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// link-static-files creates a directory of symlinks.
//
// Reads netstring-encoded pairs from stdin: dest src dest src ...
// where dest is relative to $out and src is an absolute path.
// Creates $out/dest -> src as a symlink, creating parent dirs as needed.
//
// Netstring format: "<length>:<content>,"
package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strconv"
)

func readNetstring(r *bufio.Reader) (string, error) {
	lenStr, err := r.ReadString(':')
	if err == io.EOF && lenStr == "" {
		return "", io.EOF
	}
	if err != nil {
		return "", fmt.Errorf("reading length: %w", err)
	}
	// strip the trailing ':'
	lenStr = lenStr[:len(lenStr)-1]
	n, err := strconv.Atoi(lenStr)
	if err != nil {
		return "", fmt.Errorf("parsing length %q: %w", lenStr, err)
	}
	buf := make([]byte, n+1) // +1 for the trailing ','
	if _, err := io.ReadFull(r, buf); err != nil {
		return "", fmt.Errorf("reading content: %w", err)
	}
	if buf[n] != ',' {
		return "", fmt.Errorf("expected trailing ',', got %q", buf[n])
	}
	return string(buf[:n]), nil
}

func main() {
	out := os.Getenv("out")
	if out == "" {
		fmt.Fprintln(os.Stderr, "link-static-files: $out not set")
		os.Exit(1)
	}

	if err := os.MkdirAll(out, 0755); err != nil {
		fmt.Fprintf(os.Stderr, "link-static-files: mkdir %s: %v\n", out, err)
		os.Exit(1)
	}

	r := bufio.NewReader(os.Stdin)
	for {
		dest, err := readNetstring(r)
		if err == io.EOF {
			break
		}
		if err != nil {
			fmt.Fprintf(os.Stderr, "link-static-files: reading dest: %v\n", err)
			os.Exit(1)
		}
		src, err := readNetstring(r)
		if err != nil {
			fmt.Fprintf(os.Stderr, "link-static-files: reading src: %v\n", err)
			os.Exit(1)
		}

		destAbs := filepath.Join(out, dest)
		if err := os.MkdirAll(filepath.Dir(destAbs), 0755); err != nil {
			fmt.Fprintf(os.Stderr, "link-static-files: mkdir %s: %v\n", filepath.Dir(destAbs), err)
			os.Exit(1)
		}
		if err := os.Symlink(src, destAbs); err != nil {
			fmt.Fprintf(os.Stderr, "link-static-files: symlink %s -> %s: %v\n", destAbs, src, err)
			os.Exit(1)
		}
	}
}