package orchestrator

import (
	"context"
	"errors"
	"fmt"
	"sync"
	"time"

	v1 "github.com/garethgeorge/resticui/gen/go/v1"
	"github.com/garethgeorge/resticui/internal/config"
	"github.com/garethgeorge/resticui/internal/oplog"
	"github.com/garethgeorge/resticui/pkg/restic"
	"go.uber.org/zap"
	"google.golang.org/protobuf/proto"
)

var ErrRepoNotFound = errors.New("repo not found")
var ErrRepoInitializationFailed = errors.New("repo initialization failed")
var ErrPlanNotFound = errors.New("plan not found")

// Orchestrator is responsible for managing repos and backups.
type Orchestrator struct {
	mu        sync.Mutex
	config    *v1.Config
	OpLog     *oplog.OpLog
	repoPool  *resticRepoPool
	taskQueue taskQueue

	// now for the purpose of testing; used by Run() to get the current time.
	now func() time.Time
}

func NewOrchestrator(resticBin string, cfg *v1.Config, oplog *oplog.OpLog) *Orchestrator {
	var o *Orchestrator
	o = &Orchestrator{
		config: cfg,
		OpLog:  oplog,
		// repoPool created with a memory store to ensure the config is updated in an atomic operation with the repo pool's config value.
		repoPool: newResticRepoPool(resticBin, &config.MemoryStore{Config: cfg}),
		taskQueue: taskQueue{
			Now: func() time.Time {
				if o.now != nil {
					return o.now()
				}
				return time.Now()
			},
		},
	}
	return o
}

func (o *Orchestrator) ApplyConfig(cfg *v1.Config) error {
	o.mu.Lock()
	defer o.mu.Unlock()
	o.config = cfg

	zap.L().Debug("Applying config to orchestrator", zap.Any("config", cfg))

	// Update the config provided to the repo pool.
	if err := o.repoPool.configProvider.Update(cfg); err != nil {
		return fmt.Errorf("failed to update repo pool config: %w", err)
	}

	o.taskQueue.Reset() // reset queued tasks, this may loose any ephemeral operations scheduled by RPC. Tasks in progress are not cancelled.

	// Requeue tasks that are affected by the config change.
	for _, plan := range cfg.Plans {
		t, err := NewScheduledBackupTask(o, plan)
		if err != nil {
			return fmt.Errorf("schedule backup task for plan %q: %w", plan.Id, err)
		}
		o.ScheduleTask(t)
	}

	return nil
}

func (o *Orchestrator) GetRepo(repoId string) (repo *RepoOrchestrator, err error) {
	o.mu.Lock()
	defer o.mu.Unlock()

	r, err := o.repoPool.GetRepo(repoId)
	if err != nil {
		return nil, fmt.Errorf("get repo %q: %w", repoId, err)
	}
	return r, nil
}

func (o *Orchestrator) GetPlan(planId string) (*v1.Plan, error) {
	o.mu.Lock()
	defer o.mu.Unlock()

	if o.config.Plans == nil {
		return nil, ErrPlanNotFound
	}

	for _, p := range o.config.Plans {
		if p.Id == planId {
			return p, nil
		}
	}

	return nil, ErrPlanNotFound
}

// Run is the main orchestration loop. Cancel the context to stop the loop.
func (o *Orchestrator) Run(mainCtx context.Context) {
	zap.L().Info("starting orchestrator loop")

	for {
		if mainCtx.Err() != nil {
			zap.L().Info("shutting down orchestrator loop, context cancelled.")
			break
		}

		t := o.taskQueue.Dequeue(mainCtx)
		if t == nil {
			continue
		}

		zap.L().Info("running task", zap.String("task", t.task.Name()))
		if err := t.task.Run(mainCtx); err != nil {
			zap.L().Error("task failed", zap.String("task", t.task.Name()), zap.Error(err))
		} else {
			zap.L().Debug("task finished", zap.String("task", t.task.Name()))
		}

		curTime := time.Now()
		if o.now != nil {
			curTime = o.now()
		}

		if nextTime := t.task.Next(curTime); nextTime != nil {
			o.taskQueue.Push(scheduledTask{
				task:  t.task,
				runAt: *nextTime,
			})
		}
	}
}

func (o *Orchestrator) ScheduleTask(t Task) {
	curTime := time.Now()
	if o.now != nil {
		curTime = o.now()
	}
	nextRun := t.Next(curTime)
	if nextRun == nil {
		return
	}
	zap.L().Info("scheduling task", zap.String("task", t.Name()), zap.String("runAt", nextRun.Format(time.RFC3339)))
	o.taskQueue.Push(scheduledTask{
		task:  t,
		runAt: *nextRun,
	})
}

// resticRepoPool caches restic repos.
type resticRepoPool struct {
	mu             sync.Mutex
	resticPath     string
	repos          map[string]*RepoOrchestrator
	configProvider config.ConfigStore
}

func newResticRepoPool(resticPath string, configProvider config.ConfigStore) *resticRepoPool {
	return &resticRepoPool{
		resticPath:     resticPath,
		repos:          make(map[string]*RepoOrchestrator),
		configProvider: configProvider,
	}
}

func (rp *resticRepoPool) GetRepo(repoId string) (repo *RepoOrchestrator, err error) {
	cfg, err := rp.configProvider.Get()
	if err != nil {
		return nil, fmt.Errorf("failed to get config: %w", err)
	}

	rp.mu.Lock()
	defer rp.mu.Unlock()

	if cfg.Repos == nil {
		return nil, ErrRepoNotFound
	}

	var repoProto *v1.Repo
	for _, r := range cfg.Repos {
		if r.GetId() == repoId {
			repoProto = r
		}
	}

	if repoProto == nil {
		return nil, ErrRepoNotFound
	}

	// Check if we already have a repo for this id, if we do return it.
	repo, ok := rp.repos[repoId]
	if ok && proto.Equal(repo.repoConfig, repoProto) {
		return repo, nil
	}
	delete(rp.repos, repoId)

	var opts []restic.GenericOption
	opts = append(opts, restic.WithPropagatedEnvVars(restic.EnvToPropagate...))
	if len(repoProto.GetEnv()) > 0 {
		opts = append(opts, restic.WithEnv(repoProto.GetEnv()...))
	}
	if len(repoProto.GetFlags()) > 0 {
		opts = append(opts, restic.WithFlags(repoProto.GetFlags()...))
	}

	// Otherwise create a new repo.
	repo = newRepoOrchestrator(repoProto, restic.NewRepo(rp.resticPath, repoProto, opts...))
	rp.repos[repoId] = repo
	return repo, nil
}