limits

import { formatQuantity, formatTicks, quoteBasisOf, ticksBetween, type InstrumentConvention } from "@/lib/format"

// An undefined word keeps its default, as DataGrid's labels do.
const defined = <W extends object>(words: W | undefined): Partial<W> => Object.fromEntries(Object.entries(words ?? {}).filter(([, word]) => word !== undefined)) as Partial<W>

// Fat-finger checks are universal: a size above a line, a level too far from the market, a side the
// book may not take. The tickets already stop a missing level and a crossed market; this gives them a
// limits table, as data, and returns problems in the shape they already print. A `block` stops the
// action; a `confirm` turns it into a two-step, the blotter's ask-again. Nothing here decides a
// limit: the numbers are the desk's, the words are the consumer's, and the check runs where the
// click lands, against the draft as it is then.

export type ProblemLevel = "block" | "confirm"

export interface Problem {
  /** The field it is about: "quantity", "price", "bid", "ask", or "side". */
  field: string
  level: ProblemLevel
  /** A sentence, in the consumer's words. */
  message: string
  /** Which limit raised it: "maxQuantity", "minQuantity", "maxDistance", "sides", or a custom rule's own name. */
  rule: string
}

/** What the check reads of a draft: a ticket's side, quantity, and price, or a quote's bid and ask. */
export interface LimitsDraft {
  side?: "buy" | "sell"
  quantity?: number | null
  price?: number | null
  bid?: number | null
  ask?: number | null
}

export interface LimitsMarket {
  bid?: number | null
  ask?: number | null
  last?: number | null
  mid?: number | null
}

export interface LimitsLabels {
  /** `{n}` the quantity, `{max}` the limit. */
  quantityAbove: string
  quantityAboveConfirm: string
  /** `{n}` the quantity, `{min}` the limit. */
  quantityBelow: string
  quantityBelowConfirm: string
  /** `{field}` the level's field, `{distance}` how far, `{max}` the limit, both with their unit. */
  tooFar: string
  tooFarConfirm: string
  /** `{side}` the side. */
  sideNotAllowed: string
  buy: string
  sell: string
  /** The level's field in `{field}`: a ticket's price, a two-sided quote's bid and ask. */
  price: string
  bid: string
  ask: string
  /** The unit after a distance in ticks: a word, or a function of the count, for a plural a word can't hold. */
  ticks: string | ((n: number) => string)
  /** The unit after a distance in basis points: a word, or a function of the count. */
  bps: string | ((n: number) => string)
}

export const DEFAULT_LIMITS_LABELS: LimitsLabels = {
  quantityAbove: "{n} is above the size limit of {max}.",
  quantityAboveConfirm: "{n} is above {max}. Send it anyway?",
  quantityBelow: "{n} is below the minimum of {min}.",
  quantityBelowConfirm: "{n} is below {min}. Send it anyway?",
  tooFar: "The {field} is {distance} from the market; the limit is {max}.",
  tooFarConfirm: "The {field} is {distance} from the market, past {max}. Send it anyway?",
  sideNotAllowed: "The book does not take a {side}.",
  buy: "buy",
  sell: "sell",
  price: "price",
  bid: "bid",
  ask: "ask",
  ticks: (n) => (n === 1 ? "tick" : "ticks"),
  bps: "bp",
}

export interface LimitsContext {
  market?: LimitsMarket
  convention?: InstrumentConvention
  labels?: Partial<LimitsLabels>
}

/** A line, or two: a size to ask again past, and a size to stop at. One number is a stop. */
export type Threshold = number | { confirm?: number; block?: number }

export interface Limits {
  maxQuantity?: Threshold
  minQuantity?: Threshold
  /** How far a level may sit from the market's same side (the mid when there is none), in ticks for a price basis or basis points for the rest. */
  maxDistance?: ({ ticks: number } | { bps: number }) & { level?: ProblemLevel }
  /** The sides the book may take. A ticket's side, or, for a quote, a bid is a buy and an offer a sell. */
  sides?: readonly ("buy" | "sell")[]
  /** Your own rules, in the same shape. */
  custom?: (draft: LimitsDraft, context: LimitsContext) => Problem[]
}

function fill(template: string, values: Record<string, string | number>): string {
  return template.replace(/\{(\w+)\}/g, (_, name: string) => String(values[name] ?? ""))
}

function thresholds(t: Threshold | undefined): { confirm?: number; block?: number } {
  if (t === undefined) return {}
  return typeof t === "number" ? { block: t } : t
}

