From 412587a4572ac2c3eef7cc9e2c77bdd1d426973c Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Sun, 15 Jan 2023 15:06:47 -1000
Subject: [PATCH] Add support for streaming history

---
 src/data/history.ts | 87 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 82 insertions(+), 5 deletions(-)

diff --git a/src/data/history.ts b/src/data/history.ts
index f0b145a8f0..adab7e4d01 100644
--- a/src/data/history.ts
+++ b/src/data/history.ts
@@ -79,12 +79,8 @@ interface EntityHistoryState {
   lu: number;
 }
 
-interface EntityStateDict<T> {
-  [entity_id: string]: T;
-}
-
 export interface HistoryStreamMessage {
-  states: EntityStateDict<EntityHistoryState[]>;
+  states: HistoryStates;
   start_time?: number; // Start time of this historical chunk
   end_time?: number; // End time of this historical chunk
 }
@@ -207,6 +203,87 @@ export const subscribeHistory = (
   );
 };
 
+class HistoryStream {
+  hass: HomeAssistant;
+
+  startTime: Date;
+
+  endTime: Date;
+
+  combinedHistory: HistoryStates;
+
+  constructor(hass: HomeAssistant, startTime: Date, endTime: Date) {
+    this.hass = hass;
+    this.startTime = startTime;
+    this.endTime = endTime;
+    this.combinedHistory = {};
+  }
+
+  processMessage(streamMessage: HistoryStreamMessage): HistoryStates {
+    // Put newest ones on top. Reverse works in-place so
+    // make a copy first.
+    if (!this.combinedHistory || !this.combinedHistory.length) {
+      this.combinedHistory = streamMessage.states;
+      return this.combinedHistory;
+    }
+    if (!streamMessage.states.length) {
+      // Empty messages are still sent to
+      // indicate no more historical events
+      return this.combinedHistory;
+    }
+    const purgeBeforePythonTime = this.startTime.getTime() / 1000;
+    const newHistory: HistoryStates = {};
+    Object.keys(streamMessage.states).forEach((entityId) => {
+      newHistory[entityId] = [];
+    });
+    Object.keys(this.combinedHistory).forEach((entityId) => {
+      newHistory[entityId] = [];
+    });
+    Object.keys(newHistory).forEach((entityId) => {
+      if (
+        entityId in this.combinedHistory &&
+        entityId in streamMessage.states
+      ) {
+        newHistory[entityId] = this.combinedHistory[entityId]
+          .concat(streamMessage.states[entityId])
+          .filter((entry) => entry.lu > purgeBeforePythonTime);
+      } else if (entityId in this.combinedHistory) {
+        newHistory[entityId] = this.combinedHistory[entityId].filter(
+          (entry) => entry.lu > purgeBeforePythonTime
+        );
+      } else {
+        newHistory[entityId] = streamMessage.states[entityId];
+      }
+    });
+    this.combinedHistory = newHistory;
+    return this.combinedHistory;
+  }
+}
+
+export const subscribeHistoryStates = (
+  hass: HomeAssistant,
+  callbackFunction: (data: HistoryStates) => void,
+  startTime: Date,
+  endTime: Date,
+  entityIds: string[]
+): Promise<() => Promise<void>> => {
+  // If all specified filters are empty lists, we can return an empty list.
+  const params = {
+    type: "history/history_during_period",
+    start_time: startTime.toISOString(),
+    end_time: endTime.toISOString(),
+    minimal_response: true,
+    no_attributes: !entityIds.some((entityId) =>
+      entityIdHistoryNeedsAttributes(hass, entityId)
+    ),
+  };
+  const stream = new HistoryStream(hass, startTime, endTime);
+  return hass.connection.subscribeMessage<HistoryStreamMessage>(
+    (message) => callbackFunction(stream.processMessage(message)),
+    params
+  );
+};
+
 const equalState = (obj1: LineChartState, obj2: LineChartState) =>
   obj1.state === obj2.state &&
   // Only compare attributes if both states have an attributes object.