email-edit.clj

(ns email-edit.core
    (:import
      java.util.Base64))

(def encoder (Base64/getMimeEncoder))
(def decoder (Base64/getMimeDecoder))

(defn decode [^String s]
  (String. (.decode decoder s)))
(defn encode [^String s]
  (->> s .getBytes (.encodeToString encoder)))

(def start "Content-Type: text/html; charset=utf-8\r\nContent-Transfer-Encoding: base64")

(def end "----boundary")

(def src (slurp "src.eml"))
(def snippet
  (-> src
      (.split start)
      second
      (.split end)
      first
      .trim))

(def html
  (-> snippet
      decode
      (.replace "BLNGSW" "BLNGSV")
      (.replace "Sat 09 Mar" "Sat 06 Apr")
      encode))

(spit "dest.eml"
      (.replace src snippet html))