/** The market's side a level is measured against: the same side as the level, else the mid, else the last. */
export function marketSideFor(field: "price" | "bid" | "ask", side: "buy" | "sell" | undefined, market: LimitsMarket | undefined): number | null {
  if (!market) return null
  const pick = (...values: (number | null | undefined)[]) => values.find((v): v is number => typeof v === "number" && Number.isFinite(v)) ?? null
  const mid = pick(market.mid) ?? (typeof market.bid === "number" && typeof market.ask === "number" ? (market.bid + market.ask) / 2 : null)
  if (field === "bid") return pick(market.bid, mid, market.last)
  if (field === "ask") return pick(market.ask, mid, market.last)
  // A price on a ticket: a buyer measures against the offer, a seller against the bid.
  if (side === "buy") return pick(market.ask, mid, market.last)
  if (side === "sell") return pick(market.bid, mid, market.last)
  return pick(mid, market.last)
}

/** How far a level is from a market level in the convention's unit: ticks for a price basis, basis points for the rest. */
export function distanceFromMarket(level: number, market: number, convention: InstrumentConvention | undefined): { value: number; unit: "ticks" | "bps" } {
  if (!convention || quoteBasisOf(convention) === "price") return { value: Math.abs(ticksBetween(level, market, convention?.tick ?? 1)), unit: "ticks" }
  // A yield or a discount is quoted in percent, so a hundredth of a point is a basis point; a spread is quoted in basis points already.
  const perPoint = quoteBasisOf(convention) === "spread" ? 1 : 100
  // To a thousandth of a basis point, so 4.30 against 4.25 is 5 and not 4.999999999999982.
  return { value: Math.round(Math.abs(level - market) * perPoint * 1000) / 1000, unit: "bps" }
}

/**
 * What the limits say about a draft, in the tickets' shape, each with its level and a sentence. Empty
 * when nothing does. Quantity against the lines, each level against the market in the instrument's
 * unit, the side against the sides the book takes, then your own rules.
 */
export function checkLimits(draft: LimitsDraft, limits: Limits | undefined, context: LimitsContext = {}): Problem[] {
  if (!limits) return []
  const labels = { ...DEFAULT_LIMITS_LABELS, ...defined(context.labels) }
  const problems: Problem[] = []
  const quantity = draft.quantity
  // A fractional size prints exactly, or the prompt would round the trader's own number and
  // the limit into a lie such as "10 is above the size limit of 10".
  const size = (v: number) => (Number.isInteger(v) ? formatQuantity(v) : String(v).replace(/-/g, "−"))
  if (typeof quantity === "number" && Number.isFinite(quantity)) {
    const max = thresholds(limits.maxQuantity)
    if (max.block !== undefined && quantity > max.block) problems.push({ field: "quantity", level: "block", rule: "maxQuantity", message: fill(labels.quantityAbove, { n: size(quantity), max: size(max.block) }) })
    else if (max.confirm !== undefined && quantity > max.confirm) problems.push({ field: "quantity", level: "confirm", rule: "maxQuantity", message: fill(labels.quantityAboveConfirm, { n: size(quantity), max: size(max.confirm) }) })
    const min = thresholds(limits.minQuantity)
    if (min.block !== undefined && quantity < min.block) problems.push({ field: "quantity", level: "block", rule: "minQuantity", message: fill(labels.quantityBelow, { n: size(quantity), min: size(min.block) }) })
    else if (min.confirm !== undefined && quantity < min.confirm) problems.push({ field: "quantity", level: "confirm", rule: "minQuantity", message: fill(labels.quantityBelowConfirm, { n: size(quantity), min: size(min.confirm) }) })
  }
  if (limits.maxDistance) {
    const rule = limits.maxDistance
    const level = rule.level ?? "block"
    const max = "ticks" in rule ? { value: rule.ticks, unit: "ticks" as const } : { value: rule.bps, unit: "bps" as const }
    for (const field of ["price", "bid", "ask"] as const) {
      const value = draft[field]
      if (typeof value !== "number" || !Number.isFinite(value)) continue
      const against = marketSideFor(field, draft.side, context.market)
      if (against === null) continue
      const distance = distanceFromMarket(value, against, context.convention)
      if (distance.unit !== max.unit || !(distance.value > max.value)) continue
      const unit = (n: number) => {
        const word = labels[max.unit]
        return typeof word === "function" ? word(n) : word
      }
      const words = { field: labels[field], distance: `${formatTicks(distance.value, { signed: false })} ${unit(distance.value)}`, max: `${formatTicks(max.value, { signed: false })} ${unit(max.value)}` }
      problems.push({ field, level, rule: "maxDistance", message: fill(level === "block" ? labels.tooFar : labels.tooFarConfirm, words) })
    }
  }
  if (limits.sides) {
    const taken = new Set(limits.sides)
    const refuse = (side: "buy" | "sell", field: string) => problems.push({ field, level: "block", rule: "sides", message: fill(labels.sideNotAllowed, { side: labels[side] }) })
    if (draft.side && !taken.has(draft.side)) refuse(draft.side, "side")
    if (typeof draft.bid === "number" && !taken.has("buy")) refuse("buy", "bid")
    if (typeof draft.ask === "number" && !taken.has("sell")) refuse("sell", "ask")
  }
  if (limits.custom) problems.push(...limits.custom(draft, context))
  return problems
}

