from __future__ import annotations

from dataclasses import dataclass

from core.models import ChatSession, ConversationEvent, Message


@dataclass
class _ProjectedMessage:
    message_id: str
    ts: int = 0
    text: str = ""
    delivered_ts: int | None = None
    read_ts: int | None = None
    reactions: dict[tuple[str, str, str], dict] | None = None

    def __post_init__(self):
        if self.reactions is None:
            self.reactions = {}


def _safe_int(value, default=0) -> int:
    try:
        return int(value)
    except Exception:
        return int(default)


def _reaction_key(row: dict) -> tuple[str, str, str]:
    item = dict(row or {})
    return (
        str(item.get("source_service") or "").strip().lower(),
        str(item.get("actor") or "").strip(),
        str(item.get("emoji") or "").strip(),
    )


def _normalize_reactions(rows: list[dict] | None) -> list[dict]:
    merged = {}
    for row in list(rows or []):
        item = dict(row or {})
        key = _reaction_key(item)
        if not any(key):
            continue
        merged[key] = {
            "source_service": key[0],
            "actor": key[1],
            "emoji": key[2],
            "removed": bool(item.get("removed")),
        }
    return sorted(
        merged.values(),
        key=lambda entry: (
            str(entry.get("source_service") or ""),
            str(entry.get("actor") or ""),
            str(entry.get("emoji") or ""),
            bool(entry.get("removed")),
        ),
    )


def project_session_from_events(session: ChatSession) -> list[dict]:
    rows = list(
        ConversationEvent.objects.filter(
            user=session.user,
            session=session,
        ).order_by("ts", "created_at")
    )

    projected: dict[str, _ProjectedMessage] = {}
    order: list[str] = []

    for event in rows:
        payload = dict(event.payload or {})
        event_type = str(event.event_type or "").strip().lower()
        message_id = str(
            payload.get("message_id") or payload.get("target_message_id") or ""
        ).strip()

        if event_type == "message_created":
            message_id = str(
                payload.get("message_id") or event.origin_message_id or ""
            ).strip()
            if not message_id:
                continue
            state = projected.get(message_id)
            if state is None:
                state = _ProjectedMessage(message_id=message_id)
                projected[message_id] = state
                order.append(message_id)
            state.ts = _safe_int(payload.get("message_ts"), _safe_int(event.ts))
            state.text = str(payload.get("text") or state.text or "")
            delivered_default = _safe_int(
                payload.get("delivered_ts"), _safe_int(event.ts)
            )
            if state.delivered_ts is None:
                state.delivered_ts = delivered_default or None
            continue

        if not message_id or message_id not in projected:
            continue
        state = projected[message_id]

        if event_type == "read_receipt":
            read_ts = _safe_int(payload.get("read_ts"), _safe_int(event.ts))
            if read_ts > 0:
                if state.read_ts is None:
                    state.read_ts = read_ts
                else:
                    state.read_ts = max(int(state.read_ts or 0), read_ts)
            if state.delivered_ts is None and read_ts > 0:
                state.delivered_ts = read_ts
            continue

        if event_type in {"reaction_added", "reaction_removed"}:
            source_service = (
                str(payload.get("source_service") or event.origin_transport or "")
                .strip()
                .lower()
            )
            actor = str(payload.get("actor") or event.actor_identifier or "").strip()
            emoji = str(payload.get("emoji") or "").strip()
            if not source_service and not actor and not emoji:
                continue
            key = (source_service, actor, emoji)
            state.reactions[key] = {
                "source_service": source_service,
                "actor": actor,
                "emoji": emoji,
                "removed": bool(
                    event_type == "reaction_removed" or payload.get("remove")
                ),
            }

    output = []
    for message_id in order:
        state = projected.get(message_id)
        if state is None:
            continue
        output.append(
            {
                "message_id": str(state.message_id),
                "ts": int(state.ts or 0),
                "text": str(state.text or ""),
                "delivered_ts": (
                    int(state.delivered_ts) if state.delivered_ts is not None else None
                ),
                "read_ts": int(state.read_ts) if state.read_ts is not None else None,
                "reactions": _normalize_reactions(
                    list((state.reactions or {}).values())
                ),
            }
        )
    return output


def shadow_compare_session(session: ChatSession, detail_limit: int = 50) -> dict:
    projected_rows = project_session_from_events(session)
    projected_by_id = {str(row.get("message_id") or ""): row for row in projected_rows}

