// This is a part of encoding-next.
// Copyright (c) 2015, Simonas Kazlauskas
// See README.md and LICENSE.txt for details.

/**
 * Rotation by 13 places encoding.
 *
 * This example demonstrates how to use encoding-types package to implement your own encodings.
 */
extern crate encoding_types;

use encoding_types::*;
use std::str::from_utf8;

#[derive(Clone, Copy)]
pub struct ROT13Encoding;

impl Encoding for ROT13Encoding {
    fn name(&self) -> &'static str {
        "rot13"
    }
    fn whatwg_name(&self) -> Option<&'static str> {
        None
    }
    fn raw_encoder(&self) -> Box<dyn RawEncoder> {
        ROT13Encoder::new()
    }
    fn raw_decoder(&self) -> Box<dyn RawDecoder> {
        ROT13Decoder::new()
    }
}

#[derive(Clone, Copy)]
pub struct ROT13Encoder;

impl ROT13Encoder {
    #[allow(clippy::new_ret_no_self)]
    pub fn new() -> Box<dyn RawEncoder> {
        Box::new(ROT13Encoder)
    }
}

impl RawEncoder for ROT13Encoder {
    fn from_self(&self) -> Box<dyn RawEncoder> {
        ROT13Encoder::new()
    }
    fn is_ascii_compatible(&self) -> bool {
        true
    }

    fn raw_feed(
        &mut self,
        input: &str,
        output: &mut dyn ByteWriter,
    ) -> (usize, Option<CodecError>) {
        output.writer_hint(input.len());
        for byte in input.bytes() {
            output.write_byte(rotate_byte(byte))
        }
        (input.len(), None)
    }

    fn raw_finish(&mut self, _output: &mut dyn ByteWriter) -> Option<CodecError> {
        None
    }
}

#[derive(Clone, Copy)]
pub struct ROT13Decoder;

impl ROT13Decoder {
    #[allow(clippy::new_ret_no_self)]
    pub fn new() -> Box<dyn RawDecoder> {
        Box::new(ROT13Decoder)
    }
}

impl RawDecoder for ROT13Decoder {
    fn from_self(&self) -> Box<dyn RawDecoder> {
        ROT13Decoder::new()
    }
    fn is_ascii_compatible(&self) -> bool {
        true
    }

    fn raw_feed(
        &mut self,
        input: &[u8],
        output: &mut dyn StringWriter,
    ) -> (usize, Option<CodecError>) {
        output.writer_hint(input.len());
        let string = match from_utf8(input) {
            Ok(s) => s,
            Err(_e) => {
                return (
                    0,
                    Some(CodecError {
                        upto: 0, // Utf8Error::valid_up_to is unstable at the time of writing,
                        // therefore we can’t quite do partial parsing yet
                        cause: "input is not valid utf-8".into(),
                    }),
                );
            }
        };
        for ch in string.chars() {
            match ch {
                'a'..='z' | 'A'..='Z' => output.write_char(rotate_byte(ch as u8) as char),
                _ => output.write_char(ch),
            }
        }
        (input.len(), None)
    }

    fn raw_finish(&mut self, _output: &mut dyn StringWriter) -> Option<CodecError> {
        None
    }
}

fn rotate_byte(byte: u8) -> u8 {
    match byte {
        b'a'..=b'm' | b'A'..=b'M' => byte + 13,
        b'n'..=b'z' | b'N'..=b'Z' => byte - 13,
        _ => byte,
    }
}

fn main() {
    use std::io;
    use std::io::Read;

    let mut ret = Vec::new();
    io::stdin()
        .read_to_end(&mut ret)
        .expect("cannot read from the input");
    match ROT13Encoding.decode(&ret, DecoderTrap::Strict) {
        Ok(s) => println!("{}", s),
        Err(e) => panic!("decoder error: {}", e),
    };
}