graphql-lua/graphql/util.lua

local util = {}

function util.map(t, fn)
  local res = {}
  for k, v in pairs(t) do res[k] = fn(v, k) end
  return res
end

function util.find(t, fn)
  local res = {}
  for k, v in pairs(t) do
    if fn(v, k) then return v end
  end
end

function util.compose(f, g)
  return function(...) return f(g(...)) end
end

function util.bind1(func, x)
  return function(y)
    return func(x, y)
  end
end

function util.getParentField(context, name, step_back)
  local obj = context.objects[#context.objects - step_back]
    if obj.__type == 'List' then
      return obj.ofType.fields[name]
    else
      return obj.fields[name]
    end
end

function util.coerceValue(node, schemaType, variables)
  variables = variables or {}

  if schemaType.__type == 'NonNull' then
    return util.coerceValue(node, schemaType.ofType, variables)
  end

  if not node then
    return nil
  end

  if node.kind == 'variable' then
    return variables[node.name.value]
  end

  if schemaType.__type == 'Union' then
    local matched, result
    for k, v in ipairs(schemaType.types) do
        matched, result = pcall(util.coerceValue, node, v, variables)
        if matched then
          return result
        end
    end

    local valid_types = util.map(schemaType.types, function (t) return t.name end)
    --TODO! how to better report this error?
    error('Could not coerce "' .. tostring(node.kind) .. '" to one of union types ['..table.concat(valid_types, ",")..']')
  end

  if schemaType.__type == 'List' then
    if node.kind ~= 'list' then
      error('Expected a list')
    end

    return util.map(node.values, function(value)
      return util.coerceValue(node.values[i], schemaType.ofType, variables)
    end)
  end

  if schemaType.__type == 'InputObject' then
    if node.kind ~= 'inputObject' then
      error('Expected an input object')
    end

    return util.map(node.values, function(field)
      if not schemaType.fields[field.name] then
        error('Unknown input object field "' .. field.name .. '"')
      end

      return util.coerceValue(field.value, schemaType.fields[field.name].kind, variables)
    end)
  end

  if schemaType.__type == 'Enum' then
    if node.kind ~= 'enum' then
      error('Expected enum value, got ' .. node.kind)
    end

    if not schemaType.values[node.value] then
      error('Invalid enum value "' .. node.value .. '"')
    end

    return node.value
  end

  if schemaType.__type == 'Scalar' then
    if schemaType.parseLiteral(node) == nil then
      error('Could not coerce "' .. tostring(node.value) .. '" to "' .. schemaType.name .. '"')
    end

    return schemaType.parseLiteral(node)
  end
end

return util