package tape

import "iter"

// encoding and decoding functions must not make any allocations

type TablePushFunc func(tag uint16, value []byte) (n int, err error)

type TablePullFunc func() (tag uint16, value []byte, n int, err error)

func DecodeTable(data []byte) TablePullFunc {
	n := 0
	return func() (tag uint16, value []byte, n_ int, err error) {
		if n >= len(data) { return 0, nil, n, ErrWrongBufferLength }
		tag, nn, err := DecodeI16[uint16](data[n:])
		if err != nil { return 0, nil, n, err }
		n += nn

		if n >= len(data) { return 0, nil, n, ErrWrongBufferLength }
		length, nn, err := DecodeGBEU[uint64](data[n:])
		if err != nil { return 0, nil, n, err }
		n += nn

		end := n + int(length)
		if end > len(data) { return 0, nil, n, ErrWrongBufferLength }
		value = data[n:end]
		n += int(length)
		return tag, value, n, err
	}
}

func DecodeTableIter(data []byte) iter.Seq2[uint16, []byte] {
	return func(yield func(uint16, []byte) bool) {
		pull := DecodeTable(data)
		for {
			tag, value, _, err := pull()
			if err != nil { return }
			if !yield(tag, value) { return }
		}
	}
}

func EncodeTable(data []byte) TablePushFunc {
	return func(tag uint16, value []byte) (n int, err error) {
		if n >= len(data) { return n, ErrWrongBufferLength }
		nn, err := EncodeI16(data[n:], uint16(tag))
		if err != nil { return n, err }
		n += nn
	
		if n >= len(data) { return n, ErrWrongBufferLength }
		nn, err = EncodeGBEU(data[n:], uint(len(value)))
		if err != nil { return n, err }
		n += nn

		if n >= len(data) { return n, ErrWrongBufferLength }
		nn = copy(data[n:], value)
		n += nn
		if nn < len(value) {
			return n, ErrWrongBufferLength
		}
		
		if n >= len(data) { return n, ErrWrongBufferLength }
		data = data[n:]
		return n, nil
	}
}

func TableSize(itemLengths ...int) int {
	sum := 0
	for _, length := range itemLengths {
		sum += GBEUSize(uint(length)) + length
	}
	return sum
}