xF: deduplicate transcript logic

After the last commit it got a bit ridiculous.

xF.c

@@ -83,7 +83,7 @@ struct buffer_line
 	bool is_unimportant;
 	bool is_highlight;
 	enum relay_rendition rendition;
-	uint64_t when;                       ///< Unix timestamp in milliseconds
+	uint64_t when;                       ///< Unix timestamp in ms, for log = 0
 	struct buffer_line_item *items;
 	struct buffer_line_item *items_tail;
 
@@ -2687,6 +2687,15 @@ app_make_line_timestamp (const struct buffer_line *line)
 static void
 app_wrap_buffer_line_to_width (struct buffer_line *line, int width)
 {
+	if (!line->when)
+	{
+		struct widget *padding = app_padding (ATTRIBUTE_NORMAL, 0.25);
+		int available = MAX (0, width - 2 * padding->width);
+		app_wrap_buffer_line (line, available, available);
+		widget_destroy (padding);
+		return;
+	}
+
 	struct widget *timestamp = app_make_line_timestamp (line);
 	struct widget *time_padding = app_padding (ATTRIBUTE_TIMESTAMP, 0.25);
 	struct widget *mark = app_make_mark (line);
@@ -2704,15 +2713,6 @@ app_wrap_buffer_line_to_width (struct buffer_line *line, int width)
 	widget_destroy (padding);
 }
 
-static void
-app_wrap_log_line_to_width (struct buffer_line *line, int width)
-{
-	struct widget *padding = app_padding (ATTRIBUTE_NORMAL, 0.25);
-	int available = MAX (0, width - 2 * padding->width);
-	app_wrap_buffer_line (line, available, available);
-	widget_destroy (padding);
-}
-
 static int
 app_wrapped_line_height (const struct buffer_line *line)
 {
@@ -2732,11 +2732,24 @@ app_buffer_line_height (struct buffer_line *line)
 static struct widget *
 app_make_line (struct buffer_line *line)
 {
+	struct layout rows = {};
+	if (!line->when)
+	{
+		for (size_t i = 0; i < line->wraps_len; i++)
+		{
+			struct layout row = {};
+			app_push (&row, app_padding (ATTRIBUTE_NORMAL, 0.25));
+			app_append_line_span (&row, 0, line, &line->wraps[i]);
+			app_push (&row, app_padding (ATTRIBUTE_NORMAL, 0.25));
+			app_push (&rows, xui_hbox (row.head));
+		}
+		return xui_vbox (rows.head);
+	}
+
 	// XXX: We still use too much ATTRIBUTE_NORMAL, which basically names
 	// the <-1, -1> colour pair.  We don't use it with line items as a default
 	// because then links attribute application would get blocked.
 	chtype base = line->leaked ? g_attrs[ATTRIBUTE_EXTERNAL].attrs : 0;
-	struct layout rows = {};
 	for (size_t i = 0; i < line->wraps_len; i++)
 	{
 		struct layout row = {};
@@ -2794,19 +2807,50 @@ app_make_read_marker (void)
 	return marker;
 }
 
-static struct widget *
-app_make_log_line (const struct buffer_line *line)
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+enum transcript_visit_kind { VISIT_LINE, VISIT_READ, VISIT_DATE };
+
+typedef void (*transcript_visit_fn)
+	(enum transcript_visit_kind, struct buffer_line *, time_t, int, void *);
+
+static void
+app_walk_transcript (time_t now, transcript_visit_fn visit, void *user_data)
 {
-	struct layout rows = {};
-	for (size_t i = 0; i < line->wraps_len; i++)
+	if (g.log.visible)
 	{
-		struct layout row = {};
-		app_push (&row, app_padding (ATTRIBUTE_NORMAL, 0.25));
-		app_append_line_span (&row, 0, line, &line->wraps[i]);
-		app_push (&row, app_padding (ATTRIBUTE_NORMAL, 0.25));
-		app_push (&rows, xui_hbox (row.head));
+		for (size_t i = 0; i < g.log.lines_len; i++)
+			visit (VISIT_LINE, g.log.lines[i], 0,
+				app_wrapped_line_height (g.log.lines[i]), user_data);
+		return;
 	}
-	return xui_vbox (rows.head);
+
+	struct buffer *b = g.buffer_current;
+	if (!b)
+		return;
+
+	uint64_t unread = (uint64_t) b->new_messages + b->new_unimportant_messages;
+	const struct buffer_line *marker_before = NULL;
+	for (const struct buffer_line *line = b->lines_tail;
+		line && unread--; line = line->prev)
+		marker_before = line;
+
+	struct tm last_date = {};
+	bool have_last_date = false;
+	LIST_FOR_EACH (struct buffer_line, line, b->lines)
+	{
+		if (line == marker_before)
+			visit (VISIT_READ, NULL, line->when, READ_MARKER_HEIGHT, user_data);
+		if (!buffer_line_is_visible (b, line))
+			continue;
+
+		time_t when = line->when / 1000;
+		if (app_date_changed (when, &last_date, &have_last_date))
+			visit (VISIT_DATE, line, when, g_xui.vunit, user_data);
+		visit (VISIT_LINE, line, when, app_wrapped_line_height (line), user_data);
+	}
+	if (have_last_date && app_date_changed (now, &last_date, &have_last_date))
+		visit (VISIT_DATE, NULL, now, g_xui.vunit, user_data);
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
@@ -2823,8 +2867,7 @@ struct transcript_slice
 static struct transcript_slice
 app_make_transcript_slice (void)
 {
-	struct app_scroll_view view =
-		app_scroll_view (WIDGET_TRANSCRIPT_SCROLLBAR);
+	struct app_scroll_view view = app_scroll_view (WIDGET_TRANSCRIPT_SCROLLBAR);
 	int viewport = app_viewport_height ();
 	int view_top = app_scroll_view_origin (&view);
 	return (struct transcript_slice)
@@ -2854,113 +2897,79 @@ app_transcript_slice_offset (const struct transcript_slice *slice)
 	return slice->first_y < 0 ? 0 : slice->first_y - slice->view_top;
 }
 
