//! # riff
//! 
//! `riff` provides utility methods for reading and writing RIFF-formatted files,
//! such as Microsoft Wave, AVI or DLS files.

use std::fmt;
use std::io::Read;
use std::io::Write;
use std::io::Seek;
use std::io::SeekFrom;
use std::convert::TryInto;

/// A chunk id, also known as FourCC
#[derive(PartialEq, Eq, Clone)]
pub struct ChunkId {
  /// The raw bytes of the id
  pub value: [u8; 4]
}

/// The `RIFF` id
pub static RIFF_ID: ChunkId = ChunkId { value: [0x52, 0x49, 0x46, 0x46] };

/// The `LIST` id
pub static LIST_ID: ChunkId = ChunkId { value: [0x4C, 0x49, 0x53, 0x54] };

/// The `seqt` id
pub static SEQT_ID: ChunkId = ChunkId { value: [0x73, 0x65, 0x71, 0x74] };

impl ChunkId {
  /// Returns the value of the id as a string.
  /// 
  /// # Examples
  /// ```
  /// assert_eq!(riff::RIFF_ID.as_str(), "RIFF");
  /// ```
  /// 
  /// # Panics
  /// This function panics when the value does not represent a valid UTF-8 string.
  pub fn as_str(&self) -> &str {
    std::str::from_utf8(&self.value).unwrap()
  }

  /// Creates a new ChunkId from a string.
  /// 
  /// # Examples
  /// ```
  /// # use std::error::Error;
  /// #
  /// # fn try_main() -> Result<(), Box<Error>> {
  /// let chunk_id = riff::ChunkId::new("RIFF")?;
  /// #   Ok(())
  /// # }
  /// #
  /// # fn main() {
  /// #     try_main().unwrap();
  /// # }
  /// ```
  /// 
  /// # Errors
  /// The function fails when the string's length in bytes is not exactly 4.
  pub fn new(s: &str) -> Result<ChunkId, &str> {
    let bytes = s.as_bytes();
    if bytes.len() != 4 {
      Err("Invalid length")
    } else {
      let mut a: [u8; 4] = Default::default();
      a.copy_from_slice(&bytes[..]);
      Ok(ChunkId { value: a })
    }
  }
}

impl fmt::Display for ChunkId {
  fn fmt(&self, f: &mut std::fmt::Formatter) -> fmt::Result {
        write!(f, "'{}'", self.as_str())
  }
}

impl fmt::Debug for ChunkId {
  fn fmt(&self, f: &mut std::fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self)
  }
}

#[derive(PartialEq, Debug)]
pub enum ChunkContents {
  Data(ChunkId, Vec<u8>),
  Children(ChunkId, ChunkId, Vec<ChunkContents>),
  ChildrenNoType(ChunkId, Vec<ChunkContents>)
}

impl ChunkContents {
  pub fn write<T>(&self, writer: &mut T) -> std::io::Result<u64>
      where T: Seek + Write {
    match &self {
      &ChunkContents::Data(id, data) => {
        if data.len() as u64 > u32::MAX as u64 {
          use std::io::{Error, ErrorKind};
          return Err(Error::new(ErrorKind::InvalidData, "Data too big"));
        }

        let len = data.len() as u32;
        writer.write_all(&id.value)?;
        writer.write_all(&len.to_le_bytes())?;
        writer.write_all(&data)?;
        if len % 2 != 0 {
          let single_byte: [u8; 1] = [0];
          writer.write_all(&single_byte)?;
        }
        Ok((8 + len + (len % 2)).into())
      }
      &ChunkContents::Children(id, chunk_type, children) => {
        writer.write_all(&id.value)?;
        let len_pos = writer.seek(SeekFrom::Current(0))?;
        let zeros: [u8; 4] = [0, 0, 0, 0];
        writer.write_all(&zeros)?;
        writer.write_all(&chunk_type.value)?;
        let mut total_len: u64 = 4;
        for child in children {
          total_len = total_len + child.write(writer)?;
        }

        if total_len > u32::MAX as u64 {
          use std::io::{Error, ErrorKind};
          return Err(Error::new(ErrorKind::InvalidData, "Data too big"));
        }

        let end_pos = writer.seek(SeekFrom::Current(0))?;
        writer.seek(SeekFrom::Start(len_pos))?;
        writer.write_all(&(total_len as u32).to_le_bytes())?;
        writer.seek(SeekFrom::Start(end_pos))?;

        Ok((8 + total_len + (total_len % 2)).into())
      }
      &ChunkContents::ChildrenNoType(id, children) => {
        writer.write_all(&id.value)?;
        let len_pos = writer.seek(SeekFrom::Current(0))?;
        let zeros: [u8; 4] = [0, 0, 0, 0];
        writer.write_all(&zeros)?;
        let mut total_len: u64 = 0;
        for child in children {
          total_len = total_len + child.write(writer)?;
        }

        if total_len > u32::MAX as u64 {
          use std::io::{Error, ErrorKind};
          return Err(Error::new(ErrorKind::InvalidData, "Data too big"));
        }

        let end_pos = writer.seek(SeekFrom::Current(0))?;
        writer.seek(SeekFrom::Start(len_pos))?;
        writer.write_all(&(total_len as u32).to_le_bytes())?;
        writer.seek(SeekFrom::Start(end_pos))?;

