lib/try.go

// Licensed to Elasticsearch B.V. under one or more contributor
// license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright
// ownership. Elasticsearch B.V. licenses this file to you under
// the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

package lib

import (
	"fmt"

	"github.com/google/cel-go/cel"
	"github.com/google/cel-go/common/types"
	"github.com/google/cel-go/common/types/ref"
)

// Try returns a cel.EnvOption to configure extended functions for allowing
// errors to be weakened to strings or objects.
//
// # Try
//
// try returns either passes a value through unaltered if it is valid and
// not an error, or it returns a string or object describing the error:
//
//	try(<error>) -> <map<string,string>>
//	try(<dyn>) -> <dyn>
//	try(<error>, <string>) -> <map<string,string>>
//	try(<dyn>, <string>) -> <dyn>
//
// Examples:
//
//	try(0/1)            // return 0
//	try(0/0)            // return "division by zero"
//	try(0/0, "error")   // return {"error": "division by zero"}
//
// # Is Error
//
// is_error returns a bool indicating whether the argument is an error:
//
//	is_error(<dyn>) -> <bool>
//
// Examples:
//
//	is_error(0/1)            // return false
//	is_error(0/0)            // return true
func Try() cel.EnvOption {
	return cel.Lib(tryLib{})
}

type tryLib struct{}

func (tryLib) CompileOptions() []cel.EnvOption {
	return []cel.EnvOption{
		cel.Function("try",
			cel.Overload(
				"try_dyn",
				[]*cel.Type{cel.DynType},
				cel.DynType,
				cel.UnaryBinding(try),
				cel.OverloadIsNonStrict(),
			),
			cel.Overload(
				"try_dyn_string",
				[]*cel.Type{cel.DynType, cel.StringType},
				cel.DynType,
				cel.BinaryBinding(tryMessage),
				cel.OverloadIsNonStrict(),
			),
		),
		cel.Function("is_error",
			cel.Overload(
				"is_error_dyn",
				[]*cel.Type{cel.DynType},
				cel.BoolType,
				cel.UnaryBinding(isError),
				cel.OverloadIsNonStrict(),
			),
		),
	}
}

func (tryLib) ProgramOptions() []cel.ProgramOption { return nil }

func try(arg ref.Val) ref.Val {
	if types.IsError(arg) {
		return types.String(fmt.Sprint(arg))
	}
	return arg
}

func tryMessage(arg, msg ref.Val) ref.Val {
	str, ok := msg.(types.String)
	if !ok {
		return types.NoSuchOverloadErr()
	}
	if types.IsError(arg) {
		return types.NewRefValMap(types.DefaultTypeAdapter, map[ref.Val]ref.Val{
			str: types.String(fmt.Sprint(arg)),
		})
	}
	return arg
}

func isError(arg ref.Val) ref.Val {
	return types.Bool(types.IsError(arg))
}