package http

import (
	"bytes"
	"context"
	"encoding/json"
	"io"
	httpCore "net/http"
	"net/url"
	"time"

	"github.com/buger/jsonparser"
	"github.com/prebid/prebid-server/v4/logger"
	"github.com/prebid/prebid-server/v4/stored_requests/events"
	"github.com/prebid/prebid-server/v4/util/jsonutil"
	"golang.org/x/net/context/ctxhttp"
)

// NewHTTPEvents makes an EventProducer which creates events by pinging an external HTTP API
// for updates periodically. If refreshRate is negative, then the data will never be refreshed.
//
// It expects the following endpoint to exist remotely:
//
// GET {endpoint}
//
//	-- Returns all the known Stored Requests and Stored Imps.
//
// GET {endpoint}?last-modified={timestamp}
//
//	-- Returns the Stored Requests and Stored Imps which have been updated since the last timestamp.
//	   This timestamp will be sent in the rfc3339 format, using UTC and no timezone shift.
//	   For more info, see: https://tools.ietf.org/html/rfc3339
//
// The responses should be JSON like this:
//
//	{
//	  "requests": {
//	    "request1": { ... stored request data ... },
//	    "request2": { ... stored request data ... },
//	    "request3": { ... stored request data ... },
//	  },
//	  "imps": {
//	    "imp1": { ... stored data for imp1 ... },
//	    "imp2": { ... stored data for imp2 ... },
//	  },
//	  "responses": {
//	    "resp1": { ... stored data for resp1 ... },
//	    "resp2": { ... stored data for resp2 ... },
//	  }
//	}
//
// or
//
//	{
//	  "accounts": {
//	    "acc1": { ... config data for acc1 ... },
//	    "acc2": { ... config data for acc2 ... },
//	  },
//	}
//
// To signal deletions, the endpoint may return { "deleted": true }
// in place of the Stored Data if the "last-modified" param existed.
func NewHTTPEvents(client *httpCore.Client, endpoint string, ctxProducer func() (ctx context.Context, canceller func()), refreshRate time.Duration) *HTTPEvents {
	// If we're not given a function to produce Contexts, use the Background one.
	if ctxProducer == nil {
		ctxProducer = func() (ctx context.Context, canceller func()) {
			return context.Background(), func() {}
		}
	}
	e := &HTTPEvents{
		client:        client,
		ctxProducer:   ctxProducer,
		Endpoint:      endpoint,
		lastUpdate:    time.Now().UTC(),
		saves:         make(chan events.Save, 1),
		invalidations: make(chan events.Invalidation, 1),
	}
	logger.Infof("Loading HTTP cache from GET %s", endpoint)
	e.fetchAll()

	go e.refresh(time.Tick(refreshRate))
	return e
}

type HTTPEvents struct {
	client        *httpCore.Client
	ctxProducer   func() (ctx context.Context, canceller func())
	Endpoint      string
	invalidations chan events.Invalidation
	lastUpdate    time.Time
	saves         chan events.Save
}

func (e *HTTPEvents) fetchAll() {
	ctx, cancel := e.ctxProducer()
	defer cancel()

	resp, err := ctxhttp.Get(ctx, e.client, e.Endpoint)
	if respObj, ok := e.parse(e.Endpoint, resp, err); ok &&
		(len(respObj.StoredRequests) > 0 || len(respObj.StoredImps) > 0 || len(respObj.StoredResponses) > 0 || len(respObj.Accounts) > 0) {
		e.saves <- events.Save{
			Requests:  respObj.StoredRequests,
			Imps:      respObj.StoredImps,
			Responses: respObj.StoredResponses,
			Accounts:  respObj.Accounts,
		}
	}
}

func (e *HTTPEvents) refresh(ticker <-chan time.Time) {
	for thisTime := range ticker {
		thisTimeInUTC := thisTime.UTC()

