package netmap

import (
	"errors"
	"fmt"
	"io"
	"strconv"
	"strings"

	"git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/netmap"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/netmap/parser"
	"github.com/antlr4-go/antlr/v4"
)

// PlacementPolicy declares policy to store objects in the FrostFS container.
// Within itself, PlacementPolicy represents a set of rules to select a subset
// of nodes from FrostFS network map - node-candidates for object storage.
//
// PlacementPolicy is mutually compatible with git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/netmap.PlacementPolicy
// message. See ReadFromV2 / WriteToV2 methods.
//
// Instances can be created using built-in var declaration.
type PlacementPolicy struct {
	backupFactor uint32

	filters []netmap.Filter

	selectors []netmap.Selector

	replicas []netmap.Replica

	unique bool
}

func (p *PlacementPolicy) readFromV2(m netmap.PlacementPolicy, checkFieldPresence bool) error {
	p.replicas = m.GetReplicas()
	if checkFieldPresence {
		if len(p.replicas) == 0 {
			return errors.New("missing replicas")
		}
		if len(p.replicas) != 1 {
			for i := range p.replicas {
				if p.replicas[i].GetECDataCount() != 0 || p.replicas[i].GetECParityCount() != 0 {
					return errors.New("erasure code group must be used exclusively")
				}
			}
		}
	}

	p.backupFactor = m.GetContainerBackupFactor()
	p.selectors = m.GetSelectors()
	p.filters = m.GetFilters()
	p.unique = m.GetUnique()

	return nil
}

// Marshal encodes PlacementPolicy into a binary format of the FrostFS API
// protocol (Protocol Buffers with direct field order).
//
// See also Unmarshal.
func (p PlacementPolicy) Marshal() []byte {
	var m netmap.PlacementPolicy
	p.WriteToV2(&m)

	return m.StableMarshal(nil)
}

// Unmarshal decodes FrostFS API protocol binary format into the PlacementPolicy
// (Protocol Buffers with direct field order). Returns an error describing
// a format violation.
//
// See also Marshal.
func (p *PlacementPolicy) Unmarshal(data []byte) error {
	var m netmap.PlacementPolicy

	err := m.Unmarshal(data)
	if err != nil {
		return err
	}

	return p.readFromV2(m, false)
}

// MarshalJSON encodes PlacementPolicy into a JSON format of the FrostFS API
// protocol (Protocol Buffers JSON).
//
// See also UnmarshalJSON.
func (p PlacementPolicy) MarshalJSON() ([]byte, error) {
	var m netmap.PlacementPolicy
	p.WriteToV2(&m)

	return m.MarshalJSON()
}

// UnmarshalJSON decodes FrostFS API protocol JSON format into the PlacementPolicy
// (Protocol Buffers JSON). Returns an error describing a format violation.
//
// See also MarshalJSON.
func (p *PlacementPolicy) UnmarshalJSON(data []byte) error {
	var m netmap.PlacementPolicy

	err := m.UnmarshalJSON(data)
	if err != nil {
		return err
	}

	return p.readFromV2(m, false)
}

// ReadFromV2 reads PlacementPolicy from the netmap.PlacementPolicy message.
// Checks if the message conforms to FrostFS API V2 protocol.
//
// See also WriteToV2.
func (p *PlacementPolicy) ReadFromV2(m netmap.PlacementPolicy) error {
	return p.readFromV2(m, true)
}

// WriteToV2 writes PlacementPolicy to the session.Token message.
// The message must not be nil.
//
// See also ReadFromV2.
func (p PlacementPolicy) WriteToV2(m *netmap.PlacementPolicy) {
	m.SetContainerBackupFactor(p.backupFactor)
	m.SetFilters(p.filters)
	m.SetSelectors(p.selectors)
	m.SetReplicas(p.replicas)
	m.SetUnique(p.unique)
}

