package tensor

import (
	"reflect"

	"gorgonia.org/tensor/internal/storage"
)

// ConsOpt is a tensor construction option.
type ConsOpt func(Tensor)

// Of is a construction option for a Tensor.
func Of(a Dtype) ConsOpt {
	Register(a)
	f := func(t Tensor) {
		switch tt := t.(type) {
		case *Dense:
			tt.t = a
		case *CS:
			tt.t = a
		default:
			panic("Unsupported Tensor type")
		}
	}
	return f
}

// WithBacking is a construction option for a Tensor
// Use it as such:
//		backing := []float64{1,2,3,4}
// 		t := New(WithBacking(backing))
// It can be used with other construction options like WithShape
func WithBacking(x interface{}, argMask ...[]bool) ConsOpt {
	var mask []bool
	if len(argMask) > 0 {
		mask = argMask[0]
	}
	f := func(t Tensor) {
		if x == nil {
			return
		}
		switch tt := t.(type) {
		case *Dense:
			tt.fromSlice(x)
			if len(argMask) > 0 {
				tt.addMask(mask)
			}
		default:
			panic("Unsupported Tensor type")
		}
	}
	return f
}

// WithMask is a construction option for a Tensor
// Use it as such:
//		mask := []bool{true,true,false,false}
// 		t := New(WithBacking(backing), WithMask(mask))
// It can be used with other construction options like WithShape
// The supplied mask can be any type. If non-boolean, then tensor mask is set to true
// wherever non-zero value is obtained
func WithMask(x interface{}) ConsOpt {
	f := func(t Tensor) {
		if x == nil {
			return
		}
		switch tt := t.(type) {
		case *Dense:
			tt.MaskFromSlice(x)
		default:
			panic("Unsupported Tensor type")
		}
	}
	return f
}

// WithShape is a construction option for a Tensor. It creates the ndarray in the required shape.
func WithShape(dims ...int) ConsOpt {
	f := func(t Tensor) {
		switch tt := t.(type) {
		case *Dense:
			throw := BorrowInts(len(dims))
			copy(throw, dims)
			tt.setShape(throw...)
		case *CS:
			if len(dims) != 2 {
				panic("Only sparse matrices are supported")
			}
			throw := BorrowInts(len(dims))
			copy(throw, dims)
			tt.s = throw

		default:
			panic("Unsupported Tensor type")
		}
	}
	return f
}

// FromScalar is a construction option for representing a scalar value as a Tensor
func FromScalar(x interface{}, argMask ...[]bool) ConsOpt {
	var mask []bool
	if len(argMask) > 0 {
		mask = argMask[0]
	}

	f := func(t Tensor) {
		switch tt := t.(type) {
		case *Dense:
			xT := reflect.TypeOf(x)
			sxT := reflect.SliceOf(xT)
			xv := reflect.MakeSlice(sxT, 1, 1) // []T
			xv0 := xv.Index(0)                 // xv[0]
			xv0.Set(reflect.ValueOf(x))
			tt.array.Header.Raw = storage.AsByteSlice(xv.Interface())
			tt.t = Dtype{xT}
			tt.mask = mask

		default:
			panic("Unsupported Tensor Type")
		}
	}
	return f
}

// FromMemory is a construction option for creating a *Dense (for now) from memory location. This is a useful
// option for super large tensors that don't fit into memory - the user may need to `mmap` a file the tensor.
//
// Bear in mind that at the current stage of the ConsOpt design, the order of the ConsOpt is important.
// FromMemory  requires the *Dense's Dtype be set already.
// This would fail (and panic):
//		New(FromMemory(ptr, size), Of(Float64))
// This would not:
//		New(Of(Float64), FromMemory(ptr, size))
// This behaviour  of  requiring the ConsOpts to be in order might be changed in the future.
//
// Memory must be manually managed by the caller.
// Tensors called with this construction option will not be returned to any pool - rather, all references to the pointers will be null'd.
// Use with caution.
//go:nocheckptr
func FromMemory(ptr uintptr, memsize uintptr) ConsOpt {
	f := func(t Tensor) {
		switch tt := t.(type) {
		case *Dense:
			tt.Header.Raw = nil // GC anything if needed
			tt.Header.Raw = storage.FromMemory(ptr, memsize)
			tt.flag = MakeMemoryFlag(tt.flag, ManuallyManaged)
		default:
			panic("Unsupported Tensor type")
		}
	}
	return f
}

// WithEngine is a construction option that would cause a Tensor to be linked with an execution engine.
func WithEngine(e Engine) ConsOpt {
	f := func(t Tensor) {
		switch tt := t.(type) {
		case *Dense:
			tt.e = e
			if e != nil && !e.AllocAccessible() {
				tt.flag = MakeMemoryFlag(tt.flag, NativelyInaccessible)
			}

			tt.oe = nil
			if oe, ok := e.(standardEngine); ok {
				tt.oe = oe
			}
		case *CS:
			tt.e = e
			if e != nil && !e.AllocAccessible() {
				tt.f = MakeMemoryFlag(tt.f, NativelyInaccessible)
			}
		}
	}
	return f
}

// AsFortran creates a *Dense with a col-major layout.
// If the optional backing argument is passed, the backing is assumed to be C-order (row major), and
// it will be transposed before being used.
func AsFortran(backing interface{}, argMask ...[]bool) ConsOpt {
	var mask []bool
	if len(argMask) > 0 {
		mask = argMask[0]
	}
	f := func(t Tensor) {
		switch tt := t.(type) {
		case *Dense:
			if backing != nil {
				// put the data into the tensor, then make a clone tensor to transpose
				tt.fromSliceOrArrayer(backing)
				// create a temporary tensor, to which the transpose will be done
				tmp := NewDense(tt.Dtype(), tt.shape.Clone())
				copyArray(tmp.arrPtr(), tt.arrPtr())
				tmp.SetMask(mask)
				tmp.T()
				tmp.Transpose()
				// copy the data back to the current tensor
				copyArray(tt.arrPtr(), tmp.arrPtr())
				tt.SetMask(tmp.Mask())
				// cleanup: return the temporary tensor back to the pool
				ReturnTensor(tmp)
			}

			tt.AP.o = MakeDataOrder(tt.AP.o, ColMajor)
			if tt.AP.shape != nil {
				ReturnInts(tt.AP.strides)
				tt.AP.strides = nil
				tt.AP.strides = tt.AP.calcStrides()
			}
		case *CS:
			panic("AsFortran is not an available option for Compressed Sparse layouts")
		}
	}
	return f
}

func AsDenseDiag(backing interface{}) ConsOpt {
	f := func(t Tensor) {
		switch tt := t.(type) {
		case *Dense:
			if bt, ok := backing.(Tensor); ok {
				backing = bt.Data()
			}
			xT := reflect.TypeOf(backing)
			if xT.Kind() != reflect.Slice {
				panic("Expected a slice")
			}
			xV := reflect.ValueOf(backing)
			l := xV.Len()
			// elT := xT.Elem()

			sli := reflect.MakeSlice(xT, l*l, l*l)

			shape := Shape{l, l}
			strides := shape.CalcStrides()
			for i := 0; i < l; i++ {
				idx, err := Ltoi(shape, strides, i, i)
				if err != nil {
					panic(err)
				}

				at := sli.Index(idx)
				xi := xV.Index(i)
				at.Set(xi)
			}

			tt.fromSliceOrArrayer(sli.Interface())
			tt.setShape(l, l)

		default:
			panic("AsDenseDiag is not available as an option for CS")
		}
	}
	return f
}