Volatility-Auction Reopening

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export type JsonObject = Record<string, any>;

function num(name: string, value: unknown, positive = false, nonnegative = false): number {
  if (typeof value !== "number" || !Number.isFinite(value)) throw new TypeError(`${name} must be a finite number`);
  if (positive && value <= 0) throw new RangeError(`${name} must be positive`);
  if (nonnegative && value < 0) throw new RangeError(`${name} must be nonnegative`);
  return value;
}
function integer(name: string, value: unknown, nonnegative = false): number {
  const result = num(name, value);
  if (!Number.isInteger(result)) throw new RangeError(`${name} must be an integer`);
  if (nonnegative && result < 0) throw new RangeError(`${name} must be nonnegative`);
  return result;
}
function text(name: string, value: unknown): string {
  if (typeof value !== "string" || !value.trim()) throw new TypeError(`${name} must be a non-empty string`);
  return value;
}
function onTick(value: number, tick: number): boolean {
  return Math.abs(value / tick - Math.round(value / tick)) <= 1e-8;
}
function parseOrders(raw: unknown, tick: number): JsonObject[] {
  if (!Array.isArray(raw) || raw.length === 0) throw new RangeError("orders must be a non-empty list");
  const ids = new Set<string>(), sequences = new Set<number>();
  return raw.map((item, index) => {
    if (!item || typeof item !== "object") throw new TypeError(`orders[${index}] must be an object`);
    const order = item as JsonObject, orderId = text(`orders[${index}].order_id`, order.order_id);
    if (ids.has(orderId)) throw new RangeError("order_id values must be unique"); ids.add(orderId);
    const side = text(`orders[${index}].side`, order.side);
    if (!["buy", "sell"].includes(side)) throw new RangeError("order side must be buy or sell");
    const orderType = text(`orders[${index}].order_type`, order.order_type);
    const sequence = integer(`orders[${index}].arrival_sequence`, order.arrival_sequence, true);
    if (sequences.has(sequence)) throw new RangeError("arrival_sequence values must be unique"); sequences.add(sequence);
    const quantity = num(`orders[${index}].quantity`, order.quantity, true);
    let price: number | null = null;
    if (["market", "MOO", "MOC"].includes(orderType)) {
      if (order.price != null) throw new RangeError("market-style auction orders must not carry a price");
    } else if (["limit", "LOO", "LOC", "DAY"].includes(orderType)) {
      price = num(`orders[${index}].price`, order.price, true);
      if (!onTick(price, tick)) throw new RangeError("order price must align with tick_size");
    } else throw new RangeError(`unsupported auction order_type: ${orderType}`);
    return {order_id: orderId, side, order_type: orderType, price, quantity, arrival_sequence: sequence};
  });
}
function evaluationAt(price: number, orders: JsonObject[]): JsonObject {
  const buy = orders.filter(order => order.side === "buy" && (order.price == null || order.price >= price)).reduce((sum, order) => sum + order.quantity, 0);
  const sell = orders.filter(order => order.side === "sell" && (order.price == null || order.price <= price)).reduce((sum, order) => sum + order.quantity, 0);
  const executable = Math.min(buy, sell), imbalance = buy - sell;
  return {price, buy_quantity: buy, sell_quantity: sell, executable_quantity: executable, imbalance_quantity: imbalance, absolute_imbalance: Math.abs(imbalance), imbalance_side: imbalance > 0 ? "buy" : imbalance < 0 ? "sell" : "none"};
}
function evaluateBook(ordersRaw: unknown, referenceRaw: unknown, tickRaw: unknown, low: number | null = null, high: number | null = null): [JsonObject[], number, number, JsonObject[]] {
  const reference = num("reference_price", referenceRaw, true), tick = num("tick_size", tickRaw, true);
  if (!onTick(reference, tick)) throw new RangeError("reference_price must align with tick_size");
  const orders = parseOrders(ordersRaw, tick), priceSet = new Set<number>([reference]);
  orders.forEach(order => { if (order.price != null) priceSet.add(order.price); });
  const candidates = [...priceSet].filter(price => (low == null || price >= low - 1e-12) && (high == null || price <= high + 1e-12)).sort((a, b) => a - b);
  if (!candidates.length) throw new RangeError("no candidate price remains inside the declared collar");
  return [orders, reference, tick, candidates.map(price => evaluationAt(price, orders))];
}

