package tape

// dont smoke reflection, kids!!!!!!!!!
// totally reflectric, reflectrified, etc. this is probably souper slow but
// certainly no slower than the built in json encoder i'd imagine.
// TODO: add support for struct tags: `tape:"0000"`, tape:"0001"` so they can get
// transformed into tables with a defined schema

import "fmt"
import "reflect"

var dummyMap map[uint16] any

// EncodeAny encodes an "any" value. Returns an error if the underlying type is
// unsupported. Supported types are:
//
//   - int
//   - int<N>
//   - uint
//   - uint<N>
//   - string
//   - []<supported type>
//   - map[uint16]<supported type>
func EncodeAny(encoder *Encoder, value any, tag Tag) (n int, err error) {
	// TODO use reflection for all of this to ignore type names
	// primitives
	switch value := value.(type) {
	case int:    return encoder.WriteInt32(int32(value))
	case uint:   return encoder.WriteUint32(uint32(value))
	case int8:   return encoder.WriteInt8(value)
	case uint8:  return encoder.WriteUint8(value)
	case int16:  return encoder.WriteInt16(value)
	case uint16: return encoder.WriteUint16(value)
	case int32:  return encoder.WriteInt32(value)
	case uint32: return encoder.WriteUint32(value)
	case int64:  return encoder.WriteInt64(value)
	case uint64: return encoder.WriteUint64(value)
	case string: return EncodeAny(encoder, []byte(value), tag)
	case []byte:
		if tag.Is(LBA) {
			nn, err := encoder.WriteUintN(uint64(len(value)), tag.CN() + 1)
			n += nn; if err != nil { return n, err }
		}
		nn, err := encoder.Write(value)
		n += nn; if err != nil { return n, err }
		return n, nil
	}

	// aggregates
	reflectType := reflect.TypeOf(value)
	switch reflectType.Kind() {
	case reflect.Slice:
		return encodeAnySlice(encoder, value, tag)
	// case reflect.Array:
		// return encodeAnySlice(encoder, reflect.ValueOf(value).Slice(0, reflectType.Len()).Interface(), tag)
	case reflect.Map:
		if reflectType.Key() == reflect.TypeOf(uint16(0)) {
			return encodeAnyMap(encoder, value, tag)
		}
		return n, fmt.Errorf("cannot encode map key %T, key must be uint16", value)
	}
	return n, fmt.Errorf("cannot encode type %T", value)
}

// DecodeAny decodes data and places it into destination, which must be a
// pointer to a supported type. See [EncodeAny] for a list of supported types.
func DecodeAny(decoder *Decoder, destination any, tag Tag) (n int, err error) {
	reflectDestination := reflect.ValueOf(destination)
	if reflectDestination.Kind() != reflect.Pointer {
		return n, fmt.Errorf("expected pointer destination, not %v", destination)
	}
	return decodeAny(decoder, reflectDestination.Elem(), tag)
}

// unknownSlicePlaceholder is inserted by skeletonValue and informs the program
// that the destination for the slice needs to be generated based on the item
// tag in the OTA.
type unknownSlicePlaceholder struct { }
var unknownSlicePlaceholderType = reflect.TypeOf(unknownSlicePlaceholder { })

// decodeAny is internal to [DecodeAny]. It takes in an addressable
// [reflect.Value] as the destination.
func decodeAny(decoder *Decoder, destination reflect.Value, tag Tag) (n int, err error) {
	errWrongDestinationType := func(expected string) error {
		panic(fmt.Errorf(
		// return fmt.Errorf(
			"expected %s destination, not %v",
			expected, destination))
	}
	
