wand/reflect.go

package wand

import (
	"fmt"
	"github.com/iancoleman/strcase"
	"io"
	"reflect"
	"slices"
	"strconv"
	"strings"
)

type packedKind[T any] interface {
	Kind() reflect.Kind
	Elem() T
}

type field struct {
	name            string
	path            []string
	typ             reflect.Type
	acceptsMultiple bool
}

var (
	readerType = reflect.TypeFor[io.Reader]()
	writerType = reflect.TypeFor[io.Writer]()
)

func pack(v reflect.Value, t reflect.Type) reflect.Value {
	if v.Type() == t {
		return v
	}

	if t.Kind() == reflect.Pointer {
		pv := pack(v, t.Elem())
		p := reflect.New(t.Elem())
		p.Elem().Set(pv)
		return p
	}

	iv := pack(v, t.Elem())
	s := reflect.MakeSlice(t, 1, 1)
	s.Index(0).Set(iv)
	return s
}

func unpack[T packedKind[T]](p T, kinds ...reflect.Kind) T {
	if len(kinds) == 0 {
		kinds = []reflect.Kind{reflect.Pointer, reflect.Slice}
	}

	if slices.Contains(kinds, p.Kind()) {
		return unpack(p.Elem(), kinds...)
	}

	return p
}

func isReader(t reflect.Type) bool {
	return unpack(t) == readerType
}

func isWriter(t reflect.Type) bool {
	return unpack(t) == writerType
}

func isStruct(t reflect.Type) bool {
	t = unpack(t)
	return t.Kind() == reflect.Struct
}

func parseInt(s string, byteSize int) (int64, error) {
	bitSize := byteSize * 8
	switch {
	case strings.HasPrefix(s, "0b"):
		return strconv.ParseInt(s[2:], 2, bitSize)
	case strings.HasPrefix(s, "0x"):
		return strconv.ParseInt(s[2:], 16, bitSize)
	case strings.HasPrefix(s, "0"):
		return strconv.ParseInt(s[1:], 8, bitSize)
	default:
		return strconv.ParseInt(s[2:], 2, byteSize*8)
	}
}

func parseUint(s string, byteSize int) (uint64, error) {
	bitSize := byteSize * 8
	switch {
	case strings.HasPrefix(s, "0b"):
		return strconv.ParseUint(s[2:], 2, bitSize)
	case strings.HasPrefix(s, "0x"):
		return strconv.ParseUint(s[2:], 16, bitSize)
	case strings.HasPrefix(s, "0"):
		return strconv.ParseUint(s[1:], 8, bitSize)
	default:
		return strconv.ParseUint(s[2:], 2, bitSize)
	}
}

func canScan(t reflect.Type, s string) bool {
	switch t.Kind() {
	case reflect.Bool:
		_, err := strconv.ParseBool(s)
		return err == nil
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		_, err := parseInt(s, int(t.Size()))
		return err == nil
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		_, err := parseUint(s, int(t.Size()))
		return err == nil
	case reflect.Float32, reflect.Float64:
		_, err := strconv.ParseFloat(s, int(t.Size())*8)
		return err == nil
	case reflect.String:
		return true
	default:
		return false
	}
}

func scan(t reflect.Type, s string) any {
	p := reflect.New(t)
	switch t.Kind() {
	case reflect.Bool:
		v, _ := strconv.ParseBool(s)
		p.Elem().Set(reflect.ValueOf(v).Convert(t))
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		v, _ := parseInt(s, int(t.Size()))
		p.Elem().Set(reflect.ValueOf(v).Convert(t))
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		v, _ := parseUint(s, int(t.Size()))
		p.Elem().Set(reflect.ValueOf(v).Convert(t))
	case reflect.Float32, reflect.Float64:
		v, _ := strconv.ParseFloat(s, int(t.Size())*8)
		p.Elem().Set(reflect.ValueOf(v).Convert(t))
	default:
		p.Elem().Set(reflect.ValueOf(s).Convert(t))
	}

	return p.Elem().Interface()
}

func fieldsChecked(visited map[reflect.Type]bool, s ...reflect.Type) ([]field, error) {
	if len(s) == 0 {
		return nil, nil
	}

	var (
		anonFields  []field
		plainFields []field
	)

