term.ui: add support for multi byte/UTF-8 events (#13274)

vlib/term/ui/input_nix.c.v

@@ -6,6 +6,9 @@ module ui
 struct ExtraContext {
 mut:
 	read_buf []byte
+	// read_all_bytes causes all the raw bytes to be read as one event unit.
+	// This is cruicial for UTF-8 support since Unicode codepoints can span several bytes.
+	read_all_bytes bool = true
 }
 
 const ctx_ptr = &Context(0)

vlib/term/ui/termios_nix.c.v

@@ -258,8 +258,14 @@ fn (mut ctx Context) parse_events() {
 			event = e
 			ctx.shift(len)
 		} else {
-			event = single_char(ctx.read_buf.bytestr())
+			if ctx.read_all_bytes {
-			ctx.shift(1)
+				e, len := multi_char(ctx.read_buf.bytestr())
+				event = e
+				ctx.shift(len)
+			} else {
+				event = single_char(ctx.read_buf.bytestr())
+				ctx.shift(1)
+			}
 		}
 		if event != 0 {
 			ctx.event(event)
@@ -271,6 +277,47 @@ fn (mut ctx Context) parse_events() {
 fn single_char(buf string) &Event {
 	ch := buf[0]
 
+	mut event := &Event{
+		typ: .key_down
+		ascii: ch
+		code: KeyCode(ch)
+		utf8: ch.ascii_str()
+	}
+
+	match ch {
+		// special handling for `ctrl + letter`
+		// TODO: Fix assoc in V and remove this workaround :/
+		// 1  ... 26 { event = Event{ ...event, code: KeyCode(96 | ch), modifiers: .ctrl  } }
+		// 65 ... 90 { event = Event{ ...event, code: KeyCode(32 | ch), modifiers: .shift } }
+		// The bit `or`s here are really just `+`'s, just written in this way for a tiny performance improvement
+		// don't treat tab, enter as ctrl+i, ctrl+j
+		1...8, 11...26 {
+			event = &Event{
+				typ: event.typ
+				ascii: event.ascii
+				utf8: event.utf8
+				code: KeyCode(96 | ch)
+				modifiers: .ctrl
+			}
+		}
+		65...90 {
+			event = &Event{
+				typ: event.typ
+				ascii: event.ascii
+				utf8: event.utf8
+				code: KeyCode(32 | ch)
+				modifiers: .shift
+			}
+		}
+		else {}
+	}
+
+	return event
+}
+
+fn multi_char(buf string) (&Event, int) {
+	ch := buf[0]
+
 	mut event := &Event{
 		typ: .key_down
 		ascii: ch
@@ -306,7 +353,7 @@ fn single_char(buf string) &Event {
 		else {}
 	}
 
-	return event
+	return event, buf.len
 }
 
 // Gets an entire, independent escape sequence from the buffer