package walk

import (
	"context"
	"fmt"
	"io/fs"
	"path/filepath"
)

type filesystemWalker struct {
	root    string
	pathsCh chan string
}

func (f filesystemWalker) Root() string {
	return f.root
}

func (f filesystemWalker) Walk(_ context.Context, fn WalkFunc) error {
	relPathOffset := len(f.root) + 1

	relPathFn := func(path string) (string, error) {
		// quick optimisation for the majority of use cases
		// todo check that root is a prefix in path?
		if len(path) >= relPathOffset {
			return path[relPathOffset:], nil
		}
		return filepath.Rel(f.root, path)
	}

	walkFn := func(path string, info fs.FileInfo, _ error) error {
		if info == nil {
			return fmt.Errorf("no such file or directory '%s'", path)
		}

		relPath, err := relPathFn(path)
		if err != nil {
			return fmt.Errorf("failed to determine a relative path for %s: %w", path, err)
		}
		file := File{
			Path:    path,
			RelPath: relPath,
			Info:    info,
		}
		return fn(&file, err)
	}

	for path := range f.pathsCh {
		if err := filepath.Walk(path, walkFn); err != nil {
			return err
		}
	}

	return nil
}

func NewFilesystem(root string, paths chan string) (Walker, error) {
	return filesystemWalker{root, paths}, nil
}