qubit-id 0.2.3

/*******************************************************************************
 *
 *    Copyright (c) 2026 Haixing Hu.
 *
 *    SPDX-License-Identifier: Apache-2.0
 *
 *    Licensed under the Apache License, Version 2.0.
 *
 ******************************************************************************/
//! Sonyflake-style 63-bit ID generator.

use std::sync::{
    Arc,
    Mutex,
};
use std::thread;
use std::time::{
    Duration,
    SystemTime,
    UNIX_EPOCH,
};

use super::time_slice::TimeSlice;
use crate::{
    IdError,
    IdGenerator,
};

const DEFAULT_BITS_SEQUENCE: u8 = 8;
const DEFAULT_BITS_MACHINE: u8 = 16;
const DEFAULT_TIME_UNIT_NANOS: u128 = 10_000_000;
const MIN_TIME_UNIT_NANOS: u128 = 1_000_000;
const DEFAULT_START_MILLIS: u64 = 1_735_689_600_000;

/// Sonyflake-style generator using configurable time, sequence, and machine bits.
///
/// By default, the layout is compatible with Sonyflake's commonly documented
/// allocation: 39 bits of time in 10 ms units, 8 sequence bits, and 16 machine
/// bits. The sign bit is not used.
pub struct SonyflakeGenerator {
    bits_time: u8,
    bits_sequence: u8,
    bits_machine: u8,
    time_unit: Duration,
    start_time: SystemTime,
    machine_id: u64,
    clock: Arc<dyn Fn() -> SystemTime + Send + Sync>,
    state: Mutex<TimeSlice>,
}

impl SonyflakeGenerator {
    /// Creates a Sonyflake-style generator with default layout and epoch.
    ///
    /// # Parameters
    /// - `machine_id`: Machine identifier in `0..=65535`.
    ///
    /// # Returns
    /// A configured generator.
    ///
    /// # Errors
    /// Returns [`IdError::MachineIdOutOfRange`] when `machine_id` does not fit
    /// in the default 16-bit machine field.
    pub fn new(machine_id: u64) -> Result<Self, IdError> {
        Self::with_epoch(
            machine_id,
            UNIX_EPOCH + Duration::from_millis(DEFAULT_START_MILLIS),
        )
    }

    /// Creates a Sonyflake-style generator with default layout and explicit epoch.
    ///
    /// # Parameters
    /// - `machine_id`: Machine identifier in `0..=65535`.
    /// - `start_time`: Start time used as elapsed-time origin.
    ///
    /// # Returns
    /// A configured generator using the system clock.
    ///
    /// # Errors
    /// Returns the same errors as [`SonyflakeGenerator::with_options`].
    pub fn with_epoch(machine_id: u64, start_time: SystemTime) -> Result<Self, IdError> {
        Self::with_options(
            machine_id,
            DEFAULT_BITS_SEQUENCE,
            DEFAULT_BITS_MACHINE,
            Duration::from_nanos(DEFAULT_TIME_UNIT_NANOS as u64),
            start_time,
        )
    }

    /// Creates a Sonyflake-style generator with explicit layout.
    ///
    /// Passing `0` for either bit length selects the Sonyflake default for that
    /// field.
    ///
    /// # Parameters
    /// - `machine_id`: Machine identifier.
    /// - `bits_sequence`: Sequence bit length, or `0` for default.
    /// - `bits_machine_id`: Machine bit length, or `0` for default.
    /// - `time_unit`: Time unit; must be at least one millisecond.
    /// - `start_time`: Start time used as elapsed-time origin.
    ///
    /// # Returns
    /// A configured generator using the system clock.
    ///
    /// # Errors
    /// Returns [`IdError::InvalidBitLength`] for invalid bit allocation,
    /// [`IdError::InvalidTimeUnit`] for sub-millisecond time units,
    /// [`IdError::StartTimeAhead`] when `start_time` is in the future, or
    /// [`IdError::MachineIdOutOfRange`] when `machine_id` does not fit.
    pub fn with_options(
        machine_id: u64,
        bits_sequence: u8,
        bits_machine_id: u8,
        time_unit: Duration,
        start_time: SystemTime,
    ) -> Result<Self, IdError> {
        Self::with_clock(
            machine_id,
            bits_sequence,
            bits_machine_id,
            time_unit,
            start_time,
            SystemTime::now,
        )
    }