/** The problems that stop the action. */
export function blocks(problems: readonly Problem[]): Problem[] {
  return problems.filter((p) => p.level === "block")
}

/** The problems that ask again. */
export function confirms(problems: readonly Problem[]): Problem[] {
  return problems.filter((p) => p.level === "confirm")
}

/** The first message per field, for printing under the fields the way the tickets do. */
export function problemsByField(problems: readonly Problem[]): Record<string, string> {
  const messages = new Map<string, string>()
  for (const p of problems) if (!messages.has(p.field)) messages.set(p.field, p.message)
  return Object.fromEntries(messages)
}

// Number formatting for trading screens. Pure functions, no React, no dependencies.
// Every formatter returns NULL_TOKEN for null, undefined, NaN, and infinities, so a grid
// never prints "NaN" or "undefined" while a feed is warming up.

export const NULL_TOKEN = "–"
const MINUS = "−"

export type Nullable = number | null | undefined

export interface Locale {
  /** BCP 47 tag; defaults to en-US. */
  locale?: string
}

export type PriceConvention =
  /** Fixed decimals, e.g. equities at 2. */
  | { kind: "decimal"; decimals: number }
  /** Decimals derived from the instrument's tick size, e.g. 0.001 gives 3. */
  | { kind: "tick"; tick: number }
  /**
   * Fractional quoting. `denominator` 32 or 64; `half` renders a half tick as "+" (99-16+) or "5" (99-165);
   * `eighths` renders eighths of a tick as a trailing digit (99-162 is 99 and 16 2/8 thirty-seconds).
   */
  | { kind: "fraction"; denominator: 32 | 64; half: "+" | "5"; eighths?: boolean }

/** What a quote is typed and read in. Bills quote on discount, most bonds on price, some on yield, credit often on a spread in basis points. */
export type QuoteBasis = "price" | "yield" | "discount" | "spread"

export interface InstrumentConvention {
  price: PriceConvention
  /** Smallest price increment, used for stepping and rounding. */
  tick: number
  yieldDecimals?: number
  quantityUnit?: "notional" | "contracts"
  /** Default price. */
  quoteBasis?: QuoteBasis
  /** What a quote steps by in its basis. Default: the tick for price, 0.001 for yield and discount, 0.1 for spread. */
  quoteStep?: number
  /** Decimals for a yield, discount, or spread quote. Default 3, 3, and 1. Price quotes follow their convention. */
  quoteDecimals?: number
  /** Whether a higher quote means a lower price, so a normal market quotes the bid above the offer. Defaults by basis: yield and discount invert; price and spread do not, since a CDS spread quotes bid below offer while cash credit quotes the other way — declare it for the instrument when the default reads wrong. */
  quoteInverted?: boolean
}

function isNil(v: Nullable): v is null | undefined {
  return v === null || v === undefined || !Number.isFinite(v)
}

// One Intl.NumberFormat per locale and option set; construction is the expensive part.
const formatters = new Map<string, Intl.NumberFormat>()