// ReplicaDescriptor replica descriptor characterizes replicas of objects from
// the subset selected by a particular Selector.
type ReplicaDescriptor struct {
	m netmap.Replica
}

// SetNumberOfObjects sets number of object replicas.
func (r *ReplicaDescriptor) SetNumberOfObjects(c uint32) {
	r.m.SetCount(c)
}

// NumberOfObjects returns number set using SetNumberOfObjects.
//
// Zero ReplicaDescriptor has zero number of objects.
func (r ReplicaDescriptor) NumberOfObjects() uint32 {
	return r.m.GetCount()
}

// SetSelectorName sets name of the related Selector.
//
// Zero ReplicaDescriptor references to the root bucket's selector: it contains
// all possible nodes to store the object.
func (r *ReplicaDescriptor) SetSelectorName(s string) {
	r.m.SetSelector(s)
}

// AddReplicas adds a bunch object replica's characteristics.
//
// See also IterateReplicas.
func (p *PlacementPolicy) AddReplicas(rs ...ReplicaDescriptor) {
	off := len(p.replicas)

	p.replicas = append(p.replicas, make([]netmap.Replica, len(rs))...)

	for i := range rs {
		p.replicas[off+i] = rs[i].m
	}
}

// NumberOfReplicas returns number of replica descriptors set using AddReplicas.
//
// Zero PlacementPolicy has no replicas which is incorrect according to the
// FrostFS API protocol.
func (p PlacementPolicy) NumberOfReplicas() int {
	return len(p.replicas)
}

// ReplicaNumberByIndex returns number of object replicas from the i-th replica
// descriptor. Index MUST be in range [0; NumberOfReplicas()).
//
// Zero PlacementPolicy has no replicas.
func (p PlacementPolicy) ReplicaNumberByIndex(i int) uint32 {
	return p.replicas[i].GetCount()
}

// SetContainerBackupFactor sets container backup factor: it controls how deep
// FrostFS will search for nodes alternatives to include into container's nodes subset.
//
// Zero PlacementPolicy has zero container backup factor.
func (p *PlacementPolicy) SetContainerBackupFactor(f uint32) {
	p.backupFactor = f
}

// SetUnique sets the unique flag: it controls whether the selected replica buckets
// are disjoint or not.
//
// Zero PlacementPolicy has false unique flag.
func (p *PlacementPolicy) SetUnique(b bool) {
	p.unique = b
}

// Selector describes the bucket selection operator: choose a number of nodes
// from the bucket taking the nearest nodes to the related container by hash distance.
type Selector struct {
	m netmap.Selector
}

// SetName sets name with which the Selector can be referenced.
//
// Zero Selector is unnamed.
func (s *Selector) SetName(name string) {
	s.m.SetName(name)
}

// SetNumberOfNodes sets number of nodes to select from the bucket.
//
// Zero Selector selects nothing.
func (s *Selector) SetNumberOfNodes(num uint32) {
	s.m.SetCount(num)
}

// SelectByBucketAttribute sets attribute of the bucket to select nodes from.
//
// Zero Selector has empty attribute.
func (s *Selector) SelectByBucketAttribute(bucket string) {
	s.m.SetAttribute(bucket)
}

// SetClause sets the clause for the Selector.
func (s *Selector) SetClause(clause netmap.Clause) {
	s.m.SetClause(clause)
}

// SelectSame makes selection algorithm to select only nodes having the same values
// of the bucket attribute.
//
// Zero Selector doesn't specify selection modifier so nodes are selected randomly.
//
// See also SelectByBucketAttribute.
func (s *Selector) SelectSame() {
	s.m.SetClause(netmap.Same)
}

// SelectDistinct makes selection algorithm to select only nodes having the different values
// of the bucket attribute.
//
// Zero Selector doesn't specify selection modifier so nodes are selected randomly.
//
// See also SelectByBucketAttribute.
func (s *Selector) SelectDistinct() {
	s.m.SetClause(netmap.Distinct)
}

