/*
Copyright 2020 The Flux 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 providers

import (
	"context"
	"crypto/tls"
	"encoding/json"
	"fmt"
	"io"
	"math"
	"net/http"
	"net/url"
	"path"
	"regexp"
	"strconv"
	"time"

	flaggerv1 "github.com/fluxcd/flagger/pkg/apis/flagger/v1beta1"
)

const prometheusOnlineQuery = "vector(1)"

// PrometheusProvider executes promQL queries
type PrometheusProvider struct {
	timeout  time.Duration
	url      url.URL
	headers  http.Header
	username string
	password string
	token    string
	client   *http.Client
}

type prometheusResponse struct {
	Data struct {
		Result []struct {
			Metric struct {
				Name string `json:"name"`
			}
			Value  []interface{} `json:"value"`
			Values []interface{} `json:"values"`
		}
	}
}

// NewPrometheusProvider takes a provider spec and the credentials map,
// validates the address, extracts the bearer token or username and password values if provided and
// returns a Prometheus client ready to execute queries against the API
func NewPrometheusProvider(provider flaggerv1.MetricTemplateProvider, credentials map[string][]byte) (*PrometheusProvider, error) {
	promURL, err := url.Parse(provider.Address)
	if provider.Address == "" || err != nil {
		return nil, fmt.Errorf("%s address %s is not a valid URL", provider.Type, provider.Address)
	}

	prom := PrometheusProvider{
		timeout: 5 * time.Second,
		url:     *promURL,
		headers: provider.Headers,
		client:  http.DefaultClient,
	}

	if provider.InsecureSkipVerify {
		t := http.DefaultTransport.(*http.Transport).Clone()
		t.TLSClientConfig = &tls.Config{InsecureSkipVerify: true}
		prom.client = &http.Client{Transport: t}
	}

	if provider.SecretRef != nil {
		if token, ok := credentials["token"]; ok {
			prom.token = string(token)
		} else {

			if username, ok := credentials["username"]; ok {
				prom.username = string(username)
			} else {
				return nil, fmt.Errorf("%s credentials does not contain a username", provider.Type)
			}

			if password, ok := credentials["password"]; ok {
				prom.password = string(password)
			} else {
				return nil, fmt.Errorf("%s credentials does not contain a password", provider.Type)
			}
		}
	}

	return &prom, nil
}

// RunQuery executes the promQL query and returns the the first result as float64
func (p *PrometheusProvider) RunQuery(query string) (float64, error) {
	query = url.QueryEscape(p.trimQuery(query))
	u, err := url.Parse(fmt.Sprintf("./api/v1/query?query=%s", query))
	if err != nil {
		return 0, fmt.Errorf("url.Parse failed: %w", err)
	}
	u.Path = path.Join(p.url.Path, u.Path)

	u = p.url.ResolveReference(u)

	req, err := http.NewRequest("GET", u.String(), nil)
	if err != nil {
		return 0, fmt.Errorf("http.NewRequest failed: %w", err)
	}

	if p.headers != nil {
		req.Header = p.headers
	}

	if p.token != "" {
		req.Header.Add("Authorization", "Bearer "+p.token)
	} else if p.username != "" && p.password != "" {
		req.SetBasicAuth(p.username, p.password)
	}

	ctx, cancel := context.WithTimeout(req.Context(), p.timeout)
	defer cancel()

	r, err := p.client.Do(req.WithContext(ctx))
	if err != nil {
		return 0, fmt.Errorf("request failed: %w", err)
	}
	defer r.Body.Close()

	b, err := io.ReadAll(r.Body)
	if err != nil {
		return 0, fmt.Errorf("error reading body: %w", err)
	}

	if 400 <= r.StatusCode {
		return 0, fmt.Errorf("error response: %s", string(b))
	}

	var result prometheusResponse
	err = json.Unmarshal(b, &result)
	if err != nil {
		return 0, fmt.Errorf("error unmarshaling result: %w, '%s'", err, string(b))
	}

	var value *float64
	for _, v := range result.Data.Result {
		if v.Values != nil {
			return 0, fmt.Errorf("%w", ErrMultipleValuesReturned)
		}
		metricValue := v.Value[1]
		switch metricValue.(type) {
		case string:
			f, err := strconv.ParseFloat(metricValue.(string), 64)
			if err != nil {
				return 0, err
			}
			value = &f
		}
	}
	if value == nil || math.IsNaN(*value) {
		return 0, fmt.Errorf("%w", ErrNoValuesFound)
	}

	return *value, nil
}

// IsOnline run simple Prometheus query and returns an error if the API is unreachable
func (p *PrometheusProvider) IsOnline() (bool, error) {
	value, err := p.RunQuery(prometheusOnlineQuery)
	if err != nil {
		return false, fmt.Errorf("running query failed: %w", err)
	}

	if value != float64(1) {
		return false, fmt.Errorf("value is not 1 for query: %s", prometheusOnlineQuery)
	}

	return true, nil
}

// trimQuery takes a promql query and removes whitespace
func (p *PrometheusProvider) trimQuery(query string) string {
	space := regexp.MustCompile(`\s+`)
	return space.ReplaceAllString(query, " ")
}