use serde::{Deserialize, Serialize};
use time::Duration;

/// Configuration for the Altcha Proof-of-Work CAPTCHA module.
///
/// All fields have sensible defaults, so a [`PowSettings`] can be built with
/// `PowSettings::default()` and only the HMAC secret overridden.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PowSettings {
    /// HMAC secret used to sign challenges and used to verify submitted
    /// solutions. This MUST be set to a high-entropy value in production.
    pub hmac_secret: String,
    /// Key derivation algorithm, e.g. `"PBKDF2/SHA-256"`, `"SHA-256"`,
    /// `"ARGON2ID"`.
    pub algorithm: String,
    /// Algorithm-specific cost parameter. For `"PBKDF2/SHA-256"` this is the
    /// iteration count; for `"ARGON2ID"` it is the time cost.
    pub cost: u32,
    /// Length of the derived key in bytes.
    pub key_length: usize,
    /// Required hex prefix the derived key must start with. Lower values are
    /// harder to satisfy.
    pub key_prefix: String,
    /// Memory cost in KiB for memory-hard algorithms (Argon2id, Scrypt).
    pub memory_cost: Option<u32>,
    /// Parallelism factor for Argon2id and Scrypt.
    pub parallelism: Option<u32>,
    /// How long a generated challenge remains valid before it expires.
    pub challenge_ttl: Duration,
}

impl Default for PowSettings {
    fn default() -> Self {
        Self {
            hmac_secret: String::new(),
            algorithm: "PBKDF2/SHA-256".to_string(),
            cost: 100_000,
            key_length: 32,
            key_prefix: "00".to_string(),
            memory_cost: None,
            parallelism: None,
            challenge_ttl: Duration::minutes(5),
        }
    }
}