import { useState, useRef, useEffect, useCallback } from 'react'
import { createPortal } from 'react-dom'
import { MessageSquare, ChevronDown } from 'lucide-react'
import type { SessionSummary } from '../../types/protocol'

interface SessionSelectorProps {
  sessions: SessionSummary[]
  selectedSessionId: string | null
  onSelectSession: (sessionId: string) => void
}

export function SessionSelector({
  sessions,
  selectedSessionId,
  onSelectSession,
}: SessionSelectorProps) {
  const [isOpen, setIsOpen] = useState(false)
  const [dropdownPos, setDropdownPos] = useState<{ top: number; right: number }>({ top: 0, right: 0 })
  const triggerRef = useRef<HTMLButtonElement>(null)
  const dropdownRef = useRef<HTMLDivElement>(null)
  const selected = sessions.find((s) => s.session_id === selectedSessionId)

  const updatePosition = useCallback(() => {
    if (triggerRef.current) {
      const rect = triggerRef.current.getBoundingClientRect()
      setDropdownPos({
        top: rect.bottom + 8,
        right: window.innerWidth - rect.right,
      })
    }
  }, [])

  useEffect(() => {
    if (isOpen) {
      updatePosition()
      window.addEventListener('resize', updatePosition)
      window.addEventListener('scroll', updatePosition, true)
      return () => {
        window.removeEventListener('resize', updatePosition)
        window.removeEventListener('scroll', updatePosition, true)
      }
    }
  }, [isOpen, updatePosition])

  useEffect(() => {
    if (!isOpen) return
    const handleClick = (e: MouseEvent) => {
      const target = e.target as Node
      if (
        dropdownRef.current && !dropdownRef.current.contains(target) &&
        triggerRef.current && !triggerRef.current.contains(target)
      ) {
        setIsOpen(false)
      }
    }
    document.addEventListener('mousedown', handleClick)
    return () => document.removeEventListener('mousedown', handleClick)
  }, [isOpen])

  useEffect(() => {
    if (!isOpen) return
    const handleKey = (e: KeyboardEvent) => {
      if (e.key === 'Escape') setIsOpen(false)
    }
    document.addEventListener('keydown', handleKey)
    return () => document.removeEventListener('keydown', handleKey)
  }, [isOpen])

  if (sessions.length === 0) return null

  return (
    <>
      <button
        ref={triggerRef}
        onClick={() => setIsOpen(!isOpen)}
        disabled={sessions.length <= 1}
        className={`
          group flex items-center gap-2 rounded-lg border px-3 py-1.5 text-sm w-44 justify-between
          transition-all duration-200 ease-out
          ${sessions.length <= 1
            ? 'border-[var(--border-color)] cursor-default'
            : isOpen
              ? 'border-[var(--accent-cyan)]/40 bg-[var(--overlay-subtle)] shadow-[0_0_12px_var(--shadow-glow-sm)]'
              : 'border-[var(--border-color)] hover:border-[var(--border-accent)] hover:bg-[var(--overlay-hover)] cursor-pointer'
          }
        `}
      >
        <MessageSquare className="h-3.5 w-3.5 flex-shrink-0 text-[var(--accent-cyan)]" />
        <span className="flex-1 min-w-0 text-[var(--text-primary)] font-medium text-xs tracking-wide truncate text-center">
          {selected?.title || '无会话'}
        </span>
        {sessions.length > 1 ? (
          <span className="flex items-center gap-1 flex-shrink-0">
            <span className="text-[10px] text-[var(--text-muted)]">{sessions.length}</span>
            <ChevronDown
              className={`h-3.5 w-3.5 text-[var(--text-muted)] transition-transform duration-200 ${
                isOpen ? 'rotate-180' : ''
              }`}
            />
          </span>
        ) : (
          /* 占位保持图标位置一致 */
          <span className="w-4 flex-shrink-0" />
        )}
      </button>

      {isOpen && sessions.length > 1 && createPortal(
        <div
          ref={dropdownRef}
          className="fixed z-[9999] w-56 animate-slide-in"
          style={{ top: dropdownPos.top, right: dropdownPos.right }}
        >
          <div
            className="
              rounded-xl border border-[var(--border-color)]
              bg-[var(--bg-secondary)]/95 backdrop-blur-xl
              shadow-2xl shadow-black/40
              overflow-hidden
            "
          >
            <div className="py-1 max-h-60 overflow-y-auto">
              {sessions.map((s, index) => {
                const isActive = s.session_id === selectedSessionId
                return (
                  <button
                    key={s.session_id}
                    onClick={() => {
                      onSelectSession(s.session_id)
                      setIsOpen(false)
                    }}
                    className={`
                      group/item relative w-full flex items-center gap-3 px-4 py-2.5 text-left
                      transition-all duration-150
                      hover:bg-[var(--overlay-hover)]
                      ${isActive ? 'bg-[var(--overlay-subtle)]' : ''}
                    `}
                    style={{
                      animationDelay: `${index * 40}ms`,
                      animation: 'fade-in 0.2s ease-out both',
                    }}
                  >
                    <div
                      className={`
                        absolute left-0 top-1/2 -translate-y-1/2 w-0.5 h-5 rounded-r-full
                        transition-all duration-200
                        ${isActive ? 'bg-[var(--accent-cyan)] shadow-[0_0_8px_var(--accent-cyan)]' : 'bg-transparent'}
                      `}
                    />
                    <MessageSquare
                      className={`h-3.5 w-3.5 flex-shrink-0 transition-colors duration-200 ${
                        isActive ? 'text-[var(--accent-cyan)]' : 'text-[var(--text-muted)] group-hover/item:text-[var(--text-secondary)]'
                      }`}
                    />
                    <div className="flex-1 min-w-0">
                      <div
                        className={`text-sm truncate transition-colors duration-200 ${
                          isActive ? 'text-[var(--text-primary)] font-medium' : 'text-[var(--text-secondary)] group-hover/item:text-[var(--text-primary)]'
                        }`}
                      >
                        {s.title}
                      </div>
                    </div>
                    <span className="text-[10px] text-[var(--text-muted)] flex-shrink-0">
                      {s.message_count}
                    </span>
                  </button>
                )
              })}
            </div>
          </div>
        </div>,
        document.body
      )}
    </>
  )
}