crates-docs 0.9.0

//! Utility functions module

use crate::error::{Error, Result};
use reqwest::Client;
use reqwest_middleware::ClientBuilder;
use reqwest_retry::{policies::ExponentialBackoff, RetryTransientMiddleware};
use std::sync::{Arc, OnceLock};
use std::time::Duration;
use tokio::sync::Semaphore;

/// Global HTTP client singleton with connection pool reuse
///
/// This static instance ensures connection pooling is effective across
/// all HTTP requests in the application. The client is lazily initialized
/// on first access.
static GLOBAL_HTTP_CLIENT: OnceLock<Arc<reqwest_middleware::ClientWithMiddleware>> =
    OnceLock::new();

/// Storage for initialization error (if any)
/// Used to avoid retrying failed initialization
static INIT_ERROR: OnceLock<String> = OnceLock::new();

/// Initialize the global HTTP client singleton
///
/// # Arguments
///
/// * `config` - Performance configuration for connection pool settings
///
/// # Errors
///
/// Returns an error if HTTP client creation fails
///
/// # Note
///
/// This function is thread-safe and ensures only one thread performs the
/// expensive client initialization (including TLS setup). Subsequent calls
/// will return Ok(()) if initialization succeeded, or the original error
/// if initialization previously failed.
pub fn init_global_http_client(config: &crate::config::PerformanceConfig) -> Result<()> {
    // Fast path: already initialized
    if GLOBAL_HTTP_CLIENT.get().is_some() {
        return Ok(());
    }

    // Check if previous initialization failed
    if let Some(err_msg) = INIT_ERROR.get() {
        return Err(Error::initialization(
            "global_http_client",
            format!("Previous initialization failed: {err_msg}"),
        ));
    }

    // Slow path: try to initialize
    let client_result = create_http_client_from_config(config).build();

    match client_result {
        Ok(client) => {
            let client_arc = Arc::new(client);
            // set() returns Err if already initialized, which is fine
            let _ = GLOBAL_HTTP_CLIENT.set(client_arc);
            Ok(())
        }
        Err(e) => {
            let err_msg = format!("Failed to create global HTTP client: {e}");
            let _ = INIT_ERROR.set(err_msg.clone());
            Err(Error::initialization("global_http_client", err_msg))
        }
    }
}

/// Get the global HTTP client singleton
///
/// # Errors
///
/// Returns an error if the global HTTP client has not been initialized.
/// Call `init_global_http_client()` before using this function.
///
/// If you need automatic initialization, use `get_or_init_global_http_client()` instead.
#[must_use = "returns a Result that should be checked"]
pub fn get_global_http_client() -> Result<Arc<reqwest_middleware::ClientWithMiddleware>> {
    GLOBAL_HTTP_CLIENT.get().cloned().ok_or_else(|| {
        Error::initialization(
            "global_http_client",
            "Global HTTP client not initialized. Call init_global_http_client() first.",
        )
    })
}

/// Get or initialize the global HTTP client with default config
///
/// This is a convenience function for use cases where the client
/// might not be explicitly initialized. It uses default performance config.
///
/// # Errors
///
/// Returns an error if HTTP client creation fails (e.g., TLS initialization error).
/// This function is thread-safe and ensures only one thread performs initialization.
pub fn get_or_init_global_http_client() -> Result<Arc<reqwest_middleware::ClientWithMiddleware>> {
    // Fast path: already initialized
    if let Some(client) = GLOBAL_HTTP_CLIENT.get() {
        return Ok(client.clone());
    }

    // Use init_global_http_client with default config for thread-safe initialization
    let default_config = crate::config::PerformanceConfig::default();
    init_global_http_client(&default_config)?;

    // Now it should be initialized
    GLOBAL_HTTP_CLIENT.get().cloned().ok_or_else(|| {
        Error::initialization(
            "global_http_client",
            "HTTP client initialization failed unexpectedly".to_string(),
        )
    })
}

