/**
 * Equity volume-by-price profile from OHLC bars (not options OI).
 * Uniform volume split across bins that a bar's low–high spans.
 */

export interface VolumeProfileCandle {
  h: number;
  l: number;
  c?: number;
  v: number;
}

export interface VolumeProfileBin {
  priceLo: number;
  priceHi: number;
  mid: number;
  volume: number;
}

export interface VolumeProfileResult {
  bins: VolumeProfileBin[];
  /** Mid-price of the highest-volume bin. */
  pocMid: number | null;
  /** Value-area high / low (mids of outer bins in the value area). */
  vah: number | null;
  val: number | null;
  totalVolume: number;
}

export interface BuildVolumeProfileOpts {
  /** Number of price bins. Default 32. */
  bins?: number;
  /** Fraction of volume for value area (e.g. 0.7). Default 0.7. */
  valueAreaPct?: number;
}

/**
 * Build a volume profile from candles in the visible range.
 * Empty or zero-volume inputs return empty bins.
 */
export function buildVolumeProfile(
  candles: VolumeProfileCandle[],
  opts: BuildVolumeProfileOpts = {},
): VolumeProfileResult {
  const binCount = Math.max(2, Math.min(80, Math.floor(opts.bins ?? 32)));
  const valueAreaPct = Math.min(0.99, Math.max(0.5, opts.valueAreaPct ?? 0.7));

  const usable = candles.filter(
    (c) =>
      Number.isFinite(c.h) &&
      Number.isFinite(c.l) &&
      Number.isFinite(c.v) &&
      c.v > 0 &&
      c.h >= c.l,
  );

  if (usable.length === 0) {
    return { bins: [], pocMid: null, vah: null, val: null, totalVolume: 0 };
  }

  let priceMin = Infinity;
  let priceMax = -Infinity;
  let totalVolume = 0;
  for (const c of usable) {
    if (c.l < priceMin) priceMin = c.l;
    if (c.h > priceMax) priceMax = c.h;
    totalVolume += c.v;
  }

  // Flat range: single effective level
  if (!(priceMax > priceMin)) {
    const mid = priceMin;
    const bins: VolumeProfileBin[] = [
      { priceLo: mid, priceHi: mid, mid, volume: totalVolume },
    ];
    return { bins, pocMid: mid, vah: mid, val: mid, totalVolume };
  }

  const width = (priceMax - priceMin) / binCount;
  const volumes = new Array<number>(binCount).fill(0);

  for (const c of usable) {
    const lo = c.l;
    const hi = c.h;
    // Inclusive bins from low to high
    let i0 = Math.floor((lo - priceMin) / width);
    let i1 = Math.floor((hi - priceMin) / width);
    if (i0 < 0) i0 = 0;
    if (i1 >= binCount) i1 = binCount - 1;
    if (i1 < i0) i1 = i0;
    const n = i1 - i0 + 1;
    const share = c.v / n;
    for (let i = i0; i <= i1; i++) volumes[i] += share;
  }

  const bins: VolumeProfileBin[] = volumes.map((volume, i) => {
    const priceLo = priceMin + i * width;
    const priceHi = i === binCount - 1 ? priceMax : priceMin + (i + 1) * width;
    return {
      priceLo,
      priceHi,
      mid: (priceLo + priceHi) / 2,
      volume,
    };
  });

  // POC = max volume bin
  let pocIdx = 0;
  for (let i = 1; i < bins.length; i++) {
    if (bins[i].volume > bins[pocIdx].volume) pocIdx = i;
  }

  // Value area: expand from POC until we cover valueAreaPct of total volume
  const target = totalVolume * valueAreaPct;
  let lo = pocIdx;
  let hi = pocIdx;
  let covered = bins[pocIdx].volume;
  while (covered < target && (lo > 0 || hi < bins.length - 1)) {
    const nextLo = lo > 0 ? bins[lo - 1].volume : -1;
    const nextHi = hi < bins.length - 1 ? bins[hi + 1].volume : -1;
    if (nextHi >= nextLo) {
      hi++;
      covered += bins[hi].volume;
    } else {
      lo--;
      covered += bins[lo].volume;
    }
  }

  return {
    bins,
    pocMid: bins[pocIdx].mid,
    vah: bins[hi].priceHi,
    val: bins[lo].priceLo,
    totalVolume,
  };
}