import os
import codecs
from importlib import import_module
from urllib.request import url2pathname

from django.core.files.base import ContentFile
from django.utils.safestring import mark_safe
from django.template.loader import render_to_string
from django.utils.functional import cached_property

from compressor.cache import get_hexdigest, get_mtime
from compressor.conf import settings
from compressor.exceptions import (CompressorError, UncompressableFileError,
        FilterDoesNotExist)
from compressor.filters import CachedCompilerFilter
from compressor.storage import compressor_file_storage
from compressor.signals import post_compress
from compressor.utils import get_class, get_mod_func, staticfiles

# Some constants for nicer handling.
SOURCE_HUNK, SOURCE_FILE = 'inline', 'file'
METHOD_INPUT, METHOD_OUTPUT = 'input', 'output'


class Compressor:
    """
    Base compressor object to be subclassed for content type
    depending implementations details.
    """

    output_mimetypes = {}

    def __init__(self, resource_kind, content=None, output_prefix=None,
                 context=None, filters=None, log=None, verbosity=1, *args, **kwargs):
        if filters is None:
            self.filters = settings.COMPRESS_FILTERS[resource_kind]
        else:
            self.filters = filters
        if output_prefix is None:
            self.output_prefix = resource_kind
        else:
            self.output_prefix = output_prefix
        self.content = content or ""  # rendered contents of {% compress %} tag
        self.output_dir = settings.COMPRESS_OUTPUT_DIR.strip('/')
        self.charset = settings.DEFAULT_CHARSET
        self.split_content = []
        self.context = context or {}
        self.resource_kind = resource_kind
        self.extra_context = {}
        self.precompiler_mimetypes = dict(settings.COMPRESS_PRECOMPILERS)
        self.finders = staticfiles.finders
        self._storage = None
        self.log = log
        self.verbosity = verbosity

    def copy(self, **kwargs):
        keywords = dict(
            content=self.content,
            context=self.context,
            output_prefix=self.output_prefix,
            filters=self.filters)
        keywords.update(kwargs)
        return self.__class__(self.resource_kind, **keywords)

    @cached_property
    def storage(self):
        from compressor.storage import default_storage
        return default_storage

    def split_contents(self):
        """
        To be implemented in a subclass, should return an
        iterable with four values: kind, value, basename, element
        """
        raise NotImplementedError

    def get_template_name(self, mode):
        """
        Returns the template path for the given mode.
        """
        try:
            template = getattr(self, "template_name_%s" % mode)
            if template:
                return template
        except AttributeError:
            pass
        return "compressor/%s_%s.html" % (self.resource_kind, mode)

    def get_basename(self, url):
        """
        Takes full path to a static file (eg. "/static/css/style.css") and
        returns path with storage's base url removed (eg. "css/style.css").
        """
        try:
            base_url = self.storage.base_url
        except AttributeError:
            base_url = settings.COMPRESS_URL

        # Cast ``base_url`` to a string to allow it to be
        # a string-alike object to e.g. add ``SCRIPT_NAME``
        # WSGI param as a *path prefix* to the output URL.
        # See https://code.djangoproject.com/ticket/25598.
        base_url = str(base_url)

        if not url.startswith(base_url):
            raise UncompressableFileError("'%s' isn't accessible via "
                                          "COMPRESS_URL ('%s') and can't be "
                                          "compressed" % (url, base_url))
        basename = url.replace(base_url, "", 1)
        # drop the querystring, which is used for non-compressed cache-busting.
        return basename.split("?", 1)[0]

    def get_filepath(self, content, basename=None):
        """
        Returns file path for an output file based on contents.

        Returned path is relative to compressor storage's base url, for
        example "CACHE/css/58a8c0714e59.css".

