//! [`McpServer`] — the IdeA MCP **driving adapter** (cadrage Décision 4).
//!
//! This is the **pair of [`FsOrchestratorWatcher`](super::super::FsOrchestratorWatcher)**:
//! another entry door onto the *same* [`OrchestratorService::dispatch`]. Where the
//! watcher reads a JSON file, this server reads a JSON-RPC `tools/call`; both build
//! an [`OrchestratorCommand`] and return its [`OrchestratorOutcome`] unchanged. It
//! invents **no semantics** and **never re-routes** the reply — for `idea_ask_agent`
//! it returns `outcome.reply` inline, exactly what `dispatch` produced.
//!
//! It implements the strict MCP minimum over JSON-RPC 2.0:
//! - `initialize` → advertise protocol version + tool capability,
//! - `tools/list` → the [`tools::catalogue`],
//! - `tools/call` → map → `dispatch` → MCP tool result,
//! - notifications (e.g. `notifications/initialized`) → accepted, no reply.
//!
//! It receives `Arc<OrchestratorService>` and the target [`Project`] by injection
//! at the composition root (M3), exactly like the watcher — no application logic is
//! duplicated here.

use std::sync::Arc;

use application::OrchestratorService;
use domain::{DomainEvent, OrchestrationSource, Project};
use serde_json::{json, Value};

use super::jsonrpc::{
    error_codes, JsonRpcError, JsonRpcRequest, JsonRpcResponse, Transport, TransportError,
    JSONRPC_VERSION,
};
use super::tools::{self, ToolMapError};

/// The MCP protocol version this server speaks (advertised on `initialize`).
const MCP_PROTOCOL_VERSION: &str = "2024-11-05";

/// The IdeA MCP server: an entry adapter over [`OrchestratorService::dispatch`].
///
/// Cheap to clone the dependencies it holds; one instance serves one project's
/// agents over one transport (M3 owns one server per open project, beside the
/// watcher).
pub struct McpServer {
    service: Arc<OrchestratorService>,
    project: Project,
    /// Optional event sink (a domain [`EventBus`](domain::ports::EventBus) publish
    /// closure), the twin of the file watcher's. When set, a processed `tools/call`
    /// publishes [`DomainEvent::OrchestratorRequestProcessed`] tagged
    /// [`OrchestrationSource::Mcp`] so the presentation layer can surface that this
    /// delegation arrived through the MCP door. `None` ⇒ no publication (the server
    /// still works), so existing call sites stay valid.
    events: Option<Arc<dyn Fn(DomainEvent) + Send + Sync>>,
}

impl McpServer {
    /// Builds the server from the injected application service and target project.
    /// No event sink — use [`with_events`](Self::with_events) to surface processed
    /// requests on the bus.
    #[must_use]
    pub fn new(service: Arc<OrchestratorService>, project: Project) -> Self {
        Self {
            service,
            project,
            events: None,
        }
    }

    /// Attaches an event sink so each processed `tools/call` is republished on the
    /// bus tagged [`OrchestrationSource::Mcp`] — the MCP twin of the file watcher's
    /// `events` closure. Additive: callers that do not need observability keep using
    /// [`new`](Self::new).
    #[must_use]
    pub fn with_events(mut self, events: Arc<dyn Fn(DomainEvent) + Send + Sync>) -> Self {
        self.events = Some(events);
        self
    }

    /// Serves JSON-RPC messages from `transport` until it closes (clean EOF).
    ///
    /// Every inbound line is handled in isolation: a malformed line or an unknown
    /// method yields a JSON-RPC error response, **never a panic** and never a
    /// dropped connection. Notifications (no `id`) are processed without a reply.
    pub async fn serve<T: Transport>(&self, transport: &mut T) {
        loop {
            let raw = match transport.recv().await {
                Ok(bytes) => bytes,
                Err(TransportError::Closed) => break,
                Err(TransportError::Io(_)) => break,
            };
            if let Some(response) = self.handle_raw(&raw).await {
                let Ok(bytes) = serde_json::to_vec(&response) else {
                    continue;
                };
                if transport.send(&bytes).await.is_err() {
                    break;
                }
            }
        }
    }

    /// Parses one raw message and produces the response to send back, or `None`
    /// for a notification (no `id`) that owes no reply.
    ///
    /// Kept standalone (no transport) so the whole request→response behaviour is
    /// unit-testable over plain bytes, with no I/O.
    pub async fn handle_raw(&self, raw: &[u8]) -> Option<JsonRpcResponse> {
        let request: JsonRpcRequest = match serde_json::from_slice(raw) {
            Ok(r) => r,
            Err(e) => {
                // Could not correlate (no id parsed) ⇒ null id per JSON-RPC.
                return Some(JsonRpcResponse::error(
                    Value::Null,
                    JsonRpcError::new(error_codes::PARSE_ERROR, format!("invalid json: {e}")),
                ));
            }
        };

        if request.jsonrpc != JSONRPC_VERSION {
            let id = request.id.unwrap_or(Value::Null);
            return Some(JsonRpcResponse::error(
                id,
                JsonRpcError::new(
                    error_codes::INVALID_REQUEST,
                    format!("unsupported jsonrpc version: {}", request.jsonrpc),
                ),
            ));
        }

