//! The implementation for Version 1 UUIDs.
//!
//! Note that you need feature `v1` in order to use these features.

use crate::prelude::*;
use core::sync::atomic;

/// The number of 100 ns ticks between the UUID epoch
/// `1582-10-15 00:00:00` and the Unix epoch `1970-01-01 00:00:00`.
const UUID_TICKS_BETWEEN_EPOCHS: u64 = 0x01B2_1DD2_1381_4000;

/// A thread-safe, stateful context for the v1 generator to help ensure
/// process-wide uniqueness.
#[derive(Debug)]
pub struct Context {
    count: atomic::AtomicUsize,
}

/// Stores the number of nanoseconds from an epoch and a counter for ensuring
/// V1 ids generated on the same host are unique.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct Timestamp {
    ticks: u64,
    counter: u16,
}

impl Timestamp {
    /// Construct a `Timestamp` from its raw component values: an RFC4122
    /// timestamp and counter.
    ///
    /// RFC4122, which defines the V1 UUID, specifies a 60-byte timestamp format
    /// as the number of 100-nanosecond intervals elapsed since 00:00:00.00,
    /// 15 Oct 1582, "the date of the Gregorian reform of the Christian
    /// calendar."
    ///
    /// The counter value is used to differentiate between ids generated by
    /// the same host computer in rapid succession (i.e. with the same observed
    /// time). See the [`ClockSequence`] trait for a generic interface to any
    /// counter generators that might be used.
    ///
    /// Internally, the timestamp is stored as a `u64`. For this reason, dates
    /// prior to October 1582 are not supported.
    ///
    /// [`ClockSequence`]: trait.ClockSequence.html
    pub const fn from_rfc4122(ticks: u64, counter: u16) -> Self {
        Timestamp { ticks, counter }
    }

    /// Construct a `Timestamp` from a unix timestamp and sequence-generating
    /// `context`.
    ///
    /// A unix timestamp represents the elapsed time since Jan 1 1970. Libc's
    /// `clock_gettime` and other popular implementations traditionally
    /// represent this duration as a `timespec`: a struct with `u64` and
    /// `u32` fields representing the seconds, and "subsecond" or fractional
    /// nanoseconds elapsed since the timestamp's second began,
    /// respectively.
    ///
    /// This constructs a `Timestamp` from the seconds and fractional
    /// nanoseconds of a unix timestamp, converting the duration since 1970
    /// into the number of 100-nanosecond intervals since 00:00:00.00, 15
    /// Oct 1582 specified by RFC4122 and used internally by `Timestamp`.
    ///
    /// The function is not guaranteed to produce monotonically increasing
    /// values however. There is a slight possibility that two successive
    /// equal time values could be supplied and the sequence counter wraps back
    /// over to 0.
    ///
    /// If uniqueness and monotonicity is required, the user is responsible for
    /// ensuring that the time value always increases between calls (including
    /// between restarts of the process and device).
    pub fn from_unix(
        context: impl ClockSequence,
        seconds: u64,
        subsec_nanos: u32,
    ) -> Self {
        let counter = context.generate_sequence(seconds, subsec_nanos);
        let ticks = UUID_TICKS_BETWEEN_EPOCHS
            + seconds * 10_000_000
            + u64::from(subsec_nanos) / 100;

        Timestamp { ticks, counter }
    }

    /// Returns the raw RFC4122 timestamp and counter values stored by the
    /// `Timestamp`.
    ///
    /// The timestamp (the first, `u64` element in the tuple) represents the
    /// number of 100-nanosecond intervals since 00:00:00.00, 15 Oct 1582.
    /// The counter is used to differentiate between ids generated on the
    /// same host computer with the same observed time.
    pub const fn to_rfc4122(&self) -> (u64, u16) {
        (self.ticks, self.counter)
    }

    /// Returns the timestamp converted to the seconds and fractional
    /// nanoseconds since Jan 1 1970.
    ///
    /// Internally, the time is stored in 100-nanosecond intervals,
    /// thus the maximum precision represented by the fractional nanoseconds
    /// value is less than its unit size (100 ns vs. 1 ns).
    pub const fn to_unix(&self) -> (u64, u32) {
        (
            (self.ticks - UUID_TICKS_BETWEEN_EPOCHS) / 10_000_000,
            ((self.ticks - UUID_TICKS_BETWEEN_EPOCHS) % 10_000_000) as u32
                * 100,
        )
    }

