from collections.abc import Iterator
from dataclasses import dataclass
from datetime import datetime, timezone
from fnmatch import fnmatchcase
from itertools import chain
from pathlib import Path
from typing import Any
from urllib.parse import quote, urldefrag, urljoin, urlsplit

import mf2py
import sqlalchemy as sa
import xxhash
from bs4 import BeautifulSoup, Tag
from flask import current_app
from sqlalchemy.orm import selectinload

from .. import DATABASE as db
from .. import HUEY as huey
from ..models import SentWebmention, Source
from ..url_security import is_http_url
from .sender import send_webmention

REACTION_PROPERTIES = ("in-reply-to", "like-of", "repost-of", "bookmark-of")


class SourceScanError(Exception):
    """A source document cannot safely be processed."""


@dataclass(frozen=True)
class ScannedSource:
    path: str
    url: str
    content_hash: str
    targets: frozenset[str]


def source_url_for_path(relative_path: Path, base_url: str) -> str:
    """Derive the public source URL from its relative filesystem path."""
    directory = relative_path.parent.as_posix()

    return urljoin(base_url, f"{quote(directory, safe='/')}/")


def canonical_url(
    document: BeautifulSoup, *, relative_path: Path, base_url: str | None
) -> str | None:
    """Return the canonical URL declared by the document."""
    if (link := document.select_one('link[rel~="canonical"][href]')) is not None:
        href = link.get("href")

        if not isinstance(href, str) or not (href := href.strip()):
            raise SourceScanError("Document contains an empty canonical URL")

        if is_http_url(href):
            return href

        if base_url is None:
            raise SourceScanError(
                "Document contains a relative canonical URL, but "
                "WEBMENTIONS_SSG_SOURCE_BASE_URL is not configured"
            )

        resolved = urljoin(source_url_for_path(relative_path, base_url), href)

        if not is_http_url(resolved):
            raise SourceScanError(
                f"Canonical URL is not a valid HTTP or HTTPS URL: {href!r}"
            )

        return resolved


def property_urls(entry: dict[str, Any], property_name: str) -> Iterator[str]:
    """Yield URL values from a microformats property."""
    properties = entry.get("properties")

    if not isinstance(properties, dict):
        return

    values = properties.get(property_name)

    if not isinstance(values, list):
        return

    yield from (value for value in values if isinstance(value, str))


def parse_entry(element: Tag, base_url: str) -> dict[str, Any]:
    """Parse the source h-entry with mf2py."""
    parsed = mf2py.parse(doc=str(element), url=base_url)

    if not isinstance(parsed, dict):
        raise SourceScanError("Microformats parser did not return a document object")

    items = parsed.get("items")

    if not isinstance(items, list) or len(items) != 1:
        raise SourceScanError("Expected exactly one parsed h-entry")

    entry = items[0]

    if not isinstance(entry, dict):
        raise SourceScanError("Parsed h-entry is not an object")

    types = entry.get("type")

    if not isinstance(types, list) or "h-entry" not in types:
        raise SourceScanError("Parsed microformats item is not an h-entry")

    return entry


def primary_entry(
    document: BeautifulSoup, source_url: str
) -> tuple[Tag, dict[str, Any]]:
    """Return and validate the source h-entry."""
    entries = document.find_all(class_="h-entry")

    if len(entries) != 1:
        raise SourceScanError(f"Expected exactly one h-entry, found {len(entries)}")

    entry_element = entries[0]
    mf2_entry = parse_entry(entry_element, source_url)

    urls = tuple(property_urls(mf2_entry, "url"))

    if source_url not in urls:
        raise SourceScanError(
            f"The h-entry u-url does not match the source URL {source_url!r}: {urls!r}"
        )

    return entry_element, mf2_entry


def content_element(entry: Tag) -> Tag:
    """Return the source h-entry's e-content element."""
    contents = entry.find_all(class_="e-content")

    if len(contents) != 1:
        raise SourceScanError(f"Expected exactly one e-content, found {len(contents)}")

    return contents[0]


def normalize_target(value: str, *, base_url: str, source_url: str) -> str | None:
    """Resolve and validate a possible Webmention target URL."""
    value = value.strip()

    if not value:
        return None

    target = urljoin(base_url, value)

    if not is_http_url(target):
        return None

    if urldefrag(target)[0] == urldefrag(source_url)[0]:
        return None

    return target


def iter_targets(
    content: Tag,
    mf2_entry: dict[str, Any],
    *,
    base_url: str,
    source_url: str,
    ignored_hostnames: tuple[str, ...] = (),
) -> Iterator[str]:
    """Yield outgoing Webmention targets from an h-entry."""
    hrefs = (
        href
        for element in content.find_all("a", href=True)
        if isinstance(href := element.get("href"), str)
    )

    reactions = chain.from_iterable(
        property_urls(mf2_entry, property_name) for property_name in REACTION_PROPERTIES
    )

    for value in chain(hrefs, reactions):
        target = normalize_target(value, base_url=base_url, source_url=source_url)
        if target is not None:
            hostname = urlsplit(target).hostname or ""
            if not any(fnmatchcase(hostname, pattern) for pattern in ignored_hostnames):
                yield target


def scan_source_file(
    path: Path,
    *,
    root: Path,
    base_url: str | None,
    ignored_hostnames: tuple[str, ...] = (),
) -> ScannedSource:
    """Parse one generated source document."""
    document = BeautifulSoup(path.read_bytes(), "html5lib")

