// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

package linalg

import (
	"math"
	"math/cmplx"

	"sourcedock.dev/petrbalvin/tensor/internal/base"
	"sourcedock.dev/petrbalvin/tensor/internal/core"
)

// scalar is the element type the generic kernels serve.
type scalar interface {
	float64 | complex128
}

// absComplex returns |z|, the shared magnitude used for tolerances.
func absComplex(z complex128) float64 { return base.AbsComplex(z) }

func absOf[T scalar](v T) float64 {
	switch x := any(v).(type) {
	case float64:
		return math.Abs(x)
	case complex128:
		return cmplx.Abs(x)
	}
	return 0
}

// zeros allocates a zeroed array for internally derived shapes. The
// error is part of the signature on purpose: a caller whose shape is
// not provably valid must propagate the failure, not nil-deref.
func zeros(dt core.Dtype, shape []int) (*core.Array, error) {
	return core.Zeros(dt, shape...)
}

// finiteF64 reports whether v is neither NaN nor infinite.
func finiteF64(v float64) bool { return !math.IsNaN(v) && !math.IsInf(v, 0) }

// vecFinite reports whether every entry of v is finite.
func vecFinite(v []float64) bool {
	for _, x := range v {
		if !finiteF64(x) {
			return false
		}
	}
	return true
}

// isRealDtype reports whether a holds real (non-complex) numeric data.
func isRealDtype(a *core.Array) bool {
	switch a.Dtype() {
	case core.Float, core.Float32, core.Int:
		return true
	}
	return false
}