//! The `log` crate provides the foundational data structures for Proof-of-History,
//! an ordered log of events in time.

/// Each log entry contains three pieces of data. The 'num_hashes' field is the number
/// of hashes performed since the previous entry.  The 'id' field is the result
/// of hashing 'id' from the previous entry 'num_hashes' times.  The 'event'
/// field points to an Event that took place shortly after 'id' was generated.
///
/// If you divide 'num_hashes' by the amount of time it takes to generate a new hash, you
/// get a duration estimate since the last event. Since processing power increases
/// over time, one should expect the duration 'num_hashes' represents to decrease proportionally.
/// Though processing power varies across nodes, the network gives priority to the
/// fastest processor. Duration should therefore be estimated by assuming that the hash
/// was generated by the fastest processor at the time the entry was logged.

use hash::Sha256Hash;
use serde::Serialize;
use entry::{create_entry_mut, next_tick, Entry};
use event::Event;
use rayon::prelude::*;

/// Verifies the hashes and counts of a slice of events are all consistent.
pub fn verify_slice(events: &[Entry<Sha256Hash>], start_hash: &Sha256Hash) -> bool {
    let genesis = [Entry::new_tick(Default::default(), start_hash)];
    let event_pairs = genesis.par_iter().chain(events).zip(events);
    event_pairs.all(|(x0, x1)| x1.verify(&x0.id))
}

/// Verifies the hashes and counts of a slice of events are all consistent.
pub fn verify_slice_i64(events: &[Entry<i64>], start_hash: &Sha256Hash) -> bool {
    let genesis = [Entry::new_tick(Default::default(), start_hash)];
    let event_pairs = genesis.par_iter().chain(events).zip(events);
    event_pairs.all(|(x0, x1)| x1.verify(&x0.id))
}

/// Verifies the hashes and events serially. Exists only for reference.
pub fn verify_slice_seq<T: Serialize>(events: &[Entry<T>], start_hash: &Sha256Hash) -> bool {
    let genesis = [Entry::new_tick(0, start_hash)];
    let mut event_pairs = genesis.iter().chain(events).zip(events);
    event_pairs.all(|(x0, x1)| x1.verify(&x0.id))
}

pub fn create_entries<T: Serialize>(
    start_hash: &Sha256Hash,
    events: Vec<Event<T>>,
) -> Vec<Entry<T>> {
    let mut id = *start_hash;
    events
        .into_iter()
        .map(|event| create_entry_mut(&mut id, &mut 0, event))
        .collect()
}

/// Create a vector of Ticks of length 'len' from 'start_hash' hash and 'num_hashes'.
pub fn next_ticks(start_hash: &Sha256Hash, num_hashes: u64, len: usize) -> Vec<Entry<Sha256Hash>> {
    let mut id = *start_hash;
    let mut ticks = vec![];
    for _ in 0..len {
        let entry = next_tick(&id, num_hashes);
        id = entry.id;
        ticks.push(entry);
    }
    ticks
}

#[cfg(test)]
mod tests {
    use super::*;
    use signature::{generate_keypair, get_pubkey};
    use transaction::Transaction;
    use hash::hash;

    fn verify_slice_generic(verify_slice: fn(&[Entry<Sha256Hash>], &Sha256Hash) -> bool) {
        let zero = Sha256Hash::default();
        let one = hash(&zero);
        assert!(verify_slice(&vec![], &zero)); // base case
        assert!(verify_slice(&vec![Entry::new_tick(0, &zero)], &zero)); // singleton case 1
        assert!(!verify_slice(&vec![Entry::new_tick(0, &zero)], &one)); // singleton case 2, bad
        assert!(verify_slice(&next_ticks(&zero, 0, 2), &zero)); // inductive step

        let mut bad_ticks = next_ticks(&zero, 0, 2);
        bad_ticks[1].id = one;
        assert!(!verify_slice(&bad_ticks, &zero)); // inductive step, bad
    }

    #[test]
    fn test_verify_slice() {
        verify_slice_generic(verify_slice);
    }

    #[test]
    fn test_verify_slice_seq() {
        verify_slice_generic(verify_slice_seq::<Sha256Hash>);
    }

    #[test]
    fn test_reorder_attack() {
        let zero = Sha256Hash::default();
        let one = hash(&zero);

        // First, verify entries
        let keypair = generate_keypair();
        let tr0 = Transaction::new(&keypair, get_pubkey(&keypair), zero, zero);
        let tr1 = Transaction::new(&keypair, get_pubkey(&keypair), one, zero);
        let events = vec![Event::Transaction(tr0), Event::Transaction(tr1)];
        let mut entries = create_entries(&zero, events);
        assert!(verify_slice(&entries, &zero));

        // Next, swap two events and ensure verification fails.
        let event0 = entries[0].event.clone();
        let event1 = entries[1].event.clone();
        entries[0].event = event1;
        entries[1].event = event0;
        assert!(!verify_slice(&entries, &zero));
    }
}

#[cfg(all(feature = "unstable", test))]
mod bench {
    extern crate test;
    use self::test::Bencher;
    use log::*;

    #[bench]
    fn event_bench(bencher: &mut Bencher) {
        let start_hash = Default::default();
        let events = next_ticks(&start_hash, 10_000, 8);
        bencher.iter(|| {
            assert!(verify_slice(&events, &start_hash));
        });
    }

    #[bench]
    fn event_bench_seq(bencher: &mut Bencher) {
        let start_hash = Default::default();
        let events = next_ticks(&start_hash, 10_000, 8);
        bencher.iter(|| {
            assert!(verify_slice_seq(&events, &start_hash));
        });
    }
}