/**
 * THE RULES BLOCK, driven identically on both screens.
 *
 * The lobby (`lobby.ts`) and the solitaire New Game dialog (`main.ts`) ask the same twelve questions.
 * They used to ask them in two hand-written copies and had already drifted — the dialog had "where
 * an Extra may start" and no optional rules, the lobby the reverse — so this module owns reading,
 * writing, comparing and annotating the block, and each screen supplies only the id prefix its
 * markup uses (`lb-` or `ng-`).
 *
 * THE MARKUP ITSELF STAYS STATIC IN `play.html`, deliberately. Generating it here would be less
 * duplication, but `test/web.test.ts` drives the emitted bundle against a hand-built DOM stub with
 * no HTML parser in it (there is no jsdom in this project, and adding one to test a form is a poor
 * trade), and the ids in that stub come from scanning the real `play.html`. A test in the same suite
 * asserts both screens carry every key below, which is the drift guard the shared markup would have
 * been.
 */

import { REVENUE_MAX, REVENUE_MIN } from '../engine/content.ts';
import type { ExtraStartRule, StartingHand } from '../engine/content.ts';
import { closestPreset, differencesFrom, presetOf, presetSettings, settingsOf } from './presets.ts';
import type { PresetName, Settings } from './presets.ts';
import type { GameConfig } from '../engine/state.ts';

/**
 * How each rule is asked on screen.
 *
 * `gated` is the pair introduced 2026-08-23: a checkbox that says whether the condition applies at
 * all, plus the number it applies at. The engine's convention is that `0` switches these off, which
 * is exact but unreadable — a Cutthroat game showed two zeroes and left the player to know the
 * convention. Unchecked still WRITES 0, so nothing under this changed.
 */
type Field =
  | { key: keyof Settings; kind: 'radio'; id: string }
  | { key: keyof Settings; kind: 'number'; id: string }
  | { key: keyof Settings; kind: 'checkbox'; id: string }
  | { key: keyof Settings; kind: 'gated'; id: string };

export const FIELDS: readonly Field[] = [
  { key: 'startingHand', kind: 'radio', id: 'hand' },
  { key: 'extraStart', kind: 'radio', id: 'extra' },
  { key: 'passengerPerCoach', kind: 'number', id: 'passenger' },
  { key: 'freightPerLoad', kind: 'number', id: 'freight' },
  { key: 'trainPerTransit', kind: 'number', id: 'transit' },
  { key: 'minCombinedRevenue', kind: 'gated', id: 'minrev' },
  { key: 'maxCollisionsPerDay', kind: 'gated', id: 'colday' },
  { key: 'maxCollisionsTotal', kind: 'gated', id: 'coltotal' },
  { key: 'reducedVisibility', kind: 'checkbox', id: 'visibility' },
  { key: 'employeeRotation', kind: 'checkbox', id: 'rotation' },
  { key: 'emergencyToolbox', kind: 'checkbox', id: 'toolbox' },
  { key: 'discardTimetabled', kind: 'checkbox', id: 'tossloco' },
  { key: 'startWhistlePosts', kind: 'checkbox', id: 'whistlestart' },
];

/**
 * What `play.html` must contain for a screen to be able to ask all twelve questions — the exact
 * attribute text, so `test/web.test.ts` can assert it against the built page.
 *
 * THIS IS THE DRIFT GUARD. The two blocks are generated from one template today; this is what says
 * so tomorrow, when someone edits one of them by hand.
 */
export function fieldSelectors(prefix: string): string[] {
  const out: string[] = [];
  for (const f of FIELDS) {
    // A radio group is addressed by NAME — there is no one element carrying the field's id.
    out.push(f.kind === 'radio' ? `name="${prefix}${f.id}"` : `id="${prefix}${f.id}"`);
    if (f.kind === 'gated') out.push(`id="${prefix}${f.id}-on"`);
    out.push(`id="${prefix}${f.id}-row"`, `id="${prefix}${f.id}-hint"`);
  }
  return out;
}

