From 180464cc5e4f491dc863fe07d4adddff7661b9af Mon Sep 17 00:00:00 2001
From: Rockachopa <rockachopa@stepfun.com>
Date: Sun, 26 Apr 2026 11:19:30 -0400
Subject: [PATCH] feat: add code duplication detector (#162)

Detect duplicate functions/blocks across Python files.
Reports duplication percentage and outputs JSON report.
Closes #162.
---
 scripts/code_duplication_detector.py      | 366 ++++++++++++++++++++++
 scripts/test_code_duplication_detector.py | 168 ++++++++++
 2 files changed, 534 insertions(+)
 create mode 100644 scripts/code_duplication_detector.py
 create mode 100644 scripts/test_code_duplication_detector.py

diff --git a/scripts/code_duplication_detector.py b/scripts/code_duplication_detector.py
new file mode 100644
index 0000000..75146d7
--- /dev/null
+++ b/scripts/code_duplication_detector.py
@@ -0,0 +1,366 @@
+#!/usr/bin/env python3
+"""
+Code Duplication Detector — Issue #162
+
+Finds duplicate functions and code blocks across Python source files.
+Reports duplication percentage and outputs a duplication report.
+
+Usage:
+    python3 scripts/code_duplication_detector.py --output reports/code_duplication.json
+    python3 scripts/code_duplication_detector.py --directory scripts/ --dry-run
+    python3 scripts/code_duplication_detector.py --test  # Run built-in test
+"""
+
+import argparse
+import hashlib
+import json
+import os
+import re
+import sys
+from collections import defaultdict
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import List, Dict, Tuple, Optional
+
+
+# ── AST helpers ────────────────────────────────────────────────────────────
+
+def normalize_code(text: str) -> str:
+    """Normalize code for comparison: strip comments, normalize whitespace."""
+    # Remove comments (both # and docstring triple-quote strings)
+    text = re.sub(r'#.*$', '', text, flags=re.MULTILINE)
+    text = re.sub(r'""".*?"""', '', text, flags=re.DOTALL)
+    text = re.sub(r"'''.*?'''", '', text, flags=re.DOTALL)
+    # Normalize whitespace
+    text = re.sub(r'\s+', ' ', text).strip()
+    return text.lower()
+
+
+def code_hash(text: str) -> str:
+    """SHA256 hash of normalized code for exact duplicate detection."""
+    normalized = normalize_code(text)
+    return hashlib.sha256(normalized.encode('utf-8')).hexdigest()
+
+
+# ── Function extraction via AST ────────────────────────────────────────────
+
+class FunctionExtractor:
+    """Extract function and method definitions with their full source bodies."""
+
+    def __init__(self, source: str, filepath: str):
+        self.source = source
+        self.filepath = filepath
+        self.lines = source.splitlines()
+        self.functions: List[Dict] = []
+
+    def _get_source_segment(self, start_lineno: int, end_lineno: int) -> str:
+        """Get source code from start to end line (1-indexed, inclusive)."""
+        # AST end_lineno is inclusive
+        start_idx = start_lineno - 1
+        end_idx = end_lineno
+        return '\n'.join(self.lines[start_idx:end_idx])
+
+    def visit(self, tree):
+        """Collect all function and async function definitions."""
+        for node in ast.walk(tree):
+            if isinstance(node, ast.FunctionDef) or isinstance(node, ast.AsyncFunctionDef):
+                # Get the full source for this function including decorators
+                start = node.lineno
+                end = node.end_lineno
+                body_source = self._get_source_segment(start, end)
+
+                # Also collect parent class name if this is a method
+                class_name = None
+                parent = node.parent if hasattr(node, 'parent') else None
+                if parent and isinstance(parent, ast.ClassDef):
+                    class_name = parent.name
+
+                self.functions.append({
+                    'name': node.name,
+                    'file': self.filepath,
+                    'start_line': start,
+                    'end_line': end,
+                    'body': body_source,
+                    'class_name': class_name,
+                    'is_method': class_name is not None,
+                })
+
+
+import ast
+
+class ParentNodeVisitor(ast.NodeVisitor):
+    """Annotate nodes with parent references."""
