//! Cached discovery documents and import checks under PROTOCOL.md section 10.4.
//! Refreshes use immutable copies. The proc layer only reads serialized cache entries.
use crate::{Host, RpcResult};
use serde_json::{Value, json};
use sha2::{Digest, Sha256};
use std::{
    collections::BTreeMap,
    path::{Path, PathBuf},
};

#[derive(Clone)]
pub(crate) struct Interface {
    pub(crate) hash: String,
    pub(crate) document: Value,
    pub(crate) error: Option<Value>,
}
pub(crate) struct Graph {
    pub(crate) plugins: BTreeMap<String, Interface>,
    json: Vec<u8>,
    dot: Vec<u8>,
}

impl Default for Graph {
    /// Exposes a valid empty graph before background discovery completes.
    fn default() -> Self {
        Self {
            plugins: BTreeMap::new(),
            json: b"{\"plugins\":{}}".to_vec(),
            dot: b"digraph plugins {}\n".to_vec(),
        }
    }
}

/// Hashes exactly the bytes copied for discovery or installation.
pub(crate) fn hash(bytes: &[u8]) -> String {
    format!("{:x}", Sha256::digest(bytes))
}

/// Reads and hashes one immutable snapshot without blocking an async worker.
pub(crate) async fn read_hashed(path: PathBuf) -> std::io::Result<(Vec<u8>, String)> {
    tokio::task::spawn_blocking(move || -> std::io::Result<_> {
        let bytes = std::fs::read(path)?;
        let hash = hash(&bytes);
        Ok((bytes, hash))
    })
    .await
    .map_err(std::io::Error::other)?
}

/// Lists broken imports, optionally restricted to changed consumers or providers.
pub(crate) fn problems(
    plugins: &BTreeMap<String, Interface>,
    changed: Option<&[String]>,
) -> Vec<Value> {
    let mut failures = Vec::new();
    for (consumer, interface) in plugins {
        if let Some(imports) = interface.document["x-sausage-imports"].as_object() {
            for (provider, expected) in imports {
                if changed
                    .is_some_and(|names| !names.contains(consumer) && !names.contains(provider))
                {
                    continue;
                }
                let Some(actual) = plugins.get(provider) else {
                    failures.push(json!({"consumer":consumer,"provider":provider,"status":"missing","message":"the provider does not exist"}));
                    continue;
                };
                if let Some(error) = &actual.error {
                    failures.push(json!({"consumer":consumer,"provider":provider,"status":"unavailable","message":"discovery failed","error":error}));
                    continue;
                }
                for problem in sausage_interface::compat::check(expected, &actual.document) {
                    failures.push(json!({"consumer":consumer,"provider":provider,"status":"broken","method":problem.method,"message":problem.message,"counterexample":problem.counterexample,"display":problem.to_string()}));
                }
            }
        }
    }
    failures
}