        When `basename` argument is provided then file name (without extension)
        will be used as a part of returned file name, for example:

        get_filepath(content, "my_file.css") -> 'CACHE/css/my_file.58a8c0714e59.css'
        """
        parts = []
        if basename:
            filename = os.path.split(basename)[1]
            parts.append(os.path.splitext(filename)[0])
        parts.extend([get_hexdigest(content, 12), self.resource_kind])
        return os.path.join(self.output_dir, self.output_prefix, '.'.join(parts))

    def get_filename(self, basename):
        """
        Returns full path to a file, for example:

        get_filename('css/one.css') -> '/full/path/to/static/css/one.css'
        """
        filename = None
        # First try finding the file using the storage class.
        # This is skipped in DEBUG mode as files might be outdated in
        # compressor's final destination (COMPRESS_ROOT) during development
        if not settings.DEBUG:
            try:
                # call path first so remote storages don't make it to exists,
                # which would cause network I/O
                if self.log and self.verbosity >= 2:
                    self.log.write('Looking for \'{}\' in storage\n'.format(basename))
                filename = self.storage.path(basename)
                if not self.storage.exists(basename):
                    filename = None
            except NotImplementedError:
                # remote storages don't implement path, access the file locally
                if self.log and self.verbosity >= 2:
                    self.log.write('Remote storages don\'t implement path, looking for the file locally\n')
                if compressor_file_storage.exists(basename):
                    filename = compressor_file_storage.path(basename)
        # secondly try to find it with staticfiles
        if not filename and self.finders:
            if self.log and self.verbosity >= 2:
                if not settings.DEBUG:
                    self.log.write('\'{}\' was not found in storage, using static finders\n'.format(basename))
                else:
                    self.log.write('Using static finders for \'{}\'\n'.format(basename))
            filename = self.finders.find(url2pathname(basename))
        if filename:
            return filename
        # or just raise an exception as the last resort
        raise UncompressableFileError(
            "'%s' could not be found in the COMPRESS_ROOT '%s'%s" %
            (basename, settings.COMPRESS_ROOT,
             self.finders and " or with staticfiles." or "."))

    def get_filecontent(self, filename, charset):
        """
        Reads file contents using given `charset` and returns it as text.
        """
        if charset == 'utf-8':
            # Removes BOM
            charset = 'utf-8-sig'
        with codecs.open(filename, 'r', charset) as fd:
            try:
                return fd.read()
            except IOError as e:
                raise UncompressableFileError("IOError while processing "
                                              "'%s': %s" % (filename, e))
            except UnicodeDecodeError as e:
                raise UncompressableFileError("UnicodeDecodeError while "
                                              "processing '%s' with "
                                              "charset %s: %s" %
                                              (filename, charset, e))

    @cached_property
    def parser(self):
        return get_class(settings.COMPRESS_PARSER)(self.content)

    @cached_property
    def cached_filters(self):
        return [get_class(filter_cls) for filter_cls in self.filters]

    @cached_property
    def mtimes(self):
        return [str(get_mtime(value))
                for kind, value, basename, elem in self.split_contents()
                if kind == SOURCE_FILE]

    @cached_property
    def cachekey(self):
        return get_hexdigest(''.join(
            [self.content] + self.mtimes).encode(self.charset), 12)

    def hunks(self, forced=False):
        """
        The heart of content parsing, iterates over the
        list of split contents and looks at its kind
        to decide what to do with it. Should yield a
        bunch of precompiled and/or rendered hunks.
        """
        enabled = settings.COMPRESS_ENABLED or forced

        for kind, value, basename, elem in self.split_contents():
            precompiled = False
            attribs = self.parser.elem_attribs(elem)
            charset = attribs.get("charset", self.charset)
            options = {
                'method': METHOD_INPUT,
                'elem': elem,
                'kind': kind,
                'basename': basename,
                'charset': charset,
            }

            if kind == SOURCE_FILE:
                options = dict(options, filename=value)
                value = self.get_filecontent(value, charset)

            if self.precompiler_mimetypes:
                precompiled, value = self.precompile(value, **options)

            if enabled:
                yield self.filter(value, self.cached_filters, **options)
            elif precompiled:
                for filter_cls in self.cached_filters:
                    if filter_cls.run_with_compression_disabled:
                        value = self.filter(value, [filter_cls], **options)
                yield self.handle_output(kind, value, forced=True,
                                         basename=basename)
            else:
                yield self.parser.elem_str(elem)

    def filter_output(self, content):
        """
        Passes the concatenated content to the 'output' methods
        of the compressor filters.
        """
        return self.filter(content, self.cached_filters, method=METHOD_OUTPUT)

    def filter_input(self, forced=False):
        """
        Passes each hunk (file or code) to the 'input' methods
        of the compressor filters.
        """
        content = []
        for hunk in self.hunks(forced):
            content.append(hunk)
        return content

    def precompile(self, content, kind=None, elem=None, filename=None,
                   charset=None, **kwargs):
        """
        Processes file using a pre compiler.

