#[cfg(test)]
mod operationtest;

use std::fs::{File, OpenOptions};
use std::io::{Read, Write};

pub trait XORWorker {
    fn work(input: [&str; 2], output: &str) -> Result<(), String>;
}

pub struct Worker;

fn open(name: &str, writable: bool) -> Result<File, String> {
    let f = OpenOptions::new()
        .read(!writable)
        .write(writable)
        .create(writable)
        .open(name);
    match f {
        Ok(file) => Ok(file),
        Err(e) => Err(format!(
            "Could not open file \"{}\" for {}:\n{}",
            name,
            if writable {"writing"} else {"reading"},
            e
        )),
    }
}

const BUF_SIZE: usize = (1 << 16);

struct ReadWrapper<'a, T>
        where T: Read {
    stream: T,
    name: &'a str,
}

impl<'a, T> ReadWrapper<'a, T>
        where T: Read {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize, String> {
        match self.stream.read(buf) {
            Ok(size) => Ok(size),
            Err(e) => Err(format!(
                "Error reading \"{}\":\n{}",
                self.name,
                e
            )),
        }
    }
}

struct WriteWrapper<'a, T>
        where T: Write {
    stream: T,
    name: &'a str,
}

impl<'a, T> WriteWrapper<'a, T>
        where T: Write {
    fn write_all(&mut self, buf: &[u8]) -> Result<(), String> {
        match self.stream.write_all(buf) {
            Ok(()) => Ok(()),
            Err(e) => Err(format!(
                "Error writing \"{}\":\n{}",
                self.name,
                e
            )),
        }
    }
}

fn xor_into(dest: &mut [u8], src: &[u8]) {
    for i in 0..dest.len() {
        dest[i] ^= src[i];
    }
}

fn operate<I1, I2, O>(
        mut in1: ReadWrapper<I1>,
        mut in2: ReadWrapper<I2>,
        mut out: WriteWrapper<O>
    ) -> Result<(), String>
    where I1: Read,
    I2: Read,
    O: Write
{
    let mut in1_buffer = [0u8; BUF_SIZE]; // also used for output
    let mut in2_buffer = [0u8; BUF_SIZE];

    let mut in1_remaining = &mut[][..]; // empty at begin
    let mut in2_remaining = &[][..];

    let mut in2_finished = false;

    loop {
        let l1 = in1_remaining.len();
        let l2 = in2_remaining.len();
        match (in2_finished, l1, l2) {
            (_, 0, _) => {
                // in1 buffer is empty, read
                match in1.read(&mut in1_buffer[..])? {
                    0 => {
                        // nothing more on input1, finished
                        return Ok(());
                    },
                    size => {
                        // take data
                        in1_remaining = &mut in1_buffer[0..size];
                    },
                };
            },
            (false, other, 0) => {
                // in2 buffer is empty, read
                let toread = if other == 0 {BUF_SIZE} else {other};
                in2_remaining = &[][..];
                match in2.read(&mut in2_buffer[0..toread])? {
                    0 => {
                        // nothing more on input2
                        in2_finished = true;
                    },
                    size => {
                        in2_remaining = &in2_buffer[0..size];
                    },
                };
            },
            (true, _, 0) => {
                // Data from i1 must be streamed to output
                out.write_all(&in1_remaining)?;
                in1_remaining = &mut in1_remaining[0..0];
            },
            (_, i1size, i2size) => {
                // There is data on both sides, process it
                let amount = if i1size < i2size {i1size} else {i2size};
                xor_into(&mut in1_remaining[0..amount], &in2_remaining[0..amount]);
                out.write_all(&in1_remaining[0..amount])?;
                in1_remaining = &mut in1_remaining[amount..];
                in2_remaining = &in2_remaining[amount..];
            },
        };
    }
}

impl XORWorker for Worker {
    fn work(input: [&str; 2], output: &str) -> Result<(), String> {
        let in1 = ReadWrapper {
            stream: open(input[0], false)?,
            name: input[0],
        };
        let in2 = ReadWrapper {
            stream: open(input[1], false)?,
            name: input[1],
        };
        let out = WriteWrapper {
            stream: open(output, true)?,
            name: output,
        };

        operate(in1, in2, out)
    }
}