/** The label each field goes under in the read-only view below. */
const FIELD_LABELS: Record<keyof Settings, string> = {
  startingHand: 'Starting hand',
  extraStart: 'An Extra may start at',
  discardTimetabled: 'A Timetabled train may be discarded',
  startWhistlePosts: 'Players start with Whistle Posts, not Depots',
  passengerPerCoach: 'Passenger per coach',
  freightPerLoad: 'Freight per load',
  trainPerTransit: 'Train per transit',
  minCombinedRevenue: 'Combined Revenue floor',
  maxCollisionsPerDay: 'Collisions in one Day',
  maxCollisionsTotal: 'Collisions in the game',
  reducedVisibility: 'Reduced Visibility',
  employeeRotation: 'Employee Rotation',
  emergencyToolbox: 'Emergency Toolbox',
};

const esc = (s: string): string =>
  s.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;');

/**
 * THE WHOLE RULE SET, READ-ONLY — what a player weighing a join reads before taking a seat, and what
 * the seating screen keeps showing afterwards.
 *
 * Generated rather than a fourth copy of the form: nobody may change these, so form controls would
 * be a lie, and a `<dl>` says "this is what you are joining" in a third of the space. Fields that
 * differ from the nearest named type are amber here for the same reason they are amber in the form —
 * a non-standard game should never be a surprise.
 */
export function rulesListHtml(config: GameConfig, players: number, days: number): string {
  const settings = settingsOf(config);
  const type = presetOf(config, players, days);
  const near = closestPreset(config, players, days);
  const differing = type === 'custom' ? near.differing : [];

  const rows = (keys: (keyof Settings)[]): string =>
    keys
      .map((k) => {
        const changed = differing.includes(k) ? ' class="changed"' : '';
        return `<dt>${esc(FIELD_LABELS[k])}</dt><dd${changed}>${esc(describe(k, settings[k]))}</dd>`;
      })
      .join('');

  const head =
    `<dl><dt>Players</dt><dd>${players}</dd><dt>Days</dt><dd>${days}</dd>` +
    `<dt>Opponent-directed cards</dt><dd>not implemented yet</dd></dl>`;

  return (
    head +
    `<h4>Opening</h4><dl>${rows(['startingHand', 'extraStart', 'startWhistlePosts'])}</dl>` +
    `<h4>Train cards</h4><dl>${rows(['discardTimetabled'])}</dl>` +
    `<h4>Revenue</h4><dl>${rows(['passengerPerCoach', 'freightPerLoad', 'trainPerTransit'])}</dl>` +
    `<h4>Victory conditions</h4><dl>${rows(['minCombinedRevenue', 'maxCollisionsPerDay', 'maxCollisionsTotal'])}</dl>` +
    `<h4>Optional rules</h4><dl>${rows(['reducedVisibility', 'employeeRotation', 'emergencyToolbox'])}</dl>`
  );
}

/** What a value looks like beside its label — "Co-op default: 75", "Co-op default: six random cards". */
function describe(key: keyof Settings, value: Settings[keyof Settings]): string {
  if (typeof value === 'boolean') return value ? 'on' : 'off';
  if (key === 'startingHand') {
    const words: Record<StartingHand, string> = {
      threeRandom: 'three random',
      sixRandom: 'six random',
      threeTrackThreeOther: 'three track and three other',
    };
    return words[value as StartingHand];
  }
  if (key === 'extraStart') {
    const words: Record<ExtraStartRule, string> = {
      divisionPointsOnly: 'Division Points only',
      ownOffice: 'your own Control Point',
      anyOffice: 'any Control Point',
    };
    return words[value as ExtraStartRule];
  }
  // A victory condition at 0 is not "0" on screen, it is a condition that does not apply.
  if (value === 0 && (key === 'minCombinedRevenue' || key === 'maxCollisionsPerDay' || key === 'maxCollisionsTotal')) {
    return 'off';
  }
  return String(value);
}

