entity_relationship_generator.py

import graphviz
import json
from tempfile import NamedTemporaryFile
import os

def generate_entity_relationship_diagram(json_input: str, output_format: str) -> str:
    """
    Generates an entity relationship diagram from JSON input.

    Args:
        json_input (str): A JSON string describing the entity relationship diagram structure.
                          It must follow the Expected JSON Format Example below.

    Expected JSON Format Example:
    {
      "entities": [
        {
          "name": "Customer",
          "type": "strong",
          "attributes": [
            {"name": "customer_id", "type": "primary_key"},
            {"name": "first_name", "type": "regular"},
            {"name": "last_name", "type": "regular"},
            {"name": "email", "type": "regular"},
            {"name": "phone", "type": "multivalued", "multivalued": true},
            {"name": "age", "type": "derived", "derived": true},
            {"name": "address", "type": "composite", "composite": true}
          ]
        },
        {
          "name": "Order",
          "type": "strong",
          "attributes": [
            {"name": "order_id", "type": "primary_key"},
            {"name": "customer_id", "type": "foreign_key"},
            {"name": "order_date", "type": "regular"},
            {"name": "total_amount", "type": "regular"},
            {"name": "status", "type": "regular"},
            {"name": "shipping_address", "type": "composite", "composite": true}
          ]
        },
        {
          "name": "Product",
          "type": "strong",
          "attributes": [
            {"name": "product_id", "type": "primary_key"},
            {"name": "name", "type": "regular"},
            {"name": "description", "type": "regular"},
            {"name": "price", "type": "regular"},
            {"name": "category_id", "type": "foreign_key"},
            {"name": "stock_quantity", "type": "regular"}
          ]
        },
        {
          "name": "Category",
          "type": "strong",
          "attributes": [
            {"name": "category_id", "type": "primary_key"},
            {"name": "name", "type": "regular"},
            {"name": "description", "type": "regular"},
            {"name": "parent_category_id", "type": "foreign_key"}
          ]
        },
        {
          "name": "OrderItem",
          "type": "weak",
          "attributes": [
            {"name": "order_id", "type": "primary_key"},
            {"name": "product_id", "type": "primary_key"},
            {"name": "quantity", "type": "regular"},
            {"name": "unit_price", "type": "regular"},
            {"name": "discount", "type": "regular"}
          ]
        },
        {
          "name": "Payment",
          "type": "strong",
          "attributes": [
            {"name": "payment_id", "type": "primary_key"},
            {"name": "order_id", "type": "foreign_key"},
            {"name": "payment_method", "type": "regular"},
            {"name": "amount", "type": "regular"},
            {"name": "payment_date", "type": "regular"},
            {"name": "transaction_id", "type": "regular"}
          ]
        },
        {
          "name": "Supplier",
          "type": "strong",
          "attributes": [
            {"name": "supplier_id", "type": "primary_key"},
            {"name": "company_name", "type": "regular"},
            {"name": "contact_person", "type": "regular"},
            {"name": "email", "type": "regular"},
            {"name": "phone", "type": "multivalued", "multivalued": true},
            {"name": "address", "type": "composite", "composite": true}
          ]
        },
        {
          "name": "Review",
          "type": "weak",
          "attributes": [
            {"name": "customer_id", "type": "primary_key"},
            {"name": "product_id", "type": "primary_key"},
            {"name": "rating", "type": "regular"},
            {"name": "comment", "type": "regular"},
            {"name": "review_date", "type": "regular"}
          ]
        }
      ],
      "relationships": [
        {
          "name": "Places",
          "type": "regular",
          "entities": ["Customer", "Order"],
          "cardinalities": {
            "Customer": "1",
            "Order": "N"
          }
        },
        {
          "name": "Contains",
          "type": "identifying",
          "entities": ["Order", "OrderItem"],
          "cardinalities": {
            "Order": "1",
            "OrderItem": "N"
          }
        },
        {
          "name": "Includes",
          "type": "regular",
          "entities": ["OrderItem", "Product"],
          "cardinalities": {
            "OrderItem": "N",
            "Product": "1"
          }
        },
        {
          "name": "BelongsTo",
          "type": "regular",
          "entities": ["Product", "Category"],
          "cardinalities": {
            "Product": "N",
            "Category": "1"
          }
        },
        {
          "name": "ProcessedBy",
          "type": "regular",
          "entities": ["Order", "Payment"],
          "cardinalities": {
            "Order": "1",
            "Payment": "1"
          }
        },
        {
          "name": "Supplies",
          "type": "regular",
          "entities": ["Supplier", "Product"],
          "cardinalities": {
            "Supplier": "N",
            "Product": "M"
          }
        },
        {
          "name": "Writes",
          "type": "weak",
          "entities": ["Customer", "Review"],
          "cardinalities": {
            "Customer": "1",
            "Review": "N"
          }
        },
        {
          "name": "ReviewsProduct",
          "type": "weak",
          "entities": ["Review", "Product"],
          "cardinalities": {
            "Review": "N",
            "Product": "1"
          }
        },
        {
          "name": "Subcategory",
          "type": "regular",
          "entities": ["Category", "Category"],
          "cardinalities": {
            "Category": "1",
            "Category": "N"
          }
        }
      ]
    }