    /// Returns the timestamp converted into nanoseconds elapsed since Jan 1
    /// 1970. Internally, the time is stored in 100-nanosecond intervals,
    /// thus the maximum precision represented is less than the units it is
    /// measured in (100 ns vs. 1 ns). The value returned represents the
    /// same duration as [`Timestamp::to_unix`]; this provides it in nanosecond
    /// units for convenience.
    pub const fn to_unix_nanos(&self) -> u64 {
        (self.ticks - UUID_TICKS_BETWEEN_EPOCHS) * 100
    }
}

/// A trait that abstracts over generation of UUID v1 "Clock Sequence" values.
pub trait ClockSequence {
    /// Return a 16-bit number that will be used as the "clock sequence" in
    /// the UUID. The number must be different if the time has changed since
    /// the last time a clock sequence was requested.
    fn generate_sequence(&self, seconds: u64, subsec_nanos: u32) -> u16;
}

impl<'a, T: ClockSequence + ?Sized> ClockSequence for &'a T {
    fn generate_sequence(&self, seconds: u64, subsec_nanos: u32) -> u16 {
        (**self).generate_sequence(seconds, subsec_nanos)
    }
}

impl Uuid {
    /// Create a new UUID (version 1) using a time value + sequence +
    /// *NodeId*.
    ///
    /// When generating [`Timestamp`]s using a [`ClockSequence`], this function
    /// is only guaranteed to produce unique values if the following conditions
    /// hold:
    ///
    /// 1. The *NodeId* is unique for this process,
    /// 2. The *Context* is shared across all threads which are generating v1
    ///    UUIDs,
    /// 3. The [`ClockSequence`] implementation reliably returns unique
    ///    clock sequences (this crate provides [`Context`] for this
    ///    purpose. However you can create your own [`ClockSequence`]
    ///    implementation, if [`Context`] does not meet your needs).
    ///
    /// The NodeID must be exactly 6 bytes long.
    ///
    /// Note that usage of this method requires the `v1` feature of this crate
    /// to be enabled.
    ///
    /// # Examples
    ///
    /// A UUID can be created from a unix [`Timestamp`] with a
    /// [`ClockSequence`]:
    ///
    /// ```rust
    /// use uuid::v1::{Timestamp, Context};
    /// use uuid::Uuid;
    ///
    /// let context = Context::new(42);
    /// let ts = Timestamp::from_unix(&context, 1497624119, 1234);
    /// let uuid = Uuid::new_v1(ts, &[1, 2, 3, 4, 5, 6]).expect("failed to generate UUID");
    ///
    /// assert_eq!(
    ///     uuid.to_hyphenated().to_string(),
    ///     "f3b4958c-52a1-11e7-802a-010203040506"
    /// );
    /// ```
    ///
    /// The timestamp can also be created manually as per RFC4122:
    ///
    /// ```
    /// use uuid::v1::{Timestamp, Context};
    /// use uuid::Uuid;
    ///
    /// let context = Context::new(42);
    /// let ts = Timestamp::from_rfc4122(1497624119, 0);
    /// let uuid = Uuid::new_v1(ts, &[1, 2, 3, 4, 5, 6]).expect("failed to generate UUID");
    ///
    /// assert_eq!(
    ///     uuid.to_hyphenated().to_string(),
    ///     "5943ee37-0000-1000-8000-010203040506"
    /// );
    /// ```
    ///
    /// [`Timestamp`]: v1/struct.Timestamp.html
    /// [`ClockSequence`]: v1/struct.ClockSequence.html
    /// [`Context`]: v1/struct.Context.html
    pub fn new_v1(ts: Timestamp, node_id: &[u8]) -> Result<Self, crate::Error> {
        const NODE_ID_LEN: usize = 6;

        let len = node_id.len();
        if len != NODE_ID_LEN {
            Err(crate::builder::Error::new(NODE_ID_LEN, len))?;
        }

        let time_low = (ts.ticks & 0xFFFF_FFFF) as u32;
        let time_mid = ((ts.ticks >> 32) & 0xFFFF) as u16;
        let time_high_and_version =
            (((ts.ticks >> 48) & 0x0FFF) as u16) | (1 << 12);

        let mut d4 = [0; 8];

