feat(handler): add Context helpers (Message, Sender, Chat, Send, Reply)

Ergonomic accessors on the handler Context: Message (effective message), Sender
(message/callback/inline-query user), Chat (target chat id). Send posts to the
update's chat; Reply posts as a reply to the incoming message. Both delegate to
SendMessage with the Context as the request context.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: ernado

context.go

@@ -0,0 +1,51 @@
+package botapi
+
+// Message returns the message the update carries (new/edited message or channel
+// post), or nil.
+func (c *Context) Message() *Message { return c.Update.EffectiveMessage() }
+
+// Sender returns the user who produced the update (message sender or callback/
+// inline-query sender), or nil when there is none.
+func (c *Context) Sender() *User {
+	switch {
+	case c.Update.CallbackQuery != nil:
+		return &c.Update.CallbackQuery.From
+	case c.Update.InlineQuery != nil:
+		return &c.Update.InlineQuery.From
+	}
+	if m := c.Message(); m != nil {
+		return m.From
+	}
+	return nil
+}
+
+// Chat returns the target chat id of the update and whether one is present.
+func (c *Context) Chat() (ChatID, bool) {
+	if m := c.Message(); m != nil {
+		return ID(m.Chat.ID), true
+	}
+	if cq := c.Update.CallbackQuery; cq != nil && cq.Message != nil {
+		return ID(cq.Message.Chat.ID), true
+	}
+	return nil, false
+}
+
+// Send sends a text message to the update's chat.
+func (c *Context) Send(text string, opts ...SendOption) (*Message, error) {
+	chat, ok := c.Chat()
+	if !ok {
+		return nil, &Error{Code: 400, Description: "Bad Request: update has no chat to send to"}
+	}
+	return c.Bot.SendMessage(c, chat, text, opts...)
+}
+
+// Reply sends a text message to the update's chat as a reply to the incoming
+// message.
+func (c *Context) Reply(text string, opts ...SendOption) (*Message, error) {
+	m := c.Message()
+	if m == nil {
+		return nil, &Error{Code: 400, Description: "Bad Request: update has no message to reply to"}
+	}
+	opts = append([]SendOption{ReplyTo(m.MessageID)}, opts...)
+	return c.Bot.SendMessage(c, ID(m.Chat.ID), text, opts...)
+}

context_test.go

@@ -0,0 +1,48 @@
+package botapi
+
+import (
+	"context"
+	"testing"
+)
+
+func TestContextChatAndSender(t *testing.T) {
+	c := &Context{
+		Context: context.Background(),
+		Update: &Update{Message: &Message{
+			MessageID: 7,
+			Chat:      Chat{ID: -100500, Type: ChatTypeSupergroup},
+			From:      &User{ID: 11, Username: "ada"},
+		}},
+	}
+
+	chat, ok := c.Chat()
+	if !ok {
+		t.Fatal("Chat should be present")
+	}
+	if id, isInt := chat.(ChatIDInt); !isInt || int64(id) != -100500 {
+		t.Fatalf("Chat id = %v", chat)
+	}
+	if s := c.Sender(); s == nil || s.ID != 11 {
+		t.Fatalf("Sender = %+v", c.Sender())
+	}
+}
+
+func TestContextSenderFromCallback(t *testing.T) {
+	c := &Context{
+		Context: context.Background(),
+		Update:  &Update{CallbackQuery: &CallbackQuery{From: User{ID: 99}}},
+	}
+	if s := c.Sender(); s == nil || s.ID != 99 {
+		t.Fatalf("callback sender = %+v", c.Sender())
+	}
+}
+
+func TestContextReplyWithoutMessage(t *testing.T) {
+	c := &Context{Context: context.Background(), Bot: newTestBot(t), Update: &Update{InlineQuery: &InlineQuery{}}}
+	if _, err := c.Reply("hi"); err == nil {
+		t.Fatal("Reply with no message should error")
+	}
+	if _, ok := c.Chat(); ok {
+		t.Fatal("inline-query-only update should have no chat")
+	}
+}