		// Parse the endpoint url defined
		endpointUrl, urlErr := url.Parse(e.Endpoint)

		// Error with url parsing
		if urlErr != nil {
			logger.Errorf("Disabling refresh HTTP cache from GET '%s': %v", e.Endpoint, urlErr)
			return
		}

		// Parse the url query string
		urlQuery := endpointUrl.Query()

		// See the last-modified query param
		urlQuery.Set("last-modified", e.lastUpdate.Format(time.RFC3339))

		// Rebuild
		endpointUrl.RawQuery = urlQuery.Encode()

		// Convert to string
		endpoint := endpointUrl.String()

		logger.Infof("Refreshing HTTP cache from GET '%s'", endpoint)

		ctx, cancel := e.ctxProducer()
		resp, err := ctxhttp.Get(ctx, e.client, endpoint)
		if respObj, ok := e.parse(endpoint, resp, err); ok {
			invalidations := events.Invalidation{
				Requests:  extractInvalidations(respObj.StoredRequests),
				Imps:      extractInvalidations(respObj.StoredImps),
				Responses: extractInvalidations(respObj.StoredResponses),
				Accounts:  extractInvalidations(respObj.Accounts),
			}
			if len(respObj.StoredRequests) > 0 || len(respObj.StoredImps) > 0 || len(respObj.StoredResponses) > 0 || len(respObj.Accounts) > 0 {
				e.saves <- events.Save{
					Requests:  respObj.StoredRequests,
					Imps:      respObj.StoredImps,
					Responses: respObj.StoredResponses,
					Accounts:  respObj.Accounts,
				}
			}
			if len(invalidations.Requests) > 0 || len(invalidations.Imps) > 0 || len(invalidations.Responses) > 0 || len(invalidations.Accounts) > 0 {
				e.invalidations <- invalidations
			}
			e.lastUpdate = thisTimeInUTC
		}
		cancel()
	}
}

// parse unpacks the HTTP response and sends the relevant events to the channels.
// It returns true if everything was successful, and false if any errors occurred.
func (e *HTTPEvents) parse(endpoint string, resp *httpCore.Response, err error) (*responseContract, bool) {
	if err != nil {
		logger.Errorf("Failed call: GET %s for Stored Requests: %v", endpoint, err)
		return nil, false
	}
	defer resp.Body.Close()

	respBytes, err := io.ReadAll(resp.Body)
	if err != nil {
		logger.Errorf("Failed to read body of GET %s for Stored Requests: %v", endpoint, err)
		return nil, false
	}

	if resp.StatusCode != httpCore.StatusOK {
		logger.Errorf("Got %d response from GET %s for Stored Requests. Response body was: %s", resp.StatusCode, endpoint, string(respBytes))
		return nil, false
	}

	var respObj responseContract
	if err := jsonutil.UnmarshalValid(respBytes, &respObj); err != nil {
		logger.Errorf("Failed to unmarshal body of GET %s for Stored Requests: %v", endpoint, err)
		return nil, false
	}

	return &respObj, true
}

func extractInvalidations(changes map[string]json.RawMessage) []string {
	deletedIDs := make([]string, 0, len(changes))
	for id, msg := range changes {
		if value, _, _, err := jsonparser.Get(msg, "deleted"); err == nil && bytes.Equal(value, []byte("true")) {
			delete(changes, id)
			deletedIDs = append(deletedIDs, id)
		}
	}
	return deletedIDs
}

func (e *HTTPEvents) Saves() <-chan events.Save {
	return e.saves
}

func (e *HTTPEvents) Invalidations() <-chan events.Invalidation {
	return e.invalidations
}

type responseContract struct {
	StoredRequests  map[string]json.RawMessage `json:"requests"`
	StoredImps      map[string]json.RawMessage `json:"imps"`
	StoredResponses map[string]json.RawMessage `json:"responses"`
	Accounts        map[string]json.RawMessage `json:"accounts"`
}