local PING_PROMPT = 'reply with exactly: pong';

local DEFAULT_TIMEOUT_SECONDS = 1200;
local DEFAULT_LUA_EXEC_MAX_RETRIES = 2;
local DEFAULT_LUA_EXEC_TIMEOUT_SECONDS = 5;

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 tablePack(...)
  return { n = select('#', ...), ... };
end

local function endsWithNewline(s)
  return type(s) == 'string' and string.sub(s, -1) == '\n';
end

local function valuesToLine(values, first, last)
  local parts = {};
  for i = first, last do
    parts[#parts + 1] = tostring(values[i]);
  end
  return table.concat(parts, '\t');
end

local function classifyLuaRuntimeError(err)
  local text = tostring(err or '');
  if string.find(text, 'attempt to', 1, true) and string.find(text, 'nil value', 1, true) then
    return 'identifier';
  end
  if string.find(text, 'global', 1, true) and string.find(text, 'nil', 1, true) then
    return 'identifier';
  end
  return 'other';
end

local function renderOutput(output)
  if output == nil or output == '' then
    return '(no output)';
  end
  return output;
end

local function buildLuaExecPrompt(userPrompt)
  return table.concat({
    'Write ComputerCraft Lua code to answer this user request.',
    'Reply with raw Lua code only. Do not use markdown fences or explanations.',
    'The code runs locally with normal ComputerCraft globals available.',
    'Use print() or write() for values that should be sent back. Returned values are captured too.',
    '',
    'User request:',
    userPrompt,
  }, '\n');
end

local function buildLuaCorrectionPrompt(userPrompt, code, err, errorKind)
  return table.concat({
    'The previous ComputerCraft Lua failed.',
    'Reply with corrected raw Lua code only. Do not use markdown fences or explanations.',
    '',
    'Original user request:',
    userPrompt,
    '',
    'Error kind: ' .. tostring(errorKind),
    'Error:',
    tostring(err),
    '',
    'Previous code:',
    code,
  }, '\n');
end

local function buildLuaOutputPrompt(userPrompt, output)
  return table.concat({
    'The Lua executed successfully.',
    'Answer the original user request in natural language using the output below.',
    'Do not write more Lua unless the user explicitly asked for code.',
    '',
    'Original user request:',
    userPrompt,
    '',
    'Lua output:',
    renderOutput(output),
  }, '\n');
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 resolveLuaExecMaxRetries(options)
    local n = tonumber(options.maxRetries);
    if n and n >= 0 then return math.floor(n); end
    return DEFAULT_LUA_EXEC_MAX_RETRIES;
  end

  local function resolveLuaExecTimeout(options)
    if options.luaTimeoutSeconds == false then return nil; end
    local n = tonumber(options.luaTimeoutSeconds);
    if n and n > 0 then return n; end
    return DEFAULT_LUA_EXEC_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 persist = options.persist ~= false;
    local sessionId = options.sessionId;
    if persist and sessionId == nil then
      sessionId = settingsLib.get('opencc.session_id');
    end

    if not sessionId or sessionId == '' then
      local body, code = doPost(cfg, '/session', { title = options.sessionTitle or '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;
      if persist then
        settingsLib.set('opencc.session_id', sessionId);
        if settingsLib.save then settingsLib.save(); end
      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
      if persist then
        settingsLib.unset('opencc.session_id');
        if settingsLib.save then settingsLib.save(); end
      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.createLuaExecutor(options)
    options = options or {};
    local baseEnv = options.env or _G;
    local live = options.live ~= false;
    local livePrint = options.print or print;
    local liveWrite = options.write or write;
    local timeoutSeconds = resolveLuaExecTimeout(options);

    return function(code)
      local buffer = {};

      local function append(text)
        buffer[#buffer + 1] = text;
      end

      local function capturedPrint(...)
        local values = tablePack(...);
        local line = valuesToLine(values, 1, values.n);
        append(line .. '\n');
        if live then livePrint(...); end
      end

