clawft-core 0.6.4

//! Planning strategies with guard rails.
//!
//! Implements ReAct (Reason+Act) and Plan-and-Execute strategies for the
//! router, with configurable guard rails to prevent infinite loops and
//! cost runaway.
//!
//! # Guard rails
//!
//! | Parameter | Default | Description |
//! |-----------|---------|-------------|
//! | `max_planning_depth` | 10 | Max planning steps before forced termination |
//! | `max_planning_cost_usd` | 1.0 | Hard budget cap for LLM calls during planning |
//! | `planning_step_timeout` | 60s | Max duration for a single planning step |
//! | Circuit breaker | 3 | Consecutive no-op steps before abort |
//!
//! # Configuration
//!
//! ```toml
//! [router.planning]
//! max_planning_depth = 10
//! max_planning_cost_usd = 1.0
//! planning_step_timeout = "60s"
//! circuit_breaker_no_op_limit = 3
//! ```

use std::time::Duration;

use serde::{Deserialize, Serialize};
use tracing::warn;

/// Default maximum planning depth.
const DEFAULT_MAX_DEPTH: u32 = 10;

/// Default maximum planning cost in USD.
const DEFAULT_MAX_COST_USD: f64 = 1.0;

/// Default planning step timeout in seconds.
const DEFAULT_STEP_TIMEOUT_SECS: u64 = 60;

/// Default number of consecutive no-op steps before circuit breaker.
const DEFAULT_NO_OP_LIMIT: u32 = 3;

/// Planning strategy.
#[non_exhaustive]
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum PlanningStrategy {
    /// Reason+Act loop: alternate between reasoning about the current
    /// state and taking an action.
    #[serde(alias = "ReAct")]
    React,

    /// Plan-and-Execute: generate a full plan first, then execute
    /// each step sequentially.
    #[serde(alias = "PlanAndExecute")]
    PlanAndExecute,
}

/// Configuration for the planning router.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PlanningConfig {
    /// Maximum number of planning steps before forced termination.
    #[serde(default = "default_max_depth")]
    pub max_planning_depth: u32,

    /// Hard budget cap for LLM calls during planning (USD).
    #[serde(default = "default_max_cost")]
    pub max_planning_cost_usd: f64,

    /// Maximum duration for a single planning step.
    #[serde(
        default = "default_step_timeout",
        serialize_with = "serialize_duration_secs",
        deserialize_with = "deserialize_duration_secs"
    )]
    pub planning_step_timeout: Duration,

    /// Number of consecutive no-op steps before circuit breaker triggers.
    #[serde(default = "default_no_op_limit")]
    pub circuit_breaker_no_op_limit: u32,
}

fn default_max_depth() -> u32 {
    DEFAULT_MAX_DEPTH
}

fn default_max_cost() -> f64 {
    DEFAULT_MAX_COST_USD
}

fn default_step_timeout() -> Duration {
    Duration::from_secs(DEFAULT_STEP_TIMEOUT_SECS)
}

fn default_no_op_limit() -> u32 {
    DEFAULT_NO_OP_LIMIT
}

impl Default for PlanningConfig {
    fn default() -> Self {
        Self {
            max_planning_depth: default_max_depth(),
            max_planning_cost_usd: default_max_cost(),
            planning_step_timeout: default_step_timeout(),
            circuit_breaker_no_op_limit: default_no_op_limit(),
        }
    }
}

/// Reason a planning session was terminated.
#[non_exhaustive]
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum TerminationReason {
    /// Planning completed successfully.
    Completed,
    /// Maximum depth reached.
    MaxDepthReached,
    /// Budget cap exceeded.
    BudgetExceeded,
    /// Step timeout exceeded.
    StepTimeout,
    /// Circuit breaker triggered (too many no-op steps).
    CircuitBreaker,
    /// Cancelled by user or agent shutdown.
    Cancelled,
}

/// Result of a planning step.
#[derive(Debug, Clone)]
pub struct PlanningStepResult {
    /// Step number (0-indexed).
    pub step: u32,
    /// Whether this step produced actionable output.
    pub is_actionable: bool,
    /// Cost of this step in USD.
    pub cost_usd: f64,
    /// Duration of this step.
    pub duration: Duration,
    /// Output from this step.
    pub output: String,
}

/// Outcome of a planning session, including partial results.
#[derive(Debug, Clone)]
pub struct PlanningOutcome {
    /// Strategy that was used.
    pub strategy: PlanningStrategy,
    /// Why the planning session ended.
    pub termination_reason: TerminationReason,
    /// Number of steps executed.
    pub steps_executed: u32,
    /// Total cost in USD.
    pub total_cost_usd: f64,
    /// Total duration.
    pub total_duration: Duration,
    /// Results from each step.
    pub step_results: Vec<PlanningStepResult>,
    /// Human-readable explanation of the outcome.
    pub explanation: String,
}

