package main

import (
	"fmt"
	"io/fs"
	"log"
	"os"
	"path/filepath"
)

// processHardlinks creates hardlinks in destBase/destSubdir mirroring the
// structure found at contentPath (either a single file or a directory tree).
func processHardlinks(cfg *Config, contentPath, destSubdir string) error {
	info, err := os.Stat(contentPath)
	if err != nil {
		return fmt.Errorf("stat %q: %w", contentPath, err)
	}

	destDir := filepath.Join(cfg.DestBase, destSubdir)

	if info.IsDir() {
		return hardlinkDir(contentPath, destDir)
	}
	return hardlinkFile(contentPath, filepath.Join(destDir, filepath.Base(contentPath)))
}

// hardlinkDir walks srcDir and recreates the directory tree under destDir,
// creating hardlinks for every file found.
func hardlinkDir(srcDir, destDir string) error {
	return filepath.WalkDir(srcDir, func(srcPath string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}

		rel, err := filepath.Rel(srcDir, srcPath)
		if err != nil {
			return err
		}
		destPath := filepath.Join(destDir, rel)

		if d.IsDir() {
			if err := os.MkdirAll(destPath, 0755); err != nil {
				return fmt.Errorf("mkdir %q: %w", destPath, err)
			}
			return nil
		}

		return hardlinkFile(srcPath, destPath)
	})
}

// hardlinkFile creates a hardlink at destPath pointing to srcPath.
// It creates parent directories as needed and skips if the link already exists.
func hardlinkFile(srcPath, destPath string) error {
	if err := os.MkdirAll(filepath.Dir(destPath), 0755); err != nil {
		return fmt.Errorf("mkdir %q: %w", filepath.Dir(destPath), err)
	}

	if _, err := os.Lstat(destPath); err == nil {
		log.Printf("skip (already exists): %s", destPath)
		return nil
	}

	if err := os.Link(srcPath, destPath); err != nil {
		return fmt.Errorf("hardlink %q -> %q: %w", srcPath, destPath, err)
	}

	log.Printf("hardlinked: %s -> %s", srcPath, destPath)
	return nil
}