package tensor

import "fmt"

// DType represents the data type of a tensor
type DType int

const (
	Float32  DType = 0
	Float16  DType = 1
	BFloat16 DType = 2
	Int8     DType = 3 // Legacy/Internal
	Int4     DType = 4 // Legacy/Internal
	Int32    DType = 5
	Q4_K     DType = 22
	Q3_K     DType = 23
	Q5_K     DType = 24
	Q6_K     DType = 26
	Q8_K     DType = 27
	Q2_K     DType = 28
)

func (d DType) String() string {
	switch d {
	case Float32:
		return "Float32"
	case Float16:
		return "Float16"
	case BFloat16:
		return "BFloat16"
	case Int8:
		return "Int8"
	case Int4:
		return "Int4"
	case Int32:
		return "Int32"
	case Q4_K:
		return "Q4_K"
	case Q3_K:
		return "Q3_K"
	case Q5_K:
		return "Q5_K"
	case Q6_K:
		return "Q6_K"
	case Q8_K:
		return "Q8_K"
	case Q2_K:
		return "Q2_K"
	default:
		return fmt.Sprintf("DType(%d)", d)
	}
}

func (d DType) Size() int {
	switch d {
	case Float32:
		return 4
	case Float16:
		return 2
	case BFloat16:
		return 2
	case Int8:
		return 1
	case Int4:
		return 0 // bitpacked
	case Q4_K:
		return 0 // block based
	case Q3_K:
		return 0 // block based
	case Q5_K:
		return 0 // block based
	case Q6_K:
		return 0 // block based
	case Q8_K:
		return 0 // block based
	case Q2_K:
		return 0 // block based
	default:
		panic("unknown dtype")
	}
}

// Shape represents tensor dimensions
type Shape []int

func (s Shape) NumElements() int {
	if len(s) == 0 {
		return 0
	}
	n := 1
	for _, d := range s {
		n *= d
	}
	return n
}

func (s Shape) String() string {
	return fmt.Sprintf("%v", []int(s))
}

// DeviceType represents where tensor data lives
type DeviceType int

const (
	CPU DeviceType = iota
	CUDA
)

// DevicePlacement captures a target device and GPU ordinal (for CUDA).
// GPU is ignored for CPU placements.
type DevicePlacement struct {
	Type DeviceType
	GPU  int
}

// Normalize ensures a valid placement with sane defaults.
func (p DevicePlacement) Normalize() DevicePlacement {
	if p.Type != CUDA {
		return DevicePlacement{Type: CPU, GPU: -1}
	}
	if p.GPU < 0 {
		return DevicePlacement{Type: CUDA, GPU: 0}
	}
	return p
}

// TensorWithPlacement adds placement to the tensor interface.
type TensorWithPlacement interface {
	Tensor
	Placement() DevicePlacement
}

// Tensor is a minimal core interface
// Operations are handled by standalone functions in ops/, matmul/, nn/
type Tensor interface {
	Shape() Shape
	DType() DType
	Device() DeviceType
	Data() interface{}
}