extern crate byteorder;

use std::error;
use std::fmt;
use std::io;
use std::str;

use self::byteorder::{ByteOrder, BigEndian, LittleEndian};

use super::{Catalog, Message};

/// Represents an error encountered while parsing an MO file.
#[derive(Debug)]
pub enum Error {
    /// An incorrect magic number has been encountered
    BadMagic,
    /// An invalid byte sequence for the given encoding has been encountered
    DecodingError,
    /// An unexpected EOF occured
    Eof,
    /// An I/O error occured
    Io(io::Error),
}
// Can not use use `Error::*` as per this issue:
// (https://github.com/rust-lang/rust/issues/4865)
use Error::{BadMagic, DecodingError, Eof, Io};

impl error::Error for Error {
    fn description(&self) -> &str {
        match *self {
            BadMagic => "bad magic number",
            DecodingError => "invalid byte sequence in a string",
            Eof => "unxpected end of file",
            Io(ref err) => err.description(),
        }
    }
}

impl fmt::Display for Error {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        let self_err: &error::Error = self;
        write!(fmt, "{}", self_err.description())
    }
}

impl From<io::Error> for Error {
    fn from(inner: io::Error) -> Error {
        Io(inner)
    }
}

/// According to the given magic number of a MO file,
/// returns the function which reads a `u32` in the relevant endianness.
fn get_read_u32_fn(magic: &[u8]) -> Option<fn(&[u8]) -> u32> {
    if magic == [0xde, 0x12, 0x04, 0x95] {
        Some(LittleEndian::read_u32)
    } else if magic == [0x95, 0x04, 0x12, 0xde] {
        Some(BigEndian::read_u32)
    } else {
        None
    }
}

fn from_utf8(bytes: &[u8]) -> Result<&str, Error> {
    str::from_utf8(bytes).map_err(|_| DecodingError)
}

pub fn parse_catalog<R: io::Read>(mut file: R) -> Result<Catalog, Error> {
    let mut contents = vec![];
    let n = try!(file.read_to_end(&mut contents));
    if n < 28 {
        return Err(Eof);
    }

    let read_u32 = match get_read_u32_fn(&contents[0..4]) {
        Some(f) => f,
        None => return Err(BadMagic),
    };

    // ignore hashing tables (bytes at 20..28)
    let num_strings = read_u32(&contents[8..12]) as usize;
    let mut off_otable = read_u32(&contents[12..16]) as usize;
    let mut off_ttable = read_u32(&contents[16..20]) as usize;
    if n < off_otable || n < off_ttable {
        return Err(Eof);
    }

    let mut catalog = Catalog::new();
    for _ in 0..num_strings {
        let id;
        let context;
        let translated: Vec<&str>;
        // Parse the original string
        {
            if n < off_otable + 8 {
                return Err(Eof);
            }
            let len = read_u32(&contents[off_otable..off_otable + 4]) as usize;
            let off = read_u32(&contents[off_otable + 4..off_otable + 8]) as usize;
            // +1 compensates for the ending NUL byte which is not included in length
            if n < off + len + 1 {
                return Err(Eof);
            }
            let mut original = &contents[off..off + len + 1];
            // check for context
            context = match original.iter().position(|x| *x == 4) {
                Some(idx) => {
                    let ctx = &original[..idx];
                    original = &original[idx + 1..];
                    Some(try!(from_utf8(ctx)))
                }
                None => None,
            };
            // extract msg_id singular, ignoring the plural
            id = match original.iter().position(|x| *x == 0).map(|i| &original[..i]) {
                Some(b) => try!(from_utf8(b)),
                None => return Err(Eof),
            };
        }

        // Parse the translation strings
        {
            if n < off_ttable + 8 {
                return Err(Eof);
            }
            let len = read_u32(&contents[off_ttable..off_ttable + 4]) as usize;
            let off = read_u32(&contents[off_ttable + 4..off_ttable + 8]) as usize;
            // +1 compensates for the ending NUL byte which is not included in length
            if n < off + len + 1 {
                return Err(Eof);
            }
            let decode_results = (&contents[off..off + len])
                                     .split(|x| *x == 0)
                                     .map(from_utf8)
                                     .collect::<Vec<_>>();
            if decode_results.iter().any(|r| r.is_err()) {
                return Err(DecodingError);
            }
            translated = decode_results.into_iter().map(|r| r.unwrap()).collect();
        }

        catalog.insert(Message::new(id, context, translated));

        off_otable += 8;
        off_ttable += 8;
    }


    Ok(catalog)
}

#[test]
fn test_get_read_u32_fn() {
    use std::mem;

    assert!(get_read_u32_fn(&[]).is_none());
    assert!(get_read_u32_fn(&[0xde, 0x12, 0x04, 0x95, 0x00]).is_none());

    {
        let le_ptr: *const ();
        let ret_ptr;
        unsafe {
            le_ptr = mem::transmute(LittleEndian::read_u32);
            ret_ptr = mem::transmute(get_read_u32_fn(&[0xde, 0x12, 0x04, 0x95]).unwrap());
        }
        assert_eq!(le_ptr, ret_ptr);
    }

    {
        let be_ptr: *const ();
        let ret_ptr;
        unsafe {
            be_ptr = mem::transmute(BigEndian::read_u32);
            ret_ptr = mem::transmute(get_read_u32_fn(&[0x95, 0x04, 0x12, 0xde]).unwrap());
        }
        assert_eq!(be_ptr, ret_ptr);
    }
}

#[test]
fn test_parse_catalog() {
    macro_rules! assert_variant {
        ($value:expr, $variant:path) => {
            match $value {
                $variant => (),
                _ => panic!("Expected {:?}, got {:?}", $variant, $value),
            }
        };
    }

    let fluff = [0; 24]; // zeros to pad our magic test cases to satisfy the length requirements

    {
        let mut reader = vec![1u8, 2, 3];
        reader.extend(fluff.iter().cloned());
        let err = parse_catalog(&reader[..]).unwrap_err();
        assert_variant!(err, Eof);
    }

    {
        let mut reader = vec![1u8, 2, 3, 4];
        reader.extend(fluff.iter().cloned());
        let err = parse_catalog(&reader[..]).unwrap_err();
        assert_variant!(err, BadMagic);
    }

    {
        let mut reader = vec![0x95, 0x04, 0x12, 0xde];
        reader.extend(fluff.iter().cloned());
        assert!(parse_catalog(&reader[..]).is_ok());
    }

    {
        let mut reader = vec![0xde, 0x12, 0x04, 0x95];
        reader.extend(fluff.iter().cloned());
        assert!(parse_catalog(&reader[..]).is_ok());
    }

    {
        let reader: &[u8] = include_bytes!("../test_cases/1.mo");
        let catalog = parse_catalog(reader).unwrap();
        assert_eq!(catalog.strings.len(), 1);
        assert_eq!(catalog.strings["this is context\x04Text"],
                   Message::new("Text", Some("this is context"), vec!["Tekstas", "Tekstai"]));
    }

    {
        let reader: &[u8] = include_bytes!("../test_cases/2.mo");
        let catalog = parse_catalog(reader).unwrap();
        assert_eq!(catalog.strings.len(), 2);
        assert_eq!(catalog.strings["Image"],
                   Message::new("Image", None, vec!["Nuotrauka", "Nuotraukos"]));
    }

    {
        let reader: &[u8] = include_bytes!("../test_cases/invalid_utf8.mo");
        let err = parse_catalog(reader).unwrap_err();
        assert_variant!(err, DecodingError);
    }
}