export type SettingsForm = {
  read(): Settings;
  /** `suggestions` fills the placeholder of a switched-off condition, so ticking it back on has a
   * number to offer rather than an empty box. */
  write(values: Settings, suggestions: Settings): void;
  /**
   * Paint the block against a named type: every field that differs goes amber and every field gets
   * its "<Type> default: x" hint. Returns what differs, for the summary line the screen draws.
   */
  mark(name: PresetName, players: number, days: number): (keyof Settings)[];
  /** Custom with no named baseline to compare against — clears the paint rather than lying. */
  clearMarks(): void;
  /** Called whenever the player changes any rule; the screen answers by selecting Custom. */
  onEdit(fn: (key: keyof Settings) => void): void;
  /** Read-only for the join preview and the seating screen: shown in full, changeable by nobody. */
  setEditable(on: boolean): void;
  /** Employee Rotation is meaningless at one player — disabled with a note rather than hidden, so
   * the two screens still read the same. */
  setEmployeeRotationAvailable(on: boolean): void;
};

const $ = <T extends HTMLElement = HTMLElement>(id: string): T | null =>
  document.getElementById(id) as T | null;

export function settingsForm(prefix: string): SettingsForm {
  const el = <T extends HTMLElement = HTMLElement>(id: string): T | null => $<T>(`${prefix}${id}`);
  const radios = (name: string): HTMLInputElement[] =>
    Array.from(document.querySelectorAll<HTMLInputElement>(`input[name="${prefix}${name}"]`));
  const checkedRadio = (name: string): string | null =>
    radios(name).find((r) => r.checked)?.value ?? null;

  let editHandler: ((key: keyof Settings) => void) | null = null;
  let editable = true;

  function num(id: string, fallback: number): number {
    const raw = el<HTMLInputElement>(id)?.value ?? '';
    return raw.trim() === '' || !Number.isFinite(Number(raw)) ? fallback : Math.round(Number(raw));
  }

  function readGated(id: string): number {
    // Unchecked IS zero — the engine's "off". The number in the box is kept so re-ticking restores it.
    if (el<HTMLInputElement>(`${id}-on`)?.checked !== true) return 0;
    return Math.max(0, num(id, 0));
  }

  function read(): Settings {
    return {
      startingHand: (checkedRadio('hand') ?? 'sixRandom') as StartingHand,
      extraStart: (checkedRadio('extra') ?? 'anyOffice') as ExtraStartRule,
      passengerPerCoach: clampRevenue(num('passenger', 1)),
      freightPerLoad: clampRevenue(num('freight', 1)),
      trainPerTransit: clampRevenue(num('transit', 0)),
      minCombinedRevenue: readGated('minrev'),
      maxCollisionsPerDay: readGated('colday'),
      maxCollisionsTotal: readGated('coltotal'),
      reducedVisibility: el<HTMLInputElement>('visibility')?.checked === true,
      employeeRotation: el<HTMLInputElement>('rotation')?.checked === true,
      emergencyToolbox: el<HTMLInputElement>('toolbox')?.checked === true,
      discardTimetabled: el<HTMLInputElement>('tossloco')?.checked === true,
      startWhistlePosts: el<HTMLInputElement>('whistlestart')?.checked === true,
    };
  }

  function write(values: Settings, suggestions: Settings): void {
    for (const r of radios('hand')) r.checked = r.value === values.startingHand;
    for (const r of radios('extra')) r.checked = r.value === values.extraStart;
    setNumber('passenger', values.passengerPerCoach);
    setNumber('freight', values.freightPerLoad);
    setNumber('transit', values.trainPerTransit);
    writeGated('minrev', values.minCombinedRevenue, suggestions.minCombinedRevenue);
    writeGated('colday', values.maxCollisionsPerDay, suggestions.maxCollisionsPerDay);
    writeGated('coltotal', values.maxCollisionsTotal, suggestions.maxCollisionsTotal);
    setChecked('visibility', values.reducedVisibility);
    setChecked('rotation', values.employeeRotation);
    setChecked('toolbox', values.emergencyToolbox);
    setChecked('tossloco', values.discardTimetabled);
    setChecked('whistlestart', values.startWhistlePosts);
  }

  function setNumber(id: string, value: number): void {
    const input = el<HTMLInputElement>(id);
    if (input) input.value = String(value);
  }

