// Symphonia
// Copyright (c) 2020 The Project Symphonia Developers.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

//! The `units` module provides definitions for common units.

/// A `TimeStamp` represents an instantenous instant in time since the start of a stream. One
/// `TimeStamp` "tick" is equivalent to the stream's `TimeBase` in seconds.
pub type TimeStamp = u64;

/// A `Duration` indicates a positive span of time.
pub type Duration = u64;

/// `Time` represents a duration of time in seconds, or the number of seconds since an arbitrary
/// epoch. `Time` is stored as an integer number of seconds plus any remaining fraction of a second
/// as a floating point value.
#[derive(Debug, Default, Copy, Clone, PartialEq, PartialOrd)]
pub struct Time {
    pub seconds: u64,
    pub frac: f64,
}

impl Time {
    const SECONDS_PER_MINUTE: u64 = 60;
    const SECONDS_PER_HOUR: u64 = 60 * 60;
    const NANOSECONDS_PER_SECOND: u32 = 1_000_000_000;
    const NANOSECONDS_PER_SECOND_INV: f64 = 1.0 / 1_000_000_000.0;

    pub fn new(seconds: u64, frac: f64) -> Self {
        Time { seconds, frac }
    }

    pub fn from_ss(s: u8, ns: u32) -> Option<Time> {
        if s > 59 || ns >= Time::NANOSECONDS_PER_SECOND {
            return None;
        }

        let seconds = u64::from(s);
        let frac = Time::NANOSECONDS_PER_SECOND_INV * f64::from(ns);

        Some(Time { seconds, frac })
    }

    pub fn from_mmss(m: u8, s: u8, ns: u32) -> Option<Time> {
        if m > 59 || s > 59 || ns >= Time::NANOSECONDS_PER_SECOND {
            return None;
        }

        let seconds = (Time::SECONDS_PER_MINUTE * u64::from(m)) + u64::from(s);
        let frac = Time::NANOSECONDS_PER_SECOND_INV * f64::from(ns);

        Some(Time { seconds, frac })
    }

    pub fn from_hhmmss(h: u32, m: u8, s: u8, ns: u32) -> Option<Time> {
        if m > 59 || s > 59 || ns >= Time::NANOSECONDS_PER_SECOND {
            return None;
        }

        let seconds = (Time::SECONDS_PER_HOUR * u64::from(h))
                            + (Time::SECONDS_PER_MINUTE * u64::from(m))
                            + u64::from(s);

        let frac = Time::NANOSECONDS_PER_SECOND_INV * f64::from(ns);

        Some(Time { seconds, frac })
    }
}

impl From<u8> for Time {
    fn from(seconds: u8) -> Self { Time::new(u64::from(seconds), 0.0) }
}

impl From<u16> for Time {
    fn from(seconds: u16) -> Self { Time::new(u64::from(seconds), 0.0) }
}

impl From<u32> for Time {
    fn from(seconds: u32) -> Self { Time::new(u64::from(seconds), 0.0) }
}

impl From<u64> for Time {
    fn from(seconds: u64) -> Self { Time::new(seconds, 0.0) }
}

impl From<f32> for Time {
    fn from(seconds: f32) -> Self {
        if seconds >= 0.0 {
            Time::new(seconds.trunc() as u64, f64::from(seconds.fract()))
        }
        else {
            Time::new(0, 0.0)
        }
    }
}

impl From<f64> for Time {
    fn from(seconds: f64) -> Self {
        if seconds >= 0.0 {
            Time::new(seconds.trunc() as u64, seconds.fract())
        }
        else {
            Time::new(0, 0.0)
        }
    }
}

#[derive(Debug, Default, Copy, Clone, PartialEq)]
/// A `TimeBase` is the conversion factor between a `TimeStamp` and real-world seconds.
pub struct TimeBase {
    /// The numerator.
    pub numer: u32,
    /// The denominator.
    pub denom: u32,
}

impl TimeBase {
    /// Creates a new `TimeBase`. Panics if either the numerator or denominator is 0.
    pub fn new(numer: u32, denom: u32) -> Self {
        if numer == 0 || denom == 0{
            panic!("TimeBase cannot have 0 numerator or denominator");
        }

        TimeBase { numer, denom }
    }

    /// Accurately calculates a `Time` using the `TimeBase` and the provided `TimeStamp`. On
    /// overflow, the seconds field of `Time` wraps.
    pub fn calc_time(&self, ts: TimeStamp) -> Time {
        assert!(self.numer > 0 && self.denom > 0, "TimeBase numerator or denominator are 0.");

        // The dividend requires up-to 96-bits (32-bit timebase numerator * 64-bit timestamp).
        let dividend = u128::from(ts) * u128::from(self.numer);

