Add a sample decomposition to try to use OpenFisca Web API.

Using this API is more complicated than expected for a waterfall.

src/lib/decomposition.ts

+interface Decomposition {
+  code: string
+  short_name: string
+  children?: Decomposition[]
+}
+
+export const decomposition: Decomposition = {
+  code: "revenu_disponible",
+  short_name: "Revenu disponible",
+  children: [
+    {
+      code: "revenus_nets_du_travail",
+      short_name: "Revenus nets",
+      children: [
+        {
+          code: "salaire_net",
+          short_name: "Salaire net",
+          children: [
+            {
+              code: "salaire_imposable",
+              short_name: "Salaire imposable",
+              children: [
+                {
+                  code: "salaire_de_base",
+                  short_name: "Salaire brut",
+                  children: [
+                    {
+                      code: "salaire_super_brut_hors_allegements",
+                      short_name: "Salaire super brut HA",
+                      children: [
+                        {
+                          code: "salaire_super_brut",
+                          short_name: "Salaire super brut",
+                          children: [
+                            {
+                              code: "cout_du_travail",
+                              short_name: "Coût du travail",
+                            },
+                            {
+                              code: "credit_impot_competitivite_emploi",
+                              short_name: "CICE",
+                            },
+                            {
+                              code: "aide_premier_salarie",
+                              short_name: "Aide premier salarié",
+                            },
+                            {
+                              code: "aide_embauche_pme",
+                              short_name: "Aide PME",
+                            },
+                            { code: "tehr", short_name: "Taxe exceptionnelle" },
+                          ],
+                        },
+                        { code: "allegement_fillon", short_name: "Fillon" },
+                      ],
+                    },
+                    {
+                      code: "cotisations_employeur",
+                      short_name: "Cotisations employeur",
+                    },
+                  ],
+                },
+                {
+                  code: "cotisations_salariales",
+                  short_name: "Cotisations salariales",
+                },
+                {
+                  code: "csg_deductible_salaire",
+                  short_name: "CSG déductible",
+                },
+              ],
+            },
+            { code: "csg_imposable_salaire", short_name: "CSG imposable" },
+            { code: "crds_salaire", short_name: "CRDS" },
+          ],
+        },
+      ],
+    },
+    {
+      code: "prestations_sociales",
+      short_name: "Prestations sociales",
+      children: [
+        {
+          code: "minima_sociaux",
+          short_name: "Minima sociaux",
+          children: [
+            { code: "rsa", short_name: "RSA" },
+            { code: "ppa", short_name: "PPA" },
+          ],
+        },
+      ],
+    },
+    { code: "ppe", short_name: "PPE" },
+    {
+      code: "impots_directs",
+      short_name: "Impôts directs",
+      children: [{ code: "irpp", short_name: "Impôt sur le revenu" }],
+    },
+  ],
+}
+
+export function* walkDecomposition(
+  decomposition: Decomposition,
+): Generator<Decomposition, void, unknown> {
+  yield decomposition
+  for (const child of decomposition.children ?? []) {
+    yield* walkDecomposition(child)
+  }
+}

src/routes/calculations/index.svelte

 <script context="module" lang="ts">
-  export async function load({ page, fetch, session, context }) {
-    const url = "https://fr.openfisca.org/api/latest/calculate"
+  import { decomposition, walkDecomposition } from "$lib/decomposition"
+
+  // See https://github.com/cbenz/openfisca-interactive/blob/master/waterfall.ipynb
+  const year = 2017
+  const variablesDecomposition = Object.fromEntries(
+    [...walkDecomposition(decomposition)]
+      .filter(
+        (node) =>
+          ![
+            "aide_embauche_pme",
+            "aide_premier_salarie",
+            "allegement_fillon",
+            "cotisations_employeur",
+            "cotisations_salariales",
+            "cout_du_travail",
+            "crds_salaire",
+            "credit_impot_competitivite_emploi",
+            "csg_deductible_salaire",
+            "csg_imposable_salaire",
+            "irpp",
+            "minima_sociaux",
+            "ppa",
+            "ppe",
+            "prestations_sociales",
+            "revenus_nets_du_travail",
+            "rsa",
+            "salaire_de_base",
+            "salaire_imposable",
+            "salaire_net",
+            "salaire_super_brut",
+            "salaire_super_brut_hors_allegements",
+            "tehr",
+          ].includes(node.code),
+      )
+      .map((node) => [node.code, { [year]: null }]),
+  )
   const situation = {
     individus: {
       Claude: {
         salaire_de_base: {
-            "2017": 20000,
+          [year]: 20000,
         },
       },
       Dominique: {
         salaire_de_base: {
-            "2017": 30000,
+          [year]: 30000,
         },
       },
       Camille: {},
@@ -20,12 +54,7 @@
         personne_de_reference: ["Claude"],
         conjoint: ["Dominique"],
         enfants: ["Camille"],
-          revenu_disponible: {
-            "2017": null,
-          },
-          impots_directs: {
-            "2017": null,
-          },
+        ...variablesDecomposition,
       },
     },
     familles: {
@@ -41,6 +70,9 @@
       },
     },
   }
+
+  export async function load({ page, fetch, session, context }) {
+    const url = "https://fr.openfisca.org/api/latest/calculate"
     const res = await fetch(url, {
       body: JSON.stringify(situation, null, 2),
       headers: {
@@ -49,17 +81,23 @@
       method: "POST",
     })
 
-    if (res.ok) {
+    if (!res.ok) {
+      console.error(
+        `Erreur ${res.status} while POSTing ${url}\n${JSON.stringify(
+          situation,
+          null,
+          2,
+        )}\n\n${await res.text()}`,
+      )
       return {
-        props: {
-          simulation: await res.json(),
-        },
+        status: res.status,
+        error: new Error(`Could not load ${url}`),
       }
     }
-
     return {
-      status: res.status,
-      error: new Error(`Could not load ${url}`),
+      props: {
+        simulation: await res.json(),
+      },
     }
   }
 </script>