"""
Pydantic models for financial document extraction.
Option C: Common core + type-specific extensions.
"""

from pydantic import BaseModel, Field
from typing import Optional, List, Literal
from enum import Enum


class AnomalyCategory(str, Enum):
    """Categories of anomalies the model can detect."""
    ARITHMETIC = "arithmetic_error"
    MISSING_FIELD = "missing_field"
    FORMAT = "format_anomaly"
    BUSINESS_LOGIC = "business_logic"
    CROSS_FIELD = "cross_field"


class Severity(str, Enum):
    """Severity levels for detected anomalies."""
    LOW = "low"
    MEDIUM = "medium"
    HIGH = "high"


class Party(BaseModel):
    """Represents an entity (vendor, buyer, etc.)."""
    name: Optional[str] = None
    address: Optional[str] = None


class CommonFields(BaseModel):
    """Fields shared across all financial document types."""
    document_type: Literal["invoice", "purchase_order", "receipt", "bank_statement"]
    date: Optional[str] = None
    issuer: Optional[Party] = None
    recipient: Optional[Party] = None
    total_amount: Optional[float] = None
    currency: Optional[str] = "USD"


class LineItem(BaseModel):
    """A single line item in a financial document."""
    description: str
    quantity: Optional[float] = None
    unit_price: Optional[float] = None
    amount: Optional[float] = None


# === Type-Specific Extensions ===

class InvoiceFields(BaseModel):
    """Fields specific to invoices."""
    invoice_number: Optional[str] = None
    due_date: Optional[str] = None
    payment_terms: Optional[str] = None
    tax_amount: Optional[float] = None
    subtotal: Optional[float] = None


class PurchaseOrderFields(BaseModel):
    """Fields specific to purchase orders."""
    po_number: Optional[str] = None
    delivery_date: Optional[str] = None
    shipping_address: Optional[str] = None
    referenced_invoice: Optional[str] = None


class ReceiptFields(BaseModel):
    """Fields specific to receipts."""
    receipt_number: Optional[str] = None
    payment_method: Optional[str] = None
    store_location: Optional[str] = None
    cashier: Optional[str] = None


class BankStatementFields(BaseModel):
    """Fields specific to bank statements."""
    account_number: Optional[str] = None
    statement_period: Optional[str] = None
    opening_balance: Optional[float] = None
    closing_balance: Optional[float] = None


class AnomalyFlag(BaseModel):
    """A single anomaly detected in the document."""
    category: AnomalyCategory
    field: str
    severity: Severity
    description: str


class DocumentExtraction(BaseModel):
    """
    Top-level extraction result.
    Schema Option C: Common core + type-specific extensions.
    """
    common: CommonFields
    line_items: Optional[List[LineItem]] = []
    type_specific: dict = {}  # Flexible dict to handle all doc types
    flags: List[AnomalyFlag] = []
    confidence_score: float = Field(ge=0.0, le=1.0, default=0.95)

    def has_anomalies(self) -> bool:
        """Check if any anomalies were detected."""
        return len(self.flags) > 0

    def high_severity_flags(self) -> List[AnomalyFlag]:
        """Return only high-severity anomalies."""
        return [f for f in self.flags if f.severity == Severity.HIGH]