import { useEffect, useRef, useState } from 'react'
import { createPortal } from 'react-dom'
import './ClampText.css'

/**
 * Splits a block of AI prose into a finding and its working.
 *
 * The employees write the conclusion first and the evidence after it —
 * "POSP-77341 is active and empanelled for motor." then four sentences of
 * registry detail. So the first sentence already IS the summary, and lifting it
 * out gives one without inventing text or asking the model for a second field
 * it would have to be trusted to keep in step with the first.
 *
 * Returns null when the split would be useless: no sentence terminator, a first
 * sentence so long it is the paragraph again, or one so short it is a fragment
 * rather than a finding. Those fall back to plain folding.
 */
function splitLead(value) {
  const m = value.match(/^(.{40,220}?[.!?])(\s+)(\S[\s\S]*)$/)
  if (!m) return null
  return { lead: m[1].trim(), rest: m[3].trim() }
}

/**
 * The full text, in a dialog.
 *
 * The reasoning used to expand INLINE, and in the audit rail — 320px wide, one
 * entry per step — a 1,500-character rationale pushed the rest of the lead's
 * history off the screen to read one sentence of it. Nobody reads a paragraph
 * in a sidebar. It opens over the page instead: the finding stays on the line,
 * the working is one click away and one Escape back.
 */
function ProseDialog({ title, lead, body, onClose }) {
  const ref = useRef(null)
  const restore = useRef(null)

  useEffect(() => {
    restore.current = document.activeElement
    ref.current?.focus()
    const onKey = (e) => { if (e.key === 'Escape') onClose() }
    document.addEventListener('keydown', onKey)
    // The page behind must not scroll under the dialog.
    const prev = document.body.style.overflow
    document.body.style.overflow = 'hidden'
    return () => {
      document.removeEventListener('keydown', onKey)
      document.body.style.overflow = prev
      // Focus goes back to the button that opened this, not to the top of the
      // document — otherwise a keyboard reader loses their place in the trail.
      if (restore.current instanceof HTMLElement) restore.current.focus()
    }
  }, [onClose])

  return createPortal(
    <div className="prose__scrim" onClick={onClose} role="presentation">
      <div
        className="prose__dlg"
        role="dialog"
        aria-modal="true"
        aria-label={title || 'Full text'}
        tabIndex={-1}
        ref={ref}
        onClick={(e) => e.stopPropagation()}
      >
        <div className="prose__head">
          <h3>{title || 'In full'}</h3>
          <button type="button" onClick={onClose} aria-label="Close">
            <svg viewBox="0 0 14 14" aria-hidden="true">
              <path d="M3.5 3.5l7 7M10.5 3.5l-7 7" fill="none" stroke="currentColor"
                    strokeWidth="1.6" strokeLinecap="round" />
            </svg>
          </button>
        </div>
        <div className="prose__body">
          {/* The finding stays at the top and stays emphasised — a reader who
              opened this to check one thing should not have to find it again. */}
          {lead ? <p className="prose__lead">{lead}</p> : null}
          {body.split(/\n{2,}/).map((para, i) => <p key={i}>{para}</p>)}
        </div>
      </div>
    </div>,
    document.body,
  )
}

/**
 * Prose, reduced to its point.
 *
 * The AI employees write at length — a recommendation rationale runs past 1,500
 * characters — and a screen that prints all of it is a document. Short text is
 * shown as it is; anything longer shows its finding and puts the working behind
 * one click.
 *
 * Whether to fold is decided on length, not by measuring the rendered box: a
 * ref-and-measure pass would reflow on every resize to answer a question the
 * string itself already answers.
 */
export default function ClampText({ text, title, lines = 3, threshold = 150 }) {
  const [open, setOpen] = useState(false)
  const value = String(text)

  if (value.length <= threshold) return <p className="clamp__text clamp__text--short">{value}</p>

  const split = splitLead(value)

  return (
    <div className="clamp">
      {split
        ? <p className="clamp__lead">{split.lead}</p>
        : <p className="clamp__text" style={{ '--clamp-lines': lines }}>{value}</p>}
      <button type="button" className="clamp__more" onClick={() => setOpen(true)}>
        {split ? 'Read the reasoning' : 'Read in full'}
        <svg viewBox="0 0 12 12" aria-hidden="true">
          <path d="M4 2.5 8 6l-4 3.5" fill="none" stroke="currentColor" strokeWidth="1.5"
                strokeLinecap="round" strokeLinejoin="round" />
        </svg>
      </button>
      {open ? (
        <ProseDialog
          title={title}
          lead={split?.lead}
          body={split ? split.rest : value}
          onClose={() => setOpen(false)}
        />
      ) : null}
    </div>
  )
}