/** True for a time a `Date` can hold: a finite number of milliseconds within 8.64e15 of the epoch either way. */
export const isInstant = (ms: unknown): ms is number => Number.isFinite(ms) && Math.abs(ms as number) <= 8.64e15

export function numberFormat(locale: string | undefined, options: Intl.NumberFormatOptions): Intl.NumberFormat {
  const key = `${locale ?? "en-US"}|${JSON.stringify(options)}`
  let nf = formatters.get(key)
  if (!nf) {
    nf = new Intl.NumberFormat(locale ?? "en-US", options)
    formatters.set(key, nf)
  }
  return nf
}

function fixed(v: number, decimals: number, locale?: string, extra: Intl.NumberFormatOptions = {}): string {
  return numberFormat(locale, { minimumFractionDigits: decimals, maximumFractionDigits: decimals, ...extra }).format(v)
}

function typographicMinus(s: string): string {
  return s.replace(/-/g, MINUS)
}

/** Decimal places needed to show a price on this tick grid. 0.001 gives 3, 1/32 gives 5, 1 gives 0. Capped at `max`. */
export function decimalsFromTick(tick: number, max = 8): number {
  if (!Number.isFinite(tick) || tick <= 0) return 0
  for (let d = 0; d <= max; d++) {
    const scaled = tick * 10 ** d
    if (Math.abs(scaled - Math.round(scaled)) < 1e-9 * Math.max(1, scaled)) return d
  }
  return max
}

/** Nearest price on the tick grid, cleaned of float noise. */
export function roundToTick(v: number, tick: number): number {
  if (!Number.isFinite(v) || !Number.isFinite(tick) || tick <= 0) return v
  return Number((Math.round(v / tick) * tick).toFixed(decimalsFromTick(tick)))
}

/** Move `steps` ticks (negative allowed) from the nearest grid price. */
export function stepByTick(v: number, tick: number, steps: number): number {
  return roundToTick(roundToTick(v, tick) + steps * tick, tick)
}

/** Whole-number and sub-tick decomposition on an integer grid so 32nds never drift. */
function decomposeFraction(v: number, c: Extract<PriceConvention, { kind: "fraction" }>) {
  const sub = c.eighths ? 8 : 2
  const unitsPerWhole = c.denominator * sub
  const total = Math.round(Math.abs(v) * unitsPerWhole)
  const whole = Math.floor(total / unitsPerWhole)
  const rem = total - whole * unitsPerWhole
  const ticks = Math.floor(rem / sub)
  const subticks = rem - ticks * sub
  return { negative: v < 0 && total > 0, whole, ticks, subticks, sub }
}

/** 99.515625 as "99-16+" (32nds, half "+"), "99-165" (half "5"), or "99-164" with eighths. */
export function formatFraction(v: Nullable, c: Extract<PriceConvention, { kind: "fraction" }>): string {
  if (isNil(v)) return NULL_TOKEN
  const { negative, whole, ticks, subticks, sub } = decomposeFraction(v, c)
  // From 1e21 a whole part prints in exponent form, and further up the scaling overflows: neither is the notation,
  // and parsePrice refuses the same range.
  if (!(whole < 1e21)) return NULL_TOKEN
  let tail = ""
  if (subticks !== 0) {
    if (c.eighths) tail = String(subticks)
    else tail = c.half
  }
  void sub
  return `${negative ? MINUS : ""}${whole}-${String(ticks).padStart(2, "0")}${tail}`
}

export function formatPrice(v: Nullable, c: PriceConvention, l?: Locale): string {
  if (isNil(v)) return NULL_TOKEN
  switch (c.kind) {
    case "decimal":
      return typographicMinus(fixed(v, c.decimals, l?.locale))
    case "tick":
      return typographicMinus(fixed(roundToTick(v, c.tick), decimalsFromTick(c.tick), l?.locale))
    case "fraction":
      return formatFraction(v, c)
  }
}

/**
 * Numeric text, trimmed and with either minus sign read as "-", with its thousands separators removed, or null when a
 * comma in it isn't one. A comma groups
 * thousands in the whole part only: a first group of one to three digits with no leading zero, then groups of three,
 * and none after the point or among the 32nds, so "99,5" from a decimal-comma keyboard is no number, never 995. With
 * `decimals`, for text whose notation prints digits after the point, one comma with nothing after the whole part is
 * no number either, since "4,253" reads as 4253 grouped or as 4.253 typed with a decimal comma; two or more groups,
 * or a point or a fraction's dash after them, can only be grouping. Text without a comma comes back trimmed with the minus
 * read, and the rest of any text is left to the caller's own pattern, which decides what is a number.
 */
export function stripGrouping(input: string, options: { decimals: boolean }): string | null {
  const text = input.trim().replace(/−/g, "-")
  if (!text.includes(",")) return text
  const m = /^([+-]?)([1-9]\d{0,2}(?:,\d{3})+)((?:[.-].*)?)$/.exec(text)
  if (!m || m[3]!.includes(",")) return null
  const whole = m[2]!
  if (options.decimals && !m[3] && whole.indexOf(",") === whole.lastIndexOf(",")) return null
  return m[1]! + whole.replace(/,/g, "") + m[3]!
}

