import { useCallback, useEffect, useState } from 'react'
import { api, type Document, type DocumentVersion } from '../../api/client'

// HistoryPanel is the "time machine" drawer: every snapshot Petal kept of this
// document, newest first, with a one-click preview and restore. It's the safety
// net that makes trusting Petal with real writing reasonable — a bad edit or a
// regretted rewrite is always recoverable, and restoring is itself undoable
// (the server keeps a pre_restore copy). Bilingual, zh-first, to match chrome.

interface Props {
  docId: string
  onClose: () => void
  // Called after a successful restore with the freshly-restored document so the
  // editor can reload it.
  onRestored: (doc: Document) => void
}

// kindLabel maps a snapshot kind to its bilingual badge + accent color.
const KIND: Record<DocumentVersion['kind'], { zh: string; en: string; color: string }> = {
  manual: { zh: '保存点', en: 'Saved point', color: 'var(--color-accent)' },
  auto: { zh: '自动', en: 'Auto', color: 'var(--color-muted)' },
  pre_restore: { zh: '恢复前', en: 'Before restore', color: 'var(--color-lavender)' },
}

// relativeTime renders a UTC timestamp as a gentle "x minutes ago" string.
function relativeTime(iso: string): string {
  const then = new Date(iso).getTime()
  const secs = Math.max(0, Math.round((Date.now() - then) / 1000))
  if (secs < 60) return 'just now · 刚刚'
  const mins = Math.round(secs / 60)
  if (mins < 60) return `${mins} min ago · ${mins} 分钟前`
  const hrs = Math.round(mins / 60)
  if (hrs < 24) return `${hrs} hr ago · ${hrs} 小时前`
  const days = Math.round(hrs / 24)
  return `${days} day${days > 1 ? 's' : ''} ago · ${days} 天前`
}

export function HistoryPanel({ docId, onClose, onRestored }: Props) {
  const [versions, setVersions] = useState<DocumentVersion[] | null>(null)
  const [error, setError] = useState(false)
  const [selected, setSelected] = useState<DocumentVersion | null>(null)
  const [preview, setPreview] = useState<DocumentVersion | null>(null)
  const [busy, setBusy] = useState(false)

  const load = useCallback(async () => {
    setError(false)
    try {
      setVersions(await api.listVersions(docId))
    } catch {
      setError(true)
    }
  }, [docId])

  useEffect(() => {
    void load()
  }, [load])

  // Escape closes the drawer.
  useEffect(() => {
    const onKey = (e: KeyboardEvent) => {
      if (e.key === 'Escape') onClose()
    }
    window.addEventListener('keydown', onKey)
    return () => window.removeEventListener('keydown', onKey)
  }, [onClose])

  const choose = useCallback(
    async (v: DocumentVersion) => {
      setSelected(v)
      setPreview(null)
      try {
        setPreview(await api.getVersion(docId, v.id))
      } catch {
        setPreview(null)
      }
    },
    [docId],
  )

  const restore = useCallback(async () => {
    if (!selected) return
    setBusy(true)
    try {
      const doc = await api.restoreVersion(docId, selected.id)
      onRestored(doc)
      onClose()
    } catch {
      setBusy(false)
    }
  }, [docId, selected, onRestored, onClose])

  return (
    <div className="petal-no-print fixed inset-0 z-40 flex justify-end">
      {/* Backdrop */}
      <div
        className="absolute inset-0"
        style={{ background: 'rgba(61, 46, 57, 0.18)' }}
        onClick={onClose}
      />

      <aside
        className="relative flex h-full w-full max-w-[380px] flex-col"
        style={{
          background: 'var(--color-surface)',
          borderLeft: '1px solid var(--color-border)',
          boxShadow: 'var(--shadow-soft)',
        }}
      >
        <header
          className="flex items-center justify-between px-5 py-4"
          style={{ borderBottom: '1px solid var(--color-border)' }}
        >
          <div>
            <div className="text-base font-extrabold text-plum">历史 · History</div>
            <div className="text-xs" style={{ color: 'var(--color-muted)' }}>
              Every saved moment — nothing is ever lost 🌸
            </div>
          </div>
          <button
            type="button"
            aria-label="Close history"
            onClick={onClose}
            className="flex h-8 w-8 items-center justify-center rounded-full text-lg"
            style={{ color: 'var(--color-muted)' }}
            onMouseEnter={(e) => (e.currentTarget.style.background = 'var(--color-surface-alt)')}
            onMouseLeave={(e) => (e.currentTarget.style.background = 'transparent')}
          >
            ✕
          </button>
        </header>

