//! Deterministic email ID generation using UUID v5.
//!
//! Emails synced from IMAP/JMAP get a UUID derived from their Message-ID header,
//! so the same email produces the same ID on every device. Manually created emails
//! (no Message-ID) fall back to random UUIDs.

use crate::id_types::EmailId;
use uuid::Uuid;

/// Fixed namespace UUID for GoingsOn email IDs (generated once, never changes).
pub const GOINGSON_EMAIL_NS: Uuid = Uuid::from_bytes([
    0x7a, 0x3b, 0x8c, 0x2d, 0x4e, 0x5f, 0x6a, 0x1b,
    0x9c, 0x0d, 0x8e, 0x7f, 0xa2, 0xb3, 0xc4, 0xd5,
]);

/// Generate a deterministic email ID from a Message-ID header.
///
/// - `Some(message_id)` → UUID v5 from namespace + message_id bytes
/// - `None` → random UUID v4 (for manually created emails without Message-ID)
pub fn deterministic_email_id(message_id: Option<&str>) -> EmailId {
    match message_id {
        Some(mid) => EmailId::from(Uuid::new_v5(&GOINGSON_EMAIL_NS, mid.as_bytes())),
        None => EmailId::new(),
    }
}

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

    #[test]
    fn same_message_id_same_uuid() {
        let a = deterministic_email_id(Some("<abc@example.com>"));
        let b = deterministic_email_id(Some("<abc@example.com>"));
        assert_eq!(a, b);
    }

    #[test]
    fn different_message_ids_different_uuids() {
        let a = deterministic_email_id(Some("<abc@example.com>"));
        let b = deterministic_email_id(Some("<def@example.com>"));
        assert_ne!(a, b);
    }

    #[test]
    fn none_gives_random_uuid() {
        let a = deterministic_email_id(None);
        let b = deterministic_email_id(None);
        assert_ne!(a, b);
    }

    #[test]
    fn v5_uuid_version() {
        let id = deterministic_email_id(Some("<test@example.com>"));
        assert_eq!(id.get_version_num(), 5);
    }
}