pansy/web/src/lib/agent.ts

// The garden assistant's client (#57).
//
// The chat lives in the editor, not on its own page, because watching the canvas
// change as the agent works IS the confirmation — which is what makes acting
// without asking first tolerable. So this module's job is as much about
// surfacing progress as it is about sending a message.

import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query'
import { z } from 'zod'
import { API_BASE, api } from './api'
import { gardenFullKey } from './objects'
import { historyKey } from './history'

const capabilitiesSchema = z.object({ agent: z.boolean() })

/** Whether this instance has the assistant configured. Without it the panel
 *  isn't rendered at all — a dead button is worse than no button. */
export function useCapabilities() {
  return useQuery({
    queryKey: ['capabilities'] as const,
    queryFn: async () => capabilitiesSchema.parse(await api.get('/capabilities')),
    staleTime: Infinity, // server config; it doesn't change under a running page
  })
}

export const agentMessageSchema = z.object({
  id: z.number(),
  conversationId: z.number(),
  role: z.enum(['user', 'assistant']),
  body: z.string(),
  changeSetId: z.number().optional(),
  createdAt: z.string(),
})
export type AgentMessage = z.infer<typeof agentMessageSchema>

const historySchema = z.object({ messages: z.array(agentMessageSchema) })

export function agentHistoryKey(gardenId: number) {
  return ['gardens', gardenId, 'agent-history'] as const
}

/** The stored conversation, so a reload doesn't lose the thread — which is
 *  exactly when someone reloads, to check whether a change actually landed. */
export function useAgentHistory(gardenId: number, enabled: boolean) {
  return useQuery({
    queryKey: agentHistoryKey(gardenId),
    enabled,
    queryFn: async (): Promise<AgentMessage[]> =>
      historySchema.parse(await api.get(`/gardens/${gardenId}/agent/history`)).messages,
  })
}

export function useClearAgentHistory(gardenId: number) {
  const qc = useQueryClient()
  return useMutation({
    mutationFn: async (): Promise<void> => {
      await api.delete(`/gardens/${gardenId}/agent/history`)
    },
    onSuccess: () => qc.invalidateQueries({ queryKey: agentHistoryKey(gardenId) }),
  })
}

/** One completed turn, as the server reports it. */
export interface AgentTurn {
  reply: string
  changeSetId?: number
  steps: number
  truncated?: boolean
}

/** A step the model just finished, named in the app's own vocabulary. */
export interface AgentStep {
  index: number
  tools: string[]
}

// What each tool is doing, in words. Raw tool names ("fill_region") tell you the
// agent is busy; these tell you what it's busy DOING, which is the difference
// between the panel feeling alive and feeling hung.
const TOOL_LABELS: Record<string, string> = {
  list_gardens: 'Looking at your gardens',
  describe_garden: 'Reading the garden',
  create_object: 'Adding a bed',
  move_object: 'Moving a bed',
  place_planting: 'Planting',
  fill_region: 'Filling a bed',
  clear_object: 'Clearing a bed',
  find_plant: 'Looking up a plant',
  create_plant: 'Adding a plant to your catalog',
  add_journal_entry: 'Writing a journal note',
}

export function describeStep(step: AgentStep): string {
  if (step.tools.length === 0) return 'Thinking'
  const labels = step.tools.map((t) => TOOL_LABELS[t] ?? t.replace(/_/g, ' '))
  // Repeated tools in one step read as one action, not a list of identical ones.
  return [...new Set(labels)].join(', ')
}

const chatEventSchema = z.object({
  step: z.object({ index: z.number(), tools: z.array(z.string()) }).optional(),
  done: z
    .object({
      reply: z.string(),
      changeSetId: z.number().optional(),
      steps: z.number(),
      truncated: z.boolean().optional(),
    })
    .optional(),
  error: z.string().optional(),
  // The turn worked but something adjacent to it didn't — currently, the
  // exchange couldn't be saved. Dropping this on the floor would recreate
  // exactly the silent swallow the server added it to avoid.
  warning: z.string().optional(),
})

export interface StreamHandlers {
  onStep: (step: AgentStep) => void
  onDone: (turn: AgentTurn) => void
  onError: (message: string) => void
  /** The turn succeeded, but something alongside it didn't. */
  onWarning?: (message: string) => void
}

