#!/usr/bin/env python3
"""
Test Coverage Checker — 6.6

Identifies changed source files, checks for corresponding test changes,
and reports code without test coverage.

Usage:
    python3 scripts/test_coverage_checker.py
    python3 scripts/test_coverage_checker.py --format json
    python3 scripts/test_coverage_checker.py --compare HEAD~1  # Compare against a specific ref

Acceptance:
  - Identifies changed source files   (git diff --name-only HEAD)
  - Checks for corresponding test changes (matches source→test file mapping)
  - Reports: code without tests        (lists coverage gaps)
  - Output: coverage gap              (structured text/JSON)
"""

import argparse
import json
import subprocess
import sys
from pathlib import Path
from typing import List, Tuple, Optional

REPO_ROOT = Path(__file__).resolve().parent.parent


def run_git_diff(ref: str = "HEAD") -> List[str]:
    """Return list of changed file paths relative to given ref."""
    result = subprocess.run(
        ["git", "diff", "--name-only", ref],
        capture_output=True, text=True, cwd=REPO_ROOT
    )
    if result.returncode != 0:
        print(f"ERROR: git diff failed: {result.stderr}")
        sys.exit(1)
    return [p for p in result.stdout.splitlines() if p.strip()]


def is_source_file(path: str) -> bool:
    """True if path is a Python source file (not test)."""
    return path.endswith(".py") and not path.startswith("tests/") and "/test" not in Path(path).name


def is_test_file(path: str) -> bool:
    """True if path is a test file."""
    if not path.endswith(".py"):
        return False
    name = Path(path).name
    # Test files: test_*.py or *_test.py or in tests/ directory
    return (name.startswith("test_") or name.endswith("_test.py") or path.startswith("tests/"))


def source_to_test_path(src_path: str) -> str:
    """
    Map a source file path to its expected test file path.
    Convention: scripts/<name>.py -> tests/test_<name>.py
                <module>.py -> tests/test_<module>.py
    """
    name = Path(src_path).name
    stem = Path(name).stem  # without .py
    # Common mapping: script name -> test_ prefix in tests/
    test_name = f"test_{stem}.py"
    return str(Path("tests") / test_name)


def test_file_exists() -> bool:
    """Check if the test file exists in the repo."""
    return (REPO_ROOT / test_rel).exists()


def analyze_coverage(changed_files: List[str]) -> dict:
    """
    For each changed source file, check if corresponding test file also changed.
    Returns structured coverage gap report.
    """
    changed_sources = [f for f in changed_files if is_source_file(f)]
    changed_tests = [f for f in changed_files if is_test_file(f)]

    # Build set of test file paths that changed (relative paths)
    changed_test_set = set(changed_tests)

    # Build coverage gap
    uncovered_sources = []
    covered_sources = []
    for src in changed_sources:
        coverage_entry = {"file": src}
        # Check: does the corresponding test file also appear in changed files?
        test_rel = source_to_test_path(src)
        if test_rel in changed_test_set:
            coverage_entry["status"] = "covered"
            coverage_entry["test_file"] = test_rel
            covered_sources.append(coverage_entry)
        else:
            coverage_entry["status"] = "missing"
            coverage_entry["suggested_test"] = test_rel
            uncovered_sources.append(coverage_entry)

    return {
        "repo": REPO_ROOT.name,
        "changed_sources": len(changed_sources),
        "changed_tests": len(changed_tests),
        "covered_sources": len(covered_sources),
        "uncovered_sources": len(uncovered_sources),
        "coverage_ratio": (
            len(covered_sources) / len(changed_sources)
            if changed_sources else 1.0
        ),
        "covered": covered_sources,
        "uncovered": uncovered_sources,
        "all_changed": changed_files,
    }


def main():
    parser = argparse.ArgumentParser(description="Test Coverage Checker")
    parser.add_argument("--format", choices=["text", "json"], default="text",
                        help="Output format")
    parser.add_argument("--compare", default="HEAD",
                        help="Git ref to compare against (default: HEAD)")
    args = parser.parse_args()

    # Step 1: Identify changed files
    print(f"Scanning changes vs {args.compare}...")
    changed_files = run_git_diff(args.compare)
    if not changed_files:
        print("No changed files detected.")
        sys.exit(0)

    # Step 2: Analyze coverage
    report = analyze_coverage(changed_files)

    if args.format == "json":
        print(json.dumps(report, indent=2))
        sys.exit(0)

    # Text output
    print("=" * 60)
    print("  TEST COVERAGE CHECKER")
    print("=" * 60)
    print(f"  Repository:  {report['repo']}")
    print(f"  Changed files total: {len(changed_files)}")
    print(f"  Source files changed: {report['changed_sources']}")
    print(f"  Test files changed:   {report['changed_tests']}")
    print()
    print(f"  Coverage (sources with test changes): {report['coverage_ratio']:.0%}")
    print(f"    Covered:   {report['covered_sources']} source file(s)")
    print(f"    Uncovered: {report['uncovered_sources']} source file(s)")
    print()

    if report["uncovered"]:
        print("  COVERAGE GAP — Source files without corresponding test changes:")
        print("  " + "-" * 54)
        for item in report["uncovered"]:
            print(f"    {item['file']}")
            print(f"      Suggested test: {item['suggested_test']}")
        print()
        print("  ACTION: Write or update tests for the files above.")
        sys.exit(1)  # Non-zero exit to flag coverage gap
    else:
        print("  All changed source files have corresponding test coverage.")

    print("=" * 60)


if __name__ == "__main__":
    main()