csv-adapter-core 0.1.1

//! Production hardening utilities for core module
//!
//! This module provides:
//! - Bounded queues for rate limiting
//! - Circuit breakers for failure detection
//! - Timeout configuration
//! - Memory limits enforcement

use std::collections::VecDeque;
use std::time::Duration;

/// Maximum number of items in bounded queues
pub const MAX_SEAL_REGISTRY_SIZE: usize = 1000;

/// Maximum number of entries in caches
pub const MAX_CACHE_SIZE: usize = 1000;

/// Maximum number of entries in registries
pub const MAX_REGISTRY_SIZE: usize = 10000;

/// Default timeout for RPC calls
pub const DEFAULT_RPC_TIMEOUT: Duration = Duration::from_secs(30);

/// Default timeout for health checks
pub const DEFAULT_HEALTH_CHECK_TIMEOUT: Duration = Duration::from_secs(5);

/// Default maximum failures before circuit opens
pub const DEFAULT_CIRCUIT_MAX_FAILURES: usize = 5;

/// Default reset timeout for circuit breaker
pub const DEFAULT_CIRCUIT_RESET_TIMEOUT: Duration = Duration::from_secs(60);

/// Bounded queue for enforcing size limits on collections
///
/// Prevents unbounded growth of caches, registries, and other
/// in-memory data structures that could lead to memory exhaustion.
#[derive(Clone, Debug)]
pub struct BoundedQueue<T> {
    queue: VecDeque<T>,
    max_size: usize,
}

impl<T> BoundedQueue<T> {
    /// Create a new bounded queue with the given maximum size
    pub fn new(max_size: usize) -> Self {
        Self {
            queue: VecDeque::new(),
            max_size,
        }
    }

    /// Push an item to the back of the queue
    ///
    /// Returns `true` if the item was added, `false` if the queue is full.
    pub fn push(&mut self, item: T) -> bool {
        if self.queue.len() >= self.max_size {
            return false;
        }
        self.queue.push_back(item);
        true
    }

    /// Pop an item from the front of the queue (FIFO order)
    pub fn pop(&mut self) -> Option<T> {
        self.queue.pop_front()
    }

    /// Returns the number of items in the queue
    pub fn len(&self) -> usize {
        self.queue.len()
    }

    /// Returns `true` if the queue is empty
    pub fn is_empty(&self) -> bool {
        self.queue.is_empty()
    }

    /// Returns `true` if the queue is at maximum capacity
    pub fn is_full(&self) -> bool {
        self.queue.len() >= self.max_size
    }
}

impl<T> Default for BoundedQueue<T> {
    fn default() -> Self {
        Self::new(MAX_SEAL_REGISTRY_SIZE)
    }
}

/// Circuit breaker state for managing service availability
#[derive(Clone, Debug, PartialEq)]
pub enum CircuitState {
    /// Normal operation — requests are allowed
    Closed,
    /// Failure threshold exceeded — requests are blocked
    Open,
    /// Testing recovery — a single request is allowed through
    HalfOpen,
}

/// Circuit breaker for failure detection and automatic service isolation
///
/// Transitions from `Closed` to `Open` when failures exceed the threshold,
/// then to `HalfOpen` after a timeout period to test recovery.
pub struct CircuitBreaker {
    failure_count: usize,
    max_failures: usize,
    last_failure_time: Option<std::time::SystemTime>,
    reset_timeout: Duration,
    state: CircuitState,
}

impl CircuitBreaker {
    /// Create a new circuit breaker with the given failure threshold and reset timeout
    pub fn new(max_failures: usize, reset_timeout: Duration) -> Self {
        Self {
            failure_count: 0,
            max_failures,
            last_failure_time: None,
            reset_timeout,
            state: CircuitState::Closed,
        }
    }

    /// Record a failure and potentially trip the circuit open
    pub fn record_failure(&mut self) {
        self.failure_count += 1;
        self.last_failure_time = Some(std::time::SystemTime::now());

        if self.failure_count >= self.max_failures {
            self.state = CircuitState::Open;
        }
    }

    /// Record a success, resetting the circuit to closed state
    pub fn record_success(&mut self) {
        self.failure_count = 0;
        self.state = CircuitState::Closed;
    }

    /// Check whether a request should be allowed through
    ///
    /// Returns `true` if the circuit is closed, or if the timeout
    /// has elapsed and the circuit is transitioning to half-open.
    pub fn allow_request(&mut self) -> bool {
        match self.state {
            CircuitState::Closed => true,
            CircuitState::Open => {
                if let Some(last_failure) = self.last_failure_time {
                    if last_failure.elapsed().unwrap_or_default() > self.reset_timeout {
                        self.state = CircuitState::HalfOpen;
                        true
                    } else {
                        false
                    }
                } else {
                    self.state = CircuitState::HalfOpen;
                    true
                }
            }
            CircuitState::HalfOpen => true,
        }
    }

    /// Returns the current circuit state
    pub fn state(&self) -> &CircuitState {
        &self.state
    }

    /// Returns the current consecutive failure count
    pub fn failure_count(&self) -> usize {
        self.failure_count
    }
}

impl Default for CircuitBreaker {
    fn default() -> Self {
        Self::new(DEFAULT_CIRCUIT_MAX_FAILURES, DEFAULT_CIRCUIT_RESET_TIMEOUT)
    }
}

/// Timeout configuration for RPC calls and health checks
#[derive(Clone, Debug)]
pub struct TimeoutConfig {
    /// Timeout for individual RPC calls
    pub rpc_call: Duration,
    /// Timeout for health check requests
    pub health_check: Duration,
}

impl Default for TimeoutConfig {
    fn default() -> Self {
        Self {
            rpc_call: DEFAULT_RPC_TIMEOUT,
            health_check: DEFAULT_HEALTH_CHECK_TIMEOUT,
        }
    }
}

/// Memory limits configuration for caches and registries
#[derive(Clone, Debug)]
pub struct MemoryLimits {
    /// Maximum number of entries in caches
    pub cache_size: usize,
    /// Maximum number of entries in registries
    pub registry_size: usize,
}

impl Default for MemoryLimits {
    fn default() -> Self {
        Self {
            cache_size: MAX_CACHE_SIZE,
            registry_size: MAX_REGISTRY_SIZE,
        }
    }
}