use serde::{Deserialize, Serialize};
use serde_dhall::StaticType;
use serde_json as json;

use std::fs;
use std::io::Write;

use std::path::PathBuf;
use structopt::StructOpt;
use secrecy::ExposeSecret;

use age::x25519::Recipient;

#[derive(Deserialize, Serialize, StaticType, Debug)]
#[serde(rename_all="lowercase")]
enum Lang {
    de,
    en
}

#[derive(Deserialize, Serialize, StaticType, Debug)]
struct Survey {
    title: String,
    description: String,
    questions: Vec<Question>,
    pubkey: Option<String>,
    lang: Lang
}

#[derive(Deserialize, Serialize, StaticType, Debug)]
struct Question {
    question: String,
    name: String,
    space: AnswerSpace,
}

#[derive(Deserialize, Serialize, StaticType, Debug)]
enum AnswerSpace {
    Single(Vec<String>),
    Multiple(Vec<String>),
    YesOrNo,
    Freeform(String),
}

#[derive(StructOpt, Debug)]
struct Options {
    /// a dhall configuration file that describes a survey
    #[structopt(long, short, parse(from_os_str))]
    config_file: PathBuf,
    /// encrypt the survey with a passphrase (will be printed to stderr)
    #[structopt(long, short)]
    encrypt: bool,
    /// file to write the configuration to (will otherwise print to stdout)
    #[structopt(long, short)]
    out_file: Option<PathBuf>
}

fn main () {
    let opt = Options::from_args();

    let config_file = std::fs::read_to_string(opt.config_file).unwrap();

    // hacky way to get a "prelude" in dhall which doesn't have to be
    // imported: just wrap our input code into a dhall "let"-statement.
    // Probably doesn't scale very vell, though ...
    let code = format!(
        "let Question = {} \nlet Answers = {} \nlet Lang = {}\nin {}",
        Question::static_type(),
        AnswerSpace::static_type(),
        Lang::static_type(),
        config_file
    );
    match serde_dhall::from_str(&code)
        .static_type_annotation()
        .parse::<Survey>()
    {
        Err(e) => {
            eprintln!("There is an error in your dhall code!\n{}", e);
            std::process::exit(1);
        },
        Ok(data) => {
            let json = json::to_string(&data).unwrap();

            // if a public key is given to encrypt the survey, ad-hoc typecheck it
            // (not sure if the dhall crate allows defining custom types which are
            // opaque to dhall ...)
            match data.pubkey {
                Some (key) => key.parse::<Recipient>().is_err(),
                None => false
            }.then(|| {
                println!("field pubkey is not a valid public key, aborting ...");
                std::process::exit(1);
            });


            // out here to avoid borrowing issues — if it were in the password
            // branch below, it would go out of scope at its end, since .as_slice()
            // just borrows its argument
            let mut encrypted = vec![];
            // are we restricting access to the survey? if so, encrypt it with
            // the password as passphrase.
            let outdata = match opt.encrypt {
                false => json.as_bytes(),
                true => {
                    let key = age::x25519::Identity::generate();
                    let pubkey = key.to_public();
                    let encryptor = age::Encryptor::with_recipients(vec![Box::new(pubkey)]);
                    let mut writer = encryptor.wrap_output(&mut encrypted).unwrap();
                    writer.write_all(&json.as_bytes()).unwrap();
                    writer.finish().unwrap();
                    eprintln!("Passphrase for this survey: {}", key.to_string().expose_secret());
                    encrypted.as_slice()
                }
            };
            match opt.out_file {
                Some(file) => fs::write(file.clone(), outdata)
                    .expect(&format!("cannot write to file {:?}!", file)),
                None => {
                    let mut out = std::io::stdout();
                    out.write_all(outdata).unwrap();
                    out.flush().unwrap()
                }
            };
        }
    }
}