from __future__ import annotations

import logging
from typing import TYPE_CHECKING, Any, Iterator, List, Mapping, Optional, Type, TypeVar, Union
from urllib.parse import urlsplit

from mkdocs.structure.files import Files
from mkdocs.structure.pages import Page
from mkdocs.utils import nest_paths

if TYPE_CHECKING:
    from mkdocs.config.defaults import MkDocsConfig


log = logging.getLogger(__name__)


class Navigation:
    def __init__(self, items: List[Union[Page, Section, Link]], pages: List[Page]) -> None:
        self.items = items  # Nested List with full navigation of Sections, Pages, and Links.
        self.pages = pages  # Flat List of subset of Pages in nav, in order.

        self.homepage = None
        for page in pages:
            if page.is_homepage:
                self.homepage = page
                break

    homepage: Optional[Page]
    """The [page][mkdocs.structure.pages.Page] object for the homepage of the site."""

    pages: List[Page]
    """A flat list of all [page][mkdocs.structure.pages.Page] objects contained in the navigation."""

    def __repr__(self):
        return '\n'.join(item._indent_print() for item in self)

    def __iter__(self) -> Iterator[Union[Page, Section, Link]]:
        return iter(self.items)

    def __len__(self) -> int:
        return len(self.items)


class Section:
    def __init__(self, title: str, children: List[Union[Page, Section, Link]]) -> None:
        self.title = title
        self.children = children

        self.parent = None
        self.active = False

    def __repr__(self):
        return f"Section(title='{self.title}')"

    title: str
    """The title of the section."""

    parent: Optional[Section]
    """The immediate parent of the section or `None` if the section is at the top level."""

    children: List[Union[Page, Section, Link]]
    """An iterable of all child navigation objects. Children may include nested sections, pages and links."""

    @property
    def active(self) -> bool:
        """
        When `True`, indicates that a child page of this section is the current page and
        can be used to highlight the section as the currently viewed section. Defaults
        to `False`.
        """
        return self.__active

    @active.setter
    def active(self, value: bool):
        """Set active status of section and ancestors."""
        self.__active = bool(value)
        if self.parent is not None:
            self.parent.active = bool(value)

    is_section: bool = True
    """Indicates that the navigation object is a "section" object. Always `True` for section objects."""

    is_page: bool = False
    """Indicates that the navigation object is a "page" object. Always `False` for section objects."""

    is_link: bool = False
    """Indicates that the navigation object is a "link" object. Always `False` for section objects."""

    @property
    def ancestors(self):
        if self.parent is None:
            return []
        return [self.parent] + self.parent.ancestors

    def _indent_print(self, depth=0):
        ret = ['{}{}'.format('    ' * depth, repr(self))]
        for item in self.children:
            ret.append(item._indent_print(depth + 1))
        return '\n'.join(ret)


class Link:
    def __init__(self, title: str, url: str):
        self.title = title
        self.url = url
        self.parent = None

    def __repr__(self):
        title = f"'{self.title}'" if (self.title is not None) else '[blank]'
        return f"Link(title={title}, url='{self.url}')"

    title: str
    """The title of the link. This would generally be used as the label of the link."""

    url: str
    """The URL that the link points to. The URL should always be an absolute URLs and
    should not need to have `base_url` prepended."""

    parent: Optional[Section]
    """The immediate parent of the link. `None` if the link is at the top level."""

    children: None = None
    """Links do not contain children and the attribute is always `None`."""

    active: bool = False
    """External links cannot be "active" and the attribute is always `False`."""

    is_section: bool = False
    """Indicates that the navigation object is a "section" object. Always `False` for link objects."""

    is_page: bool = False
    """Indicates that the navigation object is a "page" object. Always `False` for link objects."""

    is_link: bool = True
    """Indicates that the navigation object is a "link" object. Always `True` for link objects."""

    @property
    def ancestors(self):
        if self.parent is None:
            return []
        return [self.parent] + self.parent.ancestors

    def _indent_print(self, depth=0):
        return '{}{}'.format('    ' * depth, repr(self))


def get_navigation(files: Files, config: Union[MkDocsConfig, Mapping[str, Any]]) -> Navigation:
    """Build site navigation from config and files."""
    nav_config = config['nav'] or nest_paths(f.src_uri for f in files.documentation_pages())
    items = _data_to_navigation(nav_config, files, config)
    if not isinstance(items, list):
        items = [items]

    # Get only the pages from the navigation, ignoring any sections and links.
    pages = _get_by_type(items, Page)

    # Include next, previous and parent links.
    _add_previous_and_next_links(pages)
    _add_parent_links(items)

    missing_from_config = [file for file in files.documentation_pages() if file.page is None]
    if missing_from_config:
        log.info(
            'The following pages exist in the docs directory, but are not '
            'included in the "nav" configuration:\n  - {}'.format(
                '\n  - '.join(file.src_path for file in missing_from_config)
            )
        )
        # Any documentation files not found in the nav should still have an associated page, so we
        # create them here. The Page object will automatically be assigned to `file.page` during
        # its creation (and this is the only way in which these page objects are accessible).
        for file in missing_from_config:
            Page(None, file, config)

    links = _get_by_type(items, Link)
    for link in links:
        scheme, netloc, path, query, fragment = urlsplit(link.url)
        if scheme or netloc:
            log.debug(f"An external link to '{link.url}' is included in the 'nav' configuration.")
        elif link.url.startswith('/'):
            log.debug(
                f"An absolute path to '{link.url}' is included in the 'nav' "
                "configuration, which presumably points to an external resource."
            )
        else:
            msg = (
                f"A relative path to '{link.url}' is included in the 'nav' "
                "configuration, which is not found in the documentation files"
            )
            log.warning(msg)
    return Navigation(items, pages)


def _data_to_navigation(data, files: Files, config: Union[MkDocsConfig, Mapping[str, Any]]):
    if isinstance(data, dict):
        return [
            _data_to_navigation((key, value), files, config)
            if isinstance(value, str)
            else Section(title=key, children=_data_to_navigation(value, files, config))
            for key, value in data.items()
        ]
    elif isinstance(data, list):
        return [
            _data_to_navigation(item, files, config)[0]
            if isinstance(item, dict) and len(item) == 1
            else _data_to_navigation(item, files, config)
            for item in data
        ]
    title, path = data if isinstance(data, tuple) else (None, data)
    file = files.get_file_from_path(path)
    if file:
        return Page(title, file, config)
    return Link(title, path)


T = TypeVar('T')


def _get_by_type(nav, t: Type[T]) -> List[T]:
    ret = []
    for item in nav:
        if isinstance(item, t):
            ret.append(item)
        if item.children:
            ret.extend(_get_by_type(item.children, t))
    return ret


def _add_parent_links(nav) -> None:
    for item in nav:
        if item.is_section:
            for child in item.children:
                child.parent = item
            _add_parent_links(item.children)


def _add_previous_and_next_links(pages: List[Page]) -> None:
    bookended = [None, *pages, None]
    zipped = zip(bookended[:-2], pages, bookended[2:])
    for page0, page1, page2 in zipped:
        page1.previous_page, page1.next_page = page0, page2