use bevy::prelude::Resource;
use figment::Figment;
use figment::providers::{Env, Format, Serialized, Toml};
use serde::{Deserialize, Serialize};

#[derive(Debug, Resource, Serialize, Deserialize)]
pub struct AppConfig {
    pub network: QuicConfig,
    pub simulation: SimulationConfig,
    pub observability: ObservabilityConfig,
}

#[derive(Debug, Serialize, Deserialize)]
pub struct SimulationConfig {
    pub tick_rate_hz: u32,
    pub max_entities: usize,
}

#[derive(Debug, Serialize, Deserialize)]
pub struct QuicConfig {
    pub server_port: u16,
    pub server_interface: String,
    pub server_cert: String,
    pub server_key: String,
    pub t1_capacity: usize,
    pub t2_capacity: usize,
    pub t3_capacity: usize,
    /// Bench-only knob. When > 0, the substrate spawns a synthetic T3
    /// driver that issues toggling Relay commands to every connected device
    /// at the configured rate, exercising the real outbound code path.
    /// Off by default (0.0) in production. Override via env:
    /// `APP_NETWORK__SYNTHETIC_T3_RATE_HZ=100`.
    #[serde(default)]
    pub synthetic_t3_rate_hz: f64,
}

#[derive(Debug, Serialize, Deserialize)]
pub struct ObservabilityConfig {
    /// When true, install the Prometheus exporter at startup. Disable for
    /// environments where the metrics port collides or scraping is undesired.
    pub metrics_enabled: bool,
    /// Bind address for the `/metrics` HTTP listener.
    pub metrics_listen: String,
}

impl Default for AppConfig {
    fn default() -> Self {
        Self {
            network : QuicConfig {
                server_port: 9000,
                server_interface: "0.0.0.0".to_string(),
                server_cert: "certs/server.crt".to_string(),
                server_key: "certs/server.key".to_string(),
                t1_capacity: 1024,
                t2_capacity: 512,
                t3_capacity: 256,
                synthetic_t3_rate_hz: 0.0,
            },
            simulation: SimulationConfig {
                tick_rate_hz: 60,
                max_entities: 10000,
            },
            observability: ObservabilityConfig {
                metrics_enabled: true,
                metrics_listen: "0.0.0.0:9100".to_string(),
            },
        }
    }
}

impl AppConfig {
    pub fn load(config_file: &str) -> Result<Self, figment::Error> {
        Figment::new()
            .merge(Serialized::defaults(Self::default()))  // compiled-in defaults
            .merge(Toml::file(config_file))                // config file
            // env overrides — `__` is the nesting separator so
            // `APP_NETWORK__SERVER_PORT=9001` overrides `network.server_port`.
            .merge(Env::prefixed("APP_").split("__"))
            .extract()
    }
}