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use std::cmp;
use std::fmt;
use std::io;
use std::io::{Error,ErrorKind,Result};
use std::mem;

use crate::utils::memutils;
use std::alloc::{GlobalAlloc, Layout};


// implement Write trait for &[i8] (a.k.a. &[c_char])
pub trait Write {
    fn write(&mut self, buf: &[u8]) -> Result<usize>;
    fn flush(&mut self) -> Result<()>;
    fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
        while !buf.is_empty() {
            match self.write(buf) {
                Ok(0) => return Err(Error::new(ErrorKind::WriteZero,
                                               "failed to write whole buffer")),
                Ok(n) => buf = &buf[n..],
                Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
                Err(e) => return Err(e),
            }
        }
        Ok(())
    }
    fn write_fmt(&mut self, fmt: fmt::Arguments) -> Result<()> {
        // Create a shim which translates a Write to a fmt::Write and saves
        // off I/O errors. instead of discarding them
        struct Adaptor<'a, T: ?Sized + 'a> {
            inner: &'a mut T,
            error: Result<()>,
        }

        impl<'a, T: Write + ?Sized> fmt::Write for Adaptor<'a, T> {
            fn write_str(&mut self, s: &str) -> fmt::Result {
                match self.inner.write_all(s.as_bytes()) {
                    Ok(()) => Ok(()),
                    Err(e) => {
                        self.error = Err(e);
                        Err(fmt::Error)
                    }
                }
            }
        }

        let mut output = Adaptor { inner: self, error: Ok(()) };
        match fmt::write(&mut output, fmt) {
            Ok(()) => Ok(()),
            Err(..) => {
                // check if the error came from the underlying `Write` or not
                if output.error.is_err() {
                    output.error
                } else {
                    Err(Error::new(ErrorKind::Other, "formatter error"))
                }
            }
        }
    }
    fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
}

impl<'a> Write for &'a mut [i8] {
    #[inline]
    fn write(&mut self, data: &[u8]) -> io::Result<usize> {
        let amt = cmp::min(data.len(), self.len());
        let (a, b) = mem::replace(self, &mut []).split_at_mut(amt);
        let a_u8 = unsafe { &mut *(a as *mut [i8] as *mut [u8]) };
        a_u8.copy_from_slice(&data[..amt]);
        *self = b;
        Ok(amt)
    }

    #[inline]
    fn write_all(&mut self, data: &[u8]) -> io::Result<()> {
        if self.write(data)? == data.len() {
            Ok(())
        } else {
            Err(Error::new(ErrorKind::WriteZero, "failed to write whole buffer"))
        }
    }

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

// Set up postgres allocator
pub struct PostgresAllocator;
unsafe impl GlobalAlloc for PostgresAllocator {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        return memutils::c::MemoryContextAlloc(
            memutils::CurrentMemoryContext, layout.size());
    }
    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
        memutils::c::pfree(ptr);
    }
}