// SetFilterName sets reference to pre-filtering nodes for selection.
//
// Zero Selector has no filtering reference.
//
// See also Filter.SetName.
func (s *Selector) SetFilterName(f string) {
	s.m.SetFilter(f)
}

// AddSelectors adds a Selector bunch to form the subset of the nodes
// to store container objects.
//
// Zero PlacementPolicy does not declare selectors.
func (p *PlacementPolicy) AddSelectors(ss ...Selector) {
	off := len(p.selectors)

	p.selectors = append(p.selectors, make([]netmap.Selector, len(ss))...)

	for i := range ss {
		p.selectors[off+i] = ss[i].m
	}
}

// Filter contains rules for filtering the node sets.
type Filter struct {
	m netmap.Filter
}

// SetName sets name with which the Filter can be referenced or, for inner filters,
// to which the Filter references. Top-level filters MUST be named. The name
// MUST NOT be '*'.
//
// Zero Filter is unnamed.
func (x *Filter) SetName(name string) {
	x.m.SetName(name)
}

func (x *Filter) setAttribute(key string, op netmap.Operation, val string) {
	x.m.SetKey(key)
	x.m.SetOp(op)
	x.m.SetValue(val)
}

// Equal applies the rule to accept only nodes with the same attribute value.
//
// Method SHOULD NOT be called along with other similar methods.
func (x *Filter) Equal(key, value string) {
	x.setAttribute(key, netmap.EQ, value)
}

// NotEqual applies the rule to accept only nodes with the distinct attribute value.
//
// Method SHOULD NOT be called along with other similar methods.
func (x *Filter) NotEqual(key, value string) {
	x.setAttribute(key, netmap.NE, value)
}

// NumericGT applies the rule to accept only nodes with the numeric attribute
// greater than given number.
//
// Method SHOULD NOT be called along with other similar methods.
func (x *Filter) NumericGT(key string, num int64) {
	x.setAttribute(key, netmap.GT, strconv.FormatInt(num, 10))
}

// NumericGE applies the rule to accept only nodes with the numeric attribute
// greater than or equal to given number.
//
// Method SHOULD NOT be called along with other similar methods.
func (x *Filter) NumericGE(key string, num int64) {
	x.setAttribute(key, netmap.GE, strconv.FormatInt(num, 10))
}

// NumericLT applies the rule to accept only nodes with the numeric attribute
// less than given number.
//
// Method SHOULD NOT be called along with other similar methods.
func (x *Filter) NumericLT(key string, num int64) {
	x.setAttribute(key, netmap.LT, strconv.FormatInt(num, 10))
}

// NumericLE applies the rule to accept only nodes with the numeric attribute
// less than or equal to given number.
//
// Method SHOULD NOT be called along with other similar methods.
func (x *Filter) NumericLE(key string, num int64) {
	x.setAttribute(key, netmap.LE, strconv.FormatInt(num, 10))
}

func (x *Filter) setInnerFilters(op netmap.Operation, filters []Filter) {
	x.setAttribute("", op, "")

	inner := x.m.GetFilters()
	if rem := len(filters) - len(inner); rem > 0 {
		inner = append(inner, make([]netmap.Filter, rem)...)
	}

	for i := range filters {
		inner[i] = filters[i].m
	}

	x.m.SetFilters(inner)
}

// LogicalOR applies the rule to accept only nodes which satisfy at least one
// of the given filters.
//
// Method SHOULD NOT be called along with other similar methods.
func (x *Filter) LogicalOR(filters ...Filter) {
	x.setInnerFilters(netmap.OR, filters)
}

// LogicalAND applies the rule to accept only nodes which satisfy all the given
// filters.
//
// Method SHOULD NOT be called along with other similar methods.
func (x *Filter) LogicalAND(filters ...Filter) {
	x.setInnerFilters(netmap.AND, filters)
}

