// Copyright 2016-2018, Pulumi Corporation.
//
// 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 deploy

import (
	"context"

	"github.com/pkg/errors"
	"github.com/pulumi/pulumi/pkg/diag"
	"github.com/pulumi/pulumi/pkg/resource"
	"github.com/pulumi/pulumi/pkg/resource/deploy/providers"
	"github.com/pulumi/pulumi/pkg/resource/graph"
	"github.com/pulumi/pulumi/pkg/util/contract"
	"github.com/pulumi/pulumi/pkg/util/logging"
	"github.com/pulumi/pulumi/pkg/util/result"
)

// planExecutor is responsible for taking a plan and driving it to completion.
// Its primary responsibility is to own a `stepGenerator` and `stepExecutor`, serving
// as the glue that links the two subsystems together.
type planExecutor struct {
	plan *Plan // The plan that we are executing

	stepGen  *stepGenerator // step generator owned by this plan
	stepExec *stepExecutor  // step executor owned by this plan
}

// reportExecResult issues an appropriate diagnostic depending on went wrong.
func (pe *planExecutor) reportExecResult(message string, preview bool) {
	kind := "update"
	if preview {
		kind = "preview"
	}

	pe.reportError("", errors.New(kind+" "+message))
}

// reportError reports a single error to the executor's diag stream with the indicated URN for context.
func (pe *planExecutor) reportError(urn resource.URN, err error) {
	pe.plan.Diag().Errorf(diag.RawMessage(urn, err.Error()))
}

// Execute executes a plan to completion, using the given cancellation context and running a preview
// or update.
func (pe *planExecutor) Execute(callerCtx context.Context, opts Options, preview bool) result.Result {
	// Set up a goroutine that will signal cancellation to the plan's plugins if the caller context is cancelled. We do
	// not hang this off of the context we create below because we do not want the failure of a single step to cause
	// other steps to fail.
	done := make(chan bool)
	defer close(done)
	go func() {
		select {
		case <-callerCtx.Done():
			logging.V(4).Infof("planExecutor.Execute(...): signalling cancellation to providers...")
			cancelErr := pe.plan.ctx.Host.SignalCancellation()
			if cancelErr != nil {
				logging.V(4).Infof("planExecutor.Execute(...): failed to signal cancellation to providers: %v", cancelErr)
			}
		case <-done:
			logging.V(4).Infof("planExecutor.Execute(...): exiting provider canceller")
		}
	}()

	// Before doing anything else, optionally refresh each resource in the base checkpoint.
	if opts.Refresh {
		if res := pe.refresh(callerCtx, opts, preview); res != nil {
			return res
		}
		if opts.RefreshOnly {
			return nil
		}
	}

	// Begin iterating the source.
	src, res := pe.plan.source.Iterate(callerCtx, opts, pe.plan)
	if res != nil {
		return res
	}

	// Set up a step generator for this plan.
	pe.stepGen = newStepGenerator(pe.plan, opts)

	// Retire any pending deletes that are currently present in this plan.
	if res := pe.retirePendingDeletes(callerCtx, opts, preview); res != nil {
		return res
	}

	// Derive a cancellable context for this plan. We will only cancel this context if some piece of the plan's
	// execution fails.
	ctx, cancel := context.WithCancel(callerCtx)

	// Set up a step generator and executor for this plan.
	pe.stepExec = newStepExecutor(ctx, cancel, pe.plan, opts, preview, false)

	// We iterate the source in its own goroutine because iteration is blocking and we want the main loop to be able to
	// respond to cancellation requests promptly.
	type nextEvent struct {
		Event  SourceEvent
		Result result.Result
	}
	incomingEvents := make(chan nextEvent)
	go func() {
		for {
			event, sourceErr := src.Next()
			select {
			case incomingEvents <- nextEvent{event, sourceErr}:
				if event == nil {
					return
				}
			case <-done:
				logging.V(4).Infof("planExecutor.Execute(...): incoming events goroutine exiting")
				return
			}
		}
	}()

