/**
 * # series/state — the canonical market state per signal instrument (RUNTIME §2)
 *
 * One causal coordinate per signal instrument: `spot`, `hod`/`lod` (+ their timestamps),
 * the **opening range**, `vwap`, `prior_close`, and the session **phase**. It is updated
 * **only** from bus events via {@link CanonicalState.applyEvent} — the single ingress —
 * and every derived series (the window metrics, the provider) reads back through it;
 * nothing is recomputed per consumer (RUNTIME §2). State at event *N* is a pure function
 * of events `≤ N` (no look-ahead, RUNTIME §0/§7).
 *
 * ## VWAP — time-weighted (documented choice)
 * The v1 bus `SpotPayload` is `{ instrument, px }` — it carries **no volume**. VWAP is
 * therefore **time-weighted**: each price is weighted by the time it prevailed, so
 * `vwap = Σ pxᵢ·dtᵢ / Σ dtᵢ` where `dtᵢ` is the interval price *i* was the standing quote
 * (the left-price of each interval). This is the honest reduction the data supports; the
 * accumulator is generic over the weight, so a future volume-bearing SPOT specializes to
 * true volume-weighting with no change to callers. Before the second tick there is no
 * elapsed interval, so vwap reads the first spot (a degenerate single-sample average).
 *
 * ## prior_close — injected, not on the v1 META
 * `prior_close` is a *cross-session* fact and the v1 `MetaPayload`
 * (`session_date/instruments/mode/bus_schema`) does not carry it. It is injected via
 * {@link CanonicalStateConfig.priorClose} at construction. Absent that, `prior_close`
 * reads UNKNOWN and any statement referencing it de-arms cleanly (fail-closed, RUNTIME §8).
 *
 * ## Opening range — first N minutes
 * The opening range is the high/low of spot over the first `openingRangeMinutes` (default
 * 5) of the session, anchored at the **first SPOT tick's ts** (the session's first observed
 * price). It reads UNKNOWN until that first tick; once the window elapses it is frozen.
 *
 * ## Inclusive vs exclusive levels — the pane/trigger split (RUNTIME §2)
 * `hod`/`lod` (and `or_high`/`or_low` while the range is still forming) come in **two
 * flavours**. The plain getters (`hod`, `lod`, `orHigh`, `orLow`) are **inclusive** of the
 * current sample — the true running extreme a pane/frame should display. The **`*Trigger`**
 * getters (`hodTrigger`, …) are **exclusive** of the current sample: the value as it stood
 * **before** this event's spot was folded in. Trigger evaluation reads the exclusive flavour
 * so `spot crosses above hod` can actually fire — a fresh high IS a cross above the prior
 * high (the trader idiom). With the inclusive value the current spot is already baked into
 * `hod`, so `spot > hod` is never true and the cross can never fire. The exclusive value is
 * captured at the top of {@link CanonicalState.onSpot}, before the extreme is updated; a
 * non-SPOT event leaves it untouched (there is no new sample to be exclusive of).
 */

import type { BusEvent, SessionPhase } from "../bus/index.ts";
import { UNKNOWN, durationMs, type Unknown } from "./types.ts";
import { WindowEngine, type WindowConfig } from "./windows.ts";

/** A `(value, ts)` reading — a level with the injected timestamp it was set at. */
export interface Stamped {
  readonly value: number;
  readonly ts: number;
}

export interface CanonicalStateConfig {
  /** The signal instrument this state tracks. Only SPOT ticks for this symbol drive it. */
  readonly instrument: string;
  /** Prior session's close (cross-session; not on the v1 META). UNKNOWN if omitted. */
  readonly priorClose?: number;
  /** Opening-range span in minutes (default 5). */
  readonly openingRangeMinutes?: number;
  /** Window-engine configuration (baseline capacity, warmup floor, sample cap). */
  readonly windows?: WindowConfig;
}

export class CanonicalState {
  readonly instrument: string;
  readonly windows: WindowEngine;

  private readonly orMs: number;
  private readonly priorCloseVal: number | undefined;

  private spotVal: number | undefined;
  private spotTs: number | undefined;
  private hodVal: Stamped | undefined;
  private lodVal: Stamped | undefined;

  // exclusive-of-current-sample levels (the trigger flavour): the extreme as it stood BEFORE
  // this event's spot was folded in. Captured at the top of onSpot; untouched by non-SPOT events.
  private hodExclVal: number | undefined;
  private lodExclVal: number | undefined;
  private orHiExclVal: number | undefined;
  private orLoExclVal: number | undefined;

  private orAnchorTs: number | undefined;
  private orHi: number | undefined;
  private orLo: number | undefined;

  // time-weighted VWAP accumulators
  private vwapNum = 0;
  private vwapDen = 0;
  private lastPx: number | undefined;
  private lastPxTs: number | undefined;

  private phaseVal: SessionPhase | undefined;

  constructor(cfg: CanonicalStateConfig) {
    this.instrument = cfg.instrument;
    this.priorCloseVal = cfg.priorClose;
    this.orMs = durationMs(cfg.openingRangeMinutes ?? 5, "m");
    this.windows = new WindowEngine(cfg.windows ?? {});
  }

