95 lines
2.7 KiB
Go
95 lines
2.7 KiB
Go
// Copyright 2023 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package ext
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import (
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"fmt"
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"github.com/google/cel-go/cel"
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"github.com/google/cel-go/common/types"
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"github.com/google/cel-go/common/types/ref"
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"github.com/google/cel-go/common/types/traits"
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)
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// Lists returns a cel.EnvOption to configure extended functions for list manipulation.
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// As a general note, all indices are zero-based.
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// # Slice
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//
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// Returns a new sub-list using the indexes provided.
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//
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// <list>.slice(<int>, <int>) -> <list>
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//
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// Examples:
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//
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// [1,2,3,4].slice(1, 3) // return [2, 3]
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// [1,2,3,4].slice(2, 4) // return [3 ,4]
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func Lists() cel.EnvOption {
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return cel.Lib(listsLib{})
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}
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type listsLib struct{}
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// LibraryName implements the SingletonLibrary interface method.
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func (listsLib) LibraryName() string {
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return "cel.lib.ext.lists"
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}
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// CompileOptions implements the Library interface method.
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func (listsLib) CompileOptions() []cel.EnvOption {
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listType := cel.ListType(cel.TypeParamType("T"))
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return []cel.EnvOption{
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cel.Function("slice",
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cel.MemberOverload("list_slice",
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[]*cel.Type{listType, cel.IntType, cel.IntType}, listType,
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cel.FunctionBinding(func(args ...ref.Val) ref.Val {
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list := args[0].(traits.Lister)
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start := args[1].(types.Int)
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end := args[2].(types.Int)
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result, err := slice(list, start, end)
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if err != nil {
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return types.WrapErr(err)
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}
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return result
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}),
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),
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),
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}
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}
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// ProgramOptions implements the Library interface method.
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func (listsLib) ProgramOptions() []cel.ProgramOption {
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return []cel.ProgramOption{}
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}
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func slice(list traits.Lister, start, end types.Int) (ref.Val, error) {
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listLength := list.Size().(types.Int)
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if start < 0 || end < 0 {
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return nil, fmt.Errorf("cannot slice(%d, %d), negative indexes not supported", start, end)
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}
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if start > end {
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return nil, fmt.Errorf("cannot slice(%d, %d), start index must be less than or equal to end index", start, end)
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}
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if listLength < end {
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return nil, fmt.Errorf("cannot slice(%d, %d), list is length %d", start, end, listLength)
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}
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var newList []ref.Val
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for i := types.Int(start); i < end; i++ {
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val := list.Get(i)
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newList = append(newList, val)
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}
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return types.DefaultTypeAdapter.NativeToValue(newList), nil
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}
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