/
if.go
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/
if.go
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// Mgmt
// Copyright (C) 2013-2024+ James Shubin and the project contributors
// Written by James Shubin <james@shubin.ca> and the project contributors
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
//
// Additional permission under GNU GPL version 3 section 7
//
// If you modify this program, or any covered work, by linking or combining it
// with embedded mcl code and modules (and that the embedded mcl code and
// modules which link with this program, contain a copy of their source code in
// the authoritative form) containing parts covered by the terms of any other
// license, the licensors of this program grant you additional permission to
// convey the resulting work. Furthermore, the licensors of this program grant
// the original author, James Shubin, additional permission to update this
// additional permission if he deems it necessary to achieve the goals of this
// additional permission.
package structs
import (
"context"
"fmt"
"github.com/purpleidea/mgmt/lang/interfaces"
"github.com/purpleidea/mgmt/lang/types"
)
const (
// IfFuncName is the unique name identifier for this function.
IfFuncName = "if"
)
// IfFunc is a function that passes through the value of the correct branch
// based on the conditional value it gets.
type IfFunc struct {
Type *types.Type // this is the type of the if expression output we hold
init *interfaces.Init
last types.Value // last value received to use for diff
result types.Value // last calculated output
}
// String returns a simple name for this function. This is needed so this struct
// can satisfy the pgraph.Vertex interface.
func (obj *IfFunc) String() string {
return IfFuncName
}
// Validate tells us if the input struct takes a valid form.
func (obj *IfFunc) Validate() error {
if obj.Type == nil {
return fmt.Errorf("must specify a type")
}
return nil
}
// Info returns some static info about itself.
func (obj *IfFunc) Info() *interfaces.Info {
var typ *types.Type
if obj.Type != nil { // don't panic if called speculatively
typ = &types.Type{
Kind: types.KindFunc, // function type
Map: map[string]*types.Type{
"c": types.TypeBool, // conditional must be a boolean
"a": obj.Type, // true branch must be this type
"b": obj.Type, // false branch must be this type too
},
Ord: []string{"c", "a", "b"}, // conditional, and two branches
Out: obj.Type, // result type must match
}
}
return &interfaces.Info{
Pure: true,
Memo: false, // TODO: ???
Sig: typ,
Err: obj.Validate(),
}
}
// Init runs some startup code for this if expression function.
func (obj *IfFunc) Init(init *interfaces.Init) error {
obj.init = init
return nil
}
// Stream takes an input struct in the format as described in the Func and Graph
// methods of the Expr, and returns the actual expected value as a stream based
// on the changing inputs to that value.
func (obj *IfFunc) Stream(ctx context.Context) error {
defer close(obj.init.Output) // the sender closes
for {
select {
case input, ok := <-obj.init.Input:
if !ok {
return nil // can't output any more
}
//if err := input.Type().Cmp(obj.Info().Sig.Input); err != nil {
// return errwrap.Wrapf(err, "wrong function input")
//}
if obj.last != nil && input.Cmp(obj.last) == nil {
continue // value didn't change, skip it
}
obj.last = input // store for next
var result types.Value
if input.Struct()["c"].Bool() {
result = input.Struct()["a"] // true branch
} else {
result = input.Struct()["b"] // false branch
}
// skip sending an update...
if obj.result != nil && result.Cmp(obj.result) == nil {
continue // result didn't change
}
obj.result = result // store new result
case <-ctx.Done():
return nil
}
select {
case obj.init.Output <- obj.result: // send
// pass
case <-ctx.Done():
return nil
}
}
}