"""
Transparent PyPI proxy implementing PEP 503 (Simple API).

Provides endpoints that allow pip to use Orchard as a PyPI index URL.
Artifacts are cached on first access through configured upstream sources.
"""

import hashlib
import logging
import re
from typing import Optional
from urllib.parse import urljoin, urlparse, quote, unquote

import httpx
from fastapi import APIRouter, Depends, HTTPException, Request, Response
from fastapi.responses import StreamingResponse, HTMLResponse
from sqlalchemy.orm import Session

from .database import get_db
from .models import UpstreamSource, CachedUrl, Artifact, Project, Package, Tag
from .storage import S3Storage, get_storage
from .config import get_env_upstream_sources

logger = logging.getLogger(__name__)

router = APIRouter(prefix="/pypi", tags=["pypi-proxy"])

# Timeout configuration for proxy requests
PROXY_CONNECT_TIMEOUT = 30.0
PROXY_READ_TIMEOUT = 60.0


def _get_pypi_upstream_sources(db: Session) -> list[UpstreamSource]:
    """Get all enabled upstream sources configured for PyPI."""
    # Get database sources
    db_sources = (
        db.query(UpstreamSource)
        .filter(
            UpstreamSource.source_type == "pypi",
            UpstreamSource.enabled == True,
        )
        .order_by(UpstreamSource.priority)
        .all()
    )

    # Get env sources
    env_sources = [
        s for s in get_env_upstream_sources()
        if s.source_type == "pypi" and s.enabled
    ]

    # Combine and sort by priority
    all_sources = list(db_sources) + list(env_sources)
    return sorted(all_sources, key=lambda s: s.priority)


def _build_auth_headers(source) -> dict:
    """Build authentication headers for an upstream source."""
    headers = {}

    if hasattr(source, 'auth_type'):
        if source.auth_type == "bearer":
            password = source.get_password() if hasattr(source, 'get_password') else getattr(source, 'password', None)
            if password:
                headers["Authorization"] = f"Bearer {password}"
        elif source.auth_type == "api_key":
            custom_headers = source.get_headers() if hasattr(source, 'get_headers') else {}
            if custom_headers:
                headers.update(custom_headers)

    return headers


def _get_basic_auth(source) -> Optional[tuple[str, str]]:
    """Get basic auth credentials if applicable."""
    if hasattr(source, 'auth_type') and source.auth_type == "basic":
        username = getattr(source, 'username', None)
        if username:
            password = source.get_password() if hasattr(source, 'get_password') else getattr(source, 'password', '')
            return (username, password or '')
    return None


def _get_base_url(request: Request) -> str:
    """
    Get the external base URL, respecting X-Forwarded-Proto header.

    When behind a reverse proxy that terminates SSL, the request.base_url
    will show http:// even though the external URL is https://. This function
    checks the X-Forwarded-Proto header to determine the correct scheme.
    """
    base_url = str(request.base_url).rstrip('/')

    # Check for X-Forwarded-Proto header (set by reverse proxies)
    forwarded_proto = request.headers.get('x-forwarded-proto')
    if forwarded_proto:
        # Replace the scheme with the forwarded protocol
        parsed = urlparse(base_url)
        base_url = f"{forwarded_proto}://{parsed.netloc}{parsed.path}"

    return base_url


def _rewrite_package_links(html: str, base_url: str, package_name: str, upstream_base_url: str) -> str:
    """
    Rewrite download links in a PyPI simple page to go through our proxy.

    Args:
        html: The HTML content from upstream
        base_url: Our server's base URL
        package_name: The package name for the URL path
        upstream_base_url: The upstream URL used to fetch this page (for resolving relative URLs)

    Returns:
        HTML with rewritten download links
    """
    # Pattern to match href attributes in anchor tags
    # PyPI simple pages have links like:
    # <a href="https://files.pythonhosted.org/packages/.../file.tar.gz#sha256=...">file.tar.gz</a>
    # Or relative URLs from Artifactory like:
    # <a href="../../packages/packages/62/35/.../requests-0.10.0.tar.gz#sha256=...">

    def replace_href(match):
        original_url = match.group(1)

        # Resolve relative URLs to absolute using the upstream base URL
        if not original_url.startswith(('http://', 'https://')):
            # Split off fragment before resolving
            url_without_fragment = original_url.split('#')[0]
            fragment_part = original_url[len(url_without_fragment):]
            absolute_url = urljoin(upstream_base_url, url_without_fragment) + fragment_part
        else:
            absolute_url = original_url

