package tape

import "iter"

// encoding and decoding functions must not make any allocations

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

func DecodeTable(data []byte) iter.Seq2[uint16, []byte] {
	return func(yield func(tag uint16, value []byte) bool) {
		n := 0
		for {
			tag, nn, err := DecodeI16[uint16](data[n:])
			if err != nil { return }
			n += nn

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

			value := data[n:n + int(length)]
			yield(tag, value)
			n += int(length)
		}
	}
}

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
}