pip install google-generativeai

export GEMINI_API_KEY="your-key-here"

import subprocess
import sys

def collect_git_history(repo_path: str, since: str = "1 week ago", until: str = "HEAD") -> tuple[str, list[dict]]:
    """
    Returns (full_patch_text, list_of_commit_metadata).
    `since` accepts anything git understands: '7 days ago', 'v1.2.3', a SHA, etc.
    """
    # Collect the full unified diff
    patch_result = subprocess.run(
        ["git", "log", "--patch", "--no-merges", f"--since={since}", f"--until={until}",
         "--pretty=format:COMMIT: %H%nAuthor: %an <%ae>%nDate: %ci%nMessage: %s%n"],
        cwd=repo_path,
        capture_output=True,
        text=True,
        check=True
    )

    # Collect lightweight metadata for the summary header
    meta_result = subprocess.run(
        ["git", "log", "--no-merges", f"--since={since}", f"--until={until}",
         "--pretty=format:%H|%an|%ci|%s"],
        cwd=repo_path,
        capture_output=True,
        text=True,
        check=True
    )

    commits = []
    for line in meta_result.stdout.strip().splitlines():
        if not line:
            continue
        sha, author, date, *msg_parts = line.split("|")
        commits.append({
            "sha": sha[:8],
            "author": author,
            "date": date,
            "message": "|".join(msg_parts)
        })

    return patch_result.stdout, commits

SYSTEM_PROMPT = """You are a senior staff engineer performing a structured code review
of a git commit history. Your job is to analyse the provided patch text and return a
single JSON object — nothing else, no markdown fences, no explanation outside the JSON.

The JSON object must match this schema exactly:

{
  "summary": "2-3 sentence plain-English summary of the overall change set",
  "changed_areas": [
    {
      "path": "path/to/file_or_directory",
      "change_type": "added | modified | deleted | renamed",
      "description": "what changed and why it likely changed"
    }
  ],
  "risk_flags": [
    {
      "severity": "low | medium | high",
      "area": "file or component",
      "reason": "specific, concrete reason this change carries risk"
    }
  ],
  "patterns": [
    "notable cross-commit pattern, refactor theme, or repeated change"
  ],
  "changelog_entry": "A polished, user-facing changelog entry in Markdown. Use ## [Unreleased] as the heading. Group under Added, Changed, Fixed, Removed as appropriate."
}

Be specific. Do not flag risk without a concrete reason tied to the actual diff.
Do not invent changes that are not present in the patch text."""


def build_prompt(patch_text: str, commits: list[dict]) -> str:
    commit_count = len(commits)
    authors = list({c["author"] for c in commits})
    date_range = f"{commits[-1]['date'][:10]} to {commits[0]['date'][:10]}" if commits else "unknown"

    header = (
        f"ANALYSIS REQUEST\n"
        f"Commits: {commit_count}\n"
        f"Authors: {', '.join(authors)}\n"
        f"Date range: {date_range}\n\n"
        f"FULL PATCH TEXT FOLLOWS\n"
        f"{'='*60}\n"
    )

    return header + patch_text

import google.generativeai as genai
import json
import os

def analyze_with_gemma(patch_text: str, commits: list[dict]) -> dict:
    genai.configure(api_key=os.environ["GEMINI_API_KEY"])

    model = genai.GenerativeModel(
        model_name="gemma-4-31b-it",
        system_instruction=SYSTEM_PROMPT,
        generation_config=genai.GenerationConfig(
            temperature=0.2,      # Low temperature for consistent structured output
            top_p=0.9,
            max_output_tokens=4096,
        )
    )

    prompt = build_prompt(patch_text, commits)

    print(f"Sending {len(prompt.split()):,} words to Gemma 4 31B...", file=sys.stderr)

    response = model.generate_content(prompt)

    raw = response.text.strip()