// Whether a convention's own text carries digits after the point, or a fraction's ticks.
const printsDecimals = (c: PriceConvention) => (c.kind === "fraction" ? true : c.kind === "decimal" ? c.decimals > 0 : decimalsFromTick(c.tick) > 0)

/**
 * Inverse of formatPrice for ticket entry. Accepts the convention's own notation and a plain decimal.
 * Returns null when the text is not a price. Fraction input: "99-16+", "99-165", "99-162", "99-16", "99".
 */
export function parsePrice(s: string, c: PriceConvention): number | null {
  const text = stripGrouping(s, { decimals: printsDecimals(c) })
  if (!text) return null
  if (c.kind === "fraction") {
    const m = /^([+-]?)(\d+)(?:-(\d{1,2})([+0-9])?)?$/.exec(text)
    if (m) {
      const [, sign, wholeText, ticksText, tail] = m
      const ticks = ticksText ? Number(ticksText) : 0
      if (ticks >= c.denominator) return null
      let subFraction = 0
      if (tail === "+") subFraction = 0.5
      else if (tail !== undefined) {
        const digit = Number(tail)
        if (c.eighths) {
          if (digit > 7) return null
          subFraction = digit / 8
        } else if (c.half === "5" && digit === 5) subFraction = 0.5
        else if (digit === 0) subFraction = 0
        else return null
      }
      const value = Number(wholeText) + (ticks + subFraction) / c.denominator
      // What cannot print back in the notation is refused: unit scaling must stay finite, the
      // whole part must stay out of exponent form (1e21 up), and "-0" stays plain zero.
      if (value >= 1e21 || !Number.isFinite(value * c.denominator * (c.eighths ? 8 : 2))) return null
      return value === 0 ? 0 : sign === "-" ? -value : value
    }
  }
  if (!/^[+-]?(\d+\.?\d*|\.\d+)$/.test(text)) return null
  const n = Number(text)
  if (!Number.isFinite(n)) return null
  // Every convention keeps the promise the reference row makes: what parses can print back.
  // Intl prints tick and decimal prices in full digits at any finite size, so only fraction
  // notation carries the 1e21 bound; tick scaling must stay finite, and zero stays plain zero.
  if (c.kind === "tick") {
    const rounded = roundToTick(n, c.tick)
    return Number.isFinite(rounded) ? (rounded === 0 ? 0 : rounded) : null
  }
  if (c.kind === "decimal") {
    const fixed = Number(n.toFixed(c.decimals))
    return fixed === 0 ? 0 : fixed
  }
  // A decimal typed into a fraction convention snaps to the printable grid, so the value a field
  // reports is the price its formatted text shows. The magnitude rounds, as the formatter rounds,
  // so a negative tie snaps away from zero the way it prints.
  const unitsPerWhole = c.denominator * (c.eighths ? 8 : 2)
  const units = Math.round(Math.abs(n) * unitsPerWhole)
  // Scaling can overflow a finite input, a magnitude from 1e21 up prints in exponent form the
  // notation cannot parse back, and a sub-half-unit negative would make negative zero.
  if (!Number.isFinite(units) || units / unitsPerWhole >= 1e21) return null
  return units === 0 ? 0 : (n < 0 ? -units : units) / unitsPerWhole
}

/** 4.2531 as "4.253%". */
export function formatYield(v: Nullable, o: { decimals?: number; suffix?: "%" | "" } & Locale = {}): string {
  if (isNil(v)) return NULL_TOKEN
  return typographicMinus(fixed(v, o.decimals ?? 3, o.locale)) + (o.suffix ?? "%")
}

/** 12.5 as "12.5 bp"; signed gives "+12.5 bp". */
export function formatBps(v: Nullable, o: { decimals?: number; signed?: boolean; unit?: "bp" | "bps" | "" } & Locale = {}): string {
  if (isNil(v)) return NULL_TOKEN
  const unit = o.unit ?? "bp"
  const body = o.signed ? formatSigned(v, { decimals: o.decimals ?? 1, locale: o.locale }) : typographicMinus(fixed(v, o.decimals ?? 1, o.locale))
  return unit ? `${body} ${unit}` : body
}

