package router

import (
	"fmt"
	"strings"
)

const (
	compContextPlain int = iota
	compContextRegex

	startRegex byte = '{'
	stopRegex  byte = '}'
)

func pathCompiler(path string) (string, error) {
	var err error
	res := make([]byte, 0)
	var pos int = compContextPlain
	var depth int = 0
	pattern := make([]byte, 0)
	for _, b := range []byte(path) {
		switch pos {
		case compContextPlain:
			switch b {
			case stopRegex:
				depth -= 1
				res = append(res, b)
			case startRegex:
				depth += 1
				pos = compContextRegex // pattern started
				pattern = make([]byte, 0)
			default:
				res = append(res, b)
			}
		case compContextRegex:
			switch b {
			case startRegex:
				depth += 1
			case stopRegex:
				depth -= 1
				if depth == 0 {
					pattern = convertRegexp(pattern)
					res = append(res, pattern...)
					pos = compContextPlain // pattern ended
				}
			default:
				pattern = append(pattern, b)
			}
		}
	}
	if depth != 0 {
		err = fmt.Errorf("Unbalanced brackets into pattern")
	}
	return string(res), err
}

const (
	defaultRegexp = `[a-zA-Z0-9_][/\-\.a-zA-Z0-9_%%=:~]+`
)

func convertRegexp(src []byte) []byte {
	var res string
	const patternSeps = ":"
	parts := strings.SplitN(string(src), patternSeps, 2)
	if len(parts) == 1 {
		parts = append(parts, defaultRegexp)
	}
	res = fmt.Sprintf("(?<%s>%s)", parts[0], parts[1])
	return []byte(res)
}