feat(Purchase): add change cash.

tienda_ilusion/don_confiao/frontend/don-confiao/src/components/Purchase.vue

@@ -116,16 +116,35 @@
           readonly
           persistent-placeholder="true"
         ></v-text-field>
-        <v-select
-          :items="payment_methods"
-          v-model="purchase.payment_method"
-          item-title="text"
-          item-value="value"
-          label="Pago en"
-        ></v-select>
+        <v-container v-if="calculateTotal > 0">
+          <v-select
+            :items="payment_methods"
+            v-model="purchase.payment_method"
+            item-title="text"
+            item-value="value"
+            label="Pago en"
+          ></v-select>
+          <v-text-field
+            v-if="purchase.payment_method === 'CASH'"
+            v-model="payment_cash"
+            label="Dinero"
+            prefix="$"
+            type="number"
+            :error-messages="isValidPayment ? [] : ['El dinero debe ser mayor o igual al total']"
+            :disable="calculateTotal === 0"
+          ></v-text-field>
+          <v-text-field
+            v-if="purchase.payment_method === 'CASH'"
+            :value="calculateChange"
+            label="Devuelta"
+            prefix="$"
+            readonly
+            presistent-placeholder="true"
+          ></v-text-field>
+        </v-container>
         <v-btn @click="submit" color="green">Comprar</v-btn>
-      </v-form>
-    </v-container>
+  </v-form>
+</v-container>
 </template>
 
 <script>
@@ -144,6 +163,7 @@
        valid: false,
        client_search: '',
        product_search: '',
+       payment_cash: 0,
        payment_methods: [
          {'text': 'Efectivo', 'value': 'CASH'},
          {'text': 'Confiar', 'value': 'CONFIAR'},
@@ -153,7 +173,7 @@
          date: this.getCurrentDate(),
          customer: null,
          notes: '',
-         payment_method: {'text': 'Efectivo', 'value': 'CASH'},
+         payment_method: null,
          saleline_set: [{product:'', unit_price: 0, quantity: 0, unit: ''}],
        },
        rules: {
@@ -182,6 +202,23 @@
          return total + this.calculateSubtotal(saleline);
        }, 0);
      },
+     calculateChange() {
+       if (this.purchase.payment_method === 'CASH') {
+         return (this.payment_cash || 0) - this.calculateTotal;
+       } else {
+         return 0;
+       }
+     },
+     isValidPayment() {
+       if (this.calculateTotal === 0) {
+         return false;
+       }
+       if (this.purchase.payment_method === 'CASH' && this.payment_cash < this.calculateTotal) {
+         return false;
+       }
+       return true;
+     },
+
      filteredClients() {
        return this.clients.filter(client => {
          if (this.client_search === '') {