/// HTTP client builder with retry support
///
/// This builder creates a `reqwest_middleware::ClientWithMiddleware` that includes
/// automatic retry functionality for transient failures.
pub struct HttpClientBuilder {
    timeout: Duration,
    connect_timeout: Duration,
    read_timeout: Duration,
    pool_max_idle_per_host: usize,
    pool_idle_timeout: Duration,
    user_agent: String,
    enable_gzip: bool,
    enable_brotli: bool,
    max_retries: u32,
    retry_initial_delay: Duration,
    retry_max_delay: Duration,
}

impl Default for HttpClientBuilder {
    fn default() -> Self {
        Self {
            timeout: Duration::from_secs(30),
            connect_timeout: Duration::from_secs(10),
            read_timeout: Duration::from_secs(30),
            pool_max_idle_per_host: 10,
            pool_idle_timeout: Duration::from_secs(90),
            user_agent: format!("CratesDocsMCP/{}", crate::VERSION),
            enable_gzip: true,
            enable_brotli: true,
            max_retries: 3,
            retry_initial_delay: Duration::from_millis(100),
            retry_max_delay: Duration::from_secs(10),
        }
    }
}

impl HttpClientBuilder {
    /// Create a new HTTP client builder
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    /// Set request timeout
    #[must_use]
    pub fn timeout(mut self, timeout: Duration) -> Self {
        self.timeout = timeout;
        self
    }

    /// Set connection timeout
    #[must_use]
    pub fn connect_timeout(mut self, connect_timeout: Duration) -> Self {
        self.connect_timeout = connect_timeout;
        self
    }

    /// Set read timeout
    #[must_use]
    pub fn read_timeout(mut self, read_timeout: Duration) -> Self {
        self.read_timeout = read_timeout;
        self
    }

    /// Set connection pool size
    #[must_use]
    pub fn pool_max_idle_per_host(mut self, max_idle: usize) -> Self {
        self.pool_max_idle_per_host = max_idle;
        self
    }

    /// Set pool idle timeout
    #[must_use]
    pub fn pool_idle_timeout(mut self, idle_timeout: Duration) -> Self {
        self.pool_idle_timeout = idle_timeout;
        self
    }

    /// Set User-Agent
    #[must_use]
    pub fn user_agent(mut self, user_agent: String) -> Self {
        self.user_agent = user_agent;
        self
    }

    /// Enable/disable Gzip compression
    #[must_use]
    pub fn enable_gzip(mut self, enable: bool) -> Self {
        self.enable_gzip = enable;
        self
    }

    /// Enable/disable Brotli compression
    #[must_use]
    pub fn enable_brotli(mut self, enable: bool) -> Self {
        self.enable_brotli = enable;
        self
    }

    /// Set max retry attempts
    #[must_use]
    pub fn max_retries(mut self, max_retries: u32) -> Self {
        self.max_retries = max_retries;
        self
    }

    /// Set retry initial delay
    #[must_use]
    pub fn retry_initial_delay(mut self, delay: Duration) -> Self {
        self.retry_initial_delay = delay;
        self
    }

    /// Set retry max delay
    #[must_use]
    pub fn retry_max_delay(mut self, delay: Duration) -> Self {
        self.retry_max_delay = delay;
        self
    }

    /// Build HTTP client with middleware chain
    ///
    /// This method builds a `reqwest_middleware::ClientWithMiddleware` that includes
    /// automatic retry functionality using exponential backoff for transient failures.
    ///
    /// # Returns
    ///
    /// Returns a `ClientWithMiddleware` that can be used like a regular `reqwest::Client`
    /// but with automatic retry on transient errors.
    pub fn build(self) -> Result<reqwest_middleware::ClientWithMiddleware> {
        let mut builder = Client::builder()
            .timeout(self.timeout)
            .connect_timeout(self.connect_timeout)
            .pool_max_idle_per_host(self.pool_max_idle_per_host)
            .pool_idle_timeout(self.pool_idle_timeout)
            .user_agent(&self.user_agent);

        // reqwest 0.13 enables gzip and brotli by default
        // To disable, use .no_gzip() and .no_brotli()
        if !self.enable_gzip {
            builder = builder.no_gzip();
        }

        if !self.enable_brotli {
            builder = builder.no_brotli();
        }

        let client = builder
            .build()
            .map_err(|e| Error::http_request("BUILD", "client", 0, e.to_string()))?;