  /** The single ingress. Applies a bus event to the canonical state — SPOT (this
   * instrument) drives price/level/vwap/windows; HEARTBEAT carries the session phase; all
   * other streams are ignored here (they are handled by other modules). Idempotent-safe on
   * unrelated events. */
  applyEvent(ev: BusEvent): void {
    if (ev.stream === "TICK") {
      if (ev.type === "SPOT") {
        if (ev.instrument === this.instrument) this.onSpot(ev.ts, ev.px);
      } else if (ev.type === "HEARTBEAT") {
        if (ev.phase !== undefined) this.phaseVal = ev.phase;
      }
    }
    // META/BOOK/DETECTOR/PLAN/ORDER/WAKE/CONTROL/REGIME: not canonical-state inputs here.
  }

  private onSpot(ts: number, px: number): void {
    // Capture the exclusive (pre-this-sample) extremes BEFORE folding px in — the trigger
    // flavour, so `spot crosses above hod` fires on a fresh high (RUNTIME §2, file header).
    this.hodExclVal = this.hodVal?.value;
    this.lodExclVal = this.lodVal?.value;
    this.orHiExclVal = this.orHi;
    this.orLoExclVal = this.orLo;

    // time-weighted VWAP: the *previous* price prevailed from lastPxTs to now.
    if (this.lastPx !== undefined && this.lastPxTs !== undefined) {
      const dt = ts - this.lastPxTs;
      if (dt > 0) {
        this.vwapNum += this.lastPx * dt;
        this.vwapDen += dt;
      }
    }
    this.lastPx = px;
    this.lastPxTs = ts;

    this.spotVal = px;
    this.spotTs = ts;

    if (this.hodVal === undefined || px > this.hodVal.value) this.hodVal = { value: px, ts };
    if (this.lodVal === undefined || px < this.lodVal.value) this.lodVal = { value: px, ts };

    // opening range: anchored at the first spot, frozen once the window elapses.
    if (this.orAnchorTs === undefined) this.orAnchorTs = ts;
    if (ts <= this.orAnchorTs + this.orMs) {
      this.orHi = this.orHi === undefined ? px : Math.max(this.orHi, px);
      this.orLo = this.orLo === undefined ? px : Math.min(this.orLo, px);
    }

    this.windows.pushSpot(ts, px);
  }

  // ── scalar readers (UNKNOWN until warm) ─────────────────────────────────────

  get spot(): number | Unknown {
    return this.spotVal ?? UNKNOWN;
  }
  get spotStamp(): Stamped | Unknown {
    return this.spotVal !== undefined && this.spotTs !== undefined
      ? { value: this.spotVal, ts: this.spotTs }
      : UNKNOWN;
  }
  get hod(): number | Unknown {
    return this.hodVal?.value ?? UNKNOWN;
  }
  get hodStamp(): Stamped | Unknown {
    return this.hodVal ?? UNKNOWN;
  }
  get lod(): number | Unknown {
    return this.lodVal?.value ?? UNKNOWN;
  }
  get lodStamp(): Stamped | Unknown {
    return this.lodVal ?? UNKNOWN;
  }

  // ── exclusive-of-current-sample levels (the TRIGGER flavour, RUNTIME §2) ─────
  /** `hod` as it stood before this event's spot — so a fresh high is a cross above it. */
  get hodTrigger(): number | Unknown {
    return this.hodExclVal ?? UNKNOWN;
  }
  /** `lod` as it stood before this event's spot — so a fresh low is a cross below it. */
  get lodTrigger(): number | Unknown {
    return this.lodExclVal ?? UNKNOWN;
  }
  /** `or_high` exclusive of the current sample while the range forms; the frozen level after. */
  get orHighTrigger(): number | Unknown {
    return this.orHiExclVal ?? UNKNOWN;
  }
  /** `or_low` exclusive of the current sample while the range forms; the frozen level after. */
  get orLowTrigger(): number | Unknown {
    return this.orLoExclVal ?? UNKNOWN;
  }
  get priorClose(): number | Unknown {
    return this.priorCloseVal ?? UNKNOWN;
  }
  get orHigh(): number | Unknown {
    return this.orHi ?? UNKNOWN;
  }
  get orLow(): number | Unknown {
    return this.orLo ?? UNKNOWN;
  }
  get phase(): SessionPhase | Unknown {
    return this.phaseVal ?? UNKNOWN;
  }

  /** Time-weighted VWAP (see file header). UNKNOWN before the first spot; the first spot's
   * price until an interval accrues; the weighted average thereafter. */
  get vwap(): number | Unknown {
    if (this.spotVal === undefined) return UNKNOWN;
    if (this.vwapDen === 0) return this.spotVal; // single sample: degenerate average
    return this.vwapNum / this.vwapDen;
  }

  reset(): void {
    this.spotVal = undefined;
    this.spotTs = undefined;
    this.hodVal = undefined;
    this.lodVal = undefined;
    this.hodExclVal = undefined;
    this.lodExclVal = undefined;
    this.orHiExclVal = undefined;
    this.orLoExclVal = undefined;
    this.orAnchorTs = undefined;
    this.orHi = undefined;
    this.orLo = undefined;
    this.vwapNum = 0;
    this.vwapDen = 0;
    this.lastPx = undefined;
    this.lastPxTs = undefined;
    this.phaseVal = undefined;
    this.windows.reset();
  }
}