import { Solar } from 'lunar-typescript';
import { BRANCHES, STEM_INFO } from './constants';
import type {
  BaziChart,
  CivilTime,
  EarthlyBranchName,
  ElementSeasonalState,
  FiveElement,
  FourSeason,
  HeavenlyStemName,
  PillarKey,
  SeasonContext,
  SeasonalStatesContext,
  SolarTermDistance,
  TwelveGrowthLabel,
  TwelveGrowthPosition,
  TwelveGrowthStage,
} from './types';

const TWELVE_GROWTH: ReadonlyArray<{
  stage: TwelveGrowthStage;
  stageLabel: TwelveGrowthLabel;
}> = [
  { stage: 'changsheng', stageLabel: '长生' },
  { stage: 'muyu', stageLabel: '沐浴' },
  { stage: 'guandai', stageLabel: '冠带' },
  { stage: 'linguan', stageLabel: '临官' },
  { stage: 'diwang', stageLabel: '帝旺' },
  { stage: 'shuai', stageLabel: '衰' },
  { stage: 'bing', stageLabel: '病' },
  { stage: 'si', stageLabel: '死' },
  { stage: 'mu', stageLabel: '墓' },
  { stage: 'jue', stageLabel: '绝' },
  { stage: 'tai', stageLabel: '胎' },
  { stage: 'yang', stageLabel: '养' },
];

const GROWTH_START: Record<HeavenlyStemName, EarthlyBranchName> = {
  甲: '亥',
  乙: '午',
  丙: '寅',
  丁: '酉',
  戊: '寅',
  己: '酉',
  庚: '巳',
  辛: '子',
  壬: '申',
  癸: '卯',
};

const MONTH_SEASON: Record<EarthlyBranchName, FourSeason> = {
  寅: 'spring',
  卯: 'spring',
  辰: 'spring',
  巳: 'summer',
  午: 'summer',
  未: 'summer',
  申: 'autumn',
  酉: 'autumn',
  戌: 'autumn',
  亥: 'winter',
  子: 'winter',
  丑: 'winter',
};

const SEASON_LABEL = {
  spring: '春',
  summer: '夏',
  autumn: '秋',
  winter: '冬',
} as const;

const SEASONAL_STATE_LABEL = {
  wang: '旺',
  xiang: '相',
  xiu: '休',
  qiu: '囚',
  si: '死',
} as const;

const SEASONAL_STATES: Record<
  FourSeason,
  Record<FiveElement, keyof typeof SEASONAL_STATE_LABEL>
> = {
  spring: { wood: 'wang', fire: 'xiang', water: 'xiu', metal: 'qiu', earth: 'si' },
  summer: { fire: 'wang', earth: 'xiang', wood: 'xiu', water: 'qiu', metal: 'si' },
  autumn: { metal: 'wang', water: 'xiang', earth: 'xiu', fire: 'qiu', wood: 'si' },
  winter: { water: 'wang', wood: 'xiang', metal: 'xiu', earth: 'qiu', fire: 'si' },
};

function positiveModulo(value: number, modulus: number): number {
  return ((value % modulus) + modulus) % modulus;
}

export function getTwelveGrowthStage(
  stem: HeavenlyStemName,
  branch: EarthlyBranchName,
): { stage: TwelveGrowthStage; stageLabel: TwelveGrowthLabel } {
  const startIndex = BRANCHES.indexOf(GROWTH_START[stem]);
  const branchIndex = BRANCHES.indexOf(branch);
  const stageIndex = STEM_INFO[stem].yinYang === 'yang'
    ? positiveModulo(branchIndex - startIndex, BRANCHES.length)
    : positiveModulo(startIndex - branchIndex, BRANCHES.length);
  const result = TWELVE_GROWTH[stageIndex];
  if (!result) throw new RangeError(`无法计算${stem}在${branch}的十二长生`);
  return result;
}

export function getSeasonalStates(
  monthBranch: EarthlyBranchName,
): SeasonalStatesContext {
  const season = MONTH_SEASON[monthBranch];
  const states = SEASONAL_STATES[season];
  const byElement = Object.fromEntries(
    (Object.keys(states) as FiveElement[]).map((element) => {
      const state = states[element];
      const value: ElementSeasonalState = {
        state,
        stateLabel: SEASONAL_STATE_LABEL[state],
      };
      return [element, value];
    }),
  ) as Record<FiveElement, ElementSeasonalState>;