// AddFilters adds a Filter bunch that will be applied when selecting nodes.
//
// Zero PlacementPolicy has no filters.
func (p *PlacementPolicy) AddFilters(fs ...Filter) {
	off := len(p.filters)

	p.filters = append(p.filters, make([]netmap.Filter, len(fs))...)

	for i := range fs {
		p.filters[off+i] = fs[i].m
	}
}

// WriteStringTo encodes PlacementPolicy into human-readably query and writes
// the result into w. Returns w's errors directly.
//
// See also DecodeString.
// nolint: funlen
func (p PlacementPolicy) WriteStringTo(w io.StringWriter) (err error) {
	if p.unique {
		if _, err := w.WriteString("UNIQUE\n"); err != nil {
			return err
		}
	}

	delim := ""

	for i := range p.replicas {
		c := p.replicas[i].GetCount()
		s := p.replicas[i].GetSelector()

		if c != 0 {
			_, err = w.WriteString(fmt.Sprintf("%sREP %d", delim, c))
		} else {
			ecx, ecy := p.replicas[i].GetECDataCount(), p.replicas[i].GetECParityCount()
			_, err = w.WriteString(fmt.Sprintf("%sEC %d.%d", delim, ecx, ecy))
		}
		if s != "" {
			_, err = w.WriteString(fmt.Sprintf(" IN %s", s))
		}

		if err != nil {
			return err
		}

		delim = "\n"
	}

	if p.backupFactor > 0 {
		_, err = w.WriteString(fmt.Sprintf("\nCBF %d", p.backupFactor))
		if err != nil {
			return err
		}
	}

	var s string

	for i := range p.selectors {
		_, err = w.WriteString(fmt.Sprintf("\nSELECT %d", p.selectors[i].GetCount()))
		if err != nil {
			return err
		}

		if s = p.selectors[i].GetAttribute(); s != "" {
			var clause string

			switch p.selectors[i].GetClause() {
			case netmap.Same:
				clause = "SAME "
			case netmap.Distinct:
				clause = "DISTINCT "
			default:
				clause = ""
			}

			_, err = w.WriteString(fmt.Sprintf(" IN %s%s", clause, s))
			if err != nil {
				return err
			}
		}

		if s = p.selectors[i].GetFilter(); s != "" {
			_, err = w.WriteString(" FROM " + s)
			if err != nil {
				return err
			}
		}

		if s = p.selectors[i].GetName(); s != "" {
			_, err = w.WriteString(" AS " + s)
			if err != nil {
				return err
			}
		}
	}

	for i := range p.filters {
		_, err = w.WriteString("\nFILTER ")
		if err != nil {
			return err
		}

		err = writeFilterStringTo(w, p.filters[i], false)
		if err != nil {
			return err
		}
	}

	return nil
}

func writeFilterStringTo(w io.StringWriter, f netmap.Filter, mayNeedOuterBrackets bool) error {
	var err error
	var s string
	op := f.GetOp()
	unspecified := op == 0

	if s = f.GetKey(); s != "" {
		_, err = w.WriteString(fmt.Sprintf("%s %s %s", escapeString(s), op, escapeString(f.GetValue())))
		if err != nil {
			return err
		}
	} else if s = f.GetName(); unspecified && s != "" {
		_, err = w.WriteString(fmt.Sprintf("@%s", s))
		if err != nil {
			return err
		}
	}

	inner := f.GetFilters()

	if op == netmap.NOT {
		_, err = w.WriteString(op.String() + " (")
		if err != nil {
			return err
		}
		err = writeFilterStringTo(w, inner[0], false)
		if err != nil {
			return err
		}
		_, err = w.WriteString(")")
		if err != nil {
			return err
		}
	} else {
		useBrackets := mayNeedOuterBrackets && op == netmap.OR && len(inner) > 1
		if useBrackets {
			_, err = w.WriteString("(")
			if err != nil {
				return err
			}
		}
		for i := range inner {
			if i != 0 {
				_, err = w.WriteString(" " + op.String() + " ")
				if err != nil {
					return err
				}
			}
			err = writeFilterStringTo(w, inner[i], true)
			if err != nil {
				return err
			}
		}
		if useBrackets {
			_, err = w.WriteString(")")
			if err != nil {
				return err
			}
		}
	}