        // Notification (no id): never reply (the `?` short-circuits to `None`).
        let id = request.id.clone()?;

        let result = self.dispatch_method(&request.method, request.params).await;
        Some(match result {
            Ok(value) => JsonRpcResponse::success(id, value),
            Err(error) => JsonRpcResponse::error(id, error),
        })
    }

    /// Routes a method name to its handler.
    async fn dispatch_method(
        &self,
        method: &str,
        params: Option<Value>,
    ) -> Result<Value, JsonRpcError> {
        match method {
            "initialize" => Ok(self.initialize_result()),
            "tools/list" => Ok(self.tools_list_result()),
            "tools/call" => self.tools_call(params.unwrap_or(Value::Null)).await,
            other => Err(JsonRpcError::new(
                error_codes::METHOD_NOT_FOUND,
                format!("method not found: {other}"),
            )),
        }
    }

    /// The `initialize` result: protocol version, server identity, and the fact
    /// that we expose tools.
    fn initialize_result(&self) -> Value {
        json!({
            "protocolVersion": MCP_PROTOCOL_VERSION,
            "capabilities": { "tools": {} },
            "serverInfo": { "name": "idea-orchestrator", "version": env!("CARGO_PKG_VERSION") }
        })
    }

    /// The `tools/list` result: the catalogue as MCP tool descriptors.
    fn tools_list_result(&self) -> Value {
        let tools: Vec<Value> = tools::catalogue()
            .into_iter()
            .map(|t| {
                json!({
                    "name": t.name,
                    "description": t.description,
                    "inputSchema": t.input_schema,
                })
            })
            .collect();
        json!({ "tools": tools })
    }

    /// `tools/call`: map the tool to an [`OrchestratorCommand`], `dispatch` it, and
    /// fold the [`OrchestratorOutcome`](application::OrchestratorOutcome) into an MCP
    /// tool result. The `idea_ask_agent` reply is returned **inline** — never
    /// re-routed.
    async fn tools_call(&self, params: Value) -> Result<Value, JsonRpcError> {
        let name = params
            .get("name")
            .and_then(Value::as_str)
            .ok_or_else(|| {
                JsonRpcError::new(error_codes::INVALID_PARAMS, "missing tool `name`")
            })?
            .to_owned();
        let arguments = params.get("arguments").cloned().unwrap_or(json!({}));

        let command = tools::map_tool_call(&name, &arguments).map_err(map_err_to_jsonrpc)?;

        let result = self.service.dispatch(&self.project, command).await;
        // Surface the processed delegation on the bus, tagged as the MCP door — the
        // twin of the file watcher's publish. `ok` mirrors the dispatch outcome; the
        // action is the tool name. No-op when no sink is attached.
        self.publish_processed(&name, result.is_ok());
        match result {
            Ok(outcome) => {
                // The text the agent sees: the reply for an `ask`, else the detail.
                let text = outcome.reply.clone().unwrap_or_else(|| outcome.detail.clone());
                Ok(tool_result_text(&text, false))
            }
            // A failed IdeA command is reported as a tool execution error
            // (`isError: true`) rather than a protocol error: the agent can read
            // it and decide, and the connection stays healthy.
            Err(e) => Ok(tool_result_text(&e.to_string(), true)),
        }
    }

    /// Publishes [`DomainEvent::OrchestratorRequestProcessed`] for a handled
    /// `tools/call`, tagged [`OrchestrationSource::Mcp`]. The requester id is the
    /// stable `"mcp"` label until the per-session transport bind (open point S-MCP)
    /// carries the connected agent's identity. No-op without an event sink.
    fn publish_processed(&self, action: &str, ok: bool) {
        if let Some(publish) = &self.events {
            publish(DomainEvent::OrchestratorRequestProcessed {
                requester_id: "mcp".to_owned(),
                action: action.to_owned(),
                ok,
                source: OrchestrationSource::Mcp,
            });
        }
    }
}

/// Builds an MCP `tools/call` result with a single text content block.
fn tool_result_text(text: &str, is_error: bool) -> Value {
    json!({
        "content": [ { "type": "text", "text": text } ],
        "isError": is_error
    })
}

/// Maps a [`ToolMapError`] to the right JSON-RPC error code.
fn map_err_to_jsonrpc(err: ToolMapError) -> JsonRpcError {
    match err {
        ToolMapError::UnknownTool(_) => {
            JsonRpcError::new(error_codes::METHOD_NOT_FOUND, err.to_string())
        }
        ToolMapError::BadArguments(_) | ToolMapError::Invalid(_) => {
            JsonRpcError::new(error_codes::INVALID_PARAMS, err.to_string())
        }
    }
}