/// Router that applies planning strategies with guard rails.
pub struct PlanningRouter {
    strategy: PlanningStrategy,
    config: PlanningConfig,
}

impl PlanningRouter {
    /// Create a new planning router.
    pub fn new(strategy: PlanningStrategy, config: PlanningConfig) -> Self {
        Self { strategy, config }
    }

    /// Create a planning router with default configuration.
    pub fn with_defaults(strategy: PlanningStrategy) -> Self {
        Self::new(strategy, PlanningConfig::default())
    }

    /// Get the configured strategy.
    pub fn strategy(&self) -> PlanningStrategy {
        self.strategy
    }

    /// Get the planning configuration.
    pub fn config(&self) -> &PlanningConfig {
        &self.config
    }

    /// Validate a planning step against guard rails.
    ///
    /// Returns `Some(TerminationReason)` if a limit has been reached,
    /// or `None` if the step is within limits.
    pub fn check_guard_rails(
        &self,
        current_step: u32,
        total_cost_usd: f64,
        consecutive_no_ops: u32,
    ) -> Option<TerminationReason> {
        if current_step >= self.config.max_planning_depth {
            warn!(
                step = current_step,
                max = self.config.max_planning_depth,
                "planning depth limit reached"
            );
            return Some(TerminationReason::MaxDepthReached);
        }

        if total_cost_usd >= self.config.max_planning_cost_usd {
            warn!(
                cost = total_cost_usd,
                max = self.config.max_planning_cost_usd,
                "planning budget cap exceeded"
            );
            return Some(TerminationReason::BudgetExceeded);
        }

        if consecutive_no_ops >= self.config.circuit_breaker_no_op_limit {
            warn!(
                no_ops = consecutive_no_ops,
                limit = self.config.circuit_breaker_no_op_limit,
                "circuit breaker triggered: too many no-op steps"
            );
            return Some(TerminationReason::CircuitBreaker);
        }

        None
    }

    /// Build a partial results explanation for the given termination reason.
    pub fn explain_termination(
        &self,
        reason: &TerminationReason,
        steps: u32,
        cost: f64,
    ) -> String {
        match reason {
            TerminationReason::Completed => {
                format!("Planning completed successfully after {steps} steps (${cost:.4} spent).")
            }
            TerminationReason::MaxDepthReached => {
                format!(
                    "Planning terminated: maximum depth of {} steps reached. \
                     Partial results from {steps} steps returned (${cost:.4} spent).",
                    self.config.max_planning_depth
                )
            }
            TerminationReason::BudgetExceeded => {
                format!(
                    "Planning terminated: budget cap of ${:.2} exceeded (${cost:.4} spent). \
                     Partial results from {steps} steps returned.",
                    self.config.max_planning_cost_usd
                )
            }
            TerminationReason::StepTimeout => {
                format!(
                    "Planning terminated: step timeout of {:?} exceeded at step {steps}. \
                     Partial results returned (${cost:.4} spent).",
                    self.config.planning_step_timeout
                )
            }
            TerminationReason::CircuitBreaker => {
                format!(
                    "Planning terminated: {} consecutive no-op steps detected (circuit breaker). \
                     Partial results from {steps} steps returned (${cost:.4} spent).",
                    self.config.circuit_breaker_no_op_limit
                )
            }
            TerminationReason::Cancelled => {
                format!(
                    "Planning cancelled by user or agent shutdown at step {steps} (${cost:.4} spent)."
                )
            }
        }
    }
}

impl std::fmt::Debug for PlanningRouter {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("PlanningRouter")
            .field("strategy", &self.strategy)
            .field("config", &self.config)
            .finish()
    }
}

fn serialize_duration_secs<S>(d: &Duration, s: S) -> Result<S::Ok, S::Error>
where
    S: serde::Serializer,
{
    s.serialize_u64(d.as_secs())
}

fn deserialize_duration_secs<'de, D>(d: D) -> Result<Duration, D::Error>
where
    D: serde::Deserializer<'de>,
{
    let secs = u64::deserialize(d)?;
    Ok(Duration::from_secs(secs))
}

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

    #[test]
    fn planning_config_defaults() {
        let cfg = PlanningConfig::default();
        assert_eq!(cfg.max_planning_depth, 10);
        assert!((cfg.max_planning_cost_usd - 1.0).abs() < f64::EPSILON);
        assert_eq!(cfg.planning_step_timeout, Duration::from_secs(60));
        assert_eq!(cfg.circuit_breaker_no_op_limit, 3);
    }

