browser/visual_regression.py

import os
import hashlib
from PIL import Image, ImageChops
import io
from browser.screenshot import take

_baselines: dict[str, str] = {}   # url → baseline screenshot path


async def check(url: str) -> dict:
    """Compare current screenshot with baseline. Returns diff report."""
    current_path = await take(url, label="regression")

    if current_path.startswith("screenshot_error"):
        return {"check": "visual_regression", "overall": "error", "summary": current_path}

    if url not in _baselines:
        _baselines[url] = current_path
        return {
            "check": "visual_regression",
            "overall": "ok",
            "baseline_set": True,
            "summary": "✅ Baseline screenshot saved — will compare next run",
        }

    baseline_path = _baselines[url]

    if not os.path.exists(baseline_path):
        _baselines[url] = current_path
        return {
            "check": "visual_regression",
            "overall": "ok",
            "summary": "✅ Baseline reset (previous file missing)",
        }

    try:
        img_base    = Image.open(baseline_path).convert("RGB")
        img_current = Image.open(current_path).convert("RGB")

        # Resize to same dimensions for comparison
        if img_base.size != img_current.size:
            img_current = img_current.resize(img_base.size, Image.LANCZOS)

        diff        = ImageChops.difference(img_base, img_current)
        diff_pixels = sum(sum(row) for row in diff.getdata())
        total_pixels= img_base.width * img_base.height * 3 * 255
        diff_pct    = round((diff_pixels / total_pixels) * 100, 2)

        if diff_pct > 20:
            status  = "error"
            summary = f"🚨 Visual change detected: {diff_pct}% of page changed!"
        elif diff_pct > 5:
            status  = "warning"
            summary = f"⚠️ Minor visual change: {diff_pct}% of page changed"
        else:
            status  = "ok"
            summary = f"✅ No significant visual change ({diff_pct}%)"

        # Update baseline on major accepted change
        _baselines[url] = current_path

        return {
            "check": "visual_regression",
            "overall": status,
            "diff_percent": diff_pct,
            "baseline_path": baseline_path,
            "current_path": current_path,
            "summary": summary,
        }

    except Exception as e:
        return {
            "check": "visual_regression",
            "overall": "error",
            "summary": f"❌ Visual comparison failed: {e}",
        }