/**
 * earth-now.co
 * Author:  Simon-Pierre Boucher
 * Contact: contact@spboucher.ai
 * File:    apps/ingest/src/sources/usgs.ts
 * Purpose: USGS FDSN event service — count endpoint fetcher and pure GeoJSON parsers (event-driven, no interpolation)
 */

import { type FetchLike, defaultFetch } from "../fetch-like.js";

export const USGS_FDSN_BASE = "https://earthquake.usgs.gov/fdsnws/event/1";

/** Build the count-endpoint URL for the trailing window. nowMs is a parameter so tests stay deterministic. */
export function usgsCountUrl(
  windowHours: number,
  minMagnitude: number,
  nowMs: number = Date.now(),
): string {
  const start = new Date(nowMs - windowHours * 3_600_000).toISOString();
  return (
    `${USGS_FDSN_BASE}/count?format=geojson` +
    `&starttime=${encodeURIComponent(start)}&minmagnitude=${minMagnitude}`
  );
}

/**
 * Pure parser for the count endpoint payload: { count: n, maxAllowed: m }.
 * Throws a descriptive error on anything malformed.
 */
export function parseUsgsCount(json: unknown): number {
  if (typeof json !== "object" || json === null)
    throw new Error("USGS count parse error: payload is not an object");
  const count = (json as { count?: unknown }).count;
  if (typeof count !== "number" || !Number.isInteger(count) || count < 0)
    throw new Error(
      `USGS count parse error: 'count' must be a non-negative integer, got ${JSON.stringify(count)}`,
    );
  return count;
}

export interface UsgsLastMajor {
  mag: number;
  place: string;
  timeIso: string;
}

/**
 * Pure parser for the query endpoint (orderby=time&limit=1): features[0] → last major quake.
 * Throws a descriptive error on malformed GeoJSON.
 */
export function parseUsgsLastMajor(geojson: unknown): UsgsLastMajor {
  if (typeof geojson !== "object" || geojson === null)
    throw new Error("USGS query parse error: payload is not an object");
  const features = (geojson as { features?: unknown }).features;
  if (!Array.isArray(features) || features.length === 0)
    throw new Error("USGS query parse error: 'features' is missing or empty");
  const first = features[0] as { properties?: unknown };
  if (typeof first !== "object" || first === null || typeof first.properties !== "object" || first.properties === null)
    throw new Error("USGS query parse error: features[0].properties is missing");
  const props = first.properties as { mag?: unknown; place?: unknown; time?: unknown };
  if (typeof props.mag !== "number" || !Number.isFinite(props.mag))
    throw new Error("USGS query parse error: features[0].properties.mag is not a finite number");
  if (typeof props.place !== "string" || props.place.length === 0)
    throw new Error("USGS query parse error: features[0].properties.place is not a string");
  if (typeof props.time !== "number" || !Number.isFinite(props.time))
    throw new Error(
      "USGS query parse error: features[0].properties.time is not a millisecond timestamp",
    );
  return { mag: props.mag, place: props.place, timeIso: new Date(props.time).toISOString() };
}

/** Fetch the earthquake count for the trailing window (M >= minMagnitude). Inject fetchImpl in tests. */
export async function fetchUsgsQuakeCount(
  windowHours: number,
  minMagnitude: number,
  fetchImpl: FetchLike = defaultFetch,
): Promise<number> {
  const url = usgsCountUrl(windowHours, minMagnitude);
  const res = await fetchImpl(url);
  if (!res.ok) throw new Error(`USGS count fetch failed: HTTP ${res.status} for ${url}`);
  const text = await res.text();
  let json: unknown;
  try {
    json = JSON.parse(text);
  } catch {
    throw new Error("USGS count fetch failed: response is not valid JSON");
  }
  return parseUsgsCount(json);
}