package rules

import (
	"fmt"
	"slices"
	"strings"

	"github.com/AdguardTeam/golibs/errors"
	"github.com/AdguardTeam/urlfilter/internal/ufnet"
	"github.com/miekg/dns"
)

// Rule is a base interface for all filtering rules.
//
// TODO(a.garipov):  Rename to Interface.
type Rule interface {
	// Text returns the original rule text.
	//
	// TODO(a.garipov):  Replace with String.
	Text() (s string)

	// GetFilterListID returns ID of the filter list this rule belongs to.
	//
	// TODO(a.garipov):  Rename to ListID.
	GetFilterListID() (id ListID)
}

// NewRule creates a new filtering rule from the specified line.  It returns nil
// if the line is empty or if it is a comment.
func NewRule(line string, id ListID) (r Rule, err error) {
	if line = strings.TrimSpace(line); line == "" || isComment(line) {
		return nil, nil
	}

	if isCosmetic(line) {
		return NewCosmeticRule(line, id)
	}

	// TODO(a.garipov):  Optimize.
	hr, err := NewHostRule(line, id)
	if err == nil {
		return hr, nil
	}

	return NewNetworkRule(line, id)
}

// isComment returns true if the line is a comment.
func isComment(line string) (ok bool) {
	if len(line) == 0 {
		return false
	}

	if line[0] == '!' {
		return true
	}

	if line[0] == '#' {
		if len(line) == 1 {
			return true
		}

		// Now we should check that this is not a cosmetic rule.
		for _, marker := range cosmeticRulesMarkers {
			if startsAtIndexWith(line, 0, marker) {
				return false
			}
		}

		return true
	}

	return false
}

// parseDomains parses the $domain modifier or cosmetic rules domains.  sep is
// the separator character.  For network rules it is '|'; for cosmetic, ','.
func parseDomains(domains, sep string) (permittedDomains, restrictedDomains []string, err error) {
	if domains == "" {
		// TODO(a.garipov):  Here and in the whole package, use the standard
		// error values.
		return nil, nil, errors.Error("no domains specified")
	}

	list := strings.Split(domains, sep)
	for i := range list {
		d := list[i]
		restricted := false
		if strings.HasPrefix(d, "~") {
			restricted = true
			d = d[1:]
		}

		if !ufnet.IsDomainName(d) && !strings.HasSuffix(d, ".*") {
			err = fmt.Errorf("invalid domain specified: %s", domains)

			return permittedDomains, restrictedDomains, err
		}

		if restricted {
			restrictedDomains = append(restrictedDomains, d)
		} else {
			permittedDomains = append(permittedDomains, d)
		}
	}

	return permittedDomains, restrictedDomains, nil
}

// strToRRType converts s to a DNS resource record (RR) type.  s may be in any
// letter case.
func strToRRType(s string) (rr RRType, err error) {
	// TypeNone and TypeReserved are special cases in package dns.
	if strings.EqualFold(s, "none") || strings.EqualFold(s, "reserved") {
		return 0, errors.Error("dns rr type is none or reserved")
	}

	rr, ok := dns.StringToType[strings.ToUpper(s)]
	if !ok {
		return 0, fmt.Errorf("dns rr type %q is invalid", s)
	}

	return rr, nil
}

// parseDNSTypes parses the $dnstype modifier.  types is the list of types.
func parseDNSTypes(types string) (permittedTypes, restrictedTypes []RRType, err error) {
	if types == "" {
		return nil, nil, errors.Error("no dns record types specified")
	}

	list := strings.Split(types, "|")
	for i, rrStr := range list {
		if len(rrStr) == 0 {
			return nil, nil, fmt.Errorf("dns record type %d is empty", i)
		}

		restricted := rrStr[0] == '~'
		if restricted {
			rrStr = rrStr[1:]
		}

		var rr RRType
		rr, err = strToRRType(rrStr)
		if err != nil {
			return nil, nil, fmt.Errorf("type %d (%q): %w", i, rrStr, err)
		}

		if restricted {
			restrictedTypes = append(restrictedTypes, rr)
		} else {
			permittedTypes = append(permittedTypes, rr)
		}
	}

	return permittedTypes, restrictedTypes, nil
}

// isValidCTag returns true if ctag value format is correct.
func isValidCTag(s string) (ok bool) {
	for _, ch := range s {
		if (ch < 'a' || ch > 'z') && (ch < '0' || ch > '9') && ch != '_' {
			return false
		}
	}

