//! A simple library to decode dlc files to a readable format.
//! 
//! ## Usage
//! Add `dlc_decrypter` as a dependency in `Cargo.toml`:
//!
//! ```toml
//! [dependencies]
//! dlc_decrypter = { git = "https://github.com/Bubblepoint/dlc-decoder" }
//! ```
//! 
//! Use the `dlc_decrypter::DlcDecoder` to decrypt a .dlc file or datapackage:
//! 
//! ```rust
//! extern crate dlc_decrypter;
//! 
//! fn main() {
//!     // Create the DlcDecoder
//!     let dd = dlc_decrypter::DlcDecoder::new();
//! 
//!     // loop over all arguments for the programm
//!     // skip the first one because it's the programm
//!     // own name
//!     for arg in std::env::args().skip(1) {
//!         // hand over the file path
//!         let dlc = dd.from_file(arg);
//! 
//!         // print the result
//!         println!("DLC: {:?}", dlc);
//!     }
//! }
//! ```
//! 
//! ## Thanks
//! * [Bubblepoint](https://github.com/Bubblepoint) for creating and maintaing the crate.
//! 
//! ## License
//! Distributed under the [MIT License](LICENSE).


// Programmer Information
// DLC = Download Link Container. It's often used for downloading.  
// Step 1: Split the file in 2 parts. Part 1 is the data. Part 2 are the last 88 chars from the file are the data_key.  
// Step 2: Send the data_key to the service.jdownloader.org (with an app specific id) to get an other key.  
// Step 3: Remove the surrounding <rc></rc> from the returned key and base64 decode the value.  
// Step 4: AES/CBC decrypt the data from Step 3 with an app specific key/iv.  
// Step 5: Base64 decode the data part from Step 1.  
// Step 6: AES/CBC decrypt the data from Step 5 with the result from Step 4 as key/iv.  
// Step 7: Base64 decode the result from Step 6. Now you have an XML.  
// Step 8: The values in the xml are Base64 encoded. So you have to decode the values.  

#[macro_use] extern crate error_chain;
extern crate reqwest;
extern crate crypto;
extern crate regex;
extern crate base64;

pub mod error;

use error::*;
use std::io::Read;
use std::ops::Deref;
use std::fs::File;
use std::str;
use reqwest::Client;
use reqwest::header::{Connection, UserAgent};
use crypto::{buffer, aes, blockmodes };
use crypto::buffer::{ ReadBuffer, WriteBuffer };
use regex::Regex;



/// Link struct which holds the data of a file and the link.
///
/// Fields:
/// 
/// - url: where to find the corrsponding file online
/// - name: name of the corrsponding file
/// - size: of the file
#[derive(Debug, Clone)]
pub struct DlcLink {
    pub url: String,
    pub name: String,
    pub size: String
}

impl DlcLink {
    fn new() -> DlcLink {
        DlcLink {
            url: String::new(),
            name: String::new(),
            size: String::new(),
        }
    }
}

/// The readable result of an .dlc file. 
/// 
/// It holds the information about:
/// 
/// - name: of the .dlc package
/// - password: ??? pwd to encrypt ???
/// - files: the corresponding files of the package
#[derive(Debug, Clone)]
pub struct DlcPackage {
    pub name: String,
    pub password: String,
    pub files: Vec<DlcLink>,
}

impl DlcPackage {
    fn new() -> DlcPackage {
        DlcPackage {
            name: String::new(),
            password: String::new(),
            files: Vec::new(),
        }
    }
}

/// Struct to decode the .dlc file or data into an readable format.
#[derive(Debug)]
pub struct DlcDecoder {
    jd_app_name: String,
    jd_decryption_key: Vec<u8>,
    jd_decryption_iv: Vec<u8>
}

impl DlcDecoder {
    /// Create a new DlcDecoder with a standard login to jdownloader.
    pub fn new() -> DlcDecoder {
        DlcDecoder {
            jd_app_name: "pylo".to_string(),
            jd_decryption_key: b"cb99b5cbc24db398".to_vec(),
            jd_decryption_iv: b"9bc24cb995cb8db3".to_vec()
        }
    }

    // Set a different JDownloader credential to login, than the default ones.
    pub fn set_credentials<S, D>(&mut self, name: S, key: D, iv: D) 
    where S: Into<String>, D: Into<Vec<u8>> {
        self.jd_app_name = name.into();
        self.jd_decryption_key = key.into();
        self.jd_decryption_iv = iv.into();
    }

    /// Decrypt a specified .dlc file
    pub fn from_file<P: Into<String>>(&self, path: P) -> Result<DlcPackage> {
        // read the file
        let mut file = File::open(path.into())?;
        let mut data = Vec::new();
        file.read_to_end(&mut data)?;

        // return the decrypted dlc package
        self.from_data(&data)
    }

    /// Decrypt the contet of a .dlc file.
    pub fn from_data(&self, data: &[u8]) -> Result<DlcPackage> {
        // decrypt the .dlc data
        let data = self.decrypt_dlc(data)?;

        // parse the dlc header data
        let mut dlc = self.parse_header(&data)?;

        // parse the dlc body
        self.parse_body(&mut dlc, &data)?;

