use base64::engine::general_purpose::URL_SAFE_NO_PAD;
use base64::Engine;
use rand_core::{OsRng, RngCore};
use sha2::{Digest, Sha256};

/// An opaque bearer token handed to the client exactly once at login.
/// Only its hash is persisted.
pub struct SessionToken(String);

impl std::fmt::Debug for SessionToken {
    /// Redacted so tokens cannot leak through logs or panic messages.
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str("SessionToken(<redacted>)")
    }
}

impl SessionToken {
    pub(crate) fn generate() -> SessionToken {
        let mut bytes = [0u8; 32];
        OsRng.fill_bytes(&mut bytes);
        SessionToken(URL_SAFE_NO_PAD.encode(bytes))
    }

    /// The secret value to return to the client. Deliberately not `Display`
    /// so tokens cannot leak into logs by accident.
    pub fn secret(&self) -> &str {
        &self.0
    }
}

/// Hash used as the storage key for a token.
pub(crate) fn hash_token(secret: &str) -> String {
    let digest = Sha256::digest(secret.as_bytes());
    URL_SAFE_NO_PAD.encode(digest)
}