import type { Plugin } from "@opencode-ai/plugin"
import { spawn } from "bun"

/**
 * tmux-panes plugin
 *
 * When opencode spawns a background subagent, this plugin automatically opens
 * a new tmux pane showing that subagent's live TUI via `opencode attach`.
 * The pane closes when the subagent session ends.
 *
 * Only activates when running inside a tmux session (TMUX env var is set).
 */

const isInsideTmux = () => Boolean(process.env.TMUX)
const getCurrentPaneId = () => process.env.TMUX_PANE

const plugin: Plugin = async (ctx) => {
	if (!isInsideTmux()) return {}

	const sessions = new Map<string, string>() // sessionId → tmux paneId
	const sourcePaneId = getCurrentPaneId()
	const serverUrl = ctx.serverUrl.toString()

	return {
		event: async ({ event }) => {
			// Spawn a new pane when a subagent session is created
			if (event.type === "session.created") {
				const info = (event as any).properties?.info
				// parentID presence distinguishes subagents from the root session
				if (!info?.id || !info?.parentID) return
				const sessionId: string = info.id
				if (sessions.has(sessionId)) return

				const cmd = `opencode attach ${serverUrl} --session ${sessionId}`
				const proc = spawn(
					[
						"tmux",
						"split-window",
						"-h", // horizontal split
						"-d", // don't focus the new pane
						"-P",
						"-F",
						"#{pane_id}", // print the new pane's ID
						...(sourcePaneId ? ["-t", sourcePaneId] : []),
						cmd,
					],
					{ stdout: "pipe", stderr: "pipe" },
				)

				const paneId = (await new Response(proc.stdout).text()).trim()
				if ((await proc.exited) === 0 && paneId) {
					sessions.set(sessionId, paneId)
				}
			}

			// Kill the pane when the subagent session ends
			if (event.type === "session.deleted") {
				const info = (event as any).properties?.info
				const paneId = sessions.get(info?.id)
				if (paneId) {
					spawn(["tmux", "kill-pane", "-t", paneId], {
						stdout: "ignore",
						stderr: "ignore",
					})
					sessions.delete(info.id)
				}
			}
		},
	}
}

export default plugin