import { openSync } from 'fs'
import { ReadStream } from 'tty'
import type { RenderOptions } from '../ink.js'
import { isEnvTruthy } from './envUtils.js'
import { logError } from './log.js'

// Cached stdin override - computed once per process
let cachedStdinOverride: ReadStream | undefined | null = null

/**
 * Gets a ReadStream for /dev/tty when stdin is piped.
 * This allows interactive Ink rendering even when stdin is a pipe.
 * Result is cached for the lifetime of the process.
 */
function getStdinOverride(): ReadStream | undefined {
 // Return cached result if already computed
 if (cachedStdinOverride !== null) {
 return cachedStdinOverride
 }

 // No override needed if stdin is already a TTY
 if (process.stdin.isTTY) {
 cachedStdinOverride = undefined
 return undefined
 }

 // Skip in CI environments
 if (isEnvTruthy(process.env.CI)) {
 cachedStdinOverride = undefined
 return undefined
 }

 // Skip if running MCP (input hijacking breaks MCP)
 if (process.argv.includes('mcp')) {
 cachedStdinOverride = undefined
 return undefined
 }

 // No /dev/tty on Windows
 if (process.platform === 'win32') {
 cachedStdinOverride = undefined
 return undefined
 }

 // Try to open /dev/tty as an alternative input source
 try {
 const ttyFd = openSync('/dev/tty', 'r')
 const ttyStream = new ReadStream(ttyFd)
 // Explicitly set isTTY to true since we know /dev/tty is a TTY.
 // This is needed because some runtimes (like Bun's compiled binaries)
 // may not correctly detect isTTY on ReadStream created from a file descriptor.
 ttyStream.isTTY = true
 cachedStdinOverride = ttyStream
 return cachedStdinOverride
 } catch (err) {
 logError(err as Error)
 cachedStdinOverride = undefined
 return undefined
 }
}

/**
 * Returns base render options for Ink, including stdin override when needed.
 * Use this for all render() calls to ensure piped input works correctly.
 *
 * @param exitOnCtrlC - Whether to exit on Ctrl+C (usually false for dialogs)
 */
export function getBaseRenderOptions(
 exitOnCtrlC: boolean = false,
): RenderOptions {
 const stdin = getStdinOverride()
 const options: RenderOptions = { exitOnCtrlC }
 if (stdin) {
 options.stdin = stdin
 }
 return options
}