        Ok(dlc)
    }

    /******************* Private Functions *****************/
    fn decrypt_dlc(&self, data: &[u8]) -> Result<String> {
        // check if the file is to short to get the key out of it
        if data.len() <= 88 {
            bail!("Corrupted data");
        };

        // split between data and key
        let (data, key) = data.split_at(data.len() - 88);

        // get decrypten key
        let key = self.get_jd_decryption_key(key)?;

        // decrypt the key
        let key = DlcDecoder::decrypt_raw_data(&key, &self.jd_decryption_key, &self.jd_decryption_iv)?;

        // decrypt the content
        let data = base64::decode(data)?;
        let data = DlcDecoder::decrypt_raw_data(&data, key.deref(), key.deref())?;
        
        // format to text
        let data = base64::decode(&data)?;
        let data = String::from_utf8(data)?;

        return Ok(data);
    }

    fn decrypt_raw_data(data: &[u8], key: &[u8], iv: &[u8]) -> Result<Vec<u8>> {
        // create decryptor and set keys & values
        let mut decryptor = aes::cbc_decryptor(
            aes::KeySize::KeySize128,
            key,
            iv,
            blockmodes::NoPadding,
        );

        // create the buffer objects
        let mut buffer = [0; 4096];
        let mut read_buffer = buffer::RefReadBuffer::new(data);
        let mut writ_buffer = buffer::RefWriteBuffer::new(&mut buffer);
        let mut result = Vec::new();

        loop {
            // decrypt the buffer
            if decryptor.decrypt(&mut read_buffer, &mut writ_buffer, true).is_err() {
                bail!("Can't decrypt");
            }

            // when the write_buffer is empty, the decryption is finished
            if writ_buffer.is_empty() {
                break;
            }

            // add the encrypted data to the result
            result.extend_from_slice(writ_buffer.take_read_buffer().take_remaining());
        };

        // remove tailing zeros
        result.retain(|x| *x !=  0 as u8);

        return Ok(result);
    }

    fn get_jd_decryption_key(&self, key: &[u8]) -> Result<Vec<u8>> {
        // build the request url
        let url = format!("http://service.jdownloader.org/dlcrypt/service.php?srcType=dlc&destType={}&data={}", &self.jd_app_name, str::from_utf8(key)?);

        // build up the request
        let client = Client::new();
        let mut res = client.get(&url)
            .header(Connection::close())
            .header(UserAgent::new("Mozilla/5.3 (Windows; U; Windows NT 5.1; de; rv:1.8.1.6) Gecko/2232 Firefox/3.0.0.R"))
            .send()?;

        // read the response
        let mut key = Vec::new();
        res.read_to_end(&mut key)?;

        // check if response is long enough
        if key.len() != 33 {
            bail!("Unexpected Error");
        };

        // remove <rc> and </rc>
        let key = base64::decode(&key[4..28])?;

        Ok(key)
    }

    fn parse_header(&self, data: &str) -> Result<DlcPackage> {
        let mut dlc = DlcPackage::new();

        // get the package information
        let re = Regex::new(r#"<package ([^>]*)"#)?;
        let pck = re.find(&data).ok_or("Can't find package in data")?.as_str();

        // extract the name
        let re = Regex::new(r#"name="([^"])*""#)?;
        let t = re.find(&pck).ok_or("Can't find name in data")?;
        dlc.name = String::from_utf8(base64::decode(&pck[t.start()+6..t.end()-1])?)?;
        
        // extract the password
        let re = Regex::new(r#"passwords="([^"])*""#)?;
        let t = re.find(&pck).ok_or("Can't find name in data")?;
        dlc.password = String::from_utf8(base64::decode(&pck[t.start()+11..t.end()-1])?)?;
 
        Ok(dlc)
    }

    fn parse_body(&self, dlc: &mut DlcPackage, data: &str) -> Result<()> {
        // split at each file attribute
        let mut files_xml: Vec<&str> = data.split("<file>").collect();
        // remove the first one, becuase this is the header
        files_xml.remove(0);

        // loop over all files and parse them
        for f in files_xml {
            let details: Vec<&str> = f.split("<").collect();
            let mut link = DlcLink::new();
                for d in details {
                    if d.len() > 3 && d[..3] == "url".to_string() {
                        let buf = self.file_details(d.to_string(), 4);
                        link.url = buf;
                    } else if d.len() > 8 && d[..8] == "filename".to_string() {
                        let buf = self.file_details(d.to_string(), 9);
                        link.name = buf;
                    } else if d.len() > 4 && d[..4] == "size".to_string() {
                        let buf = self.file_details(d.to_string(), 5);
                        link.size = buf;
                    }
                }
            dlc.files.push(link);
        }

        Ok(())
    }

    fn file_details(&self, data: String, pos: usize) -> String {
        // try to decode the data
        let buf: String = match base64::decode(&data[pos..]) {
            Ok(x)  => {
                match String::from_utf8(x) {
                    Ok(x)  => x,
                    Err(_) => data[pos..].to_string(),
                }
            },
            Err(_) => data[pos..].to_string(),
        };
        buf
    }
}