        Ok((8 + total_len + (total_len % 2)).into())
      }
    }
  }
}

/// A chunk, also known as a form
#[derive(PartialEq, Eq, Debug)]
pub struct Chunk {
  pos: u64,
  id: ChunkId,
  len: u32,
}

/// An iterator over the children of a `Chunk`
pub struct Iter<'a, T>
    where T: Seek + Read {
  end: u64,
  cur: u64,
  stream: &'a mut T
}

impl<'a, T> Iterator for Iter<'a, T>
    where T: Seek + Read {
  type Item = Chunk;

  fn next(&mut self) -> Option<Self::Item> {
    if self.cur >= self.end {
      return None
    }

    let chunk = Chunk::read(&mut self.stream, self.cur).unwrap();
    let len = chunk.len() as u64;
    self.cur = self.cur + len + 8 + (len % 2);
    Some(chunk)
  }
}

impl Chunk {
  /// Returns the `ChunkId` of this chunk.
  pub fn id(&self) -> ChunkId {
    self.id.clone()
  }

  /// Returns the number of bytes in this chunk.
  pub fn len(&self) -> u32 {
    self.len
  }

  /// Returns the offset of this chunk from the start of the stream.
  pub fn offset(&self) -> u64 {
    self.pos
  }

  /// Reads the chunk type of this chunk.
  /// 
  /// Generally only valid for `RIFF` and `LIST` chunks.
  pub fn read_type<T>(&self, stream: &mut T) -> std::io::Result<ChunkId>
      where T: Read + Seek {
    stream.seek(SeekFrom::Start(self.pos + 8))?;

    let mut fourcc : [u8; 4] = [0; 4];
    stream.read_exact(&mut fourcc)?;

    Ok(ChunkId { value: fourcc })
  }

  /// Reads a chunk from the specified position in the stream.
  pub fn read<T>(stream: &mut T, pos: u64) -> std::io::Result<Chunk>
      where T: Read + Seek {
    stream.seek(SeekFrom::Start(pos))?;

    let mut fourcc : [u8; 4] = [0; 4];
    stream.read_exact(&mut fourcc)?;

    let mut len : [u8; 4] = [0; 4];
    stream.read_exact(&mut len)?;

    Ok(Chunk {
      pos: pos,
      id: ChunkId { value: fourcc },
      len: u32::from_le_bytes(len)
    })
  }
  
  /// Reads the entirety of the contents of a chunk.
  pub fn read_contents<T>(&self, stream: &mut T) -> std::io::Result<Vec<u8>>
      where T: Read + Seek {
    stream.seek(SeekFrom::Start(self.pos + 8))?;

    let mut data: Vec<u8> = vec![0; self.len.try_into().unwrap()];
    stream.read_exact(&mut data)?;

    Ok(data)
  }

  /// Returns an iterator over the children of the chunk.
  /// 
  /// If the chunk has children but is noncompliant, e.g. it has
  /// no type identifier (like `seqt` chunks), use `iter_no_type` instead.
  pub fn iter<'a, T>(&self, stream: &'a mut T) -> Iter<'a, T>
      where T: Seek + Read {
        Iter {
      cur: self.pos + 12,
      end: self.pos + 4 + (self.len as u64),
      stream: stream
    }
  }

  /// Returns an iterator over the chilren of the chunk. Only valid for
  /// noncompliant chunks that have children but no chunk type identifier
  /// (like `seqt` chunks).
  pub fn iter_no_type<'a, T>(&self, stream: &'a mut T) -> Iter<'a, T>
      where T: Seek + Read {
        Iter {
      cur: self.pos + 8,
      end: self.pos + 4 + (self.len as u64),
      stream: stream
    }
  }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn chunkid_from_str() {
        assert_eq!(ChunkId::new("RIFF").unwrap(), RIFF_ID);
        assert_eq!(ChunkId::new("LIST").unwrap(), LIST_ID);
        assert_eq!(ChunkId::new("seqt").unwrap(), SEQT_ID);

        assert_eq!(ChunkId::new("123 ").unwrap(),
          ChunkId { value: [0x31, 0x32, 0x33, 0x20] });

        assert_eq!(ChunkId::new("123"), Err("Invalid length"));
        assert_eq!(ChunkId::new("12345"), Err("Invalid length"));
    }

    #[test]
    fn chunkid_to_str() {
      assert_eq!(RIFF_ID.as_str(), "RIFF");
      assert_eq!(LIST_ID.as_str(), "LIST");
      assert_eq!(SEQT_ID.as_str(), "seqt");
      assert_eq!(ChunkId::new("123 ").unwrap().as_str(), "123 ");
    }

    #[test]
    fn chunkid_format() {
      assert_eq!(format!("{}", RIFF_ID), "'RIFF'");
      assert_eq!(format!("{}", LIST_ID), "'LIST'");
      assert_eq!(format!("{}", SEQT_ID), "'seqt'");

      assert_eq!(format!("{:?}", RIFF_ID), "'RIFF'");
      assert_eq!(format!("{:?}", LIST_ID), "'LIST'");
      assert_eq!(format!("{:?}", SEQT_ID), "'seqt'");
    }
}