	switch tag.WithoutCN() {
	case SI:
		// SI: (none)
		err = setInt(destination, uint64(tag.CN()))
		if err != nil { return n, err }
	case LI:
		// LI: <value: IntN>
		nn, err := decodeAndSetInt(decoder, destination, tag.CN() + 1)
		n += nn; if err != nil { return n, err }
	case FP:
		// FP: <value: FloatN>
		nn, err := decodeAndSetFloat(decoder, destination, tag.CN() + 1)
		n += nn; if err != nil { return n, err }
	case SBA:
		// SBA: <data: U8>*
		buffer := make([]byte, tag.CN())
		nn, err := decoder.Read(buffer)
		n += nn; if err != nil { return n, err }
		err = setByteArray(destination, buffer)
		if err != nil { return n, err }
	case LBA:
		// LBA: <length: UN> <data: U8>*
		length, nn, err := decoder.ReadUintN(tag.CN() + 1)
		n += nn; if err != nil { return n, err }
		buffer := make([]byte, length)
		nn, err = decoder.Read(buffer)
		n += nn; if err != nil { return n, err }
		err = setByteArray(destination, buffer)
		if err != nil { return n, err }
	case OTA:
		// OTA: <length: UN> <elementTag: tape.Tag> <values>*
		length, nn, err := decoder.ReadUintN(tag.CN() + 1)
		n += nn; if err != nil { return n, err }
		oneTag, nn, err := decoder.ReadTag()
		n += nn; if err != nil { return n, err }
		if destination.Kind() != reflect.Slice {
			return n, errWrongDestinationType("slice")
		}
		if destination.Cap() < int(length) {
			destination.Grow(destination.Cap() - int(length))
		}
		destination.SetLen(int(length))
		for index := range length {
			nn, err := decodeAny(decoder, destination.Index(int(index)), oneTag)
			n += nn; if err != nil { return n, err }
		}
	case KTV:
		// KTV: <length: UN> (<key: U16> <tag: Tag> <value>)*
		table := destination
		if table.Type() != reflect.TypeOf(dummyMap) {
			return n, errWrongDestinationType("map[uint16] any")
		}
		length, nn, err := decoder.ReadUintN(tag.CN() + 1)
		n += nn; if err != nil { return n, err }
		table.Clear()
		for _ = range length {
			key, nn, err := decoder.ReadUint16()
			n += nn; if err != nil { return n, err }
			itemTag, nn, err := decoder.ReadTag()
			n += nn; if err != nil { return n, err }
			value, err := skeletonValue(decoder, itemTag)
			if err != nil { return n, err }
			nn, err = decodeAny(decoder, value.Elem(), itemTag)
			n += nn; if err != nil { return n, err }
			table.SetMapIndex(reflect.ValueOf(key), value)
		}
	default:
		return n, fmt.Errorf("unknown TN %d", tag.TN())
	}
	return n, nil
}

// TagAny returns the correct tag for an "any" value. Returns an error if the
// underlying type is unsupported. See [EncodeAny] for a list of supported
// types.
func TagAny(value any) (Tag, error) {
	// TODO use reflection for all of this to ignore type names
	// primitives
	switch value := value.(type) {
	case int,   uint:   return LI.WithCN(3), nil
	case int8,  uint8:  return LI.WithCN(0), nil
	case int16, uint16: return LI.WithCN(1), nil
	case int32, uint32: return LI.WithCN(3), nil
	case int64, uint64: return LI.WithCN(7), nil
	case string:        return bufferLenTag(len(value)), nil
	case []byte:        return bufferLenTag(len(value)), nil
	}
	
	// aggregates
	reflectType := reflect.TypeOf(value)
	switch reflectType.Kind() {
	case reflect.Slice: return OTA.WithCN(IntBytes(uint64(reflect.ValueOf(value).Len())) - 1), nil
	case reflect.Array: return OTA.WithCN(reflectType.Len()), nil
	case reflect.Map:
		if reflectType.Key() == reflect.TypeOf(uint16(0)) {
			return KTV.WithCN(IntBytes(uint64(reflect.ValueOf(value).Len())) - 1), nil
		}
		return 0, fmt.Errorf("cannot encode map key %T, key must be uint16", value)
	}
	return 0, fmt.Errorf("cannot get tag of type %T", value)
}

