//! Binary data conversion utilities.

use crate::durandal::err::*;
use std::{fmt, num::NonZeroU16};

#[doc(hidden)]
#[macro_export]
macro_rules! _durandal_read_impl {
   // big endian
   (BE $b:ident $nam:ident u16 $n:expr) => {
      _durandal_read_impl!($b u16::from_be_bytes, $nam 2 $n);
   };
   (BE $b:ident $nam:ident i16 $n:expr) => {
      _durandal_read_impl!($b i16::from_be_bytes, $nam 2 $n);
   };
   (BE $b:ident $nam:ident u32 $n:expr) => {
      _durandal_read_impl!($b u32::from_be_bytes, $nam 4 $n);
   };
   (BE $b:ident $nam:ident i32 $n:expr) => {
      _durandal_read_impl!($b i32::from_be_bytes, $nam 4 $n);
   };
   (BE $b:ident $nam:ident as usize u16 $n:expr) => {
      _durandal_read_impl!($b u16::from_be_bytes, $nam 2 $n);
      let $nam = $nam as usize;
   };
   (BE $b:ident $nam:ident as usize u32 $n:expr) => {
      _durandal_read_impl!($b u32::from_be_bytes, $nam 4 $n);
      let $nam = $nam as usize;
   };

   // little endian
   (LE $b:ident $nam:ident u16 $n:expr) => {
      _durandal_read_impl!($b u16::from_le_bytes $nam 2 $n);
   };
   (LE $b:ident $nam:ident i16 $n:expr) => {
      _durandal_read_impl!($b i16::from_le_bytes $nam 2 $n);
   };
   (LE $b:ident $nam:ident u32 $n:expr) => {
      _durandal_read_impl!($b u32::from_le_bytes $nam 4 $n);
   };
   (LE $b:ident $nam:ident i32 $n:expr) => {
      _durandal_read_impl!($b i32::from_le_bytes $nam 4 $n);
   };
   (LE $b:ident $nam:ident as usize u16 $n:expr) => {
      _durandal_read_impl!($b u16::from_le_bytes $nam 2 $n);
      let $nam = $nam as usize;
   };
   (LE $b:ident $nam:ident as usize u32 $n:expr) => {
      _durandal_read_impl!($b u32::from_le_bytes $nam 4 $n);
      let $nam = $nam as usize;
   };

   // either endianness
   ($e:ident $b:ident $nam:ident Angle $n:expr) => {
      _durandal_read_impl!($e $b $nam u16 $n);
      let $nam = Angle::from_bits($nam);
   };
   ($e:ident $b:ident $nam:ident Fixed $n:expr) => {
      _durandal_read_impl!($e $b $nam u32 $n);
      let $nam = Fixed::from_bits($nam);
   };
   ($e:ident $b:ident $nam:ident Unit $n:expr) => {
      _durandal_read_impl!($e $b $nam u16 $n);
      let $nam = Unit::from_bits($nam);
   };
   ($e:ident $b:ident $nam:ident OptU16 $n:expr) => {
      _durandal_read_impl!($e $b $nam u16 $n);
      let $nam = OptU16::from_repr($nam);
   };

   // generic endianness
   ($_:ident $b:ident $nam:ident u8 $n:expr) => {
      let $nam = $b[$n];
   };
   ($_:ident $b:ident $nam:ident array u8 $n:expr) => {
      let $nam = &$b[$n];
   };
   ($_:ident $b:ident $nam:ident i8 $n:expr) => {
      let $nam = $b[$n] as i8;
   };
   ($_:ident $b:ident $nam:ident Ident $n:expr) => {
      let $nam = [$b[$n], $b[$n + 1], $b[$n + 2], $b[$n + 3]];
   };
   ($_:ident $b:ident $nam:ident $f:ident $n:expr) => {
      let $nam = $f(&$b[$n])?;
   };
   ($_:ident $b:ident $nam:ident nt $f:ident $n:expr) => {
      let $nam = $f(&$b[$n]);
   };

   // worker - creates let statement
   ($b:ident $pth:path , $nam:ident 2 $n:expr) => {
      let $nam = $pth([$b[$n], $b[$n + 1]]);
   };
   ($b:ident $pth:path , $nam:ident 4 $n:expr) => {
      let $nam = $pth([$b[$n], $b[$n + 1], $b[$n + 2], $b[$n + 3]]);
   };
}

