#!/usr/bin/env python3
"""JSON linter: validates and pretty-prints JSON files with structured output."""
import json
import sys
from pathlib import Path

def validate_json_file(filepath: str) -> dict:
    """Validate a JSON file and return structured result."""
    result = {"file": filepath, "valid": False, "error": None, "type": None, "keys": []}
    
    try:
        content = Path(filepath).read_text()
        data = json.loads(content)
        result["valid"] = True
        result["type"] = type(data).__name__
        
        if isinstance(data, dict):
            result["keys"] = sorted(data.keys())
        elif isinstance(data, list):
            result["length"] = len(data)
    except FileNotFoundError:
        result["error"] = "File not found"
    except json.JSONDecodeError as e:
        result["error"] = f"JSON parse error at line {e.lineno}, col {e.colno}: {e.msg}"
    except Exception as e:
        result["error"] = str(e)
    
    return result

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print(json.dumps({"error": "Usage: json_lint.py <file.json>"}))
        sys.exit(1)
    
    result = validate_json_file(sys.argv[1])
    print(json.dumps(result, indent=2))
    sys.exit(0 if result["valid"] else 1)