// voter: A simple CGI vote recorder, approval-voting-style
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, version 3.

use rand::prelude::*;
use std::collections::{HashMap, HashSet};
use std::io::prelude::*;
use std::path::{Path, PathBuf};

const DATA_PATH: &str = "/var/lib/voter";
const COOKIE_NAME: &[u8] = b"__Secure-id";
const COOKIE_LENGTH: usize = 12;

fn validate_path(path: &str) -> Result<PathBuf, cgi::Response> {
    let invalid_path = || cgi::text_response(404, "Invalid path");
    if path == "/" {
        return Err(cgi::text_response(404, "(This is the voting place.  You should have been given a more specific URL for the specific thing you've been invited to vote on.)"));
    }
    if path.contains("..") || !path.starts_with('/') {
        return Err(invalid_path());
    }
    let dir = Path::new(&format!("{DATA_PATH}{path}")).to_path_buf();
    if !dir
        .canonicalize()
        .map_err(|_| invalid_path())?
        .starts_with(DATA_PATH)
    {
        return Err(invalid_path());
    }
    if !dir.is_dir() {
        return Err(invalid_path());
    }
    Ok(dir)
}

fn get_voter(request: &cgi::Request) -> Result<&[u8], cgi::Response> {
    // Expect exactly one cookie, exactly as we generate it.
    let cookie = request
        .headers()
        .get(cgi::http::header::COOKIE)
        .map(cgi::http::HeaderValue::as_bytes)
        .and_then(|c| c.strip_prefix(COOKIE_NAME))
        .and_then(|c| c.strip_prefix(b"="))
        .ok_or_else(|| cgi::text_response(400, "Invalid cookie"))?;
    if cookie.len() != COOKIE_LENGTH || cookie.contains(&b' ') || cookie.contains(&b';') {
        Err(cgi::text_response(400, "Invalid cookie"))
    } else {
        Ok(cookie)
    }
}

fn tally_votes(dir: &Path) -> std::io::Result<HashMap<String, HashSet<String>>> {
    let mut tally: HashMap<String, HashSet<String>> = HashMap::new();
    match std::fs::File::open(dir.to_owned().join("votes")) {
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(tally),
        Err(e) => Err(e),
        Ok(vfile) => {
            for liner in std::io::BufReader::new(vfile).lines() {
                let line = liner?;
                if let Some((voter, datum)) = line.split_once(' ') {
                    if voter.len() == COOKIE_LENGTH {
                        if let Some((vote, candidate)) = datum.split_once(' ') {
                            if vote == "0" {
                                if let Some(entry) = tally.get_mut(candidate) {
                                    entry.remove(voter);
                                }
                            } else if vote == "1" {
                                tally
                                    .entry(candidate.to_owned())
                                    .or_default()
                                    .insert(voter.to_owned());
                            }
                        }
                    }
                }
            }
            Ok(tally)
        }
    }
}

fn read_elim_list(dir: &Path) -> std::io::Result<HashSet<String>> {
    match std::fs::File::open(dir.join("eliminated")) {
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(HashSet::new()),
        Err(e) => Err(e),
        Ok(elimfile) => std::io::BufReader::new(elimfile).lines().collect(),
    }
}

fn valid_id_char(c: u8) -> bool {
    c.is_ascii_alphanumeric()
}

fn make_random_id() -> [u8; COOKIE_LENGTH] {
    let mut id = [0; COOKIE_LENGTH];
    for c in &mut id {
        while !valid_id_char(*c) {
            *c = random();
        }
    }
    id
}

fn set_cookie(mut response: cgi::Response, path: &str) -> Result<cgi::Response, cgi::Response> {
    response.headers_mut().append(
        cgi::http::header::SET_COOKIE,
        cgi::http::header::HeaderValue::from_bytes(
            &[
                COOKIE_NAME,
                b"=",
                &make_random_id(),
                b"; Secure; HttpOnly; SameSite=Strict; Max-Age=30000000; Path=",
                path.as_bytes(),
            ]
            .concat(),
        )
        .map_err(|_| cgi::text_response(503, "Couldn't make cookie"))?,
    );
    Ok(response)
}

const HTML_HEADER: &str = "<!DOCTYPE html>
<html>
  <head>
    <meta charset=\"utf-8\">
    <title>Vote!</title>
    <style>
      th { font-size: 70%; text-align: left }
      input { transform: scale(1.5) }
      .eliminated { text-decoration: line-through; }
      div { animation: 2s infinite linear spin }
      @keyframes spin {
        from { transform:rotate(0) }
        to { transform:rotate(1turn) }
      }
    </style>
    <script>
      window.onload = function() {
        for (cb of document.getElementsByTagName('input')) {
          if (cb.parentElement.parentElement.classList.contains('eliminated'))
            continue;
          cb.addEventListener('click', (function(cb) {
            return function() {
              cb.style.display = 'none'
              const spin = document.createElement('div')
              spin.appendChild(document.createTextNode('⏳'))
              cb.parentElement.insertBefore(spin, cb)