    relative_path = path.relative_to(root)

    source_url = canonical_url(document, relative_path=relative_path, base_url=base_url)

    if source_url is None:
        if base_url is None:
            raise SourceScanError(
                "Document has no canonical URL and "
                "WEBMENTIONS_SSG_SOURCE_BASE_URL is not configured"
            )

        source_url = source_url_for_path(relative_path, base_url)

    entry_element, mf2_entry = primary_entry(document, source_url)

    content = content_element(entry_element)

    return ScannedSource(
        path=relative_path.as_posix(),
        url=source_url,
        content_hash=xxhash.xxh3_128_hexdigest(str(entry_element).encode("utf-8")),
        targets=frozenset(
            iter_targets(
                content,
                mf2_entry,
                base_url=source_url,
                source_url=source_url,
                ignored_hostnames=ignored_hostnames,
            )
        ),
    )


def create_source(scanned: ScannedSource, scan_time: datetime) -> Source:
    """Create a source from a newly discovered document."""
    source = Source(
        path=scanned.path,
        url=scanned.url,
        content_hash=scanned.content_hash,
        revision=1,
        last_seen_at=scan_time,
        revised_at=scan_time,
        deleted_at=None,
    )

    for target in scanned.targets:
        source.sent_webmentions.append(
            SentWebmention(target=target, active=True, desired_revision=1)
        )

    return source


def update_source(
    source: Source, scanned: ScannedSource, scan_time: datetime
) -> Source:
    """Update a source from a newly scanned revision."""
    if source.url != scanned.url:
        raise SourceScanError(
            f"Source path {source.path!r} changed public URL "
            f"from {source.url!r} to {scanned.url!r}"
        )

    source.last_seen_at = scan_time

    if source.deleted_at is None and source.content_hash == scanned.content_hash:
        return source

    source.revision += 1
    source.content_hash = scanned.content_hash
    source.revised_at = scan_time
    source.deleted_at = None

    existing = {webmention.target: webmention for webmention in source.sent_webmentions}

    for webmention in existing.values():
        webmention.active = webmention.target in scanned.targets
        webmention.desired_revision = source.revision

        if not webmention.active and webmention.sent_revision is None:
            webmention.processed_revision = source.revision

    for target in scanned.targets:
        if target not in existing:
            source.sent_webmentions.append(
                SentWebmention(
                    target=target, active=True, desired_revision=source.revision
                )
            )

    return source


@huey.lock_task("scan-webmention-sources")
def scan_sources() -> None:
    """Scan generated source documents and queue pending Webmentions."""
    directory = current_app.config.get("WEBMENTIONS_SSG_SOURCE_DIRECTORY")

    if directory is None:
        return

    root = Path(directory).expanduser().resolve(strict=True)

    if not root.is_dir():
        raise RuntimeError(f"Source directory is not a directory: {root}")

    base_url = current_app.config.get("WEBMENTIONS_SSG_SOURCE_BASE_URL")

    if base_url is not None:
        if not is_http_url(base_url):
            raise RuntimeError(
                "WEBMENTIONS_SSG_SOURCE_BASE_URL must be an absolute HTTP or HTTPS URL"
            )
        base_url = f"{base_url.rstrip('/')}/"

    ignored_hostnames = tuple(
        pattern.lower().rstrip(".")
        for pattern in current_app.config.get("WEBMENTIONS_SSG_IGNORED_HOSTNAMES", ())
    )

    sources_by_path = {
        source.path: source
        for source in db.session.scalars(
            sa.select(Source).options(selectinload(Source.sent_webmentions))
        )
    }

    seen_paths: set[str] = set()
    scanned_count = 0
    scan_time = datetime.now(timezone.utc)

    for index_path in root.rglob("index.html"):
        relative_path = index_path.relative_to(root)

        if relative_path.parent == Path("."):
            continue

        seen_paths.add(relative_path.as_posix())

        try:
            scanned = scan_source_file(
                index_path,
                root=root,
                base_url=base_url,
                ignored_hostnames=ignored_hostnames,
            )

            if (source := sources_by_path.get(scanned.path)) is None:
                source = create_source(scanned, scan_time)
                db.session.add(source)
            else:
                source = update_source(source, scanned, scan_time)

            sources_by_path[source.path] = source
            scanned_count += 1

        except (OSError, SourceScanError) as exc:
            current_app.logger.warning("Could not scan source %s: %s", index_path, exc)

    for path, source in sources_by_path.items():
        if source.deleted_at is not None or path in seen_paths:
            continue

        source.revision += 1
        source.revised_at = scan_time
        source.deleted_at = scan_time

        for webmention in source.sent_webmentions:
            webmention.active = False
            webmention.desired_revision = source.revision

            if webmention.sent_revision is None:
                webmention.processed_revision = source.revision

    # Persist the desired state before queueing any work.
    db.session.commit()

    pending_count = 0

    for identifier in db.session.scalars(
        sa.select(SentWebmention.uuid)
        .where(
            sa.or_(
                SentWebmention.processed_revision.is_(None),
                SentWebmention.processed_revision < SentWebmention.desired_revision,
            )
        )
        .order_by(SentWebmention.uuid)
    ):
        send_webmention(identifier)
        pending_count += 1

    current_app.logger.info(
        "Webmention source scan complete: %d sources scanned, %d pending sends",
        scanned_count,
        pending_count,
    )