#!/usr/bin/env node
/**
 * Normalize every symlink/junction in a copied harness tree so the tree is
 * self-contained: no link may resolve to a path outside the tree.
 *
 * A pnpm workspace is held together by links inside node_modules. On Windows
 * those are often **junctions** (absolute-path reparse points) because real
 * symlinks need Developer Mode or an admin shell; even plain symlinks can be
 * absolute. `build-harness.mjs` copies the working tree with
 * `cpSync(..., { recursive: true })`, which — with the default
 * `dereference: false` — recreates every link verbatim, so the packaged harness
 * keeps pointing at the BUILD machine's dev tree: it reads dev resources on the
 * same machine and dangles on any other. This module rewrites each such link to
 * a RELATIVE target inside the harness (mirroring the dev layout), and copies
 * the real content of any genuinely external target in so nothing escapes.
 *
 * Pure Node, no Electron and no workspace TS program: imported by
 * `scripts/build-harness.mjs` / `scripts/verify-harness.mjs` and unit-tested
 * from `tests/harness-relink.spec.ts`.
 * @module dsh-desktop/harness-relink
 */

import {
  cpSync, existsSync, lstatSync, mkdirSync, mkdtempSync, readdirSync, readlinkSync, rmSync, symlinkSync,
} from 'node:fs'
import { tmpdir } from 'node:os'
import { dirname, isAbsolute, join, relative, resolve, sep } from 'node:path'

/** True when `p` resolves inside `root` (or is `root` itself). */
export function isWithin(root, p) {
  const rel = relative(resolve(root), resolve(p))
  return rel === '' || (rel !== '..' && !rel.startsWith(`..${sep}`) && !isAbsolute(rel))
}

/** The link's own kind so Windows creates the right reparse point ('dir'/'file'). */
function linkKind(target) {
  try {
    return lstatSync(target).isDirectory() ? 'dir' : 'file'
  } catch {
    return 'dir'
  }
}

/** Remove a link and copy the target's real content into its place. */
function dereferenceInto(link, target) {
  rmSync(link, { force: true })
  cpSync(target, link, { recursive: true, dereference: true })
}

/** Rewrite `link` as a relative symlink to `mirrored`; dereference on failure. */
function relinkTo(link, mirrored, report) {
  const rel = relative(dirname(link), mirrored)
  try {
    rmSync(link, { force: true })
    symlinkSync(rel, link, linkKind(mirrored))
    report.normalized += 1
  } catch (error) {
    // Symlink creation failed (e.g. no Developer Mode on Windows): a compact
    // portable link is impossible, so copy the target content in instead.
    try {
      dereferenceInto(link, mirrored)
      report.dereferenced += 1
    } catch (copyError) {
      report.errors.push(`${link} -> ${mirrored} (${String(copyError)})`)
    }
  }
}

/**
 * Walk `out` and normalize every symlink/junction to a relative in-tree link.
 * Idempotent: a link already pointing inside the tree is left alone.
 * @param out - the harness root.
 * @param repoRoot - the repository root whose layout `out` mirrors.
 * @returns per-kind counts plus any unrecoverable errors.
 */
export function relinkHarness(out, repoRoot) {
  const report = { normalized: 0, dereferenced: 0, unchanged: 0, removed: 0, errors: [] }
  forEachLink(out, (link) => {
    const target = readlinkSync(link)
    const abs = resolve(dirname(link), target)
    if (isWithin(out, abs)) {
      if (!existsSync(abs)) {
        // A link inside the tree whose target is absent points at a workspace
        // package the harness does not ship (python/sdk-runtime, examples, …).
        // It cannot resolve and is not part of the runtime: drop it.
        rmSync(link, { force: true })
        report.removed += 1
      } else if (relative(dirname(link), abs) === target) {
        // Already inside the tree: make sure the link is a relative in-tree path.
        report.unchanged += 1
      } else {
        relinkTo(link, abs, report)
      }
    } else if (isWithin(repoRoot, abs)) {
      // Points at the dev tree: mirror the target into the harness and relink.
      const mirrored = join(out, relative(repoRoot, abs))
      if (existsSync(mirrored)) {
        relinkTo(link, mirrored, report)
      } else if (isWithin(abs, out)) {
        // The target contains the harness itself (e.g. the desktop shell
        // package, which the harness deliberately does not ship). Copying it in
        // would recurse into the bundle and it is not part of the runtime
        // closure, so the link cannot be made self-contained — drop it.
        rmSync(link, { force: true })
        report.removed += 1
      } else if (existsSync(abs)) {
        try {
          dereferenceInto(link, abs)
          report.dereferenced += 1
        } catch (error) {
          report.errors.push(`${link} -> ${abs} (${String(error)})`)
        }
      } else {
        report.errors.push(`${link} -> ${abs} (dangling)`)
      }
    } else if (existsSync(abs)) {
      // Genuinely external target (e.g. a global store): copy content in.
      try {
        dereferenceInto(link, abs)
        report.dereferenced += 1
      } catch (error) {
        report.errors.push(`${link} -> ${abs} (${String(error)})`)
      }
    } else {
      report.errors.push(`${link} -> ${abs} (dangling)`)
    }
  })
  return report
}

/**
 * Every symlink/junction whose target escapes `out` or no longer exists. A
 * non-empty result means the harness is NOT detached from its build machine.
 */
export function findEscapingLinks(out) {
  const escaping = []
  forEachLink(out, (link) => {
    const abs = resolve(dirname(link), readlinkSync(link))
    if (!isWithin(out, abs) || !existsSync(abs)) escaping.push(link)
  })
  return escaping
}

/** Throw unless the tree is self-contained (no escaping or dangling links). */
export function assertSelfContained(out) {
  const escaping = findEscapingLinks(out)
  if (escaping.length === 0) return
  const listed = escaping.slice(0, 20).join('\n  ')
  throw new Error(
    `harness is NOT self-contained: ${escaping.length} link(s) resolve outside it or are dangling:\n  ${listed}`,
  )
}

/**
 * Whether the current host can create (relative) directory symlinks. Windows
 * without Developer Mode (and without an admin shell) cannot; without this
 * capability the packaged harness could not be relinked compactly.
 */
export function probeSymlinkSupport() {
  const base = mkdtempSync(join(tmpdir(), 'dsh-symlink-probe-'))
  const target = join(base, 'target')
  const link = join(base, 'link')
  try {
    // The target must exist: Windows refuses a directory link to a missing
    // target, and on POSIX existsSync() would report a dangling link as absent.
    mkdirSync(target, { recursive: true })
    symlinkSync(target, link, 'dir')
    return existsSync(link)
  } catch {
    return false
  } finally {
    rmSync(base, { recursive: true, force: true })
  }
}

/**
 * Visit every symlink/junction under `root` without following into any link.
 * Junctions are reported as symlinks by `lstat` on Windows; because the walk
 * never recurses through a link, it cannot loop or escape the tree.
 */
function forEachLink(root, fn) {
  const stack = [resolve(root)]
  const seen = new Set()
  while (stack.length > 0) {
    const dir = stack.pop()
    if (dir === undefined || seen.has(dir)) continue
    seen.add(dir)
    let entries
    try {
      entries = readdirSync(dir, { withFileTypes: true })
    } catch {
      continue
    }
    for (const entry of entries) {
      const path = join(dir, entry.name)
      let stat
      try {
        stat = lstatSync(path)
      } catch {
        continue
      }
      if (stat.isSymbolicLink()) {
        fn(path)
      } else if (stat.isDirectory()) {
        stack.push(path)
      }
    }
  }
}