use std::{error::Error, fmt, io::{self, ErrorKind, Read, Write}, str};

#[derive(Default, Clone, Copy)]
pub enum Style {
    #[default]
    Plain,
    Spaces,
    Prefixed,
    Table,
}

#[derive(Debug)]
pub struct ParseStyleError;

impl fmt::Display for ParseStyleError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{self:?}")
    }
}

impl Error for ParseStyleError {}

impl str::FromStr for Style {
    type Err = ParseStyleError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s {
            "plain" => Ok(Self::Plain),
            "spaces" => Ok(Self::Spaces),
            "prefixed"  => Ok(Self::Prefixed),
            "table" => Ok(Self::Table),
            _ => Err(ParseStyleError),
        }
    }
}

pub struct Encoder<R: Read, W: Write> {
    reader: R,
    writer: W,
    style: Style,
    wrap: Option<usize>,
}

impl<R: Read, W: Write> Encoder<R, W> {
    pub fn new(reader: R, writer: W, style: Option<Style>, mut wrap: Option<usize>) -> Self {
        let style = style.unwrap_or_default();
        if let Style::Table = style {
            wrap = match wrap {
                Some(u) => Some(u),
                None => Some(5),
            };
        }
        Self {
            reader,
            writer,
            style,
            wrap,
        }
    }

    pub fn encode(mut self) -> Result<W, io::Error> {
        let mut bytes = self.reader.bytes();
        let mut total = 0;
        loop {
            match bytes.next() {
                Some(Ok(b)) => match self.style {
                    Style::Plain => {
                        if let Some(w) = self.wrap {
                            if total > 0 && total % w == 0 {
                                writeln!(self.writer)?;
                            }
                        }
                        write!(self.writer, "{b:08b}")?;
                    }
                    Style::Spaces => {
                        if let Some(w) = self.wrap {
                            if total > 0 && total % w == 0 {
                                writeln!(self.writer)?;
                            } else {
                                write!(self.writer, " ")?;
                            }
                        } else if total > 0 {
                            write!(self.writer, " ")?;
                        }
                        write!(self.writer, "{b:08b}")?;
                    }
                    Style::Prefixed => {
                        if let Some(w) = self.wrap {
                            if total > 0 && total % w == 0 {
                                writeln!(self.writer)?;
                            } else if total > 0 {
                                write!(self.writer, " ")?;
                            }
                        } else if total > 0 {
                            write!(self.writer, " ")?;
                        }
                        write!(self.writer, "{b:#010b}")?;
                    }
                    Style::Table => {
                        if let Some(w) = self.wrap {
                            if total % w == 0 {
                                if total > 0 {
                                    write!(self.writer, "\n{total:>5}\t{b:#010b}")?;
                                } else {
                                    write!(self.writer, "{total:>5}\t{b:#010b}")?;
                                }
                            } else {
                                write!(self.writer, " {b:#010b}")?;
                            }
                        } else {
                            unreachable!();
                        }
                    }
                },
                Some(Err(e)) if e.kind() == ErrorKind::UnexpectedEof => break,
                Some(Err(e)) if e.kind() == ErrorKind::Interrupted => continue,
                Some(Err(e)) => return Err(e),
                None => break,
            }
            total += 1;
        }
        if let Some(w) = self.wrap {
            if total % w != 0 {
                writeln!(self.writer)?;
            }
        } else {
            writeln!(self.writer)?;
        }
        Ok(self.writer)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn hello_plain() {
        let encoder = Encoder::new("Hello, World!".as_bytes(), vec![], None, None);
        assert_eq!(
            encoder.encode().unwrap(),
            b"01001000011001010110110001101100011011110010110000100000010101110110111101110010011011000110010000100001\n"
        );
    }

    #[test]
    fn hello_spaced() {
        let encoder = Encoder::new(
            "Hello, World!".as_bytes(),
            vec![],
            Some(Style::Spaces),
            None,
        );
        assert_eq!(
            encoder.encode().unwrap(),
            b"01001000 01100101 01101100 01101100 01101111 00101100 00100000 01010111 01101111 01110010 01101100 01100100 00100001\n"
        );
    }

    #[test]
    fn hello_prefixed() {
        let encoder = Encoder::new(
            "Hello, World!".as_bytes(),
            vec![],
            Some(Style::Prefixed),
            None,
        );
        assert_eq!(
            encoder.encode().unwrap(),
            b"0b01001000 0b01100101 0b01101100 0b01101100 0b01101111 0b00101100 0b00100000 0b01010111 0b01101111 0b01110010 0b01101100 0b01100100 0b00100001\n"
        );
    }

    #[test]
    fn hello_prefixed_wrapped() {
        let encoder = Encoder::new(
            "Hello, World!".as_bytes(),
            vec![],
            Some(Style::Prefixed),
            Some(4),
        );
        assert_eq!(
            encoder.encode().unwrap(),
            b"0b01001000 0b01100101 0b01101100 0b01101100\n0b01101111 0b00101100 0b00100000 0b01010111\n0b01101111 0b01110010 0b01101100 0b01100100\n0b00100001\n"
        );
    }

    #[test]
    fn hello_table() {
        let encoder = Encoder::new(
            "Hello, World!".as_bytes(),
            vec![],
            Some(Style::Table),
            Some(4),
        );
        assert_eq!(
            encoder.encode().unwrap(),
            b"    0\t0b01001000 0b01100101 0b01101100 0b01101100\n    4\t0b01101111 0b00101100 0b00100000 0b01010111\n    8\t0b01101111 0b01110010 0b01101100 0b01100100\n   12\t0b00100001\n"
        );
    }
}