    # Strip markdown fences if the model adds them despite instructions
    if raw.startswith("```

"):
        raw = raw.split("

```")[1]
        if raw.startswith("json"):
            raw = raw[4:]

    return json.loads(raw)

from datetime import datetime

def print_report(analysis: dict, commits: list[dict]) -> None:
    print("\n" + "="*60)
    print("GIT HISTORY ANALYSIS — Gemma 4 31B")
    print("="*60)
    print(f"\nCommits analysed: {len(commits)}")
    print(f"\nSUMMARY\n{analysis['summary']}\n")

    if analysis.get("risk_flags"):
        print("RISK FLAGS")
        for flag in sorted(analysis["risk_flags"], key=lambda f: {"high": 0, "medium": 1, "low": 2}[f["severity"]]):
            icon = {"high": "🔴", "medium": "🟡", "low": "🟢"}[flag["severity"]]
            print(f"  {icon} [{flag['severity'].upper()}] {flag['area']}")
            print(f"     {flag['reason']}")
        print()

    if analysis.get("patterns"):
        print("PATTERNS DETECTED")
        for p in analysis["patterns"]:
            print(f"  • {p}")
        print()

    print("CHANGED AREAS")
    for area in analysis.get("changed_areas", []):
        print(f"  [{area['change_type'].upper():8}] {area['path']}")
        print(f"             {area['description']}")
    print()


def write_changelog(analysis: dict, output_path: str) -> None:
    entry = analysis.get("changelog_entry", "")
    if not entry:
        return

    # Inject today's date if the entry has a placeholder
    entry = entry.replace("[Unreleased]", f"[Unreleased] — {datetime.today().strftime('%Y-%m-%d')}")

    with open(output_path, "w") as f:
        f.write(entry + "\n")

    print(f"Changelog written to {output_path}", file=sys.stderr)

import argparse

def main():
    parser = argparse.ArgumentParser(
        description="Analyse a git commit range with Gemma 4 31B"
    )
    parser.add_argument("repo", help="Path to git repository")
    parser.add_argument("--since", default="1 week ago",
                        help="Start of range (default: '1 week ago'). Accepts any git date or ref.")
    parser.add_argument("--until", default="HEAD",
                        help="End of range (default: HEAD)")
    parser.add_argument("--changelog", default=None,
                        help="Write changelog entry to this file")
    parser.add_argument("--json", dest="json_out", default=None,
                        help="Write full JSON report to this file")
    args = parser.parse_args()

    patch_text, commits = collect_git_history(args.repo, args.since, args.until)

    if not commits:
        print("No commits found in the specified range.", file=sys.stderr)
        sys.exit(0)

    analysis = analyze_with_gemma(patch_text, commits)
    print_report(analysis, commits)

    if args.changelog:
        write_changelog(analysis, args.changelog)

    if args.json_out:
        with open(args.json_out, "w") as f:
            json.dump(analysis, f, indent=2)
        print(f"Full JSON report written to {args.json_out}", file=sys.stderr)


if __name__ == "__main__":
    main()

python git_analyzer.py . --since "1 week ago"

python git_analyzer.py /path/to/repo \
  --since v1.4.0 \
  --until v1.5.0 \
  --changelog CHANGELOG.md \
  --json report.json

python git_analyzer.py . --since "14 days ago" --changelog CHANGELOG.md

============================================================
GIT HISTORY ANALYSIS — Gemma 4 31B
============================================================

Commits analysed: 23

SUMMARY
This sprint focused on migrating the authentication layer from session
cookies to JWTs, with supporting changes to the user model and API
middleware. Three unrelated bug fixes were included. No database
migrations were added despite schema-adjacent changes in user.py.

RISK FLAGS
  🔴 [HIGH]  src/auth/middleware.py
             Token expiry is set to 0 in the new JWT config, which
             disables expiry entirely. This appears unintentional given
             the surrounding comments referencing a 24h TTL.
  🟡 [MEDIUM] src/models/user.py
             The `last_login` field is now written in two places with
             different timezone handling (UTC in the old path, local
             time in the new one). Cross-commit inconsistency introduced
             in commits a3f1cc and 9d02bb.

PATTERNS DETECTED
  • JWT migration touched 11 files across 8 commits — no single
    atomic commit, suggesting iterative discovery during implementation
  • Four separate commits add logging statements then remove them,
    indicating debug churn that could have been a feature branch

CHANGED AREAS
  [MODIFIED ] src/auth/middleware.py
               Core auth middleware rewritten to validate Bearer tokens
               instead of reading from session. Old session path removed.
  [MODIFIED ] src/models/user.py
               Added jwt_secret field; last_login timezone handling changed
  [ADDED    ] src/auth/token.py
               New module for JWT encode/decode with HS256
  ...