import { useEffect, useRef, useState } from 'react'

interface CertificateStatus {
  eligible: boolean
  studyTitle: string
  completedCount: number
  totalCount: number
  token: string | null
  issuedAt: string | null
}

interface Props {
  studySlug: string
  onIssued?: () => void
}

function formatDate(iso: string | null) {
  if (!iso) return ''
  try {
    return new Date(iso).toLocaleDateString('en-US', { year: 'numeric', month: 'long', day: 'numeric' })
  } catch {
    return ''
  }
}

function drawCertificate(
  canvas: HTMLCanvasElement,
  studyTitle: string,
  displayName: string,
  issuedAt: string,
) {
  const W = 900
  const H = 630
  canvas.width = W
  canvas.height = H
  const ctx = canvas.getContext('2d')!

  // Background
  ctx.fillStyle = '#1a1710'
  ctx.fillRect(0, 0, W, H)

  // Gold border (outer)
  ctx.strokeStyle = '#c8952a'
  ctx.lineWidth = 8
  ctx.strokeRect(16, 16, W - 32, H - 32)

  // Gold border (inner)
  ctx.strokeStyle = '#e0b840'
  ctx.lineWidth = 2
  ctx.strokeRect(28, 28, W - 56, H - 56)

  // Header label
  ctx.fillStyle = '#8a7f5a'
  ctx.font = '700 15px Georgia, serif'
  ctx.textAlign = 'center'
  ctx.fillText('VERSE BY VERSE WITH NATE', W / 2, 80)

  // "Certificate of Completion"
  ctx.fillStyle = '#e0b840'
  ctx.font = 'italic 700 38px Georgia, serif'
  ctx.fillText('Certificate of Completion', W / 2, 145)

  // Decorative line
  ctx.strokeStyle = '#c8952a'
  ctx.lineWidth = 1.5
  ctx.beginPath()
  ctx.moveTo(W / 2 - 200, 162)
  ctx.lineTo(W / 2 + 200, 162)
  ctx.stroke()

  // "This certifies that"
  ctx.fillStyle = '#b8a87a'
  ctx.font = '16px Georgia, serif'
  ctx.fillText('This certifies that', W / 2, 210)

  // Name
  ctx.fillStyle = '#f5f0e8'
  ctx.font = 'italic 700 44px Georgia, serif'
  ctx.fillText(displayName, W / 2, 272)

  // Underline the name
  const nameWidth = ctx.measureText(displayName).width
  ctx.strokeStyle = '#e0b840'
  ctx.lineWidth = 1
  ctx.beginPath()
  ctx.moveTo(W / 2 - nameWidth / 2, 282)
  ctx.lineTo(W / 2 + nameWidth / 2, 282)
  ctx.stroke()

  // "has successfully completed"
  ctx.fillStyle = '#b8a87a'
  ctx.font = '16px Georgia, serif'
  ctx.fillText('has successfully completed', W / 2, 322)

  // Study title
  ctx.fillStyle = '#f5f0e8'
  ctx.font = '700 28px Georgia, serif'
  ctx.fillText(studyTitle, W / 2, 372)

  // Date line
  ctx.fillStyle = '#8a7f5a'
  ctx.font = '14px Georgia, serif'
  ctx.fillText(`Awarded on ${formatDate(issuedAt)}`, W / 2, 430)

  // Decorative flourish bottom
  ctx.strokeStyle = '#c8952a'
  ctx.lineWidth = 1.5
  ctx.beginPath()
  ctx.moveTo(W / 2 - 180, 460)
  ctx.lineTo(W / 2 + 180, 460)
  ctx.stroke()

