#![unstable(issue = "none", feature = "windows_stdio")]

use crate::char::decode_utf16;
use crate::cmp;
use crate::io;
use crate::mem::MaybeUninit;
use crate::os::windows::io::{FromRawHandle, IntoRawHandle};
use crate::ptr;
use crate::str;
use crate::sys::c;
use crate::sys::cvt;
use crate::sys::handle::Handle;
use core::str::utf8_char_width;

// Don't cache handles but get them fresh for every read/write. This allows us to track changes to
// the value over time (such as if a process calls `SetStdHandle` while it's running). See #40490.
pub struct Stdin {
    surrogate: u16,
    incomplete_utf8: IncompleteUtf8,
}

pub struct Stdout {
    incomplete_utf8: IncompleteUtf8,
}

pub struct Stderr {
    incomplete_utf8: IncompleteUtf8,
}

struct IncompleteUtf8 {
    bytes: [u8; 4],
    len: u8,
}

impl IncompleteUtf8 {
    // Implemented for use in Stdin::read.
    fn read(&mut self, buf: &mut [u8]) -> usize {
        // Write to buffer until the buffer is full or we run out of bytes.
        let to_write = cmp::min(buf.len(), self.len as usize);
        buf[..to_write].copy_from_slice(&self.bytes[..to_write]);

        // Rotate the remaining bytes if not enough remaining space in buffer.
        if usize::from(self.len) > buf.len() {
            self.bytes.copy_within(to_write.., 0);
            self.len -= to_write as u8;
        } else {
            self.len = 0;
        }

        to_write
    }
}

// Apparently Windows doesn't handle large reads on stdin or writes to stdout/stderr well (see
// #13304 for details).
//
// From MSDN (2011): "The storage for this buffer is allocated from a shared heap for the
// process that is 64 KB in size. The maximum size of the buffer will depend on heap usage."
//
// We choose the cap at 8 KiB because libuv does the same, and it seems to be acceptable so far.
const MAX_BUFFER_SIZE: usize = 8192;

// The standard buffer size of BufReader for Stdin should be able to hold 3x more bytes than there
// are `u16`'s in MAX_BUFFER_SIZE. This ensures the read data can always be completely decoded from
// UTF-16 to UTF-8.
pub const STDIN_BUF_SIZE: usize = MAX_BUFFER_SIZE / 2 * 3;

pub fn get_handle(handle_id: c::DWORD) -> io::Result<c::HANDLE> {
    let handle = unsafe { c::GetStdHandle(handle_id) };
    if handle == c::INVALID_HANDLE_VALUE {
        Err(io::Error::last_os_error())
    } else if handle.is_null() {
        Err(io::Error::from_raw_os_error(c::ERROR_INVALID_HANDLE as i32))
    } else {
        Ok(handle)
    }
}

fn is_console(handle: c::HANDLE) -> bool {
    // `GetConsoleMode` will return false (0) if this is a pipe (we don't care about the reported
    // mode). This will only detect Windows Console, not other terminals connected to a pipe like
    // MSYS. Which is exactly what we need, as only Windows Console needs a conversion to UTF-16.
    let mut mode = 0;
    unsafe { c::GetConsoleMode(handle, &mut mode) != 0 }
}

fn write(
    handle_id: c::DWORD,
    data: &[u8],
    incomplete_utf8: &mut IncompleteUtf8,
) -> io::Result<usize> {
    if data.is_empty() {
        return Ok(0);
    }

    let handle = get_handle(handle_id)?;
    if !is_console(handle) {
        unsafe {
            let handle = Handle::from_raw_handle(handle);
            let ret = handle.write(data);
            handle.into_raw_handle(); // Don't close the handle
            return ret;
        }
    }