      local function capturedWrite(text)
        text = tostring(text or '');
        append(text);
        if live then liveWrite(text); end
      end

      local env = setmetatable({
        print = capturedPrint,
        write = capturedWrite,
      }, { __index = baseEnv });
      local chunk, loadErr = load(code, 'ai-lua-exec', 't', env);
      if not chunk then
        return false, tostring(loadErr), 'syntax';
      end

      local result;
      local finished = false;
      local function runner()
        result = tablePack(pcall(chunk));
        finished = true;
      end

      if timeoutSeconds then
        parallel.waitForAny(runner, function() sleep(timeoutSeconds); end);
      else
        runner();
      end

      if not finished then
        return false, 'lua execution timed out after ' .. tostring(timeoutSeconds) .. 's', 'other';
      end
      if not result[1] then
        return false, tostring(result[2]), classifyLuaRuntimeError(result[2]);
      end
      if result.n > 1 then
        if #buffer > 0 and not endsWithNewline(buffer[#buffer]) then
          append('\n');
        end
        append(valuesToLine(result, 2, result.n) .. '\n');
      end
      return true, table.concat(buffer), nil;
    end;
  end

  function api.luaExec(userPrompt, options)
    options = options or {};
    if isBlank(userPrompt) then
      return false, { error = 'missing prompt; usage: ai lua-exec <prompt>', attempts = 0 };
    end

    local log = options.log or function() end;
    local executor = options.executor or api.createLuaExecutor(options);
    local maxRetries = resolveLuaExecMaxRetries(options);
    local maxAttempts = maxRetries + 1;
    local sessionId;

    local function askOptions()
      return {
        persist = false,
        sessionId = sessionId,
        sessionTitle = 'cc-ai lua-exec',
        serverUrl = options.serverUrl,
        username = options.username,
        password = options.password,
        timeoutSeconds = options.timeoutSeconds,
      };
    end

    log('requesting Lua from AI');
    local ok, result = api.ask(buildLuaExecPrompt(userPrompt), askOptions());
    if not ok then
      return false, { error = result, attempts = 0, errorKind = 'ai' };
    end
    sessionId = result.sessionId;
    log('session: ' .. sessionId);

    local code = result.reply;
    for attempt = 1, maxAttempts do
      log('attempt ' .. tostring(attempt) .. '/' .. tostring(maxAttempts));
      log('code:\n' .. code);

      local execOk, outputOrErr, errorKind = executor(code);
      if execOk then
        local output = outputOrErr or '';
        log('output:\n' .. renderOutput(output));
        log('requesting final reply');
        local finalOk, finalResult = api.ask(buildLuaOutputPrompt(userPrompt, output), askOptions());
        if not finalOk then
          return false, {
            error = finalResult,
            attempts = attempt,
            errorKind = 'ai',
            code = code,
            output = output,
            sessionId = sessionId,
          };
        end
        log('final reply received');
        return true, {
          reply = finalResult.reply,
          output = output,
          code = code,
          attempts = attempt,
          sessionId = sessionId,
        };
      end

      errorKind = errorKind or 'other';
      log('error (' .. tostring(errorKind) .. '):\n' .. tostring(outputOrErr));
      if (errorKind ~= 'syntax' and errorKind ~= 'identifier') or attempt >= maxAttempts then
        return false, {
          error = outputOrErr,
          attempts = attempt,
          errorKind = errorKind,
          code = code,
          sessionId = sessionId,
          retryExhausted = attempt >= maxAttempts,
        };
      end

      log('requesting corrected Lua');
      local correctionOk, correctionResult = api.ask(
        buildLuaCorrectionPrompt(userPrompt, code, outputOrErr, errorKind),
        askOptions()
      );
      if not correctionOk then
        return false, {
          error = correctionResult,
          attempts = attempt,
          errorKind = 'ai',
          code = code,
          sessionId = sessionId,
        };
      end
      code = correctionResult.reply;
    end

    return false, { error = 'lua-exec failed unexpectedly', attempts = maxAttempts };
  end

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

  return api;
end

return createAi;