links/invest/models.py

from django.db import models
from django.core.validators import MinValueValidator
from decimal import Decimal


class Portfolio(models.Model):
    """Represents an investment account/portfolio (e.g., 'MOMO', 'User IBKR')."""
    name = models.CharField(max_length=100)
    created_at = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.name

    class Meta:
        ordering = ['name']


class Stock(models.Model):
    """
    Current holdings snapshot for a portfolio.
    Only stores stock_code and quantity - NO price stored.
    Real-time prices fetched from Yahoo Finance on demand.
    """
    portfolio = models.ForeignKey(Portfolio, on_delete=models.CASCADE, related_name='stocks')
    stock_code = models.CharField(max_length=20, help_text="Stock ticker code, e.g., 'NVDA', '9988.HK'")
    quantity = models.DecimalField(
        max_digits=20,
        decimal_places=6,
        default=Decimal('0'),
        validators=[MinValueValidator(Decimal('0'))],
        help_text="Number of shares held"
    )

    class Meta:
        unique_together = [('portfolio', 'stock_code')]
        ordering = ['stock_code']

    def __str__(self):
        return f"{self.stock_code} ({self.portfolio.name})"


class Transaction(models.Model):
    """
    Historical buy/sell transactions.
    Used to calculate avg_cost and derive P/L on demand.
    """
    ACTION_BUY = 'BUY'
    ACTION_SELL = 'SELL'
    ACTION_CHOICES = [(ACTION_BUY, 'Buy'), (ACTION_SELL, 'Sell')]

    portfolio = models.ForeignKey(Portfolio, on_delete=models.CASCADE, related_name='transactions')
    action = models.CharField(max_length=4, choices=ACTION_CHOICES)
    stock_code = models.CharField(max_length=20, help_text="Stock ticker code, e.g., 'NVDA', '9988.HK'")
    quantity = models.DecimalField(
        max_digits=20,
        decimal_places=6,
        validators=[MinValueValidator(Decimal('0.000001'))],
        help_text="Number of shares"
    )
    price_per_share = models.DecimalField(
        max_digits=20,
        decimal_places=6,
        validators=[MinValueValidator(Decimal('0'))],
        help_text="Price per share at time of transaction"
    )
    date = models.DateField()

    created_at = models.DateTimeField(auto_now_add=True)

    class Meta:
        ordering = ['-date', '-created_at']

    def __str__(self):
        return f"{self.action} {self.quantity} {self.stock_code} @ {self.price_per_share} on {self.date}"