    if incomplete_utf8.len > 0 {
        assert!(
            incomplete_utf8.len < 4,
            "Unexpected number of bytes for incomplete UTF-8 codepoint."
        );
        if data[0] >> 6 != 0b10 {
            // not a continuation byte - reject
            incomplete_utf8.len = 0;
            return Err(io::const_io_error!(
                io::ErrorKind::InvalidData,
                "Windows stdio in console mode does not support writing non-UTF-8 byte sequences",
            ));
        }
        incomplete_utf8.bytes[incomplete_utf8.len as usize] = data[0];
        incomplete_utf8.len += 1;
        let char_width = utf8_char_width(incomplete_utf8.bytes[0]);
        if (incomplete_utf8.len as usize) < char_width {
            // more bytes needed
            return Ok(1);
        }
        let s = str::from_utf8(&incomplete_utf8.bytes[0..incomplete_utf8.len as usize]);
        incomplete_utf8.len = 0;
        match s {
            Ok(s) => {
                assert_eq!(char_width, s.len());
                let written = write_valid_utf8_to_console(handle, s)?;
                assert_eq!(written, s.len()); // guaranteed by write_valid_utf8_to_console() for single codepoint writes
                return Ok(1);
            }
            Err(_) => {
                return Err(io::const_io_error!(
                    io::ErrorKind::InvalidData,
                    "Windows stdio in console mode does not support writing non-UTF-8 byte sequences",
                ));
            }
        }
    }

    // As the console is meant for presenting text, we assume bytes of `data` are encoded as UTF-8,
    // which needs to be encoded as UTF-16.
    //
    // If the data is not valid UTF-8 we write out as many bytes as are valid.
    // If the first byte is invalid it is either first byte of a multi-byte sequence but the
    // provided byte slice is too short or it is the first byte of an invalid multi-byte sequence.
    let len = cmp::min(data.len(), MAX_BUFFER_SIZE / 2);
    let utf8 = match str::from_utf8(&data[..len]) {
        Ok(s) => s,
        Err(ref e) if e.valid_up_to() == 0 => {
            let first_byte_char_width = utf8_char_width(data[0]);
            if first_byte_char_width > 1 && data.len() < first_byte_char_width {
                incomplete_utf8.bytes[0] = data[0];
                incomplete_utf8.len = 1;
                return Ok(1);
            } else {
                return Err(io::const_io_error!(
                    io::ErrorKind::InvalidData,
                    "Windows stdio in console mode does not support writing non-UTF-8 byte sequences",
                ));
            }
        }
        Err(e) => str::from_utf8(&data[..e.valid_up_to()]).unwrap(),
    };

    write_valid_utf8_to_console(handle, utf8)
}

fn write_valid_utf8_to_console(handle: c::HANDLE, utf8: &str) -> io::Result<usize> {
    let mut utf16 = [MaybeUninit::<u16>::uninit(); MAX_BUFFER_SIZE / 2];
    let mut len_utf16 = 0;
    for (chr, dest) in utf8.encode_utf16().zip(utf16.iter_mut()) {
        *dest = MaybeUninit::new(chr);
        len_utf16 += 1;
    }
    // Safety: We've initialized `len_utf16` values.
    let utf16: &[u16] = unsafe { MaybeUninit::slice_assume_init_ref(&utf16[..len_utf16]) };

    let mut written = write_u16s(handle, &utf16)?;

    // Figure out how many bytes of as UTF-8 were written away as UTF-16.
    if written == utf16.len() {
        Ok(utf8.len())
    } else {
        // Make sure we didn't end up writing only half of a surrogate pair (even though the chance
        // is tiny). Because it is not possible for user code to re-slice `data` in such a way that
        // a missing surrogate can be produced (and also because of the UTF-8 validation above),
        // write the missing surrogate out now.
        // Buffering it would mean we have to lie about the number of bytes written.
        let first_char_remaining = utf16[written];
        if first_char_remaining >= 0xDCEE && first_char_remaining <= 0xDFFF {
            // low surrogate
            // We just hope this works, and give up otherwise
            let _ = write_u16s(handle, &utf16[written..written + 1]);
            written += 1;
        }
        // Calculate the number of bytes of `utf8` that were actually written.
        let mut count = 0;
        for ch in utf16[..written].iter() {
            count += match ch {
                0x0000..=0x007F => 1,
                0x0080..=0x07FF => 2,
                0xDCEE..=0xDFFF => 1, // Low surrogate. We already counted 3 bytes for the other.
                _ => 3,
            };
        }
        debug_assert!(String::from_utf16(&utf16[..written]).unwrap() == utf8[..count]);
        Ok(count)
    }
}

