plugmem-mcp 0.1.2

//! `plugmem-mcp` — a Model Context Protocol server exposing a plugmem memory to
//! AI agents (and any program that can spawn a process and speak JSON over a
//! pipe: Python `subprocess`, Node `child_process`, an agent runner).
//!
//! Transport: stdio, newline-delimited JSON-RPC 2.0 (one message per line).
//! Hand-rolled with `serde_json` (no MCP SDK, no async runtime). It is a
//! **sidecar process, not a daemon**: the host spawns it and talks on
//! stdin/stdout; it listens on no port and serves one memory file for its
//! lifetime. Cross-language / many-reader use is many processes over the file
//! MVCC, not one network server.
//!
//! In a Rust program you do not need this — embed [`plugmem_host`] directly
//! (the engine in your process, like linking SQLite). MCP is the door for
//! agents and other languages.
//!
//! Layout, so protocol, behavior and wording are each editable in isolation:
//! `rpc` owns the JSON-RPC envelope and the stdio loop, `tools` the tool
//! definitions and their execution, and `messages` every model-facing string.

mod messages;
mod rpc;
mod tools;

use std::path::PathBuf;
use std::process::ExitCode;
use std::sync::Arc;

use clap::Parser;

/// Environment variable naming the database file (below the `--db` flag).
const ENV_DB: &str = "PLUGMEM_DB";
/// Default database file when neither flag nor env is given.
const DEFAULT_DB: &str = "plugmem.db";

/// Command-line arguments. The host wires these once in its MCP config.
#[derive(Parser)]
#[command(name = "plugmem-mcp", version, about = messages::ABOUT_CLI)]
struct Args {
    /// Memory file to serve (else $PLUGMEM_DB, else ./plugmem.db).
    #[arg(long)]
    db: Option<PathBuf>,
    /// config.toml path (else $PLUGMEM_CONFIG, else the XDG default).
    #[arg(long)]
    config: Option<PathBuf>,
    /// Observe-only: open a shared snapshot of another process's writer. Serves
    /// the read verbs plus `plugmem_generation`/`plugmem_refresh`; write verbs
    /// are refused. Requires a checkpointed database.
    #[arg(long)]
    read_only: bool,
    /// Worker threads for concurrent requests (else `[server].workers`, else
    /// half the available cores, at least 1).
    #[arg(long)]
    workers: Option<usize>,
}

fn main() -> ExitCode {
    let args = Args::parse();
    let path = args
        .db
        .or_else(|| std::env::var_os(ENV_DB).map(PathBuf::from))
        .unwrap_or_else(|| PathBuf::from(DEFAULT_DB));

    // Read config.toml once: the shared loader builds the engine settings; the
    // server reads its own `[server].workers` from the same table. A failure
    // here (a bad config, or the file already locked by another writer) is
    // fatal: report to stderr and exit, so the spawning host sees the server
    // did not start.
    let table = match plugmem_host::read_config(args.config.as_deref()) {
        Ok(t) => t,
        Err(e) => {
            eprintln!("plugmem-mcp: {e}");
            return ExitCode::from(2);
        }
    };
    let workers = args
        .workers
        .unwrap_or_else(|| resolve_workers(table.as_ref()));
    let settings = match plugmem_host::Settings::from_table(table.as_ref()) {
        Ok(s) => s,
        Err(e) => {
            eprintln!("plugmem-mcp: {e}");
            return ExitCode::from(2);
        }
    };

    // Read-only: open a shared snapshot of another process's writer and keep the
    // embedder to embed recall queries (the read-only handle has none). Default:
    // open the single writer handle, consuming the settings (embedder included).
    let shared = if args.read_only {
        let embedder = settings.embedder;
        match plugmem_host::Database::open_readonly(&path, settings.config) {
            Ok(db) => rpc::Shared::Reader(Arc::new(tools::ReaderShared::new(db, embedder))),
            Err(e) => {
                eprintln!("plugmem-mcp: {}: {e}", path.display());
                return ExitCode::from(2);
            }
        }
    } else {
        match settings.open(&path) {
            Ok(db) => rpc::Shared::Writer(db),
            Err(e) => {
                eprintln!("plugmem-mcp: {}: {e}", path.display());
                return ExitCode::from(2);
            }
        }
    };

    rpc::serve(shared, workers);
    ExitCode::SUCCESS
}

/// The worker count: `[server].workers` if a positive integer, else half the
/// available parallelism (at least 1) — leaving cores for the agent, the OS and
/// a local embedder rather than monopolizing the machine.
fn resolve_workers(table: Option<&toml::Table>) -> usize {
    table
        .and_then(|t| t.get("server"))
        .and_then(toml::Value::as_table)
        .and_then(|s| s.get("workers"))
        .and_then(toml::Value::as_integer)
        .filter(|n| *n > 0)
        .map(|n| n as usize)
        .unwrap_or_else(default_workers)
}

/// Half the available cores, at least 1.
fn default_workers() -> usize {
    std::thread::available_parallelism()
        .map(|n| (n.get() / 2).max(1))
        .unwrap_or(1)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn workers_from_config_else_default() {
        let table: toml::Table = "[server]\nworkers = 3\n".parse().unwrap();
        assert_eq!(resolve_workers(Some(&table)), 3);

        // No `[server]` / no table / non-positive → the default (>= 1).
        let empty: toml::Table = "[engine]\ndim = 8\n".parse().unwrap();
        assert!(resolve_workers(Some(&empty)) >= 1);
        assert!(resolve_workers(None) >= 1);
        let zero: toml::Table = "[server]\nworkers = 0\n".parse().unwrap();
        assert!(resolve_workers(Some(&zero)) >= 1);

        assert!(default_workers() >= 1);
    }
}