// FlowAggregator — owns the predicted-volume integrator + net-flow selection
// + remaining-time projection for the pumping-station basin.
//
// Pure domain. Takes a context bag with the live MeasurementContainer, the
// basin geometry, and the merged config; mutates measurements in place and
// keeps a tiny piece of integrator state internally.

const { interpolation } = require('generalFunctions');

const DEFAULT_FLOW_THRESHOLD = 1e-4;
const DEFAULT_FLOW_VARIANTS = ['measured', 'predicted'];
const DEFAULT_LEVEL_VARIANTS = ['measured', 'predicted'];
const DEFAULT_FLOW_POSITIONS = {
  inflow: ['in', 'upstream'],
  outflow: ['out', 'downstream'],
};

class FlowAggregator {
  constructor(ctx = {}) {
    if (!ctx.measurements) throw new Error('FlowAggregator: ctx.measurements is required');
    if (!ctx.basin) throw new Error('FlowAggregator: ctx.basin is required');

    this.measurements = ctx.measurements;
    this.basin = ctx.basin;
    this.config = ctx.config || {};
    this.logger = ctx.logger || null;
    this._interp = ctx.interpolation || new interpolation();

    this.flowVariants = ctx.flowVariants || DEFAULT_FLOW_VARIANTS;
    this.levelVariants = ctx.levelVariants || DEFAULT_LEVEL_VARIANTS;
    this.flowPositions = ctx.flowPositions || DEFAULT_FLOW_POSITIONS;

    const cfgThresh = Number(this.config?.general?.flowThreshold);
    this.flowThreshold = Number.isFinite(ctx.flowThreshold)
      ? ctx.flowThreshold
      : (Number.isFinite(cfgThresh) ? cfgThresh : DEFAULT_FLOW_THRESHOLD);

    this._predictedFlowState = null;
    this._lastNetFlow = { value: 0, source: null, direction: 'steady' };
    this._lastRemaining = { seconds: null, source: null };
  }

  resetState(timestamp = Date.now()) {
    this._predictedFlowState = { inflow: 0, outflow: 0, lastTimestamp: timestamp };
  }

  update() {
    const flowUnit = 'm3/s';
    const now = Date.now();

    const inflow = this.measurements.sum('flow', 'predicted', this.flowPositions.inflow, flowUnit) || 0;
    const outflow = this.measurements.sum('flow', 'predicted', this.flowPositions.outflow, flowUnit) || 0;

    if (!this._predictedFlowState) this._predictedFlowState = { inflow, outflow, lastTimestamp: now };

    const tPrev = this._predictedFlowState.lastTimestamp ?? now;
    const dt = Math.max((now - tPrev) / 1000, 0);
    const dV = dt > 0 ? (inflow - outflow) * dt : 0;

    const volSeries = this.measurements.type('volume').variant('predicted').position('atequipment');
    const currentVol = volSeries.getCurrentValue('m3');
    const nextVol = (currentVol ?? this.basin.minVol ?? 0) + dV;
    const writeTs = tPrev + dt * 1000;

    volSeries.value(nextVol, writeTs, 'm3').unit('m3');

    const surfaceArea = this.basin.surfaceArea;
    const nextLevel = surfaceArea > 0 ? Math.max(nextVol, 0) / surfaceArea : 0;
    this.measurements.type('level').variant('predicted').position('atequipment')
      .value(nextLevel, writeTs, 'm').unit('m');

    const percent = this._interp.interpolate_lin_single_point(
      nextVol, this.basin.minVol, this.basin.maxVolAtOverflow, 0, 100
    );
    this.measurements.type('volumePercent').variant('predicted').position('atequipment')
      .value(percent, writeTs, '%');

    this._predictedFlowState = { inflow, outflow, lastTimestamp: writeTs };
  }

  selectBestNetFlow() {
    const type = 'flow';
    const unit = this.measurements.getUnit(type) || 'm3/s';

    for (const variant of this.flowVariants) {
      const bucket = this.measurements.measurements?.[type]?.[variant];
      if (!bucket || Object.keys(bucket).length === 0) continue;

      const inflow = this.measurements.sum(type, variant, this.flowPositions.inflow, unit) || 0;
      const outflow = this.measurements.sum(type, variant, this.flowPositions.outflow, unit) || 0;
      if (Math.abs(inflow) < this.flowThreshold && Math.abs(outflow) < this.flowThreshold) continue;

      const net = inflow - outflow;
      this.measurements.type('netFlowRate').variant(variant).position('atequipment')
        .value(net, Date.now(), unit);
      const result = { value: net, source: variant, direction: this.deriveDirection(net) };
      this._lastNetFlow = result;
      return result;
    }

    for (const variant of this.levelVariants) {
      const rate = this._levelRate(variant);
      if (!Number.isFinite(rate)) continue;
      const net = rate * this.basin.surfaceArea;
      const result = { value: net, source: `level:${variant}`, direction: this.deriveDirection(net) };
      this._lastNetFlow = result;
      return result;
    }

    if (this.logger) this.logger.warn('No usable measurements to compute net flow; assuming steady.');
    const result = { value: 0, source: null, direction: 'steady' };
    this._lastNetFlow = result;
    return result;
  }

  computeRemainingTime(netFlow) {
    if (!netFlow || Math.abs(netFlow.value) < this.flowThreshold) {
      this._lastRemaining = { seconds: null, source: null };
      return this._lastRemaining;
    }

    const { overflowLevel, outflowLevel, surfaceArea } = this.basin;
    if (!Number.isFinite(surfaceArea) || surfaceArea <= 0) {
      this._lastRemaining = { seconds: null, source: null };
      return this._lastRemaining;
    }

    for (const variant of this.levelVariants) {
      const lvl = this.measurements.type('level').variant(variant).position('atequipment').getCurrentValue('m');
      if (!Number.isFinite(lvl)) continue;

      const remainingHeight = netFlow.value > 0
        ? Math.max(overflowLevel - lvl, 0)
        : Math.max(lvl - outflowLevel, 0);
      const seconds = (remainingHeight * surfaceArea) / Math.abs(netFlow.value);
      if (!Number.isFinite(seconds)) continue;

      this._lastRemaining = { seconds, source: `${netFlow.source}/${variant}` };
      return this._lastRemaining;
    }

    this._lastRemaining = { seconds: null, source: netFlow.source };
    return this._lastRemaining;
  }

  deriveDirection(netFlow) {
    if (netFlow > this.flowThreshold) return 'filling';
    if (netFlow < -this.flowThreshold) return 'draining';
    return 'steady';
  }

  tick() {
    this.update();
    const netFlow = this.selectBestNetFlow();
    const remaining = this.computeRemainingTime(netFlow);
    return { netFlow, remaining };
  }

  snapshot() {
    return {
      direction: this._lastNetFlow.direction,
      netFlow: this._lastNetFlow.value,
      flowSource: this._lastNetFlow.source,
      secondsRemaining: this._lastRemaining.seconds,
    };
  }

  _levelRate(variant) {
    const m = this.measurements.type('level').variant(variant).position('atequipment').get();
    if (!m || !m.values || m.values.length < 2) return null;
    const current = m.getLaggedSample?.(0);
    const previous = m.getLaggedSample?.(1);
    if (!current || !previous || previous.timestamp == null) return null;
    const dt = (current.timestamp - previous.timestamp) / 1000;
    if (!Number.isFinite(dt) || dt <= 0) return null;
    return (current.value - previous.value) / dt;
  }
}

module.exports = FlowAggregator;