From b27b68908c8f6964b9ddfd96ef6803152d45940d Mon Sep 17 00:00:00 2001
From: Carlos Narro <carlos@relabtive.com>
Date: Sat, 30 May 2026 12:18:48 +0200
Subject: [PATCH] feat: derive cantidades from minimal measurements

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 mvp/b2c/src/budget/derive.ts        | 39 ++++++++++++++++++++++
 mvp/b2c/tests/budget/derive.test.ts | 50 +++++++++++++++++++++++++++++
 2 files changed, 89 insertions(+)
 create mode 100644 mvp/b2c/src/budget/derive.ts
 create mode 100644 mvp/b2c/tests/budget/derive.test.ts

diff --git a/mvp/b2c/src/budget/derive.ts b/mvp/b2c/src/budget/derive.ts
new file mode 100644
index 0000000..0cdc97b
--- /dev/null
+++ b/mvp/b2c/src/budget/derive.ts
@@ -0,0 +1,39 @@
+import type { BudgetInputs, PricingConfig, TipoReforma } from './types';
+
+export interface Cantidades {
+  m2Suelo: number;
+  m2Pared: number;
+  mlMobiliario: number;
+  perimetro: number;
+  alturaTecho: number;
+}
+
+const M2_MEDIANA: Record<TipoReforma, number> = {
+  cocina: 10,
+  bano: 5,
+  salon: 20,
+  comedor: 16,
+  integral: 70,
+  otro: 12,
+};
+
+// Metros lineales de mobiliario por metro de perímetro. Solo cocina/baño.
+const FACTOR_MOBILIARIO: Partial<Record<TipoReforma, number>> = {
+  cocina: 0.5,
+  bano: 0.3,
+};
+
+export function deriveCantidades(inputs: BudgetInputs, config: PricingConfig): Cantidades {
+  const m2Suelo =
+    inputs.m2Suelo != null && inputs.m2Suelo > 0
+      ? inputs.m2Suelo
+      : M2_MEDIANA[inputs.tipoReforma];
+  const alturaTecho =
+    inputs.alturaTecho != null && inputs.alturaTecho > 0
+      ? inputs.alturaTecho
+      : config.alturaTechoDefault;
+  const perimetro = 4 * Math.sqrt(m2Suelo);
+  const m2Pared = perimetro * alturaTecho;
+  const mlMobiliario = perimetro * (FACTOR_MOBILIARIO[inputs.tipoReforma] ?? 0);
+  return { m2Suelo, m2Pared, mlMobiliario, perimetro, alturaTecho };
+}
diff --git a/mvp/b2c/tests/budget/derive.test.ts b/mvp/b2c/tests/budget/derive.test.ts
new file mode 100644
index 0000000..f5efffd
--- /dev/null
+++ b/mvp/b2c/tests/budget/derive.test.ts
@@ -0,0 +1,50 @@
+import { describe, it, expect } from 'vitest';
+import { deriveCantidades } from '@/budget/derive';
+import type { BudgetInputs, PricingConfig } from '@/budget/types';
+
+const config: PricingConfig = {
+  alturaTechoDefault: 2.5,
+  factorZona: {},
+  manoObra: { demolicion: 0, fontaneria: 0, electricidad: 0, mano_de_obra: 0 },
+};
+
+function inputs(partial: Partial<BudgetInputs>): BudgetInputs {
+  return {
+    tipoReforma: 'cocina',
+    m2Suelo: null,
+    alturaTecho: null,
+    calidadGlobal: 'media',
+    estructural: false,
+    provincia: null,
+    materialSelections: {},
+    ...partial,
+  };
+}
+
+describe('deriveCantidades', () => {
+  it('usa m² aportados y deriva perímetro y paredes con números limpios', () => {
+    // m2Suelo=16 -> sqrt=4 -> perimetro=16 -> pared=16*2.5=40 -> mobiliario=16*0.5=8 (cocina)
+    const c = deriveCantidades(inputs({ m2Suelo: 16 }), config);
+    expect(c.m2Suelo).toBe(16);
+    expect(c.perimetro).toBe(16);
+    expect(c.m2Pared).toBe(40);
+    expect(c.mlMobiliario).toBe(8);
+    expect(c.alturaTecho).toBe(2.5);
+  });
+
+  it('cae a la mediana por tipo cuando no hay m²', () => {
+    const c = deriveCantidades(inputs({ tipoReforma: 'bano', m2Suelo: null }), config);
+    expect(c.m2Suelo).toBe(5); // mediana baño
+  });
+
+  it('usa la altura aportada por encima del default', () => {
+    const c = deriveCantidades(inputs({ m2Suelo: 16, alturaTecho: 3 }), config);
+    expect(c.alturaTecho).toBe(3);
+    expect(c.m2Pared).toBe(48); // 16 * 3
+  });
+
+  it('no calcula mobiliario para tipos sin cocina/baño', () => {
+    const c = deriveCantidades(inputs({ tipoReforma: 'salon', m2Suelo: 16 }), config);
+    expect(c.mlMobiliario).toBe(0);
+  });
+});