	if s = f.GetName(); s != "" && !unspecified {
		_, err = w.WriteString(" AS " + s)
		if err != nil {
			return err
		}
	}

	return nil
}

// DecodeString decodes PlacementPolicy from the string composed using
// WriteStringTo. Returns error if s is malformed.
func (p *PlacementPolicy) DecodeString(s string) error {
	var v policyVisitor

	input := antlr.NewInputStream(s)
	lexer := parser.NewQueryLexer(input)
	lexer.RemoveErrorListeners()
	lexer.AddErrorListener(&v)
	stream := antlr.NewCommonTokenStream(lexer, 0)

	pp := parser.NewQuery(stream)
	pp.BuildParseTrees = true

	pp.RemoveErrorListeners()
	pp.AddErrorListener(&v)
	pl := pp.Policy().Accept(&v)

	if len(v.errors) != 0 {
		return v.errors[0]
	}

	parsed, ok := pl.(*PlacementPolicy)
	if !ok {
		return fmt.Errorf("unexpected parsed instance type %T", pl)
	} else if parsed == nil {
		return errors.New("parsed nil value")
	}

	if err := validatePolicy(*parsed); err != nil {
		return fmt.Errorf("invalid policy: %w", err)
	}

	*p = *parsed

	return nil
}

// SelectFilterExpr is an expression containing only selectors and filters.
// It's useful to evaluate their effect before being used in a policy.
type SelectFilterExpr struct {
	cbf      uint32
	selector *netmap.Selector
	filters  []netmap.Filter
}

// DecodeString decodes a string into a SelectFilterExpr.
// Returns an error if s is malformed.
func DecodeSelectFilterString(s string) (*SelectFilterExpr, error) {
	var v policyVisitor

	input := antlr.NewInputStream(s)
	lexer := parser.NewQueryLexer(input)
	lexer.RemoveErrorListeners()
	lexer.AddErrorListener(&v)
	stream := antlr.NewCommonTokenStream(lexer, 0)

	pp := parser.NewQuery(stream)
	pp.BuildParseTrees = true

	pp.RemoveErrorListeners()
	pp.AddErrorListener(&v)
	sfExpr := pp.SelectFilterExpr().Accept(&v)

	if len(v.errors) != 0 {
		return nil, v.errors[0]
	}

	parsed, ok := sfExpr.(*SelectFilterExpr)
	if !ok {
		return nil, fmt.Errorf("unexpected parsed instance type %T", sfExpr)
	}

	return parsed, nil
}

var (
	// errUnknownFilter is returned when a value of FROM in a query is unknown.
	errUnknownFilter = errors.New("filter not found")
	// errUnknownSelector is returned when a value of IN is unknown.
	errUnknownSelector = errors.New("policy: selector not found")
	// errSyntaxError is returned for errors found by ANTLR parser.
	errSyntaxError = errors.New("policy: syntax error")
	// errRedundantSelector is returned for errors found by selectors policy validator.
	errRedundantSelector = errors.New("policy: found redundant selector")
	// errUnnamedSelector is returned for errors found by selectors policy validator.
	errUnnamedSelector = errors.New("policy: unnamed selectors are useless, " +
		"make sure to pair REP and SELECT clauses: \"REP .. IN X\" + \"SELECT ... AS X\"")
	// errRedundantSelector is returned for errors found by filters policy validator.
	errRedundantFilter = errors.New("policy: found redundant filter")
	// errECFewSelectors is returned when EC keyword is used without UNIQUE keyword.
	errECFewSelectors = errors.New("policy: too few nodes to select")
)

type policyVisitor struct {
	errors []error
	parser.BaseQueryVisitor
	antlr.DefaultErrorListener
}

func (p *policyVisitor) SyntaxError(_ antlr.Recognizer, _ any, line, column int, msg string, _ antlr.RecognitionException) {
	p.reportError(fmt.Errorf("%w: line %d:%d %s", errSyntaxError, line, column, msg))
}

func (p *policyVisitor) reportError(err error) any {
	p.errors = append(p.errors, err)
	return nil
}

