use std::{
    sync::Arc,
    time::{Duration, Instant},
};

use axum::response::Response;
use bytes::Bytes;
use shared_contracts::{
    puzzle_gallery::{PuzzleGalleryResponse, PuzzleGalleryWorkRefResponse},
    puzzle_works::PuzzleWorkSummaryResponse,
};
use tokio::{
    sync::{Mutex, MutexGuard, RwLock},
    time,
};

use crate::{api_response::json_success_data_bytes_response, request_context::RequestContext};

const PUZZLE_GALLERY_PRIMARY_ITEM_COUNT: usize = 10;
const PUZZLE_GALLERY_PREVIEW_REF_COUNT: usize = 10;
const PUZZLE_GALLERY_CACHE_TTL: Duration = Duration::from_secs(5);
const PUZZLE_GALLERY_CACHE_MAX_IDLE: Duration = Duration::from_secs(300);
const PUZZLE_GALLERY_CACHE_CLEANUP_INTERVAL: Duration = Duration::from_secs(60);

#[derive(Clone, Debug)]
pub struct PuzzleGalleryCache {
    inner: Arc<RwLock<Option<PuzzleGalleryCacheEntry>>>,
    rebuild_lock: Arc<Mutex<()>>,
}

#[derive(Clone, Debug)]
struct PuzzleGalleryCacheEntry {
    data_json: Bytes,
    built_at: Instant,
}

#[derive(Clone, Debug)]
pub struct PuzzleGalleryCachedResponse {
    data_json: Bytes,
}

impl PuzzleGalleryCachedResponse {
    pub fn data_json_len(&self) -> usize {
        self.data_json.len()
    }
}

impl PuzzleGalleryCache {
    pub fn new() -> Self {
        Self {
            inner: Arc::new(RwLock::new(None)),
            rebuild_lock: Arc::new(Mutex::new(())),
        }
    }

    pub async fn acquire_rebuild_guard(&self) -> MutexGuard<'_, ()> {
        self.rebuild_lock.lock().await
    }

    pub async fn read_fresh_response(&self) -> Option<PuzzleGalleryCachedResponse> {
        let guard = self.inner.read().await;
        let entry = guard.as_ref()?;
        let now = Instant::now();
        if now.duration_since(entry.built_at) > PUZZLE_GALLERY_CACHE_TTL {
            return None;
        }
        Some(PuzzleGalleryCachedResponse {
            data_json: entry.data_json.clone(),
        })
    }

    pub async fn store_response(
        &self,
        response: PuzzleGalleryResponse,
    ) -> Result<PuzzleGalleryCachedResponse, serde_json::Error> {
        let now = Instant::now();
        let cached = PuzzleGalleryCachedResponse {
            data_json: Bytes::from(serde_json::to_vec(&response)?),
        };
        *self.inner.write().await = Some(PuzzleGalleryCacheEntry {
            data_json: cached.data_json.clone(),
            built_at: now,
        });
        Ok(cached)
    }

    pub fn spawn_cleanup_task(&self) {
        let cache = self.clone();
        tokio::spawn(async move {
            let mut interval = time::interval(PUZZLE_GALLERY_CACHE_CLEANUP_INTERVAL);
            loop {
                interval.tick().await;
                cache.cleanup_idle_entry().await;
            }
        });
    }

    async fn cleanup_idle_entry(&self) {
        let mut guard = self.inner.write().await;
        if let Some(entry) = guard.as_ref()
            && Instant::now().duration_since(entry.built_at) > PUZZLE_GALLERY_CACHE_MAX_IDLE
        {
            *guard = None;
        }
    }
}

pub fn build_puzzle_gallery_window_response(
    items: Vec<PuzzleWorkSummaryResponse>,
) -> PuzzleGalleryResponse {
    let total_count = items.len().min(u32::MAX as usize) as u32;
    let preview_refs = items
        .iter()
        .skip(PUZZLE_GALLERY_PRIMARY_ITEM_COUNT)
        .take(PUZZLE_GALLERY_PREVIEW_REF_COUNT)
        .map(|item| PuzzleGalleryWorkRefResponse {
            work_id: item.work_id.clone(),
            profile_id: item.profile_id.clone(),
        })
        .collect::<Vec<_>>();
    let next_cursor = items
        .get(PUZZLE_GALLERY_PRIMARY_ITEM_COUNT + PUZZLE_GALLERY_PREVIEW_REF_COUNT)
        .map(|item| item.profile_id.clone());
    let has_more =
        items.len() > PUZZLE_GALLERY_PRIMARY_ITEM_COUNT + PUZZLE_GALLERY_PREVIEW_REF_COUNT;

    PuzzleGalleryResponse {
        items: items
            .into_iter()
            .take(PUZZLE_GALLERY_PRIMARY_ITEM_COUNT)
            .collect(),
        preview_refs,
        has_more,
        next_cursor,
        total_count,
    }
}

pub fn puzzle_gallery_cached_json(
    request_context: &RequestContext,
    response: PuzzleGalleryCachedResponse,
) -> Response {
    json_success_data_bytes_response(Some(request_context), response.data_json)
}

#[cfg(test)]
mod tests {
    use super::*;

    fn build_summary(index: usize) -> PuzzleWorkSummaryResponse {
        PuzzleWorkSummaryResponse {
            work_id: format!("work-{index}"),
            profile_id: format!("profile-{index}"),
            owner_user_id: "user-1".to_string(),
            source_session_id: None,
            author_display_name: "作者".to_string(),
            work_title: format!("作品 {index}"),
            work_description: "描述".to_string(),
            level_name: "第一关".to_string(),
            summary: "摘要".to_string(),
            theme_tags: Vec::new(),
            cover_image_src: None,
            cover_asset_id: None,
            publication_status: "published".to_string(),
            updated_at: "2026-05-01T00:00:00Z".to_string(),
            published_at: None,
            play_count: 0,
            remix_count: 0,
            like_count: 0,
            recent_play_count_7d: 0,
            point_incentive_total_half_points: 0,
            point_incentive_claimed_points: 0,
            point_incentive_total_points: 0.0,
            point_incentive_claimable_points: 0,
            publish_ready: true,
            generation_status: Some("ready".to_string()),
            levels: Vec::new(),
        }
    }

    #[test]
    fn build_window_returns_primary_cards_preview_refs_and_cursor() {
        let response =
            build_puzzle_gallery_window_response((0..25).map(build_summary).collect::<Vec<_>>());

        assert_eq!(response.total_count, 25);
        assert_eq!(response.items.len(), 10);
        assert_eq!(response.preview_refs.len(), 10);
        assert_eq!(response.items[0].profile_id, "profile-0");
        assert_eq!(response.items[9].profile_id, "profile-9");
        assert_eq!(response.preview_refs[0].profile_id, "profile-10");
        assert_eq!(response.preview_refs[9].profile_id, "profile-19");
        assert!(response.has_more);
        assert_eq!(response.next_cursor.as_deref(), Some("profile-20"));
    }

    #[test]
    fn build_window_handles_short_gallery_without_more_cursor() {
        let response =
            build_puzzle_gallery_window_response((0..8).map(build_summary).collect::<Vec<_>>());

        assert_eq!(response.total_count, 8);
        assert_eq!(response.items.len(), 8);
        assert!(response.preview_refs.is_empty());
        assert!(!response.has_more);
        assert_eq!(response.next_cursor, None);
    }
}