package tape

import "fmt"
import "iter"
import "slices"

// encoding and decoding functions must not make any allocations

// ArrayPushFunc adds an item to an array that is being encoded.
type ArrayPushFunc func(value []byte) (n int, err error)

// ArrayPullFunc gets the next item of an array that is being decoded.
type ArrayPullFunc func() (value []byte, n int, err error)

// DecodePASTA decodes a packed single-type array.
func DecodePASTA(data []byte, itemLength int) ArrayPullFunc {
	n := 0
	return func() (value []byte, n_ int, err error) {
		if n > len(data) - itemLength {
			return nil, 0, fmt.Errorf("decoding PASTA: %w", ErrWrongBufferLength)
		}
		value = data[n:n + itemLength]
		n += itemLength
		return value, itemLength, nil
	}
}

// DecodePASTAIter decodes a packed single-type array and returns it as an
// iterator.
func DecodePASTAIter(data []byte, itemLength int) iter.Seq[[]byte] {
	return slices.Chunk(data, itemLength)
}

// EncodePASTA encodes a packed single-type array.
func EncodePASTA(data []byte, itemLength int) ArrayPushFunc {
	n := 0
	return func(value []byte) (n_ int, err error) {
		if n > len(data) - itemLength {
			return 0, fmt.Errorf("encoding PASTA: %w", ErrWrongBufferLength)
		}
		copy(data[n:], value)
		n += itemLength
		return itemLength, nil
	}
}

// PASTASize returns the size of a packed single-type array.
func PASTASize(length, itemLength int) int {
	return length * itemLength
}

// DecodeVILA encodes a variable item length array.
func DecodeVILA(data []byte) ArrayPullFunc {
	n := 0
	return func() (value []byte, n_ int, err error) {
		if n >= len(data) { return nil, n_, fmt.Errorf("decoding VILA: %w", ErrWrongBufferLength) }
		length, nn, err := DecodeGBEU[uint](data[n:])
		n += nn
		n_ += nn
		if err != nil { return nil, n_, err }
		
		if n > len(data) - int(length) {
			return nil, n_, fmt.Errorf("decoding VILA: %w", ErrWrongBufferLength)
		}
		value = data[n:n + int(length)]
		n += int(length)
		n_ += int(length)
		return value, int(length), nil
	}
}

// DecodeVILAIter decodes a variable item length array and returns it as an
// iterator.
func DecodeVILAIter(data []byte) iter.Seq[[]byte] {
	return func(yield func([]byte) bool) {
		pull := DecodeVILA(data)
		for {
			value, _, err := pull()
			if err != nil { return }
			if !yield(value) { return }
		}
	}
}

// EncodeVILA encodes a variable item length array.
func EncodeVILA(data []byte) ArrayPushFunc {
	n := 0
	return func(value []byte) (n_ int, err error) {
		if n >= len(data) { return n_, fmt.Errorf("encoding VILA: %w", ErrWrongBufferLength) }
		nn, err := EncodeGBEU(data[n:], uint(len(value)))
		n += nn
		n_ += nn
		if err != nil { return n, err }
		
		if n >= len(data) { return n_, fmt.Errorf("encoding VILA: %w", ErrWrongBufferLength) }
		nn = copy(data[n:], value)
		n += nn
		n_ += nn
		if nn != len(value) { return n_, fmt.Errorf("encoding VILA: %w", ErrWrongBufferLength) }
		return n_, err
	}
}

// VILASize returns the size of a variable item length array.
func VILASize(items ...[]byte) int {
	size := 0
	for _, item := range items {
		size += GBEUSize[uint](uint(len(item)))
		size += len(item)
	}
	return size
}

// DecodeStringArray decodes a VILA string array from the given data.
func DecodeStringArray[T String](data []byte) (result []T, n int, err error) {
	pull := DecodeVILA(data)
	for {
		item, nn, err := pull()
		n += nn
		if err != nil { return nil, n, err }
		result = append(result, T(item))
	}
	return result, n, nil
}

// EncodeStringArray encodes a VILA string array into the given buffer.
func EncodeStringArray[T String](buffer []byte, value []T) (n int, err error) {
	push := EncodeVILA(buffer)
	for _, item := range value {
		nn, err := push([]byte(item))
		n += nn
		if err != nil { return n, err }
	}
	return n, nil
}

// StringArraySize returns the size of a VILA string array.
func StringArraySize[T String](value []T) int {
	size := 0
	for _, item := range value {
		size += GBEUSize[uint](uint(len(item)))
		size += len(item)
	}
	return size
}

// DecodeI8Array decodes a packed array of 8 bit integers from the given data.
func DecodeI8Array[T Int8](data []byte) (result []T, n int, err error) {
	result = make([]T, len(data))
	for index, item := range data {
		result[index] = T(item)
	}
	return result, len(data), nil
}

// EncodeI8Array encodes a packed array of 8 bit integers into the given buffer.
func EncodeI8Array[T Int8](buffer []byte, value []T) (n int, err error) {
	if len(buffer) != len(value) { return 0, fmt.Errorf("encoding []int8: %w", ErrWrongBufferLength) }
	for index, item := range value {
		buffer[index] = byte(item)
	}
	return len(buffer), nil
}

