import { useEffect, useState } from 'react';
import { Loader2, Sparkles } from 'lucide-react';
import { Badge } from './ui/badge';
import { Button } from './ui/button';
import { Card, CardContent, CardDescription, CardHeader, CardTitle } from './ui/card';
import { Input } from './ui/input';
import { Label } from './ui/label';
import { Textarea } from './ui/textarea';
import { cn } from '@/lib/utils';
import { api } from '@/lib/api';
import type { TemplateMeta } from '@shared/scenario';

interface Props {
  /** A generate (LLM) call is in flight — disables the form's controls. */
  busy?: boolean;
  onBack: () => void;
  /**
   * Step 1: design the draft world + checkpoint list. The form hands over the
   * selected template's full metadata (the review screen shows its name/year)
   * plus the description and the effective start year.
   */
  onGenerate: (template: TemplateMeta, description: string, year: number) => void;
}

/** The year input is an empty string ("use the template's default") or a number. */
const YEAR_MIN = 1000;
const YEAR_MAX = 3000;

/**
 * "Create scenario" — step 1 of the dynamic path (v0.31, #52). The user picks
 * one of the light era templates (a card each: name, default year, blurb),
 * writes a free-text description of the world they want, and may override the
 * start year (the field is pre-filled from the selected template; leaving it
 * empty keeps the template's default). "Generate world" posts the draft
 * request; on success the app moves to the checkpoint review screen, on
 * failure it toasts and stays here (the form's local state is preserved).
 */
export default function ScenarioForm({ busy = false, onBack, onGenerate }: Props) {
  const [templates, setTemplates] = useState<TemplateMeta[]>([]);
  const [templatesError, setTemplatesError] = useState<string | null>(null);
  const [selectedId, setSelectedId] = useState<string | null>(null);
  const [description, setDescription] = useState('');
  // Pre-filled from the selected template's default year (the user can edit).
  const [yearText, setYearText] = useState('');

  // Load the era-template manifest on mount (the form is the only consumer).
  useEffect(() => {
    let alive = true;
    api
      .listScenarioTemplates()
      .then((r) => alive && setTemplates(r.templates))
      .catch((e: unknown) => alive && setTemplatesError(e instanceof Error ? e.message : String(e)));
    return () => {
      alive = false;
    };
  }, []);

  const selected = templates.find((t) => t.id === selectedId) ?? null;
  const effectiveYear =
    yearText.trim() === '' ? NaN : Number.parseInt(yearText.trim(), 10);
  const yearValid =
    Number.isInteger(effectiveYear) && effectiveYear >= YEAR_MIN && effectiveYear <= YEAR_MAX;

  const canGenerate = !busy && selected !== null && description.trim() !== '' && yearValid;

  const selectTemplate = (t: TemplateMeta) => {
    setSelectedId(t.id);
    // Selecting an era pre-fills the year with that era's default (the user
    // can still edit it afterwards).
    setYearText(String(t.year));
  };

  const generate = () => {
    if (!canGenerate || !selected) return;
    onGenerate(selected, description.trim(), effectiveYear);
  };

  return (
    <div className="mx-auto max-w-4xl px-6 py-8" data-testid="scenario-form">
      <Button variant="ghost" size="sm" onClick={onBack} className="mb-4">
        ← Back to scenarios
      </Button>
      <h1 className="text-3xl font-bold tracking-tight">Create a scenario</h1>
      <p className="mt-2 max-w-2xl text-sm leading-relaxed text-muted-foreground">
        Design your own world: pick an era, describe what should be true, and the AI will draft the
        world and an opening set of advisor checkpoints for your review. Nothing is saved until you
        finalize.
      </p>

      {/* 1 — the era template (a card each). */}
      <h2 className="mb-3 mt-8 text-lg font-semibold">
        1 · Pick an era <span className="font-normal text-muted-foreground">(required)</span>
      </h2>
      {templatesError ? (
        <p className="rounded-lg border border-destructive/40 bg-destructive/10 p-3 text-sm text-destructive">
          Could not load the era templates: {templatesError}
        </p>
      ) : templates.length === 0 ? (
        <p className="rounded-lg border border-border/60 bg-card/40 p-3 text-sm text-muted-foreground">
          Loading era templates…
        </p>
      ) : (
        <div className="grid gap-4 sm:grid-cols-3">
          {templates.map((t) => {
            const isSel = t.id === selectedId;
            return (
              <Card
                key={t.id}
                className={cn(
                  'flex cursor-pointer flex-col transition',
                  isSel ? 'ring-2 ring-primary/60' : 'hover:ring-1 hover:ring-primary/40',
                )}
                data-testid="template-card"
                data-template-id={t.id}
                data-selected={isSel ? 'true' : 'false'}
                onClick={() => selectTemplate(t)}
              >
                <CardHeader>
                  <div className="flex items-start justify-between gap-2">
                    <CardTitle className="text-base">{t.name}</CardTitle>
                    <Badge variant="secondary" className="shrink-0 text-xs">
                      {t.year}
                    </Badge>
                  </div>
                  <CardDescription className="text-sm leading-relaxed">
                    {t.eraDescription}
                  </CardDescription>
                </CardHeader>
                <CardContent className="mt-auto">
                  <div
                    className={cn(
                      'flex items-center gap-2 text-xs',
                      isSel ? 'font-medium text-primary' : 'text-muted-foreground',
                    )}
                  >
                    <Sparkles className="size-3.5" />
                    {isSel ? 'Selected' : 'Start from this era'}
                  </div>
                </CardContent>
              </Card>
            );
          })}
        </div>
      )}

      {/* 2 — the description (+ optional year override). */}
      <h2 className="mb-3 mt-8 text-lg font-semibold">
        2 · Describe your world <span className="font-normal text-muted-foreground">(required)</span>
      </h2>
      <div className="space-y-4 rounded-lg border border-border/60 bg-card/40 p-4">
        <Textarea
          value={description}
          onChange={(e) => setDescription(e.target.value)}
          placeholder="e.g. “A cold-war world where the space race decided the Cold War — two blocs orbit, and the arctic shipping lanes are the new flashpoint.”"
          rows={4}
          disabled={busy}
          data-testid="scenario-description"
        />
        <div className="flex items-center gap-3">
          <Label htmlFor="scenario-year-input" className="shrink-0 text-sm">
            Start year
          </Label>
          <Input
            id="scenario-year-input"
            type="number"
            inputMode="numeric"
            value={yearText}
            onChange={(e) => setYearText(e.target.value)}
            placeholder={selected ? `default ${selected.year}` : 'pick an era first'}
            min={YEAR_MIN}
            max={YEAR_MAX}
            disabled={busy || !selected}
            className="w-32"
            data-testid="scenario-year"
          />
          <span className="text-xs text-muted-foreground">
            {yearValid ? `The game begins on ${effectiveYear}-01-01.` : 'Leave empty for the era default, or use a year between 1000 and 3000.'}
          </span>
        </div>
      </div>

      {/* Generate. */}
      <div className="mt-8">
        <Button className="h-11 w-full" onClick={generate} disabled={!canGenerate} data-testid="generate-scenario">
          {busy ? <Loader2 className="size-4 animate-spin" /> : <Sparkles className="size-4" />}
          {busy ? 'Generating world…' : 'Generate world'}
        </Button>
        {busy && (
          <p className="mt-2 flex items-center justify-center gap-1.5 text-xs text-muted-foreground">
            <span className="sim-pulse inline-block size-1.5 rounded-full bg-primary" />
            The world-builder is thinking — this can take a few seconds.
          </p>
        )}
      </div>
    </div>
  );
}