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+(ns clarktown.parser
+ (:require
+ [clojure.string :as string]))
+
+
+(defn- stitch-code-blocks
+ "Since code blocks can span multiple blocks (a block is separated by
+ two line breaks from another block) , we need to stitch them together
+ into one block in order for a block parser to be able to do anything
+ with it."
+ [blocks]
+ (loop [stitched-blocks []
+ code-block-started? false
+ blocks blocks]
+ (if (empty? blocks)
+ stitched-blocks
+ (let [block (first blocks)]
+ (if (and (string/starts-with? (string/trim block) "```")
+ (not (string/ends-with? (string/trim block) "```")))
+ (recur (conj stitched-blocks block)
+ true
+ (drop 1 blocks))
+ (if code-block-started?
+ (let [last-block (last stitched-blocks)
+ last-block-index (- (count stitched-blocks) 1)]
+ (if (string/ends-with? (string/trim block) "```")
+ (recur (assoc stitched-blocks last-block-index (str last-block "\n\n" block))
+ false
+ (drop 1 blocks))
+ (recur (assoc stitched-blocks last-block-index (str last-block "\n\n" block))
+ true
+ (drop 1 blocks))))
+ (recur (conj stitched-blocks block)
+ false
+ (drop 1 blocks))))))))
+
+
+(defn- find-parser-by-block
+ "Find a parser from `parsers` that matches the given `block`."
+ [parsers block]
+ (->> parsers
+ (filter
+ (fn [{:keys [matcher]}]
+ (when matcher
+ (matcher block))))
+ first))
+
+
+(defn- parse-block-with-known-parser
+ "Parses a given `block` with a known `parser`."
+ [parser parsers block]
+ (loop [block block
+ renderers (:renderers parser)]
+ (if (empty? renderers)
+ block
+ (let [renderer (first renderers)]
+ (recur (renderer block parsers)
+ (drop 1 renderers))))))
+
+
+(defn- parse-block-with-unknown-parsers
+ "Parses the given `block` with all the parsers that do not have
+ a matcher function, useful for any fallback parsing one might want
+ to do."
+ [parsers block]
+ (loop [block block
+ parsers (filter #(= nil (:matcher %)) parsers)]
+ (if (empty? parsers)
+ block
+ (loop [block block
+ renderers (:renderers (first parsers))]
+ (if (empty? renderers)
+ block
+ (let [renderer (first renderers)]
+ (recur (renderer block parsers)
+ (drop 1 renderers))))))))
+
+
+(defn- parse-blocks
+ "Parses each individual Markdown block, given as `blocks`, with
+ the list of `parsers`."
+ [blocks parsers]
+ (for [block blocks]
+ (if-let [parser (find-parser-by-block parsers block)]
+ (parse-block-with-known-parser parser parsers block)
+ (parse-block-with-unknown-parsers parsers block))))
+
+
+(defn parse
+ "Parses given `markdown` with `parsers`."
+ [markdown parsers]
+ (let [blocks (-> (string/split markdown #"\n\n")
+ stitch-code-blocks)
+ parsed-blocks (parse-blocks blocks parsers)]
+ (string/join "" parsed-blocks)))