2 files changed, 29 insertions, 2 deletions
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..e46e79c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+.scrollback
diff --git a/index.js b/index.js
index d91d459..294ad72 100644
--- a/index.js
+++ b/index.js
@@ -1,5 +1,5 @@
 const path = require('node:path')
-const {promises: {readFile}, createReadStream} = require('node:fs')
+const {promises: {readFile}, readFileSync, createReadStream, createWriteStream} = require('node:fs')
 const {createServer} = require('node:http')
 const {createHash, randomBytes} = require('node:crypto')
 const Readline = require('node:readline');
@@ -12,18 +12,44 @@ const readline = Readline.createInterface({
   prompt: '> ',
 });
 
-
 const MAX_EVENTS = 100
 
+// Event emitter and buffer for late joiners
 const chatEvents = new EventEmitter()
+let bufferDirty = true
 let eventBuffer = []
 chatEvents.on('event', ev => {
   eventBuffer = [...eventBuffer, ev].slice(0, MAX_EVENTS)
+  bufferDirty = true
   readline.clearLine()
   console.log(JSON.stringify(ev))
   readline.prompt()
 })
 
+// Populate buffer on startup
+const scrollbackFile = path.join(__dirname, '.scrollback')
+try {
+  eventBuffer = readFileSync(scrollbackFile, {encoding: 'utf8'}).split('\n')
+    .map(line => {
+      try {
+        return JSON.parse(line)
+      } catch {
+        return null
+      }
+    }).filter(event => !!event)
+  bufferDirty = false
+} catch { }
+
+// Sync buffer to disk every second
+setInterval(async () => {
+  if (!bufferDirty) return
+
+  const fileStream = createWriteStream(scrollbackFile, {flags: 'w', encoding: 'utf8'})
+  for (const event of eventBuffer) {
+    await new Promise(res => fileStream.write(JSON.stringify(event) + '\n', 'utf8', res))
+  }
+}, 1000)
+
 let currentUsers = {}
 
 readline.on('line', (line) => {