	for i := 0; i < s[0].NumField(); i++ {
		sf := s[0].Field(i)
		sft := sf.Type
		am := acceptsMultiple(sft)
		sft = unpack(sft)
		sfn := sf.Name
		sfn = strcase.ToKebab(sfn)
		switch sft.Kind() {
		case reflect.Bool,
			reflect.Int,
			reflect.Int8,
			reflect.Int16,
			reflect.Int32,
			reflect.Int64,
			reflect.Uint,
			reflect.Uint8,
			reflect.Uint16,
			reflect.Uint32,
			reflect.Uint64,
			reflect.Float32,
			reflect.Float64,
			reflect.String:
			plainFields = append(plainFields, field{
				name:            sfn,
				path:            []string{sf.Name},
				typ:             sft,
				acceptsMultiple: am,
			})
		case reflect.Interface:
			if sft.NumMethod() == 0 {
				plainFields = append(plainFields, field{
					name:            sfn,
					path:            []string{sf.Name},
					typ:             sft,
					acceptsMultiple: am,
				})
			}
		case reflect.Struct:
			if visited[sft] {
				return nil, fmt.Errorf("circular type definitions not allowed: %s", sft.Name())
			}

			if visited == nil {
				visited = make(map[reflect.Type]bool)
			}

			visited[sft] = true
			sff, err := fieldsChecked(visited, sft)
			if err != nil {
				return nil, err
			}

			if sf.Anonymous {
				anonFields = append(anonFields, sff...)
			} else {
				for i := range sff {
					sff[i].name = sfn + "-" + sff[i].name
					sff[i].path = append([]string{sf.Name}, sff[i].path...)
					sff[i].acceptsMultiple = sff[i].acceptsMultiple || am
				}

				plainFields = append(plainFields, sff...)
			}
		}
	}

	mf := make(map[string]field)
	for _, fi := range anonFields {
		mf[fi.name] = fi
	}

	for _, fi := range plainFields {
		mf[fi.name] = fi
	}

	var f []field
	for _, fi := range mf {
		f = append(f, fi)
	}

	ff, err := fieldsChecked(visited, s[1:]...)
	if err != nil {
		return nil, err
	}

	return append(f, ff...), nil
}

func fields(s ...reflect.Type) []field {
	f, _ := fieldsChecked(nil, s...)
	return f
}

func boolFields(f []field) []field {
	var b []field
	for _, fi := range f {
		if fi.typ.Kind() == reflect.Bool {
			b = append(b, fi)
		}
	}

	return b
}

func mapFields(impl any) map[string][]field {
	v := reflect.ValueOf(impl)
	t := v.Type()
	t = unpack(t)
	s := structParameters(t)
	f := fields(s...)
	mf := make(map[string][]field)
	for _, fi := range f {
		mf[fi.name] = append(mf[fi.name], fi)
	}

	return mf
}

func filterParameters(t reflect.Type, f func(reflect.Type) bool) []reflect.Type {
	var s []reflect.Type
	for i := 0; i < t.NumIn(); i++ {
		p := t.In(i)
		p = unpack(p)
		if f(p) {
			s = append(s, p)
		}
	}

	return s
}

func positionalParameters(t reflect.Type) []reflect.Type {
	return filterParameters(t, func(p reflect.Type) bool {
		return p.Kind() != reflect.Struct
	})
}

func ioParameters(p []reflect.Type) ([]int, []int) {
	var (
		reader []int
		writer []int
	)

	for i, pi := range p {
		switch {
		case isReader(pi):
			reader = append(reader, i)
		case isWriter(pi):
			writer = append(writer, i)
		}
	}

	return reader, writer
}

func structParameters(t reflect.Type) []reflect.Type {
	return filterParameters(t, func(p reflect.Type) bool {
		return p.Kind() == reflect.Struct
	})
}

func compatibleTypes(t ...reflect.Type) bool {
	if len(t) < 2 {
		return true
	}

	t0 := t[0]
	t1 := t[1]
	switch t0.Kind() {
	case reflect.Bool:
		return t1.Kind() == reflect.Bool
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		switch t1.Kind() {
		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
			return true
		default:
			return false
		}
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		switch t1.Kind() {
		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
			return true
		default:
			return false
		}
	case reflect.Float32, reflect.Float64:
		switch t1.Kind() {
		case reflect.Float32, reflect.Float64:
			return true
		default:
			return false
		}
	case reflect.String:
		return t1.Kind() == reflect.String
	case reflect.Interface:
		return t1.Kind() == reflect.Interface && t0.NumMethod() == 0 && t1.NumMethod() == 0
	default:
		return false
	}
}

func acceptsMultiple(t reflect.Type) bool {
	if t.Kind() == reflect.Slice {
		return true
	}

	switch t.Kind() {
	case reflect.Pointer, reflect.Slice:
		return acceptsMultiple(t.Elem())
	default:
		return false
	}
}