Problem Statement

Write a subroutine, function, whatever it may be called in your language, that takes an integer number and returns an English text sequence starting with the English cardinal representation of that integer, the word 'is' and then the English cardinal representation of the count of characters that made up the first word, followed by a comma. Continue the sequence by using the previous count word as the first word of the next phrase, append 'is' and the cardinal count of the letters in that word. Continue until you reach four. Since four has four characters, finish by adding the words 'four is magic' and a period. All integers will eventually wind up at four. For instance, suppose your are given the integer 3. Convert 3 to Three, add is , then the cardinal character count of three, or five, with a comma to separate if from the next phrase. Continue the sequence five is four, (five has four letters), and finally, four is magic. For reference, here are outputs for 0 through 9.

You can choose to use a library, (module, external routine, whatever) to do the cardinal conversions as long as the code is easily and freely available to the public.
If you roll your own, make the routine accept at minimum any integer from 0 up to 999999. If you use a pre-made library, support at least up to unsigned 64 bit integers. (or the largest integer supported in your language if it is less.) Four is magic is a popular code-golf task. This is not code golf. Write legible, idiomatic and well formatted code.

Let's start with the solution:

names =. 'one';'two';'three';'four';'five';'six';'seven';'eight';'nine';'ten';'eleven';'twelve';'thirteen';'fourteen';'fifteen';'sixteen';'seventeen';'eighteen';'nineteen'

tens =. '';'twenty';'thirty';'forty';'fifty';'sixty';'seventy';'eighty';'ninety'

NB. selects the xth element from list y
lookup =: >@{:@{.

NB. string formatting
addspace =: ((' '"_, ]) ` ]) @. (<&0 @ {: @ $)

NB. numbers in range 1 to 19
s1 =: lookup&names

NB. numbers in range 20 to 99
s2d=: (lookup&tens @ <. @ %&10) , addspace @ (s1 @ (10&|))

NB. numbers in range 100 to 999
s3d =: s1 @ (<.@%&100), ' hundred', addspace @ s2d @ (100&|)

NB. numbers in range 1 to 999
s123d =: s1 ` s2d ` s3d @. (>& 19 + >&99)

NB. numbers in range 1000 to 999999
s456d =: (s123d @<.@%&1000), ' thousand', addspace @ s123d @ (1000&|)

NB. stringify numbers in range 1 to 999999
stringify =: s123d ` s456d @. (>&999)

NB. takes an int and returns an int of the length of the string of the input
lengthify =: {: @ $ @ stringify 

NB. determines the string that should go after ' is '
what =: ((stringify @ lengthify), (', '"_)) ` ('magic'"_) @. (=&4)

runonce =: stringify , ' is ', what

run =: runonce, ((run @ lengthify) ` (''"_) @. (=&4))

doall =: run"0

inputs =: 4 8 16 25 89 365 2586 25865 369854 

doall inputs