reflection: WIP

Signed-off-by: Alejandro Mery <amery@jpi.io>

go.mod

@@ -2,20 +2,22 @@ module asciigoat.org/core
 
 go 1.19
 
-require github.com/mgechev/revive v1.3.3
+require (
+	github.com/fatih/structtag v1.2.0
+	github.com/mgechev/revive v1.3.3
+	github.com/pkg/errors v0.9.1
+)
 
 require (
 	github.com/BurntSushi/toml v1.3.2 // indirect
 	github.com/chavacava/garif v0.0.0-20230608123814-4bd63c2919ab // indirect
 	github.com/fatih/color v1.15.0 // indirect
-	github.com/fatih/structtag v1.2.0 // indirect
 	github.com/mattn/go-colorable v0.1.13 // indirect
 	github.com/mattn/go-isatty v0.0.17 // indirect
 	github.com/mattn/go-runewidth v0.0.9 // indirect
 	github.com/mgechev/dots v0.0.0-20210922191527-e955255bf517 // indirect
 	github.com/mitchellh/go-homedir v1.1.0 // indirect
 	github.com/olekukonko/tablewriter v0.0.5 // indirect
-	github.com/pkg/errors v0.9.1 // indirect
 	golang.org/x/sys v0.11.0 // indirect
 	golang.org/x/tools v0.12.0 // indirect
 )

reflection/error.go

@@ -0,0 +1,69 @@
+package reflection
+
+import (
+	"bytes"
+	"fmt"
+	"reflect"
+)
+
+// An InvalidUnmarshalError describes an invalid argument passed to New.
+// (It must be a non-nil pointer.)
+type InvalidUnmarshalError struct {
+	Method string
+	Prefix string
+
+	reflect.Type
+}
+
+func (e *InvalidUnmarshalError) Error() string {
+	var buf bytes.Buffer
+
+	if e.Prefix != "" {
+		_, _ = fmt.Fprintf(&buf, "%s: ", e.Prefix)
+	}
+
+	method := e.Method
+	if method == "" {
+		method = "New"
+	}
+
+	_, _ = fmt.Fprintf(&buf, "%s(", method)
+
+	switch {
+	case e.Type == nil:
+		_, _ = buf.WriteString("nil")
+	case e.Type.Kind() != reflect.Pointer:
+		_, _ = fmt.Fprintf(&buf, "%s %s", "non-pointer", e.Type.String())
+	default:
+		_, _ = fmt.Fprintf(&buf, "%s %s", "nil", e.Type.String())
+	}
+
+	_, _ = buf.WriteString(")")
+
+	return buf.String()
+}
+
+// An UnmarshalTypeError tells something went wrong while processing
+// a type.
+type UnmarshalTypeError struct {
+	Prefix string
+	Err    error
+
+	reflect.Type
+}
+
+func (e UnmarshalTypeError) Unwrap() error {
+	return e.Err
+}
+
+func (e UnmarshalTypeError) Error() string {
+	var buf bytes.Buffer
+
+	if e.Prefix != "" {
+		_, _ = fmt.Fprintf(&buf, "%s: ", e.Prefix)
+	}
+
+	_, _ = fmt.Fprintf(&buf, "%s: %s", e.Type.String(), e.Err)
+
+	return buf.String()
+}

reflection/reflect_help.go

@@ -0,0 +1,16 @@
+package reflection
+
+import (
+	"fmt"
+	"reflect"
+)
+
+func structFieldName(sf reflect.StructField) string {
+	if sf.Anonymous {
+		idx := sf.Index[len(sf.Index)-1]
+
+		return fmt.Sprintf("%s-%v", "anonymous", idx)
+	}
+
+	return sf.Name
+}

