Add time_format config for custom strftime strings

This lets the user change to any time format they want in the bar.
As part of this, we also change the bar to re-draw every second (to
allow using seconds in the time format string).

src/config/BarConfig.zig

@@ -12,6 +12,7 @@ const NodeName = enum {
     vertical_padding,
     horizontal_padding,
     margins,
+    time_format,
 };
 const MarginsNodeName = enum { top, right, bottom, left };
 
@@ -38,6 +39,10 @@ vertical_padding: u8 = 5,
 /// Horizontal padding between bar edges and content, in pixels
 horizontal_padding: u8 = 5,
 
+/// strftime format string for the clock display.
+/// null means use the default.
+time_format: ?[]const u8 = null,
+
 pub fn toBarOptions(config: BarConfig) Bar.Options {
     return .{
         .fonts = config.fonts orelse "monospace:size=14",
@@ -52,6 +57,7 @@ pub fn toBarOptions(config: BarConfig) Bar.Options {
         },
         .vertical_padding = config.vertical_padding,
         .horizontal_padding = config.horizontal_padding,
+        .time_format = config.time_format orelse Bar.default_time_format,
     };
 }
 
@@ -92,7 +98,18 @@ pub fn load(config: *Config, parser: *kdl.Parser, hostname: ?[]const u8) !void {
                                 logWarnInvalidNodeArg(name, val_str);
                             }
                         },
-
+                        .time_format => {
+                            if (node.argcount() < 1) {
+                                logWarnMissingNodeArg(name, "format string");
+                                continue;
+                            }
+                            if (validateTimeFormat(val_str)) {
+                                config.bar_config.?.time_format = utils.gpa.dupe(u8, val_str) catch @panic("Out of memory");
+                                logDebugSettingNode(name, val_str);
+                            } else {
+                                logWarnInvalidNodeArg(name, val_str);
+                            }
+                        },
                         .margins => next_child_block = .margins,
                         inline .background_color,
                         .text_color,
@@ -192,15 +209,26 @@ inline fn logWarnInvalidNodeArg(node_name: anytype, node_value: []const u8) void
     }
 }
 
+fn validateTimeFormat(format: []const u8) bool {
+    // Try formatting with a dummy time to validate the format string
+    var buf: [255]u8 = undefined;
+    var writer = Io.Writer.fixed(&buf);
+    const dummy_time = zeit.Time{};
+    dummy_time.strftime(&writer, format) catch return false;
+    return true;
+}
+
 inline fn logWarnMissingNodeArg(node_name: NodeName, comptime arg: []const u8) void {
     log.warn("\"bar.{s}\" missing " ++ arg ++ " argument. Ignoring", .{@tagName(node_name)});
 }
 
 const std = @import("std");
 const fmt = std.fmt;
+const Io = std.Io;
 
 const kdl = @import("kdl");
 const pixman = @import("pixman");
+const zeit = @import("zeit");
 
 const utils = @import("../utils.zig");
 const Bar = @import("../Bar.zig");