From ba379a1b4a97ee7eb56bed726f1c4edd76f76bb8 Mon Sep 17 00:00:00 2001
From: Tulir Asokan <tulir@maunium.net>
Date: Sat, 17 Mar 2018 14:32:01 +0200
Subject: Add basic username/id autocompletion

---
 advanced-inputfield.go | 11 ++++++++---
 view-main.go           | 39 +++++++++++++++++++++++++++++++++++++--
 2 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/advanced-inputfield.go b/advanced-inputfield.go
index 97fbfab..8b5b47a 100644
--- a/advanced-inputfield.go
+++ b/advanced-inputfield.go
@@ -79,7 +79,7 @@ type AdvancedInputField struct {
 	done func(tcell.Key)
 
 	// An optional function which is called when the user presses tab.
-	tabComplete func(text string, cursorOffset int)
+	tabComplete func(text string, cursorOffset int) string
 }
 
 // NewAdvancedInputField returns a new input field.
@@ -205,7 +205,7 @@ func (field *AdvancedInputField) SetDoneFunc(handler func(key tcell.Key)) *Advan
 	return field
 }
 
-func (field *AdvancedInputField) SetTabCompleteFunc(handler func(text string, cursorOffset int)) *AdvancedInputField {
+func (field *AdvancedInputField) SetTabCompleteFunc(handler func(text string, cursorOffset int) string) *AdvancedInputField {
 	field.tabComplete = handler
 	return field
 }
@@ -429,7 +429,12 @@ func (field *AdvancedInputField) InputHandler() func(event *tcell.EventKey, setF
 			}
 		case tcell.KeyTab: // Tab-completion
 			if field.tabComplete != nil {
-				field.tabComplete(field.text, field.cursorOffset)
+				oldWidth := runewidth.StringWidth(field.text)
+				field.text = field.tabComplete(field.text, field.cursorOffset)
+				newWidth := runewidth.StringWidth(field.text)
+				if oldWidth != newWidth {
+					field.cursorOffset += newWidth - oldWidth
+				}
 			}
 		case tcell.KeyEnter, tcell.KeyEscape: // We're done.
 			if field.done != nil {
diff --git a/view-main.go b/view-main.go
index 5a3a70c..219e603 100644
--- a/view-main.go
+++ b/view-main.go
@@ -17,10 +17,13 @@
 package main
 
 import (
+	"fmt"
 	"strings"
 	"time"
+	"unicode"
 
 	"github.com/gdamore/tcell"
+	"github.com/mattn/go-runewidth"
 	"maunium.net/go/gomatrix"
 	"maunium.net/go/tview"
 )
@@ -96,11 +99,43 @@ func (view *MainView) InputChanged(text string) {
 	}
 }
 
-func (view *MainView) InputTabComplete(text string, cursorOffset int) {
+func findWordToTabComplete(text string) string {
+	output := ""
+	runes := []rune(text)
+	for i := len(runes) - 1; i >= 0; i-- {
+		if unicode.IsSpace(runes[i]) {
+			break
+		}
+		output = string(runes[i]) + output
+	}
+	return output
+}
+
+func (view *RoomView) AutocompleteUser(existingText string) (completions []string) {
+	for _, user := range view.room.GetMembers() {
+		if strings.HasPrefix(user.DisplayName, existingText) {
+			completions = append(completions, user.DisplayName)
+		} else if strings.HasPrefix(user.UserID, existingText) {
+			completions = append(completions, user.UserID)
+		}
+	}
+	return
+}
+
+func (view *MainView) InputTabComplete(text string, cursorOffset int) string {
 	roomView, _ := view.rooms[view.CurrentRoomID()]
 	if roomView != nil {
-		// text[0:cursorOffset]
+		str := runewidth.Truncate(text, cursorOffset, "")
+		word := findWordToTabComplete(str)
+		userCompletions := roomView.AutocompleteUser(word)
+		if len(userCompletions) == 1 {
+			text = str[0:len(str)-len(word)] + userCompletions[0] + text[len(str):]
+		} else if len(userCompletions) > 1 && len(userCompletions) < 6 {
+			roomView.status.Clear()
+			fmt.Fprintf(roomView.status, "Completions: %s", strings.Join(userCompletions, ", "))
+		}
 	}
+	return text
 }
 
 func (view *MainView) InputDone(key tcell.Key) {
-- 
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