        This is the place where files like coffee script are processed.
        """
        if not kind:
            return False, content
        attrs = self.parser.elem_attribs(elem)
        mimetype = attrs.get("type", None)
        if mimetype is None:
            return False, content

        filter_or_command = self.precompiler_mimetypes.get(mimetype)
        if filter_or_command is None:
            if mimetype in self.output_mimetypes:
                return False, content
            raise CompressorError("Couldn't find any precompiler in "
                                  "COMPRESS_PRECOMPILERS setting for "
                                  "mimetype '%s'." % mimetype)

        mod_name, cls_name = get_mod_func(filter_or_command)
        try:
            mod = import_module(mod_name)
        except (ImportError, TypeError):
            filter = CachedCompilerFilter(
                content=content, filter_type=self.resource_kind, filename=filename,
                charset=charset, command=filter_or_command, mimetype=mimetype)
            return True, filter.input(**kwargs)
        try:
            precompiler_class = getattr(mod, cls_name)
        except AttributeError:
            raise FilterDoesNotExist('Could not find "%s".' % filter_or_command)
        filter = precompiler_class(
            content, attrs=attrs, filter_type=self.resource_kind, charset=charset,
            filename=filename)
        return True, filter.input(**kwargs)

    def filter(self, content, filters, method, **kwargs):
        for filter_cls in filters:
            filter_func = getattr(
                filter_cls(content, filter_type=self.resource_kind), method)
            try:
                if callable(filter_func):
                    content = filter_func(**kwargs)
            except NotImplementedError:
                pass
        return content

    def output(self, mode='file', forced=False, basename=None):
        """
        The general output method, override in subclass if you need to do
        any custom modification. Calls other mode specific methods or simply
        returns the content directly.
        """
        output = '\n'.join(self.filter_input(forced))

        if not output:
            return ''

        if settings.COMPRESS_ENABLED or forced:
            filtered_output = self.filter_output(output)
            return self.handle_output(mode, filtered_output, forced, basename)

        return output

    def handle_output(self, mode, content, forced, basename=None):
        # Then check for the appropriate output method and call it
        output_func = getattr(self, "output_%s" % mode, None)
        if callable(output_func):
            return output_func(mode, content, forced, basename)
        # Total failure, raise a general exception
        raise CompressorError(
            "Couldn't find output method for mode '%s'" % mode)

    def output_file(self, mode, content, forced=False, basename=None):
        """
        The output method that saves the content to a file and renders
        the appropriate template with the file's URL.
        """
        new_filepath = self.get_filepath(content, basename=basename)
        if not self.storage.exists(new_filepath) or forced:
            self.storage.save(new_filepath, ContentFile(content.encode(self.charset)))
        url = mark_safe(self.storage.url(new_filepath))
        return self.render_output(mode, {"url": url})

    def output_inline(self, mode, content, forced=False, basename=None):
        """
        The output method that directly returns the content for inline
        display.
        """
        return self.render_output(mode, {"content": content})

    def output_preload(self, mode, content, forced=False, basename=None):
        """
        The output method that returns <link> with rel="preload" and
        proper href attribute for given file.
        """
        return self.output_file(mode, content, forced, basename)

    def render_output(self, mode, context=None):
        """
        Renders the compressor output with the appropriate template for
        the given mode and template context.
        """
        # Just in case someone renders the compressor outside
        # the usual template rendering cycle
        if 'compressed' not in self.context:
            self.context['compressed'] = {}

        self.context['compressed'].update(context or {})
        self.context['compressed'].update(self.extra_context)

        if hasattr(self.context, 'flatten'):
            # Passing Contexts to Template.render is deprecated since Django 1.8.
            final_context = self.context.flatten()
        else:
            final_context = self.context

        post_compress.send(sender=self.__class__, type=self.resource_kind,
                           mode=mode, context=final_context)
        template_name = self.get_template_name(mode)
        return render_to_string(template_name, context=final_context)
