local PING_PROMPT = 'reply with exactly: pong';

local DEFAULT_TIMEOUT_SECONDS = 1200;

local B64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

local function base64encode(s)
  local pad = (3 - #s % 3) % 3;
  s = s .. string.rep('\0', pad);
  local r = {};
  for i = 1, #s, 3 do
    local a, b, c = s:byte(i), s:byte(i + 1), s:byte(i + 2);
    local n = a * 65536 + b * 256 + c;
    r[#r + 1] = B64:sub(math.floor(n / 262144) % 64 + 1, math.floor(n / 262144) % 64 + 1)
             .. B64:sub(math.floor(n / 4096) % 64 + 1, math.floor(n / 4096) % 64 + 1)
             .. B64:sub(math.floor(n / 64) % 64 + 1, math.floor(n / 64) % 64 + 1)
             .. B64:sub(n % 64 + 1, n % 64 + 1);
  end
  local result = table.concat(r);
  if pad > 0 then
    result = result:sub(1, #result - pad) .. string.rep('=', pad);
  end
  return result;
end

local function trimTrailingSlash(s)
  return (s:gsub('/+$', ''));
end

local function isBlank(s)
  return type(s) ~= 'string' or string.match(s, '^%s*$') ~= nil;
end

local function readAllAndClose(response)
  local body = response.readAll();
  response.close();
  return body;
end

local function statusCode(response)
  if response.getResponseCode then
    return response.getResponseCode();
  end
  return nil;
end

local function extractTextParts(parts)
  local texts = {};
  for _, part in ipairs(parts) do
    if part.type == 'text' and type(part.text) == 'string' then
      texts[#texts + 1] = part.text;
    end
  end
  return table.concat(texts, '');
end

local function sessionTime(session)
  if type(session) ~= 'table' or type(session.time) ~= 'table' then
    return 0;
  end
  return tonumber(session.time.updated or session.time.created) or 0;
end

local function createAi(opts)
  opts = opts or {};

  local httpLib = opts.http or http;
  local settingsLib = opts.settings or settings;

  local api = {};

  local function resolveTimeout(options)
    local raw = options.timeoutSeconds;
    if raw == nil then raw = settingsLib.get('opencc.timeout_seconds'); end
    local n = tonumber(raw);
    if n and n > 0 then return n; end
    return DEFAULT_TIMEOUT_SECONDS;
  end

  local function resolveConfig(options)
    local url = options.serverUrl or settingsLib.get('opencc.server_url');
    if not url or url == '' then
      return nil, 'missing opencc.server_url; run: set opencc.server_url <url>';
    end
    local username = options.username or settingsLib.get('opencc.username') or 'opencode';
    local password = options.password or settingsLib.get('opencc.password') or '';
    return {
      url = trimTrailingSlash(url),
      username = username,
      password = password,
      timeoutSeconds = resolveTimeout(options),
    };
  end

  local function buildHeaders(cfg)
    local headers = {
      ['Content-Type'] = 'application/json',
      ['Accept'] = 'application/json',
    };
    if cfg.password and cfg.password ~= '' then
      headers['Authorization'] = 'Basic ' .. base64encode(cfg.username .. ':' .. cfg.password);
    end
    return headers;
  end

  local function doGet(cfg, path)
    local response, _, errorResponse = httpLib.get({
      url = cfg.url .. path,
      headers = buildHeaders(cfg),
      timeout = cfg.timeoutSeconds,
    });
    response = response or errorResponse;
    if not response then
      return nil, 'serveur injoignable';
    end
    local code = statusCode(response);
    local body = readAllAndClose(response);
    return body, code;
  end

  local function doPost(cfg, path, payload)
    local response, _, errorResponse = httpLib.post({
      url = cfg.url .. path,
      body = textutils.serializeJSON(payload),
      headers = buildHeaders(cfg),
      timeout = cfg.timeoutSeconds,
    });
    response = response or errorResponse;
    if not response then
      return nil, 'serveur injoignable';
    end
    local code = statusCode(response);
    local body = readAllAndClose(response);
    return body, code;
  end

  function api.clearSession()
    settingsLib.unset('opencc.session_id');
    if settingsLib.save then settingsLib.save(); end
  end

  function api.listSessions(options)
    options = options or {};
    local cfg, err = resolveConfig(options);
    if not cfg then return false, err; end

    local body, code = doGet(cfg, '/session');
    if not body then return false, code; end
    if code and code ~= 200 then
      return false, 'erreur serveur: HTTP ' .. tostring(code);
    end

    local decoded = textutils.unserializeJSON(body);
    if type(decoded) ~= 'table' then
      return false, 'reponse invalide';
    end
    table.sort(decoded, function(a, b)
      return sessionTime(a) > sessionTime(b);
    end);
    return true, decoded;
  end

  function api.ask(prompt, options)
    options = options or {};
    if isBlank(prompt) then
      return false, 'missing prompt; usage: ai <prompt>';
    end

    local cfg, err = resolveConfig(options);
    if not cfg then return false, err; end

    local sessionId = options.sessionId;
    if sessionId == nil then
      sessionId = settingsLib.get('opencc.session_id');
    end

    if not sessionId or sessionId == '' then
      local body, code = doPost(cfg, '/session', { title = 'cc-ai' });
      if not body then return false, code; end
      if code and code ~= 200 then
        return false, 'impossible de creer une session: HTTP ' .. tostring(code);
      end
      local decoded = textutils.unserializeJSON(body);
      if type(decoded) ~= 'table' or type(decoded.id) ~= 'string' then
        return false, 'reponse session invalide';
      end
      sessionId = decoded.id;
      settingsLib.set('opencc.session_id', sessionId);
      if settingsLib.save then settingsLib.save(); end
    end

    local body, code = doPost(cfg, '/session/' .. sessionId .. '/message', {
      parts = { { type = 'text', text = prompt } },
    });
    if not body then return false, code; end
    if code == 404 then
      settingsLib.unset('opencc.session_id');
      if settingsLib.save then settingsLib.save(); end
      return false, 'session introuvable; lance: ai new <prompt>';
    end
    if code and code ~= 200 then
      return false, 'erreur message: HTTP ' .. tostring(code);
    end

    local decoded = textutils.unserializeJSON(body);
    if type(decoded) ~= 'table' or type(decoded.parts) ~= 'table' then
      return false, 'reponse message invalide';
    end

    local reply = extractTextParts(decoded.parts);
    if reply == '' then
      return false, 'reponse vide';
    end

    return true, { reply = reply, sessionId = sessionId };
  end

  function api.ping(options)
    return api.ask(PING_PROMPT, options);
  end

  return api;
end

return createAi;