"""Top-K retrieval evaluator + scene-change PARTIAL recorder (AZ-423 / FT-P-19).

Two pure-logic helpers feeding AC-8.6 (AZ-423):

* **AC-1 — scale-ratio retrievability**: for each of the 60
  ``still-image-set-60`` images the SUT runs top-K=10 retrieval against
  its tile cache. The AC passes iff EVERY image has at least one
  retrieved tile whose centre lies within 100 m of the image's true
  centre. This is a "set_contains" check — we do NOT care which rank
  the matching tile occupies, only that it appears in the top-K.

* **AC-2 — scene-change subset PARTIAL**: for the 2 paired
  ``_gmaps.png`` reference images the cross-domain matcher runs; the
  helper records the boolean outcome AND tags the subset's overall
  result as ``PARTIAL`` unconditionally — because N=2 is too small to
  yield a meaningful pass/fail statistic, and the traceability matrix
  documents this AC as PARTIAL irrespective of count.

The scenario test pulls per-frame retrieval candidates from the FDR
``retrieval-topk`` record stream and per-image scene-change outcomes
from the cross-domain matcher's FDR record stream; this module only
decides whether the parsed inputs satisfy the AC.

Public-boundary discipline: NO imports from ``src/gps_denied_onboard``.
"""

from __future__ import annotations

import csv
from dataclasses import dataclass
from pathlib import Path
from typing import Iterable, Sequence

from .geo import distance_m

# ─────────────────────── FDR record kinds & schema ───────────────────────

RETRIEVAL_TOPK_FDR_KIND = "retrieval-topk"
SCENE_CHANGE_MATCH_FDR_KIND = "scene-change-match"

TOP_K_REQUIRED = 10
TOP_K_DISTANCE_TOLERANCE_M = 100.0

# Scene-change-pair convention: image `AD<NNNNNN>.jpg` paired with
# `AD<NNNNNN>_gmaps.png`. Only 2 pairs exist in the project's static
# fixture set (`still-image-sat-refs-2`).
SCENE_CHANGE_PAIRED_IMAGE_IDS: tuple[str, ...] = ("AD000001", "AD000002")
SCENE_CHANGE_SUBSET_PARTIAL_LABEL = "PARTIAL"


@dataclass(frozen=True)
class CandidateTile:
    """One top-K candidate the SUT retrieved from its tile cache.

    ``centre_lat_deg`` / ``centre_lon_deg`` is the WGS84 centre of the
    tile's footprint per ``TileMetadata.centre_wgs84``.
    """

    tile_id: str
    centre_lat_deg: float
    centre_lon_deg: float


@dataclass(frozen=True)
class TopKQuery:
    """One image's top-K=10 retrieval result, plus the GT centre.

    The scenario test produces one of these per image; the helper
    decides AC-1 per-image and overall.
    """

    image_id: str
    true_centre_lat_deg: float
    true_centre_lon_deg: float
    candidates: tuple[CandidateTile, ...]


@dataclass(frozen=True)
class TopKImageReport:
    """Per-image AC-1 outcome.

    ``min_distance_m`` is the nearest candidate's distance (m) to the
    true centre; ``None`` when ``candidates`` is empty (the helper
    treats that as failure).
    """

    image_id: str
    candidate_count: int
    min_distance_m: float | None
    pass_distance: bool


@dataclass(frozen=True)
class TopKAggregateReport:
    """AC-1 of FT-P-19: every image's top-K covers the true centre."""

    entries: tuple[TopKImageReport, ...]
    max_distance_m: float
    expected_image_count: int

    @property
    def pass_count(self) -> int:
        return sum(1 for e in self.entries if e.pass_distance)

    @property
    def failing_entries(self) -> tuple[TopKImageReport, ...]:
        return tuple(e for e in self.entries if not e.pass_distance)

    @property
    def passes(self) -> bool:
        if len(self.entries) != self.expected_image_count:
            return False
        return self.pass_count == self.expected_image_count


def evaluate_top_k_within_distance(
    queries: Sequence[TopKQuery],
    *,
    max_distance_m: float = TOP_K_DISTANCE_TOLERANCE_M,
    expected_image_count: int = 60,
) -> TopKAggregateReport:
    """AC-1: every image's top-K must include a tile within ``max_distance_m`` m.

