package blocklist

import (
	"bufio"
	"os"
	"strings"
)

type Blocklist struct {
	domains map[string]struct{}
}

func Load(path string) (*Blocklist, error) {
	bl := &Blocklist{domains: make(map[string]struct{})}
	f, err := os.Open(path)
	if err != nil {
		if os.IsNotExist(err) {
			return bl, nil
		}
		return nil, err
	}
	defer f.Close()

	sc := bufio.NewScanner(f)
	for sc.Scan() {
		line := strings.TrimSpace(sc.Text())
		if line == "" || line[0] == '#' || line[0] == '!' {
			continue
		}
		domain := parseLine(line)
		if domain != "" && !strings.HasPrefix(domain, "*.") {
			bl.domains[strings.ToLower(domain)] = struct {}{}
		}
	}
	return bl, sc.Err()
}

func parseLine(line string) string {
	line = strings.TrimSpace(line)

	// 1. Hosts: "0.0.0.0 domain" "127.0.0.1 domain # comment"
	if strings.HasPrefix(line, "0.0.0.0 ") {
		line = line[8:]
	} else if strings.HasPrefix(line, "127.0.0.1 ") {
		line = line[10:]
	} else if strings.HasPrefix(line, "||") {
		// 2. AdGuard / uBlock: "||domain^$attr"
		line = line[2:]
		// Cut at ^ or $
		if idx := strings.IndexAny(line, "^$"); idx >= 0 {
			line = line[:idx]
		}
	}

	if idx := strings.IndexAny(line, " \t#"); idx >= 0 {
		line = line[:idx]
	}

	line = strings.TrimSpace(line)
	line = strings.TrimSuffix(line, ".")

	if strings.ContainsAny(line, "/:\\?") {
		return ""
	}
	return line
}

func (bl *Blocklist) Blocked(qname string) bool {
	qname = strings.ToLower(qname)
	qname = strings.TrimSuffix(qname, ".")
	_, ok := bl.domains[qname]
	return ok
}