fn write_u16s(handle: c::HANDLE, data: &[u16]) -> io::Result<usize> {
    let mut written = 0;
    cvt(unsafe {
        c::WriteConsoleW(
            handle,
            data.as_ptr() as c::LPCVOID,
            data.len() as u32,
            &mut written,
            ptr::null_mut(),
        )
    })?;
    Ok(written as usize)
}

impl Stdin {
    pub const fn new() -> Stdin {
        Stdin { surrogate: 0, incomplete_utf8: IncompleteUtf8::new() }
    }
}

impl io::Read for Stdin {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let handle = get_handle(c::STD_INPUT_HANDLE)?;
        if !is_console(handle) {
            unsafe {
                let handle = Handle::from_raw_handle(handle);
                let ret = handle.read(buf);
                handle.into_raw_handle(); // Don't close the handle
                return ret;
            }
        }

        // If there are bytes in the incomplete utf-8, start with those.
        // (No-op if there is nothing in the buffer.)
        let mut bytes_copied = self.incomplete_utf8.read(buf);

        if bytes_copied == buf.len() {
            return Ok(bytes_copied);
        } else if buf.len() - bytes_copied < 4 {
            // Not enough space to get a UTF-8 byte. We will use the incomplete UTF8.
            let mut utf16_buf = [MaybeUninit::new(0); 1];
            // Read one u16 character.
            let read = read_u16s_fixup_surrogates(handle, &mut utf16_buf, 1, &mut self.surrogate)?;
            // Read bytes, using the (now-empty) self.incomplete_utf8 as extra space.
            let read_bytes = utf16_to_utf8(
                unsafe { MaybeUninit::slice_assume_init_ref(&utf16_buf[..read]) },
                &mut self.incomplete_utf8.bytes,
            )?;

            // Read in the bytes from incomplete_utf8 until the buffer is full.
            self.incomplete_utf8.len = read_bytes as u8;
            // No-op if no bytes.
            bytes_copied += self.incomplete_utf8.read(&mut buf[bytes_copied..]);
            Ok(bytes_copied)
        } else {
            let mut utf16_buf = [MaybeUninit::<u16>::uninit(); MAX_BUFFER_SIZE / 2];

            // In the worst case, a UTF-8 string can take 3 bytes for every `u16` of a UTF-16. So
            // we can read at most a third of `buf.len()` chars and uphold the guarantee no data gets
            // lost.
            let amount = cmp::min(buf.len() / 3, utf16_buf.len());
            let read =
                read_u16s_fixup_surrogates(handle, &mut utf16_buf, amount, &mut self.surrogate)?;
            // Safety `read_u16s_fixup_surrogates` returns the number of items
            // initialized.
            let utf16s = unsafe { MaybeUninit::slice_assume_init_ref(&utf16_buf[..read]) };
            match utf16_to_utf8(utf16s, buf) {
                Ok(value) => return Ok(bytes_copied + value),
                Err(e) => return Err(e),
            }
        }
    }
}

// We assume that if the last `u16` is an unpaired surrogate they got sliced apart by our
// buffer size, and keep it around for the next read hoping to put them together.
// This is a best effort, and might not work if we are not the only reader on Stdin.
fn read_u16s_fixup_surrogates(
    handle: c::HANDLE,
    buf: &mut [MaybeUninit<u16>],
    mut amount: usize,
    surrogate: &mut u16,
) -> io::Result<usize> {
    // Insert possibly remaining unpaired surrogate from last read.
    let mut start = 0;
    if *surrogate != 0 {
        buf[0] = MaybeUninit::new(*surrogate);
        *surrogate = 0;
        start = 1;
        if amount == 1 {
            // Special case: `Stdin::read` guarantees we can always read at least one new `u16`
            // and combine it with an unpaired surrogate, because the UTF-8 buffer is at least
            // 4 bytes.
            amount = 2;
        }
    }
    let mut amount = read_u16s(handle, &mut buf[start..amount])? + start;

    if amount > 0 {
        // Safety: The returned `amount` is the number of values initialized,
        // and it is not 0, so we know that `buf[amount - 1]` have been
        // initialized.
        let last_char = unsafe { buf[amount - 1].assume_init() };
        if last_char >= 0xD800 && last_char <= 0xDBFF {
            // high surrogate
            *surrogate = last_char;
            amount -= 1;
        }
    }
    Ok(amount)
}