    db_rows = list(
        Message.objects.filter(user=session.user, session=session)
        .order_by("ts", "id")
        .values(
            "id",
            "ts",
            "text",
            "delivered_ts",
            "read_ts",
            "receipt_payload",
        )
    )
    db_by_id = {str(row.get("id")): dict(row) for row in db_rows}

    counters = {
        "missing_in_projection": 0,
        "missing_in_db": 0,
        "text_mismatch": 0,
        "ts_mismatch": 0,
        "delivered_ts_mismatch": 0,
        "read_ts_mismatch": 0,
        "reactions_mismatch": 0,
    }
    details = []
    cause_counts = {
        "missing_event_write": 0,
        "ambiguous_reaction_target": 0,
        "payload_normalization_gap": 0,
    }
    cause_samples = {key: [] for key in cause_counts.keys()}
    cause_sample_limit = min(5, max(0, int(detail_limit)))

    def _record_detail(
        message_id: str, issue: str, cause: str, extra: dict | None = None
    ):
        if cause in cause_counts:
            cause_counts[cause] += 1
        row = {"message_id": message_id, "issue": issue, "cause": cause}
        if extra:
            row.update(dict(extra))
        if len(details) < max(0, int(detail_limit)):
            details.append(row)
        if cause in cause_samples and len(cause_samples[cause]) < cause_sample_limit:
            cause_samples[cause].append(row)

    for message_id, db_row in db_by_id.items():
        projected = projected_by_id.get(message_id)
        if projected is None:
            counters["missing_in_projection"] += 1
            _record_detail(message_id, "missing_in_projection", "missing_event_write")
            continue

        db_text = str(db_row.get("text") or "")
        projected_text = str(projected.get("text") or "")
        if db_text != projected_text:
            counters["text_mismatch"] += 1
            _record_detail(
                message_id,
                "text_mismatch",
                "payload_normalization_gap",
                {"db": db_text, "projected": projected_text},
            )

        db_ts = _safe_int(db_row.get("ts"), 0)
        projected_ts = _safe_int(projected.get("ts"), 0)
        if db_ts != projected_ts:
            counters["ts_mismatch"] += 1
            _record_detail(
                message_id,
                "ts_mismatch",
                "payload_normalization_gap",
                {"db": db_ts, "projected": projected_ts},
            )

        db_delivered_ts = db_row.get("delivered_ts")
        projected_delivered_ts = projected.get("delivered_ts")
        if (db_delivered_ts is None) != (projected_delivered_ts is None) or (
            db_delivered_ts is not None
            and projected_delivered_ts is not None
            and int(db_delivered_ts) != int(projected_delivered_ts)
        ):
            counters["delivered_ts_mismatch"] += 1
            _record_detail(
                message_id,
                "delivered_ts_mismatch",
                "payload_normalization_gap",
                {
                    "db": db_delivered_ts,
                    "projected": projected_delivered_ts,
                },
            )

        db_read_ts = db_row.get("read_ts")
        projected_read_ts = projected.get("read_ts")
        if (db_read_ts is None) != (projected_read_ts is None) or (
            db_read_ts is not None
            and projected_read_ts is not None
            and int(db_read_ts) != int(projected_read_ts)
        ):
            counters["read_ts_mismatch"] += 1
            _record_detail(
                message_id,
                "read_ts_mismatch",
                "payload_normalization_gap",
                {"db": db_read_ts, "projected": projected_read_ts},
            )

        db_reactions = _normalize_reactions(
            list((db_row.get("receipt_payload") or {}).get("reactions") or [])
        )
        projected_reactions = _normalize_reactions(
            list(projected.get("reactions") or [])
        )
        if db_reactions != projected_reactions:
            counters["reactions_mismatch"] += 1
            cause = "payload_normalization_gap"
            strategy = str(
                (
                    (db_row.get("receipt_payload") or {}).get(
                        "reaction_last_match_strategy"
                    )
                    or ""
                )
            ).strip()
            if strategy == "nearest_ts_window":
                cause = "ambiguous_reaction_target"
            _record_detail(
                message_id,
                "reactions_mismatch",
                cause,
                {"db": db_reactions, "projected": projected_reactions},
            )

    for message_id in projected_by_id.keys():
        if message_id not in db_by_id:
            counters["missing_in_db"] += 1
            _record_detail(message_id, "missing_in_db", "payload_normalization_gap")

    mismatch_total = int(sum(int(value or 0) for value in counters.values()))
    return {
        "session_id": str(session.id),
        "db_message_count": len(db_rows),
        "projected_message_count": len(projected_rows),
        "mismatch_total": mismatch_total,
        "counters": counters,
        "cause_counts": cause_counts,
        "cause_samples": cause_samples,
        "details": details,
    }