    The helper computes the nearest candidate's Vincenty distance to
    the true centre for each query and decides per-image. The image
    passes iff at least one candidate is within ``max_distance_m``;
    the aggregate passes iff every image passes AND the total query
    count matches ``expected_image_count``.

    Raises ``ValueError`` on ``max_distance_m <= 0``.
    """
    if max_distance_m <= 0:
        raise ValueError(f"max_distance_m must be > 0, got {max_distance_m}")

    entries: list[TopKImageReport] = []
    for q in queries:
        if not q.candidates:
            entries.append(
                TopKImageReport(
                    image_id=q.image_id,
                    candidate_count=0,
                    min_distance_m=None,
                    pass_distance=False,
                )
            )
            continue
        distances = [
            distance_m(
                q.true_centre_lat_deg,
                q.true_centre_lon_deg,
                c.centre_lat_deg,
                c.centre_lon_deg,
            )
            for c in q.candidates
        ]
        min_d = min(distances)
        entries.append(
            TopKImageReport(
                image_id=q.image_id,
                candidate_count=len(q.candidates),
                min_distance_m=min_d,
                pass_distance=min_d <= max_distance_m,
            )
        )
    return TopKAggregateReport(
        entries=tuple(entries),
        max_distance_m=max_distance_m,
        expected_image_count=expected_image_count,
    )


# ─────────────────────── AC-2 scene-change subset ───────────────────────


@dataclass(frozen=True)
class SceneChangeMatch:
    """One paired-image cross-domain matcher outcome."""

    image_id: str  # e.g. "AD000001"; pairs implicitly with `<image_id>_gmaps.png`
    matched: bool
    inlier_count: int | None  # informational; ``None`` when the matcher didn't report it


@dataclass(frozen=True)
class SceneChangeSubsetReport:
    """AC-2 of FT-P-19: scene-change subset is structurally PARTIAL.

    The subset's overall_label is ALWAYS ``PARTIAL`` — even when both
    images match successfully — because N=2 is too small for a
    meaningful pass/fail statistic and the traceability matrix
    documents AC-8.6 as PARTIAL irrespective of outcome count.
    """

    entries: tuple[SceneChangeMatch, ...]
    expected_image_ids: tuple[str, ...] = SCENE_CHANGE_PAIRED_IMAGE_IDS
    overall_label: str = SCENE_CHANGE_SUBSET_PARTIAL_LABEL

    @property
    def matched_count(self) -> int:
        return sum(1 for e in self.entries if e.matched)

    @property
    def coverage_complete(self) -> bool:
        """True iff every expected paired-image id has an entry.

        Coverage is a structural completeness check (did we collect
        results for both AD000001 and AD000002?); it is independent
        of the matcher pass/fail outcome.
        """
        observed = {e.image_id for e in self.entries}
        return observed == set(self.expected_image_ids)


def evaluate_scene_change_subset(
    matches: Sequence[SceneChangeMatch],
    *,
    expected_image_ids: Sequence[str] = SCENE_CHANGE_PAIRED_IMAGE_IDS,
) -> SceneChangeSubsetReport:
    """AC-2: record the paired-image matcher outcomes and emit PARTIAL.

    The result is intentionally lenient on pass/fail count — the PARTIAL
    annotation comes from the spec, not from the data.
    """
    return SceneChangeSubsetReport(
        entries=tuple(matches),
        expected_image_ids=tuple(expected_image_ids),
    )


# ─────────────────────── CSV evidence emission ───────────────────────

TOP_K_CSV_HEADER: tuple[str, ...] = (
    "image_id",
    "candidate_count",
    "min_distance_m",
    "pass_distance",
)
SCENE_CHANGE_CSV_HEADER: tuple[str, ...] = (
    "image_id",
    "matched",
    "inlier_count",
    "subset_label",
)


def write_top_k_csv(path: Path, report: TopKAggregateReport) -> None:
    """Write per-image AC-1 results to ``path`` (CSV, UTF-8, LF newlines).

