import { realpath, stat } from 'fs/promises'
import { getPlatform } from '../platform.js'
import { which } from '../which.js'

async function probePath(p: string): Promise<string | null> {
  try {
    return (await stat(p)).isFile() ? p : null
  } catch {
    return null
  }
}

/**
 * Attempts to find PowerShell on the system via PATH.
 * Prefers pwsh (PowerShell Core 7+), falls back to powershell (5.1).
 *
 * On Linux, if PATH resolves to a snap launcher (/snap/…) — directly or
 * via a symlink chain like /usr/bin/pwsh → /snap/bin/pwsh — probe known
 * apt/rpm install locations instead: the snap launcher can hang in
 * subprocesses while snapd initializes confinement, but the underlying
 * binary at /opt/microsoft/powershell/7/pwsh is reliable. On
 * Windows/macOS, PATH is sufficient.
 */
export async function findPowerShell(): Promise<string | null> {
  const pwshPath = await which('pwsh')
  if (pwshPath) {
    // Snap launcher hangs in subprocesses. Prefer the direct binary.
    // Check both the resolved PATH entry and its symlink target: on
    // some distros /usr/bin/pwsh is a symlink to /snap/bin/pwsh, which
    // would bypass a naive startsWith('/snap/') on the which() result.
    if (getPlatform() === 'linux') {
      const resolved = await realpath(pwshPath).catch(() => pwshPath)
      if (pwshPath.startsWith('/snap/') || resolved.startsWith('/snap/')) {
        const direct =
          (await probePath('/opt/microsoft/powershell/7/pwsh')) ??
          (await probePath('/usr/bin/pwsh'))
        if (direct) {
          const directResolved = await realpath(direct).catch(() => direct)
          if (
            !direct.startsWith('/snap/') &&
            !directResolved.startsWith('/snap/')
          ) {
            return direct
          }
        }
      }
    }
    return pwshPath
  }

  const powershellPath = await which('powershell')
  if (powershellPath) {
    return powershellPath
  }

  return null
}

let cachedPowerShellPath: Promise<string | null> | null = null

/**
 * Gets the cached PowerShell path. Returns a memoized promise that
 * resolves to the PowerShell executable path or null.
 */
export function getCachedPowerShellPath(): Promise<string | null> {
  if (!cachedPowerShellPath) {
    cachedPowerShellPath = findPowerShell()
  }
  return cachedPowerShellPath
}

export type PowerShellEdition = 'core' | 'desktop'

/**
 * Infers the PowerShell edition from the binary name without spawning.
 * - `pwsh` / `pwsh.exe` → 'core' (PowerShell 7+: supports `&&`, `||`, `?:`, `??`)
 * - `powershell` / `powershell.exe` → 'desktop' (Windows PowerShell 5.1:
 *   no pipeline chain operators, stderr-sets-$? bug, UTF-16 default encoding)
 *
 * PowerShell 6 (also `pwsh`, no `&&`) has been EOL since 2020 and is not
 * a realistic install target, so 'core' safely implies 7+ semantics.
 *
 * Used by the tool prompt to give version-appropriate syntax guidance so
 * the model doesn't emit `cmd1 && cmd2` on 5.1 (parser error) or avoid
 * `&&` on 7+ where it's the correct short-circuiting operator.
 */
export async function getPowerShellEdition(): Promise<PowerShellEdition | null> {
  const p = await getCachedPowerShellPath()
  if (!p) return null
  // basename without extension, case-insensitive. Covers:
  //   C:\Program Files\PowerShell\7\pwsh.exe
  //   /opt/microsoft/powershell/7/pwsh
  //   C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe
  const base = p
    .split(/[/\\]/)
    .pop()!
    .toLowerCase()
    .replace(/\.exe$/, '')
  return base === 'pwsh' ? 'core' : 'desktop'
}

/**
 * Resets the cached PowerShell path. Only for testing.
 */
export function resetPowerShellCache(): void {
  cachedPowerShellPath = null
}