#!/usr/bin/env python3
"""json_diff.py - Compare two JSON files for structural equality.

Usage: python3 json_diff.py <file1.json> <file2.json>

Returns exit code 0 if JSON structures match (ignoring key order in objects),
1 if they differ, 2 on error. Outputs the diff to stdout.
"""

import json
import sys
from pathlib import Path


def normalize_json(data):
    """Recursively normalize JSON: sort dict keys, convert lists."""
    if isinstance(data, dict):
        return {k: normalize_json(data[k]) for k in sorted(data.keys())}
    elif isinstance(data, list):
        return [normalize_json(item) for item in data]
    else:
        return data


def json_equal(file1: str, file2: str) -> tuple:
    """Compare two JSON files. Returns (equal: bool, diff: str, error: str|None)."""
    try:
        data1 = json.loads(Path(file1).read_text())
        data2 = json.loads(Path(file2).read_text())
        
        norm1 = normalize_json(data1)
        norm2 = normalize_json(data2)
        
        if norm1 == norm2:
            return True, "", None
        
        diff_lines = []
        diff_lines.append(f"Files differ:")
        diff_lines.append(f"  {file1}: {json.dumps(norm1, indent=2)[:500]}")
        diff_lines.append(f"  {file2}: {json.dumps(norm2, indent=2)[:500]}")
        
        return False, "\n".join(diff_lines), None
        
    except FileNotFoundError as e:
        return False, "", f"File not found: {e.filename}"
    except json.JSONDecodeError as e:
        return False, "", f"JSON error in {e.doc}: line {e.lineno}"
    except Exception as e:
        return False, "", str(e)


def main():
    if len(sys.argv) != 3:
        print("Usage: python3 json_diff.py <file1.json> <file2.json>", file=sys.stderr)
        sys.exit(2)
    
    result, diff, error = json_equal(sys.argv[1], sys.argv[2])
    
    if error:
        print(f"Error: {error}", file=sys.stderr)
        sys.exit(2)
    
    if result:
        print("STRUCTURALLY EQUAL")
        sys.exit(0)
    else:
        print(diff)
        sys.exit(1)


if __name__ == "__main__":
    main()