/*
    This file is part of gnix (https://codeberg.org/metamuffin/gnix)
    which is licensed under the GNU Affero General Public License (version 3); see /COPYING.
    Copyright (C) 2025 metamuffin <metamuffin.org>
*/
//! 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, Full};
use serde::Deserialize;
use serde_yml::Value;
use sha2::{Digest, Sha256};
use std::{collections::HashMap, future::Future, pin::Pin, sync::Arc};
use tokio::sync::RwLock;

pub struct CacheKind;

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

struct Cache {
    entries: RwLock<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_yml::from_value::<CacheConfig>(config)?;
        Ok(Arc::new(Cache {
            config,
            entries: HashMap::new().into(),
        }))
    }
}
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 {
            // not very fast
            let mut hasher = Sha256::new();
            hasher.update(request.method().as_str().len().to_be_bytes());
            hasher.update(request.method().as_str());
            hasher.update(request.uri().path().len().to_be_bytes());
            hasher.update(request.uri().path());
            hasher.update(if request.uri().query().is_some() {
                [1]
            } else {
                [0]
            });
            if let Some(q) = request.uri().query() {
                hasher.update(q.len().to_be_bytes());
                hasher.update(q);
            }
            hasher.update(request.headers().len().to_be_bytes());
            for (k, v) in request.headers() {
                hasher.update(k.as_str().len().to_be_bytes());
                hasher.update(v.as_bytes().len().to_be_bytes());
                hasher.update(k);
                hasher.update(v);
            }
            let key: [u8; 32] = hasher.finalize().into();

            if let Some(resp) = self.entries.read().await.get(&key) {
                return Ok(resp
                    .to_owned()
                    .map(|b| Full::new(b).map_err(|e| match e {}).boxed()));
            }

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

            let h = response.headers().to_owned();
            let s = response.status().to_owned();
            let body = response.collect().await?.to_bytes();

            let mut r1 = Response::new(Full::new(body.clone()).map_err(|e| match e {}).boxed());
            *r1.headers_mut() = h.clone();
            *r1.status_mut() = s;

            let mut r2 = Response::new(body);
            *r2.headers_mut() = h;
            *r2.status_mut() = s;
            self.entries.write().await.insert(key, r2);

            Ok(r1)
        })
    }
}