from datetime import datetime
from sqlalchemy import select, func, desc as sa_desc, asc as sa_asc, literal
from sqlalchemy.ext.asyncio import AsyncSession

from backend.models.author import Author
from backend.models.post import Post
from backend.models.comment import Comment


async def list_authors(
    db: AsyncSession,
    subreddit_id: int | None = None,
    sort_by: str = "total_comments",
    sort_order: str = "desc",
    since: datetime | None = None,
    until: datetime | None = None,
    page: int = 1,
    per_page: int = 25,
) -> tuple[list[dict], int]:
    # Always compute counts from actual data
    post_count = select(func.count(Post.id)).where(Post.author_id == Author.id)
    comment_count = select(func.count(Comment.id)).where(Comment.author_id == Author.id)

    if subreddit_id:
        post_count = post_count.where(Post.subreddit_id == subreddit_id)
        comment_count = comment_count.join(Post).where(Post.subreddit_id == subreddit_id)
    if since:
        post_count = post_count.where(Post.created_utc >= since)
        comment_count = comment_count.where(Comment.created_utc >= since)
    if until:
        post_count = post_count.where(Post.created_utc <= until)
        comment_count = comment_count.where(Comment.created_utc <= until)

    post_sub = post_count.correlate(Author).scalar_subquery().label("total_posts")
    comment_sub = comment_count.correlate(Author).scalar_subquery().label("total_comments")

    base = select(Author, post_sub, comment_sub)

    # Only show authors with activity
    having_activity = base.having(
        (post_sub > 0) | (comment_sub > 0)
    ).group_by(Author.id)

    # Count total active authors
    count_stmt = select(func.count()).select_from(having_activity.subquery())
    total = (await db.execute(count_stmt)).scalar() or 0

    # Sort by computed counts
    if sort_by == "total_posts":
        sort_col = post_sub
    else:
        sort_col = comment_sub

    order_fn = sa_desc if sort_order == "desc" else sa_asc
    query = base.order_by(order_fn(sort_col)).offset((page - 1) * per_page).limit(per_page)

    result = await db.execute(query)
    authors = []
    for row in result.all():
        author = row[0]
        data = {c.name: getattr(author, c.name) for c in author.__table__.columns}
        data["total_posts"] = row[1] or 0
        data["total_comments"] = row[2] or 0
        authors.append(data)

    return authors, total


async def get_author(db: AsyncSession, author_id: int) -> dict | None:
    post_count = (
        select(func.count(Post.id))
        .where(Post.author_id == author_id)
        .scalar_subquery()
    )
    comment_count = (
        select(func.count(Comment.id))
        .where(Comment.author_id == author_id)
        .scalar_subquery()
    )
    result = await db.execute(
        select(Author, post_count.label("total_posts"), comment_count.label("total_comments"))
        .where(Author.id == author_id)
    )
    row = result.first()
    if not row:
        return None
    author = row[0]
    data = {c.name: getattr(author, c.name) for c in author.__table__.columns}
    data["total_posts"] = row[1] or 0
    data["total_comments"] = row[2] or 0
    return data