    /// Creates a Sonyflake-style generator with an explicit clock.
    ///
    /// # Parameters
    /// - `machine_id`: Machine identifier.
    /// - `bits_sequence`: Sequence bit length, or `0` for default.
    /// - `bits_machine_id`: Machine bit length, or `0` for default.
    /// - `time_unit`: Time unit; must be at least one millisecond.
    /// - `start_time`: Start time used as elapsed-time origin.
    /// - `clock`: Function returning the current time.
    ///
    /// # Returns
    /// A configured generator.
    ///
    /// # Errors
    /// Returns the same validation errors as [`SonyflakeGenerator::with_options`].
    pub fn with_clock<F>(
        machine_id: u64,
        bits_sequence: u8,
        bits_machine_id: u8,
        time_unit: Duration,
        start_time: SystemTime,
        clock: F,
    ) -> Result<Self, IdError>
    where
        F: Fn() -> SystemTime + Send + Sync + 'static,
    {
        let bits_sequence = Self::normalize_bits("sequence", bits_sequence, DEFAULT_BITS_SEQUENCE)?;
        let bits_machine = Self::normalize_bits("machine", bits_machine_id, DEFAULT_BITS_MACHINE)?;
        let bits_time = 63_u8
            .checked_sub(bits_sequence)
            .and_then(|value| value.checked_sub(bits_machine))
            .ok_or(IdError::InvalidBitLength {
                name: "time",
                bits: 0,
                reason: "63 - sequence bits - machine bits must be at least 32",
            })?;
        if bits_time < 32 {
            return Err(IdError::InvalidBitLength {
                name: "time",
                bits: bits_time,
                reason: "time bit length must be at least 32",
            });
        }

        let nanos = time_unit.as_nanos();
        if nanos < MIN_TIME_UNIT_NANOS {
            return Err(IdError::InvalidTimeUnit {
                nanos,
                min_nanos: MIN_TIME_UNIT_NANOS,
            });
        }

        if start_time > clock() {
            return Err(IdError::StartTimeAhead);
        }

        let max_machine_id = (1_u64 << bits_machine) - 1;
        if machine_id > max_machine_id {
            return Err(IdError::MachineIdOutOfRange {
                machine_id,
                max: max_machine_id,
            });
        }

        Ok(Self {
            bits_time,
            bits_sequence,
            bits_machine,
            time_unit,
            start_time,
            machine_id,
            clock: Arc::new(clock),
            state: Mutex::new(TimeSlice::with_sequence(0, (1_u64 << bits_sequence) - 1)),
        })
    }

    /// Normalizes and validates a Sonyflake bit length.
    ///
    /// # Parameters
    /// - `name`: Name of the setting for diagnostics.
    /// - `bits`: Provided bit length.
    /// - `default_bits`: Default bit length used when `bits` is zero.
    ///
    /// # Returns
    /// Normalized bit length.
    ///
    /// # Errors
    /// Returns [`IdError::InvalidBitLength`] when the normalized value is 31 or
    /// greater.
    fn normalize_bits(name: &'static str, bits: u8, default_bits: u8) -> Result<u8, IdError> {
        let normalized = if bits == 0 { default_bits } else { bits };
        if normalized >= 31 {
            return Err(IdError::InvalidBitLength {
                name,
                bits: normalized,
                reason: "bit length must be less than 31",
            });
        }
        Ok(normalized)
    }

    /// Returns the number of time bits.
    ///
    /// # Returns
    /// Time bit length.
    pub const fn bits_time(&self) -> u8 {
        self.bits_time
    }

    /// Returns the number of sequence bits.
    ///
    /// # Returns
    /// Sequence bit length.
    pub const fn bits_sequence(&self) -> u8 {
        self.bits_sequence
    }

    /// Returns the number of machine bits.
    ///
    /// # Returns
    /// Machine bit length.
    pub const fn bits_machine(&self) -> u8 {
        self.bits_machine
    }

    /// Returns the maximum representable elapsed time unit.
    ///
    /// # Returns
    /// Maximum elapsed time value.
    pub const fn max_elapsed_time(&self) -> u64 {
        (1_u64 << self.bits_time) - 1
    }

    /// Returns the maximum representable sequence.
    ///
    /// # Returns
    /// Maximum sequence number.
    pub const fn max_sequence(&self) -> u64 {
        (1_u64 << self.bits_sequence) - 1
    }

    /// Returns the maximum representable machine identifier.
    ///
    /// # Returns
    /// Maximum machine identifier.
    pub const fn max_machine_id(&self) -> u64 {
        (1_u64 << self.bits_machine) - 1
    }

