import * as path from 'path'
import assert from 'assert'

const IS_WINDOWS = process.platform === 'win32'

/**
 * Similar to path.dirname except normalizes the path separators and slightly better handling for Windows UNC paths.
 *
 * For example, on Linux/macOS:
 * - `/               => /`
 * - `/hello          => /`
 *
 * For example, on Windows:
 * - `C:\             => C:\`
 * - `C:\hello        => C:\`
 * - `C:              => C:`
 * - `C:hello         => C:`
 * - `\               => \`
 * - `\hello          => \`
 * - `\\hello         => \\hello`
 * - `\\hello\world   => \\hello\world`
 */
export function dirname(p: string): string {
  // Normalize slashes and trim unnecessary trailing slash
  p = safeTrimTrailingSeparator(p)

  // Windows UNC root, e.g. \\hello or \\hello\world
  if (IS_WINDOWS && /^\\\\[^\\]+(\\[^\\]+)?$/.test(p)) {
    return p
  }

  // Get dirname
  let result = path.dirname(p)

  // Trim trailing slash for Windows UNC root, e.g. \\hello\world\
  if (IS_WINDOWS && /^\\\\[^\\]+\\[^\\]+\\$/.test(result)) {
    result = safeTrimTrailingSeparator(result)
  }

  return result
}

/**
 * Roots the path if not already rooted. On Windows, relative roots like `\`
 * or `C:` are expanded based on the current working directory.
 */
export function ensureAbsoluteRoot(root: string, itemPath: string): string {
  assert(root, `ensureAbsoluteRoot parameter 'root' must not be empty`)
  assert(itemPath, `ensureAbsoluteRoot parameter 'itemPath' must not be empty`)

  // Already rooted
  if (hasAbsoluteRoot(itemPath)) {
    return itemPath
  }

  // Windows
  if (IS_WINDOWS) {
    // Check for itemPath like C: or C:foo
    if (itemPath.match(/^[A-Z]:[^\\/]|^[A-Z]:$/i)) {
      let cwd = process.cwd()
      assert(
        cwd.match(/^[A-Z]:\\/i),
        `Expected current directory to start with an absolute drive root. Actual '${cwd}'`
      )

      // Drive letter matches cwd? Expand to cwd
      if (itemPath[0].toUpperCase() === cwd[0].toUpperCase()) {
        // Drive only, e.g. C:
        if (itemPath.length === 2) {
          // Preserve specified drive letter case (upper or lower)
          return `${itemPath[0]}:\\${cwd.substr(3)}`
        }
        // Drive + path, e.g. C:foo
        else {
          if (!cwd.endsWith('\\')) {
            cwd += '\\'
          }
          // Preserve specified drive letter case (upper or lower)
          return `${itemPath[0]}:\\${cwd.substr(3)}${itemPath.substr(2)}`
        }
      }
      // Different drive
      else {
        return `${itemPath[0]}:\\${itemPath.substr(2)}`
      }
    }
    // Check for itemPath like \ or \foo
    else if (normalizeSeparators(itemPath).match(/^\\$|^\\[^\\]/)) {
      const cwd = process.cwd()
      assert(
        cwd.match(/^[A-Z]:\\/i),
        `Expected current directory to start with an absolute drive root. Actual '${cwd}'`
      )

      return `${cwd[0]}:\\${itemPath.substr(1)}`
    }
  }

  assert(
    hasAbsoluteRoot(root),
    `ensureAbsoluteRoot parameter 'root' must have an absolute root`
  )

  // Otherwise ensure root ends with a separator
  if (root.endsWith('/') || (IS_WINDOWS && root.endsWith('\\'))) {
    // Intentionally empty
  } else {
    // Append separator
    root += path.sep
  }

  return root + itemPath
}

/**
 * On Linux/macOS, true if path starts with `/`. On Windows, true for paths like:
 * `\\hello\share` and `C:\hello` (and using alternate separator).
 */
export function hasAbsoluteRoot(itemPath: string): boolean {
  assert(itemPath, `hasAbsoluteRoot parameter 'itemPath' must not be empty`)

  // Normalize separators
  itemPath = normalizeSeparators(itemPath)

  // Windows
  if (IS_WINDOWS) {
    // E.g. \\hello\share or C:\hello
    return itemPath.startsWith('\\\\') || /^[A-Z]:\\/i.test(itemPath)
  }

  // E.g. /hello
  return itemPath.startsWith('/')
}

/**
 * On Linux/macOS, true if path starts with `/`. On Windows, true for paths like:
 * `\`, `\hello`, `\\hello\share`, `C:`, and `C:\hello` (and using alternate separator).
 */
export function hasRoot(itemPath: string): boolean {
  assert(itemPath, `isRooted parameter 'itemPath' must not be empty`)

  // Normalize separators
  itemPath = normalizeSeparators(itemPath)

  // Windows
  if (IS_WINDOWS) {
    // E.g. \ or \hello or \\hello
    // E.g. C: or C:\hello
    return itemPath.startsWith('\\') || /^[A-Z]:/i.test(itemPath)
  }

  // E.g. /hello
  return itemPath.startsWith('/')
}

/**
 * Removes redundant slashes and converts `/` to `\` on Windows
 */
export function normalizeSeparators(p: string): string {
  p = p || ''

  // Windows
  if (IS_WINDOWS) {
    // Convert slashes on Windows
    p = p.replace(/\//g, '\\')

    // Remove redundant slashes
    const isUnc = /^\\\\+[^\\]/.test(p) // e.g. \\hello
    return (isUnc ? '\\' : '') + p.replace(/\\\\+/g, '\\') // preserve leading \\ for UNC
  }

  // Remove redundant slashes
  return p.replace(/\/\/+/g, '/')
}

/**
 * Normalizes the path separators and trims the trailing separator (when safe).
 * For example, `/foo/ => /foo` but `/ => /`
 */
export function safeTrimTrailingSeparator(p: string): string {
  // Short-circuit if empty
  if (!p) {
    return ''
  }

  // Normalize separators
  p = normalizeSeparators(p)

  // No trailing slash
  if (!p.endsWith(path.sep)) {
    return p
  }

  // Check '/' on Linux/macOS and '\' on Windows
  if (p === path.sep) {
    return p
  }

  // On Windows check if drive root. E.g. C:\
  if (IS_WINDOWS && /^[A-Z]:\\$/i.test(p)) {
    return p
  }

  // Otherwise trim trailing slash
  return p.substr(0, p.length - 1)
}