// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

//! Defines the internal connection ID

/// A connection ID which is stable and internally identifies a connection over
/// the whole lifetime of an endpoint.
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct InternalConnectionId(u64);

/// Generates internal connection IDs.
///
/// Connection IDs are only internal if they are generated by the same generator.
pub struct InternalConnectionIdGenerator {
    next: u64,
}

impl InternalConnectionIdGenerator {
    /// Returns a new InternalConnectionIdGenerator
    pub fn new() -> Self {
        Self { next: 0 }
    }

    /// Returns a new InternalConnectionId
    pub fn generate_id(&mut self) -> InternalConnectionId {
        let result = self.next;
        // This should never happen in production.
        // If the generator generates 1 million IDs per second,
        // the number will overflow after 213503982 days of operation.
        // Even with 1 billion IDs per second - which requires the CPU to spend
        // a significant amount of time generating IDs - it will take years to
        // overflow.
        self.next = self.next.checked_add(1).expect("Connection ID overflow");

        InternalConnectionId(result)
    }
}

impl From<InternalConnectionId> for u64 {
    fn from(internal_conn_id: InternalConnectionId) -> u64 {
        internal_conn_id.0
    }
}

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

    #[test]
    fn connection_id_generator_test() {
        let mut id_generator = InternalConnectionIdGenerator::new();

        for i in 0..128u64 {
            let id = id_generator.generate_id();
            assert_eq!(InternalConnectionId(i), id);
        }
    }
}