-static int
-app_append_log_rows (struct layout *rows)
-{
-	struct transcript_slice slice = app_make_transcript_slice ();
-	for (size_t i = 0; i < g.log.lines_len; i++)
-	{
-		struct buffer_line *line = g.log.lines[i];
-		if (app_transcript_row_is_visible
-			(&slice, app_wrapped_line_height (line)))
-			app_push (rows, app_make_log_line (line));
-	}
-	return app_transcript_slice_offset (&slice);
-}
-
-static int
-app_append_buffer_rows (struct layout *rows, time_t now)
-{
-	struct buffer *b = g.buffer_current;
-	if (!b)
-		return 0;
-
-	uint64_t unread = (uint64_t) b->new_messages + b->new_unimportant_messages;
-	const struct buffer_line *marker_before = NULL;
-	for (const struct buffer_line *line = b->lines_tail;
-		line && unread--; line = line->prev)
-		marker_before = line;
-
-	struct transcript_slice slice = app_make_transcript_slice ();
-	struct tm last_date = {};
-	bool have_last_date = false;
-	LIST_FOR_EACH (struct buffer_line, line, b->lines)
-	{
-		if (line == marker_before
-		 && app_transcript_row_is_visible (&slice, READ_MARKER_HEIGHT))
-			app_push (rows, app_make_read_marker ());
-		if (!buffer_line_is_visible (b, line))
-			continue;
-
-		time_t when = line->when / 1000;
-		if (app_date_changed (when, &last_date, &have_last_date)
-		 && app_transcript_row_is_visible (&slice, g_xui.vunit))
-			app_push (rows, app_make_date_change_marker (when));
-		if (app_transcript_row_is_visible
-			(&slice, app_wrapped_line_height (line)))
-			app_push (rows, app_make_line (line));
-	}
-	if (have_last_date && app_date_changed (now, &last_date, &have_last_date)
-	 && app_transcript_row_is_visible (&slice, g_xui.vunit))
-		app_push (rows, app_make_date_change_marker (now));
-	return app_transcript_slice_offset (&slice);
-}
-
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
+struct transcript_layout_ctx
+{
+	struct transcript_slice slice;
+	struct layout rows;
+};
+
+static void
+transcript_layout_visit (enum transcript_visit_kind kind,
+	struct buffer_line *line, time_t when, int height, void *user_data)
+{
+	struct transcript_layout_ctx *c = user_data;
+	if (!app_transcript_row_is_visible (&c->slice, height))
+		return;
+
+	switch (kind)
+	{
+	break; case VISIT_LINE:
+		app_push (&c->rows, app_make_line (line));
+	break; case VISIT_READ:
+		app_push (&c->rows, app_make_read_marker ());
+	break; case VISIT_DATE:
+		app_push (&c->rows, app_make_date_change_marker (when));
+	}
+}
+
 static struct widget *
 app_make_transcript (time_t now)
 {
-	struct layout rows = {};
-	int offset = g.log.visible
-		? app_append_log_rows (&rows)
-		: app_append_buffer_rows (&rows, now);
+	struct transcript_layout_ctx ctx =
+		{ .slice = app_make_transcript_slice () };
+	app_walk_transcript (now, transcript_layout_visit, &ctx);
 
-	struct widget *transcript = xui_vbox (rows.head);
+	struct widget *transcript = xui_vbox (ctx.rows.head);
 	transcript->on_allocated = app_on_viewport_allocated;
 	transcript->widget_id = WIDGET_TRANSCRIPT;
-	transcript->userdata = offset;
+	transcript->userdata = app_transcript_slice_offset (&ctx.slice);
 	transcript->width = transcript->height = -1;
 	return transcript;
 }
 
