from __future__ import annotations

from datetime import datetime
from uuid import UUID

from pydantic import BaseModel, ConfigDict, Field


DATA_FORMAT_VERSION = 1


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

    id: UUID
    title: str = Field(..., min_length=1, max_length=100)
    created_at: datetime
    started_at: datetime | None = None
    done_at: datetime | None = None


class StoragePayloadV1(BaseModel):
    model_config = ConfigDict(extra="forbid")

    version: int = Field(default=DATA_FORMAT_VERSION)
    tasks: list[StoredTask] = Field(default_factory=list)


class StoragePayload(BaseModel):
    """
    Canonical in-memory storage payload.
    This model allows safe parsing of the top-level version field
    before delegating to a concrete versioned schema.
    """

    model_config = ConfigDict(extra="allow")

    version: int


def upgrade_payload(raw_data: dict) -> StoragePayloadV1:
    """
    Upgrade any supported payload version to the latest schema.
    """
    payload = StoragePayload.model_validate(raw_data)

    if payload.version == 1:
        parsed_v1 = StoragePayloadV1.model_validate(raw_data)
        return StoragePayloadV1(
            version=DATA_FORMAT_VERSION,
            tasks=parsed_v1.tasks,
        )

    raise ValueError(
        f"Unsupported storage payload version: {payload.version}. "
        f"Supported versions: 1..{DATA_FORMAT_VERSION}",
    )