/** Dollar value of a basis point as whole currency; compact gives "$1.23K". */
export function formatDv01(v: Nullable, o: { currency?: string; compact?: boolean } & Locale = {}): string {
  if (isNil(v)) return NULL_TOKEN
  const currency = o.currency ?? "USD"
  if (o.compact) {
    const symbol = numberFormat(o.locale, { style: "currency", currency, currencyDisplay: "narrowSymbol", maximumFractionDigits: 0 })
      .formatToParts(0)
      .find((p) => p.type === "currency")?.value ?? ""
    return `${v < 0 ? MINUS : ""}${symbol}${formatNotional(Math.abs(v), { compact: true, locale: o.locale })}`
  }
  return typographicMinus(numberFormat(o.locale, { style: "currency", currency, currencyDisplay: "narrowSymbol", maximumFractionDigits: 0 }).format(v))
}

/** 1250000 as "1.25M" (compact), "1.25mm" (unit "mm", the desk's word for millions, never scaled further), or "1,250,000.00". Compact suffixes K, M, B, T. */
export function formatNotional(v: Nullable, o: { compact?: boolean; decimals?: number; unit?: "mm" } & Locale = {}): string {
  if (isNil(v)) return NULL_TOKEN
  const decimals = o.decimals ?? 2
  if (o.unit === "mm") return typographicMinus(numberFormat(o.locale, { minimumFractionDigits: 0, maximumFractionDigits: decimals }).format(v / 1e6)) + "mm"
  if (!o.compact) return typographicMinus(fixed(v, decimals, o.locale))
  const abs = Math.abs(v)
  const [divisor, suffix] = abs >= 1e12 ? [1e12, "T"] : abs >= 1e9 ? [1e9, "B"] : abs >= 1e6 ? [1e6, "M"] : abs >= 1e3 ? [1e3, "K"] : [1, ""]
  return typographicMinus(fixed(v / divisor, suffix ? decimals : 0, o.locale)) + suffix
}

/** "+0.12", "−0.12" (U+2212), and "0.00" for zero: flat carries no sign. */
export function formatSigned(v: Nullable, o: { decimals?: number } & Locale = {}): string {
  if (isNil(v)) return NULL_TOKEN
  return typographicMinus(fixed(v, o.decimals ?? 2, o.locale, { signDisplay: "exceptZero" }))
}

/** 1.234 as "1.23%"; signed gives "+1.23%". */
export function formatPercent(v: Nullable, o: { decimals?: number; signed?: boolean } & Locale = {}): string {
  if (isNil(v)) return NULL_TOKEN
  const decimals = o.decimals ?? 2
  return (o.signed ? formatSigned(v, { decimals, locale: o.locale }) : typographicMinus(fixed(v, decimals, o.locale))) + "%"
}

/** Whole quantities with grouping: 1000000 as "1,000,000". */
export function formatQuantity(v: Nullable, l?: Locale): string {
  if (isNil(v)) return NULL_TOKEN
  return typographicMinus(fixed(Math.round(v), 0, l?.locale))
}

/**
 * A coupon the way a run prints it: 4.125 as "4 1/8", 4.5 as "4 1/2", 4 as "4", 0 as "0" (coupons step in eighths).
 * One off the eighths grid prints as a plain decimal, "4.1". `style: "decimal"` prints "4.125%".
 */
export function formatCoupon(v: Nullable, o: { style?: "fraction" | "decimal"; decimals?: number } & Locale = {}): string {
  if (isNil(v)) return NULL_TOKEN
  if (o.style === "decimal") return typographicMinus(fixed(v, o.decimals ?? 3, o.locale)) + "%"
  const eighths = Math.round(Math.abs(v) * 8)
  if (Math.abs(eighths / 8 - Math.abs(v)) > 1e-9) return typographicMinus(numberFormat(o.locale, { minimumFractionDigits: 0, maximumFractionDigits: o.decimals ?? 3 }).format(v))
  const whole = Math.floor(eighths / 8)
  const rem = eighths % 8
  const fraction = rem === 0 ? "" : rem % 4 === 0 ? "1/2" : rem % 2 === 0 ? `${rem / 2}/4` : `${rem}/8`
  const body = fraction ? (whole ? `${whole} ${fraction}` : fraction) : String(whole)
  return `${v < 0 && eighths > 0 ? MINUS : ""}${body}`
}

/** A date as an instant, a millisecond count, or a string `Date` can read. A date-only string ("2034-05-15") is that day in UTC. */
export type DateLike = Date | number | string

function toDate(d: DateLike | null | undefined): Date | null {
  if (d === null || d === undefined) return null
  const date = d instanceof Date ? d : new Date(d)
  return Number.isNaN(date.getTime()) ? null : date
}

const dateFormatters = new Map<string, Intl.DateTimeFormat>()