    /// Composes a Sonyflake-style ID from explicit parts.
    ///
    /// # Parameters
    /// - `elapsed_time`: Time units elapsed since the start time.
    /// - `sequence`: Sequence value inside the time unit.
    /// - `machine_id`: Machine identifier.
    ///
    /// # Returns
    /// Encoded ID.
    ///
    /// # Errors
    /// Returns range errors when any part does not fit the configured layout.
    pub fn compose(
        &self,
        elapsed_time: u64,
        sequence: u64,
        machine_id: u64,
    ) -> Result<u64, IdError> {
        if elapsed_time > self.max_elapsed_time() {
            return Err(IdError::TimestampOverflow {
                timestamp: elapsed_time,
                max: self.max_elapsed_time(),
            });
        }
        if sequence > self.max_sequence() {
            return Err(IdError::SequenceOverflow {
                sequence,
                max: self.max_sequence(),
            });
        }
        if machine_id > self.max_machine_id() {
            return Err(IdError::MachineIdOutOfRange {
                machine_id,
                max: self.max_machine_id(),
            });
        }
        Ok((elapsed_time << (self.bits_sequence + self.bits_machine))
            | (sequence << self.bits_machine)
            | machine_id)
    }

    /// Extracts elapsed time from a Sonyflake-style ID.
    ///
    /// # Parameters
    /// - `id`: ID generated by this layout.
    ///
    /// # Returns
    /// Elapsed time units since the start time.
    pub fn extract_elapsed_time(&self, id: u64) -> u64 {
        id >> (self.bits_sequence + self.bits_machine)
    }

    /// Extracts sequence from a Sonyflake-style ID.
    ///
    /// # Parameters
    /// - `id`: ID generated by this layout.
    ///
    /// # Returns
    /// Sequence number.
    pub fn extract_sequence(&self, id: u64) -> u64 {
        let mask = ((1_u64 << self.bits_sequence) - 1) << self.bits_machine;
        (id & mask) >> self.bits_machine
    }

    /// Extracts machine ID from a Sonyflake-style ID.
    ///
    /// # Parameters
    /// - `id`: ID generated by this layout.
    ///
    /// # Returns
    /// Machine identifier.
    pub fn extract_machine_id(&self, id: u64) -> u64 {
        id & ((1_u64 << self.bits_machine) - 1)
    }

    /// Converts a time value into elapsed Sonyflake units.
    ///
    /// # Parameters
    /// - `time`: Time to convert.
    ///
    /// # Returns
    /// Elapsed time units since the start time.
    ///
    /// # Errors
    /// Returns [`IdError::TimeBeforeEpoch`] when `time` is before `start_time`.
    fn elapsed_time_for(&self, time: SystemTime) -> Result<u64, IdError> {
        let elapsed = time
            .duration_since(self.start_time)
            .map_err(|_| IdError::TimeBeforeEpoch)?;
        let elapsed_units = elapsed.as_nanos() / self.time_unit.as_nanos();
        if elapsed_units > u128::from(self.max_elapsed_time()) {
            return Err(IdError::TimestampOverflow {
                timestamp: u64::try_from(elapsed_units).unwrap_or(u64::MAX),
                max: self.max_elapsed_time(),
            });
        }
        Ok(elapsed_units as u64)
    }

    /// Reads the current elapsed time from the configured clock.
    ///
    /// # Returns
    /// Current elapsed time units.
    ///
    /// # Errors
    /// Returns [`IdError::TimeBeforeEpoch`] when the clock is before start time.
    fn current_elapsed_time(&self) -> Result<u64, IdError> {
        self.elapsed_time_for((self.clock)())
    }
}

impl IdGenerator<u64> for SonyflakeGenerator {
    type Error = IdError;

    /// Generates the next Sonyflake-style ID.
    fn next_id(&self) -> Result<u64, Self::Error> {
        let mut state = self
            .state
            .lock()
            .expect("generator state mutex should not be poisoned");
        let current = self.current_elapsed_time()?;

        if state.timestamp < current {
            state.timestamp = current;
            state.sequence = 0;
        } else {
            state.sequence = (state.sequence + 1) & self.max_sequence();
            if state.sequence == 0 {
                state.timestamp += 1;
                let overtime = state.timestamp.saturating_sub(current);
                drop(state);
                thread::sleep(Duration::from_nanos(
                    (u128::from(overtime) * self.time_unit.as_nanos()) as u64,
                ));
                state = self
                    .state
                    .lock()
                    .expect("generator state mutex should not be poisoned");
            }
        }

        self.compose(state.timestamp, state.sequence, self.machine_id)
    }
}