/// Telemetry configuration, populated from environment variables.
///
/// Follows the OpenTelemetry environment variable specification:
/// <https://opentelemetry.io/docs/specs/otel/configuration/sdk-environment-variables/>
#[derive(Debug, Clone)]
pub struct TelemetryConfig {
    pub service_name: String,
    pub service_version: String,
    pub otlp_endpoint: String,
    pub otlp_protocol: OtlpProtocol,
    pub traces_enabled: bool,
    pub metrics_enabled: bool,
    pub logs_enabled: bool,
    pub log_format: LogFormat,
    pub log_level: String,
}

#[derive(Debug, Clone, PartialEq)]
pub enum OtlpProtocol {
    Grpc,
    HttpProtobuf,
}

#[derive(Debug, Clone, PartialEq)]
pub enum LogFormat {
    Json,
    Pretty,
}

impl Default for TelemetryConfig {
    fn default() -> Self {
        Self {
            service_name: env_or("OTEL_SERVICE_NAME", "imks"),
            service_version: env_or("OTEL_SERVICE_VERSION", env!("CARGO_PKG_VERSION")),
            otlp_endpoint: env_or("OTEL_EXPORTER_OTLP_ENDPOINT", "http://localhost:4317"),
            otlp_protocol: detect_otlp_protocol(),
            traces_enabled: env_bool("OTEL_TRACES_ENABLED", true),
            metrics_enabled: env_bool("OTEL_METRICS_ENABLED", true),
            logs_enabled: env_bool("OTEL_LOGS_ENABLED", true),
            log_format: detect_log_format(),
            log_level: env_or("RUST_LOG", "info"),
        }
    }
}

impl TelemetryConfig {
    pub fn from_env() -> Self {
        Self::default()
    }
}

fn env_or(key: &str, default: &str) -> String {
    std::env::var(key).unwrap_or_else(|_| default.to_string())
}

fn env_bool(key: &str, default: bool) -> bool {
    std::env::var(key)
        .map(|v| matches!(v.to_lowercase().as_str(), "true" | "1" | "yes" | "on"))
        .unwrap_or(default)
}

fn detect_otlp_protocol() -> OtlpProtocol {
    match std::env::var("OTEL_EXPORTER_OTLP_PROTOCOL")
        .unwrap_or_default()
        .to_lowercase()
        .as_str()
    {
        "http/protobuf" | "http/binary" => OtlpProtocol::HttpProtobuf,
        _ => OtlpProtocol::Grpc, // default to gRPC as project already depends on tonic
    }
}

fn detect_log_format() -> LogFormat {
    match std::env::var("LOG_FORMAT")
        .unwrap_or_else(|_| "json".to_string())
        .to_lowercase()
        .as_str()
    {
        "pretty" | "text" | "console" => LogFormat::Pretty,
        _ => LogFormat::Json, // default to JSON for structured logging
    }
}