'use client';

import type { ReactElement } from 'react';
import {
  parseMovementExpression, MOVEMENT_EXPRESSION_MAX_DEPTH, MOVEMENT_EXPRESSION_MAX_LEAVES,
  type MovementExpression,
} from '@/game/movement-expression-promises';
import { Button } from './ui/button';
import { Input } from './ui/input';

type TerritoryChoice = { id: string; name: string };
export function movementExpressionInputError(value: unknown): string | null {
  try { parseMovementExpression(value); return null; }
  catch (error) { return error instanceof Error ? error.message : 'Choose a valid ground-movement expression.'; }
}

// Structural edits preserve repairable destination and numeric drafts. The
// detached valid placeholders are used only to check tree shape and limits.
const structuralDraft = (node: MovementExpression): MovementExpression => node.kind === 'move'
  ? { ...node, territory: 'carthag', minimum: 1 }
  : { ...node, terms: node.terms.map(structuralDraft) };
const inputSize = (node: MovementExpression): { leaves: number; depth: number } => {
  if (node.kind === 'move') return { leaves: 1, depth: 0 };
  const sizes = node.terms.map(inputSize);
  return { leaves: sizes.reduce((sum, child) => sum + child.leaves, 0), depth: 1 + Math.max(0, ...sizes.map(child => child.depth)) };
};

/** Hook-free controlled tree. The server decides future route feasibility. */
export function MovementExpressionFields({ value, territories, disabled, onChange }: {
  value: MovementExpression;
  territories: readonly TerritoryChoice[];
  disabled: boolean;
  onChange: (expression: MovementExpression) => void;
}) {
  const newLeaf = (): MovementExpression => ({ kind: 'move', territory: territories[0]?.id ?? 'carthag', minimum: 1 });
  const size = inputSize(value), error = movementExpressionInputError(value);
  const commit = (next: MovementExpression) => {
    if (!disabled && !movementExpressionInputError(structuralDraft(next))) onChange(next);
  };
  const render = (node: MovementExpression, path: string, replace: (next: MovementExpression) => MovementExpression,
    remove?: () => MovementExpression): ReactElement => {
    const id = `truth-movement-expression-${path}`;
    const allowed = (next: MovementExpression) => !disabled && !movementExpressionInputError(structuralDraft(replace(next)));
    const change = (next: MovementExpression) => commit(replace(next));
    const wrap = (kind: 'and' | 'or'): MovementExpression => ({ kind, terms: [node, newLeaf()] });
    return <fieldset key={path} data-movement-expression-path={path} className="grid min-w-0 gap-2 p-2">
      <legend>{node.kind === 'move' ? `Movement condition ${path}` : `Movement group ${path} · ${node.kind.toUpperCase()}`}</legend>
      {node.kind === 'move' ? <>
        <label htmlFor={`${id}-territory`}>Ground-movement destination</label>
        <select id={`${id}-territory`} value={territories.some(destination => destination.id === node.territory) ? node.territory : ''}
          disabled={disabled} aria-invalid={!territories.some(destination => destination.id === node.territory)}
          onChange={event => change({ ...node, territory: event.currentTarget.value })}>
          <option value="">Choose a printed Arrakis territory</option>
          {territories.map(destination => <option key={destination.id} value={destination.id}>{destination.name}</option>)}
        </select>
        <label htmlFor={`${id}-minimum`}>Minimum physical forces in one ground move</label>
        <Input id={`${id}-minimum`} type="number" min={1} max={20} step={1} required disabled={disabled}
          value={Number.isNaN(node.minimum) ? '' : node.minimum} aria-invalid={!!movementExpressionInputError(node)}
          onChange={event => change({ ...node, minimum: event.currentTarget.valueAsNumber })} />
      </> : <>
        <label htmlFor={`${id}-meaning`}>Movement group {path} meaning</label>
        <select id={`${id}-meaning`} value={node.kind} disabled={disabled} onChange={event => {
          const kind = event.currentTarget.value;
          if (kind === 'and' || kind === 'or') change({ ...node, kind });
        }}>
          <option value="and">All conditions · AND</option>
          <option value="or">At least one condition · OR</option>
        </select>
        {node.terms.map((term, index) => render(term, `${path}.${index + 1}`,
          next => replace({ ...node, terms: node.terms.map((old, i) => i === index ? next : old) }),
          () => {
            const terms = node.terms.filter((_, i) => i !== index);
            return replace(terms.length === 1 ? terms[0] : { ...node, terms });
          }))}
        <div className="flex flex-wrap gap-2">
          <Button type="button" data-movement-expression-control={`add-${path}`}
            disabled={!allowed({ ...node, terms: [...node.terms, newLeaf()] })}
            onClick={() => change({ ...node, terms: [...node.terms, newLeaf()] })}>Add movement condition</Button>
          {(['and', 'or'] as const).map(kind => {
            const next: MovementExpression = { ...node, terms: [...node.terms, { kind, terms: [newLeaf(), newLeaf()] }] };
            return <Button key={kind} type="button" data-movement-expression-control={`nested-${kind}-${path}`}
              disabled={!allowed(next)} onClick={() => change(next)}>Add nested {kind.toUpperCase()} group</Button>;
          })}
        </div>
      </>}
      <div className="flex flex-wrap gap-2">
        {(['and', 'or'] as const).map(kind => <Button key={kind} type="button" data-movement-expression-control={`${kind}-${path}`}
          disabled={!allowed(wrap(kind))} onClick={() => change(wrap(kind))}>Group with {kind.toUpperCase()}</Button>)}
        {remove && <Button type="button" data-movement-expression-control={`remove-${path}`} disabled={disabled}
          onClick={() => commit(remove())}>Remove {node.kind === 'move' ? 'condition' : 'group'}</Button>}
      </div>
    </fieldset>;
  };
  return <fieldset disabled={disabled} data-testid="movement-expression"
    className="grid min-w-0 gap-2 [&_select]:min-w-0 [&_select]:max-w-full [&_button]:max-w-full [&_button]:min-h-11 [&_button]:h-auto [&_button]:py-2 [&_button]:whitespace-normal">
    <legend>Ground-movement expression</legend>
    <p className="fine">
      AND requires every condition; OR requires at least one. No makes the whole expression false,
      not necessarily every condition. Legal alternatives remain available; the question does not pin a fixed branch.
      Each condition needs one future actual ground move after the answer, before your Movement turn ends this round.
      Smaller moves never add together; a shipment can prepare a move but does not fulfill a condition.
    </p>
    <p className="fine">App input limits: {MOVEMENT_EXPRESSION_MAX_LEAVES} conditions and {MOVEMENT_EXPRESSION_MAX_DEPTH} levels of grouping.
      Groups do not count as conditions. These are input limits, not additional printed rules.</p>
    <p className="fine">{size.leaves} / {MOVEMENT_EXPRESSION_MAX_LEAVES} conditions · {size.depth} / {MOVEMENT_EXPRESSION_MAX_DEPTH} levels of grouping</p>
    {error && <p role="alert">{error}</p>}
    {render(value, '1', next => next)}
  </fieldset>;
}