              const req = new XMLHttpRequest()
              req.addEventListener('load', function(e) {
                cb.parentElement.removeChild(cb.previousElementSibling)
                if (req.status == 200) {
                    cb.style.display = ''
                    const delta = cb.checked ? 1 : -1
                    const count_td = cb.parentElement.previousElementSibling
                    count_td.textContent = parseInt(count_td.textContent) + delta
                } else {
                   cb.parentElement.insertBefore(document.createTextNode('❗'), cb)
                }
              })
              req.open('PUT', window.location.href)
              req.send((cb.checked ? 1 : 0) + ' ' + cb.parentElement.nextElementSibling.innerHTML)
            }
          })(cb))
          cb.disabled = false
        }
      }
      function num_cmp(a, b) {
        return parseInt(b.textContent) - parseInt(a.textContent)
      }
      function str_cmp(a, b) {
        if (a.textContent < b.textContent) return -1
        if (a.textContent > b.textContent) return 1
        return 0
      }
      function checked_cmp(a, b) {
        vs = [a, b].map(x => {
          const v = x.children[0].checked + 0
          return isNaN(v) ? -1 : v
        })
        return vs[1] - vs[0]
      }
      function sort_table(col, cmp) {
        const rows = Array.from(document.getElementsByTagName('tr'))
        rows.shift()
        rows.sort((a, b) => cmp(a.children[col], b.children[col]))
        for (row of rows) {
          row.parentElement.appendChild(row)
        }
      }
    </script>
  </head>
  <body>
    <table>
      <tr>
        <th onclick='sort_table(0, num_cmp)'>Count</th>
        <th onclick='sort_table(1, checked_cmp)'>Vote</th>
        <th onclick='sort_table(2, str_cmp)'>Candidate</th>
      </tr>";
const HTML_FOOTER: &str = "
    </table>
  </body>
</html>";

fn supports(tally: &HashMap<String, HashSet<String>>, me: &str, candidate: &str) -> bool {
    tally
        .get(candidate)
        .map_or(false, |supporters| supporters.contains(me))
}

fn prompt_for_vote(dir: &Path, request: &cgi::Request) -> Result<cgi::Response, cgi::Response> {
    let voter = get_voter(request);
    let me = if let Ok(id) = voter {
        std::str::from_utf8(id).ok()
    } else {
        None
    };
    let tally = tally_votes(dir).map_err(|_| cgi::text_response(503, "Couldn't tally votes"))?;
    let elim =
        read_elim_list(dir).map_err(|_| cgi::text_response(503, "Couldn't read eliminations"))?;
    let cfile = std::fs::File::open(dir.join("candidates"))
        .map_err(|_| cgi::text_response(503, "No candidates"))?;
    let mut response = cgi::html_response(
        200,
        std::iter::once(Ok(HTML_HEADER.to_owned()))
            .chain(std::io::BufReader::new(cfile).lines().map(|rc| {
                rc.map(|c| {
                    let count = tally.get(&c).map_or(0, std::collections::HashSet::len);
                    let checked = if me.map_or(false, |me| supports(&tally, me, &c)) {
                        "checked"
                    } else {
                        ""
                    };
                    let class = if elim.contains(&c) { "eliminated" } else { "" };
                    format!(
                        "<tr class=\"{class}\">
                        <td>{count}</td>
                        <td><input type=\"checkbox\" autocomplete=\"off\" {checked} disabled></td>
                        <td>{c}</td>
                        </tr>"
                    )
                })
            }))
            .chain(std::iter::once(Ok(HTML_FOOTER.to_owned())))
            .collect::<std::io::Result<String>>()
            .map_err(|_| cgi::text_response(503, "Missing candidates"))?,
    );
    if voter.is_err() {
        response = set_cookie(response, request.uri().path())?;
    }
    Ok(response)
}

fn write_vote(dir: &Path, voter: &[u8], vote: &[u8]) -> std::io::Result<()> {
    let datum = [voter, b" ", vote, b"\n"].concat();
    let vpath = dir.join("votes");
    let vfile = std::fs::File::options()
        .append(true)
        .create(true)
        .open(vpath)?;
    let mut vlock = fd_lock::RwLock::new(vfile);
    vlock.write()?.write_all(&datum)?;
    Ok(())
}

fn record_vote(dir: &Path, request: &cgi::Request) -> Result<cgi::Response, cgi::Response> {
    let body = request.body();
    // Valid votes look like "0 foo" or "1 bar"
    if body.len() < 3
        || (body[0] != b'0' && body[0] != b'1')
        || body[1] != b' '
        || body.contains(&b'\n')
    {
        return Err(cgi::text_response(415, "Invalid vote"));
    }
    write_vote(dir, get_voter(request)?, body)
        .map_err(|_| cgi::text_response(503, "Couldn't record vote"))?;
    Ok(cgi::text_response(200, "Vote recorded"))
}

fn strip_body(mut response: cgi::Response) -> cgi::Response {
    response.body_mut().clear();
    response
}

fn respond(request: &cgi::Request) -> Result<cgi::Response, cgi::Response> {
    let dir = validate_path(request.uri().path())?;
    match *request.method() {
        cgi::http::Method::HEAD => prompt_for_vote(&dir, request).map(strip_body),
        cgi::http::Method::GET => prompt_for_vote(&dir, request),
        cgi::http::Method::PUT => record_vote(&dir, request),
        _ => Err(cgi::text_response(405, "Huh?")),
    }
}

fn respond_or_report_error(request: cgi::Request) -> cgi::Response {
    match respond(&request) {
        Ok(result) => result,
        Err(error) => error,
    }
}

cgi::cgi_main! { respond_or_report_error }