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// LLSD for Rust - Parser and Writer for the LLSD format.
// Copyright (C) 2017-2018  Leonardo Schwarz <mail@leoschwarz.com>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

//! Handles auto detecting the representation of the format.

use data::Value;

lazy_static! {
    pub static ref PREFIX_BINARY: Vec<u8> = "<? LLSD/BINARY ?>\n".bytes().collect();
    pub static ref PREFIX_XML: Vec<u8> = "<?xml ".bytes().collect();
    pub static ref PREFIX_NOTATION: Vec<u8> = "<?llsd/notation?>\n".bytes().collect();
}

#[derive(Debug)]
pub enum Representation {
    Binary,
    Xml,
    Notation,
    Unknown,
}

fn determine_representation(buf: &[u8]) -> Representation {
    if buf.starts_with(&PREFIX_BINARY[..]) {
        Representation::Binary
    } else if buf.starts_with(&PREFIX_XML[..]) {
        Representation::Xml
    } else if buf.starts_with(&PREFIX_NOTATION[..]) {
        Representation::Notation
    } else {
        Representation::Unknown
    }
}

#[derive(Debug, Fail)]
pub enum ReadError {
    #[fail(display = "Reading binary LLSD failed: {}", _0)]
    ReadBinary(#[cause] ::binary::ReadError),

    #[fail(display = "Reading xml LLSD failed: {}", _0)]
    ReadXml(#[cause] ::xml::ReadError),

    #[fail(display = "Invalid LLSD representation: {:?}", _0)]
    InvalidRepresentation(Representation),
}

/// Read a value from either Binary or XML LLSD representation.
///
/// The format will be detected automatically by checking the document header.
pub fn read_value(buf: &[u8]) -> Result<Value, ReadError> {
    let repr = determine_representation(buf);
    match repr {
        Representation::Binary => {
            use std::io::BufReader;

            let mut reader = BufReader::new(&buf[PREFIX_BINARY.len()..]);
            ::binary::read_value(&mut reader).map_err(|e| ReadError::ReadBinary(e))
        }
        Representation::Xml => ::xml::read_value(buf).map_err(|e| ReadError::ReadXml(e)),
        Representation::Notation | Representation::Unknown => {
            Err(ReadError::InvalidRepresentation(repr))
        }
    }
}