// VisitPolicy implements parser.QueryVisitor interface.
func (p *policyVisitor) VisitPolicy(ctx *parser.PolicyContext) any {
	if len(p.errors) != 0 {
		return nil
	}

	pl := new(PlacementPolicy)

	pl.unique = ctx.UNIQUE() != nil

	stmts := ctx.GetChildren()
	for _, r := range stmts {
		var res *netmap.Replica
		var ok bool
		switch r := r.(type) {
		case parser.IRepStmtContext:
			res, ok = r.Accept(p).(*netmap.Replica)
		case parser.IEcStmtContext:
			res, ok = r.Accept(p).(*netmap.Replica)
		default:
			continue
		}
		if !ok {
			return nil
		}

		pl.replicas = append(pl.replicas, *res)
	}

	if cbfStmt := ctx.CbfStmt(); cbfStmt != nil {
		cbf, ok := cbfStmt.(*parser.CbfStmtContext).Accept(p).(uint32)
		if !ok {
			return nil
		}
		pl.SetContainerBackupFactor(cbf)
	}

	selStmts := ctx.AllSelectStmt()
	pl.selectors = make([]netmap.Selector, 0, len(selStmts))

	for _, s := range selStmts {
		res, ok := s.Accept(p).(*netmap.Selector)
		if !ok {
			return nil
		}

		pl.selectors = append(pl.selectors, *res)
	}

	filtStmts := ctx.AllFilterStmt()
	pl.filters = make([]netmap.Filter, 0, len(filtStmts))

	for _, f := range filtStmts {
		pl.filters = append(pl.filters, *f.Accept(p).(*netmap.Filter))
	}

	return pl
}

func (p *policyVisitor) VisitSelectFilterExpr(ctx *parser.SelectFilterExprContext) any {
	if len(p.errors) != 0 {
		return nil
	}

	sfExpr := new(SelectFilterExpr)

	if cbfStmt := ctx.CbfStmt(); cbfStmt != nil {
		cbf, ok := cbfStmt.(*parser.CbfStmtContext).Accept(p).(uint32)
		if !ok {
			return nil
		}
		sfExpr.cbf = cbf
	}

	if selStmt := ctx.SelectStmt(); selStmt != nil {
		sel, ok := selStmt.Accept(p).(*netmap.Selector)
		if !ok {
			return nil
		}
		sfExpr.selector = sel
	}

	filtStmts := ctx.AllFilterStmt()
	sfExpr.filters = make([]netmap.Filter, 0, len(filtStmts))

	for _, f := range filtStmts {
		sfExpr.filters = append(sfExpr.filters, *f.Accept(p).(*netmap.Filter))
	}

	return sfExpr
}

func (p *policyVisitor) VisitCbfStmt(ctx *parser.CbfStmtContext) any {
	cbf, err := strconv.ParseUint(ctx.GetBackupFactor().GetText(), 10, 32)
	if err != nil {
		return p.reportError(errInvalidNumber)
	}

	return uint32(cbf)
}

// VisitRepStmt implements parser.QueryVisitor interface.
func (p *policyVisitor) VisitRepStmt(ctx *parser.RepStmtContext) any {
	num, err := strconv.ParseUint(ctx.GetCount().GetText(), 10, 32)
	if err != nil {
		return p.reportError(errInvalidNumber)
	}

	rs := new(netmap.Replica)
	rs.SetCount(uint32(num))

