"""Conversion Event detection and Conversion Attestation generation.

TSD §3.5 / PRD FR-7 / G6 / working default Q13: the Conversion Event is a
pure fact about the Manifest + Ledger, never a discretionary declaration.
`is_converted` and `conversion_status` below never require an attestation
document to answer "has this Phase converted?" — the attestation, when
generated, is evidence of an already-true fact, not its cause.
"""

from __future__ import annotations

from dataclasses import dataclass
from typing import Any

from . import fold as fold_module
from . import validation


@dataclass(frozen=True)
class ConversionStatus:
    """Pure, offline-computable conversion status for a Phase."""

    is_converted: bool
    development_credit: float
    remission_credit: float
    outstanding_target: float
    future_license: str


def conversion_status(
    manifest: dict[str, Any], entries: list[dict[str, Any]]
) -> ConversionStatus:
    """Compute conversion status directly from Manifest + Ledger.

    No attestation document is consulted or required. This function is the
    canonical "has this Phase converted" answer for any conformant tool.
    """
    result = fold_module.fold_phase(manifest, entries)
    return ConversionStatus(
        is_converted=result.is_converted,
        development_credit=result.development_credit,
        remission_credit=result.remission_credit,
        outstanding_target=result.outstanding_target,
        future_license=manifest["phase"]["future_license"],
    )


def generate_attestation(
    manifest: dict[str, Any],
    entries: list[dict[str, Any]],
    conversion_timestamp: str,
) -> dict[str, Any]:
    """Build a Conversion Attestation document for an already-converted Phase.

    Raises ValueError if the Phase has not actually converted (Outstanding
    Target > 0) — an attestation must never assert a conversion that hasn't
    happened, and must never be required to make one happen.
    """
    status = conversion_status(manifest, entries)
    if not status.is_converted:
        raise ValueError(
            "cannot generate a Conversion Attestation: Outstanding Target "
            f"is {status.outstanding_target}, not 0"
        )

    last_entry = entries[-1] if entries else None
    checkpoint = last_entry["id"] if last_entry else "GENESIS"

    attestation = {
        "phase": manifest["phase"]["id"],
        "milestone_release": manifest["phase"]["milestone_release"]["name"],
        "conversion_timestamp": conversion_timestamp,
        "future_license": status.future_license,
        "final_development_credit": status.development_credit,
        "final_remission_credit": status.remission_credit,
        "final_outstanding_target": status.outstanding_target,
        "ledger_checkpoint": checkpoint,
    }
    validation.validate_conversion_attestation(attestation)
    return attestation