feat: add codebase genome diff script for structural change detection

Introduces genome_diff.py — a tool for detecting structural changes between
two git refs: file-level changes, function/class signature modifications,
and dependency import changes.

Addresses #132.

scripts/genome_diff.py

@@ -0,0 +1,288 @@
+#!/usr/bin/env python3
+"""
+Codebase Genome Diff — Detect structural changes between two versions.
+
+Compares two git refs (commits, branches, tags) and produces a human-readable
+report of structural changes:
+  • Added/removed/renamed files
+  • Changed functions/classes (signature modifications)
+  • New dependencies (imports, requirements, etc.)
+
+Usage:
+    python3 scripts/genome_diff.py --ref1 <commit1> --ref2 <commit2>
+    python3 scripts/genome_diff.py --ref1 main --ref2 feature-branch
+    python3 scripts/genome_diff.py --ref1 v1.0 --ref2 v2.0 --output report.txt
+"""
+
+import argparse
+import json
+import os
+import re
+import subprocess
+import sys
+from dataclasses import dataclass, field
+from typing import List, Dict, Any, Optional
+
+SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(0, SCRIPT_DIR)
+from diff_analyzer import DiffAnalyzer, ChangeCategory
+
+
+@dataclass
+class FunctionChange:
+    file: str
+    name: str
+    kind: str  # 'function' or 'class'
+    change_type: str  # 'added' or 'removed' (simplified)
+    old_line: Optional[int] = None
+    new_line: Optional[int] = None
+
+
+@dataclass
+class DependencyChange:
+    file: str
+    module: str
+    change_type: str  # 'added' or 'removed' or 'modified'
+    line: int = 0
+
+
+@dataclass
+class GenomeDiffReport:
+    ref1: str
+    ref2: str
+    file_changes: List[Dict[str, Any]] = field(default_factory=list)
+    function_changes: List[FunctionChange] = field(default_factory=list)
+    dependency_changes: List[DependencyChange] = field(default_factory=list)
+    total_files_changed: int = 0
+    total_functions_changed: int = 0
+    total_dependencies_changed: int = 0
+
+    def to_dict(self) -> Dict[str, Any]:
+        return {
+            "ref1": self.ref1,
+            "ref2": self.ref2,
+            "summary": {
+                "files": self.total_files_changed,
+                "functions": self.total_functions_changed,
+                "dependencies": self.total_dependencies_changed,
+            },
+            "file_changes": self.file_changes,
+            "function_changes": [fc.__dict__ for fc in self.function_changes],
+            "dependency_changes": [dc.__dict__ for dc in self.dependency_changes],
+        }
+
+    def human_report(self) -> str:
+        lines = []
+        lines.append(f"Codebase Genome Diff: {self.ref1} → {self.ref2}")
+        lines.append("=" * 60)
+        lines.append(f"  Files changed: {self.total_files_changed}")
+        lines.append(f"  Functions changed: {self.total_functions_changed}")
+        lines.append(f"  Dependencies changed: {self.total_dependencies_changed}")
+        lines.append("")
+
+        for fc in self.file_changes:
+            kind = []
+            if fc.get('is_new'):
+                kind.append("NEW")
+            if fc.get('is_deleted'):
+                kind.append("DELETED")
+            if fc.get('is_renamed'):
+                kind.append("RENAMED")
+            if fc.get('is_binary'):
+                kind.append("BINARY")
+            kind_str = f" [{', '.join(kind)}]" if kind else ""
+            lines.append(f"  {fc['path']}{kind_str}  (+{fc['added_lines']}/-{fc['deleted_lines']})")
+        lines.append("")
+
+        for fc in self.function_changes:
+            op = {'added': '+', 'removed': '-', 'modified': '~'}.get(fc.change_type, '?')
+            lines.append(f"  [{op}] {fc.file}: {fc.kind} '{fc.name}'")
+        lines.append("")
+
+        for dc in self.dependency_changes:
+            op = '+' if dc.change_type == 'added' else '-'
+            lines.append(f"  [{op}] {dc.file}: {dc.module}")
+        lines.append("")
+
+        return "\n".join(lines)
+
+
+def run_git_diff(ref1: str, ref2: str) -> str:
+    result = subprocess.run(
+        ['git', 'diff', '--unified=0', f'{ref1}...{ref2}'],
+        capture_output=True, text=True, cwd=SCRIPT_DIR
+    )
+    if result.returncode not in (0, 1):
+        print(f"git diff failed: {result.stderr}", file=sys.stderr)
+        sys.exit(1)
+    return result.stdout
+
+
+def extract_function_changes(diff_text: str) -> List[FunctionChange]:
+    changes: List[FunctionChange] = []
+    pattern = re.compile(r'^([+\-])\s*(def|class)\s+(\w+)', re.MULTILINE)
+    hunk_header_re = re.compile(r'^@@\s+-(\d+)(?:,(\d+))?\s+\+(\d+)(?:,(\d+))?\s+@@')
+    current_old_line: Optional[int] = None
+    current_new_line: Optional[int] = None
+
+    for line in diff_text.split('\n'):
+        hdr = hunk_header_re.match(line)
+        if hdr:
+            current_old_line = int(hdr.group(1))
+            current_new_line = int(hdr.group(3))
+            continue
+        m = pattern.match(line)
+        if m:
+            op = m.group(1)
+            kind = m.group(2)
+            name = m.group(3)
+            change_type = "added" if op == '+' else "removed"
+            line_num = current_new_line if change_type == "added" else current_old_line
+            changes.append(FunctionChange(
+                file="<unknown>",
+                name=name,
+                kind=kind,
+                change_type=change_type,
+                new_line=line_num if change_type == "added" else None,
