find-duplicate-logic

name	find-duplicate-logic
description	Find duplicate business logic (copy/paste blocks + structurally similar functions). Works best on TS/JS projects. Produces a proof-based refactor report.
allowed-tools	Read, Grep, Glob, Bash(rg *), Bash(git *), Bash(node *), Bash(python3 *), Bash(find *), Bash(ls *), Bash(sed *), Bash(awk *), Bash(sort *), Bash(uniq *), Bash(wc *), Bash(test *)
disable-model-invocation	false

Find Duplicate Logic

How to select the folder

Preferred usage: /find-duplicate-logic <path>

Examples:

• /find-duplicate-logic .
• /find-duplicate-logic src
• /find-duplicate-logic libs/shared
• /find-duplicate-logic apps/web

If no argument is provided

1. List top-level folders.
2. Ask the user which one to scan.
3. Stop and wait for the user to re-run the command with the chosen path.

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0) Resolve scope (folder selection)

If $ARGUMENTS is empty or blank:

• Run: !ls -1
• Show a short list of likely project folders (src, apps, libs, packages, backend, etc.)
• Ask: “Which folder should I scan? Re-run: /find-duplicate-logic <folder>”
• Do not proceed.

Otherwise:

• Set SCOPE = $ARGUMENTS
• Verify the folder exists:
  • !test -e "$ARGUMENTS" && echo "OK: $ARGUMENTS" || echo "ERROR: path not found: $ARGUMENTS"

If path is missing:

• Ask the user to provide a valid folder path (examples included).
• Stop.

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1) Rules

• Do not modify files.
• Provide proof for every duplicate: file path + line ranges and/or a reproducible command.
• Focus on logic, not generated boilerplate.
• Ignore noise folders by default: node_modules, dist, build, .git, coverage.

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2) Quick repo context

• Repo root: !git rev-parse --show-toplevel 2>/dev/null || pwd
• Working tree summary: !git status --porcelain=v1 | head -n 50

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3) Pass A — Exact-ish duplicates (copy/paste)

Goal: find identical (or near-identical) repeated blocks.

Run a lightweight 8-line window fingerprint over common code files: !python3 .claude/scripts/find_duplicates.py "$ARGUMENTS"

Next:

• Pick the most meaningful hits (not boilerplate).
• Open the relevant files and extract a short snippet (max ~20 lines) as proof.

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4) Pass B — Structural duplicates (similar logic, not identical)

Goal: spot “same algorithm, different names/constants”.

4.1 Hotspot searches (heuristics)

Run these and look for repeated patterns in different places:

• Collections / transforms:
  • !rg -n "(map\\(|reduce\\(|filter\\(|flatMap\\()" "$ARGUMENTS" | head -n 150
• Error handling:
  • !rg -n "(try\\s*\\{|catch\\s*\\(|throw\\s+new\\s+Error)" "$ARGUMENTS" | head -n 150
• HTTP / API calls:
  • !rg -n "(fetch\\(|axios\\.|HttpClient|http\\.(get|post|put|delete))" "$ARGUMENTS" | head -n 150
• Formatting / normalization:
  • !rg -n "(format|formatter|parse|sanitize|normalize|trim\\(|replace\\()" "$ARGUMENTS" | head -n 150
• Validation:
  • !rg -n "(validate|validation|schema|zod|yup|joi)" "$ARGUMENTS" | head -n 150

4.2 Function candidates (TS/JS-centric)

Find function declarations / arrow funcs:

• !rg -n "export\\s+function\\s+\\w+\\(|function\\s+\\w+\\(|const\\s+\\w+\\s*=\\s*\\(.*\\)\\s*=>\\s*\\{" -S "$ARGUMENTS" | head -n 250

Then:

1. Identify clusters where bodies “feel the same” (same sequence of steps).
2. Read each function body and compare.
3. Mark as Probable duplicate when >60% of structure matches.

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5) Output format (final report)

Produce a report with these sections:

A) Confirmed duplicates (copy/paste)

For each item:

• Title: what the logic does
• Occurrences: path:lineStart-lineEnd list
• Proof: short snippet or “how to reproduce” command
• Risk: bugfix divergence / inconsistent behavior / extra maintenance
• Refactor plan: where to extract (shared util/service), suggested API

B) Probable duplicates (structural similarity)

For each cluster:

• Files involved
• What differs (constants, small branches, naming)
• Best refactor strategy:
  • parameterized helper
  • shared utility module
  • strategy pattern / adapter
  • shared service with injected config
• Minimal test checklist after refactor

C) Top 3 quick wins

Pick 3 highest ROI refactors:

• small extraction
• removes most duplication
• lowest risk

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6) Noise control

When you suspect boilerplate/generated code:

• Label it as Boilerplate / ignore
• Do not include it in Top 3 quick wins