/**
 * A maturity as a run prints it: "05/15/34", or "05/15/2034" with `year: "numeric"`. Read in UTC, so a
 * date-only string prints as that day wherever the screen is.
 */
export function formatMaturity(d: DateLike | null | undefined, o: { year?: "2-digit" | "numeric" } & Locale = {}): string {
  const date = toDate(d)
  if (!date) return NULL_TOKEN
  const key = `${o.locale ?? "en-US"}|${o.year ?? "2-digit"}`
  let f = dateFormatters.get(key)
  if (!f) {
    f = new Intl.DateTimeFormat(o.locale ?? "en-US", { month: "2-digit", day: "2-digit", year: o.year ?? "2-digit", timeZone: "UTC" })
    dateFormatters.set(key, f)
  }
  return f.format(date)
}

/** Whole UTC days from `now` (the moment, by default) to a maturity. Negative once it has passed; null when the date does not read. */
export function daysToMaturity(d: DateLike | null | undefined, now: DateLike = Date.now()): number | null {
  const maturity = toDate(d)
  const from = toDate(now)
  if (!maturity || !from) return null
  const day = (x: Date) => Date.UTC(x.getUTCFullYear(), x.getUTCMonth(), x.getUTCDate())
  return Math.round((day(maturity) - day(from)) / 86_400_000)
}

/** How many ticks `a` is from `b`, signed, to the nearest eighth of a tick: 99-17 against 99-16+ on a 1/64 tick is 1. NaN when a side is not a number or the tick is not positive. */
export function ticksBetween(a: number, b: number, tick: number): number {
  if (!Number.isFinite(a) || !Number.isFinite(b) || !(tick > 0)) return NaN
  return Math.round(((a - b) / tick) * 8) / 8
}

/** A count of ticks: "+1", "−0.5", "0", up to three decimals and no trailing zeros. Signed unless told otherwise; `unit` adds a word; `grouping: false` drops the thousands separators, for an editor's text. */
export function formatTicks(v: Nullable, o: { signed?: boolean; unit?: string; grouping?: boolean } & Locale = {}): string {
  if (isNil(v)) return NULL_TOKEN
  const body = typographicMinus(numberFormat(o.locale, { minimumFractionDigits: 0, maximumFractionDigits: 3, signDisplay: o.signed === false ? "auto" : "exceptZero", ...(o.grouping === false ? { useGrouping: false } : {}) }).format(v))
  return o.unit ? `${body} ${o.unit}` : body
}

/**
 * The class a number wears (contract rule 14): lining, tabular figures whatever the font, in the numeric family.
 * `--tradecn-font-numeric` is the sans by default, so letters stay proportional and only the digits take one
 * width, which is what a column of prices wants. docs/typography.md has the reasoning and the tokens.
 */
export const NUMERIC_CLASS = "font-(family-name:--tradecn-font-numeric) lining-nums tabular-nums"
/** The same figures in the mono stack, `--tradecn-font-mono`: for a fraction quote, so digits and the dash take one width; tails still lengthen a quote. */
export const MONO_NUMERIC_CLASS = "font-(family-name:--tradecn-font-mono) lining-nums tabular-nums"

/**
 * The class for a number printed under a convention: a fraction price (99-16+) sets in the mono stack, so
 * digits and the dash take one width down a column; a tailed quote still runs longer than an untailed one.
 * Every other price, and every quote in another basis, keeps the numeric family.
 */
export function numericFontClass(c?: PriceConvention | InstrumentConvention | null): string {
  const price = c && "price" in c ? (quoteBasisOf(c) === "price" ? c.price : null) : c
  return price?.kind === "fraction" ? MONO_NUMERIC_CLASS : NUMERIC_CLASS
}

/** The word for a quote field's label, per basis. */
export const QUOTE_BASIS_LABELS: Record<QuoteBasis, string> = { price: "Price", yield: "Yield", discount: "Discount", spread: "Spread" }

const QUOTE_DEFAULTS: Record<Exclude<QuoteBasis, "price">, { step: number; decimals: number }> = {
  yield: { step: 0.001, decimals: 3 },
  discount: { step: 0.001, decimals: 3 },
  spread: { step: 0.1, decimals: 1 },
}

export function quoteBasisOf(c: InstrumentConvention): QuoteBasis {
  return c.quoteBasis ?? "price"
}

