web: Move web app to ‘web’ directory.

Ever since we started bundling the app with webpack, there’s been less
and less overlap between our ‘static’ directory (files belonging to
the frontend app) and Django’s interpretation of the ‘static’
directory (files served directly to the web).

Split the app out to its own ‘web’ directory outside of ‘static’, and
remove all the custom collectstatic --ignore rules.  This makes it
much clearer what’s actually being served to the web, and what’s being
bundled by webpack.  It also shrinks the release tarball by 3%.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

web/src/navigate.js

@@ -0,0 +1,140 @@
+import * as message_lists from "./message_lists";
+import * as message_viewport from "./message_viewport";
+import * as rows from "./rows";
+import * as unread_ops from "./unread_ops";
+
+function go_to_row(msg_id) {
+    message_lists.current.select_id(msg_id, {then_scroll: true, from_scroll: true});
+}
+
+export function up() {
+    message_viewport.set_last_movement_direction(-1);
+    const msg_id = message_lists.current.prev();
+    if (msg_id === undefined) {
+        return;
+    }
+    go_to_row(msg_id);
+}
+
+export function down(with_centering) {
+    message_viewport.set_last_movement_direction(1);
+
+    if (message_lists.current.is_at_end()) {
+        if (with_centering) {
+            // At the last message, scroll to the bottom so we have
+            // lots of nice whitespace for new messages coming in.
+            const $current_msg_table = rows.get_table(message_lists.current.table_name);
+            message_viewport.scrollTop(
+                $current_msg_table.safeOuterHeight(true) - message_viewport.height() * 0.1,
+            );
+            unread_ops.process_scrolled_to_bottom();
+        }
+
+        return;
+    }
+
+    // Normal path starts here.
+    const msg_id = message_lists.current.next();
+    if (msg_id === undefined) {
+        return;
+    }
+    go_to_row(msg_id);
+}
+
+export function to_home() {
+    message_viewport.set_last_movement_direction(-1);
+    const first_id = message_lists.current.first().id;
+    message_lists.current.select_id(first_id, {then_scroll: true, from_scroll: true});
+}
+
+export function to_end() {
+    const next_id = message_lists.current.last().id;
+    message_viewport.set_last_movement_direction(1);
+    message_lists.current.select_id(next_id, {then_scroll: true, from_scroll: true});
+    unread_ops.process_scrolled_to_bottom();
+}
+
+function amount_to_paginate() {
+    // Some day we might have separate versions of this function
+    // for Page Up vs. Page Down, but for now it's the same
+    // strategy in either direction.
+    const info = message_viewport.message_viewport_info();
+    const page_size = info.visible_height;
+
+    // We don't want to page up a full page, because Zulip users
+    // are especially worried about missing messages, so we want
+    // a little bit of the old page to stay on the screen.  The
+    // value chosen here is roughly 2 or 3 lines of text, but there
+    // is nothing sacred about it, and somebody more anal than me
+    // might wish to tie this to the size of some particular DOM
+    // element.
+    const overlap_amount = 55;
+
+    let delta = page_size - overlap_amount;
+
+    // If the user has shrunk their browser a whole lot, pagination
+    // is not going to be very pleasant, but we can at least
+    // ensure they go in the right direction.
+    if (delta < 1) {
+        delta = 1;
+    }
+
+    return delta;
+}
+
+export function page_up_the_right_amount() {
+    // This function's job is to scroll up the right amount,
+    // after the user hits Page Up.  We do this ourselves
+    // because we can't rely on the browser to account for certain
+    // page elements, like the compose box, that sit in fixed
+    // positions above the message pane.  For other scrolling
+    // related adjustments, try to make those happen in the
+    // scroll handlers, not here.
+    const delta = amount_to_paginate();
+    message_viewport.scrollTop(message_viewport.scrollTop() - delta);
+}
+
+export function page_down_the_right_amount() {
+    // see also: page_up_the_right_amount
+    const delta = amount_to_paginate();
+    message_viewport.scrollTop(message_viewport.scrollTop() + delta);
+}
+
+export function page_up() {
+    if (message_viewport.at_top() && !message_lists.current.empty()) {
+        message_lists.current.select_id(message_lists.current.first().id, {then_scroll: false});
+    } else {
+        page_up_the_right_amount();
+    }
+}
+
+export function page_down() {
+    if (message_viewport.at_bottom() && !message_lists.current.empty()) {
+        message_lists.current.select_id(message_lists.current.last().id, {then_scroll: false});
+        unread_ops.process_scrolled_to_bottom();
+    } else {
+        page_down_the_right_amount();
+    }
+}
+
+export function scroll_to_selected() {
+    const $selected_row = message_lists.current.selected_row();
+    if ($selected_row && $selected_row.length !== 0) {
+        message_viewport.recenter_view($selected_row);
+    }
+}
+
+let scroll_to_selected_planned = false;
+
+export function plan_scroll_to_selected() {
+    scroll_to_selected_planned = true;
+}
+
+export function maybe_scroll_to_selected() {
+    // If we have made a plan to scroll to the selected message but
+    // deferred doing so, do so here.
+    if (scroll_to_selected_planned) {
+        scroll_to_selected();
+        scroll_to_selected_planned = false;
+    }
+}