🧠 Scenario: Building a Node.js API Project with a Team

You and 2 developers are building:

payment-api/
 ├── app.js
 ├── package.json
 └── README.md

We’ll go from:

✔ Creating repo ✔ Branching ✔ Conflict ✔ Rebase vs Merge ✔ Undo mistakes ✔ PR flow ✔ Production tagging ✔ Disaster recovery

---

1️⃣ What Git Actually Does (Example)

Imagine:

Day 1 → You write login feature Day 2 → Teammate writes payment feature Day 3 → You both change same file

Git keeps snapshots of every version.

Git was created by Linus Torvalds and powers platforms like GitHub.

---

2️⃣ Starting a Real Project

Step 1 — Create folder

mkdir payment-api
cd payment-api
git init

Now Git creates .git folder.

---

3️⃣ First Commit (Real Example)

Create app.js

console.log("Payment API started");

Check status:

git status

It shows:

Untracked files:
  app.js

Add & commit:

git add app.js
git commit -m "Initial commit: Setup payment API"

👉 What happened internally?

Git created:

• Blob (file content)
• Tree (folder structure)
• Commit (snapshot)

---

4️⃣ Connect to GitHub (Real Example)

You create repo in GitHub UI.

Then:

git remote add origin https://github.com/yuva/payment-api.git
git branch -M main
git push -u origin main

Now code is online.

---

5️⃣ Real Team Workflow (Feature Branch)

You are adding Login API

git checkout -b feature/login

Edit app.js

console.log("Payment API started");

function login() {
  console.log("User logged in");
}

login();

Commit:

git add .
git commit -m "Add login feature"
git push origin feature/login

Now you create a Pull Request in GitHub.

---

6️⃣ Meanwhile Teammate Changes Same File 😬

Your teammate creates:

git checkout -b feature/payment

They edit app.js:

console.log("Payment API started");

function processPayment() {
  console.log("Payment processed");
}

processPayment();

They merge into main.

---

7️⃣ Now You Try To Merge 😱 (Conflict Example)

You:

git checkout main
git pull
git merge feature/login

Git says:

CONFLICT (content): Merge conflict in app.js

File becomes:

console.log("Payment API started");

<<<<<<< HEAD
function processPayment() {
  console.log("Payment processed");
}
=======
function login() {
  console.log("User logged in");
}
>>>>>>> feature/login

---

8️⃣ How You Fix Conflict (Real Fix)

You edit file manually:

console.log("Payment API started");

function login() {
  console.log("User logged in");
}

function processPayment() {
  console.log("Payment processed");
}

login();
processPayment();

Then:

git add app.js
git commit -m "Resolve merge conflict"

✅ Conflict resolved.

---

9️⃣ Merge vs Rebase (With Example)

Merge

Creates extra commit:

Merge branch 'feature/login'

History looks like:

      feature/login
         \
main ---- M

---

Rebase (Cleaner)

Instead:

git checkout feature/login
git rebase main

Now history becomes linear:

main ---- login commit

✔ Cleaner history ⚠ Don’t rebase shared branches

---

🔟 Undo Mistakes (Real Situations)

---

❌ Situation 1: Wrong Commit Message

git commit --amend -m "Correct message"

---

❌ Situation 2: Accidentally Committed .env

git rm --cached .env
echo ".env" >> .gitignore
git commit -m "Remove .env from tracking"

---

❌ Situation 3: Delete Last Commit But Keep Code

git reset --soft HEAD~1

---

❌ Situation 4: Completely Delete Last Commit

git reset --hard HEAD~1

---

1️⃣1️⃣ Recover Deleted Branch (Disaster Recovery)

You deleted branch accidentally:

git branch -D feature/login

Recover:

git reflog
git checkout -b recovered <commit-id>

Git never truly forgets immediately.

---

1️⃣2️⃣ Stash Example (Real Scenario)

You are coding but boss says switch branch urgently.

git stash
git checkout main

Later:

git checkout feature/login
git stash pop

Your work returns.

---

1️⃣3️⃣ Production Release Example

After testing:

git tag v1.0
git push origin v1.0

Now CI/CD pipeline triggers Docker build.

Example:

docker build -t payment-api:v1.0 .

---

1️⃣4️⃣ Real DevOps Flow (Enterprise Level)

Typical company flow:

1. Developer → feature branch
2. PR → code review
3. CI runs tests
4. Merge to main
5. Tag release
6. Docker build
7. Deploy via Terraform
8. Monitor

---

1️⃣5️⃣ Advanced Real Scenario: Squash Commits

You made 5 small commits:

fix bug
fix typo
update console
remove space
final fix

Before PR:

git rebase -i HEAD~5

Change to:

pick first
squash others

Now only 1 clean commit.

---

1️⃣6️⃣ Real Multi-Developer Collaboration Flow

Team uses:

GitHub Flow (Most Modern Teams)

• main (production)
• feature branches
• PR review
• CI pipeline

Used widely in GitHub based teams.

---

1️⃣7️⃣ Git Internal Storage (Advanced Understanding)

Inside:

.git/

You’ll find:

• objects/
• refs/
• HEAD

Git stores everything as hashed objects (SHA).

---

1️⃣8️⃣ Real Interview Level Questions

Q: Difference between revert and reset?

• reset → rewrites history
• revert → creates new undo commit

---

Q: Detached HEAD?

When you checkout specific commit:

git checkout 3e4f5a

You are not on branch.

---

🎯 Complete Real Project Flow Summary

git clone
git checkout -b feature/api
# code
git add .
git commit -m "Add API"
git push origin feature/api
# create PR
# merge
git checkout main
git pull
git tag v1.1
git push origin v1.1

---