// Agent personas — named, role-scoped sub-system prompts.
// Each persona stacks on top of the main systemPrompt to specialize the
// assistant for a task. Persisted in localStorage; reactive across tabs.

import { useEffect, useSyncExternalStore } from "react"

export type Agent = {
  id: string
  name: string
  role: string
  prompt: string
}

export const DEFAULT_AGENTS: Agent[] = [
  {
    id: "generalist",
    name: "Atlas",
    role: "Generalist",
    prompt:
      "You handle anything: chat, planning, summaries, casual questions. Match the user's tone. Keep replies as long as the task deserves — terse for quick questions, detailed when explaining.",
  },
  {
    id: "coder",
    name: "Forge",
    role: "Software engineer",
    prompt:
      "You are a senior software engineer. Write idiomatic, well-typed code. Prefer concrete examples over abstract advice. When asked to fix a bug, identify root cause before patching. Use markdown code blocks with language tags. Mention edge cases briefly when relevant.",
  },
  {
    id: "writer",
    name: "Inkwell",
    role: "Writer",
    prompt:
      "You are a prose writer. Produce vivid, well-paced text — short stories, copy, emails, essays. Vary sentence length. Show, don't tell. When the user asks for a draft, deliver the draft, not a description of it.",
  },
  {
    id: "researcher",
    name: "Pilot",
    role: "Researcher",
    prompt:
      "You are a careful researcher. Structure answers as: claim → evidence → caveat. Distinguish what is well-established from what is uncertain. Refuse to fabricate citations — if you don't know, say so.",
  },
  {
    id: "ui-driver",
    name: "Cursor",
    role: "UI Operator",
    prompt:
      "You specialize in driving this app's UI on the user's behalf. Prefer doing over explaining. When the user asks for an action, emit an action block immediately. When they ask a question about the app, answer concisely and offer to do it.",
  },
]

const STORAGE_KEY = "crema.agents"
const ACTIVE_KEY = "crema.assistant.activeAgent"
const CHANGE_EVENT = "crema:agents-change"

function isAgent(v: unknown): v is Agent {
  return (
    !!v &&
    typeof v === "object" &&
    typeof (v as Agent).id === "string" &&
    typeof (v as Agent).name === "string" &&
    typeof (v as Agent).role === "string" &&
    typeof (v as Agent).prompt === "string"
  )
}

function readFromStorage(): Agent[] {
  if (typeof window === "undefined") return DEFAULT_AGENTS
  try {
    const raw = localStorage.getItem(STORAGE_KEY)
    if (!raw) return DEFAULT_AGENTS
    const parsed = JSON.parse(raw)
    if (!Array.isArray(parsed)) return DEFAULT_AGENTS
    const cleaned = parsed.filter(isAgent)
    return cleaned.length > 0 ? cleaned : DEFAULT_AGENTS
  } catch {
    return DEFAULT_AGENTS
  }
}

export function loadAgents(): Agent[] {
  return readFromStorage()
}

export function saveAgents(next: Agent[]) {
  if (typeof window === "undefined") return
  localStorage.setItem(STORAGE_KEY, JSON.stringify(next))
  window.dispatchEvent(new CustomEvent(CHANGE_EVENT))
}

export function resetAgents() {
  saveAgents(DEFAULT_AGENTS)
}

let cached: Agent[] | null = null

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

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

function getServerSnapshot(): Agent[] {
  return DEFAULT_AGENTS
}

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

export function loadActiveAgentId(): string {
  if (typeof window === "undefined") return DEFAULT_AGENTS[0].id
  try {
    return localStorage.getItem(ACTIVE_KEY) ?? DEFAULT_AGENTS[0].id
  } catch {
    return DEFAULT_AGENTS[0].id
  }
}

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

export function composeSystemPrompt(
  base: string,
  agent: Agent | undefined,
): string {
  if (!agent) return base
  return `${base}\n\nActive persona: ${agent.name} — ${agent.role}\n${agent.prompt}`
}

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