From 0501e5000ba50fd8903405c7d18871b1dfe9e07f Mon Sep 17 00:00:00 2001
From: David Buezas <david.buezas@gmail.com>
Date: Sat, 12 Nov 2022 12:12:49 +0100
Subject: [PATCH] Fix #132. Negative years (e.g zooming out) break fetching and
 rendering

Fix parsing of negative iso dates
Default x axis type to date to avoid the axis defaulting to numbers when all traces are empty.
---
 src/cache/Cache.ts       |  3 +++
 src/plotly-graph-card.ts | 26 ++++++++++++++++++++++----
 src/themed-layout.ts     |  1 +
 3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/src/cache/Cache.ts b/src/cache/Cache.ts
index 525d14f..dc4414d 100644
--- a/src/cache/Cache.ts
+++ b/src/cache/Cache.ts
@@ -98,6 +98,8 @@ export function getEntityKey(entity: EntityConfig) {
   }
   throw new Error(`Entity malformed:${JSON.stringify(entity)}`);
 }
+
+const MIN_SAFE_TIMESTAMP = Date.parse("0001-01-02T00:00:00.000Z");
 export default class Cache {
   ranges: Record<string, TimestampRange[]> = {};
   histories: Record<string, EntityState[]> = {};
@@ -132,6 +134,7 @@ export default class Cache {
     significant_changes_only: boolean,
     minimal_response: boolean
   ) {
+    range = range.map((n) => Math.max(MIN_SAFE_TIMESTAMP, n)); // HA API can't handle negative years
     return (this.busy = this.busy
       .catch(() => {})
       .then(async () => {
diff --git a/src/plotly-graph-card.ts b/src/plotly-graph-card.ts
index 08d0358..e6eaaa4 100644
--- a/src/plotly-graph-card.ts
+++ b/src/plotly-graph-card.ts
@@ -263,10 +263,28 @@ export class PlotlyGraph extends HTMLElement {
     return [start, end + msPad];
   }
   getVisibleRange() {
-    return this.contentEl.layout.xaxis!.range!.map((date) =>
-      // if autoscale is used after scrolling, plotly returns the dates as numbers instead of strings
-      Number.isFinite(date) ? date : +parseISO(date)
-    );
+    console.log(this.contentEl.layout.xaxis!.range);
+    return this.contentEl.layout.xaxis!.range!.map((date) => {
+      // if autoscale is used after scrolling, plotly returns the dates as timestamps (numbers) instead of iso strings
+      if (Number.isFinite(date)) return date;
+      if (date.startsWith("-")) {
+        /*
+         The function parseISO can't handle negative dates.
+         To work around that, I'm parsing it without the minus, and then manually calculating the timestamp from that.
+         The arithmetic has a twist because timestamps start on 1970 and not on year zero,
+         so the distance to a the year zero has to be calculated by subtracting the "zero year" timestamp.
+         positive_date = -date (which is negative)
+         timestamp = (year 0) - (time from year 0)
+         timestamp = (year 0) - (positive_date - year 0)
+         timestamp = 2 * (year 0) - positive_date
+         timestamp = 2 * (year 0) - (-date)
+        */
+        return (
+          2 * +parseISO("0000-01-01 00:00:00.000") - +parseISO(date.slice(1))
+        );
+      }
+      return +parseISO(date);
+    });
   }
   async enterBrowsingMode() {
     this.isBrowsing = true;
diff --git a/src/themed-layout.ts b/src/themed-layout.ts
index 6d6459e..109fd77 100644
--- a/src/themed-layout.ts
+++ b/src/themed-layout.ts
@@ -14,6 +14,7 @@ const defaultLayout: Partial<Plotly.Layout> = {
   dragmode: "pan",
   xaxis: {
     autorange: false,
+    type: "date",
     // automargin: true, // it makes zooming very jumpy
   },
   yaxis: {