//! Runtime configuration for mesh networking.
//!
//! This module provides centralized configuration with sensible defaults
//! and validation. Configuration can be loaded from files, environment
//! variables, or set programmatically.

use std::path::PathBuf;
use std::time::Duration;

use serde::{Deserialize, Serialize};

use crate::error::{ConfigError, MeshResult};
use crate::transport::CryptoMode;

/// Top-level mesh node configuration.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(default)]
pub struct MeshConfig {
    /// Node identity configuration.
    pub identity: IdentityConfig,
    /// Announce protocol configuration.
    pub announce: AnnounceConfig,
    /// Routing configuration.
    pub routing: RoutingConfig,
    /// Store-and-forward configuration.
    pub store: StoreConfig,
    /// Transport configuration.
    pub transport: TransportConfig,
    /// Crypto configuration.
    pub crypto: CryptoConfig,
    /// Rate limiting configuration.
    pub rate_limit: RateLimitConfig,
    /// Logging configuration.
    pub logging: LoggingConfig,
}

impl Default for MeshConfig {
    fn default() -> Self {
        Self {
            identity: IdentityConfig::default(),
            announce: AnnounceConfig::default(),
            routing: RoutingConfig::default(),
            store: StoreConfig::default(),
            transport: TransportConfig::default(),
            crypto: CryptoConfig::default(),
            rate_limit: RateLimitConfig::default(),
            logging: LoggingConfig::default(),
        }
    }
}

impl MeshConfig {
    /// Load configuration from a TOML file.
    pub fn from_file(path: &PathBuf) -> MeshResult<Self> {
        let content = std::fs::read_to_string(path).map_err(|e| {
            ConfigError::Parse(format!("failed to read config file: {}", e))
        })?;
        Self::from_toml(&content)
    }

    /// Parse configuration from TOML string.
    pub fn from_toml(toml: &str) -> MeshResult<Self> {
        let config: Self = toml::from_str(toml).map_err(|e| {
            ConfigError::Parse(format!("TOML parse error: {}", e))
        })?;
        config.validate()?;
        Ok(config)
    }

    /// Serialize to TOML string.
    pub fn to_toml(&self) -> MeshResult<String> {
        toml::to_string_pretty(self).map_err(|e| {
            ConfigError::Parse(format!("TOML serialize error: {}", e)).into()
        })
    }

    /// Validate configuration values.
    pub fn validate(&self) -> MeshResult<()> {
        self.announce.validate()?;
        self.routing.validate()?;
        self.store.validate()?;
        self.rate_limit.validate()?;
        Ok(())
    }

    /// Create a minimal config for constrained devices.
    pub fn constrained() -> Self {
        Self {
            store: StoreConfig {
                max_messages: 100,
                max_keypackages: 50,
                ..Default::default()
            },
            routing: RoutingConfig {
                max_entries: 100,
                ..Default::default()
            },
            announce: AnnounceConfig {
                interval: Duration::from_secs(1800), // 30 min
                ..Default::default()
            },
            crypto: CryptoConfig {
                default_mode: CryptoMode::MlsLiteUnsigned,
                ..Default::default()
            },
            ..Default::default()
        }
    }
}

/// Identity configuration.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(default)]
pub struct IdentityConfig {
    /// Path to persist identity keypair.
    pub keypair_path: Option<PathBuf>,
    /// Whether to auto-generate keypair if missing.
    pub auto_generate: bool,
}

impl Default for IdentityConfig {
    fn default() -> Self {
        Self {
            keypair_path: None,
            auto_generate: true,
        }
    }
}

/// Announce protocol configuration.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(default)]
pub struct AnnounceConfig {
    /// Interval between periodic announcements.
    #[serde(with = "humantime_serde")]
    pub interval: Duration,
    /// Maximum age before announce is considered stale.
    #[serde(with = "humantime_serde")]
    pub max_age: Duration,
    /// Maximum propagation hops.
    pub max_hops: u8,
    /// Capabilities to advertise.
    pub capabilities: u16,
    /// Whether to include KeyPackage hash in announces.
    pub include_keypackage: bool,
}

impl Default for AnnounceConfig {
    fn default() -> Self {
        Self {
            interval: Duration::from_secs(600),      // 10 min
            max_age: Duration::from_secs(1800),      // 30 min
            max_hops: 8,
            capabilities: 0x0003, // CAP_RELAY | CAP_STORE
            include_keypackage: true,
        }
    }
}