/** Whether a higher quote means a lower price for this instrument: declared, else by basis — yield and discount invert, price and spread do not. */
export function quoteInvertedOf(c: InstrumentConvention): boolean {
  if (c.quoteInverted !== undefined) return c.quoteInverted
  const basis = quoteBasisOf(c)
  return basis === "yield" || basis === "discount"
}

/** What a quote steps by in its basis: the tick for a price, else `quoteStep` or the basis default. */
export function quoteStepOf(c: InstrumentConvention): number {
  const basis = quoteBasisOf(c)
  return basis === "price" ? c.tick : (c.quoteStep ?? QUOTE_DEFAULTS[basis].step)
}

function quoteDecimalsOf(c: InstrumentConvention): number {
  const basis = quoteBasisOf(c)
  return basis === "price" ? 0 : (c.quoteDecimals ?? QUOTE_DEFAULTS[basis].decimals)
}

/** A quote in the instrument's basis: a price by its convention, else a fixed decimal with the basis's decimals and no unit, since the field's label says the basis. */
export function formatQuote(v: Nullable, c: InstrumentConvention, l?: Locale): string {
  if (isNil(v)) return NULL_TOKEN
  if (quoteBasisOf(c) === "price") return formatPrice(v, c.price, l)
  return typographicMinus(fixed(roundToTick(v, quoteStepOf(c)), quoteDecimalsOf(c), l?.locale))
}

/** Inverse of formatQuote for a quote field. A price takes its notation or a decimal; the others take a decimal and snap to the quote step. Null when the text is not a quote. */
export function parseQuote(s: string, c: InstrumentConvention): number | null {
  if (quoteBasisOf(c) === "price") return parsePrice(s, c.price)
  const text = stripGrouping(s, { decimals: quoteDecimalsOf(c) > 0 })
  if (text === null || !/^[+-]?(\d+\.?\d*|\.\d+)$/.test(text)) return null
  const n = Number(text)
  if (!Number.isFinite(n)) return null
  // Snapping divides by the step, which can overflow where the raw number does not; what
  // cannot print back is not a quote.
  const snapped = roundToTick(n, quoteStepOf(c))
  return Number.isFinite(snapped) ? snapped : null
}

/** Move a quote by `steps` of its step, from the nearest grid value. */
export function stepQuote(v: number, c: InstrumentConvention, steps: number): number {
  return stepByTick(v, quoteStepOf(c), steps)
}

/** Bind a convention once per instrument; a grid column calls `formatters[row.instrumentId].price(v)`, a quote field its `quote`, `parseQuote`, and `stepQuote`. */
export function createInstrumentFormatter(c: InstrumentConvention, l?: Locale) {
  return {
    tick: c.tick,
    basis: quoteBasisOf(c),
    quoteStep: quoteStepOf(c),
    price: (v: Nullable) => formatPrice(v, c.price, l),
    yield: (v: Nullable) => formatYield(v, { decimals: c.yieldDecimals ?? 3, locale: l?.locale }),
    step: (v: number, steps: number) => stepByTick(v, c.tick, steps),
    parsePrice: (s: string) => parsePrice(s, c.price),
    quantity: (v: Nullable) => formatQuantity(v, l),
    quote: (v: Nullable) => formatQuote(v, c, l),
    parseQuote: (s: string) => parseQuote(s, c),
    stepQuote: (v: number, steps: number) => stepQuote(v, c, steps),
  }
}

:root {
  --tradecn-font-accessible: 'Atkinson Hyperlegible Next', 'Atkinson Hyperlegible', ui-sans-serif, system-ui, sans-serif;
  --tradecn-font-accessible-mono: 'Atkinson Hyperlegible Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --tradecn-font-mono: 'JetBrains Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --tradecn-font-numeric: var(--tradecn-font-sans);
  --tradecn-font-sans: 'Inter', ui-sans-serif, system-ui, sans-serif;
}

.dark {
  --tradecn-font-accessible: 'Atkinson Hyperlegible Next', 'Atkinson Hyperlegible', ui-sans-serif, system-ui, sans-serif;
  --tradecn-font-accessible-mono: 'Atkinson Hyperlegible Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --tradecn-font-mono: 'JetBrains Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --tradecn-font-numeric: var(--tradecn-font-sans);
  --tradecn-font-sans: 'Inter', ui-sans-serif, system-ui, sans-serif;
}

:root[data-accessibility="hyperlegible"], [data-accessibility="hyperlegible"] {
  --tradecn-font-sans: var(--tradecn-font-accessible);
  --tradecn-font-mono: var(--tradecn-font-accessible-mono);
}