// Package assets provisions the static assets bundled into the binary
// (fonts, shaders, and terms-of-service pages) into a per-user assets
// directory at application startup.
package assets

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

// embeddedRoot is the directory in the source tree (and therefore in the
// embedded FS) where the bundled assets live. It mirrors the nix store
// layout, but consumers expect the assets directly under the assets dir,
// so this root is stripped during provisioning.
const embeddedRoot = "share/radiantwave"

// ProvisionAssets provisions the bundled static assets (fonts, shaders, and
// terms-of-service pages) into destDir, stripping the embedded
// share/radiantwave root so the files land directly in destDir rather than
// in a nested share/radiantwave/ subdirectory. Existing files are
// overwritten so the deployed assets always match the running binary.
func ProvisionAssets(bundled fs.FS, destDir string) error {
	root, err := fs.Sub(bundled, embeddedRoot)
	if err != nil {
		return fmt.Errorf("bundled assets missing %s root: %w", embeddedRoot, err)
	}
	return Provision(root, destDir)
}

// Provision copies every file from the embedded filesystem into destDir,
// preserving the relative directory structure. Existing files are
// overwritten so the deployed assets always match the running binary.
func Provision(bundled fs.FS, destDir string) error {
	return fs.WalkDir(bundled, ".", func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}

		src, err := bundled.Open(path)
		if err != nil {
			return fmt.Errorf("opening bundled asset %s: %w", path, err)
		}
		defer src.Close()

		dst := filepath.Join(destDir, filepath.FromSlash(path))
		if err := os.MkdirAll(filepath.Dir(dst), 0755); err != nil {
			return fmt.Errorf("creating asset directory for %s: %w", path, err)
		}

		out, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
		if err != nil {
			return fmt.Errorf("creating asset file %s: %w", dst, err)
		}
		if _, err := io.Copy(out, src); err != nil {
			out.Close()
			return fmt.Errorf("writing asset file %s: %w", dst, err)
		}
		if err := out.Close(); err != nil {
			return fmt.Errorf("closing asset file %s: %w", dst, err)
		}
		return nil
	})
}