = max(idx - context_before, 0)
        first_line_after_context = idx + context_after + 1
        context_lines = chunk[first_line_to_include:first_line_after_context]

        line_contents = [
            _context_line(line) for line in context_lines
            if _is_diff_content(line)]
        # TODO: johbo: Interim fixup, the diff chunks drop the final newline.
        # Once they are fixed, we can drop this line here.
        if line_contents:
            line_contents[-1] = (
                line_contents[-1][0], line_contents[-1][1].rstrip('\n') + '\n')
        return line_contents

    def find_context(self, path, context, offset=0):
        """
        Finds the given `context` inside of the diff.

        Use the parameter `offset` to specify which offset the target line has
        inside of the given `context`. This way the correct diff line will be
        returned.

        :param offset: Shall be used to specify the offset of the main line
            within the given `context`.
        """
        if offset < 0 or offset >= len(context):
            raise ValueError(
                "Only positive values up to the length of the context "
                "minus one are allowed.")

        matches = []
        file_diff = self._get_file_diff(path)

        for chunk in file_diff['chunks']:
            context_iter = iter(context)
            for line_idx, line in enumerate(chunk):
                try:
                    if _context_line(line) == context_iter.next():
                        continue
                except StopIteration:
                    matches.append((line_idx, chunk))
                context_iter = iter(context)

        # Increment position and triger StopIteration
        # if we had a match at the end
        line_idx += 1
        try:
            context_iter.next()
        except StopIteration:
            matches.append((line_idx, chunk))

        effective_offset = len(context) - offset
        found_at_diff_lines = [
            _line_to_diff_line_number(chunk[idx - effective_offset])
            for idx, chunk in matches]

        return found_at_diff_lines

    def _get_file_diff(self, path):
        for file_diff in self.parsed_diff:
            if file_diff['filename'] == path:
                break
        else:
            raise FileNotInDiffException("File {} not in diff".format(path))
        return file_diff

    def _find_chunk_line_index(self, file_diff, diff_line):
        for chunk in file_diff['chunks']:
            for idx, line in enumerate(chunk):
                if line['old_lineno'] == diff_line.old:
                    return chunk, idx
                if line['new_lineno'] == diff_line.new:
                    return chunk, idx
        raise LineNotInDiffException(
            "The line {} is not part of the diff.".format(diff_line))


def _is_diff_content(line):
    return line['action'] in (
        Action.UNMODIFIED, Action.ADD, Action.DELETE)


def _context_line(line):
    return (line['action'], line['line'])


DiffLineNumber = collections.namedtuple('DiffLineNumber', ['old', 'new'])


def _line_to_diff_line_number(line):
    new_line_no = line['new_lineno'] or None
    old_line_no = line['old_lineno'] or None
    return DiffLineNumber(old=old_line_no, new=new_line_no)


class FileNotInDiffException(Exception):
    """
    Raised when the context for a missing file is requested.

    If you request the context for a line in a file which is not part of the
    given diff, then this exception is raised.
    """


class LineNotInDiffException(Exception):
    """
    Raised when the context for a missing line is requested.

    If you request the context for a line in a file and this line is not
    part of the given diff, then this exception is raised.
    """


class DiffLimitExceeded(Exception):
    pass