	// The main loop. We'll continuously select for incoming events and the cancellation signal. There are
	// a three ways we can exit this loop:
	//  1. The SourceIterator sends us a `nil` event. This means that we're done processing source events and
	//     we should begin processing deletes.
	//  2. The SourceIterator sends us an error. This means some error occurred in the source program and we
	//     should bail.
	//  3. The stepExecCancel cancel context gets canceled. This means some error occurred in the step executor
	//     and we need to bail. This can also happen if the user hits Ctrl-C.
	canceled, res := func() (bool, result.Result) {
		logging.V(4).Infof("planExecutor.Execute(...): waiting for incoming events")
		for {
			select {
			case event := <-incomingEvents:
				logging.V(4).Infof("planExecutor.Execute(...): incoming event (nil? %v, %v)", event.Event == nil, event.Result)

				if event.Result != nil {
					if !event.Result.IsBail() {
						pe.reportError("", event.Result.Error())
					}
					cancel()

					// We reported any errors above.  So we can just bail now.
					return false, result.Bail()
				}

				if event.Event == nil {
					deleteSteps := pe.stepGen.GenerateDeletes()
					deletes := pe.stepGen.ScheduleDeletes(deleteSteps)

					// ScheduleDeletes gives us a list of lists of steps. Each list of steps can safely be executed in
					// parallel, but each list must execute completes before the next list can safely begin executing.
					//
					// This is not "true" delete parallelism, since there may be resources that could safely begin
					// deleting but we won't until the previous set of deletes fully completes. This approximation is
					// conservative, but correct.
					for _, antichain := range deletes {
						logging.V(4).Infof("planExecutor.Execute(...): beginning delete antichain")
						tok := pe.stepExec.ExecuteParallel(antichain)
						tok.Wait(ctx)
						logging.V(4).Infof("planExecutor.Execute(...): antichain complete")
					}

					// We're done here - signal completion so that the step executor knows to terminate.
					pe.stepExec.SignalCompletion()
					return false, nil
				}

				if res := pe.handleSingleEvent(event.Event); res != nil {
					if resErr := res.Error(); resErr != nil {
						logging.V(4).Infof("planExecutor.Execute(...): error handling event: %v", resErr)
						pe.reportError(pe.plan.generateEventURN(event.Event), resErr)
					}
					cancel()
					return false, result.Bail()
				}
			case <-ctx.Done():
				logging.V(4).Infof("planExecutor.Execute(...): context finished: %v", ctx.Err())

				// NOTE: we use the presence of an error in the caller context in order to distinguish caller-initiated
				// cancellation from internally-initiated cancellation.
				return callerCtx.Err() != nil, nil
			}
		}
	}()

	pe.stepExec.WaitForCompletion()
	logging.V(4).Infof("planExecutor.Execute(...): step executor has completed")

	if res != nil && res.IsBail() {
		return res
	}

	// Figure out if execution failed and why. Step generation and execution errors trump cancellation.
	if res != nil || pe.stepExec.Errored() || pe.stepGen.hasPolicyViolations {
		// TODO(cyrusn): We seem to be losing any information about the original 'res's errors.  Should
		// we be doing a merge here?
		pe.reportExecResult("failed", preview)
		return result.Bail()
	} else if canceled {
		pe.reportExecResult("canceled", preview)
		return result.Bail()
	}

	return res
}

// handleSingleEvent handles a single source event. For all incoming events, it produces a chain that needs
// to be executed and schedules the chain for execution.
func (pe *planExecutor) handleSingleEvent(event SourceEvent) result.Result {
	contract.Require(event != nil, "event != nil")

	var steps []Step
	var res result.Result
	switch e := event.(type) {
	case RegisterResourceEvent:
		logging.V(4).Infof("planExecutor.handleSingleEvent(...): received RegisterResourceEvent")
		steps, res = pe.stepGen.GenerateSteps(e)
	case ReadResourceEvent:
		logging.V(4).Infof("planExecutor.handleSingleEvent(...): received ReadResourceEvent")
		steps, res = pe.stepGen.GenerateReadSteps(e)
	case RegisterResourceOutputsEvent:
		logging.V(4).Infof("planExecutor.handleSingleEvent(...): received register resource outputs")
		pe.stepExec.ExecuteRegisterResourceOutputs(e)
		return nil
	}

