//! Feed page: items from followed users, projects, and tags.

use crate::extractors::ValidatedQuery;
use axum::extract::State;
use axum::response::IntoResponse;
use serde::Deserialize;
use sqlx::PgPool;
use tower_sessions::Session;

use crate::{
    auth::AuthUser, constants, db, error::Result, helpers::get_csrf_token, templates::FeedTemplate,
    types::DiscoverItem,
};

/// Query parameters for the feed page.
#[derive(Debug, Deserialize)]
pub(super) struct FeedQuery {
    pub page: Option<u32>,
}

/// GET /feed: paginated feed of items from followed users, projects, and tags.
#[tracing::instrument(skip_all, name = "feed::feed_page")]
pub(super) async fn feed_page(
    State(db): State<PgPool>,
    session: Session,
    AuthUser(user): AuthUser,
    ValidatedQuery(query): ValidatedQuery<FeedQuery>,
) -> Result<impl IntoResponse> {
    let csrf_token = get_csrf_token(&session).await;
    let session_user = Some(user.clone());

    // Clamp the upper bound too (matches admin/git pagination); the i64 widening
    // below already prevents the overflow panic, but an unbounded page is a
    // pointless huge offset (Run #2 UX MINOR).
    let page = query.page.unwrap_or(1).clamp(1, 1_000_000_000);
    // Widen to i64 BEFORE multiplying, `(page - 1) * FEED_PAGE_SIZE` in u32
    // overflows for a large `?page=` (garbage offset in release, panic in debug).
    let offset = (page as i64 - 1) * constants::FEED_PAGE_SIZE as i64;

    let total_items = db::follows::count_followed_feed_items(&db, user.id).await? as u32;
    let total_pages =
        (total_items + constants::FEED_PAGE_SIZE - 1) / constants::FEED_PAGE_SIZE.max(1);

    let db_items = db::follows::get_followed_feed_items(
        &db,
        user.id,
        constants::FEED_PAGE_SIZE as i64,
        offset,
    )
    .await?;

    let items: Vec<DiscoverItem> = db_items.into_iter().map(DiscoverItem::from).collect();

    // Compute the "showing X–Y" labels in i64 (saturating) to avoid the u32
    // overflow `offset as u32 + FEED_PAGE_SIZE` would hit for a large `?page=`.
    let showing_start = if total_items == 0 {
        0
    } else {
        offset.saturating_add(1).clamp(0, u32::MAX as i64) as u32
    };
    let showing_end = offset
        .saturating_add(constants::FEED_PAGE_SIZE as i64)
        .min(total_items as i64)
        .clamp(0, u32::MAX as i64) as u32;
    let pagination_range = super::pagination::build_pagination_range(page, total_pages);

    Ok(FeedTemplate {
        csrf_token,
        session_user,
        items,
        total_items,
        current_page: page,
        total_pages,
        pagination_range,
        showing_start,
        showing_end,
    })
}