package queryrange

import (
	"context"
	"fmt"
	"net/http"
	"sync"
	"time"

	"github.com/go-kit/log/level"
	"github.com/opentracing/opentracing-go"
	"github.com/prometheus/prometheus/model/timestamp"
	"github.com/weaveworks/common/httpgrpc"
	"github.com/weaveworks/common/user"

	"github.com/grafana/loki/pkg/logproto"
	"github.com/grafana/loki/pkg/logql"
	"github.com/grafana/loki/pkg/querier/queryrange/queryrangebase"
	"github.com/grafana/loki/pkg/tenant"
	"github.com/grafana/loki/pkg/util"
	"github.com/grafana/loki/pkg/util/spanlogger"
	"github.com/grafana/loki/pkg/util/validation"
)

const (
	limitErrTmpl = "maximum of series (%d) reached for a single query"
)

var (
	ErrMaxQueryParalellism = fmt.Errorf("querying is disabled, please contact your Loki operator")
)

// Limits extends the cortex limits interface with support for per tenant splitby parameters
type Limits interface {
	queryrangebase.Limits
	logql.Limits
	QuerySplitDuration(string) time.Duration
	MaxQuerySeries(string) int
	MaxEntriesLimitPerQuery(string) int
	MinShardingLookback(string) time.Duration
}

type limits struct {
	Limits
	splitDuration time.Duration
}

func (l limits) QuerySplitDuration(user string) time.Duration {
	return l.splitDuration
}

// WithSplitByLimits will construct a Limits with a static split by duration.
func WithSplitByLimits(l Limits, splitBy time.Duration) Limits {
	return limits{
		Limits:        l,
		splitDuration: splitBy,
	}
}

// cacheKeyLimits intersects Limits and CacheSplitter
type cacheKeyLimits struct {
	Limits
}

func (l cacheKeyLimits) GenerateCacheKey(userID string, r queryrangebase.Request) string {
	split := l.QuerySplitDuration(userID)

	var currentInterval int64
	if denominator := int64(split / time.Millisecond); denominator > 0 {
		currentInterval = r.GetStart() / denominator
	}

	// include both the currentInterval and the split duration in key to ensure
	// a cache key can't be reused when an interval changes
	return fmt.Sprintf("%s:%s:%d:%d:%d", userID, r.GetQuery(), r.GetStep(), currentInterval, split)
}

type limitsMiddleware struct {
	Limits
	next queryrangebase.Handler
}

// NewLimitsMiddleware creates a new Middleware that enforces query limits.
func NewLimitsMiddleware(l Limits) queryrangebase.Middleware {
	return queryrangebase.MiddlewareFunc(func(next queryrangebase.Handler) queryrangebase.Handler {
		return limitsMiddleware{
			next:   next,
			Limits: l,
		}
	})
}

func (l limitsMiddleware) Do(ctx context.Context, r queryrangebase.Request) (queryrangebase.Response, error) {
	log, ctx := spanlogger.New(ctx, "limits")
	defer log.Finish()

	tenantIDs, err := tenant.TenantIDs(ctx)
	if err != nil {
		return nil, httpgrpc.Errorf(http.StatusBadRequest, err.Error())
	}

	// Clamp the time range based on the max query lookback.

	if maxQueryLookback := validation.SmallestPositiveNonZeroDurationPerTenant(tenantIDs, l.MaxQueryLookback); maxQueryLookback > 0 {
		minStartTime := util.TimeToMillis(time.Now().Add(-maxQueryLookback))

		if r.GetEnd() < minStartTime {
			// The request is fully outside the allowed range, so we can return an
			// empty response.
			level.Debug(log).Log(
				"msg", "skipping the execution of the query because its time range is before the 'max query lookback' setting",
				"reqStart", util.FormatTimeMillis(r.GetStart()),
				"redEnd", util.FormatTimeMillis(r.GetEnd()),
				"maxQueryLookback", maxQueryLookback)

			return NewEmptyResponse(r)
		}

		if r.GetStart() < minStartTime {
			// Replace the start time in the request.
			level.Debug(log).Log(
				"msg", "the start time of the query has been manipulated because of the 'max query lookback' setting",
				"original", util.FormatTimeMillis(r.GetStart()),
				"updated", util.FormatTimeMillis(minStartTime))

			r = r.WithStartEnd(minStartTime, r.GetEnd())
		}
	}

	// Enforce the max query length.
	if maxQueryLength := validation.SmallestPositiveNonZeroDurationPerTenant(tenantIDs, l.MaxQueryLength); maxQueryLength > 0 {
		queryLen := timestamp.Time(r.GetEnd()).Sub(timestamp.Time(r.GetStart()))
		if queryLen > maxQueryLength {
			return nil, httpgrpc.Errorf(http.StatusBadRequest, validation.ErrQueryTooLong, queryLen, maxQueryLength)
		}
	}

	return l.next.Do(ctx, r)
}

type seriesLimiter struct {
	hashes map[uint64]struct{}
	rw     sync.RWMutex
	buf    []byte // buf used for hashing to avoid allocations.

	maxSeries int
	next      queryrangebase.Handler
}

type seriesLimiterMiddleware int

// newSeriesLimiter creates a new series limiter middleware for use for a single request.
func newSeriesLimiter(maxSeries int) queryrangebase.Middleware {
	return seriesLimiterMiddleware(maxSeries)
}