  function setChecked(id: string, on: boolean): void {
    const input = el<HTMLInputElement>(id);
    if (input) input.checked = on;
  }

  function writeGated(id: string, value: number, suggestion: number): void {
    const box = el<HTMLInputElement>(`${id}-on`);
    const input = el<HTMLInputElement>(id);
    if (box) box.checked = value > 0;
    if (input) {
      // A switched-off condition shows an empty box with the suggestion as its placeholder, rather
      // than a `0` the player has to decode.
      input.value = value > 0 ? String(value) : '';
      input.placeholder = String(suggestion);
      input.disabled = !editable || value === 0;
    }
  }

  function mark(name: PresetName, players: number, days: number): (keyof Settings)[] {
    const want = presetSettings(name, players, days);
    const differing = differencesFrom(name, read(), players, days);
    const label = presetLabelOf(name);
    for (const f of FIELDS) {
      const row = el(`${f.id}-row`);
      const hint = el(`${f.id}-hint`);
      const off = differing.includes(f.key);
      row?.classList.toggle('changed', off);
      if (hint) hint.textContent = `${label} default: ${describe(f.key, want[f.key])}`;
    }
    return differing;
  }

  function clearMarks(): void {
    for (const f of FIELDS) {
      el(`${f.id}-row`)?.classList.remove('changed');
      const hint = el(`${f.id}-hint`);
      if (hint) hint.textContent = '';
    }
  }

  function setEditable(on: boolean): void {
    editable = on;
    for (const f of FIELDS) {
      if (f.kind === 'radio') {
        for (const r of radios(f.id)) r.disabled = !on;
        continue;
      }
      const input = el<HTMLInputElement>(f.id);
      if (input) {
        // A gated number stays disabled when its own condition is off, whatever the block's state.
        const gatedOff = f.kind === 'gated' && el<HTMLInputElement>(`${f.id}-on`)?.checked !== true;
        input.disabled = !on || gatedOff;
      }
      if (f.kind === 'gated') {
        const box = el<HTMLInputElement>(`${f.id}-on`);
        if (box) box.disabled = !on;
      }
    }
  }

  function setEmployeeRotationAvailable(on: boolean): void {
    const input = el<HTMLInputElement>('rotation');
    if (input) {
      input.disabled = !on || !editable;
      if (!on) input.checked = false;
    }
    el('rotation-row')?.classList.toggle('unavailable', !on);
  }

  /** One change handler for every control — the screens all answer it the same way (select Custom). */
  for (const f of FIELDS) {
    const fire = (): void => editHandler?.(f.key);
    if (f.kind === 'radio') {
      for (const r of radios(f.id)) r.onchange = fire;
      continue;
    }
    const input = el<HTMLInputElement>(f.id);
    if (input) {
      input.oninput = fire;
      input.onchange = fire;
    }
    if (f.kind === 'gated') {
      const box = el<HTMLInputElement>(`${f.id}-on`);
      if (box) {
        box.onchange = () => {
          const number = el<HTMLInputElement>(f.id);
          if (number) {
            number.disabled = !box.checked || !editable;
            // Ticking a condition back on with an empty box takes the suggestion showing in it,
            // so "on" never means "on, at zero".
            if (box.checked && number.value.trim() === '') number.value = number.placeholder;
          }
          fire();
        };
      }
    }
  }

  return {
    read,
    write,
    mark,
    clearMarks,
    onEdit: (fn) => void (editHandler = fn),
    setEditable,
    setEmployeeRotationAvailable,
  };
}

function clampRevenue(n: number): number {
  return Math.max(REVENUE_MIN, Math.min(REVENUE_MAX, n));
}

/** Kept local rather than imported from `presets.ts`'s `preset()`, which would drag the whole table
 * in for one word — and this is the only place a hint needs it. */
function presetLabelOf(name: PresetName): string {
  const labels: Record<PresetName, string> = {
    solitaire: 'Solitaire',
    coop: 'Co-op',
    competitive: 'Competitive',
    cutthroat: 'Cutthroat',
  };
  return labels[name];
}