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composite.go
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composite.go
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// Mgmt
// Copyright (C) 2013-2018+ 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 <http://www.gnu.org/licenses/>.
package structs
import (
"fmt"
"github.com/purpleidea/mgmt/lang/interfaces"
"github.com/purpleidea/mgmt/lang/types"
errwrap "github.com/pkg/errors"
)
// CompositeFunc is a function that passes through the value it receives. It is
// used to take a series of inputs to a list, map or struct, and return that
// value as a stream that depends on those inputs. It helps the list, map, and
// struct's that fulfill the Expr interface but expressing a Func method.
type CompositeFunc struct {
Type *types.Type // this is the type of the composite value we hold
Len int // length of list or map (if used)
init *interfaces.Init
last types.Value // last value received to use for diff
result types.Value // last calculated output
closeChan chan struct{}
}
// Validate makes sure we've built our struct properly.
func (obj *CompositeFunc) Validate() error {
if obj.Type == nil {
return fmt.Errorf("must specify a type")
}
switch obj.Type.Kind {
case types.KindList:
fallthrough
case types.KindMap:
fallthrough
case types.KindStruct:
return nil
}
return fmt.Errorf("can't compose type `%s`", obj.Type.String())
}
// Info returns some static info about itself.
func (obj *CompositeFunc) Info() *interfaces.Info {
typ := &types.Type{
Kind: types.KindFunc, // function type
Map: make(map[string]*types.Type),
Ord: []string{},
Out: obj.Type, // this is the output type for the expression
}
switch obj.Type.Kind {
case types.KindList: // wrapped in a struct with `length` many keys
for i := 0; i < obj.Len; i++ {
// FIXME: should we .Title the fields or add a prefix?
key := fmt.Sprintf("%d", i)
typ.Map[key] = obj.Type.Val // type of each list element
typ.Ord = append(typ.Ord, key)
}
case types.KindMap: // wrapped in a struct with named keys
for i := 0; i < obj.Len; i++ {
// each key and val has a value to pass in, and we have
// a known number of kv pairs, so we pass each in with
// the index of the kv pair as found in the parse order
key1 := fmt.Sprintf("key:%d", i)
typ.Map[key1] = obj.Type.Key // type of each map key
typ.Ord = append(typ.Ord, key1)
key2 := fmt.Sprintf("val:%d", i)
typ.Map[key2] = obj.Type.Val // type of each map val
typ.Ord = append(typ.Ord, key2)
}
case types.KindStruct:
// map it directly, each key is the right input!
typ.Map = obj.Type.Map
typ.Ord = obj.Type.Ord
}
return &interfaces.Info{
Pure: true,
Memo: false, // TODO: ???
Sig: typ,
Err: obj.Validate(),
}
}
// Init runs some startup code for this composite function.
func (obj *CompositeFunc) Init(init *interfaces.Init) error {
obj.init = init
obj.closeChan = make(chan struct{})
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 *CompositeFunc) Stream() 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
switch obj.Type.Kind {
case types.KindList:
// XXX: this duplicates the same logic that exists in Value() as implemented on *ExprList
// XXX: have this call that function to get the result?
result = obj.Type.New() // new list
input := input.(*types.StructValue) // must be!
for i := 0; i < obj.Len; i++ { // build it
value, exists := input.Lookup(fmt.Sprintf("%d", i)) // argNames as integers!
if !exists {
return fmt.Errorf("missing input index `%d`", i)
}
if err := result.(*types.ListValue).Add(value); err != nil {
return errwrap.Wrapf(err, "can't build list index `%d`", i)
}
}
case types.KindMap:
result = obj.Type.New() // new map
input := (input.(*types.StructValue)).Struct() // must be!
l := len(input)
if l%2 != 0 {
return fmt.Errorf("expected even number of inputs for a map, got: %d", l)
}
// each key should be named `key:0`, `val:0`, `key:1`, `val:1`,
// and so on for as many key pairs as we have... remember that
// the number of keys pairs is known statically in this case!
for i := 0; i < l/2; i++ { // build it
key, exists := input[fmt.Sprintf("key:%d", i)]
if !exists {
return fmt.Errorf("missing input key `key:%d`", i)
}
val, exists := input[fmt.Sprintf("val:%d", i)]
if !exists {
return fmt.Errorf("missing input val `val:%d`", i)
}
if err := result.(*types.MapValue).Add(key, val); err != nil {
return errwrap.Wrapf(err, "can't build map key with index `%d`", i)
}
}
case types.KindStruct:
result = input
}
// 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 <-obj.closeChan:
return nil
}
select {
case obj.init.Output <- obj.result: // send
// pass
case <-obj.closeChan:
return nil
}
}
}
// Close runs some shutdown code for this function and turns off the stream.
func (obj *CompositeFunc) Close() error {
close(obj.closeChan)
return nil
}