// Wrap wraps a global handler and returns a per request limited handler.
// The handler returned is thread safe.
func (slm seriesLimiterMiddleware) Wrap(next queryrangebase.Handler) queryrangebase.Handler {
	return &seriesLimiter{
		hashes:    make(map[uint64]struct{}),
		maxSeries: int(slm),
		buf:       make([]byte, 0, 1024),
		next:      next,
	}
}

func (sl *seriesLimiter) Do(ctx context.Context, req queryrangebase.Request) (queryrangebase.Response, error) {
	// no need to fire a request if the limit is already reached.
	if sl.isLimitReached() {
		return nil, httpgrpc.Errorf(http.StatusBadRequest, limitErrTmpl, sl.maxSeries)
	}
	res, err := sl.next.Do(ctx, req)
	if err != nil {
		return res, err
	}
	promResponse, ok := res.(*LokiPromResponse)
	if !ok {
		return res, nil
	}
	if promResponse.Response == nil {
		return res, nil
	}
	sl.rw.Lock()
	var hash uint64
	for _, s := range promResponse.Response.Data.Result {
		lbs := logproto.FromLabelAdaptersToLabels(s.Labels)
		hash, sl.buf = lbs.HashWithoutLabels(sl.buf, []string(nil)...)
		sl.hashes[hash] = struct{}{}
	}
	sl.rw.Unlock()
	if sl.isLimitReached() {
		return nil, httpgrpc.Errorf(http.StatusBadRequest, limitErrTmpl, sl.maxSeries)
	}
	return res, nil
}

func (sl *seriesLimiter) isLimitReached() bool {
	sl.rw.RLock()
	defer sl.rw.RUnlock()
	return len(sl.hashes) > sl.maxSeries
}

type limitedRoundTripper struct {
	next   http.RoundTripper
	limits Limits

	codec      queryrangebase.Codec
	middleware queryrangebase.Middleware
}

// NewLimitedRoundTripper creates a new roundtripper that enforces MaxQueryParallelism to the `next` roundtripper across `middlewares`.
func NewLimitedRoundTripper(next http.RoundTripper, codec queryrangebase.Codec, limits Limits, middlewares ...queryrangebase.Middleware) http.RoundTripper {
	transport := limitedRoundTripper{
		next:       next,
		codec:      codec,
		limits:     limits,
		middleware: queryrangebase.MergeMiddlewares(middlewares...),
	}
	return transport
}

type work struct {
	req    queryrangebase.Request
	ctx    context.Context
	result chan result
}

type result struct {
	response queryrangebase.Response
	err      error
}

func newWork(ctx context.Context, req queryrangebase.Request) work {
	return work{
		req:    req,
		ctx:    ctx,
		result: make(chan result, 1),
	}
}

func (rt limitedRoundTripper) RoundTrip(r *http.Request) (*http.Response, error) {
	var (
		wg           sync.WaitGroup
		intermediate = make(chan work)
		ctx, cancel  = context.WithCancel(r.Context())
	)
	defer func() {
		cancel()
		wg.Wait()
	}()

	// Do not forward any request header.
	request, err := rt.codec.DecodeRequest(ctx, r, nil)
	if err != nil {
		return nil, err
	}

	if span := opentracing.SpanFromContext(ctx); span != nil {
		request.LogToSpan(span)
	}
	tenantIDs, err := tenant.TenantIDs(ctx)
	if err != nil {
		return nil, httpgrpc.Errorf(http.StatusBadRequest, err.Error())
	}

	parallelism := validation.SmallestPositiveIntPerTenant(tenantIDs, rt.limits.MaxQueryParallelism)
	if parallelism < 1 {
		return nil, httpgrpc.Errorf(http.StatusTooManyRequests, ErrMaxQueryParalellism.Error())
	}

	for i := 0; i < parallelism; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for {
				select {
				case w := <-intermediate:
					resp, err := rt.do(w.ctx, w.req)
					w.result <- result{response: resp, err: err}
				case <-ctx.Done():
					return
				}
			}
		}()
	}

	response, err := rt.middleware.Wrap(
		queryrangebase.HandlerFunc(func(ctx context.Context, r queryrangebase.Request) (queryrangebase.Response, error) {
			w := newWork(ctx, r)
			select {
			case intermediate <- w:
			case <-ctx.Done():
				return nil, ctx.Err()
			}
			select {
			case response := <-w.result:
				return response.response, response.err
			case <-ctx.Done():
				return nil, ctx.Err()
			}
		})).Do(ctx, request)
	if err != nil {
		return nil, err
	}
	return rt.codec.EncodeResponse(ctx, response)
}

func (rt limitedRoundTripper) do(ctx context.Context, r queryrangebase.Request) (queryrangebase.Response, error) {
	request, err := rt.codec.EncodeRequest(ctx, r)
	if err != nil {
		return nil, err
	}

	if err := user.InjectOrgIDIntoHTTPRequest(ctx, request); err != nil {
		return nil, httpgrpc.Errorf(http.StatusBadRequest, err.Error())
	}

	response, err := rt.next.RoundTrip(request)
	if err != nil {
		return nil, err
	}
	defer func() { _ = response.Body.Close() }()

	return rt.codec.DecodeResponse(ctx, response, r)
}