Challenge

For each character of the string except for the last one, do the following:

• Output the current character.



• 
  

  Followed by randomly outputting from the following list a random number of times between 1 and 5 (inclusive):

  
  
  
  • The current character
  
  
  • The next character of the string
  
  
  • The switchcase version of the character that you are currently on
  
  
  • The switchcase version of the next character of the string.
  
  

Test Cases

String --> SSSTSStrTrIiinIIngn

, . , . , . Hello world! --> ,,, .. , ,, .... , , .. .. . HHH HHEeelLlLllooO wwOworOOrrrRllDd!!D

Programming Puzzles and Code Golf --> PrPPrRrOooooogggRgGraAraaaMMMmmmimMIiininGGgG PPPPuZzZZzZzzZzllLLEEeEsEsssS a aANnNddD C COCoooOOdeDe E GGGoOllFFf

Notes

• You only need to apply the upper/lowercase form of a character if the character is part of the upper/lowercase alphabet (A-Z/a-z).


• Your random function does not need to be uniform but it still needs to have a chance of returning any element in the list given.


• You are allowed to use any standard I/O format.


• You may assume that the length of the input is greater than or equal to two.


• You may assume that the input only consists of ASCII characters.

Gaia, 21 bytes

ṅ@ṇ+†⟨(₌¤:~+ṛ5ṛ&⟩¦$

Try it online!

ṅ			| delete the first character from the input
 @ṇ			| push the input again and delete the last character
 +†			| concatenate together, so for example 'abc' 'bcd' becomes ['ab' 'bc' 'cd']
 ⟨ ⟩¦	| for each of the elements, do:
	(₌		| take the first character and push again
	 ¤		| swap
	 :		| dup
	 ~		| swap case
	 +		| combine strings
	 ṛ		| select a character at random
	 5ṛ	| select a random integer from [1..5]
		 &	| run-length decode
		 $	| convert to string

APL (dzaima/APL), 19 bytes

Anonymous tacit prefix function.

∊2(⊣,?5⍴4⊇,,-⍤,)/

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2(…)/ apply the following infix tacit function between each character pair:

 - the switchcase

 ⍤ of

 , the concatenation of the pair

 ,, prepend the concatenation of the pair to that

 …⊇ pick the following elements from that:

  5⍴4 five fours

  ? random indices for those

∊ ϵnlist (flatten)

Charcoal, 27 bytes

ＦＬθ«Ｆ∧ι⊕‽⁵‽⭆✂θ⊖ι⊕ι¹⁺↥λ↧λ§θι

Try it online! Link is to verbose version of code. Explanation:

ＦＬθ«

Loop over all of the indices of the input string.

Ｆ∧ι⊕‽⁵

Except for the first index, loop over a random number from 1 to 5 inclusive...

‽⭆✂θ⊖ι⊕ι¹⁺↥λ↧λ

... extract the previous and next characters from the string, take the upper and lower case versions, and pick a random character of the four.

§θι

Print the character at the current index.