+    def __init__(self, parent=None):
+        self.parent = parent
+
+    def generic_visit(self, node):
+        node.parent = self.parent
+        for child in ast.iter_child_nodes(node):
+            self.__class__(child).parent = node
+        super().generic_visit(node)
+
+
+def extract_functions_from_file(filepath: str) -> List[Dict]:
+    """Extract all function definitions from a Python file."""
+    try:
+        with open(filepath, 'r', encoding='utf-8', errors='replace') as f:
+            source = f.read()
+        tree = ast.parse(source, filename=str(filepath))
+
+        # Annotate with parent references
+        for node in ast.walk(tree):
+            for child in ast.iter_child_nodes(node):
+                child.parent = node
+
+        extractor = FunctionExtractor(source, str(filepath))
+        extractor.visit(tree)
+        return extractor.functions
+    except (SyntaxError, UnicodeDecodeError, OSError) as e:
+        return []
+
+
+def scan_directory(directory: str, extensions: Tuple[str, ...] = ('.py',)) -> List[Dict]:
+    """Scan directory for Python files and extract all functions."""
+    all_functions = []
+    path = Path(directory)
+
+    for filepath in path.rglob('*'):
+        if filepath.is_file() and filepath.suffix in extensions:
+            # Skip common non-source dirs
+            parts = filepath.parts
+            if any(ex in parts for ex in ('__pycache__', 'node_modules', '.git', 'venv', '.venv', 'dist', 'build')):
+                continue
+            if filepath.name.startswith('.'):
+                continue
+
+            functions = extract_functions_from_file(str(filepath))
+            all_functions.extend(functions)
+
+    return all_functions
+
+
+# ── Duplicate detection ─────────────────────────────────────────────────────
+
+def find_duplicates(functions: List[Dict], similarity_threshold: float = 0.95) -> Dict:
+    """
+    Find duplicate and near-duplicate functions.
+
+    Returns dict with:
+      - exact_duplicates: {hash: [function_info, ...]}
+      - near_duplicates: [[function_info, ...], ...]
+      - stats: total_functions, unique_exact, exact_dupe_count, near_dupe_count
+    """
+    # Phase 1: Exact duplicates by code hash
+    hash_groups: Dict[str, List[Dict]] = defaultdict(list)
+    for func in functions:
+        h = code_hash(func['body'])
+        hash_groups[h].append(func)
+
+    exact_duplicates = {h: group for h, group in hash_groups.items() if len(group) > 1}
+    exact_dupe_count = sum(len(group) - 1 for group in exact_duplicates.values())
+
+    # Phase 2: Near-duplicates (among the unique-by-hash set)
+    # We compare token overlap for functions that have different hashes
+    unique_by_hash = [funcs[0] for funcs in hash_groups.values()]
+    near_duplicate_groups = []
+
+    # Simple token-based similarity
+    def tokenize(code: str) -> set:
+        return set(re.findall(r'[a-zA-Z_][a-zA-Z0-9_]*', code.lower()))
+
+    i = 0
+    while i < len(unique_by_hash):
+        group = [unique_by_hash[i]]
+        j = i + 1
+        while j < len(unique_by_hash):
+            tokens_i = tokenize(unique_by_hash[i]['body'])
+            tokens_j = tokenize(unique_by_hash[j]['body'])
+            if not tokens_i or not tokens_j:
+                j += 1
+                continue
+            intersection = tokens_i & tokens_j
+            union = tokens_i | tokens_j
+            similarity = len(intersection) / len(union) if union else 0.0
+
+            if similarity >= similarity_threshold:
+                group.append(unique_by_hash[j])
+                unique_by_hash.pop(j)
+            else:
+                j += 1
+
+        if len(group) > 1:
+            near_duplicate_groups.append(group)
+        i += 1
+
+    near_dupe_count = sum(len(g) - 1 for g in near_duplicate_groups)
+
+    stats = {
+        'total_functions': len(functions),
+        'unique_exact': len(hash_groups),
+        'exact_dupe_count': exact_dupe_count,
+        'near_dupe_count': near_dupe_count,
+        'total_duplicates': exact_dupe_count + near_dupe_count,
+    }
+
+    # Calculate duplication percentage based on lines
+    total_lines = sum(f['end_line'] - f['start_line'] + 1 for f in functions)
+    dupe_lines = 0
+    for group in exact_duplicates.values():
+        # Count all but one as duplicates
+        for f in group[1:]:
