Add the cascade animation as a separate widget

Signed-off-by: AnErrupTion <anerruption@disroot.org>

src/animations/Cascade.zig

@@ -0,0 +1,81 @@
+const std = @import("std");
+const math = std.math;
+
+const Cell = @import("../tui/Cell.zig");
+const TerminalBuffer = @import("../tui/TerminalBuffer.zig");
+const Widget = @import("../tui/Widget.zig");
+
+const Cascade = @This();
+
+buffer: *TerminalBuffer,
+current_auth_fails: *usize,
+max_auth_fails: usize,
+
+pub fn init(
+    buffer: *TerminalBuffer,
+    current_auth_fails: *usize,
+    max_auth_fails: usize,
+) Cascade {
+    return .{
+        .buffer = buffer,
+        .current_auth_fails = current_auth_fails,
+        .max_auth_fails = max_auth_fails,
+    };
+}
+
+pub fn widget(self: *Cascade) Widget {
+    return Widget.init(
+        self,
+        null,
+        null,
+        draw,
+        null,
+        null,
+    );
+}
+
+fn draw(self: *Cascade) void {
+    while (self.current_auth_fails.* >= self.max_auth_fails) {
+        std.Thread.sleep(std.time.ns_per_ms * 10);
+
+        var changed = false;
+        var y = self.buffer.height - 2;
+
+        while (y > 0) : (y -= 1) {
+            for (0..self.buffer.width) |x| {
+                const cell = TerminalBuffer.getCell(x, y - 1);
+                const cell_under = TerminalBuffer.getCell(x, y);
+
+                // This shouldn't happen under normal circumstances, but because
+                // this is a *secret* animation, there's no need to care that much
+                if (cell == null or cell_under == null) continue;
+
+                const char: u8 = @truncate(cell.?.ch);
+                if (std.ascii.isWhitespace(char)) continue;
+
+                const char_under: u8 = @truncate(cell_under.?.ch);
+                if (!std.ascii.isWhitespace(char_under)) continue;
+
+                changed = true;
+
+                if ((self.buffer.random.int(u16) % 10) > 7) continue;
+
+                cell.?.put(x, y);
+
+                var space = Cell.init(
+                    ' ',
+                    cell_under.?.fg,
+                    cell_under.?.bg,
+                );
+                space.put(x, y - 1);
+            }
+        }
+
+        if (!changed) {
+            std.Thread.sleep(std.time.ns_per_s * 7);
+            self.current_auth_fails.* = 0;
+        }
+
+        TerminalBuffer.presentBuffer();
+    }
+}