/**
 * Topstep's own commission on TopstepX — the part of a fill's cost the
 * gateway never reports.
 *
 * Trade/search and the user hub carry `fees` on every half-turn, but only the
 * exchange and NFA fees (NQ $1.39 a side, GC $1.66, CL $1.51, MNQ $0.36).
 * Topstep's commission — $0.50 a side on a full-size contract, $0.25 on a
 * micro — comes off the balance with no trade carrying it. Topstep's
 * "TopstepX Commissions and Fees" page totals both: NQ and ES $3.78 a round
 * turn, MNQ and MES $1.22, GC $4.32, CL $4.02. Left out, the books ran $1.00
 * a full-size round turn above the balance (2026-10-18: an XFA $27.50 off
 * after 26 NQ/GC round turns and 3 MNQ, each combine $1.00 per round turn).
 *
 * No imports, so scripts/check-instruments.mjs can test it directly.
 */

/** Per contract and side, by CME root. */
export const TOPSTEP_COMMISSION_PER_SIDE: Readonly<Record<string, number>> = {
    NQ: 0.5, MNQ: 0.25,
    ES: 0.5, MES: 0.25,
    YM: 0.5, MYM: 0.25,
    RTY: 0.5, M2K: 0.25,
    GC: 0.5, MGC: 0.25,
    SI: 0.5,
    CL: 0.5, MCL: 0.25,
    NG: 0.5,
    ZB: 0.5, ZN: 0.5, ZF: 0.5,
    '6E': 0.5, '6J': 0.5, '6B': 0.5,
};

/** A product missing from the table pays the full-size rate, so the books
 *  err toward the lower balance. */
export const TOPSTEP_COMMISSION_FALLBACK = 0.5;

/** TopstepX's product code in a contract id → the CME root, where the two
 *  differ. ENQ, GCE and CLE are seen on real fills; the rest follow the same
 *  naming, and contracts the client resolves itself override them. */
const PRODUCT_ROOTS: Readonly<Record<string, string>> = {
    ENQ: 'NQ', EP: 'ES', GCE: 'GC', SIE: 'SI', CLE: 'CL', MCLE: 'MCL', NGE: 'NG',
    USA: 'ZB', TYA: 'ZN', FVA: 'ZF', EU6: '6E', JY6: '6J', BP6: '6B',
};

/** "CON.F.US.ENQ.Z26" → "ENQ"; null for anything else. */
export function topstepxProductCode(contractId: unknown): string | null {
    const parts = String(contractId ?? '').split('.');
    return parts.length === 5 && parts[0] === 'CON' && parts[3] ? parts[3] : null;
}

/** The CME root a TopstepX contract id trades, or null when it's none this
 *  table knows. `learned` maps product codes to roots off the contracts the
 *  client resolved itself; the table covers the rest of the history. */
export function topstepxRoot(contractId: unknown, learned?: ReadonlyMap<string, string>): string | null {
    const code = topstepxProductCode(contractId);
    if (!code) return null;
    const known = (root: string | undefined) => (root !== undefined && root in TOPSTEP_COMMISSION_PER_SIDE ? root : null);
    return known(learned?.get(code)) ?? known(PRODUCT_ROOTS[code]) ?? known(code);
}

/** Topstep's commission on one fill of `size` contracts (one side). */
export function topstepCommission(root: string | null, size: number): number {
    const perSide = (root !== null ? TOPSTEP_COMMISSION_PER_SIDE[root] : undefined) ?? TOPSTEP_COMMISSION_FALLBACK;
    return Math.round(perSide * Math.abs(size || 0) * 100) / 100;
}