"""Shared immutable Task contract reference used by progress and candidates."""

from __future__ import annotations

from typing import Literal

from pydantic import BaseModel, ConfigDict, Field, model_validator


class TaskContractRef(BaseModel):
    model_config = ConfigDict(
        extra="forbid",
        frozen=True,
        str_strip_whitespace=True,
    )

    kind: Literal["root_task_anchor", "task_brief"]
    root_task_anchor_hash: str | None = Field(
        default=None,
        pattern=r"^[0-9a-f]{64}$",
    )
    task_brief_version: int | None = Field(default=None, ge=1)
    task_brief_hash: str | None = Field(default=None, pattern=r"^[0-9a-f]{64}$")

    @model_validator(mode="after")
    def validate_kind_fields(self) -> "TaskContractRef":
        if self.kind == "root_task_anchor":
            if not self.root_task_anchor_hash:
                raise ValueError("root_task_anchor requires root_task_anchor_hash")
            if self.task_brief_version is not None or self.task_brief_hash is not None:
                raise ValueError("root_task_anchor does not accept TaskBrief fields")
        else:
            if self.task_brief_version is None or not self.task_brief_hash:
                raise ValueError("task_brief requires version and hash")
            if self.root_task_anchor_hash is not None:
                raise ValueError("task_brief does not accept root_task_anchor_hash")
        return self