+                old_line=line_num if change_type == "removed" else None,
+            ))
+            # Advance line counters heuristically
+            if op == '-':
+                if current_old_line is not None:
+                    current_old_line += 1
+            elif op == '+':
+                if current_new_line is not None:
+                    current_new_line += 1
+        elif line.startswith(' '):
+            if current_old_line is not None:
+                current_old_line += 1
+            if current_new_line is not None:
+                current_new_line += 1
+        # lines starting with other prefixes (like \\ No newline) ignored
+    return changes
+
+
+def extract_dependency_changes(diff_text: str, analyzer: DiffAnalyzer) -> List[DependencyChange]:
+    changes: List[DependencyChange] = []
+    import_pattern = re.compile(
+        r'^([+\-])\s*(?:import\s+([\w\.]+)|from\s+([\w\.]+)\s+import)',
+        re.MULTILINE
+    )
+    file_diffs = analyzer._split_files(diff_text)
+    for file_diff in file_diffs:
+        file_match = re.search(r'^diff --git a/.*? b/(.*?)$', file_diff, re.MULTILINE)
+        if not file_match:
+            continue
+        filepath = file_match.group(1)
+
+        # Scan each line for import changes
+        for line in file_diff.split('\n'):
+            m = import_pattern.match(line)
+            if m:
+                change_type = "added" if m.group(1) == '+' else "removed"
+                module = m.group(2) or m.group(3)
+                changes.append(DependencyChange(
+                    file=filepath,
+                    module=module,
+                    change_type=change_type,
+                    line=0
+                ))
+
+        # Detect if this file is a dependency manifest
+        req_file_pattern = re.compile(
+            r'^[\+\-].*?(requirements(.*?)\.txt|pyproject\.toml|setup\.py|Pipfile)'
+        )
+        if any(req_file_pattern.match(line) for line in file_diff.split('\n')):
+            if not any(c.file == filepath and c.module == "<file>" for c in changes):
+                changes.append(DependencyChange(
+                    file=filepath,
+                    module="<file>",
+                    change_type="modified",
+                    line=0
+                ))
+    return changes
+
+
+def correlate_function_changes_with_files(diff_text: str, functions: List[FunctionChange]) -> List[FunctionChange]:
+    result: List[FunctionChange] = []
+    # Split diff into per-file sections
+    file_sections: List[tuple[str, str]] = []
+    current_file: Optional[str] = None
+    current_lines: List[str] = []
+    for line in diff_text.split('\n'):
+        if line.startswith('diff --git'):
+            if current_file is not None:
+                file_sections.append((current_file, '\n'.join(current_lines)))
+            m = re.match(r'^diff --git a/.*? b/(.*?)$', line)
+            current_file = m.group(1) if m else "unknown"
+            current_lines = [line]
+        else:
+            current_lines.append(line)
+    if current_file is not None:
+        file_sections.append((current_file, '\n'.join(current_lines)))
+
+    pattern = re.compile(r'^([+\-])\s*(def|class)\s+(\w+)', re.MULTILINE)
+    for filepath, section in file_sections:
+        for m in pattern.finditer(section):
+            op = m.group(1)
+            kind = m.group(2)
+            name = m.group(3)
+            change_type = "added" if op == '+' else "removed"
+            result.append(FunctionChange(
+                file=filepath,
+                name=name,
+                kind=kind,
+                change_type=change_type
+            ))
+    return result
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Codebase Genome Diff — structural changes between versions")
+    parser.add_argument("--ref1", required=True, help="First git ref (commit, branch, tag)")
+    parser.add_argument("--ref2", required=True, help="Second git ref")
+    parser.add_argument("--output", help="Write report to file")
+    parser.add_argument("--json", action="store_true", help="Output JSON instead of human report")
+    args = parser.parse_args()
+
+    try:
+        diff_text = run_git_diff(args.ref1, args.ref2)
+    except Exception as e:
+        print(f"Error: {e}", file=sys.stderr)
+        sys.exit(1)
+
+    if not diff_text.strip():
+        print(f"No differences between {args.ref1} and {args.ref2}.")
+        sys.exit(0)
+
+    analyzer = DiffAnalyzer()
+    summary = analyzer.analyze(diff_text)
+
+    file_changes = [fc.to_dict() for fc in summary.files]
+    func_changes = extract_function_changes(diff_text)
+    func_changes = correlate_function_changes_with_files(diff_text, func_changes)
+    dep_changes = extract_dependency_changes(diff_text, analyzer)
+
+    report = GenomeDiffReport(
+        ref1=args.ref1,
+        ref2=args.ref2,
+        file_changes=file_changes,
+        function_changes=func_changes,
+        dependency_changes=dep_changes,
+        total_files_changed=len(file_changes),
+        total_functions_changed=len(func_changes),
+        total_dependencies_changed=len(dep_changes),
+    )
+
+    output = json.dumps(report.to_dict(), indent=2) if args.json else report.human_report()
+
+    if args.output:
+        with open(args.output, 'w') as f:
+            f.write(output + '\n')
+        print(f"Report written to {args.output}")
+    else:
+        print(output)
+
+
+if __name__ == '__main__':
+    main()