// Package core - core types like ID and Path.
package core

import (
	"errors"
	"regexp"
	"strings"
)

var ErrNotFound = errors.New("not found")

type Page[T any] struct {
	Items  []T
	Cursor string
}

type PageReq struct {
	Limit  int
	Cursor string
}


type Path string

var pathSegment = regexp.MustCompile(`^[a-zA-Z0-9_]+$`)

func (p Path) Valid() error {
	s := string(p)
	if s == "" {
		return errors.New("path is empty")
	}
	segments := strings.Split(s, ".")
	for _, seg := range segments {
		if seg == "" {
			return errors.New("path contains empty segment")
		}
		if !pathSegment.MatchString(seg) {
			return errors.New("path segment must match [a-zA-Z0-9_]+: " + seg)
		}
	}
	return nil
}

// Contains reports whether p equals or is an ancestor of other.
// An empty path contains nothing.
func (p Path) Contains(other Path) bool {
	if p == "" {
		return true
	}
	if other == "" {
		return false 
	}
	return p == other || strings.HasPrefix(string(other), string(p)+".")
}

func (p Path) Parent() Path {
	s := string(p)
	i := strings.LastIndex(s, ".")
	if i < 0 {
		return ""
	}
	return Path(s[:i])
}

// Root returns the first segment of the path, or "" if empty.
func (p Path) Root() string {
	s := string(p)
	if i := strings.Index(s, "."); i >= 0 {
		return s[:i]
	}
	return s
}

// Segments returns all path segments.
func (p Path) Segments() []string {
	if p == "" {
		return nil
	}
	return strings.Split(string(p), ".")
}