/*
Copyright 2019 The Kubernetes 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 naming

import (
	"bytes"
	"fmt"
	"strings"
	"text/template"

	"k8s.io/apimachinery/pkg/runtime/schema"

	prom "github.com/directxman12/k8s-prometheus-adapter/pkg/client"
)

// MetricsQuery represents a compiled metrics query for some set of
// series that can be converted into an series of Prometheus expressions to
// be passed to a client.
type MetricsQuery interface {
	// Build constructs Prometheus expressions to represent this query
	// over the given group-resource.  If namespace is empty, the resource
	// is considered to be root-scoped.  extraGroupBy may be used for cases
	// where we need to scope down more specifically than just the group-resource
	// (e.g. container metrics).
	Build(series string, groupRes schema.GroupResource, namespace string, extraGroupBy []string, resourceNames ...string) (prom.Selector, error)
}

// NewMetricsQuery constructs a new MetricsQuery by compiling the given Go template.
// The delimiters on the template are `<<` and `>>`, and it may use the following fields:
// - Series: the series in question
// - LabelMatchers: a pre-stringified form of the label matchers for the resources in the query
// - LabelMatchersByName: the raw map-form of the above matchers
// - GroupBy: the group-by clause to use for the resources in the query (stringified)
// - GroupBySlice: the raw slice form of the above group-by clause
func NewMetricsQuery(queryTemplate string, resourceConverter ResourceConverter) (MetricsQuery, error) {
	templ, err := template.New("metrics-query").Delims("<<", ">>").Parse(queryTemplate)
	if err != nil {
		return nil, fmt.Errorf("unable to parse metrics query template %q: %v", queryTemplate, err)
	}

	return &metricsQuery{
		resConverter: resourceConverter,
		template:     templ,
	}, nil
}

// metricsQuery is a MetricsQuery based on a compiled Go text template.
// with the delimiters as `<<` and `>>`, and the arguments found in
// queryTemplateArgs.
type metricsQuery struct {
	resConverter ResourceConverter
	template     *template.Template
}

// queryTemplateArgs contains the arguments for the template used in metricsQuery.
type queryTemplateArgs struct {
	Series            string
	LabelMatchers     string
	LabelValuesByName map[string][]string
	GroupBy           string
	GroupBySlice      []string
}

func (q *metricsQuery) Build(series string, resource schema.GroupResource, namespace string, extraGroupBy []string, names ...string) (prom.Selector, error) {
	var exprs []string
	valuesByName := map[string][]string{}

	if namespace != "" {
		namespaceLbl, err := q.resConverter.LabelForResource(NsGroupResource)
		if err != nil {
			return "", err
		}
		exprs = append(exprs, prom.LabelEq(string(namespaceLbl), namespace))
		valuesByName[string(namespaceLbl)] = []string{namespace}
	}

	resourceLbl, err := q.resConverter.LabelForResource(resource)
	if err != nil {
		return "", err
	}
	matcher := prom.LabelEq
	targetValue := names[0]
	if len(names) > 1 {
		matcher = prom.LabelMatches
		targetValue = strings.Join(names, "|")
	}
	exprs = append(exprs, matcher(string(resourceLbl), targetValue))
	valuesByName[string(resourceLbl)] = names

	groupBy := make([]string, 0, len(extraGroupBy)+1)
	groupBy = append(groupBy, string(resourceLbl))
	groupBy = append(groupBy, extraGroupBy...)

	args := queryTemplateArgs{
		Series:            series,
		LabelMatchers:     strings.Join(exprs, ","),
		LabelValuesByName: valuesByName,
		GroupBy:           strings.Join(groupBy, ","),
		GroupBySlice:      groupBy,
	}
	queryBuff := new(bytes.Buffer)
	if err := q.template.Execute(queryBuff, args); err != nil {
		return "", err
	}

	if queryBuff.Len() == 0 {
		return "", fmt.Errorf("empty query produced by metrics query template")
	}

	return prom.Selector(queryBuff.String()), nil
}