        # Extract the filename from the URL
        parsed = urlparse(absolute_url)
        path_parts = parsed.path.split('/')
        filename = path_parts[-1] if path_parts else ''

        # Keep the hash fragment if present
        fragment = f"#{parsed.fragment}" if parsed.fragment else ""

        # Encode the absolute URL (without fragment) for safe transmission
        encoded_url = quote(absolute_url.split('#')[0], safe='')

        # Build new URL pointing to our proxy
        new_url = f"{base_url}/pypi/simple/{package_name}/{filename}?upstream={encoded_url}{fragment}"

        return f'href="{new_url}"'

    # Match href="..." patterns
    rewritten = re.sub(r'href="([^"]+)"', replace_href, html)

    return rewritten


@router.get("/simple/")
async def pypi_simple_index(
    request: Request,
    db: Session = Depends(get_db),
):
    """
    PyPI Simple API index - lists all packages.

    Proxies to the first available upstream PyPI source.
    """
    sources = _get_pypi_upstream_sources(db)

    if not sources:
        raise HTTPException(
            status_code=503,
            detail="No PyPI upstream sources configured"
        )

    # Try each source in priority order
    last_error = None
    for source in sources:
        try:
            headers = {"User-Agent": "Orchard-PyPI-Proxy/1.0"}
            headers.update(_build_auth_headers(source))
            auth = _get_basic_auth(source)

            # Use URL as-is - users should provide full path including /simple
            simple_url = source.url.rstrip('/') + '/'

            timeout = httpx.Timeout(PROXY_READ_TIMEOUT, connect=PROXY_CONNECT_TIMEOUT)

            with httpx.Client(timeout=timeout, follow_redirects=False) as client:
                response = client.get(
                    simple_url,
                    headers=headers,
                    auth=auth,
                )

                # Handle redirects manually to avoid loops
                if response.status_code in (301, 302, 303, 307, 308):
                    redirect_url = response.headers.get('location')
                    if redirect_url:
                        # Follow the redirect once
                        response = client.get(
                            redirect_url,
                            headers=headers,
                            auth=auth,
                            follow_redirects=False,
                        )

                if response.status_code == 200:
                    # Return the index as-is (links are to package pages, not files)
                    # We could rewrite these too, but for now just proxy
                    content = response.text

                    # Rewrite package links to go through our proxy
                    base_url = _get_base_url(request)
                    content = re.sub(
                        r'href="([^"]+)/"',
                        lambda m: f'href="{base_url}/pypi/simple/{m.group(1)}/"',
                        content
                    )

                    return HTMLResponse(content=content)

                last_error = f"HTTP {response.status_code}"

        except httpx.ConnectError as e:
            last_error = f"Connection failed: {e}"
            logger.warning(f"PyPI proxy: failed to connect to {source.url}: {e}")
        except httpx.TimeoutException as e:
            last_error = f"Timeout: {e}"
            logger.warning(f"PyPI proxy: timeout connecting to {source.url}: {e}")
        except Exception as e:
            last_error = str(e)
            logger.warning(f"PyPI proxy: error fetching from {source.url}: {e}")

    raise HTTPException(
        status_code=502,
        detail=f"Failed to fetch package index from upstream: {last_error}"
    )


@router.get("/simple/{package_name}/")
async def pypi_package_versions(
    request: Request,
    package_name: str,
    db: Session = Depends(get_db),
):
    """
    PyPI Simple API package page - lists all versions/files for a package.

    Proxies to upstream and rewrites download links to go through our cache.
    """
    sources = _get_pypi_upstream_sources(db)

    if not sources:
        raise HTTPException(
            status_code=503,
            detail="No PyPI upstream sources configured"
        )

    base_url = _get_base_url(request)

    # Normalize package name (PEP 503)
    normalized_name = re.sub(r'[-_.]+', '-', package_name).lower()

    # Try each source in priority order
    last_error = None
    for source in sources:
        try:
            headers = {"User-Agent": "Orchard-PyPI-Proxy/1.0"}
            headers.update(_build_auth_headers(source))
            auth = _get_basic_auth(source)

