"""The Decision Memo object.

One question per memo. A memo carries the question, the requested act, the
binding level, the brief, a hashed packet, highlights pointing into it, and the
binding slice committing *which scope this act is being entered into*.

`binding.target` is the **act-scope**. It is never derived from the token's
`tenant` claim, which is a membership fact about the principal
(`GH-DEC-2026-013` §5, PR-08).
"""

from __future__ import annotations

import re
from dataclasses import dataclass, field, replace
from enum import Enum

#: approval-engine's digest format. We validate the shape and NEVER compute one.
APPROVAL_DIGEST_RE = re.compile(r"^sha256:[0-9a-f]{64}$")


class BindingLevel(str, Enum):
    ACKNOWLEDGMENT = "acknowledgment"
    ORGANIZATIONAL = "organizational"
    AES = "aes"
    QES = "qes"


class StepKind(str, Enum):
    # Weak — acknowledgment only. `accept` is illegal here on purpose.
    INFORM = "inform"
    COMMENT = "comment"
    REVIEW = "review"
    ACKNOWLEDGE = "acknowledge"
    # Co-sign
    MITZEICHNUNG = "mitzeichnung"
    APPROVE = "approve"
    # Bind
    SCHLUSSZEICHNUNG = "schlusszeichnung"
    SIGN = "sign"
    SEAL = "seal"

    @property
    def is_weak(self) -> bool:
        return self in (StepKind.INFORM, StepKind.COMMENT, StepKind.REVIEW, StepKind.ACKNOWLEDGE)

    @property
    def is_bind(self) -> bool:
        return self in (StepKind.SCHLUSSZEICHNUNG, StepKind.SIGN, StepKind.SEAL)


@dataclass(frozen=True)
class PacketItem:
    """A hashed document in the packet.

    Field names follow ``canonicalize.normalize_packet``, which is the governed
    contract the published vectors depend on — ``item_id``, not ``id``. ``label``
    is UI-only and is deliberately outside the hash: renaming a document does
    not change what was shown.
    """

    item_id: str
    label: str
    hash: str


@dataclass(frozen=True)
class Highlight:
    """A pointer into the packet.

    Highlights are an aid to attention, never a filter. Acknowledging them does
    not narrow what is bound — the whole instrument is bound (PR-12/W-highlights).
    """

    id: str
    item_id: str
    note: str
    required_ack: bool = False
    severity: str = "informational"
    locator: dict = field(default_factory=dict)


@dataclass(frozen=True)
class Identifier:
    scheme: str
    value: str


@dataclass(frozen=True)
class Principal:
    """A party in the binding slice.

    A dataclass rather than a dict because the canonicalizer requires
    ``display_name``, ``id`` and ``kind``, and a missing one is a runtime
    KeyError deep inside hashing rather than a visible defect at construction.
    """

    id: str
    kind: str
    display_name: str
    role: str | None = None
    identifiers: tuple[Identifier, ...] = ()

    def as_document(self) -> dict:
        out: dict = {"display_name": self.display_name, "id": self.id, "kind": self.kind}
        if self.role:
            out["role"] = self.role
        if self.identifiers:
            out["identifiers"] = [
                {"scheme": i.scheme, "value": i.value} for i in self.identifiers
            ]
        return out


@dataclass(frozen=True)
class Scope:
    """The act-scope. What the person is entering, not who they are."""

    kind: str
    id: str
    label: str
    environment: str | None = None
    requires_new_bind: bool = False


@dataclass(frozen=True)
class BindingSlice:
    """Committed and signed. Inside ``view_hash``."""

    principal: Principal
    target: Scope
    terms: str | None = None
    justification: str | None = None


@dataclass(frozen=True)
class Hat:
    """A role. Not a scope — `hats are not scopes` (INTENT invariant)."""

    id: str
    label: str
    elevates: bool = False

    def as_document(self) -> dict:
        return {"id": self.id, "label": self.label, "elevates": self.elevates}


@dataclass(frozen=True)
class Awareness:
    """Shown on the same surface, hashed separately, never signed.

    Typed for the same reason ``Principal`` is: the canonicalizer requires a
    shape, and a malformed one should fail at construction rather than deep
    inside hashing.

