//! `AgentDefinition` -- declarative specification for instantiating a
//! subagent from workflow scripts or programmatic calls.
//!
//! Also provides a shared [`spawn_subagent_with_drain`] helper that
//! eliminates the channel-creation + drain-thread boilerplate duplicated
//! across `auto/mod.rs`, `review/mod.rs`, and `workflow/engine/mod.rs`.

use super::event::SubagentEvent;
use serde::{Deserialize, Serialize};

/// Declarative specification for instantiating a subagent: name, role,
/// optional system prompt, allowed tools, step budget, and temperature.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct AgentDefinition {
    pub name: String,
    pub role: String,
    pub system_prompt: Option<String>,
    pub allowed_tools: Option<Vec<String>>,
    pub max_steps: Option<usize>,
    pub temperature: Option<f32>,
}

impl AgentDefinition {
    /// Create an agent definition with the required name and role; all
    /// optional fields start as `None`.
    pub fn new(name: String, role: String) -> Self {
        AgentDefinition {
            name,
            role,
            system_prompt: None,
            allowed_tools: None,
            max_steps: None,
            temperature: None,
        }
    }

    /// Builder method: set the system prompt for this agent.
    pub fn with_system_prompt(mut self, prompt: String) -> Self {
        self.system_prompt = Some(prompt);
        self
    }

    /// Builder method: set the allowed tool list for this agent.
    pub fn with_allowed_tools(mut self, tools: Vec<String>) -> Self {
        self.allowed_tools = Some(tools);
        self
    }

    /// Builder method: set the maximum step count for this agent.
    pub fn with_max_steps(mut self, steps: usize) -> Self {
        self.max_steps = Some(steps);
        self
    }

}

/// Shared subagent spawning utility: creates an mpsc channel and spawns a
/// drain thread that forwards every [`SubagentEvent`] to `on_event`.
///
/// Returns the sender half (for passing to [`run_subagent`](super::engine::run_subagent))
/// and the drain thread's join handle so the caller can keep it alive for
/// the duration of the subagent run.
///
/// # Example
///
/// ```ignore
/// let (tx, _drain) = spawn_subagent_with_drain(|event| {
///     match &event {
///         SubagentEvent::ToolCall { tool, .. } => tracing::debug!("tool: {tool}"),
///         SubagentEvent::Completed => tracing::debug!("done"),
///         _ => {}
///     }
/// });
/// let verdict = run_subagent(&ctx, &tx)?;
/// ```
///
/// # Duplication eliminated
///
/// Previously every subagent caller inlined the same 5-line pattern:
///
/// ```ignore
/// let (tx, mut rx) = tokio::sync::mpsc::channel(32);
/// let _drain = std::thread::spawn(move || {
///     while let Some(event) = rx.blocking_recv() { ... }
/// });
/// ```
///
/// Callers that need a larger buffer (e.g. workflow engine uses 64) should
/// create the channel manually instead of using this helper.
pub fn spawn_subagent_with_drain<F>(
    on_event: F,
) -> (tokio::sync::mpsc::Sender<SubagentEvent>, std::thread::JoinHandle<()>)
where
    F: Fn(SubagentEvent) + Send + 'static,
{
    let (tx, mut rx) = tokio::sync::mpsc::channel(32);
    let drain = std::thread::spawn(move || {
        while let Some(event) = rx.blocking_recv() {
            on_event(event);
        }
    });
    (tx, drain)
}