        // Create retry policy with exponential backoff
        let retry_policy = ExponentialBackoff::builder()
            .retry_bounds(self.retry_initial_delay, self.retry_max_delay)
            .build_with_max_retries(self.max_retries);

        // Build client with retry middleware
        Ok(ClientBuilder::new(client)
            .with(RetryTransientMiddleware::new_with_policy(retry_policy))
            .build())
    }

    /// Build HTTP client without retry support
    ///
    /// This method returns a plain `reqwest::Client` without any middleware.
    /// Use [`build`](Self::build) for retry support.
    pub fn build_plain(self) -> Result<Client> {
        let mut builder = Client::builder()
            .timeout(self.timeout)
            .connect_timeout(self.connect_timeout)
            .pool_max_idle_per_host(self.pool_max_idle_per_host)
            .pool_idle_timeout(self.pool_idle_timeout)
            .user_agent(&self.user_agent);

        if !self.enable_gzip {
            builder = builder.no_gzip();
        }

        if !self.enable_brotli {
            builder = builder.no_brotli();
        }

        builder
            .build()
            .map_err(|e| Error::http_request("BUILD", "client", 0, e.to_string()))
    }
}

/// Create HTTP client builder from performance config
///
/// This function creates an `HttpClientBuilder` pre-configured with settings
/// from the provided `PerformanceConfig`. The resulting client will include
/// automatic retry functionality.
#[must_use]
pub fn create_http_client_from_config(
    config: &crate::config::PerformanceConfig,
) -> HttpClientBuilder {
    HttpClientBuilder::new()
        .timeout(Duration::from_secs(config.http_client_timeout_secs))
        .connect_timeout(Duration::from_secs(config.http_client_connect_timeout_secs))
        .read_timeout(Duration::from_secs(config.http_client_read_timeout_secs))
        .pool_max_idle_per_host(config.http_client_pool_size)
        .pool_idle_timeout(Duration::from_secs(
            config.http_client_pool_idle_timeout_secs,
        ))
        .max_retries(config.http_client_max_retries)
        .retry_initial_delay(Duration::from_millis(
            config.http_client_retry_initial_delay_ms,
        ))
        .retry_max_delay(Duration::from_millis(config.http_client_retry_max_delay_ms))
}

/// Rate limiter
pub struct RateLimiter {
    semaphore: Arc<Semaphore>,
    max_permits: usize,
}

impl RateLimiter {
    /// Create a new rate limiter
    #[must_use]
    pub fn new(max_permits: usize) -> Self {
        Self {
            semaphore: Arc::new(Semaphore::new(max_permits)),
            max_permits,
        }
    }

    /// Acquire permit (blocks until available)
    pub async fn acquire(&self) -> Result<tokio::sync::SemaphorePermit<'_>> {
        self.semaphore
            .acquire()
            .await
            .map_err(|e| Error::Other(format!("Failed to acquire rate limit permit: {e}")))
    }

    /// Try to acquire permit (non-blocking)
    #[must_use]
    pub fn try_acquire(&self) -> Option<tokio::sync::SemaphorePermit<'_>> {
        self.semaphore.try_acquire().ok()
    }

    /// Get current number of available permits
    #[must_use]
    pub fn available_permits(&self) -> usize {
        self.semaphore.available_permits()
    }

    /// Get maximum number of permits
    #[must_use]
    pub fn max_permits(&self) -> usize {
        self.max_permits
    }
}

/// Response compression utilities
pub mod compression {
    use crate::error::{Error, Result};
    use flate2::write::GzEncoder;
    use flate2::Compression;
    use std::io::Write;

    /// Compress data (Gzip)
    pub fn gzip_compress(data: &[u8]) -> Result<Vec<u8>> {
        let mut encoder = GzEncoder::new(Vec::new(), Compression::default());
        encoder
            .write_all(data)
            .map_err(|e| Error::Other(format!("Gzip compression failed: {e}")))?;
        encoder
            .finish()
            .map_err(|e| Error::Other(format!("Gzip compression finalize failed: {e}")))
    }