reflection/reflection.go

@@ -0,0 +1,40 @@
+// Package reflection helps Marshalling/Unmarshalling data to structs
+package reflection
+
+import (
+	"reflect"
+)
+
+// Reflection provides Marshalling/Unmarshalling oriented view
+// of a value
+type Reflection struct {
+	v reflect.Value
+
+	types map[reflect.Type]TypeInfo
+}
+
+// Value returns the object it reflects
+func (r *Reflection) Value() any {
+	return r.v.Interface()
+}
+
+// New creates a Reflection of the given pointer
+func New(v any) (*Reflection, error) {
+	rv := reflect.ValueOf(v)
+
+	if rv.Kind() != reflect.Pointer || rv.IsNil() {
+		err := &InvalidUnmarshalError{Type: rv.Type()}
+		return nil, err
+	}
+
+	r := &Reflection{
+		v:     rv,
+		types: make(map[reflect.Type]TypeInfo),
+	}
+
+	if err := r.scan(); err != nil {
+		return nil, err
+	}
+
+	return r, nil
+}

reflection/scan.go

@@ -0,0 +1,37 @@
+package reflection
+
+import (
+	"reflect"
+)
+
+func (r *Reflection) scanType(rt reflect.Type) error {
+	switch rt.Kind() {
+	case reflect.Pointer, reflect.Slice:
+		rt = rt.Elem()
+	}
+
+	if _, ok := r.types[rt]; ok {
+		// cached
+		return nil
+	}
+
+	ti, err := NewTypeInfo(rt)
+	if err != nil {
+		return &UnmarshalTypeError{Type: rt, Err: err}
+	}
+
+	r.types[rt] = ti
+
+	for i := range ti.fields {
+		err := r.scanType(ti.fields[i].sf.Type)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (r *Reflection) scan() error {
+	return r.scanType(r.v.Type())
+}

reflection/typeinfo.go

@@ -0,0 +1,108 @@
+package reflection
+
+import (
+	"log"
+	"reflect"
+
+	"github.com/fatih/structtag"
+	"github.com/pkg/errors"
+)
+
+// TypeInfo ...
+type TypeInfo struct {
+	rt reflect.Type
+
+	fields []TypeInfoField
+}
+
+// Type ...
+func (ti *TypeInfo) Type() reflect.Type {
+	return ti.rt
+}
+
+// Kind ...
+func (ti *TypeInfo) Kind() reflect.Kind {
+	return ti.rt.Kind()
+}
+
+// TypeInfoField ...
+type TypeInfoField struct {
+	sf   reflect.StructField
+	tags *structtag.Tags
+
+	Name string
+}
+
+// Type ...
+func (tif *TypeInfoField) Type() reflect.Type {
+	return tif.sf.Type
+}
+
+// Kind ...
+func (tif *TypeInfoField) Kind() reflect.Kind {
+	return tif.sf.Type.Kind()
+}
+
+// Tag ...
+func (tif *TypeInfoField) Tag(key string) (*structtag.Tag, bool) {
+	if tif.tags != nil {
+		tag, _ := tif.tags.Get(key)
+		if tag != nil {
+			return tag, true
+		}
+	}
+	return nil, false
+}
+
+// NewTypeInfo ...
+func NewTypeInfo(rt reflect.Type) (TypeInfo, error) {
+	log.Printf("%s.%s: %s (%s)", "reflection", "NewTypeInfo", rt, rt.Kind())
+
+	ti := TypeInfo{
+		rt: rt,
+	}
+
+	err := ti.init()
+	return ti, err
+}
+
+func (ti *TypeInfo) init() error {
+	switch ti.Kind() {
+	case reflect.Struct:
+		return ti.initStruct()
+	default:
+		return nil
+	}
+}
+
+func (ti *TypeInfo) initStruct() error {
+	// load fields
+	n := ti.rt.NumField()
+	fields := make([]TypeInfoField, 0, n)
+	for i := 0; i < n; i++ {
+		sf := ti.rt.Field(i)
+		tags, err := structtag.Parse(string(sf.Tag))
+
+		if err != nil {
+			// tag parse error
+			err = &UnmarshalTypeError{
+				Type: ti.rt,
+				Err:  errors.Wrap(err, structFieldName(sf)),
+			}
+			return err
+		}
+
+		if sf.IsExported() {
+			log.Printf("%s.%s:   [%v]: %q %s (%s)",
+				"reflection", "NewTypeInfo",
+				i, structFieldName(sf), sf.Type, sf.Type.Kind())
+
+			fields = append(fields, TypeInfoField{
+				sf:   sf,
+				tags: tags,
+			})
+		}
+	}
+	ti.fields = fields
+	return nil
+}