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# Parse css
#
# A very simple css parser that can parse `key:value;` pairs.
#
# @param text The css text to parse
parse_css <- function(text) {
# break into separate lines; for now, ignore the possibility of
# quoted or escaped semicolon
lines <- strsplit(text, ";", fixed = TRUE)[[1]]
# parse each line and return list of key--value pairs
unlist(lapply(lines, parse_css_line), recursive = FALSE)
}
parse_css_line <- function(line) {
pattern <- "\\s*(\\S+)\\s*:\\s*(\"(.*)\"|'(.*)'|(\\S*))\\s*"
m <- attributes(regexpr(pattern, line, perl = TRUE))
if (m$capture.start[1] > 0) {
key <- substr(line, m$capture.start[1], m$capture.start[1] + m$capture.length[1] - 1)
} else key <- NULL
if (m$capture.start[3] > 0) {
value <- substr(line, m$capture.start[3], m$capture.start[3] + m$capture.length[3] - 1)
} else if (m$capture.start[4] > 0) {
value <- substr(line, m$capture.start[4], m$capture.start[4] + m$capture.length[4] - 1)
} else if (m$capture.start[5] > 0) {
value <- substr(line, m$capture.start[5], m$capture.start[5] + m$capture.length[5] - 1)
} else value <- NULL
if (is.null(key)) list()
else list2(!!key := value)
}
parse_css_unit <- function(x) {
pattern <- "^((-?\\d+\\.?\\d*)(%|[a-zA-Z]+)|(0))$"
m <- attributes(regexpr(pattern, x, perl = TRUE))
if (m$capture.start[4] > 0) {
# matched null value
return(list(value = 0, unit = "pt"))
} else {
if (m$capture.start[2] > 0) {
value <- as.numeric(
substr(x, m$capture.start[2], m$capture.start[2] + m$capture.length[2] - 1)
)
if (m$capture.start[3] > 0) {
unit <- substr(x, m$capture.start[3], m$capture.start[3] + m$capture.length[3] - 1)
return(list(value = value, unit = unit))
}
}
}
stop(paste0("The string '", x, "' does not represent a valid CSS unit."), call. = FALSE)
}
convert_css_unit_pt <- function(x) {
u <- parse_css_unit(x)
switch(
u$unit,
pt = u$value,
px = (72/96)*u$value,
`in` = 72*u$value,
cm = (72/2.54)*u$value,
mm = (72/25.4)*u$value,
stop(paste0("Cannot convert ", u$value, u$unit, " to pt."), call. = FALSE)
)
}
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