	if sel := ctx.GetSelector(); sel != nil {
		rs.SetSelector(sel.GetText())
	}

	return rs
}

// VisitRepStmt implements parser.QueryVisitor interface.
func (p *policyVisitor) VisitEcStmt(ctx *parser.EcStmtContext) any {
	dataCount, err := strconv.ParseUint(ctx.GetData().GetText(), 10, 32)
	if err != nil {
		return p.reportError(errInvalidNumber)
	}
	parityCount, err := strconv.ParseUint(ctx.GetParity().GetText(), 10, 32)
	if err != nil {
		return p.reportError(errInvalidNumber)
	}

	rs := new(netmap.Replica)
	rs.SetECDataCount(uint32(dataCount))
	rs.SetECParityCount(uint32(parityCount))

	if sel := ctx.GetSelector(); sel != nil {
		rs.SetSelector(sel.GetText())
	}

	return rs
}

// VisitSelectStmt implements parser.QueryVisitor interface.
func (p *policyVisitor) VisitSelectStmt(ctx *parser.SelectStmtContext) any {
	res, err := strconv.ParseUint(ctx.GetCount().GetText(), 10, 32)
	if err != nil {
		return p.reportError(errInvalidNumber)
	}

	s := new(netmap.Selector)
	s.SetCount(uint32(res))

	if clStmt := ctx.Clause(); clStmt != nil {
		s.SetClause(clauseFromString(clStmt.GetText()))
	}

	if bStmt := ctx.GetBucket(); bStmt != nil {
		s.SetAttribute(ctx.GetBucket().GetText())
	}

	s.SetFilter(ctx.GetFilter().GetText()) // either ident or wildcard

	if ctx.AS() != nil {
		s.SetName(ctx.GetName().GetText())
	}
	return s
}

// VisitFilterStmt implements parser.QueryVisitor interface.
func (p *policyVisitor) VisitFilterStmt(ctx *parser.FilterStmtContext) any {
	f := p.VisitFilterExpr(ctx.GetExpr().(*parser.FilterExprContext)).(*netmap.Filter)
	f.SetName(ctx.GetName().GetText())
	return f
}

func (p *policyVisitor) VisitFilterExpr(ctx *parser.FilterExprContext) any {
	if eCtx := ctx.Expr(); eCtx != nil {
		return eCtx.Accept(p)
	}

	if inner := ctx.GetInner(); inner != nil {
		return inner.Accept(p)
	}

	f := new(netmap.Filter)
	op := operationFromString(ctx.GetOp().GetText())
	f.SetOp(op)

	if op == netmap.NOT {
		f1 := *ctx.GetF1().Accept(p).(*netmap.Filter)
		f.SetFilters([]netmap.Filter{f1})
		return f
	}

	f1 := *ctx.GetF1().Accept(p).(*netmap.Filter)
	f2 := *ctx.GetF2().Accept(p).(*netmap.Filter)

	// Consider f1=(.. AND ..) AND f2. This can be merged because our AND operation
	// is of arbitrary arity. ANTLR generates left-associative parse-tree by default.
	if f1.GetOp() == op {
		f.SetFilters(append(f1.GetFilters(), f2))
		return f
	}

	f.SetFilters([]netmap.Filter{f1, f2})

	return f
}

// VisitFilterKey implements parser.QueryVisitor interface.
func (p *policyVisitor) VisitFilterKey(ctx *parser.FilterKeyContext) any {
	if id := ctx.Ident(); id != nil {
		return id.GetText()
	}

	str := ctx.STRING().GetText()
	return str[1 : len(str)-1]
}

func (p *policyVisitor) VisitFilterValue(ctx *parser.FilterValueContext) any {
	if id := ctx.Ident(); id != nil {
		return id.GetText()
	}

