// Copyright 2019 Drone IO, Inc.
//
// 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 events

import (
	"context"
	"encoding/json"
	"io"
	"net/http"
	"strconv"
	"time"

	"github.com/drone/drone/core"
	"github.com/drone/drone/handler/api/render"

	"github.com/go-chi/chi"
)

// HandleLogStream creates an http.HandlerFunc that streams builds logs
// to the http.Response in an event stream format.
func HandleLogStream(
	repos core.RepositoryStore,
	builds core.BuildStore,
	stages core.StageStore,
	steps core.StepStore,
	stream core.LogStream,
) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		var (
			namespace = chi.URLParam(r, "owner")
			name      = chi.URLParam(r, "name")
		)
		number, err := strconv.ParseInt(chi.URLParam(r, "number"), 10, 64)
		if err != nil {
			render.BadRequest(w, err)
			return
		}
		stageNumber, err := strconv.Atoi(chi.URLParam(r, "stage"))
		if err != nil {
			render.BadRequest(w, err)
			return
		}
		stepNumber, err := strconv.Atoi(chi.URLParam(r, "step"))
		if err != nil {
			render.BadRequest(w, err)
			return
		}
		repo, err := repos.FindName(r.Context(), namespace, name)
		if err != nil {
			render.NotFound(w, err)
			return
		}
		build, err := builds.FindNumber(r.Context(), repo.ID, number)
		if err != nil {
			render.NotFound(w, err)
			return
		}
		stage, err := stages.FindNumber(r.Context(), build.ID, stageNumber)
		if err != nil {
			render.NotFound(w, err)
			return
		}
		step, err := steps.FindNumber(r.Context(), stage.ID, stepNumber)
		if err != nil {
			render.NotFound(w, err)
			return
		}

		h := w.Header()
		h.Set("Content-Type", "text/event-stream")
		h.Set("Cache-Control", "no-cache")
		h.Set("Connection", "keep-alive")
		h.Set("X-Accel-Buffering", "no")

		f, ok := w.(http.Flusher)
		if !ok {
			return
		}

		io.WriteString(w, ": ping\n\n")
		f.Flush()

		ctx, cancel := context.WithCancel(r.Context())
		defer cancel()

		enc := json.NewEncoder(w)
		linec, errc := stream.Tail(ctx, step.ID)
		if errc == nil {
			io.WriteString(w, "event: error\ndata: eof\n\n")
			return
		}

	L:
		for {
			select {
			case <-ctx.Done():
				break L
			case <-errc:
				break L
			case <-time.After(time.Hour):
				break L
			case <-time.After(pingInterval):
				io.WriteString(w, ": ping\n\n")
			case line := <-linec:
				io.WriteString(w, "data: ")
				enc.Encode(line)
				io.WriteString(w, "\n\n")
				f.Flush()
			}
		}

		io.WriteString(w, "event: error\ndata: eof\n\n")
		f.Flush()
	}
}