refactor: move modules into levels

01_essentials/02-history/README.md

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+# Module 02: Viewing History
+
+## Learning Objectives
+
+In this module, you will:
+- Understand commit history and how to navigate it
+- Use `git log` to view commit history with various formats
+- Use `git show` to view specific commit details
+- Use `git diff` to compare changes between commits
+- Understand commit hashes and references
+
+## Challenge
+
+### Setup
+
+Run the setup script to create your challenge environment:
+
+```powershell
+.\setup.ps1
+```
+
+This will create a `challenge/` directory with a Git repository that already has some commit history.
+
+### Your Task
+
+You'll explore an existing Git repository that contains multiple commits. Your goal is to use Git commands to discover information about the repository's history.
+
+The setup script will create an `answers.md` file in the challenge directory with questions for you to answer. Fill in your answers directly in that file.
+
+**Suggested Approach:**
+
+1. Navigate to the challenge directory: `cd challenge`
+2. Open `answers.md` to see the questions
+3. View the commit history: `git log`
+4. Try different log formats: `git log --oneline`, `git log --stat`
+5. View specific commits: `git show <commit-hash>`
+6. Compare commits: `git diff <commit1> <commit2>`
+7. Fill in your answers in `answers.md`
+
+> **Important Notes:**
+> - You can use any Git commands you like to explore the repository
+> - Fill in your answers directly in the `answers.md` file (there are placeholder sections for each answer)
+> - Try different `git log` options to see which format you prefer
+> - Commit hashes can be referenced by their full hash or just the first 7 characters
+
+## Key Concepts
+
+- **Commit Hash**: A unique identifier (SHA-1 hash) for each commit. You can use the full hash or just the first few characters.
+- **Commit Message**: A description of what changed in that commit, written by the author.
+- **Commit History**: The chronological record of all changes made to a repository.
+- **HEAD**: A pointer to the current commit you're working from.
+- **Diff**: A view showing the differences between two versions of files.
+
+## Understanding Diff Output
+
+When you run `git diff` between commits, the output can look confusing at first. Here's how to read it:
+
+### Example Diff Output
+
+```diff
+diff --git a/app.py b/app.py
+index 1a2b3c4..5d6e7f8 100644
+--- a/app.py
++++ b/app.py
+@@ -1,5 +1,7 @@
+ # app.py - Main application file
++from auth import login, logout
+
+ def main():
+     print("Welcome to My App!")
+-    # Application initialization code here
++    login("user", "password")
+     pass
+```
+
+### Breaking It Down
+
+**1. File Header**
+```diff
+diff --git a/app.py b/app.py
+```
+- Shows which file is being compared
+- `a/app.py` = old version (before)
+- `b/app.py` = new version (after)
+
+**2. Metadata**
+```diff
+index 1a2b3c4..5d6e7f8 100644
+--- a/app.py
++++ b/app.py
+```
+- `---` indicates the old version
+- `+++` indicates the new version
+- The hashes (1a2b3c4, 5d6e7f8) are internal Git identifiers
+
+**3. Change Location (Hunk Header)**
+```diff
+@@ -1,5 +1,7 @@
+```
+- `@@ -1,5 +1,7 @@` tells you where changes occurred
+- `-1,5` = in the old file, starting at line 1, showing 5 lines
+- `+1,7` = in the new file, starting at line 1, showing 7 lines
+- The file grew by 2 lines (from 5 to 7)
+
+**4. The Actual Changes**
+
+Lines are prefixed with symbols:
+- ` ` (space) = unchanged line (context)
+- `-` (minus) = line removed from old version (shown in red in terminal)
+- `+` (plus) = line added in new version (shown in green in terminal)
+
+In our example:
+```diff
+ # app.py - Main application file          ← unchanged
++from auth import login, logout             ← added (new)
+
+ def main():                                ← unchanged
+     print("Welcome to My App!")            ← unchanged
+-    # Application initialization code here ← removed (old)
++    login("user", "password")              ← added (new)
+     pass                                   ← unchanged
+```
+
+### Reading Multiple Files
+
+If multiple files changed, you'll see multiple diff sections:
+
+```diff
+diff --git a/app.py b/app.py
+[changes to app.py]
+
+diff --git a/auth.py b/auth.py
+[changes to auth.py]
+```
+
+### Pro Tips
+
+- **Context lines**: Unchanged lines around changes help you understand where the change happened
+- **Color coding**: In your terminal, deletions are usually red, additions are green
+- **No newline warning**: If you see `\ No newline at end of file`, it means the file doesn't end with a newline character (usually not important for beginners)
+- **Binary files**: For images or other binary files, Git just says "Binary files differ"
+
+### Try It Yourself
+
+In this module's challenge, you'll use:
+```bash
+git diff <commit1> <commit2> app.py
+```
+
+Pay attention to:
+- Which lines were added (green, with `+`)
+- Which lines were removed (red, with `-`)
+- The surrounding context (white, with space)
+
+## Useful Commands
+
+```bash
+git log                      # View commit history
+git log --oneline            # Compact one-line format
+git log --stat               # Show files changed in each commit
+git log --graph              # Show branch graph (more useful with branches)
+git show <commit>            # View specific commit details
+git show <commit>:<file>     # View a file from a specific commit
+git diff <commit1> <commit2> # Compare two commits
+git diff <commit>            # Compare commit with current working directory
+```
+
+## Verification
+
+Once you've filled in your answers in `answers.md`, verify your solution:
+
+```powershell
+.\verify.ps1
+```
+
+The verification script will check that your answers contain the expected information.
+
+## Need to Start Over?
+
+If you want to reset the challenge and start fresh:
+
+```powershell
+.\reset.ps1
+```
+
+This will remove the challenge directory and run the setup script again, giving you a clean slate.