package buffer

import (
	"encoding/binary"
	"fmt"
	"unsafe"
)

// ReadAsUint64 reads an uint64 from r and stores the result into c with pointer type casting into type T.
func ReadAsUint64[T any](r Reader, c *T) (n int64, err error) {
	/* #nosec G103 -- behavior and consequences well understood, pointer type cast */
	return ReadUint64(r, (*uint64)(unsafe.Pointer(c)))
}

// ReadAsUint32 reads an uint32 from r and stores the result into c with pointer type casting into type T.
func ReadAsUint32[T any](r Reader, c *T) (n int64, err error) {
	/* #nosec G103 -- behavior and consequences well understood, pointer type cast */
	return ReadUint32(r, (*uint32)(unsafe.Pointer(c)))
}

// ReadAsUint16 reads an uint16 from r and stores the result into c with pointer type casting into type T.
func ReadAsUint16[T any](r Reader, c *T) (n int64, err error) {
	/* #nosec G103 -- behavior and consequences well understood, pointer type cast */
	return ReadUint16(r, (*uint16)(unsafe.Pointer(c)))
}

// ReadAsUint8 reads an uint8 from r and stores the result into c with pointer type casting into type T.
func ReadAsUint8[T any](r Reader, c *T) (n int64, err error) {
	/* #nosec G103 -- behavior and consequences well understood, pointer type cast */
	return ReadUint8(r, (*uint8)(unsafe.Pointer(c)))
}

// ReadAsUint64Slice reads a slice of uint64 from r and stores the result into c with pointer type casting into type T.
func ReadAsUint64Slice[T any](r Reader, c []T) (n int64, err error) {
	/* #nosec G103 -- behavior and consequences well understood, pointer type cast */
	return ReadUint64Slice(r, *(*[]uint64)(unsafe.Pointer(&c)))
}

// ReadAsUint32Slice reads a slice of uint32 from r and stores the result into c with pointer type casting into type T.
func ReadAsUint32Slice[T any](r Reader, c []T) (n int64, err error) {
	/* #nosec G103 -- behavior and consequences well understood, pointer type cast */
	return ReadUint32Slice(r, *(*[]uint32)(unsafe.Pointer(&c)))
}

// ReadAsUint16Slice reads a slice of uint16 from r and stores the result into c with pointer type casting into type T.
func ReadAsUint16Slice[T any](r Reader, c []T) (n int64, err error) {
	/* #nosec G103 -- behavior and consequences well understood, pointer type cast */
	return ReadUint16Slice(r, *(*[]uint16)(unsafe.Pointer(&c)))
}

// ReadAsUint8Slice reads a slice of uint8 from r and stores the result into c with pointer type casting into type T.
func ReadAsUint8Slice[T any](r Reader, c []T) (n int64, err error) {
	/* #nosec G103 -- behavior and consequences well understood, pointer type cast */
	return ReadUint8Slice(r, *(*[]uint8)(unsafe.Pointer(&c)))
}

// Read reads a slice of bytes from r and copies it on c.
func Read(r Reader, c []byte) (n int64, err error) {
	slice, err := r.Peek(len(c))
	if err != nil {
		return int64(len(slice)), err
	}
	copy(c, slice)
	nint, err := r.Discard(len(c))
	return int64(nint), err
}

// ReadUint8 reads a byte from r and stores the result into *c.
func ReadUint8(r Reader, c *uint8) (n int64, err error) {

	if c == nil {
		return 0, fmt.Errorf("cannot ReadUint8: c is nil")
	}

	slice, err := r.Peek(1)
	if err != nil {
		return int64(len(slice)), err
	}

	// Reads one byte
	*c = uint8(slice[0])

	nint, err := r.Discard(1)

	return int64(nint), err
}

// ReadUint8Slice reads a slice of byte from r and stores the result into c.
func ReadUint8Slice(r Reader, c []uint8) (n int64, err error) {
	nint, err := r.Read(c)
	return int64(nint), err
}