    Idempotent: overwrites ``path`` if it exists.
    Raises ``OSError`` if the parent directory does not exist.
    """
    with path.open("w", encoding="utf-8", newline="") as fh:
        writer = csv.writer(fh, lineterminator="\n")
        writer.writerow(TOP_K_CSV_HEADER)
        for e in report.entries:
            writer.writerow(
                [
                    e.image_id,
                    e.candidate_count,
                    "" if e.min_distance_m is None else f"{e.min_distance_m:.4f}",
                    "true" if e.pass_distance else "false",
                ]
            )


def write_scene_change_csv(path: Path, report: SceneChangeSubsetReport) -> None:
    """Write paired-image AC-2 results to ``path`` (CSV) with PARTIAL tag.

    Every row carries the subset's ``overall_label`` so a downstream
    consumer can group / filter by it without joining tables.
    """
    with path.open("w", encoding="utf-8", newline="") as fh:
        writer = csv.writer(fh, lineterminator="\n")
        writer.writerow(SCENE_CHANGE_CSV_HEADER)
        for e in report.entries:
            writer.writerow(
                [
                    e.image_id,
                    "true" if e.matched else "false",
                    "" if e.inlier_count is None else e.inlier_count,
                    report.overall_label,
                ]
            )


# ─────────────────────── FDR record projection ───────────────────────


def project_topk_record_to_query(
    payload: object, true_centre_lat_deg: float, true_centre_lon_deg: float
) -> TopKQuery | None:
    """Project one FDR ``retrieval-topk`` payload onto a ``TopKQuery``.

    The payload is expected to carry:

    * ``image_id`` (str)
    * ``candidates`` — list[dict] of {tile_id, centre_lat_deg, centre_lon_deg}

    Returns ``None`` when the payload is malformed (missing fields, wrong
    shape) — the scenario logs the skip and treats it as failure at
    aggregate time.
    """
    if not isinstance(payload, dict):
        return None
    image_id = payload.get("image_id")
    raw_candidates = payload.get("candidates")
    if not isinstance(image_id, str) or not isinstance(raw_candidates, (list, tuple)):
        return None
    candidates: list[CandidateTile] = []
    for c in raw_candidates:
        if not isinstance(c, dict):
            continue
        tile_id = c.get("tile_id")
        lat = c.get("centre_lat_deg")
        lon = c.get("centre_lon_deg")
        if (
            not isinstance(tile_id, str)
            or not isinstance(lat, (int, float))
            or not isinstance(lon, (int, float))
        ):
            continue
        candidates.append(
            CandidateTile(
                tile_id=tile_id,
                centre_lat_deg=float(lat),
                centre_lon_deg=float(lon),
            )
        )
    return TopKQuery(
        image_id=image_id,
        true_centre_lat_deg=true_centre_lat_deg,
        true_centre_lon_deg=true_centre_lon_deg,
        candidates=tuple(candidates),
    )


def project_scene_change_record(payload: object) -> SceneChangeMatch | None:
    """Project one FDR ``scene-change-match`` payload onto a ``SceneChangeMatch``.

    Expected payload shape:

    * ``image_id`` (str)
    * ``matched`` (bool)
    * ``inlier_count`` (int | None) — optional

    Returns ``None`` on malformed input.
    """
    if not isinstance(payload, dict):
        return None
    image_id = payload.get("image_id")
    matched = payload.get("matched")
    if not isinstance(image_id, str) or not isinstance(matched, bool):
        return None
    inlier_raw = payload.get("inlier_count")
    inlier_count: int | None
    if inlier_raw is None:
        inlier_count = None
    elif isinstance(inlier_raw, bool) or not isinstance(inlier_raw, int):
        inlier_count = None
    else:
        inlier_count = inlier_raw
    return SceneChangeMatch(
        image_id=image_id, matched=matched, inlier_count=inlier_count
    )


def iter_topk_payloads(records: Iterable[object]) -> Iterable[object]:
    """Filter an iterable of FDR records, yielding ``retrieval-topk`` payloads."""
    for rec in records:
        rt = getattr(rec, "record_type", None)
        if rt == RETRIEVAL_TOPK_FDR_KIND:
            yield getattr(rec, "payload", None)


def iter_scene_change_payloads(records: Iterable[object]) -> Iterable[object]:
    """Filter an iterable of FDR records, yielding ``scene-change-match`` payloads."""
    for rec in records:
        rt = getattr(rec, "record_type", None)
        if rt == SCENE_CHANGE_MATCH_FDR_KIND:
            yield getattr(rec, "payload", None)