package tools

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

func resolvePath(baseDir, path string) (string, error) {
	resolved, canonicalBase, err := resolveLexicalPath(baseDir, path)
	if err != nil {
		return "", err
	}
	canonical, err := filepath.EvalSymlinks(resolved)
	if err != nil {
		return "", err
	}
	if !isWithinDir(canonical, canonicalBase) {
		return "", fmt.Errorf("path escapes the project directory through a symbolic link: %s", path)
	}
	return canonical, nil
}

// resolvePathForWrite resolves a path that may not exist yet while preventing
// existing parent-directory symlinks from escaping the project directory.
func resolvePathForWrite(baseDir, path string) (string, error) {
	resolved, canonicalBase, err := resolveLexicalPath(baseDir, path)
	if err != nil {
		return "", err
	}

	existing := resolved
	var suffix []string
	for {
		_, err := os.Lstat(existing)
		if err == nil {
			break
		}
		if !os.IsNotExist(err) {
			return "", err
		}
		parent := filepath.Dir(existing)
		if parent == existing {
			return "", err
		}
		suffix = append(suffix, filepath.Base(existing))
		existing = parent
	}

	canonical, err := filepath.EvalSymlinks(existing)
	if err != nil {
		return "", err
	}
	for i := len(suffix) - 1; i >= 0; i-- {
		canonical = filepath.Join(canonical, suffix[i])
	}
	if !isWithinDir(canonical, canonicalBase) {
		return "", fmt.Errorf("path escapes the project directory through a symbolic link: %s", path)
	}
	return canonical, nil
}

func resolveLexicalPath(baseDir, path string) (string, string, error) {
	if path == "" {
		path = "."
	}
	if filepath.IsAbs(path) {
		return "", "", fmt.Errorf("absolute paths are not allowed; use a path relative to the project directory")
	}
	absBase, err := filepath.Abs(baseDir)
	if err != nil {
		return "", "", err
	}
	canonicalBase, err := filepath.EvalSymlinks(absBase)
	if err != nil {
		return "", "", err
	}
	resolved := filepath.Clean(filepath.Join(absBase, path))
	if !isWithinDir(resolved, absBase) {
		return "", "", fmt.Errorf("path escapes the project directory: %s", path)
	}
	return resolved, canonicalBase, nil
}

func isWithinDir(path, dir string) bool {
	rel, err := filepath.Rel(dir, path)
	if err != nil {
		return false
	}
	if rel == ".." || strings.HasPrefix(rel, ".."+string(filepath.Separator)) {
		return false
	}
	return true
}