// ReadUint16 reads a uint16 from r and stores the result into *c.
func ReadUint16(r Reader, c *uint16) (n int64, err error) {

	if c == nil {
		return 0, fmt.Errorf("cannot ReadUint16: c is nil")
	}

	slice, err := r.Peek(2)
	if err != nil {
		return int64(len(slice)), err
	}

	// Reads one byte
	*c = binary.LittleEndian.Uint16(slice)

	nint, err := r.Discard(2)

	return int64(nint), err
}

// ReadUint16Slice reads a slice of uint16 from r and stores the result into c.
func ReadUint16Slice(r Reader, c []uint16) (n int64, err error) {

	// c is empty, return
	if len(c) == 0 {
		return
	}

	for len(c) > 0 {
		size := r.Size()
		if len(c)<<1 < size {
			size = len(c) << 1
		}

		var slice []byte
		if slice, err = r.Peek(size); err != nil {
			return n + int64(len(slice)), err
		}

		buffered := len(slice) >> 1

		if N := len(c); N <= buffered {

			for i, j := 0, 0; i < N; i, j = i+1, j+2 {
				c[i] = binary.LittleEndian.Uint16(slice[j:])
			}

			nint, derr := r.Discard(N << 1)

			return n + int64(nint), derr
		}

		if buffered == 0 {
			return n, ErrZeroProgress
		}

		for i, j := 0, 0; i < buffered; i, j = i+1, j+2 {
			c[i] = binary.LittleEndian.Uint16(slice[j:])
		}

		var inc int
		if inc, err = r.Discard(buffered << 1); err != nil {
			return n + int64(inc), err
		}

		n += int64(inc)
		c = c[buffered:]
	}

	return n, nil
}

// ReadUint16SliceBounded is the bounded-length variant of ReadUint16Slice.
func ReadUint16SliceBounded(r Reader, length int) (out []uint16, n int64, err error) {
	if length < 0 {
		return nil, 0, ErrSliceTooLarge
	}
	if length > MaxSliceLen() {
		return nil, 0, ErrSliceTooLarge
	}
	out = make([]uint16, length)
	n, err = ReadUint16Slice(r, out)
	return out, n, err
}

// ReadUint32 reads a uint32 from r and stores the result into *c.
func ReadUint32(r Reader, c *uint32) (n int64, err error) {

	if c == nil {
		return 0, fmt.Errorf("cannot ReadUint32: c is nil")
	}

	slice, err := r.Peek(4)
	if err != nil {
		return int64(len(slice)), err
	}

	// Reads one byte
	*c = binary.LittleEndian.Uint32(slice)

	nint, err := r.Discard(4)

	return int64(nint), err
}

// ReadUint32Slice reads a slice of uint32 from r and stores the result into c.
//
// See ReadUint64Slice for the zero-progress / unbounded-recursion guard.
// Same iterative implementation, applied to 4-byte stride.
func ReadUint32Slice(r Reader, c []uint32) (n int64, err error) {

	// c is empty, return
	if len(c) == 0 {
		return
	}

	for len(c) > 0 {
		size := r.Size()
		if len(c)<<2 < size {
			size = len(c) << 2
		}

		var slice []byte
		if slice, err = r.Peek(size); err != nil {
			return n + int64(len(slice)), err
		}

		buffered := len(slice) >> 2

		if N := len(c); N <= buffered {

			for i, j := 0, 0; i < N; i, j = i+1, j+4 {
				c[i] = binary.LittleEndian.Uint32(slice[j:])
			}

			nint, derr := r.Discard(N << 2)

			return n + int64(nint), derr
		}

		if buffered == 0 {
			return n, ErrZeroProgress
		}

		for i, j := 0, 0; i < buffered; i, j = i+1, j+4 {
			c[i] = binary.LittleEndian.Uint32(slice[j:])
		}

		var inc int
		if inc, err = r.Discard(buffered << 2); err != nil {
			return n + int64(inc), err
		}

		n += int64(inc)
		c = c[buffered:]
	}

	return n, nil
}

// ReadUint32SliceBounded is the bounded-length variant of ReadUint32Slice.
func ReadUint32SliceBounded(r Reader, length int) (out []uint32, n int64, err error) {
	if length < 0 {
		return nil, 0, ErrSliceTooLarge
	}
	if length > MaxSliceLen() {
		return nil, 0, ErrSliceTooLarge
	}
	out = make([]uint32, length)
	n, err = ReadUint32Slice(r, out)
	return out, n, err
}

