Programming and the art of shoe polishing

One of the most most undocumented occupational hazards of being a software engineer is that the rest of the world is not privy to our thought process, nor do they have a deeper understanding of what we do. Yes, coding is a part of it, and a very big part of it, but, it is understanding of the system that separates good engineers from the bad ones. Coding is easy, coding a system is hard. There is a whole lot of difference between learning english and writing a novel. Just as an exercise, let's imagine that the task at hand is polishing shoes. Our protagonist is the engineer(SE). The product manager(PM), the quality assurance(QA) engineer & shoe polisher(SP) have the supporting roles in this play.

Bad Engineer's Life
PM: I want our company to polish shoes. We will provide supplies to our shoe polisher team who will polish the shoes.
SE: I'll get on it.

[CODE]
- Distribute shoes to each SP(shoe polisher).
- Distribute polish to each SP.
- Ask each SP to use the given polish on each shoe.
- Take shoes from them.


QA: Hey! Your team used brown polish on black shoes. I'm filing a bug.
SE: Oops. I didn't know that. Let me fix it.

[CODE]
- Distribute shoes to each SP(shoe polisher).
- Each shoe has a COLOR.
- Distribute polish to each SP. Each polish has a COLOR.
- Ask each SP to use the given polish(COLOR) on each shoe(COLOR).
- Take shoes from them.


QA: Hey! Your team put black leather polish on my black canvas shoes. I'm filing a bug.
SE: Oops. Hey, why would the customer even want to polish canvas shoes?! Please test my system  properly.
QA: I don't care. You should not ruin your customer's shoes.
SE: Let me talk to PM.

PM: You should not ruin your customer's shoes.
SE: Ok.

[CODE]
- Distribute shoes to each SP(shoe polisher).
- If shoe is CANVAS then return to the customer.
- Each shoe has a COLOR.
- Distribute polish to each SP.
- Each polish has a COLOR.
- Ask each SP to use the given polish(COLOR) on each shoe(COLOR).
- Take shoes from them.


QA: Hey! SP still polishes my hip hemp shoes from SF. And why should the customer wait for shoe distribution to get his canvas shoe back? I'm filing a bug. Hey PM, the code is unstable!!
PM: Hmmm :(
SE: Let me fix it.

[CODE]
- Get shoes from Customer.
- Return shoe if NOT leather shoes.
- Distribute shoes to each SP(shoe polisher).
- Each shoe has a COLOR.
- Distribute polish to each SP.
- Each polish has a COLOR.
- Ask each SP to use the given polish(COLOR) on each shoe(COLOR).
- Take shoes from them.


QA: After 1 work day, the shoes don't look polished. Something is not working.
SE: I don't know, it works for me. Can you try it again and let me know?
-- After one day --
QA: See.. I told you so. I'm filing a bug.
SE: Oops.. the polish got over after a day. Let me add more polish each day.

[CODE]
- Get shoes from Customer.
- Return shoe if NOT leather shoes.
- Distribute shoes to each SP(shoe polisher).
- Each shoe has a COLOR.
- Distribute polish to each SP.
- Each polish has a COLOR.
- Ask each SP to use the given polish(COLOR) on each shoe(COLOR).
- If SP is working more than a day, then distribute more supplies to each SP.
- Take shoes from them.


QA: The product passes the test cases.
PM: We can sell this code to SUPER-MEGA-STORE then. Let us do some scale testing. They order around 100 shoe polishes a day! This could be a big order for us. I feel like Steve Jobs.
QA: Sure, whatever, I'll test out the cases.

QA: PM, we polish 100 shoes in a week! We need to handle that many in a day!
PM: SE.. make it so!
SE: I'll try. We can handle around 15 shoes in a day, we need to get 7 times as many SPs, maybe 6 times if we get stronger and faster SPs.
PM: Hmmm... We'll have to pass the cost to SUPER-MEGA-STORE

SUPER-MEGA-STORE: We like the fonts on sign board outside your establishment, take our money                                           and give us the product please.
--- After Deployment ---

SUPER-MEGA-STORE: Hey, nobody wears black leather shoes in our Sunnyvale store. We have too many unused black polish cans in our stores right now.
SE: I'll fix it.
...
SUPER-MEGA-STORE: Hey, one of the SP died while working. The shoes are now piling on!
SE: I'll fix it.

[CODE]
- Get shoes from Customer.
- Return shoe if NOT leather shoes.
- Distribute shoes to each SP(shoe polisher).
- Each shoe has a COLOR.
- Distribute polish to each SP.
- Each polish has a COLOR.
- Ask each SP to use the given polish(COLOR) on each shoe(COLOR).
- If SP is working more than a day.
- If polish(COLOR) is over, replace it.
- If SP is dead, get new SP.
- Take shoes from them.