    /// Decompress data (Gzip)
    pub fn gzip_decompress(data: &[u8]) -> Result<Vec<u8>> {
        let mut decoder = flate2::read::GzDecoder::new(data);
        let mut decompressed = Vec::new();
        std::io::Read::read_to_end(&mut decoder, &mut decompressed)
            .map_err(|e| Error::Other(format!("Gzip decompression failed: {e}")))?;
        Ok(decompressed)
    }
}

/// String utilities
pub mod string {
    /// Truncate string and add ellipsis (UTF-8 safe)
    ///
    /// # Arguments
    /// * `s` - The string to truncate
    /// * `max_len` - Maximum number of characters (not bytes) to keep, including ellipsis
    ///
    /// # Examples
    /// ```
    /// use crates_docs::utils::string::truncate_with_ellipsis;
    /// // Basic ASCII truncation
    /// assert_eq!(truncate_with_ellipsis("hello world", 8), "hello...");
    /// assert_eq!(truncate_with_ellipsis("short", 10), "short");
    /// // UTF-8 safe: works with multi-byte characters
    /// assert_eq!(truncate_with_ellipsis("你好世界", 3), "...");
    /// assert_eq!(truncate_with_ellipsis("你好世界", 4), "你好世界"); // 4 chars <= max_len, no truncation
    /// assert_eq!(truncate_with_ellipsis("你好世界", 5), "你好世界"); // 4 chars <= max_len, no truncation
    /// assert_eq!(truncate_with_ellipsis("你好世界你好", 4), "你...");   // 4 chars > max_len-3, truncate
    /// ```
    #[must_use]
    pub fn truncate_with_ellipsis(s: &str, max_len: usize) -> String {
        // If max_len is 3 or less, just return ellipsis
        if max_len <= 3 {
            return "...".to_string();
        }

        // Collect characters to properly handle UTF-8
        let chars: Vec<char> = s.chars().collect();

        // If string is short enough, return it as-is
        if chars.len() <= max_len {
            return s.to_string();
        }

        // Truncate to max_len - 3 characters and add ellipsis
        let truncated: String = chars.iter().take(max_len - 3).collect();
        format!("{truncated}...")
    }

    /// Safely parse number
    pub fn parse_number<T: std::str::FromStr>(s: &str, default: T) -> T {
        s.parse().unwrap_or(default)
    }

    /// Check if string is empty or blank
    #[must_use]
    pub fn is_blank(s: &str) -> bool {
        s.trim().is_empty()
    }
}

/// Time utilities
pub mod time {
    use chrono::{DateTime, Utc};

    /// Get current timestamp (milliseconds)
    #[must_use]
    pub fn current_timestamp_ms() -> i64 {
        Utc::now().timestamp_millis()
    }

    /// Format datetime
    #[must_use]
    pub fn format_datetime(dt: &DateTime<Utc>) -> String {
        dt.format("%Y-%m-%d %H:%M:%S%.3f").to_string()
    }

    /// Calculate elapsed time (milliseconds)
    #[must_use]
    pub fn elapsed_ms(start: std::time::Instant) -> u128 {
        start.elapsed().as_millis()
    }
}

/// Validation utilities
pub mod validation {
    use crate::error::Error;

    /// Maximum allowed length for crate names (100 characters)
    const MAX_CRATE_NAME_LENGTH: usize = 100;
    /// Maximum allowed length for version strings (50 characters)
    const MAX_VERSION_LENGTH: usize = 50;
    /// Maximum allowed length for search queries (200 characters)
    const MAX_SEARCH_QUERY_LENGTH: usize = 200;

    /// Validate crate name
    pub fn validate_crate_name(name: &str) -> Result<(), Error> {
        if name.is_empty() {
            return Err(Error::Other("Crate name cannot be empty".to_string()));
        }

        if name.len() > MAX_CRATE_NAME_LENGTH {
            return Err(Error::Other("Crate name is too long".to_string()));
        }

        // Basic validation: only allow letters, digits, underscores, hyphens
        if !name
            .chars()
            .all(|c| c.is_ascii_alphanumeric() || c == '_' || c == '-')
        {
            return Err(Error::Other(
                "Crate name contains invalid characters".to_string(),
            ));
        }

