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//! Contains items responsible for dealing with the `"fmt "` chunk of wave files.

use std::convert::TryFrom;

/// Value signifying PCM data.
pub const WAV_FORMAT_PCM: u16 = 0x01;
/// Value signifying IEEE float data.
pub const WAV_FORMAT_IEEE_FLOAT: u16 = 0x03;

/// Structure for the `"fmt "` chunk of wave files, specifying key information
/// about the enclosed data.
///
/// This struct supports only PCM and IEEE float data, which is to say there is
/// no extra members for compressed format data.
#[derive(Debug, Default, Copy, Clone, Hash, PartialEq, Eq)]
#[allow(missing_docs)]
pub struct Header {
    pub audio_format: u16,
    pub channel_count: u16,
    pub sampling_rate: u32,
    pub bytes_per_second: u32,
    pub bytes_per_sample: u16,
    pub bits_per_sample: u16,
}

impl Header {
    /// Creates a new Header object.
    ///
    /// ## Note
    ///
    /// While the [`crate::read`] and [`crate::write`] functions only support
    /// uncompressed PCM/IEEE for the audio format, the option is given here to
    /// select any audio format for custom implementations of wave features.
    ///
    /// ## Parameters
    ///
    /// * `audio_format` - Audio format. Only [`WAV_FORMAT_PCM`] (0x01) and
    ///                    [`WAV_FORMAT_IEEE_FLOAT`] (0x03) are supported.
    /// * `channel_count` - Channel count, the number of channels each sample
    ///                     has. Generally 1 (mono) or 2 (stereo).
    /// * `sampling_rate` - Sampling rate (e.g. 44.1kHz, 48kHz, 96kHz, etc.).
    /// * `bits_per_sample` - Number of bits in each (sub-channel) sample.
    ///                       Generally 8, 16, 24, or 32.
    ///
    /// ## Example
    ///
    /// ```
    /// let h = wav::Header::new(wav::header::WAV_FORMAT_PCM, 2, 48_000, 16);
    /// ```
    pub fn new(
        audio_format: u16,
        channel_count: u16,
        sampling_rate: u32,
        bits_per_sample: u16,
    ) -> Header {
        Header {
            audio_format,
            channel_count,
            sampling_rate,
            bits_per_sample,
            bytes_per_second: (((bits_per_sample >> 3) * channel_count) as u32) * sampling_rate,
            bytes_per_sample: ((bits_per_sample >> 3) * channel_count) as u16,
        }
    }
}

impl From<Header> for [u8; 16] {
    fn from(h: Header) -> Self {
        let mut v: [u8; 16] = [0; 16];

        let b = h.audio_format.to_le_bytes();
        v[0] = b[0];
        v[1] = b[1];
        let b = h.channel_count.to_le_bytes();
        v[2] = b[0];
        v[3] = b[1];
        let b = h.sampling_rate.to_le_bytes();
        v[4] = b[0];
        v[5] = b[1];
        v[6] = b[2];
        v[7] = b[3];
        let b = h.bytes_per_second.to_le_bytes();
        v[8] = b[0];
        v[9] = b[1];
        v[10] = b[2];
        v[11] = b[3];
        let b = h.bytes_per_sample.to_le_bytes();
        v[12] = b[0];
        v[13] = b[1];
        let b = h.bits_per_sample.to_le_bytes();
        v[14] = b[0];
        v[15] = b[1];

        v
    }
}

impl From<[u8; 16]> for Header {
    fn from(v: [u8; 16]) -> Self {
        let audio_format = u16::from_le_bytes([v[0], v[1]]);
        let channel_count = u16::from_le_bytes([v[2], v[3]]);
        let sampling_rate = u32::from_le_bytes([v[4], v[5], v[6], v[7]]);
        let bytes_per_second = u32::from_le_bytes([v[8], v[9], v[10], v[11]]);
        let bytes_per_sample = u16::from_le_bytes([v[12], v[13]]);
        let bits_per_sample = u16::from_le_bytes([v[14], v[15]]);

        Header {
            audio_format,
            channel_count,
            sampling_rate,
            bytes_per_second,
            bytes_per_sample,
            bits_per_sample,
        }
    }
}

impl TryFrom<&[u8]> for Header {
    type Error = &'static str;

    /// ## Errors
    ///
    /// This function will return an error if the given slice is smaller than 16 bytes.
    fn try_from(v: &[u8]) -> Result<Self, Self::Error> {
        if v.len() < 16 {
            Err("Slice is smaller than the minimum-required 16 bytes")
        } else {
            let mut a: [u8; 16] = [0; 16];
            a.copy_from_slice(&v[0..16]);
            Ok(Header::from(a))
        }
    }
}