//! Rust-Bitcoin IO Library
//!
//! Because the core `std::io` module is not yet exposed in `no-std` Rust, building `no-std`
//! applications which require reading and writing objects via standard traits is not generally
//! possible. While there is ongoing work to improve this situation, this module is not likely to
//! be available for applications with broad rustc version support for some time.
//!
//! Thus, this library exists to export a minmal version of `std::io`'s traits which `no-std`
//! applications may need. With the `std` feature, these traits are also implemented for the
//! `std::io` traits, allowing standard objects to be used wherever the traits from this crate are
//! required.
//!
//! This traits are not one-for-one drop-ins, but are as close as possible while still implementing
//! `std::io`'s traits without unnecessary complexity.

#![cfg_attr(not(feature = "std"), no_std)]
// Experimental features we need.
#![cfg_attr(docsrs, feature(doc_auto_cfg))]

#[cfg(any(feature = "alloc", feature = "std"))]
extern crate alloc;

mod error;
mod macros;

use core::cmp;
use core::convert::TryInto;

#[rustfmt::skip]                // Keep public re-exports separate.
pub use self::error::{Error, ErrorKind};

pub type Result<T> = core::result::Result<T, Error>;

/// A generic trait describing an input stream. See [`std::io::Read`] for more info.
pub trait Read {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize>;

    #[inline]
    fn read_exact(&mut self, mut buf: &mut [u8]) -> Result<()> {
        while !buf.is_empty() {
            match self.read(buf) {
                Ok(0) => return Err(ErrorKind::UnexpectedEof.into()),
                Ok(len) => buf = &mut buf[len..],
                Err(e) if e.kind() == ErrorKind::Interrupted => {}
                Err(e) => return Err(e),
            }
        }
        Ok(())
    }

    #[inline]
    fn take(&mut self, limit: u64) -> Take<Self> { Take { reader: self, remaining: limit } }
}

pub struct Take<'a, R: Read + ?Sized> {
    reader: &'a mut R,
    remaining: u64,
}

impl<'a, R: Read + ?Sized> Read for Take<'a, R> {
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        let len = cmp::min(buf.len(), self.remaining.try_into().unwrap_or(buf.len()));
        let read = self.reader.read(&mut buf[..len])?;
        self.remaining -= read.try_into().unwrap_or(self.remaining);
        Ok(read)
    }
}

#[cfg(feature = "std")]
impl<R: std::io::Read> Read for R {
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        Ok(<R as std::io::Read>::read(self, buf)?)
    }
}

#[cfg(not(feature = "std"))]
impl Read for &[u8] {
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        let cnt = cmp::min(self.len(), buf.len());
        buf[..cnt].copy_from_slice(&self[..cnt]);
        *self = &self[cnt..];
        Ok(cnt)
    }
}

pub struct Cursor<T> {
    inner: T,
    pos: u64,
}

impl<T: AsRef<[u8]>> Cursor<T> {
    #[inline]
    pub fn new(inner: T) -> Self { Cursor { inner, pos: 0 } }

    #[inline]
    pub fn position(&self) -> u64 { self.pos }

    #[inline]
    pub fn into_inner(self) -> T { self.inner }
}

impl<T: AsRef<[u8]>> Read for Cursor<T> {
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        let inner: &[u8] = self.inner.as_ref();
        let start_pos = self.pos.try_into().unwrap_or(inner.len());
        let read = core::cmp::min(inner.len().saturating_sub(start_pos), buf.len());
        buf[..read].copy_from_slice(&inner[start_pos..start_pos + read]);
        self.pos =
            self.pos.saturating_add(read.try_into().unwrap_or(u64::max_value() /* unreachable */));
        Ok(read)
    }
}

/// A generic trait describing an output stream. See [`std::io::Write`] for more info.
pub trait Write {
    fn write(&mut self, buf: &[u8]) -> Result<usize>;

    fn flush(&mut self) -> Result<()>;

    #[inline]
    fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
        while !buf.is_empty() {
            match self.write(buf) {
                Ok(0) => return Err(ErrorKind::UnexpectedEof.into()),
                Ok(len) => buf = &buf[len..],
                Err(e) if e.kind() == ErrorKind::Interrupted => {}
                Err(e) => return Err(e),
            }
        }
        Ok(())
    }
}

#[cfg(feature = "std")]
impl<W: std::io::Write> Write for W {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
        Ok(<W as std::io::Write>::write(self, buf)?)
    }

    #[inline]
    fn flush(&mut self) -> Result<()> { Ok(<W as std::io::Write>::flush(self)?) }
}

#[cfg(all(feature = "alloc", not(feature = "std")))]
impl Write for alloc::vec::Vec<u8> {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
        self.extend_from_slice(buf);
        Ok(buf.len())
    }

    #[inline]
    fn flush(&mut self) -> Result<()> { Ok(()) }
}

#[cfg(not(feature = "std"))]
impl<'a> Write for &'a mut [u8] {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
        let cnt = core::cmp::min(self.len(), buf.len());
        self[..cnt].copy_from_slice(&buf[..cnt]);
        *self = &mut core::mem::take(self)[cnt..];
        Ok(cnt)
    }

    #[inline]
    fn flush(&mut self) -> Result<()> { Ok(()) }
}

/// A sink to which all writes succeed. See [`std::io::Sink`] for more info.
pub struct Sink;

#[cfg(not(feature = "std"))]
impl Write for Sink {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> Result<usize> { Ok(buf.len()) }

    #[inline]
    fn write_all(&mut self, _: &[u8]) -> Result<()> { Ok(()) }

    #[inline]
    fn flush(&mut self) -> Result<()> { Ok(()) }
}

#[cfg(feature = "std")]
impl std::io::Write for Sink {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> { Ok(buf.len()) }

    #[inline]
    fn write_all(&mut self, _: &[u8]) -> std::io::Result<()> { Ok(()) }

    #[inline]
    fn flush(&mut self) -> std::io::Result<()> { Ok(()) }
}

/// Returns a sink to which all writes succeed. See [`std::io::sink`] for more info.
#[inline]
pub fn sink() -> Sink { Sink }