message-edit-history: Show original channel/topic for move only history.

If the organization only allows viewing message move history, in
the message edit history overlay for the initial message, we display
the original topic and channel of the message instead of the original
message content.

This way the overlay content is consistent with the organization
setting for viewing message edit history, and if the message content
has been edited, that original content is not viewable to other
users.

web/src/message_edit_history.ts

@@ -28,6 +28,7 @@ import * as ui_report from "./ui_report.ts";
 import * as util from "./util.ts";
 
 type EditHistoryEntry = {
+    initial_entry_for_move_history: boolean;
     edited_at_time: string;
     edited_by_notice: string;
     timestamp: number; // require to set data-message-id for overlay message row
@@ -113,6 +114,9 @@ function hide_loading_indicator(): void {
 }
 
 export function fetch_and_render_message_history(message: Message): void {
+    const move_history_only =
+        realm.realm_message_edit_history_visibility_policy ===
+        message_edit_history_visibility_policy_values.moves_only.code;
     $("#message-edit-history-overlay-container").html(render_message_history_overlay());
     open_overlay();
     show_loading_indicator();
@@ -149,10 +153,19 @@ export function fetch_and_render_message_history(message: Message): void {
                 let stream_changed;
                 let prev_stream;
                 let prev_stream_id;
+                let initial_entry_for_move_history = false;
 
                 if (index === 0) {
                     edited_by_notice = $t({defaultMessage: "Posted by {full_name}"}, {full_name});
-                    body_to_render = msg.rendered_content;
+                    if (move_history_only) {
+                        // If message history is limited to moves only, then we
+                        // display the original topic and channel for the message.
+                        initial_entry_for_move_history = true;
+                        new_topic_display_name = util.get_final_topic_display_name(msg.topic);
+                    } else {
+                        // Otherwise, we display the original message content.
+                        body_to_render = msg.rendered_content;
+                    }
                 } else if (msg.prev_topic !== undefined && msg.prev_content) {
                     edited_by_notice = $t({defaultMessage: "Edited by {full_name}"}, {full_name});
                     body_to_render = msg.content_html_diff;
@@ -195,6 +208,7 @@ export function fetch_and_render_message_history(message: Message): void {
                     body_to_render = msg.content_html_diff;
                 }
                 const item: EditHistoryEntry = {
+                    initial_entry_for_move_history,
                     edited_at_time,
                     edited_by_notice,
                     timestamp: msg.timestamp,
@@ -228,6 +242,7 @@ export function fetch_and_render_message_history(message: Message): void {
             // entries in reverse chronological order.
             if (message.is_stream) {
                 // Start with the message's current location.
+                let stream_display_name: string = get_display_stream_name(message.stream_id);
                 let stream_color: string = get_color(message.stream_id);
                 let recipient_bar_color: string = get_recipient_bar_color(stream_color);
                 for (const edit_history_entry of content_edit_history.toReversed()) {
@@ -238,10 +253,18 @@ export function fetch_and_render_message_history(message: Message): void {
                         // prior to this event, the message must have been in
                         // edit_history_event.prev_stream_id; fetch its color.
                         assert(edit_history_entry.prev_stream_id !== undefined);
+                        stream_display_name = get_display_stream_name(
+                            edit_history_entry.prev_stream_id,
+                        );
                         stream_color = get_color(edit_history_entry.prev_stream_id);
                         recipient_bar_color = get_recipient_bar_color(stream_color);
                     }
                 }
+                if (move_history_only) {
+                    // If message history is limited to moves only, then we
+                    // display the original topic and channel for the message.
+                    content_edit_history[0]!.new_stream = stream_display_name;
+                }
             }
             const rendered_list_html = render_message_edit_history({
                 edited_messages: content_edit_history,

web/templates/message_edit_history.hbs

@@ -27,6 +27,14 @@
             <div class="message_row{{#unless is_stream}} private-message{{/unless}}" role="listitem">
                 <div class="messagebox">
                     <div class="messagebox-content">
+                        {{#if initial_entry_for_move_history}}
+                        <div class="message_content message_edit_history_content">
+                            <p>{{t "Channel" }}: <span class="highlight_text_inserted">{{ new_stream }}</span></p>
+                            <p>{{t "Topic" }}:
+                                <span class="highlight_text_inserted {{#if is_empty_string_new_topic}}empty-topic-display{{/if}}">{{ new_topic_display_name }}</span>
+                            </p>
+                        </div>
+                        {{else}}
                         {{#if stream_changed}}
                         <div class="message_content message_edit_history_content">
                             <p>{{t "Channel" }}: <span class="highlight_text_inserted">{{ new_stream }}</span>
@@ -47,6 +55,7 @@
                             {{ rendered_markdown body_to_render}}
                         </div>
                         {{/if}}
+                        {{/if}}
                     </div>
                 </div>
             </div>