//! Response caching module
//!
//! Considerations:
//! - check cache header
//! - ignore responses that get too large
//! - ignore requests with body (or too large body)
//! - LRU cache pruning
//! - different backends:
//!     - in memory (HashMap)
//!     - on disk (redb? filesystem?)
//!     - external db?
use super::{Node, NodeContext, NodeKind, NodeRequest, NodeResponse};
use crate::{config::DynNode, error::ServiceError};
use anyhow::Result;
use bytes::Bytes;
use http::Response;
use http_body_util::BodyExt;
use serde::Deserialize;
use serde_yaml::Value;
use sha2::{Digest, Sha256};
use std::{collections::HashMap, future::Future, pin::Pin, sync::Arc};

pub struct CacheKind;

#[derive(Deserialize)]
struct CacheConfig {
    next: DynNode,
}

struct Cache {
    entries: HashMap<[u8; 32], Response<Bytes>>,
    config: CacheConfig,
}

impl NodeKind for CacheKind {
    fn name(&self) -> &'static str {
        "cache"
    }
    fn instanciate(&self, config: Value) -> Result<Arc<dyn Node>> {
        let config = serde_yaml::from_value::<CacheConfig>(config)?;
        Ok(Arc::new(Cache {
            config,
            entries: HashMap::new(),
        }))
    }
}
impl Node for Cache {
    fn handle<'a>(
        &'a self,
        context: &'a mut NodeContext,
        request: NodeRequest,
    ) -> Pin<Box<dyn Future<Output = Result<NodeResponse, ServiceError>> + Send + Sync + 'a>> {
        Box::pin(async move {
            // totally wrong...
            let mut hasher = Sha256::new();
            hasher.update(request.method().as_str());
            hasher.update(request.uri().path());
            if let Some(q) = request.uri().query() {
                hasher.update(q);
            }
            let key: [u8; 32] = hasher.finalize().try_into().unwrap();

            if let Some(resp) = self.entries.get(&key) {
                // Ok(resp.to_owned().map(|b| b.map_err(|e| match e {}).boxed()))
            }

            let response = self.config.next.handle(context, request).await?;

            Ok(response)
        })
    }
}