impl AnnounceConfig {
    fn validate(&self) -> MeshResult<()> {
        if self.interval < Duration::from_secs(10) {
            return Err(ConfigError::InvalidValue {
                key: "announce.interval".to_string(),
                reason: "must be at least 10 seconds".to_string(),
            }.into());
        }
        if self.max_hops == 0 || self.max_hops > 32 {
            return Err(ConfigError::InvalidValue {
                key: "announce.max_hops".to_string(),
                reason: "must be between 1 and 32".to_string(),
            }.into());
        }
        Ok(())
    }
}

/// Routing configuration.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(default)]
pub struct RoutingConfig {
    /// Maximum routing table entries.
    pub max_entries: usize,
    /// Default route TTL.
    #[serde(with = "humantime_serde")]
    pub default_ttl: Duration,
    /// How often to garbage collect expired routes.
    #[serde(with = "humantime_serde")]
    pub gc_interval: Duration,
}

impl Default for RoutingConfig {
    fn default() -> Self {
        Self {
            max_entries: 10_000,
            default_ttl: Duration::from_secs(1800), // 30 min
            gc_interval: Duration::from_secs(60),
        }
    }
}

impl RoutingConfig {
    fn validate(&self) -> MeshResult<()> {
        if self.max_entries == 0 {
            return Err(ConfigError::InvalidValue {
                key: "routing.max_entries".to_string(),
                reason: "must be at least 1".to_string(),
            }.into());
        }
        Ok(())
    }
}

/// Store-and-forward configuration.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(default)]
pub struct StoreConfig {
    /// Maximum messages in store.
    pub max_messages: usize,
    /// Maximum messages per recipient.
    pub max_per_recipient: usize,
    /// Maximum cached KeyPackages.
    pub max_keypackages: usize,
    /// Maximum KeyPackages per address.
    pub max_keypackages_per_addr: usize,
    /// Default message TTL.
    #[serde(with = "humantime_serde")]
    pub default_ttl: Duration,
    /// Path for persistent storage (None = in-memory only).
    pub persistence_path: Option<PathBuf>,
}

impl Default for StoreConfig {
    fn default() -> Self {
        Self {
            max_messages: 10_000,
            max_per_recipient: 100,
            max_keypackages: 1_000,
            max_keypackages_per_addr: 3,
            default_ttl: Duration::from_secs(24 * 3600), // 24 hours
            persistence_path: None,
        }
    }
}

impl StoreConfig {
    fn validate(&self) -> MeshResult<()> {
        if self.max_messages == 0 {
            return Err(ConfigError::InvalidValue {
                key: "store.max_messages".to_string(),
                reason: "must be at least 1".to_string(),
            }.into());
        }
        Ok(())
    }
}

/// Transport configuration.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(default)]
pub struct TransportConfig {
    /// Enable iroh/QUIC transport.
    pub enable_iroh: bool,
    /// Enable TCP transport.
    pub enable_tcp: bool,
    /// TCP listen address.
    pub tcp_listen: Option<String>,
    /// Enable LoRa transport.
    pub enable_lora: bool,
    /// LoRa device path (e.g., /dev/ttyUSB0).
    pub lora_device: Option<String>,
    /// LoRa spreading factor (7-12).
    pub lora_sf: u8,
    /// LoRa bandwidth in kHz.
    pub lora_bw: u32,
    /// Connection timeout.
    #[serde(with = "humantime_serde")]
    pub connect_timeout: Duration,
    /// Send timeout.
    #[serde(with = "humantime_serde")]
    pub send_timeout: Duration,
}

impl Default for TransportConfig {
    fn default() -> Self {
        Self {
            enable_iroh: true,
            enable_tcp: true,
            tcp_listen: None,
            enable_lora: false,
            lora_device: None,
            lora_sf: 10,
            lora_bw: 125,
            connect_timeout: Duration::from_secs(10),
            send_timeout: Duration::from_secs(30),
        }
    }
}

