import React from 'react';
import Box from '@mui/material/Box';
import type { SxProps, Theme } from '@mui/material/styles';
import { WizardLayout } from '../../templates/WizardLayout';
import { ToggleButtonGroup } from '../../atoms/ToggleButtonGroup';
import { Collapse } from '../../atoms/Collapse';
import { Typography } from '../../atoms/Typography';
import { Button } from '../../atoms/Button';
import { Divider } from '../../atoms/Divider';

// ─── Types ───────────────────────────────────────────────────────────────────

/** Form values for the intro step */
export interface IntroStepValues {
  /** Who the funeral is being arranged for */
  forWhom: 'myself' | 'someone' | null;
  /** Whether the person has passed away (only relevant when forWhom="someone") */
  hasPassedAway: 'yes' | 'no' | null;
}

/** Field-level error messages */
export interface IntroStepErrors {
  /** Error for the forWhom field */
  forWhom?: string;
  /** Error for the hasPassedAway field */
  hasPassedAway?: string;
}

/** Props for the IntroStep page component */
export interface IntroStepProps {
  /** Current form values */
  values: IntroStepValues;
  /** Callback when any field value changes */
  onChange: (values: IntroStepValues) => void;
  /** Callback when the Continue button is clicked */
  onContinue: () => void;
  /** Field-level validation errors */
  errors?: IntroStepErrors;
  /** Whether the Continue button is in a loading state */
  loading?: boolean;
  /** Navigation bar — passed through to WizardLayout */
  navigation?: React.ReactNode;
  /** Hide the help bar */
  hideHelpBar?: boolean;
  /** MUI sx prop for the root */
  sx?: SxProps<Theme>;
}

// ─── Constants ──────────────────────────────────────────────────────────────

const SUBHEADING =
  "We'll guide you through arranging a funeral, step by step. You can save your progress and come back anytime.";

// ─── Component ───────────────────────────────────────────────────────────────

/**
 * Step 1 — Intro page for the FA arrangement wizard.
 *
 * Entry point with urgency-sensitive segmentation. User selects who
 * the funeral is for, and (if arranging for someone else) whether
 * that person has passed away.
 *
 * Uses the Centered Form layout variant. Progressive disclosure:
 * selecting "Someone else" reveals the hasPassedAway question.
 * Selecting "Myself" auto-sets hasPassedAway to "no" (pre-planning).
 *
 * Pure presentation component — props in, callbacks out.
 * No routing, state management, or API calls.
 *
 * Spec: documentation/steps/steps/01_intro.yaml
 */
export const IntroStep: React.FC<IntroStepProps> = ({
  values,
  onChange,
  onContinue,
  errors,
  loading = false,
  navigation,
  hideHelpBar,
  sx,
}) => {
  const handleForWhomChange = (newValue: string | null) => {
    const forWhom = newValue as IntroStepValues['forWhom'];
    if (forWhom === 'myself') {
      // Auto-set hasPassedAway to 'no' — user is alive, pre-planning
      onChange({ forWhom, hasPassedAway: 'no' });
    } else {
      // Reset hasPassedAway when switching to "someone"
      onChange({ forWhom, hasPassedAway: null });
    }
  };

  const handleHasPassedAwayChange = (newValue: string | null) => {
    onChange({ ...values, hasPassedAway: newValue as IntroStepValues['hasPassedAway'] });
  };

  const showHasPassedAway = values.forWhom === 'someone';

  return (
    <WizardLayout variant="centered-form" navigation={navigation} hideHelpBar={hideHelpBar} sx={sx}>
      {/* Page heading — receives focus on entry for screen readers */}
      <Typography variant="display3" component="h1" sx={{ mb: 1 }} tabIndex={-1}>
        Let&apos;s get started
      </Typography>

      <Typography variant="body1" color="text.secondary" sx={{ mb: 5 }}>
        {SUBHEADING}
      </Typography>

      <Box
        component="form"
        noValidate
        aria-busy={loading}
        onSubmit={(e: React.FormEvent) => {
          e.preventDefault();
          if (!loading) onContinue();
        }}
      >
        {/* forWhom field */}
        <Box sx={{ mb: 3 }}>
          <ToggleButtonGroup
            label="Who is this funeral being arranged for?"
            options={[
              {
                value: 'myself',
                label: 'Myself',
                description: 'I want to plan my own funeral',
              },
              {
                value: 'someone',
                label: 'Someone else',
                description: 'I am arranging for a family member or friend',
              },
            ]}
            value={values.forWhom}
            onChange={handleForWhomChange}
            error={!!errors?.forWhom}
            helperText={errors?.forWhom}
            required
            fullWidth
          />
        </Box>

        {/* hasPassedAway field — revealed when forWhom="someone" */}
        <Collapse in={showHasPassedAway}>
          <Box sx={{ mb: 3 }}>
            <ToggleButtonGroup
              label="Has this person passed away?"
              options={[
                {
                  value: 'yes',
                  label: 'Yes',
                  description: 'I need to arrange a funeral now',
                },
                {
                  value: 'no',
                  label: 'No',
                  description: 'I am planning ahead',
                },
              ]}
              value={values.hasPassedAway}
              onChange={handleHasPassedAwayChange}
              error={!!errors?.hasPassedAway}
              helperText={errors?.hasPassedAway}
              required
              fullWidth
            />
          </Box>
        </Collapse>

        <Divider sx={{ my: 4 }} />

        {/* CTA */}
        <Box sx={{ display: 'flex', justifyContent: 'flex-end' }}>
          <Button type="submit" variant="contained" size="large" loading={loading}>
            Continue
          </Button>
        </Box>
      </Box>
    </WizardLayout>
  );
};

IntroStep.displayName = 'IntroStep';
export default IntroStep;