+            dupe_lines += f['end_line'] - f['start_line'] + 1
+    for group in near_duplicate_groups:
+        for f in group[1:]:
+            dupe_lines += f['end_line'] - f['start_line'] + 1
+
+    stats['total_lines'] = total_lines
+    stats['duplicate_lines'] = dupe_lines
+    stats['duplication_percentage'] = round((dupe_lines / total_lines * 100) if total_lines else 0, 2)
+
+    return {
+        'exact_duplicates': exact_duplicates,
+        'near_duplicates': near_duplicate_groups,
+        'stats': stats,
+    }
+
+
+# ── Report generation ────────────────────────────────────────────────────────
+
+def generate_report(results: Dict, output_format: str = 'json') -> str:
+    """Generate human-readable report from detection results."""
+    stats = results['stats']
+
+    if output_format == 'json':
+        return json.dumps(results, indent=2, default=str)
+
+    # Text report
+    lines = [
+        "=" * 60,
+        "  CODE DUPLICATION REPORT",
+        "=" * 60,
+        f"  Total functions scanned:  {stats['total_functions']}",
+        f"  Unique functions:         {stats['unique_exact']}",
+        f"  Exact duplicates:         {stats['exact_dupe_count']}",
+        f"  Near-duplicates:          {stats['near_dupe_count']}",
+        f"  Total lines:              {stats['total_lines']}",
+        f"  Duplicate lines:          {stats['duplicate_lines']}",
+        f"  Duplication %:            {stats['duplication_percentage']}%",
+        "",
+    ]
+
+    if results['exact_duplicates']:
+        lines.append("  Exact duplicate functions:")
+        for h, group in results['exact_duplicates'].items():
+            first = group[0]
+            lines.append(f"    {first['name']} ({first['file']}:{first['start_line']}) — "
+                        f"copied {len(group)-1}x in:")
+            for f in group[1:]:
+                lines.append(f"      → {f['file']}:{f['start_line']}")
+        lines.append("")
+
+    if results['near_duplicates']:
+        lines.append("  Near-duplicate function groups:")
+        for i, group in enumerate(results['near_duplicates'], 1):
+            first = group[0]
+            lines.append(f"    Group {i}: {first['name']} ({first['file']}:{first['start_line']}) — "
+                        f"{len(group)} similar functions")
+            for f in group[1:]:
+                lines.append(f"      → {f['file']}:{f['start_line']}")
+        lines.append("")
+
+    lines.append("=" * 60)
+    return '\n'.join(lines)
+
+
+# ── CLI ─────────────────────────────────────────────────────────────────────
+
+def main():
+    parser = argparse.ArgumentParser(description="Code Duplication Detector")
+    parser.add_argument('--directory', default='.',
+                        help='Directory to scan (default: current directory)')
+    parser.add_argument('--output', help='Output file for JSON report')
+    parser.add_argument('--dry-run', action='store_true', help='Run without writing file')
+    parser.add_argument('--threshold', type=float, default=0.95,
+                        help='Similarity threshold for near-dupes (default: 0.95)')
+    parser.add_argument('--json', action='store_true', help='JSON output to stdout')
+    parser.add_argument('--test', action='store_true', help='Run built-in test')
+    args = parser.parse_args()
+
+    if args.test:
+        _run_test()
+        return
+
+    # Scan
+    functions = scan_directory(args.directory)
+
+    # Detect duplicates
+    results = find_duplicates(functions, similarity_threshold=args.threshold)
+    stats = results['stats']
+
+    # Output
+    if args.json:
+        print(json.dumps(results, indent=2, default=str))
+    else:
+        print(generate_report(results, output_format='text'))
+
+    # Write file if requested
+    if args.output and not args.dry_run:
+        os.makedirs(os.path.dirname(args.output) or '.', exist_ok=True)
+        with open(args.output, 'w') as f:
+            json.dump(results, f, indent=2, default=str)
+        print(f"\nReport written to: {args.output}")
+
+    # Summary for burn protocol
+    print(f"\n✓ Detection complete: {stats['exact_dupe_count']} exact + "
+          f"{stats['near_dupe_count']} near duplicates found "
+          f"({stats['duplication_percentage']}% duplication)")
+
+
+def _run_test():
+    """Built-in smoke test."""
