-- Computer-side MCP execution primitives.
--
-- Protocol-agnostic building blocks for the MCP `exec-lua` / `write-file` features.
-- The transport lives elsewhere: servers/mcp-computer-server.lua reacts to sandbox
-- gateway_request events and replies through the trap-sandbox gateway (see
-- apis/libsandbox.lua). This module only knows how to run code and write files.

local function defaultOs()
  return os;
end

local function formatLabel(label)
  if type(label) ~= 'string' or label == '' then
    return 'null';
  end
  return label;
end

local function appendOutput(output, value)
  output[#output + 1] = tostring(value);
end

local function serializeReturn(value)
  local valueType = type(value);
  if valueType == 'nil' then
    return { type = 'nil' };
  end

  if valueType == 'string' or valueType == 'number' or valueType == 'boolean' then
    return { type = valueType, value = value };
  end

  local ok, serialized = pcall(textutils.serialize, value);
  if ok then
    return { type = valueType, repr = serialized };
  end
  return { type = valueType, repr = tostring(value) };
end

local function createExecEnv(output)
  local env = setmetatable({}, { __index = _G });

  env.write = function(value)
    appendOutput(output, value);
  end;

  env.print = function(...)
    local values = table.pack(...);
    for i = 1, values.n do
      if i > 1 then
        appendOutput(output, '\t');
      end
      appendOutput(output, values[i]);
    end
    appendOutput(output, '\n');
  end;

  return env;
end

local function executeSource(code, chunkName)
  local output = {};

  local fn, loadErr = load(code, chunkName, 't', createExecEnv(output));
  if not fn then
    return { ok = false, error = tostring(loadErr), output = table.concat(output) };
  end

  local values = table.pack(pcall(fn));
  if not values[1] then
    return { ok = false, error = tostring(values[2]), output = table.concat(output) };
  end

  local returns = {};
  for i = 2, values.n do
    returns[#returns + 1] = serializeReturn(values[i]);
  end
  return { ok = true, returns = returns, output = table.concat(output) };
end

local function createMcpComputer()
  local api = {};

  api.formatLabel = formatLabel;

  function api.formatPong(osLike)
    osLike = osLike or defaultOs();
    return 'pong from ' .. tostring(osLike.getComputerID())
      .. ' (Label: ' .. formatLabel(osLike.getComputerLabel()) .. ')';
  end

  function api.executeLua(code)
    if type(code) ~= 'string' or code == '' then
      return { ok = false, error = 'code must be a non-empty string', output = '' };
    end

    return executeSource(code, 'mcp-exec');
  end

  function api.executeFile(path, fsLike)
    fsLike = fsLike or fs;
    if type(path) ~= 'string' or path == '' then
      return { ok = false, error = 'path must be a non-empty string', output = '' };
    end

    local handle, openErr = fsLike.open(path, 'r');
    if not handle then
      return { ok = false, error = tostring(openErr or 'failed to open file'), output = '' };
    end

    local ok, contentOrErr = pcall(function()
      return handle.readAll();
    end);
    local closeOk, closeErr = pcall(function()
      handle.close();
    end);

    if not ok then
      return { ok = false, error = tostring(contentOrErr), output = '' };
    end
    if not closeOk then
      return { ok = false, error = tostring(closeErr), output = '' };
    end

    return executeSource(contentOrErr, '@' .. path);
  end

  function api.writeFile(path, content, fsLike)
    fsLike = fsLike or fs;
    if type(path) ~= 'string' or path == '' then
      return { ok = false, error = 'path must be a non-empty string' };
    end

    if type(content) ~= 'string' then
      return { ok = false, error = 'content must be a string' };
    end

    local handle, openErr = fsLike.open(path, 'w');
    if not handle then
      return { ok = false, error = tostring(openErr or 'failed to open file') };
    end

    local ok, writeErr = pcall(function()
      handle.write(content);
    end);
    local closeOk, closeErr = pcall(function()
      handle.close();
    end);

    if not ok then
      return { ok = false, error = tostring(writeErr) };
    end
    if not closeOk then
      return { ok = false, error = tostring(closeErr) };
    end

    return { ok = true, path = path, bytes = string.len(content) };
  end

  return api;
end

return createMcpComputer;