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options.go
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options.go
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package miruken
import (
"fmt"
"reflect"
"dario.cat/mergo"
"github.com/miruken-go/miruken/internal"
"github.com/miruken-go/miruken/promise"
)
type (
// Option provides an explicit representation of
// an optional value when the Zero value is not
// sufficient to distinguish unset values.
Option[T any] struct {
set bool
val T
}
// FromOptions is a DependencyResolver for option arguments.
FromOptions struct{}
// optCallback captures option values.
optCallback struct {
options any
}
// optionsHandler uses an option instance to merge from
// during an option resolution.
optionsHandler struct {
Handler
options any
optionsType reflect.Type
}
// optionMerger defines customer merging behavior.
optionMerger struct{}
// mergeable enables custom merge behavior.
mergeable interface {
MergeFrom(options any) bool
}
)
// Option[T]
func (o *Option[T]) Set() bool {
return o.set
}
func (o *Option[T]) Value() T {
return o.val
}
func (o *Option[T]) ValueOrDefault(val T) T {
if o.set {
return o.val
}
return val
}
func (o *Option[T]) SetValue(val T) {
o.val = val
}
func (o *Option[T]) MergeFrom(option any) bool {
if o.set {
return false
}
if other, ok := option.(Option[T]); ok && other.set {
o.val = other.val
o.set = true
return true
}
return false
}
// Set creates a new Option set to val.
func Set[T any](val T) Option[T] {
return Option[T]{true, val}
}
// Options returns a BuilderFunc that makes the provided
// options available for merging into matching options.
func Options(options any) BuilderFunc {
optType := reflect.TypeOf(options)
if optType == nil {
panic("options cannot be nil")
}
if optType.Kind() == reflect.Ptr {
optType = optType.Elem()
}
if optType.Kind() != reflect.Struct {
panic("options must be a struct or *struct")
}
return func(handler Handler) Handler {
return &optionsHandler{handler, options, optType}
}
}
func GetOptions[T any](handler Handler) (t T, ok bool) {
ok = GetOptionsInto(handler, &t)
return
}
func GetOptionsInto(handler Handler, target any) bool {
if internal.IsNil(handler) {
panic("handler cannot be nil")
}
tv := internal.TargetValue(target)
optType := tv.Type()
if optType.Kind() != reflect.Ptr {
panic(fmt.Sprintf("options: %v is not a *struct or **struct", optType))
}
optType = optType.Elem()
created := false
options := optCallback{}
switch optType.Kind() {
case reflect.Struct:
options.options = tv.Interface()
case reflect.Ptr:
if optType.Elem().Kind() != reflect.Struct {
panic(fmt.Sprintf("options: %v is not a *struct or **struct", optType))
}
created = true
if value := reflect.Indirect(tv); value.IsNil() {
options.options = reflect.New(optType.Elem()).Interface()
} else {
options.options = value.Interface()
}
}
handled := handler.Handle(options, true, nil).Handled()
if handled && created {
internal.CopyIndirect(options.options, target)
}
return handled
}
// MergeOptions merges from options into options
func MergeOptions(from, into any) bool {
return mergo.Merge(into, from,
mergo.WithAppendSlice,
mergo.WithTransformers(mergeOptions)) == nil
}
// optCallback
func (o optCallback) CanInfer() bool {
return false
}
func (o optCallback) CanFilter() bool {
return false
}
func (o optCallback) CanBatch() bool {
return false
}
// optionsHandler
func (c *optionsHandler) Handle(
callback any,
greedy bool,
composer Handler,
) HandleResult {
if callback == nil {
return NotHandled
}
tryInitializeComposer(&composer, c)
cb := callback
if comp, ok := cb.(*Composition); ok {
if cb = comp.Callback(); cb == nil {
return c.Handler.Handle(callback, greedy, composer)
}
}
if opt, ok := cb.(optCallback); ok {
options := opt.options
if reflect.TypeOf(options).Elem().AssignableTo(c.optionsType) {
merged := false
if o, ok := options.(mergeable); ok {
merged = o.MergeFrom(c.options)
} else {
merged = MergeOptions(c.options, opt.options)
}
if merged {
if greedy {
return c.Handler.Handle(callback, greedy, composer).Or(Handled)
}
return Handled
}
}
}
return c.Handler.Handle(callback, greedy, composer)
}
// FromOptions
func (o FromOptions) Validate(
typ reflect.Type,
dep DependencyArg,
) error {
if typ.Kind() == reflect.Ptr {
typ = typ.Elem()
}
if typ.Kind() != reflect.Struct {
return fmt.Errorf("FromOptions: %v is not a struct or *struct", typ)
}
return nil
}
func (o FromOptions) Resolve(
typ reflect.Type,
dep DependencyArg,
ctx HandleContext,
) (options reflect.Value, _ *promise.Promise[reflect.Value], err error) {
options = reflect.New(typ)
if GetOptionsInto(ctx, options.Interface()) {
if typ.Kind() == reflect.Ptr {
return options, nil, nil
}
return reflect.Indirect(options), nil, nil
}
if dep.Optional() {
return reflect.Zero(typ), nil, nil
}
var v reflect.Value
return v, nil, fmt.Errorf("FromOptions: unable to resolve options %v", typ)
}
// optionMerger
func (t optionMerger) Transformer(
typ reflect.Type,
) func(dst, src reflect.Value) error {
addr := false
if !typ.AssignableTo(mergeableType) && typ.Kind() != reflect.Ptr {
typ = reflect.PointerTo(typ)
addr = true
}
if !addr || typ.AssignableTo(mergeableType) {
return func(dst, src reflect.Value) error {
if addr {
dst = dst.Addr()
}
if d, ok := dst.Interface().(mergeable); ok && !internal.IsNil(d) {
if s := src.Interface(); !internal.IsNil(s) {
d.MergeFrom(s)
}
}
return nil
}
}
return nil
}
var (
mergeableType = reflect.TypeFor[mergeable]()
mergeOptions = optionMerger{}
)