//! Server configuration from the environment (SPEC §10.4). The variable list is exhaustive.

use std::net::SocketAddr;
use std::path::PathBuf;

use crate::error::AppError;

/// Default of `KVITT_DATA_DIR`.
pub const DEFAULT_DATA_DIR: &str = "/data";
/// Default of `KVITT_BIND`.
pub const DEFAULT_BIND: &str = "0.0.0.0:8080";
/// Default of `KVITT_PUBLIC_URL`.
pub const DEFAULT_PUBLIC_URL: &str = "https://icehack.asuscomm.com:8443";
/// Default of `KVITT_FCM_CREDENTIALS`.
pub const DEFAULT_FCM_CREDENTIALS: &str = "/secrets/fcm-service-account.json";
/// Default of `KVITT_FCM_PROJECT_ID`.
pub const DEFAULT_FCM_PROJECT_ID: &str = "kvitt-1337";
/// Default of `KVITT_TRUSTED_PROXY`.
pub const DEFAULT_TRUSTED_PROXY: &str = "caddy";
/// Default of `RUST_LOG`.
pub const DEFAULT_LOG_FILTER: &str = "info";

/// File name of the database inside the data directory.
pub const DATABASE_FILE: &str = "kvitt.sqlite";

/// The server's configuration. `RUST_LOG` is read by the tracing set-up in `main`, not stored here.
///
/// Nothing here touches the network or the file system: a trusted proxy host that does not resolve and a missing
/// FCM key file are both normal (no proxy: the peer address is the client; no key: push disabled).
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Config {
    /// `KVITT_DATA_DIR`: holds `kvitt.sqlite`, `pictures/`, `apk/`.
    pub data_dir: PathBuf,
    /// `KVITT_BIND`: listen address.
    pub bind: SocketAddr,
    /// `KVITT_PUBLIC_URL`: used in invite links and the landing page. Stored without a trailing slash.
    pub public_url: String,
    /// `KVITT_FCM_CREDENTIALS`: service-account key; push is disabled if the file is missing.
    pub fcm_credentials: PathBuf,
    /// `KVITT_FCM_PROJECT_ID`.
    pub fcm_project_id: String,
    /// `KVITT_TRUSTED_PROXY`: host name whose resolved address may set `X-Forwarded-For`. Resolved lazily by the
    /// rate limiter; an unresolvable name means "no proxy".
    pub trusted_proxy: String,
}

impl Config {
    /// Reads the process environment.
    pub fn from_env() -> Result<Self, AppError> {
        Self::from_lookup(|key| std::env::var(key).ok())
    }

    /// Reads the variables through `lookup` (testable without touching the process environment). Empty values count
    /// as unset.
    pub fn from_lookup(lookup: impl Fn(&str) -> Option<String>) -> Result<Self, AppError> {
        let get = |key: &str, default: &str| {
            lookup(key)
                .filter(|v| !v.trim().is_empty())
                .unwrap_or_else(|| default.to_owned())
        };
        let bind_text = get("KVITT_BIND", DEFAULT_BIND);
        let bind: SocketAddr = bind_text.parse().map_err(|e| {
            AppError::new(
                crate::error::ErrorCode::Internal,
                format!("KVITT_BIND {bind_text:?} is not ip:port: {e}"),
            )
        })?;
        Ok(Self {
            data_dir: PathBuf::from(get("KVITT_DATA_DIR", DEFAULT_DATA_DIR)),
            bind,
            public_url: get("KVITT_PUBLIC_URL", DEFAULT_PUBLIC_URL)
                .trim_end_matches('/')
                .to_owned(),
            fcm_credentials: PathBuf::from(get("KVITT_FCM_CREDENTIALS", DEFAULT_FCM_CREDENTIALS)),
            fcm_project_id: get("KVITT_FCM_PROJECT_ID", DEFAULT_FCM_PROJECT_ID),
            trusted_proxy: get("KVITT_TRUSTED_PROXY", DEFAULT_TRUSTED_PROXY),
        })
    }

    /// `<data_dir>/kvitt.sqlite`.
    pub fn database_path(&self) -> PathBuf {
        self.data_dir.join(DATABASE_FILE)
    }

    /// `<data_dir>/pictures`.
    pub fn pictures_dir(&self) -> PathBuf {
        self.data_dir.join("pictures")
    }

    /// `<data_dir>/apk`.
    pub fn apk_dir(&self) -> PathBuf {
        self.data_dir.join("apk")
    }
}

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

    #[test]
    fn defaults_when_unset_or_empty() {
        let config = Config::from_lookup(|k| (k == "KVITT_BIND").then(String::new)).unwrap();
        assert_eq!(config.data_dir, PathBuf::from("/data"));
        assert_eq!(config.bind, "0.0.0.0:8080".parse().unwrap());
        assert_eq!(config.public_url, "https://icehack.asuscomm.com:8443");
        assert_eq!(
            config.fcm_credentials,
            PathBuf::from("/secrets/fcm-service-account.json")
        );
        assert_eq!(config.fcm_project_id, "kvitt-1337");
        assert_eq!(config.trusted_proxy, "caddy");
        assert_eq!(config.database_path(), PathBuf::from("/data/kvitt.sqlite"));
    }

    #[test]
    fn overrides() {
        let config = Config::from_lookup(|k| match k {
            "KVITT_DATA_DIR" => Some("/tmp/kvitt".into()),
            "KVITT_BIND" => Some("127.0.0.1:9000".into()),
            "KVITT_PUBLIC_URL" => Some("http://192.168.1.10:8080/".into()),
            _ => None,
        })
        .unwrap();
        assert_eq!(
            config.database_path(),
            PathBuf::from("/tmp/kvitt/kvitt.sqlite")
        );
        assert_eq!(config.bind, "127.0.0.1:9000".parse().unwrap());
        assert_eq!(config.public_url, "http://192.168.1.10:8080");
    }

    #[test]
    fn bad_bind_is_an_error() {
        assert!(Config::from_lookup(|k| (k == "KVITT_BIND").then(|| "nope".into())).is_err());
    }
}