/// Reads structured data from a byte array.
///
/// First start by specifying the endianness, size and source using the syntax
/// `endian, size in source =>` where:
///
/// - `endian` is `BE` or `LE` for big- or little-endian respectively.
/// - `size` is an expression specifying the last index that should be used by
/// this macro in `source`.
/// - `source` is a `u8` slice to read data from.
///
/// After the initializer line, all lines have the syntax
/// `name = type[place] opts;` where:
///
/// - `name` is the binding to put the resulting data in.
/// - `type` is one of:
///   - `u8` or `i8`: one byte will be read at `place`.
///   - `u16` or `i16`: two bytes will be read at `place` with `from_*_bytes`.
///   - `u32` or `i32`: four bytes will be read at `place` with `from_*_bytes`.
///   - `Ident`: four bytes will be read at `place` into an array, disregarding
///      endianness, creating an `Ident` object.
///   - `Angle`: same as `u16`, but the result is passed to
///      `fixed::Angle::from_bits`, resulting in a `fixed::Angle` object.
///   - `Fixed`: same as `u32`, but the result is passed to
///      `fixed::Fixed::from_bits`, resulting in a `fixed::Fixed` object.
///   - `Unit`: same as `u16`, but the result is passed to
///      `fixed::Unit::from_bits`, resulting in a `fixed::Unit` object.
///   - `OptU16`: same as `u16`, but the result is passed to
///      `OptU16::from_repr`, resulting in an `OptU16` object.
///   - The name of a function, which is passed `&source[place]` as its only
///      argument. The function's result has the `?` operator applied to it.
/// - `opts` may be one of:
///   - `array` when `type` is `u8`: `place` is a range specifying a `u8` slice
///      to be taken from `source`.
///   - `as usize` when `type` is `u16` or `u32`: converts the resulting
///      integer to `usize` by primitive cast.
///   - `nt` when `type` is a function name: does not use the `?` operator on
///      the resulting function call
///   - Nothing at all.
/// - `place` is either an integer literal which must be representable as
///   `usize`, or a range, which may only be used when `type` is a function
///   name.
#[macro_export]
macro_rules! read_data {
   (
      $sz:expr , $ty:ident in $b:ident =>
      $( $nam:ident = $t:ident [ $n:expr ] $( $ex:ident )* ; )*
   ) => {
      if $b.len() < $sz {
         bail!("not enough data");
      }

      $($crate::_durandal_read_impl!($ty $b $nam $($ex)* $t $n);)*
   };
}

/// Creates an `Ident` from a slice.
///
/// `b` must be at least 4 bytes, or a panic will occur.
pub fn ident(b: &[u8]) -> Ident {[b[0], b[1], b[2], b[3]]}

/// Applies `u32::from_be_bytes` to a slice.
///
/// `b` must be at least 4 bytes, or a panic will occur.
pub fn u32b(b: &[u8]) -> u32 {u32::from_be_bytes([b[0], b[1], b[2], b[3]])}

/// Applies `u16::from_be_bytes` to a slice.
///
/// `b` must be at least 2 bytes, or a panic will occur.
pub fn u16b(b: &[u8]) -> u16 {u16::from_be_bytes([b[0], b[1]])}

/// Applies `i32::from_be_bytes` to a slice.
///
/// `b` must be at least 4 bytes, or a panic will occur.
pub fn i32b(b: &[u8]) -> i32 {i32::from_be_bytes([b[0], b[1], b[2], b[3]])}

/// Applies `i16::from_be_bytes` to a slice.
///
/// `b` must be at least 2 bytes, or a panic will occur.
pub fn i16b(b: &[u8]) -> i16 {i16::from_be_bytes([b[0], b[1]])}

/// Applies a read function over a slice.
///
/// Applies `read` over `b`, resulting in a vector of its return values. Each
/// iteration will pass a slice of `b` to `read` for it to read from, and then
/// increments the slice index by the second return value. When there is no
/// data left in `b`, the function returns.
pub fn rd_array<T, F>(b: &[u8], read: F) -> ResultS<Vec<T>>
   where T: Sized,
         F: Fn(&[u8]) -> ResultS<(T, usize)>
{
   let mut v = Vec::new();
   let mut p = 0;

   while p < b.len() {
      let (r, s) = read(&b[p..])?;
      v.push(r);
      p += s;
   }

   Ok(v)
}

/// Applies a read function over a slice with an offset table.
///
/// Applies `read` over each offset in `b`, of which there are `num` amount of
/// starting at `p`, resulting in a vector of its return values. Each iteration
/// reads a 32-bit big endian offset from `b`, and then passes a slice of `b`
/// to `read` starting at that offset. When all offsets have been read, the
/// function returns.
pub fn rd_ofstable<T, F>(b: &[u8],
                         mut p: usize,
                         num: usize,
                         read: F)
                         -> ResultS<Vec<T>>
   where T: Sized,
         F: Fn(&[u8]) -> ResultS<T>
{
   let mut v = Vec::with_capacity(num);

   for _ in 0..num {
      let ofs = u32b(&b[p..p + 4]) as usize;

      if ofs >= b.len() {
         bail!("not enough data");
      }

      v.push(read(&b[ofs..])?);
      p += 4;
   }

   Ok(v)
}

impl OptU16
{
   /// Creates an `OptU16` from a `u16`.
   pub fn from_repr(n: u16) -> Self
   {
      if n == u16::max_value() {
         Self(None)
      } else {
         Self(NonZeroU16::new(n + 1))
      }
   }

   /// Returns the `u16` representation.
   pub fn get_repr(&self) -> u16
   {
      match self.0 {
         None => u16::max_value(),
         Some(n) => n.get() - 1,
      }
   }

   /// Returns the `Option` representation.
   pub fn get(&self) -> Option<u16>
   {
      match self.0 {
         None => None,
         Some(n) => Some(n.get() - 1),
      }
   }
}

impl fmt::Debug for OptU16
{
   fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
   {
      match self.get() {
         None    => write!(f, "None"),
         Some(n) => write!(f, "Some({})", n),
      }
   }
}

/// A four-character-code identifier.
pub type Ident = [u8; 4];

/// An object identified by a `u16` which may be `u16::max_value()` to
/// represent a nulled value.
#[derive(serde::Serialize, serde::Deserialize)]
pub struct OptU16(Option<NonZeroU16>);

// EOF