  return {
    basis: 'month-branch-four-season',
    monthBranch,
    season,
    seasonLabel: SEASON_LABEL[season],
    byElement,
  };
}

function solarEpochSeconds(solar: Solar): number {
  const date = new Date(0);
  date.setUTCFullYear(solar.getYear(), solar.getMonth() - 1, solar.getDay());
  date.setUTCHours(solar.getHour(), solar.getMinute(), solar.getSecond(), 0);
  return Math.trunc(date.getTime() / 1000);
}

function formatChinaStandardTime(solar: Solar): string {
  const pad = (value: number) => String(value).padStart(2, '0');
  return `${String(solar.getYear()).padStart(4, '0')}-${pad(solar.getMonth())}-${pad(solar.getDay())}T${pad(solar.getHour())}:${pad(solar.getMinute())}:${pad(solar.getSecond())}+08:00`;
}

function toTermDistance(
  name: string,
  term: Solar,
  birth: Solar,
  kind: 'jie' | 'qi',
  direction: 'previous' | 'next',
): SolarTermDistance {
  return {
    name,
    kind,
    at: formatChinaStandardTime(term),
    direction,
    distanceSeconds: Math.abs(solarEpochSeconds(birth) - solarEpochSeconds(term)),
  };
}

function twelveGrowthByPillar(chart: BaziChart): Record<PillarKey, TwelveGrowthPosition> {
  const result = {} as Record<PillarKey, TwelveGrowthPosition>;
  for (const pillar of Object.values(chart.pillars)) {
    const growth = getTwelveGrowthStage(
      chart.dayMaster.stem,
      pillar.branch.name,
    );
    result[pillar.key] = {
      pillar: pillar.key,
      branch: pillar.branch.name,
      ...growth,
    };
  }
  return result;
}

export function calculateSeasonContext(
  civilTime: Required<CivilTime>,
  chart: BaziChart,
): SeasonContext {
  const birth = Solar.fromYmdHms(
    civilTime.year,
    civilTime.month,
    civilTime.day,
    civilTime.hour,
    civilTime.minute,
    civilTime.second,
  );
  const lunar = birth.getLunar();
  const previous = lunar.getPrevJieQi(false);
  const next = lunar.getNextJieQi(false);
  const previousMonthBoundary = lunar.getPrevJie(false);
  const nextMonthBoundary = lunar.getNextJie(false);

  return {
    model: 'season-context-v1',
    solarTerms: {
      previous: toTermDistance(
        previous.getName(),
        previous.getSolar(),
        birth,
        previous.isJie() ? 'jie' : 'qi',
        'previous',
      ),
      next: toTermDistance(
        next.getName(),
        next.getSolar(),
        birth,
        next.isJie() ? 'jie' : 'qi',
        'next',
      ),
      previousMonthBoundary: toTermDistance(
        previousMonthBoundary.getName(),
        previousMonthBoundary.getSolar(),
        birth,
        'jie',
        'previous',
      ),
      nextMonthBoundary: toTermDistance(
        nextMonthBoundary.getName(),
        nextMonthBoundary.getSolar(),
        birth,
        'jie',
        'next',
      ),
    },
    twelveGrowth: {
      subject: chart.dayMaster,
      direction: chart.dayMaster.yinYang === 'yang' ? 'forward' : 'reverse',
      byPillar: twelveGrowthByPillar(chart),
    },
    seasonalStates: getSeasonalStates(chart.pillars.month.branch.name),
    appliedRules: {
      solarTermProvider: 'lunar-typescript',
      solarTermPrecision: 'second',
      monthBoundaryTerms: 'jie',
      twelveGrowth: 'ten-stem-yang-forward-yin-reverse',
      seasonalStates: 'four-season-wang-xiang-xiu-qiu-si',
      earthTransition: 'not-modeled',
    },
    warnings: [
      '节气距离只表示时间间隔，season-context-v1 不把它换算成线性能量或旺衰分数。',
      '旺相休囚死按月支所属四季输出；辰、未、戌、丑月的季末土旺分段尚未建模。',
      '十二长生是日主在各地支的状态事实，不单独生成吉凶断语。',
    ],
  };
}