    Nothing here enters ``view_hash``. Defaulting a hat to last-used is required
    for situational awareness and forbidden from silently entering the signed
    payload (INTENT principle 11).
    """

    proposed_hat: Hat | None = None
    proposed_hat_source: str | None = None
    available_hats: tuple[Hat, ...] = ()
    situation_note: str | None = None

    def as_document(self) -> dict:
        out: dict = {}
        if self.proposed_hat is not None:
            out["proposed_hat"] = self.proposed_hat.as_document()
        if self.proposed_hat_source is not None:
            out["proposed_hat_source"] = self.proposed_hat_source
        if self.available_hats:
            out["available_hats"] = [h.as_document() for h in self.available_hats]
        if self.situation_note is not None:
            out["situation_note"] = self.situation_note
        return out


@dataclass(frozen=True)
class Memo:
    id: str
    version: int
    question: str
    requested_act: str
    binding_level: BindingLevel
    brief: str
    binding: BindingSlice
    step_kind: StepKind
    packet: tuple[PacketItem, ...] = ()
    highlights: tuple[Highlight, ...] = ()
    locale: str = "en"
    ui_release: str = "informed-decision@0.2.0"
    #: Co-reference to the act this memo presents.
    approval_id: str | None = None
    #: approval-engine's binding.digest over the five act fields, CARRIED here
    #: under GH-DEC-2026-015 (activated 2026-09-10 once approval-engine stated
    #: the presentation exclusion as normative and tested).
    #:
    #: It is referenced, never recomputed: this repository must not restate that
    #: digest from its own vocabulary. When present, the act-scope stops being
    #: independently canonicalized here, so the act has exactly ONE
    #: canonicalization — computed by the layer that owns it.
    approval_binding_digest: str | None = None
    sealed: bool = False

    def __post_init__(self) -> None:
        if not self.question:
            raise ValueError("a memo without a question does not render")
        if self.approval_binding_digest is not None:
            if not APPROVAL_DIGEST_RE.match(self.approval_binding_digest):
                raise ValueError(
                    "approval_binding_digest must be approval-engine's "
                    "sha256:<64 hex> form; it is carried, never computed here"
                )
            if self.approval_id is None:
                raise ValueError(
                    "a carried binding digest needs the approval it belongs to"
                )
        packet_ids = {p.item_id for p in self.packet}
        for h in self.highlights:
            if h.item_id not in packet_ids:
                raise ValueError(f"highlight {h.id} points outside the packet")

    @property
    def required_ack_ids(self) -> frozenset[str]:
        return frozenset(h.id for h in self.highlights if h.required_ack)

    def next_version(self, **changes) -> "Memo":
        """A change creates version n+1. Outstanding presentations die with it."""
        return replace(self, version=self.version + 1, **changes)

    def binding_document(self) -> dict:
        """The document ``view_hash`` is computed over.

        Note what is here and what is not: the packet and highlights are here
        because they were shown; the token's ``tenant`` claim is not, because it
        is not the act-scope.
        """
        return {
            "memo_id": self.id,
            "memo_version": self.version,
            "question": self.question,
            "requested_act": self.requested_act,
            "binding_level": self.binding_level.value,
            "brief": self.brief,
            "locale": self.locale,
            "ui_release": self.ui_release,
            **(
                {"approval_binding_digest": self.approval_binding_digest}
                if self.approval_binding_digest is not None
                else {}
            ),
            "packet": [{"item_id": p.item_id, "hash": p.hash} for p in self.packet],
            "highlights": [
                {
                    "id": h.id,
                    "item_id": h.item_id,
                    "required_ack": h.required_ack,
                    "severity": h.severity,
                    "locator": h.locator,
                }
                for h in self.highlights
            ],
            "binding": self._binding_document(),
        }

    def _binding_document(self) -> dict:
        """The binding slice, minus whatever the carried digest already covers.

        Where ``approval_binding_digest`` is present, the **act-scope** is
        omitted: `target` is act material and is covered by that digest, so
        canonicalizing it again here would be the partial recomputation in a
        second vocabulary that GH-DEC-2026-015 exists to remove.

        ``principal`` is **kept**. approval-engine's `principal` is the party
        *on whose behalf* the approval was issued; ours is the person being
        bound — the approver. Different roles, so dropping ours would remove
        *who was shown this* from `view_hash` and gut the promise this
        repository exists to make. Approval Engine confirmed these distinct
        roles in docs/approval-claim.md (a0a6029); this field remains.
        """
        out: dict = {"principal": self.binding.principal.as_document()}
        if self.approval_binding_digest is None:
            target: dict = {
                "kind": self.binding.target.kind,
                "id": self.binding.target.id,
                "label": self.binding.target.label,
                "requires_new_bind": self.binding.target.requires_new_bind,
            }
            if self.binding.target.environment is not None:
                target["environment"] = self.binding.target.environment
            out["target"] = target
        if self.binding.terms is not None:
            out["terms"] = self.binding.terms
        if self.binding.justification is not None:
            out["justification"] = self.binding.justification
        return out

    def awareness_document(self, awareness: "Awareness | None" = None) -> dict:
        """Shown on the same surface, hashed separately, never signed."""
        doc = {"memo_id": self.id, "memo_version": self.version, "locale": self.locale}
        if awareness is not None:
            doc.update(awareness.as_document())
        return doc