s0rg/crawley

package links

import (
    "bytes"
    "io"

    "github.com/tdewolff/parse/v2"
    "github.com/tdewolff/parse/v2/css"
)

const (
    braceOpen  = '('
    braceClose = ')'
)

// ExtractCSS extract urls from css files.
func ExtractCSS(r io.Reader, h URLHandler) {
    l := css.NewLexer(parse.NewInput(r))

    for {
        switch tt, text := l.Next(); tt {
        case css.ErrorToken:
            return
        case css.URLToken:
            if res, ok := extractCSSURL(text); ok {
                h(res)
            }
        }
    }
}

func extractCSSURL(v []byte) (rv string, ok bool) {
    o := bytes.IndexByte(v, braceOpen)
    c := bytes.LastIndexByte(v, braceClose)

    rv = string(bytes.Trim(v[o+1:c], codeCleanChars))

    return rv, rv != ""
}