// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package main

import (
	"context"
	"errors"
	"log"
	"sort"
	"strings"
	"sync"
	"time"

	"golang.org/x/build/gerrit"
	"golang.org/x/build/maintner"
	"golang.org/x/build/maintner/maintnerd/apipb"
)

// apiService implements apipb.MaintnerServiceServer using the Corpus c.
type apiService struct {
	c *maintner.Corpus
	// There really shouldn't be any more fields here.
	// All state should be in c.
	// A bool like "in staging" should just be a global flag.
}

func (s apiService) HasAncestor(ctx context.Context, req *apipb.HasAncestorRequest) (*apipb.HasAncestorResponse, error) {
	if len(req.Commit) != 40 {
		return nil, errors.New("invalid Commit")
	}
	if len(req.Ancestor) != 40 {
		return nil, errors.New("invalid Ancestor")
	}
	s.c.RLock()
	defer s.c.RUnlock()

	commit := s.c.GitCommit(req.Commit)
	res := new(apipb.HasAncestorResponse)
	if commit == nil {
		// TODO: wait for it? kick off a fetch of it and then answer?
		// optional?
		res.UnknownCommit = true
		return res, nil
	}
	if a := s.c.GitCommit(req.Ancestor); a != nil {
		res.HasAncestor = commit.HasAncestor(a)
	}
	return res, nil
}

func isStagingCommit(cl *maintner.GerritCL) bool {
	return cl.Commit != nil &&
		strings.Contains(cl.Commit.Msg, "DO NOT SUBMIT") &&
		strings.Contains(cl.Commit.Msg, "STAGING")
}

func tryBotStatus(cl *maintner.GerritCL, forStaging bool) (try, done bool) {
	if cl.Commit == nil {
		return // shouldn't happen
	}
	if forStaging != isStagingCommit(cl) {
		return
	}
	for _, msg := range cl.Messages {
		if msg.Version != cl.Version {
			continue
		}
		firstLine := msg.Message
		if nl := strings.IndexByte(firstLine, '\n'); nl != -1 {
			firstLine = firstLine[:nl]
		}
		if !strings.Contains(firstLine, "TryBot") {
			continue
		}
		if strings.Contains(firstLine, "Run-TryBot+1") {
			try = true
		}
		if strings.Contains(firstLine, "-Run-TryBot") {
			try = false
		}
		if strings.Contains(firstLine, "TryBot-Result") {
			done = true
		}
	}
	return
}

func tryWorkItem(cl *maintner.GerritCL) *apipb.GerritTryWorkItem {
	return &apipb.GerritTryWorkItem{
		Project:  cl.Project.Project(),
		Branch:   strings.TrimPrefix(cl.Branch(), "refs/heads/"),
		ChangeId: cl.ChangeID(),
		Commit:   cl.Commit.Hash.String(),
	}
}

func (s apiService) GetRef(ctx context.Context, req *apipb.GetRefRequest) (*apipb.GetRefResponse, error) {
	s.c.RLock()
	defer s.c.RUnlock()
	gp := s.c.Gerrit().Project(req.GerritServer, req.GerritProject)
	if gp == nil {
		return nil, errors.New("unknown gerrit project")
	}
	res := new(apipb.GetRefResponse)
	hash := gp.Ref(req.Ref)
	if hash != "" {
		res.Value = hash.String()
	}
	return res, nil
}

var tryCache struct {
	sync.Mutex
	forNumChanges int       // number of label changes in project val is valid for
	lastPoll      time.Time // of gerrit
	val           *apipb.GoFindTryWorkResponse
}

var tryBotGerrit = gerrit.NewClient("https://go-review.googlesource.com/", gerrit.NoAuth)

func (s apiService) GoFindTryWork(ctx context.Context, req *apipb.GoFindTryWorkRequest) (*apipb.GoFindTryWorkResponse, error) {
	tryCache.Lock()
	defer tryCache.Unlock()

	s.c.RLock()
	defer s.c.RUnlock()

	// Count the number of vote label changes over time. If it's
	// the same as the last query, return a cached result without
	// hitting Gerrit.
	var sumChanges int
	s.c.Gerrit().ForeachProjectUnsorted(func(gp *maintner.GerritProject) error {
		if gp.Server() != "go.googlesource.com" {
			return nil
		}
		sumChanges += gp.NumLabelChanges()
		return nil
	})

	now := time.Now()
	const maxPollInterval = 15 * time.Second

	if tryCache.val != nil &&
		(tryCache.forNumChanges == sumChanges ||
			tryCache.lastPoll.After(now.Add(-maxPollInterval))) {
		return tryCache.val, nil
	}

	tryCache.lastPoll = now

	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()
	const query = "label:Run-TryBot=1 label:TryBot-Result=0 status:open"
	cis, err := tryBotGerrit.QueryChanges(ctx, query, gerrit.QueryChangesOpt{
		Fields: []string{"CURRENT_REVISION", "CURRENT_COMMIT"},
	})
	if err != nil {
		return nil, err
	}
	tryCache.forNumChanges = sumChanges

	res := new(apipb.GoFindTryWorkResponse)
	goProj := s.c.Gerrit().Project("go.googlesource.com", "go")

	for _, ci := range cis {
		cl := s.c.Gerrit().Project("go.googlesource.com", ci.Project).CL(int32(ci.ChangeNumber))
		if cl == nil {
			log.Printf("nil Gerrit CL %v", ci.ChangeNumber)
			continue
		}
		work := tryWorkItem(cl)
		if ci.CurrentRevision != "" {
			// In case maintner is behind.
			work.Commit = ci.CurrentRevision
		}
		if work.Project != "go" {
			// Trybot on a subrepo.
			//
			// TODO: for Issue 17626, we need to append
			// master and the past two releases, but for
			// now we'll just do master.
			work.GoBranch = append(work.GoBranch, "master")
			work.GoCommit = append(work.GoCommit, goProj.Ref("refs/heads/master").String())
		}
		res.Waiting = append(res.Waiting, work)
	}

	// Sort in some stable order.
	//
	// TODO: better would be sorting by time the trybot was
	// requested, or the time of the CL. But we don't return that
	// (yet?) because the coordinator has never needed it
	// historically. But if we do a proper scheduler (Issue
	// 19178), perhaps it would be good data to have in the
	// coordinator.
	sort.Slice(res.Waiting, func(i, j int) bool {
		return res.Waiting[i].Commit < res.Waiting[j].Commit
	})
	tryCache.val = res

	log.Printf("maintnerd: GetTryWork: for label changes of %d, cached %d trywork items.",
		sumChanges, len(res.Waiting))

	return res, nil
}