export function maximumExecutableVolumeAuction(ordersRaw: unknown, referenceRaw: unknown, tickRaw: unknown): JsonObject {
  const [orders, reference, tick, evaluations] = evaluateBook(ordersRaw, referenceRaw, tickRaw);
  const maximum = Math.max(...evaluations.map(row => row.executable_quantity)), winners = evaluations.filter(row => row.executable_quantity === maximum);
  return {model: "maximum-executable-volume-candidate-set", reference_price: reference, tick_size: tick, order_count: orders.length, maximum_executable_quantity: maximum, maximum_volume_prices: winners.map(row => row.price), unique_price: winners.length === 1 ? winners[0].price : null, candidate_evaluations: evaluations, state: maximum === 0 ? "no-cross" : winners.length === 1 ? "unique-maximum" : "maximum-volume-tie"};
}

export function minimumImbalanceTieBreak(ordersRaw: unknown, referenceRaw: unknown, tickRaw: unknown): JsonObject {
  const [orders, reference, tick, evaluations] = evaluateBook(ordersRaw, referenceRaw, tickRaw);
  const maximum = Math.max(...evaluations.map(row => row.executable_quantity));
  const volumeWinners = evaluations.filter(row => row.executable_quantity === maximum);
  const minimum = Math.min(...volumeWinners.map(row => row.absolute_imbalance));
  const winners = volumeWinners.filter(row => row.absolute_imbalance === minimum);
  return {model: "maximum-volume-then-minimum-imbalance", reference_price: reference, tick_size: tick, order_count: orders.length, maximum_executable_quantity: maximum, minimum_absolute_imbalance: minimum, volume_winner_prices: volumeWinners.map(row => row.price), minimum_imbalance_prices: winners.map(row => row.price), selected_price: winners.length === 1 ? winners[0].price : null, candidate_evaluations: evaluations, state: maximum === 0 ? "no-cross" : winners.length === 1 ? "tie-resolved" : "tie-remains"};
}

function crossPrice(session: string, ordersRaw: unknown, referenceRaw: unknown, tickRaw: unknown, lowRaw: unknown, highRaw: unknown): JsonObject {
  const reference = num("reference_price", referenceRaw, true), tick = num("tick_size", tickRaw, true), low = num("collar_low", lowRaw, true), high = num("collar_high", highRaw, true);
  if (low > reference || high < reference || low > high) throw new RangeError("collar must contain the reference price");
  if (![reference, low, high].every(value => onTick(value, tick))) throw new RangeError("reference and collar prices must align with tick_size");
  const parsed = parseOrders(ordersRaw, tick), allowed = new Set(session === "opening" ? ["MOO", "LOO", "DAY"] : ["MOC", "LOC", "DAY"]);
  if (parsed.some(order => !allowed.has(order.order_type))) throw new RangeError(`unsupported order type for ${session} cross`);
  const [, , , evaluations] = evaluateBook(parsed, reference, tick, low, high);
  const maximum = Math.max(...evaluations.map(row => row.executable_quantity));
  if (maximum === 0) return {model: `declared-${session}-cross`, session, reference_price: reference, collar_low: low, collar_high: high, selected_price: null, executed_quantity: 0, imbalance_quantity: 0, selection_trace: ["no candidate price executes both sides"], candidate_evaluations: evaluations, state: "no-cross"};
  let stage = evaluations.filter(row => row.executable_quantity === maximum);
  const trace = [`maximize executable quantity at ${maximum}`];
  const minimum = Math.min(...stage.map(row => row.absolute_imbalance));
  stage = stage.filter(row => row.absolute_imbalance === minimum); trace.push(`minimize absolute imbalance at ${minimum}`);
  let selected: JsonObject;
  if (stage.length > 1) {
    const signs = new Set(stage.map(row => row.imbalance_side));
    if (signs.size === 1 && signs.has("buy")) {
      selected = stage.reduce((a, b) => a.price > b.price ? a : b); trace.push("buy surplus selects the highest remaining price");
    } else if (signs.size === 1 && signs.has("sell")) {
      selected = stage.reduce((a, b) => a.price < b.price ? a : b); trace.push("sell surplus selects the lowest remaining price");
    } else {
      selected = [...stage].sort((a, b) => Math.abs(a.price - reference) - Math.abs(b.price - reference) || a.price - b.price)[0];
      trace.push("mixed or zero surplus selects the price nearest the reference");
    }
  } else { selected = stage[0]; trace.push("the objective hierarchy leaves one price"); }
  return {model: `declared-${session}-cross`, session, reference_price: reference, collar_low: low, collar_high: high, eligible_order_count: parsed.length, selected_price: selected.price, executed_quantity: selected.executable_quantity, buy_quantity: selected.buy_quantity, sell_quantity: selected.sell_quantity, imbalance_quantity: selected.imbalance_quantity, imbalance_side: selected.imbalance_side, selection_trace: trace, candidate_evaluations: evaluations, state: "crossed"};
}