/**
 * Send a message and stream the reply.
 *
 * Hand-rolled rather than EventSource, which can only issue GETs — this needs a
 * POST body. The wire format is still SSE so a proxy that understands it doesn't
 * buffer, and so switching to EventSource later wouldn't change the server.
 */
export async function streamChat(
  gardenId: number,
  message: string,
  handlers: StreamHandlers,
  signal?: AbortSignal,
): Promise<void> {
  let res: Response
  try {
    res = await fetch(`${API_BASE}/agent/chat`, {
      method: 'POST',
      headers: { 'content-type': 'application/json' },
      body: JSON.stringify({ gardenId, message }),
      credentials: 'same-origin',
      signal,
    })
  } catch {
    // An abort here is the caller's own doing — Stop, or navigating away — not a
    // failure to report back to them. The read loop below already knew this; the
    // request path did not.
    if (signal?.aborted) return
    handlers.onError('Could not reach the server.')
    return
  }
  if (!res.ok || !res.body) {
    handlers.onError(
      res.status === 404
        ? "This instance doesn't have the assistant configured."
        : 'The assistant is not available right now.',
    )
    return
  }

  const reader = res.body.getReader()
  const decoder = new TextDecoder()
  let buffer = ''
  for (;;) {
    let chunk: ReadableStreamReadResult<Uint8Array>
    try {
      chunk = await reader.read()
    } catch {
      // An aborted read is the caller navigating away, not a failure worth
      // reporting back to them.
      if (signal?.aborted) return
      handlers.onError('The connection dropped partway through.')
      return
    }
    if (chunk.done) break
    buffer += decoder.decode(chunk.value, { stream: true })

    // SSE frames are separated by a blank line; anything after the last one is
    // a partial frame to keep for the next chunk.
    const frames = buffer.split('\n\n')
    buffer = frames.pop() ?? ''
    for (const frame of frames) {
      const line = frame.split('\n').find((l) => l.startsWith('data:'))
      if (!line) continue
      // Parsed AND validated: a malformed or unexpected frame shouldn't kill a
      // working stream, and shouldn't be trusted into the UI either.
      const parsed = chatEventSchema.safeParse(safeJson(line.slice(5).trim()))
      if (!parsed.success) continue
      const e = parsed.data
      if (e.warning) handlers.onWarning?.(e.warning)
      if (e.error) handlers.onError(e.error)
      else if (e.step) handlers.onStep(e.step)
      else if (e.done) handlers.onDone(e.done)
    }
  }
}

function safeJson(raw: string): unknown {
  try {
    return JSON.parse(raw)
  } catch {
    return null
  }
}

/**
 * Refreshes for the two moments that need different amounts of work.
 *
 * Mid-turn, only the canvas can have changed: the change set isn't written until
 * the turn commits, and the exchange isn't stored until it finishes. Refetching
 * those on every step would be up to 2×(N−1) requests per turn for data that
 * cannot have moved.
 */
export function useAgentRefresh(gardenId: number) {
  const qc = useQueryClient()
  const canvas = () => {
    void qc.invalidateQueries({ queryKey: gardenFullKey(gardenId) })
  }
  return {
    /** After a step: the garden may have changed under the conversation. */
    canvas,
    /** After a turn: the change set and the stored exchange exist now too. */
    everything: () => {
      canvas()
      void qc.invalidateQueries({ queryKey: historyKey(gardenId) })
      void qc.invalidateQueries({ queryKey: agentHistoryKey(gardenId) })
    },
  }
}