xP: add basic buffer input history

Bind M-p and M-n as in xC.

Also make all our bindings reachable on macOS.

xP/public/xP.js

@@ -197,7 +197,11 @@ rpc.addEventListener('Ping', event => {
 rpc.addEventListener('BufferUpdate', event => {
 	let e = event.detail, b = buffers.get(e.bufferName)
 	if (b === undefined) {
-		buffers.set(e.bufferName, (b = {lines: []}))
+		buffers.set(e.bufferName, (b = {
+			lines: [],
+			history: [],
+			historyAt: 0,
+		}))
 		bufferResetStats(b)
 	}
 	b.hideUnimportant = e.hideUnimportant
@@ -247,6 +251,9 @@ rpc.addEventListener('BufferActivate', event => {
 		old.inputStart = textarea.selectionStart
 		old.inputEnd = textarea.selectionEnd
 		old.inputDirection = textarea.selectionDirection
+		// Note that we effectively overwrite the newest line
+		// with the current textarea contents, and jump there.
+		old.historyAt = old.history.length
 	}
 
 	textarea.value = ''
@@ -324,6 +331,15 @@ for (let i = 0; i < 24; i++) {
 
 // ---- UI ---------------------------------------------------------------------
 
+// On macOS, the Alt/Option key transforms characters, which basically breaks
+// all event.altKey shortcuts, so require combining them with Control as well
+// on that system.
+function hasShortcutModifiers(event) {
+	// This method of detection only works with Blink browsers, as of writing.
+	return event.altKey && !event.metaKey &&
+		(navigator.userAgentData?.platform === 'macOS') === event.ctrlKey
+}
+
 let linkRE = [
 	/https?:\/\//,
 	/([^\[\](){}<>"'\s]|\([^\[\](){}<>"'\s]*\))+/,
@@ -584,27 +600,71 @@ let Input = {
 			bufferName: bufferCurrent,
 			text: textarea.value,
 		})
+
+		// b.history[b.history.length] is virtual, and is represented
+		// either by textarea contents when it's currently being edited,
+		// or by b.input in all other cases.
+		let b = buffers.get(bufferCurrent)
+		b.history.push(textarea.value)
+		b.historyAt = b.history.length
 		textarea.value = ''
 		return true
 	},
 
+	previous: textarea => {
+		let b = buffers.get(bufferCurrent)
+		if (b === undefined)
+			return false
+
+		// TODO: Ding otherwise.
+		if (b.historyAt > 0) {
+			if (b.historyAt == b.history.length)
+				b.input = textarea.value
+			textarea.value = b.history[--b.historyAt]
+		}
+		return true
+	},
+
+	next: textarea => {
+		let b = buffers.get(bufferCurrent)
+		if (b === undefined)
+			return false
+
+		// TODO: Ding otherwise.
+		if (b.historyAt < b.history.length) {
+			if (++b.historyAt == b.history.length)
+				textarea.value = b.input
+			else
+				textarea.value = b.history[b.historyAt]
+		}
+		return true
+	},
+
 	onKeyDown: event => {
 		// TODO: And perhaps on other actions, too.
 		rpc.send({command: 'Active'})
 
 		let textarea = event.currentTarget
 		let handled = false
-		switch (event.keyCode) {
-		case 9:
-			if (!event.ctrlKey && !event.metaKey && !event.altKey &&
-				!event.shiftKey)
+		if (hasShortcutModifiers(event)) {
+			switch (event.key) {
+			case 'p':
+				handled = Input.previous(textarea)
+				break
+			case 'n':
+				handled = Input.next(textarea)
+				break
+			}
+		} else if (!event.altKey && !event.ctrlKey && !event.metaKey &&
+				!event.shiftKey) {
+			switch (event.keyCode) {
+			case 9:
 				handled = Input.complete(textarea)
-			break
-		case 13:
-			if (!event.ctrlKey && !event.metaKey && !event.altKey &&
-				!event.shiftKey)
+				break
+			case 13:
 				handled = Input.submit(textarea)
-			break
+				break
+			}
 		}
 		if (handled)
 			event.preventDefault()
@@ -636,28 +696,34 @@ let Main = {
 window.addEventListener('load', () => m.mount(document.body, Main))
 
 document.addEventListener('keydown', event => {
-	if (rpc.ws == undefined || event.ctrlKey || event.metaKey)
+	if (rpc.ws == undefined || !hasShortcutModifiers(event))
 		return
 
-	if (event.altKey && event.key == 'Tab') {
+	switch (event.key) {
+	case 'Tab':
 		if (bufferLast !== undefined)
 			bufferActivate(bufferLast)
-	} else if (event.altKey && event.key == 'h') {
+		break
+	case 'h':
 		bufferToggleLog()
-	} else if (event.altKey && event.key == 'a') {
+		break
+	case 'a':
 		for (const [name, b] of buffers)
 			if (name !== bufferCurrent && b.newMessages) {
 				bufferActivate(name)
 				break
 			}
-	} else if (event.altKey && event.key == '!') {
+		break
+	case '!':
 		for (const [name, b] of buffers)
 			if (name !== bufferCurrent && b.highlighted) {
 				bufferActivate(name)
 				break
 			}
-	} else
+		break
+	default:
 		return
+	}
 
 	event.preventDefault()
 })