use anyhow::bail;

pub mod matroska;
pub mod read;
pub mod write;

#[derive(Debug, Clone)]
pub enum Master {
    Start,
    End,
}

pub trait ValueFromBuf: Sized {
    fn from_buf(buf: &[u8]) -> anyhow::Result<Self>;
}

impl ValueFromBuf for u64 {
    fn from_buf(buf: &[u8]) -> anyhow::Result<Self> {
        if buf.len() > 8 {
            bail!("u64 too big")
        }
        let mut val = 0u64;
        for byte in buf {
            val <<= 8;
            val |= *byte as u64;
        }
        Ok(val)
    }
}
impl ValueFromBuf for i64 {
    fn from_buf(buf: &[u8]) -> anyhow::Result<Self> {
        if buf.len() > 8 {
            bail!("i64 too big")
        }
        Ok(if buf[0] > 127 {
            if buf.len() == 8 {
                i64::from_be_bytes(buf.try_into().unwrap())
            } else {
                -((1 << (buf.len() * 8)) - (u64::from_buf(buf)? as i64))
            }
        } else {
            u64::from_buf(buf)? as i64
        })
    }
}
impl ValueFromBuf for f64 {
    fn from_buf(buf: &[u8]) -> anyhow::Result<Self> {
        Ok(if buf.len() == 4 {
            f32::from_be_bytes(buf.try_into().unwrap()) as f64
        } else if buf.len() == 8 {
            f64::from_be_bytes(buf.try_into().unwrap())
        } else {
            bail!("float is not 4 or 8 bytes long");
        })
    }
}

impl ValueFromBuf for Vec<u8> {
    fn from_buf(buf: &[u8]) -> anyhow::Result<Self> {
        Ok(buf.to_vec())
    }
}
impl ValueFromBuf for String {
    fn from_buf(buf: &[u8]) -> anyhow::Result<Self> {
        Ok(String::from_utf8(Vec::from(buf))?)
    }
}
impl ValueFromBuf for Master {
    /// this has an internal usage, where buf has len of 1, when an end should be constructed
    fn from_buf(buf: &[u8]) -> anyhow::Result<Self> {
        Ok(match buf.len() {
            0 => Master::Start,
            1 => Master::End,
            _ => unreachable!(),
        })
    }
}