    Returns:
        str: The filepath to the generated PNG image file.
    """
    try:
        if not json_input.strip():
            return "Error: Empty input"
            
        data = json.loads(json_input)
        
        if 'entities' not in data:
            raise ValueError("Missing required field: entities")

        dot = graphviz.Graph(comment='ER Diagram', engine='dot')
        dot.attr(rankdir='TB', bgcolor='white', pad='0.5')
        dot.attr('node', fontname='Arial', fontsize='10', color='black')
        dot.attr('edge', fontname='Arial', fontsize='9', color='black')
        
        entities = data.get('entities', [])
        relationships = data.get('relationships', [])
        
        for entity in entities:
            entity_name = entity.get('name')
            entity_type = entity.get('type', 'strong')
            attributes = entity.get('attributes', [])
            
            if not entity_name:
                continue
            
            label_parts = [entity_name]
            
            if attributes:
                attr_lines = []
                for attr in attributes:
                    attr_name = attr.get('name', '')
                    attr_type = attr.get('type', 'regular')
                    is_multivalued = attr.get('multivalued', False)
                    is_derived = attr.get('derived', False)
                    is_composite = attr.get('composite', False)
                    
                    if attr_type == 'primary_key':
                        if is_multivalued:
                            attr_display = f"PK: {{ {attr_name} }}"
                        else:
                            attr_display = f"PK: {attr_name}"
                    elif attr_type == 'foreign_key':
                        attr_display = f"FK: {attr_name}"
                    else:
                        attr_display = attr_name
                        if is_derived:
                            attr_display = f"/ {attr_display} /"
                        if is_multivalued:
                            attr_display = f"{{ {attr_display} }}"
                        if is_composite:
                            attr_display = f"( {attr_display} )"
                    
                    attr_lines.append(attr_display)
                
                if attr_lines:
                    label_parts.extend(attr_lines)
            
            label = "\\n".join(label_parts)
            
            if entity_type == 'weak':
                style = 'filled'
                fillcolor = '#e8e8e8'
                penwidth = '2'
            else:
                style = 'filled'
                fillcolor = '#d0d0d0'
                penwidth = '1'
            
            dot.node(entity_name, label, shape='box', style=style, fillcolor=fillcolor, penwidth=penwidth)
        
        for relationship in relationships:
            rel_name = relationship.get('name')
            rel_type = relationship.get('type', 'regular')
            entities_involved = relationship.get('entities', [])
            cardinalities = relationship.get('cardinalities', {})
            
            if not rel_name or len(entities_involved) < 2:
                continue
            
            if rel_type == 'identifying':
                style = 'filled'
                fillcolor = '#c0c0c0'
                penwidth = '2'
            else:
                style = 'filled'
                fillcolor = '#c0c0c0'
                penwidth = '1'
            
            dot.node(rel_name, rel_name, shape='diamond', style=style, fillcolor=fillcolor, penwidth=penwidth)
            
            for entity in entities_involved:
                cardinality = cardinalities.get(entity, '1')
                dot.edge(entity, rel_name, label=cardinality)

        with NamedTemporaryFile(delete=False, suffix=f'.{output_format}') as tmp:
            dot.render(tmp.name, format=output_format, cleanup=True)
            return f"{tmp.name}.{output_format}"

    except json.JSONDecodeError:
        return "Error: Invalid JSON format"
    except Exception as e:
        return f"Error: {str(e)}"