        Ok(())
    }

    /// Validate version number
    pub fn validate_version(version: &str) -> Result<(), Error> {
        if version.is_empty() {
            return Err(Error::Other("Version cannot be empty".to_string()));
        }

        if version.len() > MAX_VERSION_LENGTH {
            return Err(Error::Other("Version is too long".to_string()));
        }

        // Simple validation: should contain digits and dots
        if !version.chars().any(|c| c.is_ascii_digit()) {
            return Err(Error::Other("Version must contain digits".to_string()));
        }

        Ok(())
    }

    /// Validate search query
    pub fn validate_search_query(query: &str) -> Result<(), Error> {
        if query.is_empty() {
            return Err(Error::Other("Search query cannot be empty".to_string()));
        }

        if query.len() > MAX_SEARCH_QUERY_LENGTH {
            return Err(Error::Other("Search query is too long".to_string()));
        }

        Ok(())
    }
}

/// Performance monitoring
pub mod metrics {
    use std::sync::atomic::{AtomicU64, Ordering};
    use std::sync::Arc;
    use std::time::Instant;

    /// Performance counter
    #[derive(Clone)]
    pub struct PerformanceCounter {
        total_requests: Arc<AtomicU64>,
        successful_requests: Arc<AtomicU64>,
        failed_requests: Arc<AtomicU64>,
        total_response_time_ms: Arc<AtomicU64>,
    }

    impl PerformanceCounter {
        /// Create a new performance counter
        #[must_use]
        pub fn new() -> Self {
            Self {
                total_requests: Arc::new(AtomicU64::new(0)),
                successful_requests: Arc::new(AtomicU64::new(0)),
                failed_requests: Arc::new(AtomicU64::new(0)),
                total_response_time_ms: Arc::new(AtomicU64::new(0)),
            }
        }

        /// Record request start
        #[must_use]
        pub fn record_request_start(&self) -> Instant {
            self.total_requests.fetch_add(1, Ordering::Relaxed);
            Instant::now()
        }

        /// Record request completion
        #[allow(clippy::cast_possible_truncation)]
        pub fn record_request_complete(&self, start: Instant, success: bool) {
            let duration_ms = start.elapsed().as_millis() as u64;
            self.total_response_time_ms
                .fetch_add(duration_ms, Ordering::Relaxed);

            if success {
                self.successful_requests.fetch_add(1, Ordering::Relaxed);
            } else {
                self.failed_requests.fetch_add(1, Ordering::Relaxed);
            }
        }

        /// Get statistics
        #[must_use]
        pub fn get_stats(&self) -> PerformanceStats {
            let total = self.total_requests.load(Ordering::Relaxed);
            let success = self.successful_requests.load(Ordering::Relaxed);
            let failed = self.failed_requests.load(Ordering::Relaxed);
            let total_time = self.total_response_time_ms.load(Ordering::Relaxed);

            #[allow(clippy::cast_precision_loss)]
            let avg_response_time = if total > 0 {
                total_time as f64 / total as f64
            } else {
                0.0
            };

            #[allow(clippy::cast_precision_loss)]
            let success_rate = if total > 0 {
                success as f64 / total as f64 * 100.0
            } else {
                0.0
            };

            PerformanceStats {
                total_requests: total,
                successful_requests: success,
                failed_requests: failed,
                average_response_time_ms: avg_response_time,
                success_rate_percent: success_rate,
            }
        }

        /// Reset counter
        pub fn reset(&self) {
            self.total_requests.store(0, Ordering::Relaxed);
            self.successful_requests.store(0, Ordering::Relaxed);
            self.failed_requests.store(0, Ordering::Relaxed);
            self.total_response_time_ms.store(0, Ordering::Relaxed);
        }
    }

    impl Default for PerformanceCounter {
        fn default() -> Self {
            Self::new()
        }
    }

    /// Performance statistics
    #[derive(Debug, Clone, serde::Serialize)]
    pub struct PerformanceStats {
        /// Total requests
        pub total_requests: u64,
        /// Successful requests
        pub successful_requests: u64,
        /// Failed requests
        pub failed_requests: u64,
        /// Average response time (milliseconds)
        pub average_response_time_ms: f64,
        /// Success rate (percentage)
        pub success_rate_percent: f64,
    }
}