From e7b631d9bcfef6dc8f509131cbd83ac2dfbbeed4 Mon Sep 17 00:00:00 2001
From: Simon Garnier <ticketappfrance@gmail.com>
Date: Tue, 3 Mar 2026 14:10:24 +0100
Subject: [PATCH] fix: linear interpolation for thresholds of <40m2

---
 src/conso.js                 |  5 +++--
 src/interpolateLimitTable.js | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 src/interpolateLimitTable.js

diff --git a/src/conso.js b/src/conso.js
index e2e4b0c..32b9597 100644
--- a/src/conso.js
+++ b/src/conso.js
@@ -2,6 +2,7 @@ import enums from './enums.js';
 import calc_conso_eclairage from './16_conso_eclairage.js';
 import tvs from './tv.js';
 import { tv } from './utils.js';
+import { interpolateLimitTable } from './interpolateLimitTable.js';
 
 export const COEFF_EP_2_3 = 2.3;
 export const COEFF_EP_1_9 = 1.9;
@@ -340,7 +341,7 @@ export default function calc_conso(
 export function classe_bilan_dpe(ep_conso_5_usages_m2, zc_id, ca_id, Sh) {
   const ca = enums.classe_altitude[ca_id];
 
-  const cut = tvs.dpe_class_limit[ca][Math.round(Sh)] ?? [];
+  const cut = interpolateLimitTable(tvs.dpe_class_limit[ca], Sh);
 
   if (ep_conso_5_usages_m2 == null) return null;
   if (ep_conso_5_usages_m2 < (cut['A'] ?? 70)) return 'A';
@@ -363,7 +364,7 @@ export function classe_bilan_dpe(ep_conso_5_usages_m2, zc_id, ca_id, Sh) {
 export function classe_emission_ges(emission_ges_5_usages_m2, zc_id, ca_id, Sh) {
   const ca = enums.classe_altitude[ca_id];
 
-  const cut = tvs.ges_class_limit[ca][Math.round(Sh)] ?? [];
+  const cut = interpolateLimitTable(tvs.ges_class_limit[ca], Sh);
 
   if (emission_ges_5_usages_m2 == null) return null;
   if (emission_ges_5_usages_m2 < (cut['A'] ?? 6)) return 'A';
diff --git a/src/interpolateLimitTable.js b/src/interpolateLimitTable.js
new file mode 100644
index 0000000..4d26ada
--- /dev/null
+++ b/src/interpolateLimitTable.js
@@ -0,0 +1,35 @@
+export function interpolateLimitTable(table, Sh) {
+  const keys = Object.keys(table)
+    .map(Number)
+    .sort((a, b) => a - b);
+
+  const minKey = keys[0];
+  const maxKey = keys[keys.length - 1];
+
+  if (Sh <= minKey) return table[minKey];
+  if (Sh >= maxKey) return table[maxKey];
+
+  if (table[Sh]) return table[Sh];
+
+  const lo = keys.filter((k) => k <= Sh).pop();
+  const hi = keys.filter((k) => k >= Sh).shift();
+
+  const loRow = table[lo];
+  const hiRow = table[hi];
+  const t = (Sh - lo) / (hi - lo);
+
+  const result = {};
+  const allLetters = new Set([...Object.keys(loRow), ...Object.keys(hiRow)]);
+  for (const letter of allLetters) {
+    const vLo = loRow[letter];
+    const vHi = hiRow[letter];
+    if (vLo !== undefined && vHi !== undefined) {
+      result[letter] = vLo + (vHi - vLo) * t;
+    } else if (vLo !== undefined) {
+      result[letter] = vLo;
+    } else if (vHi !== undefined) {
+      result[letter] = vHi;
+    }
+  }
+  return result;
+}