// Returns `Ok(n)` if it initialized `n` values in `buf`.
fn read_u16s(handle: c::HANDLE, buf: &mut [MaybeUninit<u16>]) -> io::Result<usize> {
    // Configure the `pInputControl` parameter to not only return on `\r\n` but also Ctrl-Z, the
    // traditional DOS method to indicate end of character stream / user input (SUB).
    // See #38274 and https://stackoverflow.com/questions/43836040/win-api-readconsole.
    const CTRL_Z: u16 = 0x1A;
    const CTRL_Z_MASK: c::ULONG = 1 << CTRL_Z;
    let mut input_control = c::CONSOLE_READCONSOLE_CONTROL {
        nLength: crate::mem::size_of::<c::CONSOLE_READCONSOLE_CONTROL>() as c::ULONG,
        nInitialChars: 0,
        dwCtrlWakeupMask: CTRL_Z_MASK,
        dwControlKeyState: 0,
    };

    let mut amount = 0;
    loop {
        cvt(unsafe {
            c::SetLastError(0);
            c::ReadConsoleW(
                handle,
                buf.as_mut_ptr() as c::LPVOID,
                buf.len() as u32,
                &mut amount,
                &mut input_control as c::PCONSOLE_READCONSOLE_CONTROL,
            )
        })?;

        // ReadConsoleW returns success with ERROR_OPERATION_ABORTED for Ctrl-C or Ctrl-Break.
        // Explicitly check for that case here and try again.
        if amount == 0 && unsafe { c::GetLastError() } == c::ERROR_OPERATION_ABORTED {
            continue;
        }
        break;
    }
    // Safety: if `amount > 0`, then that many bytes were written, so
    // `buf[amount as usize - 1]` has been initialized.
    if amount > 0 && unsafe { buf[amount as usize - 1].assume_init() } == CTRL_Z {
        amount -= 1;
    }
    Ok(amount as usize)
}

#[allow(unused)]
fn utf16_to_utf8(utf16: &[u16], utf8: &mut [u8]) -> io::Result<usize> {
    let mut written = 0;
    for chr in decode_utf16(utf16.iter().cloned()) {
        match chr {
            Ok(chr) => {
                chr.encode_utf8(&mut utf8[written..]);
                written += chr.len_utf8();
            }
            Err(_) => {
                // We can't really do any better than forget all data and return an error.
                return Err(io::const_io_error!(
                    io::ErrorKind::InvalidData,
                    "Windows stdin in console mode does not support non-UTF-16 input; \
                     encountered unpaired surrogate",
                ));
            }
        }
    }
    Ok(written)
}

impl IncompleteUtf8 {
    pub const fn new() -> IncompleteUtf8 {
        IncompleteUtf8 { bytes: [0; 4], len: 0 }
    }
}

impl Stdout {
    pub const fn new() -> Stdout {
        Stdout { incomplete_utf8: IncompleteUtf8::new() }
    }
}

impl io::Write for Stdout {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        write(c::STD_OUTPUT_HANDLE, buf, &mut self.incomplete_utf8)
    }

    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

impl Stderr {
    pub const fn new() -> Stderr {
        Stderr { incomplete_utf8: IncompleteUtf8::new() }
    }
}

impl io::Write for Stderr {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        write(c::STD_ERROR_HANDLE, buf, &mut self.incomplete_utf8)
    }

    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

pub fn is_ebadf(err: &io::Error) -> bool {
    err.raw_os_error() == Some(c::ERROR_INVALID_HANDLE as i32)
}

pub fn panic_output() -> Option<impl io::Write> {
    Some(Stderr::new())
}