package structs

import (
	"bufio"
	"bytes"
	"encoding"
	"fmt"
	"io"

	"encoding/binary"

	"github.com/tuneinsight/lattigo/v4/utils/buffer"
)

type binarySerializer interface {
	encoding.BinaryMarshaler
	encoding.BinaryUnmarshaler
	io.WriterTo
	io.ReaderFrom
	// Encoder
	// Decoder
}

type Vector[T any] []T

// CopyNew creates a copy of the oject.
func (v Vector[T]) CopyNew() *Vector[T] {

	if c, isCopiable := any(new(T)).(CopyNewer[T]); !isCopiable {
		panic(fmt.Errorf("vector component of type %T does not comply to %T", new(T), c))
	}

	vcpy := Vector[T](make([]T, len(v)))
	for i, c := range v {
		vcpy[i] = *any(&c).(CopyNewer[T]).CopyNew()
	}
	return &vcpy
}

// WriteTo writes the object on an io.Writer.
// To ensure optimal efficiency and minimal allocations, the user is encouraged
// to provide a struct implementing the interface buffer.Writer, which defines
// a subset of the method of the bufio.Writer.
// If w is not compliant to the buffer.Writer interface, it will be wrapped in
// a new bufio.Writer.
// For additional information, see lattigo/utils/buffer/writer.go.
func (v *Vector[T]) WriteTo(w io.Writer) (n int64, err error) {

	if w, isWritable := any(new(T)).(io.WriterTo); !isWritable {
		return 0, fmt.Errorf("vector component of type %T does not comply to %T", new(T), w)
	}

	switch w := w.(type) {
	case buffer.Writer:
		vval := *v

		var inc int
		if inc, err = buffer.WriteInt(w, len(vval)); err != nil {
			return int64(inc), err
		}
		n += int64(inc)

		for _, c := range vval {
			inc, err := any(&c).(io.WriterTo).WriteTo(w)
			n += inc
			if err != nil {
				return n, err
			}
		}

		return n, w.Flush()

	default:
		return v.WriteTo(bufio.NewWriter(w))
	}
}

// ReadFrom reads on the object from an io.Writer.
// To ensure optimal efficiency and minimal allocations, the user is encouraged
// to provide a struct implementing the interface buffer.Reader, which defines
// a subset of the method of the bufio.Reader.
// If r is not compliant to the buffer.Reader interface, it will be wrapped in
// a new bufio.Reader.
// For additional information, see lattigo/utils/buffer/reader.go.
func (v *Vector[T]) ReadFrom(r io.Reader) (n int64, err error) {

	if r, isReadable := any(new(T)).(io.ReaderFrom); !isReadable {
		return 0, fmt.Errorf("vector component of type %T does not comply to %T", new(T), r)
	}

	// TODO: when has access to Reader's buffer, call Decode ?
	switch r := r.(type) {
	case buffer.Reader:
		var size int
		var inc int // TODO int64 in buffer package ?

		if inc, err = buffer.ReadInt(r, &size); err != nil {
			return int64(inc), fmt.Errorf("cannot read vector size: %w", err)
		}
		n += int64(inc)

		if cap(*v) < size {
			*v = make([]T, size)
		}
		*v = (*v)[:size]

		for i := range *v {
			inc, err := any(&(*v)[i]).(io.ReaderFrom).ReadFrom(r)
			n += inc
			if err != nil {
				return n, err
			}
		}

		return int64(n), nil

	default:
		return v.ReadFrom(bufio.NewReader(r))
	}
}

// BinarySize returns the size in bytes of the object
// when encoded using Encode.
func (v Vector[T]) BinarySize() (size int) {

	if s, isSizable := any(new(T)).(BinarySizer); !isSizable {
		panic(fmt.Errorf("vector component of type %T does not comply to %T", new(T), s))
	}

	size += 8
	for _, c := range v {
		size += any(&c).(BinarySizer).BinarySize()
	}
	return
}

// Encode encodes the object into a binary form on a preallocated slice of bytes
// and returns the number of bytes written.
func (v *Vector[T]) Encode(b []byte) (n int, err error) {

	if e, isEncodable := any(new(T)).(Encoder); !isEncodable {
		panic(fmt.Errorf("vector component of type %T does not comply to %T", new(T), e))
	}

	vval := *v

	binary.LittleEndian.PutUint64(b[n:], uint64(len(vval)))
	n += 8

	var inc int
	for _, c := range vval {
		if inc, err := any(&c).(Encoder).Encode(b[n:]); err != nil {
			return n + inc, err
		}
		n += inc
	}

	return
}

// Decode decodes a slice of bytes generated by Encode
// on the object and returns the number of bytes read.
func (v *Vector[T]) Decode(p []byte) (n int, err error) {

	if d, isDecodable := any(new(T)).(Decoder); !isDecodable {
		panic(fmt.Errorf("vector component of type %T does not comply to %T", new(T), d))
	}

	size := int(binary.LittleEndian.Uint64(p[n:])) // TODO: there is a bug here but it is not caught by the tests.
	n += 8

	if cap(*v) < size {
		*v = make([]T, size)
	}
	*v = (*v)[:size]

	var inc int
	for i := range *v {
		if inc, err = any(&(*v)[i]).(Decoder).Decode(p[n:]); err != nil {
			return n + inc, err
		}
		n += inc
	}

	return
}

// MarshalBinary encodes the object into a binary form on a newly allocated slice of bytes.
func (v *Vector[T]) MarshalBinary() (p []byte, err error) {
	buf := bytes.NewBuffer([]byte{})
	_, err = v.WriteTo(buf)
	return buf.Bytes(), err
}

// UnmarshalBinary decodes a slice of bytes generated by
// MarshalBinary or WriteTo on the object.
func (v *Vector[T]) UnmarshalBinary(p []byte) (err error) {
	_, err = v.ReadFrom(bytes.NewBuffer(p))
	return
}