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

package optim

import (
	"math"
	"testing"

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

// MinimiseLinearRows hands both standard rows of a two-sided constraint
// slots in the one backing block, taken in build order. A fixture with
// a two-sided row and a one-sided row pins the hand-computed optimum,
// which a row that aliased its neighbour could not reach.

func TestMinimiseLinearRowsTwoSidedConstraint(t *testing.T) {
	// minimise x1 - 2*x2 over 2 ≤ x1 + x2 ≤ 3 and 0 ≤ x1 ≤ 1: the
	// objective pushes x2 up and x1 down, so x1 = 0, x2 = 3 and the
	// optimum is -6.
	cost, err := core.FromFloats([]float64{1, -2}, 2)
	if err != nil {
		t.Fatalf("FromFloats: %v", err)
	}
	a, err := core.FromFloats([]float64{1, 1, 1, 0}, 2, 2)
	if err != nil {
		t.Fatalf("FromFloats: %v", err)
	}
	cons := LinearConstraints{
		A:     a,
		Lower: []float64{2, 0},
		Upper: []float64{3, 1},
	}
	x, value, merr := MinimiseLinearRows(cost, cons, LinearProgramOptions{})
	if merr != nil {
		t.Fatalf("MinimiseLinearRows: %v", merr)
	}
	if math.Abs(value+6) > 1e-9 {
		t.Fatalf("optimum = %v, want -6", value)
	}
	if v := x.FloatAt(0); math.Abs(v) > 1e-9 {
		t.Fatalf("x1 = %v, want 0", v)
	}
	if v := x.FloatAt(1); math.Abs(v-3) > 1e-9 {
		t.Fatalf("x2 = %v, want 3", v)
	}
}