func encodeAnySlice(encoder *Encoder, value any, tag Tag) (n int, err error) {
	// OTA: <length: UN> <elementTag: tape.Tag> <values>*
	reflectValue := reflect.ValueOf(value)
	nn, err := encoder.WriteUintN(uint64(reflectValue.Len()), tag.CN() + 1)
	n += nn; if err != nil { return n, err }
	reflectType := reflect.TypeOf(value)
	oneTag, err := TagAny(reflect.Zero(reflectType.Elem()).Interface())
	if err != nil { return n, err }
	for index := 0; index < reflectValue.Len(); index += 1 {
		item := reflectValue.Index(index).Interface()
		itemTag, err := TagAny(item)
		if err != nil { return n, err }
		if itemTag.CN() > oneTag.CN() { oneTag = itemTag }
	}
	if oneTag.Is(SBA) { oneTag += 1 << 5 }
	nn, err = encoder.WriteUint8(uint8(oneTag))
	n += nn; if err != nil { return n, err }
	for index := 0; index < reflectValue.Len(); index += 1 {
		item := reflectValue.Index(index).Interface()
		nn, err = EncodeAny(encoder, item, oneTag)
		n += nn; if err != nil { return n, err }
	}
	return n, err
}

func encodeAnyMap(encoder *Encoder, value any, tag Tag) (n int, err error) {
	// KTV: <length: UN> (<key: U16> <tag: Tag> <value>)*
	reflectValue := reflect.ValueOf(value)
	nn, err := encoder.WriteUintN(uint64(reflectValue.Len()), tag.CN() + 1)
	n += nn; if err != nil { return n, err }
	iter := reflectValue.MapRange()
	for iter.Next() {
		key   := iter.Key().Interface().(uint16)
		value := iter.Value().Interface()
		nn, err = encoder.WriteUint16(key)
		n += nn; if err != nil { return n, err }
		itemTag, err := TagAny(value)
		if err != nil { return n, err }
		nn, err = encoder.WriteUint8(uint8(itemTag))
		n += nn; if err != nil { return n, err }
		nn, err = EncodeAny(encoder, value, itemTag)
		n += nn; if err != nil { return n, err }
	}
	return n, nil
}

// setInt expects a settable destination.
func setInt(destination reflect.Value, value uint64) error {
	switch {
	case destination.CanInt():
		destination.Set(reflect.ValueOf(int64(value)).Convert(destination.Type()))
	case destination.CanUint():
		destination.Set(reflect.ValueOf(value).Convert(destination.Type()))
	default:
		return fmt.Errorf("cannot assign integer to %T", destination.Interface())
	}
	return nil
}

// setInt expects a settable destination.
func setFloat(destination reflect.Value, value float64) error {
	if !destination.CanFloat() {
		return fmt.Errorf("cannot assign float to %T", destination.Interface())
	}
	destination.Set(reflect.ValueOf(value).Convert(destination.Type()))
	return nil
}

// setByteArrayexpects a settable destination.
func setByteArray(destination reflect.Value, value []byte) error {
	typ := destination.Type()
	if typ.Kind() != reflect.Slice {
		return fmt.Errorf("cannot assign %T to ", value)
	}
	if typ.Elem() != reflect.TypeOf(byte(0)) {
		return fmt.Errorf("cannot convert %T to *[]byte", value)
	}
	destination.Set(reflect.ValueOf(value))
	return nil
}

// decodeAndSetInt expects a settable destination.
func decodeAndSetInt(decoder *Decoder, destination reflect.Value, bytes int) (n int, err error) {
	value, nn, err := decoder.ReadUintN(bytes)
	n += nn; if err != nil { return n, err }
	return n, setInt(destination, value)
}