        {
            d4[0] = (((ts.counter & 0x3F00) >> 8) as u8) | 0x80;
            d4[1] = (ts.counter & 0xFF) as u8;
        }

        d4[2..].copy_from_slice(node_id);

        Uuid::from_fields(time_low, time_mid, time_high_and_version, &d4)
    }

    /// Returns an optional [`Timestamp`] storing the timestamp and
    /// counter portion parsed from a V1 UUID.
    ///
    /// Returns `None` if the supplied UUID is not V1.
    ///
    /// The V1 timestamp format defined in RFC4122 specifies a 60-bit
    /// integer representing the number of 100-nanosecond intervals
    /// since 00:00:00.00, 15 Oct 1582.
    ///
    /// [`Timestamp`] offers several options for converting the raw RFC4122
    /// value into more commonly-used formats, such as a unix timestamp.
    ///
    /// [`Timestamp`]: v1/struct.Timestamp.html
    pub fn to_timestamp(&self) -> Option<Timestamp> {
        if self
            .get_version()
            .map(|v| v != Version::Mac)
            .unwrap_or(true)
        {
            return None;
        }

        let ticks: u64 = u64::from(self.as_bytes()[6] & 0x0F) << 56
            | u64::from(self.as_bytes()[7]) << 48
            | u64::from(self.as_bytes()[4]) << 40
            | u64::from(self.as_bytes()[5]) << 32
            | u64::from(self.as_bytes()[0]) << 24
            | u64::from(self.as_bytes()[1]) << 16
            | u64::from(self.as_bytes()[2]) << 8
            | u64::from(self.as_bytes()[3]);

        let counter: u16 = u16::from(self.as_bytes()[8] & 0x3F) << 8
            | u16::from(self.as_bytes()[9]);

        Some(Timestamp::from_rfc4122(ticks, counter))
    }
}

impl Context {
    /// Creates a thread-safe, internally mutable context to help ensure
    /// uniqueness.
    ///
    /// This is a context which can be shared across threads. It maintains an
    /// internal counter that is incremented at every request, the value ends
    /// up in the clock_seq portion of the UUID (the fourth group). This
    /// will improve the probability that the UUID is unique across the
    /// process.
    pub const fn new(count: u16) -> Self {
        Self {
            count: atomic::AtomicUsize::new(count as usize),
        }
    }
}

impl ClockSequence for Context {
    fn generate_sequence(&self, _: u64, _: u32) -> u16 {
        (self.count.fetch_add(1, atomic::Ordering::SeqCst) & 0xffff) as u16
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    use crate::std::string::ToString;

    #[test]
    fn test_new_v1() {
        let time: u64 = 1_496_854_535;
        let time_fraction: u32 = 812_946_000;
        let node = [1, 2, 3, 4, 5, 6];
        let context = Context::new(0);

        {
            let uuid = Uuid::new_v1(
                Timestamp::from_unix(&context, time, time_fraction),
                &node,
            )
            .unwrap();

            assert_eq!(uuid.get_version(), Some(Version::Mac));
            assert_eq!(uuid.get_variant(), Some(Variant::RFC4122));
            assert_eq!(
                uuid.to_hyphenated().to_string(),
                "20616934-4ba2-11e7-8000-010203040506"
            );

            let ts = uuid.to_timestamp().unwrap().to_rfc4122();

            assert_eq!(ts.0 - 0x01B2_1DD2_1381_4000, 14_968_545_358_129_460);
            assert_eq!(ts.1, 0);
        };

        {
            let uuid2 = Uuid::new_v1(
                Timestamp::from_unix(&context, time, time_fraction),
                &node,
            )
            .unwrap();

            assert_eq!(
                uuid2.to_hyphenated().to_string(),
                "20616934-4ba2-11e7-8001-010203040506"
            );
            assert_eq!(uuid2.to_timestamp().unwrap().to_rfc4122().1, 1)
        };
    }
}