// I8ArraySize returns the size of a packed 8 bit integer array. Returns 0 and
// an error if the size is too large.
func I8ArraySize[T Int8](value []T) (int, error) {
	total := len(value)
	if total > dataMaxSize { return 0, ErrDataTooLarge }
	return total, nil
}

// DecodeI16Array decodes a packed array of 16 bit integers from the given data.
func DecodeI16Array[T Int16](data []byte) (value []T, n int, err error) {
	if len(data) % 2 != 0 { return nil, 0, fmt.Errorf("decoding []int16: %w", ErrWrongBufferLength) }
	length := len(data) / 2
	result := make([]T, length)
	for index := range length {
		offset := index * 2
		result[index] = T(data[offset]) << 8 | T(data[offset + 1])
	}
	return result, len(data) / 2, nil
}

// EncodeI16Array encodes a packed array of 16 bit integers into the given buffer.
func EncodeI16Array[T Int16](buffer []byte, value []T) (n int, err error) {
	if len(buffer) != len(value) * 2 { return 0, fmt.Errorf("encoding []int16: %w", ErrWrongBufferLength) }
	for _, item := range value {
		buffer[0] = byte(item >> 8)
		buffer[1] = byte(item)
		buffer = buffer[2:]
	}
	return len(value) * 2, nil
}

// I16ArraySize returns the size of a packed 16 bit integer array. Returns 0 and
// an error if the size is too large.
func I16ArraySize[T Int16](value []T) (int, error) {
	total := len(value) * 2
	if total > dataMaxSize { return 0, ErrDataTooLarge }
	return total, nil
}

// DecodeI32Array decodes a packed array of 32 bit integers from the given data.
func DecodeI32Array[T Int32](data []byte) (value []T, n int, err error) {
	if len(data) % 4 != 0 { return nil, 0, fmt.Errorf("decoding []int32: %w", ErrWrongBufferLength) }
	length := len(data) / 4
	result := make([]T, length)
	for index := range length {
		offset := index * 4
		result[index] =
			T(data[offset + 0]) << 24 |
			T(data[offset + 1]) << 16 |
			T(data[offset + 2]) <<  8 |
			T(data[offset + 3])
	}
	return result, len(data) / 4, nil
}

// EncodeI32Array encodes a packed array of 32 bit integers into the given buffer.
func EncodeI32Array[T Int32](buffer []byte, value []T) (n int, err error) {
	if len(buffer) != len(value) * 4 { return 0, fmt.Errorf("encoding []int32: %w", ErrWrongBufferLength) }
	for _, item := range value {
		buffer[0] = byte(item >> 24)
		buffer[1] = byte(item >> 16)
		buffer[2] = byte(item >> 8)
		buffer[3] = byte(item)
		buffer = buffer[4:]
	}
	return len(value) * 4, nil
}

// I32ArraySize returns the size of a packed 32 bit integer array. Returns 0 and
// an error if the size is too large.
func I32ArraySize[T Int32](value []T) (int, error) {
	total := len(value) * 4
	if total > dataMaxSize { return 0, ErrDataTooLarge }
	return total, nil
}

// DecodeI64Array decodes a packed array of 32 bit integers from the given data.
func DecodeI64Array[T Int64](data []byte) (value []T, n int, err error) {
	if len(data) % 8 != 0 { return nil, 0, fmt.Errorf("decoding []int64: %w", ErrWrongBufferLength) }
	length := len(data) / 8
	result := make([]T, length)
	for index := range length {
		offset := index * 8
		result[index] =
			T(data[offset + 0]) << 56 |
			T(data[offset + 1]) << 48 |
			T(data[offset + 2]) << 40 |
			T(data[offset + 3]) << 32 |
			T(data[offset + 4]) << 24 |
			T(data[offset + 5]) << 16 |
			T(data[offset + 6]) <<  8 |
			T(data[offset + 7])
	}
	return result, len(data) / 8, nil
}

// EncodeI64Array encodes a packed array of 64 bit integers into the given buffer.
func EncodeI64Array[T Int64](buffer []byte, value []T) (n int, err error) {
	if len(buffer) != len(value) * 8 { return 0, fmt.Errorf("encoding []int64: %w", ErrWrongBufferLength) }
	for _, item := range value {
		buffer[0] = byte(item >> 56)
		buffer[1] = byte(item >> 48)
		buffer[2] = byte(item >> 40)
		buffer[3] = byte(item >> 32)
		buffer[4] = byte(item >> 24)
		buffer[5] = byte(item >> 16)
		buffer[6] = byte(item >> 8)
		buffer[7] = byte(item)
		buffer = buffer[8:]
	}
	return len(value) * 8, nil
}

// I64ArraySize returns the size of a packed 64 bit integer array. Returns 0 and
// an error if the size is too large.
func I64ArraySize[T Int64](value []T) (int, error) {
	total := len(value) * 8
	if total > dataMaxSize { return 0, ErrDataTooLarge }
	return total, nil
}