            # Use URL as-is - users should provide full path including /simple
            package_url = source.url.rstrip('/') + f'/{normalized_name}/'
            final_url = package_url  # Track final URL after redirects

            timeout = httpx.Timeout(PROXY_READ_TIMEOUT, connect=PROXY_CONNECT_TIMEOUT)

            with httpx.Client(timeout=timeout, follow_redirects=False) as client:
                response = client.get(
                    package_url,
                    headers=headers,
                    auth=auth,
                )

                # Handle redirects manually
                redirect_count = 0
                while response.status_code in (301, 302, 303, 307, 308) and redirect_count < 5:
                    redirect_url = response.headers.get('location')
                    if not redirect_url:
                        break

                    # Make redirect URL absolute if needed
                    if not redirect_url.startswith('http'):
                        redirect_url = urljoin(final_url, redirect_url)

                    final_url = redirect_url  # Update final URL

                    response = client.get(
                        redirect_url,
                        headers=headers,
                        auth=auth,
                        follow_redirects=False,
                    )
                    redirect_count += 1

                if response.status_code == 200:
                    content = response.text

                    # Rewrite download links to go through our proxy
                    # Pass final_url so relative URLs can be resolved correctly
                    content = _rewrite_package_links(content, base_url, normalized_name, final_url)

                    return HTMLResponse(content=content)

                if response.status_code == 404:
                    # Package not found in this source, try next
                    last_error = f"Package not found in {source.name}"
                    continue

                last_error = f"HTTP {response.status_code}"

        except httpx.ConnectError as e:
            last_error = f"Connection failed: {e}"
            logger.warning(f"PyPI proxy: failed to connect to {source.url}: {e}")
        except httpx.TimeoutException as e:
            last_error = f"Timeout: {e}"
            logger.warning(f"PyPI proxy: timeout connecting to {source.url}: {e}")
        except Exception as e:
            last_error = str(e)
            logger.warning(f"PyPI proxy: error fetching {package_name} from {source.url}: {e}")

    raise HTTPException(
        status_code=404,
        detail=f"Package '{package_name}' not found: {last_error}"
    )


@router.get("/simple/{package_name}/{filename}")
async def pypi_download_file(
    request: Request,
    package_name: str,
    filename: str,
    upstream: Optional[str] = None,
    db: Session = Depends(get_db),
    storage: S3Storage = Depends(get_storage),
):
    """
    Download a package file, caching it in Orchard.

    Args:
        package_name: The package name
        filename: The filename to download
        upstream: URL-encoded upstream URL to fetch from
    """
    if not upstream:
        raise HTTPException(
            status_code=400,
            detail="Missing 'upstream' query parameter with source URL"
        )

    # Decode the upstream URL
    upstream_url = unquote(upstream)

    # Check if we already have this URL cached
    url_hash = hashlib.sha256(upstream_url.encode()).hexdigest()
    cached_url = db.query(CachedUrl).filter(CachedUrl.url_hash == url_hash).first()

    if cached_url:
        # Serve from cache
        artifact = db.query(Artifact).filter(Artifact.id == cached_url.artifact_id).first()
        if artifact:
            logger.info(f"PyPI proxy: serving cached {filename} (artifact {artifact.id[:12]})")

            # Stream from S3
            try:
                content_stream = storage.get_stream(artifact.s3_key)

                return StreamingResponse(
                    content_stream,
                    media_type=artifact.content_type or "application/octet-stream",
                    headers={
                        "Content-Disposition": f'attachment; filename="{filename}"',
                        "Content-Length": str(artifact.size),
                        "X-Checksum-SHA256": artifact.id,
                        "X-Cache": "HIT",
                    }
                )
            except Exception as e:
                logger.error(f"PyPI proxy: error streaming cached artifact: {e}")
                # Fall through to fetch from upstream

    # Not cached - fetch from upstream
    sources = _get_pypi_upstream_sources(db)

    # Use the first available source for authentication headers
    # Note: The upstream URL may point to files.pythonhosted.org or other CDNs,
    # not the configured source URL directly, so we can't strictly validate the host
    matched_source = sources[0] if sources else None

    try:
        headers = {"User-Agent": "Orchard-PyPI-Proxy/1.0"}
        if matched_source:
            headers.update(_build_auth_headers(matched_source))
        auth = _get_basic_auth(matched_source) if matched_source else None

        timeout = httpx.Timeout(300.0, connect=PROXY_CONNECT_TIMEOUT)  # 5 minutes for large files