// decodeAndSetInt expects a settable destination.
func decodeAndSetFloat(decoder *Decoder, destination reflect.Value, bytes int) (n int, err error) {
	switch bytes {
	case 8:
		value, nn, err := decoder.ReadFloat64()
		n += nn; if err != nil { return n, err }
		return n, setFloat(destination, float64(value))
	case 4:
		value, nn, err := decoder.ReadFloat32()
		n += nn; if err != nil { return n, err }
		return n, setFloat(destination, float64(value))
	}
	return n, fmt.Errorf("cannot decode float%d", bytes * 8)
}

// skeletonValue returns a pointer value. In order for it to be set, it must be
// dereferenced using Elem().
func skeletonValue(decoder *Decoder, tag Tag) (reflect.Value, error) {
	typ, err := typeOf(decoder, tag)
	if err != nil { return reflect.Value { }, err }
	return reflect.New(typ), nil
}

// typeOf returns the type of the current tag being decoded. It does not use up
// the decoder, it only peeks.
func typeOf(decoder *Decoder, tag Tag) (reflect.Type, error) {
	switch tag.WithoutCN() {
	case SI:
		return reflect.TypeOf(uint8(0)), nil
	case LI:
		switch tag.CN() {
		case 0: return reflect.TypeOf(uint8(0)), nil
		case 1: return reflect.TypeOf(uint16(0)), nil
		case 3: return reflect.TypeOf(uint32(0)), nil
		case 7: return reflect.TypeOf(uint64(0)), nil
		}
		return nil, fmt.Errorf("unknown CN %d for LI", tag.CN())
	case FP:
		switch tag.CN() {
		case 3: return reflect.TypeOf(float32(0)), nil
		case 7: return reflect.TypeOf(float64(0)), nil
		}
		return nil, fmt.Errorf("unknown CN %d for FP", tag.CN())
	case SBA: return reflect.SliceOf(reflect.TypeOf(byte(0))), nil
	case LBA: return reflect.SliceOf(reflect.TypeOf(byte(0))), nil
	case OTA:
		elemTag, dimension, err := peekSlice(decoder, tag)
		if err != nil { return nil, err }
		if elemTag.Is(OTA) { panic("peekSlice cannot return OTA") }
		typ, err := typeOf(decoder, elemTag)
		if err != nil { return nil, err }
		for _ = range dimension {
			typ = reflect.SliceOf(typ)
		}
		return typ, nil
	case KTV: return reflect.TypeOf(dummyMap), nil
	}
	return nil, fmt.Errorf("unknown TN %d", tag.TN())
}

// peekSlice returns the element tag and dimension count of the OTA currently
// being decoded. It does not use up the decoder, it only peeks.
func peekSlice(decoder *Decoder, tag Tag) (Tag, int, error) {
	offset    := 0
	dimension := 0
	for {
		elem, populated, n, err := peekSliceOnce(decoder, tag, offset)
		if err != nil { return 0, 0, err }
		offset    += n
		dimension += 1
		if elem.Is(OTA) {
			if !populated {
				return LBA, dimension + 1, nil
			}
		} else {
			return elem, dimension, nil
		}
	}
}

// peekSliceOnce returns the element tag of the OTA located offset bytes ahead
// of the current position. It does not use up the decoder, it only peeks. The n
// return value denotes how far away from 0 it peeked. If the OTA has more than
// zero items, populated will be set to true.
func peekSliceOnce(decoder *Decoder, tag Tag, offset int) (elem Tag, populated bool, n int, err error) {
	lengthStart  := offset
	lengthEnd    := lengthStart + tag.CN() + 1
	elemTagStart := lengthEnd
	elemTagEnd   := elemTagStart + 1

	headerBytes, err := decoder.Peek(elemTagEnd)
	if err != nil { return 0, false, 0, err }

	elem = Tag(headerBytes[len(headerBytes)])
	for index := lengthStart; index < lengthEnd; index += 1 {
		if headerBytes[index] > 0 {
			populated = true
			break
		}
	}
	n = elemTagEnd

	return
}