export const operationsSyncPriority = { screen: 1, history: 2 } as const;

const LAST_INTERVAL_INDEX = -1;
const NEXT_MONTH_OFFSET = 1;
const FIRST_DAY_OF_MONTH = 1;
const EMPTY_INTERVAL_COUNT = 0;
const EMPTY_SOURCE_COUNT = 0;

export type OperationInterval = {
  accountId: string;
  from: Date;
  instrumentUid?: string;
  to: Date;
};

// Normalize duplicate/overlapping targets before creating a durable identity.
// Calendar windows keep each provider walk bounded without changing [from,to).
export function operationIntervals(
  requested: OperationInterval[],
): OperationInterval[] {
  const groups = new Map<string, OperationInterval[]>();
  for (const interval of requested) {
    // eslint-disable-next-line sonarjs/no-inverted-boolean-check -- Negation also rejects Invalid Date; >= would silently accept NaN.
    if (!(interval.from < interval.to)) {
      throw new Error('Invalid operations interval');
    }
    const key = JSON.stringify([
      interval.accountId,
      interval.instrumentUid ?? '',
    ]);
    const group = groups.get(key) ?? [];
    group.push(interval);
    groups.set(key, group);
  }
  const result: OperationInterval[] = [];
  // eslint-disable-next-line sonarjs/no-alphabetical-sort -- Code-unit ordering is intentional for canonical keys and ISO dates; locale collation would change persisted bindings.
  for (const key of [...groups.keys()].sort()) {
    const merged: OperationInterval[] = [];
    for (const interval of (groups.get(key) ?? []).sort(
      (left, right) => left.from.valueOf() - right.from.valueOf(),
    )) {
      const previous = merged.at(LAST_INTERVAL_INDEX);
      if (previous && interval.from <= previous.to) {
        previous.to = new Date(
          Math.max(previous.to.valueOf(), interval.to.valueOf()),
        );
      } else merged.push({ ...interval });
    }
    for (const interval of merged) {
      let from = interval.from;
      while (from < interval.to) {
        const nextMonth = new Date(
          Date.UTC(from.getUTCFullYear(), from.getUTCMonth() + NEXT_MONTH_OFFSET, FIRST_DAY_OF_MONTH),
        );
        const to = new Date(
          Math.min(nextMonth.valueOf(), interval.to.valueOf()),
        );
        result.push({ ...interval, from, to });
        from = to;
      }
    }
  }
  return result;
}

export function operationIntervalsOverlap(
  left: OperationInterval,
  right: OperationInterval,
): boolean {
  return (
    left.accountId === right.accountId &&
    (!left.instrumentUid ||
      !right.instrumentUid ||
      left.instrumentUid === right.instrumentUid) &&
      left.from < right.to &&
      right.from < left.to
  );
}

export function uncoveredOperationIntervals(
  requested: OperationInterval[],
  existing: OperationInterval[],
): OperationInterval[] {
  return requested.flatMap((interval) => {
    let fragments = [interval];
    for (const covered of existing) {
      fragments = fragments.flatMap((fragment) => {
        if (
          !operationIntervalsOverlap(fragment, covered) ||
          (covered.instrumentUid &&
            covered.instrumentUid !== fragment.instrumentUid)
        ) {
          return [fragment];
        }
        return [
          ...(fragment.from < covered.from
            ? [{ ...fragment, to: covered.from }]
            : []),
          ...(covered.to < fragment.to
            ? [{ ...fragment, from: covered.to }]
            : []),
        ];
      });
    }
    return fragments;
  });
}

export function confirmedOperationRanges(
  targets: OperationInterval[],
  coverage: OperationInterval[],
): Omit<OperationInterval, 'instrumentUid'>[] {
  return targets.flatMap((target) => coverage
    .filter((row) =>
      row.accountId === target.accountId &&
      (!row.instrumentUid || row.instrumentUid === target.instrumentUid) &&
      row.from < target.to && target.from < row.to,
    )
    .map((row) => ({
      accountId: target.accountId,
      from: new Date(Math.max(row.from.valueOf(), target.from.valueOf())),
      to: new Date(Math.min(row.to.valueOf(), target.to.valueOf())),
    })),
  );
}

export type OperationCoverage = OperationInterval & {
  asOf: Date;
  fetchedAt: Date;
};
const operationsFreshForMs = 3_600_000;

export function planOperationRead(
  requested: OperationInterval[],
  coverage: OperationCoverage[],
  now: Date,
  options: { force?: boolean; movingEnd?: boolean } = {},
) {
  const monthStart = new Date(
    Date.UTC(now.getUTCFullYear(), now.getUTCMonth(), FIRST_DAY_OF_MONTH),
  );
  const observedEnd = Math.max(
    ...requested.map((interval) => interval.to.valueOf()),
  );
  const load: OperationInterval[] = [];
  const intervals = operationIntervals(requested).map((target) => {
    const sources = coverage.filter(
      (row) =>
        row.accountId === target.accountId &&
        (!row.instrumentUid || row.instrumentUid === target.instrumentUid) &&
        row.from < target.to &&
        target.from < row.to,
    );
    const ranges = sources.map((row) => ({
      ...row,
      instrumentUid: target.instrumentUid,
    }));
    const current = target.from >= monthStart && target.to <= now;
    const fresh = sources.filter(
      (row) => now.valueOf() - row.fetchedAt.valueOf() < operationsFreshForMs,
    );
    let effective = target;
    if (options.movingEnd && target.to.valueOf() === observedEnd) {
      const latest = sources
        .filter(
          (row) =>
            row.asOf.valueOf() === row.to.valueOf() && row.to > target.from,
        )
        .sort((left, right) => right.to.valueOf() - left.to.valueOf())[0];
      if (latest && latest.to < target.to) {
        effective = { ...target, to: latest.to };
      }
    }
    const missing = uncoveredOperationIntervals([effective], ranges);
    const complete = missing.length === EMPTY_INTERVAL_COUNT;
    const stale =
      current &&
      sources.length > EMPTY_SOURCE_COUNT &&
      uncoveredOperationIntervals(
        ranges
          .map((row) => ({
            ...target,
            from: new Date(
              Math.max(effective.from.valueOf(), row.from.valueOf()),
            ),
            to: new Date(Math.min(effective.to.valueOf(), row.to.valueOf())),
          }))
          .filter((row) => row.from < row.to),
        fresh.map((row) => ({ ...row, instrumentUid: target.instrumentUid })),
      ).length > EMPTY_INTERVAL_COUNT;
    // The mutable tail is owned by the hourly walk; reads only load what is
    // missing, never re-verify complete or fresh intervals.
    if (options.force) load.push(target);
    else load.push(...missing);
    // Completeness is bounded by the observed end, never by the new wall clock.
    return {
      ...effective,
      availability: complete
        ? ('complete' as const)
        : sources.length
          ? ('partial' as const)
          : ('missing' as const),
      stale,
      asOf: sources.length
        ? new Date(
            Math.min(
              effective.to.valueOf(),
              Math.max(...sources.map((row) => row.asOf.valueOf())),
            ),
          )
        : null,
    };
  });
  return { intervals, load: operationIntervals(load) };
}