"""Transition Reasoning v0 (RS-005) — the Transition Planning Engine.

`assess_transition(context, target_requirements, company_profile)`: computes, per
required capability, the coverage from the company's „have" state (Phase 2A), and
emits a ranked list of `TransitionQuestionRequest` (information gaps) — NOT questions.

Deterministic; nothing is stored. A certification-derived „probably covered" is Welt 1
(a hint), so it produces a confirmation request, never „erfüllt". Python 3.9 compatible.
"""

from __future__ import annotations

from typing import Dict, List, Optional

from compliance.company import CompanyCapabilityProfile, VerificationStatus

from .schemas import (
    CapabilityCoverage,
    CoverageStatus,
    InformationGain,
    RequestPriority,
    TargetRequirement,
    TransitionAssessment,
    TransitionContext,
    TransitionQuestionRequest,
    TransitionSummary,
)

EMPTY_REQUIREMENTS: List[TargetRequirement] = []

_STATUS_RANK = {  # strongest „have" signal wins when a capability appears twice
    VerificationStatus.CONFIRMED: 3,
    VerificationStatus.INFERRED: 2,
    VerificationStatus.DECLARED: 1,
    VerificationStatus.UNKNOWN: 0,
}


def _have(profile: CompanyCapabilityProfile) -> Dict[str, VerificationStatus]:
    out: Dict[str, VerificationStatus] = {}
    for oc in profile.confirmed_capabilities:
        out[oc.capability_id] = VerificationStatus.CONFIRMED
    for c in profile.candidate_capabilities:
        cur = out.get(c.capability_id)
        if cur is None or _STATUS_RANK[c.verification_status] > _STATUS_RANK[cur]:
            out[c.capability_id] = c.verification_status
    return out


def _classify(req: TargetRequirement, have: Dict[str, VerificationStatus]) -> CoverageStatus:
    if req.unsupported:
        return CoverageStatus.UNSUPPORTED
    status = have.get(req.capability_id)
    if status == VerificationStatus.CONFIRMED:
        return CoverageStatus.ALREADY_COVERED
    if status == VerificationStatus.INFERRED:
        return CoverageStatus.PROBABLY_COVERED
    if status == VerificationStatus.DECLARED:
        return CoverageStatus.NEEDS_CONFIRMATION
    return CoverageStatus.MISSING


# coverage -> (request?, reason, base priority)
_REQUESTABLE = {
    CoverageStatus.PROBABLY_COVERED: ("Vermutlich vorhanden (aus Zertifizierung) — mit Nachweis bestätigen.", RequestPriority.MEDIUM),
    CoverageStatus.NEEDS_CONFIRMATION: ("Selbst angegeben — Nachweis steht aus.", RequestPriority.MEDIUM),
    CoverageStatus.MISSING: ("Keine Anhaltspunkte im Unternehmensprofil — klären.", RequestPriority.HIGH),
}


def _gain(coverage: CoverageStatus, n_obligations: int) -> InformationGain:
    base = InformationGain.HIGH if coverage == CoverageStatus.MISSING else (
        InformationGain.MEDIUM if coverage == CoverageStatus.NEEDS_CONFIRMATION else InformationGain.LOW
    )
    if n_obligations >= 2 and base != InformationGain.HIGH:  # more dependent obligations -> bump
        return InformationGain.HIGH if base == InformationGain.MEDIUM else InformationGain.MEDIUM
    return base


_PRIO_ORDER = {RequestPriority.HIGH: 0, RequestPriority.MEDIUM: 1, RequestPriority.LOW: 2}
_GAIN_ORDER = {InformationGain.HIGH: 0, InformationGain.MEDIUM: 1, InformationGain.LOW: 2}


def assess_transition(
    context: TransitionContext,
    target_requirements: Optional[List[TargetRequirement]] = None,
    company_profile: Optional[CompanyCapabilityProfile] = None,
) -> TransitionAssessment:
    reqs = EMPTY_REQUIREMENTS if target_requirements is None else target_requirements
    have = _have(company_profile) if company_profile is not None else {}

    coverage: List[CapabilityCoverage] = []
    requests: List[TransitionQuestionRequest] = []
    buckets: Dict[CoverageStatus, List[str]] = {s: [] for s in CoverageStatus}

    for req in reqs:
        status = _classify(req, have)
        coverage.append(
            CapabilityCoverage(
                capability_id=req.capability_id,
                status=status,
                have_status=have[req.capability_id].value if req.capability_id in have else None,
            )
        )
        buckets[status].append(req.capability_id)
        if status in _REQUESTABLE:
            reason, prio = _REQUESTABLE[status]
            requests.append(
                TransitionQuestionRequest(
                    capability_id=req.capability_id,
                    control_id=req.source_control_id,
                    reason=reason,
                    question_intent=req.question_intent,
                    expected_evidence=req.expected_evidence,
                    priority=prio,
                    information_gain=_gain(status, len(req.supports_obligations)),
                )
            )

    requests.sort(key=lambda r: (_PRIO_ORDER[r.priority], _GAIN_ORDER[r.information_gain], r.capability_id))

    summary = TransitionSummary(
        headline=(
            "%d zu klären, %d bereits abgedeckt, %d vermutlich vorhanden, %d fehlt, %d n/a, %d nicht im Korpus."
            % (len(requests), len(buckets[CoverageStatus.ALREADY_COVERED]),
               len(buckets[CoverageStatus.PROBABLY_COVERED]), len(buckets[CoverageStatus.MISSING]),
               len(buckets[CoverageStatus.NOT_APPLICABLE]), len(buckets[CoverageStatus.UNSUPPORTED]))
        ),
        what_to_clarify=[r.capability_id for r in requests],
        already_covered=buckets[CoverageStatus.ALREADY_COVERED],
        probably_covered=buckets[CoverageStatus.PROBABLY_COVERED],
        missing=buckets[CoverageStatus.MISSING],
        not_applicable=buckets[CoverageStatus.NOT_APPLICABLE],
        unsupported=buckets[CoverageStatus.UNSUPPORTED],
    )
    return TransitionAssessment(
        target_id=context.target.target_id, coverage=coverage, question_requests=requests, summary=summary
    )