Resolve the theme a Shiny request asks for

The server-side twin of theme.js's resolution, for ui <- function(request): ?theme=dark|light in the query string, else the cc_theme cookie (Domain=.calcofi.io, set by any CalCOFI site's toggle) — honoured only beside its cc_theme_src=user marker, i.e. when the visitor chose it (brand v2's persistence rule: a v1 page's default can never leak in) — else default. Pass the result as mode to cc_brand_header() so bslib's switch starts in the right state and the page never flashes the other colour.

Usage

cc_theme(request = NULL, default = c("light", "dark"))

Arguments

request: the Rook request Shiny hands a ui function (NULL → default)
default: theme when neither the URL nor a cookie says: "light", the calcofi.io convention since brand v2 (2026-09-04)

Value

"dark" or "light"

Examples

cc_theme(list(QUERY_STRING = "?theme=light"))
#> [1] "light"
cc_theme(list(HTTP_COOKIE = "cc_theme=dark; cc_theme_src=user"))
#> [1] "dark"
cc_theme(NULL)
#> [1] "light"