SUPER-MEGA-STORE: Hey, we want canvas shoes to be washed too.
SE quits.

This happens over the period of a year. SE's own unscalable and spaghetti code have tormented him. The fluidity of requirements from the customer adds fuel to the fire. When one SE quits, other SE takes his place, mutating this code even more into an unrecognizable mess.

Now let's see what happens with a more experienced engineer:

Good Engineer's Life
PM: I want our company to polish shoes. We will provide supplies to our shoe polisher team who will polish the shoes.
SE: I'll get on it. What kind of shoes though?
PM: Leather shoes.
SE: Any specific set of colors? Google lists some common colors as BLACK, BROWN, NEUTRAL, WHITE, CHERRY RED & CORDOVAN.
PM: Hmmm..
SE: Also what about speciality leather shoes like those make with crocodile leather?
PM: Market research shows that people mostly wear BLACK and BROWN shoes, so let's stick with that.
SE: Any particular brand of polish you want me to use.
PM: Use the CODEYMAN brand. We can get bulk discount from them.
-- A week later --
SE: Hey I found out that one box of polish can polish about 250 shoes. I also spoke to my SP friend. He can shine 10 shoes in a day. Do you know about how many shoes we'll be shining a day?
PM: You ask too many questions, I somewhat hate you. SUPER-MEGA-STORE might be interested, but that is just a rumor I heard. But you haven't yet started writing code.
SE: So how many shoe shines a day?
PM: About 100 maybe?
SE: So we need about 10 SPs working each day. We can have 20 SPs who work on two rotating shifts. This would reduce the downtime if something were to happen to them.
PM: Stop doing a PhD in this! I want the code.
SE: Also 100 shoes a day is 700 shoes a week, which means 3 shoe cans would be used in a week. We need to keep more inventory of cans, to keep SPs from waiting on a polish can if someone else is using it. You can use this to set a price point for the product.
PM: I hate you! Give me an ETA.
SE: I'll sketch some informal design plans and revert in 2-3 days.

.. Time goes on ..
SE: PM, I'm going to be code complete in some time. I want the QA to add test cases.
PM: So the product is done?
SE: No, I've just written the code and did some unit testing. System testing etc will take at least a  month.
PM: So the product is done? I'll tell the Sales team to sell the product.
QA: I'll start testing it as soon as I'm done testing some other thing the SE doesn't care about.

SE: Here's the code

[CODE]
- Don't allow customers without BLACK or BROWN leather shoes.
- Let there be X BLACK polish cans and Y BROWN polish cans.
- Every 12 hours:
    a. New set of 10 SPs come in.
       - If less than 10 SPs come in. Pay the exiting employees overtime to pick up the slack.
b. SPs distribute the shoes amongst themselves, trying to maximize the amount of shoes of a particular COLOR.
c. Each SP takes the cans of polish corresponding to the shoe colors he has. He decrements the number of shoe polish cans available by 1.
- If the number of shoe polish hits the threshold T, he puts an order into the system to get more polish. This way they don't have to wait for polish if it runs out.
d. If SP runs out of shoes to polish:
- He'll put the polished shoes on the rack.
- Hel'll repeat steps from b. again.
e. When SPs are ready to leave:
- If less than 10 SPs leave then:
  - Find if SP is dead and put a replacement SP for the next rotated shift.
  - If SP is hiding, then ask him to leave.
- Take shoes from them.


PM: (During review): Please use spaces instead of tabs and use the function names according to  coding standards.

QA: Hey, edge condition issues. If I'm getting 100 shoes/day and one SP dies, the backlog never goes away.
SE: Oh yeah. Let's add a fudge factor of 11 SPs. Will take care in release.

PM: How is the quality?
QA: Seems to mostly work. Not many open issues I think.
PM: Great, let's deploy it.

SUPER-MEGA-STORE: Hey, your system doesn't handle bursts of more than 110 shoe-shines. We need a burst of 200 during Christmas holidays.
PM: Sure. We can include redundancy and burstiness of shoe-shine traffic in your tarrif. This would translate to hiring seasonal workers.

SUPER-MEGA-STORE: I need to get canvas shoes washed too.
PM: That feature will be supported in the next release.

SE: Shouldn't be a big deal. I'll design similar product for canvas-shoes and encapsulate both the products behind an api that is multiplexed by shoe type.
PM: Whatever.. just do it.

SE goes home.
SE: Honey.. I'm home.
Wife: Whatever! you spend all your time at work. I hate you.

.. SE is sad.