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// Copyright 2023 Google LLC
//
// Licensed 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 ext
import (
"fmt"
"github.com/google/cel-go/cel"
"github.com/google/cel-go/common/types"
"github.com/google/cel-go/common/types/ref"
"github.com/google/cel-go/common/types/traits"
)
// Lists returns a cel.EnvOption to configure extended functions for list manipulation.
// As a general note, all indices are zero-based.
// # Slice
//
// Returns a new sub-list using the indexes provided.
//
// <list>.slice(<int>, <int>) -> <list>
//
// Examples:
//
// [1,2,3,4].slice(1, 3) // return [2, 3]
// [1,2,3,4].slice(2, 4) // return [3 ,4]
func Lists() cel.EnvOption {
return cel.Lib(listsLib{})
}
type listsLib struct{}
// LibraryName implements the SingletonLibrary interface method.
func (listsLib) LibraryName() string {
return "cel.lib.ext.lists"
}
// CompileOptions implements the Library interface method.
func (listsLib) CompileOptions() []cel.EnvOption {
listType := cel.ListType(cel.TypeParamType("T"))
return []cel.EnvOption{
cel.Function("slice",
cel.MemberOverload("list_slice",
[]*cel.Type{listType, cel.IntType, cel.IntType}, listType,
cel.FunctionBinding(func(args ...ref.Val) ref.Val {
list := args[0].(traits.Lister)
start := args[1].(types.Int)
end := args[2].(types.Int)
result, err := slice(list, start, end)
if err != nil {
return types.WrapErr(err)
}
return result
}),
),
),
}
}
// ProgramOptions implements the Library interface method.
func (listsLib) ProgramOptions() []cel.ProgramOption {
return []cel.ProgramOption{}
}
func slice(list traits.Lister, start, end types.Int) (ref.Val, error) {
listLength := list.Size().(types.Int)
if start < 0 || end < 0 {
return nil, fmt.Errorf("cannot slice(%d, %d), negative indexes not supported", start, end)
}
if start > end {
return nil, fmt.Errorf("cannot slice(%d, %d), start index must be less than or equal to end index", start, end)
}
if listLength < end {
return nil, fmt.Errorf("cannot slice(%d, %d), list is length %d", start, end, listLength)
}
var newList []ref.Val
for i := types.Int(start); i < end; i++ {
val := list.Get(i)
newList = append(newList, val)
}
return types.DefaultTypeAdapter.NativeToValue(newList), nil
}
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