package compiler

import (
	"fmt"
	"strconv"
	"strings"
	"unicode"
	"unicode/utf8"
)

// parseGoEmbed parses the text following "//go:embed" to extract the glob patterns.
// It accepts unquoted space-separated patterns as well as double-quoted and back-quoted Go strings.
// Copied from https://github.com/golang/go/blob/219fe9d547d09d3de1b024c6c8b8314dd0bf12e4/src/cmd/compile/internal/noder/noder.go#L1717-L1776
func parseGoEmbed(args string) ([]string, error) {
	var list []string
	for args = strings.TrimSpace(args); args != ""; args = strings.TrimSpace(args) {
		var path string
	Switch:
		switch args[0] {
		default:
			i := len(args)
			for j, c := range args {
				if unicode.IsSpace(c) {
					i = j
					break
				}
			}
			path = args[:i]
			args = args[i:]

		case '`':
			i := strings.Index(args[1:], "`")
			if i < 0 {
				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
			}
			path = args[1 : 1+i]
			args = args[1+i+1:]

		case '"':
			i := 1
			for ; i < len(args); i++ {
				if args[i] == '\\' {
					i++
					continue
				}
				if args[i] == '"' {
					q, err := strconv.Unquote(args[:i+1])
					if err != nil {
						return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args[:i+1])
					}
					path = q
					args = args[i+1:]
					break Switch
				}
			}
			if i >= len(args) {
				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
			}
		}

		if args != "" {
			r, _ := utf8.DecodeRuneInString(args)
			if !unicode.IsSpace(r) {
				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
			}
		}
		list = append(list, path)
	}
	return list, nil
}