impl Host {
    /// The cached JSON graph. This does not perform filesystem or RPC operations.
    pub(crate) fn graph_json(&self) -> Vec<u8> {
        self.0.graph.lock().unwrap().json.clone()
    }
    /// The cached DOT graph, with an edge for every import.
    pub(crate) fn graph_dot(&self) -> Vec<u8> {
        self.0.graph.lock().unwrap().dot.clone()
    }
    /// Plugin names currently present in the discovery cache.
    pub(crate) fn discovered_plugins(&self) -> Vec<String> {
        self.0
            .graph
            .lock()
            .unwrap()
            .plugins
            .keys()
            .cloned()
            .collect()
    }
    /// The current document, if discovery succeeded.
    pub(crate) fn discover_document(&self, plugin: &str) -> Option<Value> {
        self.0
            .graph
            .lock()
            .unwrap()
            .plugins
            .get(plugin)
            .filter(|entry| entry.error.is_none())
            .map(|entry| entry.document.clone())
    }
    /// Discovers a private copy and caches successful documents by file hash.
    pub(crate) async fn discover_copy(
        &self,
        plugin: &str,
        path: &Path,
        hash: String,
    ) -> Result<Interface, Value> {
        let request = json!(uuid::Uuid::now_v7().to_string());
        let discovery = self.route_from(
            "core".into(),
            Some(request.clone()),
            format!("{plugin}.rpc.discover"),
            json!({}),
            true,
            Some(path.to_path_buf()),
        );
        let result = tokio::time::timeout(std::time::Duration::from_secs(10), discovery).await;
        let processes: Vec<_> = self
            .0
            .state
            .lock()
            .unwrap()
            .processes
            .iter()
            .filter(|(_, process)| process.id.as_ref() == Some(&request))
            .map(|(pid, _)| pid.clone())
            .collect();
        for pid in processes {
            self.begin_stop(&pid);
        }
        let document = result
            .map_err(|_| crate::error(-32003, "plugin discovery timed out after 10 seconds"))??;
        if !document["methods"].is_array() {
            return Err(crate::error(
                -32003,
                "rpc.discover did not return an OpenRPC document",
            ));
        }
        Ok(Interface {
            hash,
            document,
            error: None,
        })
    }
    /// Refreshes every installed plugin while the caller holds the activation mutex.
    pub(crate) async fn refresh_graph(&self) -> RpcResult {
        self.refresh_graph_except(&[]).await
    }
    pub(crate) async fn refresh_graph_except(&self, candidates: &[String]) -> RpcResult {
        let mut directory = tokio::fs::read_dir(self.0.world.root.join("plugins"))
            .await
            .map_err(io_error)?;
        let mut plugins = BTreeMap::new();
        while let Some(entry) = directory.next_entry().await.map_err(io_error)? {
            if !entry.file_type().await.map_err(io_error)?.is_dir() {
                continue;
            }
            let name = entry.file_name().to_string_lossy().into_owned();
            let source = entry.path().join("plugin.wasm");
            let (bytes, hash) = match read_hashed(source).await {
                Ok(snapshot) => snapshot,
                Err(error) if error.kind() == std::io::ErrorKind::NotFound => continue,
                Err(error) => {
                    plugins.insert(
                        name,
                        Interface {
                            hash: String::new(),
                            document: Value::Null,
                            error: Some(io_error(error)),
                        },
                    );
                    continue;
                }
            };
            let previous = self.0.graph.lock().unwrap().plugins.get(&name).cloned();
            let interface = if candidates.contains(&name) {
                previous
                    .filter(|entry| entry.hash == hash)
                    .unwrap_or(Interface {
                        hash,
                        document: Value::Null,
                        error: None,
                    })
            } else if let Some(previous) =
                previous.filter(|entry| entry.hash == hash && entry.error.is_none())
            {
                previous
            } else {
                let copy = entry
                    .path()
                    .join(format!("discover-{}.wasm", uuid::Uuid::now_v7()));
                let result = match tokio::fs::write(&copy, &bytes).await {
                    Ok(()) => self.discover_copy(&name, &copy, hash.clone()).await,
                    Err(error) => Err(io_error(error)),
                };
                let _ = tokio::fs::remove_file(&copy).await;
                match result {
                    Ok(interface) => interface,
                    Err(error) => Interface {
                        hash,
                        document: Value::Null,
                        error: Some(error),
                    },
                }
            };
            plugins.insert(name, interface);
        }
        let admission = self.0.admission.write().await;
        let old_plugins = self.0.graph.lock().unwrap().plugins.clone();
        let mut upgrades = Vec::new();
        for (plugin, current) in &plugins {
            if let Some(old) = old_plugins.get(plugin).filter(|old| {
                !old.hash.is_empty() && old.hash != current.hash && current.error.is_none()
            }) {
                upgrades.push(self.snapshot_upgrade(plugin, old.hash.clone(), &current.hash));
            }
        }
        self.publish_graph(plugins);
        drop(admission);
        for upgrade in upgrades {
            self.begin_upgrade(upgrade);
        }
        Ok(json!({}))
    }
    /// Rebuilds serialized snapshots after a watcher refresh or an activation.
    pub(crate) fn publish_graph(&self, plugins: BTreeMap<String, Interface>) {
        let failures = problems(&plugins, None);
        for failure in &failures {
            self.0
                .journal
                .write("core", "core", "core", &format!("broken import {failure}"));
        }
        let mut entries = serde_json::Map::new();
        let mut dot = String::from("digraph plugins {\n");
        for (name, interface) in &plugins {
            dot.push_str(&format!("  {};\n", json!(name)));
            let mut imports = serde_json::Map::new();
            for provider in interface.document["x-sausage-imports"]
                .as_object()
                .into_iter()
                .flat_map(|imports| imports.keys())
            {
                let issues: Vec<_> = failures
                    .iter()
                    .filter(|problem| {
                        problem["consumer"] == *name && problem["provider"] == *provider
                    })
                    .cloned()
                    .collect();
                let status = issues
                    .first()
                    .and_then(|problem| problem["status"].as_str())
                    .unwrap_or("compatible");
                imports.insert(provider.clone(), json!({"status":status,"problems":issues}));
                dot.push_str(&format!(
                    "  {} -> {} [label={}];\n",
                    json!(name),
                    json!(provider),
                    json!(status)
                ));
            }
            entries.insert(
                name.clone(),
                json!({"hash":interface.hash,"imports":imports,"error":interface.error}),
            );
        }
        dot.push_str("}\n");
        let mut graph = self.0.graph.lock().unwrap();
        graph.json = serde_json::to_vec(&json!({"plugins":entries})).unwrap();
        graph.dot = dot.into_bytes();
        graph.plugins = plugins;
    }
}
/// Converts a filesystem failure into a JSON-RPC internal error.
pub(crate) fn io_error(error: std::io::Error) -> Value {
    crate::error(-32603, &error.to_string())
}