Returns a vector of [start end] offsets for substrings in s.

substring_offsets.clj

(defn substring-offsets
  "Returns a seq of [start end] offsets for substrings in s."
  [s substring]
  (when-not (empty? substring)
    (let [s (.toLowerCase s)
          substring (.toLowerCase substring)
          s-length (count s)
          substring-length (count substring)]
      (loop [offset 0
             offsets nil]
        (let [substring-start-offset (.indexOf s substring offset)]
          (if (= -1 substring-start-offset)
            offsets
            (let [substring-end-offset (+ substring-start-offset substring-length)
                  bounded-substring-end-offset (min substring-end-offset s-length)
                  substring-from-offsets (subs s
                                               substring-start-offset
                                               bounded-substring-end-offset)
                  beginning-of-string? (= 0 substring-start-offset)
                  end-of-string? (= s-length substring-end-offset)
                  char-before-substring (when-not beginning-of-string?
                                          (subs s
                                                (- substring-start-offset 1)
                                                substring-start-offset))
                  char-after-substring (when-not end-of-string?
                                         (subs s
                                               bounded-substring-end-offset
                                               (+ 1 bounded-substring-end-offset)))]
              (if (and (or beginning-of-string? (delimiter? char-before-substring))
                       (or end-of-string? (delimiter? char-after-substring))
                       (= substring substring-from-offsets))
                (recur substring-end-offset
                       (conj offsets
                             [substring-start-offset bounded-substring-end-offset]))
                offsets))))))))

(substring-offsets "The quick brown fox jumps over the lazy dog" "the")
;; => ([0 3] [31 34])