SimpleChatTCRV:Markdown: CommonLogic listitem & para extend/append

Similar to listitem before, now also allow a para to have its long
lines split into adjacent lines. Inturn the logic will take care of
merging them into single para.

The common logic wrt both flows moved into its own helper function.

tools/server/public_simplechat/typemd.mjs

@@ -40,9 +40,14 @@ export class MarkDown {
         this.html = ""
     }
 
+    /** @typedef {{prev: number, cur: number}} EmptyTrackerResult */
+
     /**
+     * Track how many adjacent empty lines have been seen till now, in the immidate past.
+     * as well as whether the current line is empty or otherwise.
      * @param {string} key
      * @param {string} line
+     * @returns {EmptyTrackerResult}
      */
     empty_tracker(key, line) {
         if (this.in.empty[key] == undefined) {
@@ -57,6 +62,46 @@ export class MarkDown {
         return {prev: prev, cur: this.in.empty[key]}
     }
 
+    /**
+     * Append a new block to the end of html.
+     * @param {string} line
+     * @param {string} startMarker
+     * @param {string} endMarker
+     */
+    appendnew(line, startMarker, endMarker) {
+        this.html += `${startMarker}${line}${endMarker}`
+    }
+
+    /**
+     * Extend to the existing last block
+     * @param {string} line
+     * @param {string} endMarker
+     */
+    extend(line, endMarker) {
+        let html = this.html
+        this.html = `${html.slice(0,html.length-endMarker.length)} ${line}${endMarker}`
+    }
+
+    /**
+     * Extend the existing block, if
+     * * there was no immidiate empty lines AND
+     * * the existing block corresponds to what is specified.
+     * Else
+     * * append a new block
+     *
+     * @param {string} line
+     * @param {string} endMarker
+     * @param {string} startMarker
+     * @param {EmptyTrackerResult} emptyTracker
+     */
+    extend_else_appendnew(line, endMarker, startMarker, emptyTracker) {
+        if ((emptyTracker.prev != 0) || (!this.html.endsWith(endMarker))) {
+            this.appendnew(line, startMarker, endMarker)
+        } else {
+            this.extend(line, endMarker)
+        }
+    }
+
     unwind_list() {
         while (true) {
             let popped = this.in.list.endType.pop()
@@ -126,12 +171,7 @@ export class MarkDown {
                 if (matchOffset[1].length < lastOffset) {
                     return false
                 }
-                if ((emptyTracker.prev != 0) || (!this.html.endsWith("</li>\n"))) {
-                    this.html += `<li>${matchOffset[2]}</li>\n`
-                } else {
-                    let html = this.html
-                    this.html = `${html.slice(0,html.length-"</li>\n".length)} ${matchOffset[2]}</li>\n`
-                }
+                this.extend_else_appendnew(matchOffset[2], "</li>\n", '<li>', emptyTracker)
                 return true
             }
         }
@@ -242,7 +282,8 @@ export class MarkDown {
             return
         }
         this.unwind_list()
-        this.html += `<p>${line}</p>`
+        let emptyTrackerPara = this.empty_tracker("para", line)
+        this.extend_else_appendnew(line, "</p>\n", "<p>", emptyTrackerPara)
     }
 
     /**