/**
 * Pure derivation of the compact LIVE line shown on a running subagent card:
 * the last text output and the last tool call of the child's history tail
 * (`subagent.history` events, oldest → newest). Renders nothing itself — the
 * SubagentLiveLine component turns this into the card's status lines.
 * Kept framework-free so the parser is unit-testable in the node environment.
 */
import type { SidebarHistoryEntry } from '../context-types.ts'

/**
 * Extract the concatenated plain text of a content-block list (the durable
 * `ContentBlock[]` shape, structurally: blocks with `type: 'text'` carry
 * `text`; anything else — tool_use, image, … — contributes nothing).
 * @param content - the raw `content` field of a message event.
 * @returns the joined text, or undefined when the message carries no text.
 */
export function contentText(content: unknown): string | undefined {
  if (!Array.isArray(content)) return undefined
  const parts: string[] = []
  for (const block of content) {
    if (block === null || typeof block !== 'object') continue
    const candidate = block as { type?: unknown; text?: unknown }
    if (candidate.type === 'text' && typeof candidate.text === 'string') {
      parts.push(candidate.text)
    }
  }
  return parts.length > 0 ? parts.join('\n') : undefined
}

/** The live status of one subagent card (both fields optional). */
export interface LastActivity {
  /** The latest assembled assistant text output in the tail. */
  text?: string
  /** The latest tool call in the tail. */
  tool?: { name: string; args: string }
}

/**
 * Fold a history tail into the last text output + last tool call (each is
 * the LAST occurrence in event order). Lifecycle events and raw
 * `assistant/chunk` rows are ignored — the card shows what the subagent is
 * doing right now, not its plumbing.
 * @param entries - the tail page from `subagent.history` (oldest → newest).
 * @returns the last text and/or tool call; an empty object when the tail has neither.
 */
export function lastActivity(entries: SidebarHistoryEntry[]): LastActivity {
  let text: string | undefined
  let tool: { name: string; args: string } | undefined
  for (const entry of entries) {
    const { type, data } = entry.event
    if (type === 'assistant/message') {
      const message = data.message as { content?: unknown } | undefined
      const extracted = contentText(message?.content)
      if (extracted !== undefined) text = extracted
    } else if (type === 'tool/call') {
      tool = {
        name: typeof data.name === 'string' ? data.name : 'tool',
        args: typeof data.arguments === 'string' ? data.arguments : '',
      }
    }
  }
  if (text === undefined && tool === undefined) return {}
  return {
    ...(text === undefined ? {} : { text }),
    ...(tool === undefined ? {} : { tool }),
  }
}