    #[test]
    fn planning_config_serde() {
        let cfg = PlanningConfig {
            max_planning_depth: 5,
            max_planning_cost_usd: 0.5,
            planning_step_timeout: Duration::from_secs(30),
            circuit_breaker_no_op_limit: 2,
        };
        let json = serde_json::to_string(&cfg).unwrap();
        let restored: PlanningConfig = serde_json::from_str(&json).unwrap();
        assert_eq!(restored.max_planning_depth, 5);
        assert!((restored.max_planning_cost_usd - 0.5).abs() < f64::EPSILON);
        assert_eq!(restored.planning_step_timeout, Duration::from_secs(30));
        assert_eq!(restored.circuit_breaker_no_op_limit, 2);
    }

    #[test]
    fn guard_rails_no_limit_hit() {
        let router = PlanningRouter::with_defaults(PlanningStrategy::React);
        assert!(router.check_guard_rails(0, 0.0, 0).is_none());
        assert!(router.check_guard_rails(5, 0.5, 1).is_none());
    }

    #[test]
    fn guard_rails_max_depth() {
        let router = PlanningRouter::with_defaults(PlanningStrategy::React);
        let result = router.check_guard_rails(10, 0.0, 0);
        assert_eq!(result, Some(TerminationReason::MaxDepthReached));
    }

    #[test]
    fn guard_rails_budget_exceeded() {
        let router = PlanningRouter::with_defaults(PlanningStrategy::React);
        let result = router.check_guard_rails(5, 1.0, 0);
        assert_eq!(result, Some(TerminationReason::BudgetExceeded));
    }

    #[test]
    fn guard_rails_circuit_breaker() {
        let router = PlanningRouter::with_defaults(PlanningStrategy::React);
        let result = router.check_guard_rails(5, 0.5, 3);
        assert_eq!(result, Some(TerminationReason::CircuitBreaker));
    }

    #[test]
    fn guard_rails_custom_limits() {
        let router = PlanningRouter::new(
            PlanningStrategy::PlanAndExecute,
            PlanningConfig {
                max_planning_depth: 3,
                max_planning_cost_usd: 0.25,
                circuit_breaker_no_op_limit: 1,
                ..Default::default()
            },
        );
        // Depth limit.
        assert_eq!(
            router.check_guard_rails(3, 0.0, 0),
            Some(TerminationReason::MaxDepthReached)
        );
        // Budget limit.
        assert_eq!(
            router.check_guard_rails(1, 0.25, 0),
            Some(TerminationReason::BudgetExceeded)
        );
        // Circuit breaker.
        assert_eq!(
            router.check_guard_rails(1, 0.0, 1),
            Some(TerminationReason::CircuitBreaker)
        );
    }

    #[test]
    fn explain_termination_messages() {
        let router = PlanningRouter::with_defaults(PlanningStrategy::React);

        let msg = router.explain_termination(&TerminationReason::Completed, 5, 0.3);
        assert!(msg.contains("successfully"));
        assert!(msg.contains("5 steps"));

        let msg = router.explain_termination(
            &TerminationReason::MaxDepthReached,
            10,
            0.8,
        );
        assert!(msg.contains("maximum depth"));
        assert!(msg.contains("Partial results"));

        let msg = router.explain_termination(
            &TerminationReason::BudgetExceeded,
            7,
            1.2,
        );
        assert!(msg.contains("budget cap"));

        let msg = router.explain_termination(
            &TerminationReason::CircuitBreaker,
            4,
            0.1,
        );
        assert!(msg.contains("no-op steps"));
        assert!(msg.contains("circuit breaker"));

        let msg = router.explain_termination(
            &TerminationReason::StepTimeout,
            3,
            0.2,
        );
        assert!(msg.contains("step timeout"));

        let msg = router.explain_termination(
            &TerminationReason::Cancelled,
            2,
            0.05,
        );
        assert!(msg.contains("cancelled"));
    }

    #[test]
    fn planning_strategy_serde() {
        let json = serde_json::to_string(&PlanningStrategy::React).unwrap();
        assert_eq!(json, "\"react\"");

        let json = serde_json::to_string(&PlanningStrategy::PlanAndExecute).unwrap();
        assert_eq!(json, "\"plan_and_execute\"");

        let restored: PlanningStrategy =
            serde_json::from_str("\"react\"").unwrap();
        assert_eq!(restored, PlanningStrategy::React);

        let restored: PlanningStrategy =
            serde_json::from_str("\"plan_and_execute\"").unwrap();
        assert_eq!(restored, PlanningStrategy::PlanAndExecute);
    }

    #[test]
    fn termination_reason_serde() {
        let json = serde_json::to_string(&TerminationReason::Completed).unwrap();
        assert_eq!(json, "\"completed\"");

        let json = serde_json::to_string(&TerminationReason::CircuitBreaker).unwrap();
        assert_eq!(json, "\"circuit_breaker\"");
    }

    #[test]
    fn router_accessors() {
        let router = PlanningRouter::with_defaults(PlanningStrategy::PlanAndExecute);
        assert_eq!(router.strategy(), PlanningStrategy::PlanAndExecute);
        assert_eq!(router.config().max_planning_depth, 10);
    }
}