/**
 * Verbose REPL/fish diagnostics when `DEBUG=1`.
 * Writes to the **session TTY** when bound (see `bindReplDebugStream`) so Pear/bare-stdio
 * logs show in the same terminal pane as the shell. Falls back to `process.stdout`, then
 * `stderr`, then `console.log`. Lines are prefixed with reset + newline so they stay
 * readable if the prompt left SGR/cursor state; expect the screen to scroll while debugging.
 */

/** @type {import('stream').Writable | null} */
let _debugStream = null

/** Bind REPL/fish stdout (e.g. bare-stdio `out`) so DEBUG lines appear in the visible terminal. */
export function bindReplDebugStream(stream) {
  _debugStream =
    stream && typeof stream.write === 'function' ? stream : null
}

export function unbindReplDebugStream() {
  _debugStream = null
}

/** @returns {boolean} */
export function isReplDebug() {
  const p = globalThis.process?.env
  return p?.DEBUG === '1'
}

function ts() {
  if (typeof globalThis.performance?.now === 'function') {
    return `${globalThis.performance.now().toFixed(2)}ms`
  }
  return `${Date.now()}`
}

function serialize(part) {
  if (typeof part === 'string') return part
  if (part === undefined) return 'undefined'
  if (part === null) return 'null'
  if (typeof part === 'number' || typeof part === 'boolean') return String(part)
  try {
    return JSON.stringify(part)
  } catch {
    return String(part)
  }
}

/**
 * @param {string} scope Short tag (e.g. fish-render, repl, booter)
 * @param {...unknown} parts Message pieces
 */
function writeDebugLine(text) {
  const payload = `\x1b[0m\n${text}\n`
  try {
    if (_debugStream && typeof _debugStream.write === 'function') {
      _debugStream.write(payload)
      return
    }
    const p = globalThis.process
    if (p?.stdout && typeof p.stdout.write === 'function') {
      p.stdout.write(payload)
      return
    }
    if (p?.stderr && typeof p.stderr.write === 'function') {
      p.stderr.write(payload)
      return
    }
    globalThis.console?.log?.(text)
  } catch {
    /* ignore */
  }
}

export function replDbg(scope, ...parts) {
  if (!isReplDebug()) return
  const line = `[${ts()}] [bare-os DEBUG:${scope}] ${parts.map(serialize).join(' ')}`
  writeDebugLine(line)
}

/**
 * Human-readable key / escape sequence for logs.
 * @param {string} key
 */
export function replDbgKeyRepr(key) {
  if (key === '\n') return '\\n'
  if (key === '\r') return '\\r'
  if (key === '\t') return '\\t'
  if (key === '\u007f') return 'DEL'
  if (key === '\u0003') return '^C'
  if (key === '\u0004') return '^D'
  if (key === '\u000c') return '^L'
  if (key === '\u0012' || (key.length === 1 && key.charCodeAt(0) === 18)) return '^R'
  if (key.startsWith('\u001b')) {
    return `CSI(${key.length}ch)=${JSON.stringify(key)}`
  }
  if (key.length === 1) {
    const c = key.charCodeAt(0)
    if (c < 32) return `^${String.fromCharCode(c + 64)}(u${c})`
    return key
  }
  return JSON.stringify(key.length > 120 ? key.slice(0, 120) + '…' : key)
}

/**
 * @param {string} label
 * @param {string} chunk
 * @param {number} [maxLen]
 */
export function replDbgChunk(label, chunk, maxLen = 256) {
  if (!isReplDebug()) return
  const s = typeof chunk === 'string' ? chunk : String(chunk)
  const t = s.length > maxLen ? s.slice(0, maxLen) + `…(+${s.length - maxLen})` : s
  const codes = [...t].slice(0, 80).map((ch) => {
    const u = ch.charCodeAt(0)
    if (u < 32 || u === 127) return `\\x${u.toString(16).padStart(2, '0')}`
    return ch
  })
  replDbg('fish-stdin', label, `len=${s.length}`, `head=${JSON.stringify(codes.join(''))}`)
}