        // For an accurate floating point division, both the dividend and divisor must have an
        // accurate floating point representation. A 64-bit floating point value has a mantissa of
        // 52 bits and can therefore accurately represent a 52-bit integer. The divisor (the
        // denominator of the timebase) is limited to 32-bits. Therefore, if the dividend
        // requires less than 52-bits, a straight-forward floating point division can be used to
        // calculate the time.
        if dividend < (1 << 52) {
            let seconds = (dividend as f64) / f64::from(self.denom);

            Time::new(seconds.trunc() as u64, seconds.fract())
        }
        else {
            // If the dividend requires more than 52 bits, calculate the integer portion using
            // integer arithmetic, then calculate the fractional part separately.
            let quotient = dividend / u128::from(self.denom);

            // The remainder is the fractional portion before being divided by the divisor (the
            // denominator). The remainder will never equal or exceed the divisor (or else the
            // fractional part would be >= 1.0), so the remainder must fit within a u32.
            let rem = (dividend - (quotient * u128::from(self.denom))) as u32;

            // Calculate the fractional portion. Since both the remainder and denominator are 32-bit
            // integers now, 64-bit floating point division will provide enough accuracy.
            let frac = f64::from(rem) / f64::from(self.denom);

            Time::new(quotient as u64, frac)
        }
    }

    /// Accurately calculates a `TimeStamp` from the given `Time` using the `TimeBase` as the
    /// conversion factor. On overflow, the `TimeStamp` wraps.
    pub fn calc_timestamp(&self, time: Time) -> TimeStamp {
        assert!(self.numer > 0 && self.denom > 0, "TimeBase numerator or denominator are 0.");
        assert!(time.frac >= 0.0 && time.frac < 1.0, "Invalid range for Time fractional part.");

        // The dividing factor.
        let k = 1.0 / f64::from(self.numer);

        // Multiplying seconds by the denominator requires up-to 96-bits (32-bit timebase
        // denominator * 64-bit timestamp).
        let product = u128::from(time.seconds) * u128::from(self.denom);

        // Like calc_time, a 64-bit floating-point value only has 52-bits of integer precision.
        // If the product requires more than 52-bits, split the product into upper and lower parts
        // and multiply by k separately, before adding back together.
        let a = if product > (1 << 52) {
            // Split the 96-bit product into 48-bit halves.
            let u = ((product & !0xffff_ffff_ffff) >> 48) as u64;
            let l = ((product &  0xffff_ffff_ffff) >>  0) as u64;

            let uk = (u as f64) * k;
            let ul = (l as f64) * k;

            // Add the upper and lower halves.
            ((uk as u64) << 48).wrapping_add(ul as u64)
        }
        else {
            ((product as f64) * k) as u64
        };

        // The fractional portion can be calculate directly using floating point arithemtic.
        let b = (k * f64::from(self.denom) * time.frac) as u64;

        a.wrapping_add(b)
    }

}

impl From<TimeBase> for f64 {
    fn from(timebase: TimeBase) -> Self {
        f64::from(timebase.numer) / f64::from(timebase.denom)
    }
}

#[cfg(test)]
mod tests {
    use super::{Time, TimeBase};

    #[test]
    fn verify_timebase() {
        // Verify accuracy of timestamp -> time
        let tb1 = TimeBase::new(1, 320);

        assert_eq!(tb1.calc_time(0), Time::new(0, 0.0));
        assert_eq!(tb1.calc_time(12_345), Time::new(38, 0.578125));
        assert_eq!(tb1.calc_time(0x0f_ffff_ffff_ffff), Time::new(14_073_748_835_532, 0.796875));
        assert_eq!(tb1.calc_time(0x10_0000_0000_0001), Time::new(14_073_748_835_532, 0.803125));
        assert_eq!(tb1.calc_time(u64::MAX), Time::new(57_646_075_230_342_348, 0.796875));

        // Verify overflow wraps seconds
        let tb2 = TimeBase::new(320, 1);
        assert_eq!(tb2.calc_time(u64::MAX), Time::new(18_446_744_073_709_551_296, 0.0));

        // Verify accuracy of time -> timestamp
        assert_eq!(tb1.calc_timestamp(Time::new(0, 0.0)), 0);
        assert_eq!(tb1.calc_timestamp(Time::new(38, 0.578125)), 12_345);
        assert_eq!(tb1.calc_timestamp(Time::new(14_073_748_835_532, 0.796875)), 0x0f_ffff_ffff_ffff);
        assert_eq!(tb1.calc_timestamp(Time::new(14_073_748_835_532, 0.803125)), 0x10_0000_0000_0001);
        assert_eq!(tb1.calc_timestamp(Time::new(57_646_075_230_342_348, 0.796875)), u64::MAX);

    }

}