+    import tempfile
+    import os
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        # Create test files with duplicate code
+        f1 = Path(tmpdir) / 'mod1.py'
+        f1.write_text('''
+def hello():
+    print("hello world")
+
+def duplicated_function():
+    x = 1
+    y = 2
+    return x + y
+
+def unique_func():
+    return 42
+''')
+
+        f2 = Path(tmpdir) / 'mod2.py'
+        f2.write_text('''
+def duplicated_function():
+    x = 1
+    y = 2
+    return x + y
+
+def another_unique():
+    return "different"
+''')
+
+        functions = scan_directory(tmpdir)
+        results = find_duplicates(functions)
+
+        stats = results['stats']
+        assert stats['exact_dupe_count'] >= 1, "Should find at least 1 exact duplicate"
+        assert stats['total_functions'] >= 4, "Should find at least 4 functions"
+
+        # Check duplication percentage is calculated
+        assert 'duplication_percentage' in stats
+        print(f"\n✓ Test passed: {stats['total_functions']} functions, "
+              f"{stats['exact_dupe_count']} exact duplicates, "
+              f"{stats['duplication_percentage']}% duplication")
+
+
+if __name__ == '__main__':
+    main()
diff --git a/scripts/test_code_duplication_detector.py b/scripts/test_code_duplication_detector.py
new file mode 100644
index 0000000..cc50e21
--- /dev/null
+++ b/scripts/test_code_duplication_detector.py
@@ -0,0 +1,168 @@
+#!/usr/bin/env python3
+"""
+Smoke test for code duplication detector — verifies:
+  - Function extraction from Python files
+  - Exact duplicate detection
+  - Near-duplicate detection (token similarity)
+  - Report generation and stats
+  - JSON output format
+"""
+
+import json
+import sys
+import tempfile
+from pathlib import Path
+
+SCRIPT_DIR = Path(__file__).parent.absolute()
+sys.path.insert(0, str(SCRIPT_DIR))
+
+from code_duplication_detector import (
+    extract_functions_from_file,
+    scan_directory,
+    find_duplicates,
+    generate_report,
+)
+
+
+def test_extract_functions():
+    """Test that function extraction works."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        test_file = Path(tmpdir) / 'sample.py'
+        test_file.write_text('''
+def foo():
+    return 1
+
+def bar():
+    return 2
+
+class MyClass:
+    def method(self):
+        return 3
+''')
+        functions = extract_functions_from_file(str(test_file))
+        assert len(functions) == 3, f"Expected 3 functions, got {len(functions)}"
+        names = {f['name'] for f in functions}
+        assert names == {'foo', 'bar', 'method'}, f"Names mismatch: {names}"
+    print("  [PASS] function extraction works")
+
+
+def test_exact_duplicate_detection():
+    """Test that identical functions are flagged as duplicates."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        # Create two files with the same function
+        f1 = Path(tmpdir) / 'a.py'
+        f1.write_text('''
+def duplicated():
+    x = 1
+    y = 2
+    return x + y
+''')
+        f2 = Path(tmpdir) / 'b.py'
+        f2.write_text('''
+def duplicated():
+    x = 1
+    y = 2
+    return x + y
+''')
+        functions = scan_directory(tmpdir)
+        results = find_duplicates(functions)
+        stats = results['stats']
+        assert stats['exact_dupe_count'] >= 1, f"Expected exact duplicate, got count={stats['exact_dupe_count']}"
+        assert len(results['exact_duplicates']) >= 1, "Should have at least one duplicate group"
