#!/usr/bin/env python3
"""
Check each guide URL in guides.csv for WCAG 2.1 AA accessibility
issues using the pa11y CLI and report results.

The script:
1. Reads guides.csv in the current directory.
2. Runs `pa11y` for each URL with the WCAG2AA standard, requesting JSON.
3. Collects the issues for every guide.
4. Removes any issue codes that appear in *every* guide.
5. Prints the filtered results to the console and writes them to
   output.txt.

Prerequisites:
    npm install -g pa11y

Usage:
    python check_wcag.py
"""
from __future__ import annotations

import csv
import json
import subprocess
import sys
from pathlib import Path
from typing import Dict, List, Set

GUIDES_CSV = Path(__file__).with_name("guides.csv")
OUTPUT_FILE = Path("output.txt")


def run_pa11y(url: str) -> List[dict]:
    """
    Run pa11y on a URL and return the parsed JSON list of issues.

    Returns an empty list if pa11y fails.
    """
    try:
        result = subprocess.run(
            ["pa11y", url, "--standard", "WCAG2AA", "--reporter", "json"],
            capture_output=True,
            text=True,
            check=False,
        )
        if result.returncode != 0:
            print(f"[WARN] pa11y returned code {result.returncode} for {url}", file=sys.stderr)
            return []
        return json.loads(result.stdout)
    except FileNotFoundError:
        print("Error: pa11y not found. Install it with `npm install -g pa11y`.", file=sys.stderr)
        sys.exit(1)
    except json.JSONDecodeError:
        print(f"[WARN] Could not parse pa11y JSON output for {url}", file=sys.stderr)
        return []


def read_guides(csv_path: Path) -> List[Dict[str, str]]:
    """Load all guides from the CSV into a list of dicts."""
    with csv_path.open(newline="", encoding="utf-8-sig") as fh:
        reader = csv.DictReader(fh)
        return list(reader)


def compute_common_codes(issues_by_guide: Dict[str, List[dict]]) -> Set[str]:
    """Return the set of issue codes that appear in every guide."""
    all_codes_iter = (
        {issue["code"] for issue in issues} for issues in issues_by_guide.values()
    )
    common_codes: Set[str] | None = None
    for codes in all_codes_iter:
        if common_codes is None:
            common_codes = codes
        else:
            common_codes &= codes
    return common_codes or set()


def format_issue(issue: dict) -> str:
    """Return a human-readable one-line representation of a pa11y issue."""
    selector = issue.get("selector", "").strip() or "N/A"
    return f"[{issue['type']}] {issue['code']}: {issue['message']}  (selector: {selector})"


def main() -> None:
    guides = read_guides(GUIDES_CSV)
    issues_by_guide: Dict[str, List[dict]] = {}

    print("Auditing guides with pa11y…\n")
    for guide in guides:
        name = guide["Name"]
        url = guide["URL"]
        print(f"• {name} — {url}")
        issues = run_pa11y(url)
        issues_by_guide[name] = issues

    common_codes = compute_common_codes(issues_by_guide)

    lines_out: List[str] = []
    lines_out.append("\nAccessibility report (WCAG 2.1 AA)")
    lines_out.append("=" * 40)

    for name, issues in issues_by_guide.items():
        filtered = [i for i in issues if i["code"] not in common_codes]
        lines_out.append(f"\nGuide: {name}")
        if not filtered:
            lines_out.append("  ✔ No unique issues found.")
            continue
        for issue in filtered:
            lines_out.append(f"  • {format_issue(issue)}")

    report_text = "\n".join(lines_out)
    print("\n" + report_text)
    OUTPUT_FILE.write_text(report_text, encoding="utf-8")
    print(f"\nReport written to {OUTPUT_FILE.resolve()}")


if __name__ == "__main__":
    main()