// Copyright 2020 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package injectproxy

import (
	"fmt"

	"github.com/prometheus/prometheus/pkg/labels"
	"github.com/prometheus/prometheus/promql/parser"
)

type Enforcer struct {
	labelMatchers map[string]*labels.Matcher
}

func NewEnforcer(ms ...*labels.Matcher) *Enforcer {
	entries := make(map[string]*labels.Matcher)

	for _, matcher := range ms {
		entries[matcher.Name] = matcher
	}

	return &Enforcer{
		labelMatchers: entries,
	}
}

// EnforceNode walks the given node recursively
// and enforces the given label enforcer on it.
//
// Whenever a parser.MatrixSelector or parser.VectorSelector AST node is found,
// their label enforcer is being potentially modified.
// If a node's label matcher has the same name as a label matcher
// of the given enforcer, then it will be replaced.
func (ms Enforcer) EnforceNode(node parser.Node) error {
	switch n := node.(type) {
	case *parser.EvalStmt:
		if err := ms.EnforceNode(n.Expr); err != nil {
			return err
		}

	case parser.Expressions:
		for _, e := range n {
			if err := ms.EnforceNode(e); err != nil {
				return err
			}
		}

	case *parser.AggregateExpr:
		if err := ms.EnforceNode(n.Expr); err != nil {
			return err
		}

	case *parser.BinaryExpr:
		if err := ms.EnforceNode(n.LHS); err != nil {
			return err
		}

		if err := ms.EnforceNode(n.RHS); err != nil {
			return err
		}

	case *parser.Call:
		if err := ms.EnforceNode(n.Args); err != nil {
			return err
		}

	case *parser.SubqueryExpr:
		if err := ms.EnforceNode(n.Expr); err != nil {
			return err
		}

	case *parser.ParenExpr:
		if err := ms.EnforceNode(n.Expr); err != nil {
			return err
		}

	case *parser.UnaryExpr:
		if err := ms.EnforceNode(n.Expr); err != nil {
			return err
		}

	case *parser.NumberLiteral, *parser.StringLiteral:
	// nothing to do

	case *parser.MatrixSelector:
		// inject labelselector
		if vs, ok := n.VectorSelector.(*parser.VectorSelector); ok {
			vs.LabelMatchers = ms.enforceMatchers(vs.LabelMatchers)
		}

	case *parser.VectorSelector:
		// inject labelselector
		n.LabelMatchers = ms.enforceMatchers(n.LabelMatchers)

	default:
		panic(fmt.Errorf("parser.Walk: unhandled node type %T", n))
	}

	return nil
}

func (ms Enforcer) enforceMatchers(targets []*labels.Matcher) []*labels.Matcher {
	var res []*labels.Matcher

	for _, target := range targets {
		if _, ok := ms.labelMatchers[target.Name]; ok {
			continue
		}

		res = append(res, target)
	}

	for _, enforcedMatcher := range ms.labelMatchers {
		res = append(res, enforcedMatcher)
	}

	return res
}