/**
 * Nearest divisional-chart change, from window-scan transitions only.
 * Question order is a switch and stays off unless the env flag is "on".
 */

export const CHART_LAYERS = ["d9", "d10", "d4", "d5", "d24", "d7", "d12", "d2", "d11", "d30", "d1"] as const;

const LAYER_DOMAIN: Readonly<Record<string, string>> = {
  d9: "relationship",
  d10: "career",
  d4: "relocation",
  d5: "education",
  d24: "education",
  d7: "family",
  d12: "family",
  d2: "finance",
  d11: "finance",
  d30: "health_pressure",
};

const LAYER_TOPIC: Readonly<Record<string, string>> = {
  d9: "婚恋",
  d10: "工作",
  d4: "住处",
  d5: "学业",
  d24: "学业",
  d7: "子女",
  d12: "父母",
  d2: "钱",
  d11: "钱",
  d30: "身体",
};

/** Not adopted. The 77-case gate was not cleared, so the switch stays off. */
export const NEAREST_BOUNDARY_PROBE_THRESHOLD_MINUTES = 5;

export type BoundaryLayer = Readonly<{
  layer: string;
  fromSign: string;
  toSign: string;
  topic: string | null;
  domain: string | null;
}>;

export type NearestBoundary = Readonly<{
  found: boolean;
  reason: "unavailable" | "no_transition" | null;
  at: string | null;
  distanceMinutes: number | null;
  layers: readonly BoundaryLayer[];
  topics: readonly string[];
  domains: readonly string[];
}>;

const EMPTY: NearestBoundary = {
  found: false, reason: "unavailable", at: null, distanceMinutes: null, layers: [], topics: [], domains: [],
};

function clock(value: string | null | undefined): number | null {
  const raw = value?.trim().slice(0, 5) ?? "";
  if (!/^(?:[01]\d|2[0-3]):[0-5]\d$/.test(raw)) return null;
  return Number(raw.slice(0, 2)) * 60 + Number(raw.slice(3, 5));
}

function distance(left: number, right: number): number {
  const span = Math.abs(left - right);
  return Math.min(span, 1440 - span);
}

export function nearestBoundaryFromTransitions(
  transitions: readonly Readonly<{ layer?: string; at?: string; from_sign?: string; to_sign?: string }>[] | null | undefined,
  recordedTime: string | null | undefined,
): NearestBoundary {
  const recorded = clock(recordedTime);
  if (recorded === null || !transitions) return EMPTY;
  const changes: { at: number; layer: string; fromSign: string; toSign: string }[] = [];
  for (const row of transitions) {
    const layer = row.layer ?? "";
    if (!CHART_LAYERS.includes(layer as (typeof CHART_LAYERS)[number])) continue;
    const before = row.from_sign;
    const after = row.to_sign;
    if (!before || !after || before === after) continue;
    const at = clock(row.at);
    if (at === null) continue;
    changes.push({ at, layer, fromSign: before, toSign: after });
  }
  if (!changes.length) return { ...EMPTY, reason: "no_transition" };
  const bestAt = changes.reduce((best, row) => {
    const next = distance(row.at, recorded);
    const current = distance(best, recorded);
    return next < current || (next === current && row.at < best) ? row.at : best;
  }, changes[0]!.at);
  const layers: BoundaryLayer[] = [];
  const seen = new Set<string>();
  for (const layer of CHART_LAYERS) {
    const row = changes.find((item) => item.at === bestAt && item.layer === layer);
    if (!row || seen.has(layer)) continue;
    seen.add(layer);
    layers.push({
      layer,
      fromSign: row.fromSign,
      toSign: row.toSign,
      topic: LAYER_TOPIC[layer] ?? null,
      domain: LAYER_DOMAIN[layer] ?? null,
    });
  }
  const topics = topicsForLayers(layers.map((row) => row.layer));
  const domains: string[] = [];
  for (const row of layers) {
    if (row.domain && !domains.includes(row.domain)) domains.push(row.domain);
  }
  return {
    found: true,
    reason: null,
    at: `${String(Math.floor(bestAt / 60)).padStart(2, "0")}:${String(bestAt % 60).padStart(2, "0")}`,
    distanceMinutes: distance(bestAt, recorded),
    layers,
    topics,
    domains,
  };
}

/** Spoken topics, in chart order. Unknown layers and D1 add nothing. */
export function topicsForLayers(layers: readonly string[]): string[] {
  const topics: string[] = [];
  for (const layer of CHART_LAYERS) {
    if (!layers.includes(layer)) continue;
    const topic = LAYER_TOPIC[layer];
    if (topic && !topics.includes(topic)) topics.push(topic);
  }
  return topics;
}

export function nearestBoundaryProbesEnabled(flag: string | undefined = process.env.RECTIFICATION_NEAREST_BOUNDARY_PROBES): boolean {
  return flag === "on";
}

/** Boundary-domain questions first; everything else keeps its incoming order. */
export function orderByBoundaryDomains<T>(
  probes: readonly T[],
  domains: readonly string[],
  domainOf: (probe: T) => string,
): readonly T[] {
  if (!domains.length || probes.length < 2) return probes;
  const wanted = new Set(domains);
  const first: T[] = [];
  const rest: T[] = [];
  for (const probe of probes) {
    const domain = domainOf(probe);
    (domain && wanted.has(domain) ? first : rest).push(probe);
  }
  if (!first.length || !rest.length) return probes;
  return [...first, ...rest];
}