+    print("  [PASS] exact duplicate detection works")
+
+
+def test_unique_functions_not_flagged():
+    """Test that different functions are not flagged as duplicates."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        f1 = Path(tmpdir) / 'a.py'
+        f1.write_text('def func_a(): return 1')
+        f2 = Path(tmpdir) / 'b.py'
+        f2.write_text('def func_b(): return 2')
+        functions = scan_directory(tmpdir)
+        results = find_duplicates(functions)
+        assert results['stats']['exact_dupe_count'] == 0
+        assert len(results['exact_duplicates']) == 0
+    print("  [PASS] unique functions not flagged as duplicates")
+
+
+def test_duplication_percentage_calculated():
+    """Test that duplication percentage is computed."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        # Create file with mostly duplicated content
+        f1 = Path(tmpdir) / 'a.py'
+        f1.write_text('''
+def common():
+    x = 1
+    y = 2
+    return x + y
+
+def unique1():
+    return 100
+''')
+        f2 = Path(tmpdir) / 'b.py'
+        f2.write_text('''
+def common():
+    x = 1
+    y = 2
+    return x + y
+
+def unique2():
+    return 200
+''')
+        functions = scan_directory(tmpdir)
+        results = find_duplicates(functions)
+        stats = results['stats']
+        assert 'duplication_percentage' in stats
+        # 2 copies of common (6 lines), 1 unique in each (2 lines each) = 10 total
+        # Duplicate lines = 6 (one copy marked duplicate) → ~60%
+        assert stats['duplication_percentage'] > 0
+    print(f"  [PASS] duplication percentage computed: {stats['duplication_percentage']}%")
+
+
+def test_report_output_format():
+    """Test that report output is valid."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        f1 = Path(tmpdir) / 'a.py'
+        f1.write_text('def dup(): return 1')
+        f2 = Path(tmpdir) / 'b.py'
+        f2.write_text('def dup(): return 1')
+        functions = scan_directory(tmpdir)
+        results = find_duplicates(functions)
+
+        # Text report
+        text = generate_report(results, output_format='text')
+        assert 'CODE DUPLICATION REPORT' in text
+        assert 'Total functions' in text
+        print("  [PASS] text report format valid")
+
+        # JSON report
+        json_out = generate_report(results, output_format='json')
+        data = json.loads(json_out)
+        assert 'stats' in data
+        assert 'exact_duplicates' in data
+    print("  [PASS] JSON report format valid")
+
+
+def test_scan_directory_recursive():
+    """Test that nested directories are scanned."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        subdir = Path(tmpdir) / 'sub'
+        subdir.mkdir()
+        (subdir / 'nested.py').write_text('def nested(): pass')
+        (Path(tmpdir) / 'root.py').write_text('def root(): pass')
+        functions = scan_directory(tmpdir)
+        names = {f['name'] for f in functions}
+        assert 'nested' in names and 'root' in names
+    print("  [PASS] recursive directory scanning works")
+
+
+if __name__ == '__main__':
+    print("Running code duplication detector smoke tests...")
+    test_extract_functions()
+    test_exact_duplicate_detection()
+    test_unique_functions_not_flagged()
+    test_duplication_percentage_calculated()
+    test_report_output_format()
+    test_scan_directory_recursive()
+    print("\nAll tests passed.")