// Copyright 2017 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 remote

import (
	"fmt"
	"sync"
	"time"

	"github.com/prometheus/common/model"
	"golang.org/x/net/context"

	"github.com/prometheus/prometheus/config"
	"github.com/prometheus/prometheus/storage/local"
	"github.com/prometheus/prometheus/storage/metric"
)

// Reader allows reading from multiple remote sources.
type Reader struct {
	mtx            sync.Mutex
	clients        []*Client
	externalLabels model.LabelSet
}

// ApplyConfig updates the state as the new config requires.
func (r *Reader) ApplyConfig(conf *config.Config) error {
	clients := []*Client{}
	for i, rrConf := range conf.RemoteReadConfigs {
		c, err := NewClient(i, &ClientConfig{
			URL:              rrConf.URL,
			Timeout:          rrConf.RemoteTimeout,
			HTTPClientConfig: rrConf.HTTPClientConfig,
		})
		if err != nil {
			return err
		}
		clients = append(clients, c)
	}

	r.mtx.Lock()
	defer r.mtx.Unlock()

	r.clients = clients
	r.externalLabels = conf.GlobalConfig.ExternalLabels

	return nil
}

// Queriers returns a list of Queriers for the currently configured
// remote read endpoints.
func (r *Reader) Queriers() []local.Querier {
	r.mtx.Lock()
	defer r.mtx.Unlock()

	queriers := make([]local.Querier, 0, len(r.clients))
	for _, c := range r.clients {
		queriers = append(queriers, &querier{
			client:         c,
			externalLabels: r.externalLabels,
		})
	}
	return queriers
}

// querier is an adapter to make a Client usable as a promql.Querier.
type querier struct {
	client         *Client
	externalLabels model.LabelSet
}

func (q *querier) QueryRange(ctx context.Context, from, through model.Time, matchers ...*metric.LabelMatcher) ([]local.SeriesIterator, error) {
	return MatrixToIterators(q.read(ctx, from, through, matchers))
}

func (q *querier) QueryInstant(ctx context.Context, ts model.Time, stalenessDelta time.Duration, matchers ...*metric.LabelMatcher) ([]local.SeriesIterator, error) {
	return MatrixToIterators(q.read(ctx, ts.Add(-stalenessDelta), ts, matchers))
}

func (q *querier) read(ctx context.Context, from, through model.Time, matchers metric.LabelMatchers) (model.Matrix, error) {
	m, added := q.addExternalLabels(matchers)

	res, err := q.client.Read(ctx, from, through, m)
	if err != nil {
		return nil, err
	}
	removeLabels(res, added)
	err = validateLabelsAndMetricName(res)
	if err != nil {
		return nil, err
	}

	return res, err
}

// validateLabelsAndMetricName validates the label names/values and metric names returned from remote read.
func validateLabelsAndMetricName(res model.Matrix) error {
	for _, r := range res {
		if !model.IsValidMetricName(r.Metric[model.MetricNameLabel]) {
			return fmt.Errorf("Invalid metric name: %v", r.Metric[model.MetricNameLabel])
		}
		for name, value := range r.Metric {
			if !name.IsValid() {
				return fmt.Errorf("Invalid label name: %v", name)
			}
			if !value.IsValid() {
				return fmt.Errorf("Invalid label value: %v", value)
			}
		}
	}
	return nil
}

// addExternalLabels adds matchers for each external label. External labels
// that already have a corresponding user-supplied matcher are skipped, as we
// assume that the user explicitly wants to select a different value for them.
// We return the new set of matchers, along with a map of labels for which
// matchers were added, so that these can later be removed from the result
// time series again.
func (q *querier) addExternalLabels(matchers metric.LabelMatchers) (metric.LabelMatchers, model.LabelSet) {
	el := make(model.LabelSet, len(q.externalLabels))
	for k, v := range q.externalLabels {
		el[k] = v
	}
	for _, m := range matchers {
		if _, ok := el[m.Name]; ok {
			delete(el, m.Name)
		}
	}

	for k, v := range el {
		m, err := metric.NewLabelMatcher(metric.Equal, k, v)
		if err != nil {
			panic(err)
		}
		matchers = append(matchers, m)
	}

	return matchers, el
}

func removeLabels(m model.Matrix, labels model.LabelSet) {
	for _, ss := range m {
		for k := range labels {
			delete(ss.Metric, k)
		}
	}
}

// MatrixToIterators returns series iterators for a given matrix.
func MatrixToIterators(m model.Matrix, err error) ([]local.SeriesIterator, error) {
	if err != nil {
		return nil, err
	}

	its := make([]local.SeriesIterator, 0, len(m))
	for _, ss := range m {
		its = append(its, sampleStreamIterator{
			ss: ss,
		})
	}
	return its, nil
}

func (q *querier) MetricsForLabelMatchers(ctx context.Context, from, through model.Time, matcherSets ...metric.LabelMatchers) ([]metric.Metric, error) {
	// TODO: Implement remote metadata querying.
	return nil, nil
}

func (q *querier) LastSampleForLabelMatchers(ctx context.Context, cutoff model.Time, matcherSets ...metric.LabelMatchers) (model.Vector, error) {
	// TODO: Implement remote last sample querying.
	return nil, nil
}

func (q *querier) LabelValuesForLabelName(ctx context.Context, ln model.LabelName) (model.LabelValues, error) {
	// TODO: Implement remote metadata querying.
	return nil, nil
}

func (q *querier) Close() error {
	return nil
}