"""Typed Pydantic IR for a candidate cost-saving measure (B1).

Pure module — **no** ``agent_framework`` and no solver. The two structural invariants
(non-negative quantities; a claimed saving may not exceed the affected items' own total)
are enforced at construction by Pydantic, so a malformed proposal can never be built. This
IR is the D7-portable contract both the deterministic validator and the LLM->IR generator
speak.
"""

from __future__ import annotations

from pydantic import BaseModel, Field, model_validator


class AffectedItem(BaseModel):
    """One project cost line a proposal claims to save against."""

    code: str
    quantity: float = Field(ge=0)  # quantities must be >= 0
    unit_cost: float = Field(gt=0)

    @property
    def total(self) -> float:
        return self.quantity * self.unit_cost


class SavingsProposal(BaseModel):
    """Typed IR for a candidate cost-saving measure (B1)."""

    project_id: str
    measure: str
    affected_items: list[AffectedItem] = Field(min_length=1)
    claimed_saving_nok: float = Field(gt=0)
    # code -> (low_unit_cost, high_unit_cost) for the Monte Carlo step; empty = degenerate.
    assumptions: dict[str, tuple[float, float]] = Field(default_factory=dict)

    @model_validator(mode="after")
    def _claim_within_affected_total(self) -> SavingsProposal:
        total = sum(item.total for item in self.affected_items)
        if self.claimed_saving_nok > total:
            raise ValueError(
                f"claimed saving {self.claimed_saving_nok} exceeds affected items' total {total}"
            )
        return self