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use std::time::Duration;

use Sample;
use Source;

/// Internal function that builds a `TakeDuration` object.
pub fn take_duration<I>(input: I, duration: Duration) -> TakeDuration<I> {
    TakeDuration {
        input: input,
        remaining_duration: duration,
        requested_duration: duration,
    }
}

/// A source that repeats the given source.
#[derive(Clone, Debug)]
pub struct TakeDuration<I> {
    input: I,
    remaining_duration: Duration,
    requested_duration: Duration,
}

impl<I> TakeDuration<I>
where
    I: Source,
    I::Item: Sample,
{
    /// Returns the duration elapsed for each sample extracted.
    #[inline]
    fn get_duration_per_sample(&self) -> Duration {
        let ns = 1000000000 / (self.input.sample_rate() as u64 * self.channels() as u64);
        // \|/ the maximum value of `ns` is one billion, so this can't fail
        Duration::new(0, ns as u32)
    }

    /// Returns a reference to the inner source.
    #[inline]
    pub fn inner(&self) -> &I {
        &self.input
    }

    /// Returns a mutable reference to the inner source.
    #[inline]
    pub fn inner_mut(&mut self) -> &mut I {
        &mut self.input
    }

    /// Returns the inner source.
    #[inline]
    pub fn into_inner(self) -> I {
        self.input
    }
}

impl<I> Iterator for TakeDuration<I>
where
    I: Source,
    I::Item: Sample,
{
    type Item = <I as Iterator>::Item;

    fn next(&mut self) -> Option<<I as Iterator>::Item> {
        let duration_per_sample = self.get_duration_per_sample();

        if self.remaining_duration <= duration_per_sample {
            None
        } else {
            if let Some(sample) = self.input.next() {
                self.remaining_duration = self.remaining_duration - duration_per_sample;
                Some(sample)
            } else {
                None
            }
        }
    }

    // TODO: size_hint
}

impl<I> Source for TakeDuration<I>
where
    I: Iterator + Source,
    I::Item: Sample,
{
    #[inline]
    fn current_frame_len(&self) -> Option<usize> {
        let remaining_nanosecs = self.remaining_duration.as_secs() * 1000000000
            + self.remaining_duration.subsec_nanos() as u64;
        let remaining_samples = remaining_nanosecs * self.input.sample_rate() as u64
            * self.channels() as u64 / 1000000000;

        if let Some(value) = self.input.current_frame_len() {
            if (value as u64) < remaining_samples {
                Some(value)
            } else {
                Some(remaining_samples as usize)
            }
        } else {
            Some(remaining_samples as usize)
        }
    }

    #[inline]
    fn channels(&self) -> u16 {
        self.input.channels()
    }

    #[inline]
    fn sample_rate(&self) -> u32 {
        self.input.sample_rate()
    }

    #[inline]
    fn total_duration(&self) -> Option<Duration> {
        if let Some(duration) = self.input.total_duration() {
            if duration < self.requested_duration {
                Some(duration)
            } else {
                Some(self.requested_duration)
            }
        } else {
            None
        }
    }
}