import type { PhenologyConfig } from '../automation/rule-config/rule-config.types';
import { daysBetween } from '../common/dates';
import {
  PHENOLOGY_PHASES,
  type PhaseSourceKey,
  type PhenologyPhaseKey,
  type SeasonNote,
} from '../season/season-types';
import type { GtsResult } from './gts';

/** GTS whose last day with data is older than this many days is not used. */
export const GTS_MAX_AGE_DAYS = 3;

export interface PhaseReport {
  phase: PhenologyPhaseKey;
  date: string;
  revoked: boolean;
}

export interface PhaseInputs {
  today: string;
  reports: readonly PhaseReport[];
  gts: GtsResult | null;
  hasCoordinates: boolean;
  /** GTS thresholds in force: configured plus calibrated. */
  thresholds: Partial<Record<PhenologyPhaseKey, number>>;
  config: PhenologyConfig;
  previous: {
    phase: PhenologyPhaseKey | null;
    source?: PhaseSourceKey | null;
  } | null;
  /** True after a report was revoked: the phase may fall back. */
  allowBackward: boolean;
}

export interface EffectivePhase {
  reportedPhase: PhenologyPhaseKey | null;
  reportedOn: string | null;
  estimatedPhase: PhenologyPhaseKey | null;
  effectivePhase: PhenologyPhaseKey | null;
  phaseSource: PhaseSourceKey | null;
  note: SeasonNote;
}

interface Candidate {
  phase: PhenologyPhaseKey;
  source: PhaseSourceKey;
}

const rankOf = (phase: PhenologyPhaseKey): number =>
  PHENOLOGY_PHASES.indexOf(phase);

/** The higher phase; the first wins a tie. */
function higher(a: Candidate | null, b: Candidate | null): Candidate | null {
  if (a === null || b === null) {
    return a ?? b;
  }
  return rankOf(b.phase) > rankOf(a.phase) ? b : a;
}

/** Reports that count for an apiary: its own and those for all apiaries. */
export function reportsApplyingTo<T extends { apiaryId: string | null }>(
  apiaryId: string,
  reports: readonly T[],
): T[] {
  return reports.filter(
    (report) => report.apiaryId === null || report.apiaryId === apiaryId,
  );
}

/**
 * Why the weather cannot decide the phase, if it cannot: no coordinates, the
 * last day with data too old, or too many gaps. Null if GTS is off or fine.
 */
export function seasonNoteFor(input: {
  useGts: boolean;
  hasCoordinates: boolean;
  today: string;
  lastDataDay: string | null;
  gtsUsable: boolean;
}): SeasonNote {
  if (!input.useGts) {
    return null;
  }
  if (!input.hasCoordinates) {
    return 'NO_COORDINATES';
  }
  // January 1st: no day of the year has passed, there is nothing to judge.
  if (input.today.endsWith('-01-01')) {
    return null;
  }
  if (
    input.lastDataDay === null ||
    daysBetween(input.lastDataDay, input.today) > GTS_MAX_AGE_DAYS
  ) {
    return 'WEATHER_STALE';
  }
  return input.gtsUsable ? null : 'WEATHER_GAPS';
}

/** The GTS that may decide today's phase; null if it is off, stale or gappy. */
export function usableGts(
  inputs: Pick<PhaseInputs, 'today' | 'gts' | 'hasCoordinates' | 'config'>,
): GtsResult | null {
  const { gts } = inputs;
  if (gts === null || !gts.usable || gts.throughDay === null) {
    return null;
  }
  const note = seasonNoteFor({
    useGts: inputs.config.useGts,
    hasCoordinates: inputs.hasCoordinates,
    today: inputs.today,
    lastDataDay: gts.throughDay,
    gtsUsable: gts.usable,
  });
  return inputs.config.useGts && note === null ? gts : null;
}

function reported(inputs: PhaseInputs): {
  phase: PhenologyPhaseKey | null;
  on: string | null;
} {
  const yearStart = `${inputs.today.slice(0, 4)}-01-01`;
  const valid = inputs.reports.filter(
    (report) =>
      !report.revoked &&
      report.date >= yearStart &&
      report.date <= inputs.today,
  );
  let phase: PhenologyPhaseKey | null = null;
  for (const report of valid) {
    if (phase === null || rankOf(report.phase) > rankOf(phase)) {
      phase = report.phase;
    }
  }
  const dates = valid.filter((r) => r.phase === phase).map((r) => r.date);
  return { phase, on: dates.length > 0 ? dates.sort()[0] : null };
}

function gtsCandidate(
  inputs: PhaseInputs,
  gts: GtsResult | null,
): Candidate | null {
  if (gts === null) {
    return null;
  }
  let best: Candidate | null = null;
  for (const phase of PHENOLOGY_PHASES) {
    const threshold = inputs.thresholds[phase];
    if (threshold !== undefined && gts.gts >= threshold) {
      best = { phase, source: 'GTS' };
    }
  }
  return best;
}

/** The latest calendar phase reached; phases with a GTS threshold are skipped while GTS decides. */
function calendarCandidate(
  inputs: PhaseInputs,
  gtsDecides: boolean,
): Candidate | null {
  const year = inputs.today.slice(0, 4);
  let best: Candidate | null = null;
  for (const phase of PHENOLOGY_PHASES) {
    if (gtsDecides && inputs.thresholds[phase] !== undefined) {
      continue;
    }
    if (`${year}-${inputs.config.calendarFallback[phase]}` <= inputs.today) {
      best = { phase, source: 'CALENDAR' };
    }
  }
  return best;
}

/**
 * The phase of an apiary today: the maximum of the user's report, the GTS
 * estimate and the calendar (the calendar only for phases without a GTS
 * threshold, or everywhere while the weather cannot be used). Within a year it
 * only moves forward, unless `allowBackward` (a report was revoked). Before
 * the first phase of the year there is no phase, and the calendar is the source.
 */
export function effectivePhaseOf(inputs: PhaseInputs): EffectivePhase {
  const gts = usableGts(inputs);
  const note = seasonNoteFor({
    useGts: inputs.config.useGts,
    hasCoordinates: inputs.hasCoordinates,
    today: inputs.today,
    lastDataDay: inputs.gts?.throughDay ?? null,
    gtsUsable: inputs.gts?.usable ?? false,
  });
  const report = reported(inputs);
  const reportCandidate: Candidate | null =
    report.phase === null ? null : { phase: report.phase, source: 'REPORT' };
  const estimate = higher(
    gtsCandidate(inputs, gts),
    calendarCandidate(inputs, gts !== null),
  );
  let chosen = higher(reportCandidate, estimate);

  const previous = inputs.previous?.phase ?? null;
  if (
    previous !== null &&
    !inputs.allowBackward &&
    (chosen === null || rankOf(previous) > rankOf(chosen.phase))
  ) {
    chosen = {
      phase: previous,
      source: inputs.previous?.source ?? chosen?.source ?? 'CALENDAR',
    };
  }
  return {
    reportedPhase: report.phase,
    reportedOn: report.on,
    estimatedPhase: estimate?.phase ?? null,
    effectivePhase: chosen?.phase ?? null,
    phaseSource: chosen?.source ?? 'CALENDAR',
    note,
  };
}