package tape

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

// encoding and decoding functions must not make any allocations

func DecodeArray(data []byte, itemLength int) iter.Seq[[]byte] {
	return slices.Chunk(data, itemLength)
}

func EncodeArray(data []byte, items ...[]byte) (n int, err error) {
	for _, item := range items {
		if n >= len(data) { return n, ErrWrongBufferLength }
		copy(data[n:], item)
		n += len(item)
	}
	return n, nil
}

func ArraySize(length, itemLength int) int {
	return length * itemLength
}

// DecodeStringArray decodes a packed string array from the given data.
func DecodeStringArray[T String](data []byte) (result []T, n int, err error) {
	for len(data) > 0 {
		if len(data) < 2 { return nil, n, fmt.Errorf("decoding []string: %w", ErrWrongBufferLength) }
		itemSize16, nn, _ := DecodeI16[uint16](data[:2])
		itemSize := int(itemSize16)
		n += nn
		data = data[nn:]
		if len(data) < itemSize { return nil, n, fmt.Errorf("decoding []string: %w", ErrWrongBufferLength) }
		result = append(result, T(data[:itemSize]))
		data = data[itemSize:]
		n += itemSize
	}
	return result, n, nil
}

// EncodeStringArray encodes a packed string array into the given buffer.
func EncodeStringArray[T String](buffer []byte, value []T) (n int, err error) {
	for _, item := range value {
		length, err := StringSize(item)
		if err != nil { return n, err }
		if len(buffer) < 2 + length { return n, fmt.Errorf("encoding []string: %w", ErrWrongBufferLength) }
		EncodeI16(buffer[:2], uint16(length))
		buffer = buffer[2:]
		copy(buffer, item)
		buffer = buffer[length:]
		n += 2 + length
	}
	if len(buffer) > 0 { return n, fmt.Errorf("encoding []string: %w", ErrWrongBufferLength) }
	return n, nil
}

// StringArraySize returns the size of a packed string array. Returns 0 and an
// error if the size is too large.
func StringArraySize[T String](value []T) (int, error) {
	total := 0
	for _, item := range value {
		total += 2 + len(item)
	}
	if total > dataMaxSize { return 0, ErrDataTooLarge }
	return total, nil
}

// 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
}