        # Fetch the file
        logger.info(f"PyPI proxy: fetching {filename} from {upstream_url}")

        with httpx.Client(timeout=timeout, follow_redirects=False) as client:
            response = client.get(
                upstream_url,
                headers=headers,
                auth=auth,
            )

            # Handle redirects manually
            redirect_count = 0
            while response.status_code in (301, 302, 303, 307, 308) and redirect_count < 5:
                redirect_url = response.headers.get('location')
                if not redirect_url:
                    break

                if not redirect_url.startswith('http'):
                    redirect_url = urljoin(upstream_url, redirect_url)

                logger.info(f"PyPI proxy: following redirect to {redirect_url}")

                # Don't send auth to different hosts
                redirect_headers = {"User-Agent": "Orchard-PyPI-Proxy/1.0"}
                redirect_auth = None
                if urlparse(redirect_url).netloc == urlparse(upstream_url).netloc:
                    redirect_headers.update(headers)
                    redirect_auth = auth

                response = client.get(
                    redirect_url,
                    headers=redirect_headers,
                    auth=redirect_auth,
                    follow_redirects=False,
                )
                redirect_count += 1

            if response.status_code != 200:
                raise HTTPException(
                    status_code=response.status_code,
                    detail=f"Upstream returned {response.status_code}"
                )

            content = response.content
            content_type = response.headers.get('content-type', 'application/octet-stream')

        # Store in S3 (computes hash and deduplicates automatically)
        from io import BytesIO
        result = storage.store(BytesIO(content))
        sha256 = result.sha256
        size = result.size

        logger.info(f"PyPI proxy: downloaded {filename}, {size} bytes, sha256={sha256[:12]}")

        # Check if artifact already exists
        existing = db.query(Artifact).filter(Artifact.id == sha256).first()
        if existing:
            # Increment ref count
            existing.ref_count += 1
            db.flush()
        else:
            # Create artifact record
            new_artifact = Artifact(
                id=sha256,
                original_name=filename,
                content_type=content_type,
                size=size,
                ref_count=1,
                created_by="pypi-proxy",
                s3_key=result.s3_key,
                checksum_md5=result.md5,
                checksum_sha1=result.sha1,
                s3_etag=result.s3_etag,
            )
            db.add(new_artifact)
            db.flush()

        # Create/get system project and package
        system_project = db.query(Project).filter(Project.name == "_pypi").first()
        if not system_project:
            system_project = Project(
                name="_pypi",
                description="System project for cached PyPI packages",
                is_public=True,
                is_system=True,
                created_by="pypi-proxy",
            )
            db.add(system_project)
            db.flush()

        # Normalize package name
        normalized_name = re.sub(r'[-_.]+', '-', package_name).lower()

        package = db.query(Package).filter(
            Package.project_id == system_project.id,
            Package.name == normalized_name,
        ).first()
        if not package:
            package = Package(
                project_id=system_project.id,
                name=normalized_name,
                description=f"PyPI package: {normalized_name}",
            )
            db.add(package)
            db.flush()

        # Create tag with filename
        existing_tag = db.query(Tag).filter(
            Tag.package_id == package.id,
            Tag.name == filename,
        ).first()
        if not existing_tag:
            tag = Tag(
                package_id=package.id,
                name=filename,
                artifact_id=sha256,
                created_by="pypi-proxy",
            )
            db.add(tag)

        # Cache the URL mapping
        existing_cached = db.query(CachedUrl).filter(CachedUrl.url_hash == url_hash).first()
        if not existing_cached:
            cached_url_record = CachedUrl(
                url_hash=url_hash,
                url=upstream_url,
                artifact_id=sha256,
            )
            db.add(cached_url_record)

        db.commit()

        # Return the file
        return Response(
            content=content,
            media_type=content_type,
            headers={
                "Content-Disposition": f'attachment; filename="{filename}"',
                "Content-Length": str(size),
                "X-Checksum-SHA256": sha256,
                "X-Cache": "MISS",
            }
        )

    except httpx.ConnectError as e:
        raise HTTPException(status_code=502, detail=f"Connection failed: {e}")
    except httpx.TimeoutException as e:
        raise HTTPException(status_code=504, detail=f"Timeout: {e}")
    except HTTPException:
        raise
    except Exception as e:
        logger.exception(f"PyPI proxy: error downloading {filename}")
        raise HTTPException(status_code=500, detail=str(e))