	return true
}

// parseCTags parses tags from the $ctag modifier.  sep is the separator
// character; for network rules it is '|'.  permittedCTags and restrictedCTags
// are sorted.
func parseCTags(value, sep string) (permittedCTags, restrictedCTags []string, err error) {
	if value == "" {
		return nil, nil, errors.ErrEmptyValue
	}

	list := strings.Split(value, sep)
	for i := range list {
		d := list[i]
		restricted := false
		if strings.HasPrefix(d, "~") {
			restricted = true
			d = d[1:]
		}

		if !isValidCTag(d) {
			return permittedCTags, restrictedCTags, fmt.Errorf("invalid ctag specified: %q", value)
		}

		if restricted {
			restrictedCTags = append(restrictedCTags, d)
		} else {
			permittedCTags = append(permittedCTags, d)
		}
	}

	// Sorting tags so that we could use binary search
	slices.Sort(permittedCTags)
	slices.Sort(restrictedCTags)

	return permittedCTags, restrictedCTags, nil
}

// parseClients parses the client modifier string with the specified separator
// byte.
//
// The $client modifier allows specifying clients this rule will be working for.
// It accepts client names, IP addresses, or CIDR address ranges.
//
// The syntax is:
//
//	$client=value1|value2|...
//
// It is also possible to restrict clients by adding a '~' before the client IP
// or name.  In this case, the rule will not be applied to this client's
// requests:
//
//	$client=~value1
//
// # Specifying client names
//
// Client names can contain spaces or other special characters.  These should be
// enclosed in quotes; both double-quotes and single-quotes are supported.  If
// the client name contains quotes, use '\' to escape them.  Commas ',' and
// pipes '|' should also be escaped.
//
// Please note, that when specifying a restricted client, you must keep `~` out
// of the quotes.
//
// Examples of the input values:
//
//	127.0.0.1
//	192.168.3.0/24
//	::
//	fe01::/64
//	'Frank\'s laptop'
//	"Frank's phone"
//	~'Mary\'s\, John\'s\, and Boris\'s laptops'
//	~Mom|~Dad|"Kids"
//
// TODO(d.kolyshev):  Use permitted and restricted as structs, not pointers.
func parseClients(value string, sep byte) (permitted, restricted *clients, err error) {
	if value == "" {
		return nil, nil, errors.ErrEmptyValue
	}

	for _, client := range splitWithEscapeCharacter(value, sep, '\\', false) {
		permitted, restricted, err = appendClient(client, permitted, restricted)
		if err != nil {
			return nil, nil, fmt.Errorf("invalid $client value: %w", err)
		}
	}

	return permitted, restricted, nil
}

// appendClient adds a client to the specified set.  Creates the set if needed.
func appendClient(
	client string,
	permittedOrig *clients,
	restrictedOrig *clients,
) (permitted, restricted *clients, err error) {
	permitted = permittedOrig
	restricted = restrictedOrig

	client, isRestricted, err := parseClient(client)
	if err != nil {
		// Don't wrap the error since it's informative enough as is.
		return permitted, restricted, err
	}

	if isRestricted {
		if restricted == nil {
			restricted = newClients()
		}
		restricted.add(client)
	} else {
		if permitted == nil {
			permitted = newClients()
		}
		permitted.add(client)
	}

	return permitted, restricted, nil
}

// parseClient parses a single client string.
func parseClient(input string) (client string, isRestricted bool, err error) {
	client = input

	// 1. Check if this is a restricted or permitted client.
	if strings.HasPrefix(client, "~") {
		isRestricted = true
		client = client[1:]
	}

	// 2. Check if quoted.
	quoteChar := isQuoted(client)

	// 3. If quoted, remove quotes.
	if quoteChar > 0 {
		client = client[1 : len(client)-1]
	}

	// 4. Unescape commas and quotes.
	client = strings.ReplaceAll(client, "\\,", ",")
	if quoteChar > 0 {
		quoteStr := string(quoteChar)
		client = strings.ReplaceAll(client, "\\"+quoteStr, quoteStr)
	}

	if client == "" {
		return "", false, fmt.Errorf("invalid value %q", input)
	}

	return client, isRestricted, nil
}

// isQuoted returns the quote character if the input is quoted, or 0 otherwise.
func isQuoted(input string) (quoteChar uint8) {
	if len(input) >= 2 &&
		(input[0] == '\'' || input[0] == '"') &&
		input[0] == input[len(input)-1] {
		quoteChar = input[0]
	}

	return quoteChar
}
