✎ Memento Text Editor — Smart Editor (Undo/Redo)

Repository: https://github.com/Tharindu714/Memento-Text-Editor-Application.git

A sleek, colourful Java Swing demo that implements the Memento design pattern to provide reliable multi-step undo/redo for a text editor. Snapshots (mementos) are captured on demand and automatically (debounced), allowing users to safely revert to any previous editing state.

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✨ Highlights

• ✅ Memento Pattern: Snapshot (memento), EditorOriginator (originator), HistoryManager (caretaker).
• ⏱️ Debounced auto-save: snapshots are created after idle so typing isn’t saved on every keystroke.
• 🔁 Multi-level Undo / Redo: step backward or forward through saved snapshots; double-click a snapshot to restore.
• 🎛️ Attractive UI: smart-home–inspired gradient header, editor pane with monospace font, history panel, shortcuts (Ctrl+Z / Ctrl+Y / Ctrl+S).
• 🛡️ Anti-pattern rules applied: immutable mementos, capped history to avoid memory bloat, decoupled UI and history management.

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🚀 Features

• Manual snapshot save and automatic snapshot on idle.
• Undo / Redo buttons and keyboard shortcuts (Ctrl+Z / Ctrl+Y).
• History list with timestamps and short previews; double-click to restore any snapshot.
• Configurable history cap (default 60).
• Status messages show snapshot actions and undo/redo feedback.

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🛠️ Build & Run

Requires Java 8+.

# from repo root
javac TextEditor_Memento_GUI.java
java TextEditor_Memento_GUI

The app opens a colourful Smart Editor window. Snapshots are stored in memory (demo). For persistence add disk-write logic in HistoryManager.

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🧭 Design Overview

Core components

• Snapshot — Memento: immutable object that stores the editor content and timestamp.
• EditorOriginator — Originator: knows how to create and restore Snapshots from current editor content.
• HistoryManager — Caretaker: stores a list of snapshots, the current index, and supports undo/redo and pruning to a maximum size.
• EditorFrame — Swing UI: editor area, history panel, controls and header.

Flow

1. User edits text → after idle (debounce) or on manual save → Originator.createSnapshot() → HistoryManager.add(snapshot).
2. Undo → HistoryManager.undo() returns previous snapshot → Originator.restore(snapshot) → UI updates text area.
3. Redo similarly returns later snapshot.

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✅ Anti-patterns avoided (rules applied)

• ❌ No exposing mutable editor internals — snapshots are immutable and only Originator creates/restores them.
• ✅ No unlimited history — history is capped (default 60); oldest snapshots removed when cap exceeds.
• ✅ No saving every keystroke — debounce implemented (1.2s) to limit snapshot frequency.
• ✅ Separation of concerns — HistoryManager does not directly manipulate UI, only stores Snapshot objects.

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📐 UML (PlantUML)

Paste into https://www.plantuml.com/plantuml to render diagrams.

Class Diagram

Sequence Diagram (Save & Undo)

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📸 Scenario

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🧪 Example usage

1. Launch the app.
2. Type some text, wait 1–2 seconds to allow auto-snapshot, then continue editing.
3. Click Undo or press Ctrl+Z to step back to previous snapshots.
4. Double-click any item in the history list to restore that specific snapshot.

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🔧 Production Notes & Extensions

• Store snapshots as diffs (deltas) or compress snapshots for very large docs to reduce memory.
• Persist snapshots to disk or cloud for session recovery.
• Make HistoryManager thread-safe and add pruning policies (LRU, time-based).
• Add visual diff preview when hovering a snapshot in history.

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📮 Contribution

Fork, add features (persistence, diff-snapshots, collaborative undo), and open PRs. Include tests for undo/redo correctness.

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📝 License

MIT — reuse and adapt freely.

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Made with care — Tharindu's Memento Text Editor demo. Happy editing! 🎉