	if num := ctx.Number(); num != nil {
		return num.GetText()
	}

	str := ctx.STRING().GetText()
	return str[1 : len(str)-1]
}

// VisitExpr implements parser.QueryVisitor interface.
func (p *policyVisitor) VisitExpr(ctx *parser.ExprContext) any {
	f := new(netmap.Filter)
	if flt := ctx.GetFilter(); flt != nil {
		f.SetName(flt.GetText())
		return f
	}

	key := ctx.GetKey().Accept(p)
	opStr := ctx.SIMPLE_OP().GetText()
	value := ctx.GetValue().Accept(p)

	f.SetKey(key.(string))
	f.SetOp(operationFromString(opStr))
	f.SetValue(value.(string))

	return f
}

// validatePolicy checks high-level constraints such as filter link in SELECT
// being actually defined in FILTER section.
func validatePolicy(p PlacementPolicy) error {
	canOmitNames := len(p.selectors) == 1 && len(p.replicas) == 1
	seenFilters := map[string]bool{}
	expectedFilters := map[string]struct{}{}
	for i := range p.filters {
		seenFilters[p.filters[i].GetName()] = true
		for _, f := range p.filters[i].GetFilters() {
			if f.GetName() != "" {
				expectedFilters[f.GetName()] = struct{}{}
			}
		}
	}

	seenSelectors := map[string]*netmap.Selector{}
	for i := range p.selectors {
		if p.selectors[i].GetName() == "" && !canOmitNames {
			return errUnnamedSelector
		}
		if flt := p.selectors[i].GetFilter(); flt != mainFilterName {
			expectedFilters[flt] = struct{}{}
			if !seenFilters[flt] {
				return fmt.Errorf("%w: '%s'", errUnknownFilter, flt)
			}
		}
		seenSelectors[p.selectors[i].GetName()] = &p.selectors[i]
	}

	for _, f := range p.filters {
		if _, ok := expectedFilters[f.GetName()]; !ok {
			return fmt.Errorf("%w: '%s'", errRedundantFilter, f.GetName())
		}
	}

	expectedSelectors := map[string]struct{}{}
	for i := range p.replicas {
		selName := p.replicas[i].GetSelector()
		if selName != "" || canOmitNames {
			expectedSelectors[selName] = struct{}{}
			if seenSelectors[selName] == nil {
				return fmt.Errorf("%w: '%s'", errUnknownSelector, selName)
			}

			dataCount := p.replicas[i].GetECDataCount()
			parityCount := p.replicas[i].GetECParityCount()
			if dataCount != 0 || parityCount != 0 {
				if c := seenSelectors[selName].GetCount(); c < dataCount+parityCount {
					return fmt.Errorf("%w: %d < %d + %d", errECFewSelectors, c, dataCount, parityCount)
				}
			}
		}
	}

	for _, s := range p.selectors {
		if _, ok := expectedSelectors[s.GetName()]; !ok {
			return fmt.Errorf("%w: to use selector '%s' use keyword IN", errRedundantSelector, s.GetName())
		}
	}

	return nil
}

func clauseFromString(s string) (c netmap.Clause) {
	if !c.FromString(strings.ToUpper(s)) {
		// Such errors should be handled by ANTLR code thus this panic.
		panic(fmt.Errorf("BUG: invalid clause: %s", c))
	}

	return
}

func operationFromString(s string) (op netmap.Operation) {
	if !op.FromString(strings.ToUpper(s)) {
		// Such errors should be handled by ANTLR code thus this panic.
		panic(fmt.Errorf("BUG: invalid operation: %s", op))
	}

	return
}

// escapeString returns single quote wrapped string.
// Wrapping rules must be kept in sync with QueryLexer.g4.
// Currently only ASCII letters, digits and underscore can be parsed without quotes.
func escapeString(s string) string {
	for _, r := range s {
		if 'a' <= r && r <= 'z' || 'A' <= r && r <= 'Z' || '0' <= r && r <= '9' || r == '_' {
			continue
		}
		return "'" + s + "'"
	}
	return s
}