        <div className="min-h-0 flex-1 overflow-y-auto px-3 py-3">
          {error ? (
            <div className="px-2 py-6 text-center text-sm" style={{ color: 'var(--color-muted)' }}>
              Couldn’t load history just now.
              <button onClick={load} className="ml-1 font-bold text-plum underline">
                Try again
              </button>
            </div>
          ) : versions === null ? (
            <div className="px-2 py-6 text-center text-sm" style={{ color: 'var(--color-muted)' }}>
              Loading…
            </div>
          ) : versions.length === 0 ? (
            <div className="px-2 py-8 text-center text-sm" style={{ color: 'var(--color-muted)' }}>
              No snapshots yet. Keep writing — Petal saves restore points as you go.
            </div>
          ) : (
            <ul className="flex flex-col gap-1.5">
              {versions.map((v) => {
                const k = KIND[v.kind]
                const active = selected?.id === v.id
                return (
                  <li key={v.id}>
                    <button
                      type="button"
                      onClick={() => choose(v)}
                      className="flex w-full flex-col gap-1 rounded-2xl px-3 py-2.5 text-left"
                      style={{
                        background: active ? 'var(--color-surface-alt)' : 'transparent',
                        border: `1px solid ${active ? 'var(--color-border)' : 'transparent'}`,
                      }}
                      onMouseEnter={(e) =>
                        (e.currentTarget.style.background = 'var(--color-surface-alt)')
                      }
                      onMouseLeave={(e) =>
                        (e.currentTarget.style.background = active
                          ? 'var(--color-surface-alt)'
                          : 'transparent')
                      }
                    >
                      <div className="flex items-center justify-between gap-2">
                        <span className="truncate text-sm font-bold text-plum">{v.title || 'Untitled'}</span>
                        <span
                          className="shrink-0 rounded-full px-2 py-0.5 text-[10px] font-bold"
                          style={{ background: k.color, color: '#fff' }}
                        >
                          {k.zh} · {k.en}
                        </span>
                      </div>
                      <div className="flex items-center justify-between gap-2 text-xs" style={{ color: 'var(--color-muted)' }}>
                        <span>{relativeTime(v.created_at)}</span>
                        <span>{v.word_count} words</span>
                      </div>
                    </button>
                  </li>
                )
              })}
            </ul>
          )}
        </div>

        {selected && (
          <div
            className="shrink-0 px-4 py-3"
            style={{ borderTop: '1px solid var(--color-border)', background: 'var(--color-surface-alt)' }}
          >
            <div className="mb-2 text-xs font-bold" style={{ color: 'var(--color-muted)' }}>
              预览 · Preview
            </div>
            <div
              className="mb-3 max-h-32 overflow-y-auto whitespace-pre-wrap rounded-xl px-3 py-2 text-sm"
              style={{
                background: 'var(--color-surface)',
                color: 'var(--color-plum)',
                fontFamily: 'var(--font-body)',
              }}
            >
              {preview ? preview.content_text || '(empty)' : 'Loading…'}
            </div>
            <button
              type="button"
              onClick={restore}
              disabled={busy}
              className="w-full rounded-full py-2.5 text-sm font-extrabold text-white disabled:opacity-60"
              style={{ background: 'var(--color-accent)' }}
              onMouseEnter={(e) => (e.currentTarget.style.background = 'var(--color-accent-hover)')}
              onMouseLeave={(e) => (e.currentTarget.style.background = 'var(--color-accent)')}
            >
              {busy ? 'Restoring…' : '恢复这个版本 · Restore this version'}
            </button>
            <div className="mt-1.5 text-center text-[11px]" style={{ color: 'var(--color-muted)' }}>
              Your current draft is saved first, so this is undoable.
            </div>
          </div>
        )}
      </aside>
    </div>
  )
}