// ReadUint64 reads a uint64 from r and stores the result into c.
func ReadUint64(r Reader, c *uint64) (n int64, err error) {

	if c == nil {
		return 0, fmt.Errorf("cannot ReadUint64: c is nil")
	}

	bytes, err := r.Peek(8)
	if err != nil {
		return int64(len(bytes)), err
	}

	// Reads one byte
	*c = binary.LittleEndian.Uint64(bytes)

	nint, err := r.Discard(8)

	return int64(nint), err
}

// ReadUint64Slice reads a slice of uint64 from r and stores the result into c.
//
// Bounded against attacker-controlled wire prefixes: if the underlying
// Reader returns a Peek shorter than 8 bytes while c still has elements to
// fill, the function returns ErrZeroProgress instead of recursing. Prior to
// this guard, a malicious upstream length prefix combined with a sparse
// Reader would exhaust the goroutine stack (issue discovered by
// luxfi/warp/pulsar FuzzPulseDeserialize, seed ccdb090e0ca0007b).
//
// The recursion in the original lattigo implementation has been replaced
// with an in-place loop, so this function now uses O(1) stack regardless of
// input length.
func ReadUint64Slice(r Reader, c []uint64) (n int64, err error) {

	// c is empty, return
	if len(c) == 0 {
		return
	}

	for len(c) > 0 {
		// Avoid EOF: bound the Peek to the smaller of available reader
		// bytes and the destination remaining bytes.
		size := r.Size()
		if len(c)<<3 < size {
			size = len(c) << 3
		}

		var slice []byte
		if slice, err = r.Peek(size); err != nil {
			return n + int64(len(slice)), err
		}

		buffered := len(slice) >> 3

		// If the slice to write on is equal or smaller than the amount peeked
		if N := len(c); N <= buffered {

			for i, j := 0, 0; i < N; i, j = i+1, j+8 {
				c[i] = binary.LittleEndian.Uint64(slice[j:])
			}

			nint, derr := r.Discard(N << 3) // Discards what was read

			return n + int64(nint), derr
		}

		// Zero-progress guard: Peek did not return enough bytes to decode
		// even one uint64 yet c still has elements to fill. Without this,
		// the original recursive implementation looped forever on
		// c[0:] == c, and Go's stack growth would eventually panic.
		if buffered == 0 {
			return n, ErrZeroProgress
		}

		// Decodes the maximum
		for i, j := 0, 0; i < buffered; i, j = i+1, j+8 {
			c[i] = binary.LittleEndian.Uint64(slice[j:])
		}

		// Discard what was peeked
		var inc int
		if inc, err = r.Discard(buffered << 3); err != nil {
			return n + int64(inc), err
		}

		n += int64(inc)
		c = c[buffered:]
	}

	return n, nil
}

// ReadUint64SliceBounded is a length-prefix-aware wrapper around
// ReadUint64Slice that rejects requested lengths exceeding MaxSliceLen()
// before allocating the destination. Use this when decoding wire formats
// where the length is read from the same untrusted stream.
func ReadUint64SliceBounded(r Reader, length int) (out []uint64, n int64, err error) {
	if length < 0 {
		return nil, 0, ErrSliceTooLarge
	}
	if length > MaxSliceLen() {
		return nil, 0, ErrSliceTooLarge
	}
	out = make([]uint64, length)
	n, err = ReadUint64Slice(r, out)
	return out, n, err
}