+struct transcript_height_ctx
+{
+	int width;
+	uint64_t height;
+};
+
+static void
+transcript_height_visit (enum transcript_visit_kind kind,
+	struct buffer_line *line, time_t when, int height, void *user_data)
+{
+	struct transcript_height_ctx *c = user_data;
+	switch (kind)
+	{
+	break; case VISIT_LINE:
+		app_wrap_buffer_line_to_width (line, c->width);
+		c->height += app_wrapped_line_height (line);
+	break; default:
+		c->height += height;
+	}
+}
+
 static int
 app_transcript_height_at (int width, time_t now)
 {
-	uint64_t height = 0;
-	if (g.log.visible)
-	{
-		for (size_t i = 0; i < g.log.lines_len; i++)
-		{
-			app_wrap_log_line_to_width (g.log.lines[i], width);
-			height += app_wrapped_line_height (g.log.lines[i]);
-		}
-		return MIN ((uint64_t) INT_MAX, height);
-	}
-
-	struct buffer *buffer = g.buffer_current;
-	if (!buffer)
-		return 0;
-
-	height = buffer_has_read_marker (buffer) ? READ_MARKER_HEIGHT : 0;
-
-	struct tm last_date = {};
-	bool have_last_date = false;
-	LIST_FOR_EACH (struct buffer_line, line, buffer->lines)
-	{
-		if (!buffer_line_is_visible (buffer, line))
-			continue;
-
-		if (app_date_changed (line->when / 1000, &last_date, &have_last_date))
-			height += g_xui.vunit;
-		app_wrap_buffer_line_to_width (line, width);
-		height += app_wrapped_line_height (line);
-	}
-	if (have_last_date && app_date_changed (now, &last_date, &have_last_date))
-		height += g_xui.vunit;
-	return MIN ((uint64_t) INT_MAX, height);
+	struct transcript_height_ctx ctx = { .width = width, .height = 0 };
+	app_walk_transcript (now, transcript_height_visit, &ctx);
+	return MIN ((uint64_t) INT_MAX, ctx.height);
 }
 
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
 static struct widget *
 app_make_middle (void)
 {
@@ -3507,52 +3516,6 @@ app_external_editor_make_file (const char *template_name, const char *contents,
 	return template;
 }
 
-static void
-app_external_editor_append_line (struct str *output,
-	const struct buffer_line *line, bool decorated)
-{
-	if (decorated)
-	{
-		str_append (output, app_format_line_timestamp (line));
-		str_append (output, app_line_mark (line->rendition));
-	}
-	LIST_FOR_EACH (struct buffer_line_item, item, line->items)
-		str_append (output, item->text);
-	str_append_c (output, '\n');
-}
-
-static struct str
-app_external_editor_make_transcript (void)
-{
-	struct str transcript = str_make ();
-	if (g.log.visible)
-	{
-		for (size_t i = 0; i < g.log.lines_len; i++)
-			app_external_editor_append_line
-				(&transcript, g.log.lines[i], false);
-		return transcript;
-	}
-
-	struct buffer *buffer = g.buffer_current;
-	struct tm last_date = {};
-	bool have_last_date = false;
-	LIST_FOR_EACH (struct buffer_line, line, buffer->lines)
-	{
-		if (!buffer_line_is_visible (buffer, line))
-			continue;
-
-		time_t when = line->when / 1000;
-		if (app_date_changed (when, &last_date, &have_last_date))
-			str_append_printf (&transcript, "%s\n", app_format_date (when));
-		app_external_editor_append_line (&transcript, line, true);
-	}
-
-	time_t now = time (NULL);
-	if (have_last_date && app_date_changed (now, &last_date, &have_last_date))
-		str_append_printf (&transcript, "%s\n", app_format_date (now));
-	return transcript;
-}
-
 static void
 app_external_editor_process_file (void)
 {
@@ -3678,6 +3641,29 @@ app_external_editor_launch (struct error **e)
 	return true;
 }
 
+static void
+transcript_text_visit (enum transcript_visit_kind kind,
+	struct buffer_line *line, time_t when, int height, void *user_data)
+{
+	struct str *s = user_data;
+	switch (kind)
+	{
+	break; case VISIT_LINE:
+		if (when)
+		{
+			str_append (s, app_format_line_timestamp (line));
+			str_append (s, app_line_mark (line->rendition));
+		}
+		LIST_FOR_EACH (struct buffer_line_item, item, line->items)
+			str_append (s, item->text);
+		str_append_c (s, '\n');
+	break; case VISIT_READ:
+		str_append (s, "---\n");
+	break; case VISIT_DATE:
+		str_append_printf (s, "%s\n", app_format_date (when));
+	}
+}
+
 static bool
 app_launch_external_editor (bool view_transcript)
 {
@@ -3689,9 +3675,10 @@ app_launch_external_editor (bool view_transcript)
 	const char *template_name = "input.XXXXXX.txt";
 	if (view_transcript)
 	{
-		struct str transcript = app_external_editor_make_transcript ();
-		contents_len = transcript.len;
-		contents = str_steal (&transcript);
+		struct str text = str_make ();
+		app_walk_transcript (time (NULL), transcript_text_visit, &text);
+		contents_len = text.len;
+		contents = str_steal (&text);
 		template_name = "transcript.XXXXXX.txt";
 	}
 	else