/// Crypto configuration.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(default)]
pub struct CryptoConfig {
    /// Default crypto mode.
    pub default_mode: CryptoMode,
    /// Whether to auto-upgrade to better crypto when available.
    pub auto_upgrade: bool,
    /// Whether to sign MLS-Lite messages.
    pub mls_lite_sign: bool,
    /// Enable post-quantum hybrid mode.
    pub enable_pq: bool,
}

impl Default for CryptoConfig {
    fn default() -> Self {
        Self {
            default_mode: CryptoMode::MlsClassical,
            auto_upgrade: true,
            mls_lite_sign: true,
            enable_pq: false, // PQ is large, opt-in
        }
    }
}

/// Rate limiting configuration.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(default)]
pub struct RateLimitConfig {
    /// Maximum announces per peer per minute.
    pub announce_per_peer_per_min: u32,
    /// Maximum messages per peer per minute.
    pub message_per_peer_per_min: u32,
    /// Maximum KeyPackage requests per minute.
    pub keypackage_requests_per_min: u32,
    /// LoRa duty cycle limit (0.0-1.0, e.g., 0.01 = 1%).
    pub lora_duty_cycle: f32,
}

impl Default for RateLimitConfig {
    fn default() -> Self {
        Self {
            announce_per_peer_per_min: 10,
            message_per_peer_per_min: 60,
            keypackage_requests_per_min: 20,
            lora_duty_cycle: 0.01, // EU868 1% default
        }
    }
}

impl RateLimitConfig {
    fn validate(&self) -> MeshResult<()> {
        if self.lora_duty_cycle < 0.0 || self.lora_duty_cycle > 1.0 {
            return Err(ConfigError::InvalidValue {
                key: "rate_limit.lora_duty_cycle".to_string(),
                reason: "must be between 0.0 and 1.0".to_string(),
            }.into());
        }
        Ok(())
    }
}

/// Logging configuration.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(default)]
pub struct LoggingConfig {
    /// Log level (trace, debug, info, warn, error).
    pub level: String,
    /// Whether to log to file.
    pub file: Option<PathBuf>,
    /// Whether to include timestamps.
    pub timestamps: bool,
    /// Whether to include span context.
    pub spans: bool,
}

impl Default for LoggingConfig {
    fn default() -> Self {
        Self {
            level: "info".to_string(),
            file: None,
            timestamps: true,
            spans: false,
        }
    }
}

// Serde helper for CryptoMode
impl Serialize for CryptoMode {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        let s = match self {
            CryptoMode::MlsHybrid => "mls-hybrid",
            CryptoMode::MlsClassical => "mls-classical",
            CryptoMode::MlsLiteSigned => "mls-lite-signed",
            CryptoMode::MlsLiteUnsigned => "mls-lite-unsigned",
        };
        serializer.serialize_str(s)
    }
}

impl<'de> Deserialize<'de> for CryptoMode {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        let s = String::deserialize(deserializer)?;
        match s.as_str() {
            "mls-hybrid" => Ok(CryptoMode::MlsHybrid),
            "mls-classical" => Ok(CryptoMode::MlsClassical),
            "mls-lite-signed" => Ok(CryptoMode::MlsLiteSigned),
            "mls-lite-unsigned" => Ok(CryptoMode::MlsLiteUnsigned),
            _ => Err(serde::de::Error::unknown_variant(
                &s,
                &["mls-hybrid", "mls-classical", "mls-lite-signed", "mls-lite-unsigned"],
            )),
        }
    }
}

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

    #[test]
    fn default_config_is_valid() {
        let config = MeshConfig::default();
        assert!(config.validate().is_ok());
    }

    #[test]
    fn constrained_config_is_valid() {
        let config = MeshConfig::constrained();
        assert!(config.validate().is_ok());
        assert_eq!(config.store.max_messages, 100);
    }

    #[test]
    fn toml_roundtrip() {
        let config = MeshConfig::default();
        let toml = config.to_toml().expect("serialize");
        let restored = MeshConfig::from_toml(&toml).expect("parse");
        assert_eq!(config.announce.max_hops, restored.announce.max_hops);
    }

    #[test]
    fn invalid_announce_interval() {
        let mut config = MeshConfig::default();
        config.announce.interval = Duration::from_secs(1); // Too short
        assert!(config.validate().is_err());
    }

    #[test]
    fn invalid_duty_cycle() {
        let mut config = MeshConfig::default();
        config.rate_limit.lora_duty_cycle = 2.0; // > 1.0
        assert!(config.validate().is_err());
    }
}