export function openingCrossPrice(orders: unknown, previousClose: unknown, tick: unknown, low: unknown, high: unknown): JsonObject {
  return crossPrice("opening", orders, previousClose, tick, low, high);
}
export function closingCrossPrice(orders: unknown, reference: unknown, tick: unknown, low: unknown, high: unknown): JsonObject {
  return crossPrice("closing", orders, reference, tick, low, high);
}

export function volatilityAuctionReopening(inputs: JsonObject): JsonObject {
  const reference = num("reference_price", inputs.reference_price, true);
  const dynamicRef = num("dynamic_reference", inputs.dynamic_reference, true), dynamicPct = num("dynamic_band_pct", inputs.dynamic_band_pct, true);
  const staticRef = num("static_reference", inputs.static_reference, true), staticPct = num("static_band_pct", inputs.static_band_pct, true);
  const potential = num("potential_continuous_price", inputs.potential_continuous_price, true), indicative = num("indicative_auction_price", inputs.indicative_auction_price, true);
  const multiplier = num("extended_band_multiplier", inputs.extended_band_multiplier, true);
  if (multiplier < 1) throw new RangeError("extended_band_multiplier must be at least one");
  const executable = num("executable_quantity", inputs.executable_quantity, false, true);
  const dynamicLow = dynamicRef * (1 - dynamicPct), dynamicHigh = dynamicRef * (1 + dynamicPct);
  const staticLow = staticRef * (1 - staticPct), staticHigh = staticRef * (1 + staticPct);
  const dynamicBreach = potential < dynamicLow || potential > dynamicHigh, staticBreach = potential < staticLow || potential > staticHigh, triggered = dynamicBreach || staticBreach;
  const expandedDynamicLow = dynamicRef * (1 - dynamicPct * multiplier), expandedDynamicHigh = dynamicRef * (1 + dynamicPct * multiplier);
  const expandedStaticLow = staticRef * (1 - staticPct * multiplier), expandedStaticHigh = staticRef * (1 + staticPct * multiplier);
  const inside = indicative >= expandedDynamicLow && indicative <= expandedDynamicHigh && indicative >= expandedStaticLow && indicative <= expandedStaticHigh;
  let state: string, reopened: boolean, reopenPrice: number | null, reason: string;
  if (!triggered) { state = "continuous"; reopened = false; reopenPrice = null; reason = "potential price remains inside both active corridors"; }
  else if (executable === 0) { state = "auction-no-cross"; reopened = false; reopenPrice = null; reason = "volatility auction has no executable quantity"; }
  else if (inside) { state = "reopened"; reopened = true; reopenPrice = indicative; reason = "indicative auction price is executable and inside both expanded corridors"; }
  else { state = "extended-volatility-auction"; reopened = false; reopenPrice = null; reason = "indicative auction price remains outside an expanded corridor"; }
  return {model: "dual-corridor-volatility-auction-reopening", reference_price: reference, potential_continuous_price: potential, dynamic_corridor: [dynamicLow, dynamicHigh], static_corridor: [staticLow, staticHigh], dynamic_breach: dynamicBreach, static_breach: staticBreach, triggered, indicative_auction_price: indicative, executable_quantity: executable, expanded_dynamic_corridor: [expandedDynamicLow, expandedDynamicHigh], expanded_static_corridor: [expandedStaticLow, expandedStaticHigh], inside_reopening_corridor: inside, reopened, reopen_price: reopenPrice, reason, state};
}

export function calculate(topicId: string, inputs: JsonObject): JsonObject {
  if (!inputs || typeof inputs !== "object" || Array.isArray(inputs)) throw new TypeError("inputs must be an object");
  if (topicId === "D12-F02-A01") return maximumExecutableVolumeAuction(inputs.orders, inputs.reference_price, inputs.tick_size);
  if (topicId === "D12-F02-A02") return minimumImbalanceTieBreak(inputs.orders, inputs.reference_price, inputs.tick_size);
  if (topicId === "D12-F02-A03") return openingCrossPrice(inputs.orders, inputs.previous_close, inputs.tick_size, inputs.collar_low, inputs.collar_high);
  if (topicId === "D12-F02-A04") return closingCrossPrice(inputs.orders, inputs.closing_reference, inputs.tick_size, inputs.collar_low, inputs.collar_high);
  if (topicId === "D12-F02-A05") return volatilityAuctionReopening(inputs);
  throw new RangeError(`unsupported topic_id: ${topicId}`);
}