  // Footer
  ctx.fillStyle = '#5a5040'
  ctx.font = '12px Georgia, serif'
  ctx.fillText('versebyversewithnate.us', W / 2, 490)
}

export function StudyCertificate({ studySlug, onIssued }: Props) {
  const [status, setStatus] = useState<CertificateStatus | null>(null)
  const [loading, setLoading] = useState(true)
  const [issuing, setIssuing] = useState(false)
  const [error, setError] = useState<string | null>(null)
  const [displayName, setDisplayName] = useState('')
  const canvasRef = useRef<HTMLCanvasElement>(null)

  useEffect(() => {
    let cancelled = false
    async function load() {
      try {
        const res = await fetch(`/api/study-certificate/${studySlug}`)
        if (!res.ok) throw new Error('unavailable')
        const data = await res.json() as CertificateStatus
        if (cancelled) return
        setStatus(data)
        // The name printed on the certificate comes from the signed-in account
        const auth = await fetch('/api/study-auth/status').then(r => (r.ok ? r.json() : null)).catch(() => null)
        if (cancelled) return
        if (auth?.displayName) setDisplayName(auth.displayName)
        else if (auth?.username) setDisplayName(auth.username)
      } catch {
        // leave status null; the panel renders nothing
      } finally {
        if (!cancelled) setLoading(false)
      }
    }
    void load()
    return () => { cancelled = true }
  }, [studySlug])

  useEffect(() => {
    if (status?.token && canvasRef.current) {
      drawCertificate(
        canvasRef.current,
        status.studyTitle,
        displayName || 'Student',
        status.issuedAt ?? new Date().toISOString(),
      )
    }
  }, [status, displayName])

  async function handleIssueCertificate() {
    setIssuing(true)
    setError(null)
    try {
      const res = await fetch(`/api/study-certificate/${studySlug}`, { method: 'POST' })
      const data = await res.json()
      if (!res.ok) { setError(data.message ?? 'Failed to issue certificate.'); return }
      setStatus(prev => prev ? { ...prev, token: data.token, issuedAt: data.issuedAt } : prev)
      onIssued?.()
    } catch {
      setError('Network error. Please try again.')
    } finally {
      setIssuing(false)
    }
  }

  function handleDownload() {
    if (!canvasRef.current) return
    const link = document.createElement('a')
    link.download = `certificate-${studySlug}.png`
    link.href = canvasRef.current.toDataURL('image/png')
    link.click()
  }

  function handleShare() {
    if (!status?.token) return
    const url = `${window.location.origin}/certificate/${status.token}`
    if (navigator.share) {
      navigator.share({ title: `Certificate – ${status.studyTitle}`, url }).catch(() => {})
    } else {
      navigator.clipboard.writeText(url).then(() => alert('Certificate link copied!')).catch(() => {})
    }
  }

  if (loading) return <p className="study-cert-loading">Checking completion status…</p>
  if (!status) return null

  const progressPct = status.totalCount > 0
    ? Math.round((status.completedCount / status.totalCount) * 100)
    : 0

  return (
    <div className="study-cert-panel">
      <h3 className="study-cert-heading">Certificate of Completion</h3>

      {!status.eligible && (
        <div className="study-cert-progress">
          <p className="study-cert-progress-label">
            {status.completedCount} of {status.totalCount} sections completed ({progressPct}%)
          </p>
          <div className="study-cert-progress-bar-wrap">
            <div
              className="study-cert-progress-bar"
              style={{ width: `${progressPct}%` }}
            />
          </div>
          <p className="study-cert-note">
            Complete all sections to earn your certificate.
          </p>
        </div>
      )}

      {status.eligible && !status.token && (
        <div className="study-cert-eligible">
          <p className="study-cert-congrats">
            🎉 Congratulations! You've completed <strong>{status.studyTitle}</strong>.
          </p>
          {error && <p className="study-cert-error">{error}</p>}
          <button
            type="button"
            className="study-cert-btn"
            onClick={handleIssueCertificate}
            disabled={issuing}
          >
            {issuing ? 'Generating…' : 'Generate My Certificate'}
          </button>
        </div>
      )}

      {status.token && (
        <div className="study-cert-issued">
          <p className="study-cert-issued-label">
            Issued on {formatDate(status.issuedAt)}
          </p>
          <canvas ref={canvasRef} className="study-cert-canvas" aria-label="Certificate of completion" />
          <div className="study-cert-actions">
            <button type="button" className="study-cert-btn" onClick={handleDownload}>
              Download PNG
            </button>
            <button type="button" className="study-cert-btn study-cert-btn--secondary" onClick={handleShare}>
              Share Link
            </button>
          </div>
        </div>
      )}
    </div>
  )
}