//! A transaction ID

use std::cmp::Ordering;
use std::fmt;
use std::str::FromStr;

use async_hash::{Digest, Hash, Output};
use async_trait::async_trait;
use get_size::GetSize;
use get_size_derive::*;
use rand::Rng;
use safecast::TryCastFrom;

use destream::IntoStream;

use tc_error::*;
use tcgeneric::{Id, NetworkTime};

/// A zero-values [`TxnId`].
pub const MIN_ID: TxnId = TxnId {
    timestamp: 0,
    nonce: 0,
};

/// The unique ID of a transaction, used for identity and ordering.
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash, GetSize)]
pub struct TxnId {
    timestamp: u64, // nanoseconds since Unix epoch
    nonce: u16,
}

impl TxnId {
    /// Construct a new `TxnId`.
    pub fn new(time: NetworkTime) -> Self {
        let mut rng = rand::thread_rng();
        let nonce = loop {
            let nonce = rng.gen();
            if nonce > 0 && nonce < (u16::MAX - 1) {
                break nonce;
            }
        };

        Self {
            timestamp: time.as_nanos(),
            nonce,
        }
    }

    /// Return the last valid TxnId before this one (e.g. to construct a range).
    pub fn prev(&self) -> Self {
        Self {
            timestamp: self.timestamp,
            nonce: self.nonce - 1,
        }
    }

    /// Return the timestamp of this `TxnId`.
    pub fn time(&self) -> NetworkTime {
        NetworkTime::from_nanos(self.timestamp)
    }

    /// Convert this `TxnId` into an [`Id`].
    pub fn to_id(&self) -> Id {
        Id::try_cast_from(self.to_string(), |_| {
            unreachable!("number failed ID validation")
        })
        .unwrap()
    }
}

impl FromStr for TxnId {
    type Err = TCError;

    fn from_str(s: &str) -> TCResult<TxnId> {
        let i = s
            .find('-')
            .ok_or_else(|| TCError::unexpected(s, "a transaction ID"))?;

        if i == s.len() - 1 {
            return Err(TCError::unexpected(s, "a transaction ID"));
        }

        let timestamp = &s[..i];
        let nonce = &s[i + 1..];

        let timestamp = timestamp
            .parse()
            .map_err(|cause| TCError::unexpected(timestamp, "a timestamp").consume(cause))?;

        let nonce = nonce
            .parse()
            .map_err(|cause| TCError::unexpected(nonce, "a nonce").consume(cause))?;

        Ok(TxnId { timestamp, nonce })
    }
}

impl Ord for TxnId {
    fn cmp(&self, other: &TxnId) -> std::cmp::Ordering {
        if self.timestamp == other.timestamp {
            self.nonce.cmp(&other.nonce)
        } else {
            self.timestamp.cmp(&other.timestamp)
        }
    }
}

impl PartialOrd for TxnId {
    fn partial_cmp(&self, other: &TxnId) -> Option<std::cmp::Ordering> {
        Some(self.cmp(other))
    }
}

impl PartialEq<str> for TxnId {
    fn eq(&self, other: &str) -> bool {
        if let Ok(other) = Self::from_str(other) {
            self == &other
        } else {
            false
        }
    }
}

impl PartialEq<Id> for TxnId {
    fn eq(&self, other: &Id) -> bool {
        self == other.as_str()
    }
}

impl PartialOrd<str> for TxnId {
    fn partial_cmp(&self, other: &str) -> Option<Ordering> {
        if let Ok(other) = Self::from_str(other) {
            self.partial_cmp(&other)
        } else {
            None
        }
    }
}

impl freqfs::Name for TxnId {
    fn partial_cmp(&self, other: &String) -> Option<Ordering> {
        if let Ok(other) = Self::from_str(other) {
            Some(self.cmp(&other))
        } else {
            None
        }
    }
}

#[async_trait]
impl destream::de::FromStream for TxnId {
    type Context = ();

    async fn from_stream<D: destream::de::Decoder>(
        context: (),
        d: &mut D,
    ) -> Result<Self, D::Error> {
        let s = <String as destream::de::FromStream>::from_stream(context, d).await?;
        Self::from_str(&s).map_err(destream::de::Error::custom)
    }
}

impl<'en> destream::en::IntoStream<'en> for TxnId {
    fn into_stream<E: destream::en::Encoder<'en>>(self, e: E) -> Result<E::Ok, E::Error> {
        self.to_string().into_stream(e)
    }
}

impl<'en> destream::en::ToStream<'en> for TxnId {
    fn to_stream<E: destream::en::Encoder<'en>>(&'en self, e: E) -> Result<E::Ok, E::Error> {
        self.to_string().into_stream(e)
    }
}

impl<D: Digest> Hash<D> for TxnId {
    fn hash(self) -> Output<D> {
        Hash::<D>::hash(&self)
    }
}

impl<'a, D: Digest> Hash<D> for &'a TxnId {
    fn hash(self) -> Output<D> {
        let mut bytes = [0u8; 10];
        bytes[..8].copy_from_slice(&self.timestamp.to_be_bytes());
        bytes[8..].copy_from_slice(&self.nonce.to_be_bytes());
        D::digest(&bytes)
    }
}

impl fmt::Display for TxnId {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}-{}", self.timestamp, self.nonce)
    }
}