// Conversation threads — multiple named chats, each with its own history,
// active agent, and pinned message indices. Persisted in localStorage.

import { useEffect, useSyncExternalStore } from "react"

export type ThreadMessage = {
  role: "user" | "assistant" | "tool"
  content: string
  /** Persona that authored this assistant message (omitted for user msgs). */
  agentId?: string
  /** Native tool calls attached to an assistant message. */
  toolCalls?: { id: string; name: string; arguments: string }[]
  /** Tool role only — id of the matching assistant tool_call. */
  toolCallId?: string
  /** Tool role only — function name. */
  name?: string
}

export type Thread = {
  id: string
  title: string
  agentId: string
  messages: ThreadMessage[]
  pinned: number[] // indices into messages[]
  createdAt: number
  updatedAt: number
}

const THREADS_KEY = "crema.assistant.threads"
const ACTIVE_KEY = "crema.assistant.activeThreadId"
const SNAPSHOT_KEY_PREFIX = "crema.assistant.thread.snapshot."
const CHANGE_EVENT = "crema:threads-change"
const MAX_BYTES = 800_000

export function newThreadId(): string {
  return `t-${Date.now().toString(36)}-${Math.random().toString(36).slice(2, 6)}`
}

function isThread(v: unknown): v is Thread {
  if (!v || typeof v !== "object") return false
  const t = v as Thread
  return (
    typeof t.id === "string" &&
    typeof t.title === "string" &&
    typeof t.agentId === "string" &&
    Array.isArray(t.messages) &&
    Array.isArray(t.pinned) &&
    typeof t.createdAt === "number" &&
    typeof t.updatedAt === "number"
  )
}

function readFromStorage(): Thread[] {
  if (typeof window === "undefined") return []
  try {
    const raw = localStorage.getItem(THREADS_KEY)
    if (!raw) return []
    const parsed = JSON.parse(raw)
    if (!Array.isArray(parsed)) return []
    return parsed.filter(isThread)
  } catch {
    return []
  }
}

function writeToStorage(threads: Thread[]) {
  if (typeof window === "undefined") return
  let serialized = JSON.stringify(threads)
  // Trim oldest threads if quota gets tight.
  let trimmed = threads
  while (serialized.length > MAX_BYTES && trimmed.length > 1) {
    trimmed = trimmed.slice(0, -1)
    serialized = JSON.stringify(trimmed)
  }
  try {
    localStorage.setItem(THREADS_KEY, serialized)
    window.dispatchEvent(new CustomEvent(CHANGE_EVENT))
  } catch {
    /* quota — bail */
  }
}

export function loadThreads(): Thread[] {
  return readFromStorage()
}

export function saveThreads(threads: Thread[]) {
  writeToStorage(threads)
}

export function loadActiveThreadId(): string | null {
  if (typeof window === "undefined") return null
  return localStorage.getItem(ACTIVE_KEY)
}

export function saveActiveThreadId(id: string | null) {
  if (typeof window === "undefined") return
  if (id) localStorage.setItem(ACTIVE_KEY, id)
  else localStorage.removeItem(ACTIVE_KEY)
  window.dispatchEvent(new CustomEvent(CHANGE_EVENT))
}

let cached: Thread[] | null = null

function subscribe(cb: () => void): () => void {
  const onChange = () => {
    cached = null
    cb()
  }
  window.addEventListener(CHANGE_EVENT, onChange)
  window.addEventListener("storage", (e) => {
    if (e.key === THREADS_KEY || e.key === ACTIVE_KEY) onChange()
  })
  return () => {
    window.removeEventListener(CHANGE_EVENT, onChange)
  }
}

function getSnapshot(): Thread[] {
  if (!cached) cached = readFromStorage()
  return cached
}
function getServerSnapshot(): Thread[] {
  return []
}

export function useThreads(): Thread[] {
  const value = useSyncExternalStore(subscribe, getSnapshot, getServerSnapshot)
  useEffect(() => {
    cached = null
  }, [])
  return value
}

export function ensureThread(
  threads: Thread[],
  fallbackAgentId: string,
): { threads: Thread[]; activeId: string } {
  const stored = loadActiveThreadId()
  if (stored && threads.some((t) => t.id === stored))
    return { threads, activeId: stored }
  if (threads.length > 0) {
    saveActiveThreadId(threads[0].id)
    return { threads, activeId: threads[0].id }
  }
  const id = newThreadId()
  const now = Date.now()
  const fresh: Thread = {
    id,
    title: "New conversation",
    agentId: fallbackAgentId,
    messages: [],
    pinned: [],
    createdAt: now,
    updatedAt: now,
  }
  saveActiveThreadId(id)
  saveThreads([fresh, ...threads])
  return { threads: [fresh, ...threads], activeId: id }
}

export function updateThread(id: string, patch: Partial<Thread>) {
  const threads = readFromStorage()
  const next = threads.map((t) =>
    t.id === id ? { ...t, ...patch, updatedAt: Date.now() } : t,
  )
  writeToStorage(next)
}

export function createThread(agentId: string, title = "New conversation"): Thread {
  const threads = readFromStorage()
  const id = newThreadId()
  const now = Date.now()
  const fresh: Thread = {
    id,
    title,
    agentId,
    messages: [],
    pinned: [],
    createdAt: now,
    updatedAt: now,
  }
  writeToStorage([fresh, ...threads])
  saveActiveThreadId(id)
  return fresh
}

export function deleteThread(id: string) {
  const threads = readFromStorage()
  const next = threads.filter((t) => t.id !== id)
  writeToStorage(next)
  if (loadActiveThreadId() === id) {
    saveActiveThreadId(next[0]?.id ?? null)
  }
}

export function snapshotThread(id: string) {
  const threads = readFromStorage()
  const t = threads.find((x) => x.id === id)
  if (!t) return
  try {
    localStorage.setItem(SNAPSHOT_KEY_PREFIX + id, JSON.stringify(t))
  } catch {
    /* quota */
  }
}

export function loadThreadSnapshot(id: string): Thread | null {
  if (typeof window === "undefined") return null
  try {
    const raw = localStorage.getItem(SNAPSHOT_KEY_PREFIX + id)
    if (!raw) return null
    const parsed = JSON.parse(raw)
    return isThread(parsed) ? parsed : null
  } catch {
    return null
  }
}

export function clearThreadSnapshot(id: string) {
  if (typeof window === "undefined") return
  localStorage.removeItem(SNAPSHOT_KEY_PREFIX + id)
}

export function deriveTitleFromFirstMessage(text: string): string {
  const trimmed = text.trim().split(/\s+/).slice(0, 8).join(" ")
  return trimmed.length > 60 ? trimmed.slice(0, 57) + "…" : trimmed || "New conversation"
}