cache.rs

use std::sync::Arc;
use std::time::Duration;

use martin_tile_utils::TileCoord;
use moka::future::Cache;
use tracing::{info, trace};

use crate::tiles::Tile;

/// Tile cache for storing rendered tile data.
#[derive(Clone, Debug)]
pub struct TileCache(Cache<TileCacheKey, Tile>);

impl TileCache {
    /// Creates a new tile cache with the specified maximum size in bytes.
    #[must_use]
    pub fn new(
        max_size_bytes: u64,
        expiry: Option<Duration>,
        idle_timeout: Option<Duration>,
    ) -> Self {
        let mut builder = Cache::builder()
            .name("tile_cache")
            .weigher(|_key: &TileCacheKey, value: &Tile| -> u32 {
                value.data.len().try_into().unwrap_or(u32::MAX)
            })
            .max_capacity(max_size_bytes)
            .support_invalidation_closures();
        if let Some(ttl) = expiry {
            builder = builder.time_to_live(ttl);
        }
        if let Some(tti) = idle_timeout {
            builder = builder.time_to_idle(tti);
        }
        Self(builder.build())
    }

    /// Gets a tile from cache or computes it using the provided function.
    pub async fn get_or_insert<F, Fut, E>(
        &self,
        source_id: String,
        xyz: TileCoord,
        query: Option<String>,
        compute: F,
    ) -> Result<Tile, Arc<E>>
    where
        F: FnOnce() -> Fut,
        Fut: Future<Output = Result<Tile, E>>,
        E: Send + Sync + 'static,
    {
        let key = TileCacheKey::new(source_id, xyz, query);
        let entry = self
            .0
            .entry(key.clone())
            .or_try_insert_with(async move { compute().await })
            .await?;

        if entry.is_fresh() {
            hotpath::gauge!("tile_cache_misses").inc(1.0);
            trace!("Tile cache MISS for {key:?}");
        } else {
            hotpath::gauge!("tile_cache_hits").inc(1.0);
            trace!(
                "Tile cache HIT for {key:?} (entries={entries}, size={size}B)",
                entries = self.0.entry_count(),
                size = self.0.weighted_size()
            );
        }

        Ok(entry.into_value())
    }

    /// Invalidates all cached tiles for a specific source.
    pub fn invalidate_source(&self, source_id: &str) {
        let source_id_owned = source_id.to_string();
        self.0
            .invalidate_entries_if(move |key, _| key.source_id == source_id_owned)
            .expect("invalidate_entries_if predicate should not error");
        info!("Invalidated tile cache for source: {source_id}");
    }

    /// Invalidates all cached tiles.
    pub fn invalidate_all(&self) {
        self.0.invalidate_all();
        info!("Invalidated all tile cache entries");
    }

    /// Returns the number of cached entries.
    #[must_use]
    pub fn entry_count(&self) -> u64 {
        self.0.entry_count()
    }

    /// Returns the total size of cached data in bytes.
    #[must_use]
    pub fn weighted_size(&self) -> u64 {
        self.0.weighted_size()
    }

    /// Runs pending maintenance tasks (e.g. processing invalidation predicates).
    pub async fn run_pending_tasks(&self) {
        self.0.run_pending_tasks().await;
    }
}

/// Optional wrapper for `TileCache`.
pub type OptTileCache = Option<TileCache>;

/// Constant representing no tile cache configuration.
pub const NO_TILE_CACHE: OptTileCache = None;

/// Cache key for tile data.
#[derive(Debug, Hash, PartialEq, Eq, Clone)]
struct TileCacheKey {
    source_id: String,
    xyz: TileCoord,
    query: Option<String>,
}

impl TileCacheKey {
    fn new(source_id: String, xyz: TileCoord, query: Option<String>) -> Self {
        Self {
            source_id,
            xyz,
            query,
        }
    }
}