	if res != nil {
		return res
	}

	pe.stepExec.ExecuteSerial(steps)
	return nil
}

// retirePendingDeletes deletes all resources that are pending deletion. Run before the start of a plan, this pass
// ensures that the engine never sees any resources that are pending deletion from a previous plan.
//
// retirePendingDeletes re-uses the plan executor's step generator but uses its own step executor.
func (pe *planExecutor) retirePendingDeletes(callerCtx context.Context, opts Options, preview bool) result.Result {
	contract.Require(pe.stepGen != nil, "pe.stepGen != nil")
	steps := pe.stepGen.GeneratePendingDeletes()
	if len(steps) == 0 {
		logging.V(4).Infoln("planExecutor.retirePendingDeletes(...): no pending deletions")
		return nil
	}

	logging.V(4).Infof("planExecutor.retirePendingDeletes(...): executing %d steps", len(steps))
	ctx, cancel := context.WithCancel(callerCtx)

	stepExec := newStepExecutor(ctx, cancel, pe.plan, opts, preview, false)
	antichains := pe.stepGen.ScheduleDeletes(steps)
	// Submit the deletes for execution and wait for them all to retire.
	for _, antichain := range antichains {
		for _, step := range antichain {
			pe.plan.Ctx().StatusDiag.Infof(diag.RawMessage(step.URN(), "completing deletion from previous update"))
		}

		tok := stepExec.ExecuteParallel(antichain)
		tok.Wait(ctx)
	}

	stepExec.SignalCompletion()
	stepExec.WaitForCompletion()

	// Like Refresh, we use the presence of an error in the caller's context to detect whether or not we have been
	// cancelled.
	canceled := callerCtx.Err() != nil
	if stepExec.Errored() {
		pe.reportExecResult("failed", preview)
		return result.Bail()
	} else if canceled {
		pe.reportExecResult("canceled", preview)
		return result.Bail()
	}
	return nil
}

// refresh refreshes the state of the base checkpoint file for the current plan in memory.
func (pe *planExecutor) refresh(callerCtx context.Context, opts Options, preview bool) result.Result {
	prev := pe.plan.prev
	if prev == nil || len(prev.Resources) == 0 {
		return nil
	}

	// Create a refresh step for each resource in the old snapshot.
	steps := make([]Step, len(prev.Resources))
	for i := range prev.Resources {
		steps[i] = NewRefreshStep(pe.plan, prev.Resources[i], nil)
	}

	// Fire up a worker pool and issue each refresh in turn.
	ctx, cancel := context.WithCancel(callerCtx)
	stepExec := newStepExecutor(ctx, cancel, pe.plan, opts, preview, true)
	stepExec.ExecuteParallel(steps)
	stepExec.SignalCompletion()
	stepExec.WaitForCompletion()

	// Rebuild this plan's map of old resources and dependency graph, stripping out any deleted resources and repairing
	// dependency lists as necessary. Note that this updates the base snapshot _in memory_, so it is critical that any
	// components that use the snapshot refer to the same instance and avoid reading it concurrently with this rebuild.
	//
	// The process of repairing dependency lists is a bit subtle. Because multiple physical resources may share a URN,
	// the ability of a particular URN to be referenced in a dependency list can change based on the dependent
	// resource's position in the resource list. For example, consider the following list of resources, where each
	// resource is a (URN, ID, Dependencies) tuple:
	//
	//     [ (A, 0, []), (B, 0, [A]), (A, 1, []), (A, 2, []), (C, 0, [A]) ]
	//
	// Let `(A, 0, [])` and `(A, 2, [])` be deleted by the refresh. This produces the following intermediate list
	// before dependency lists are repaired:
	//
	//     [ (B, 0, [A]), (A, 1, []), (C, 0, [A]) ]
	//
	// In order to repair the dependency lists, we iterate over the intermediate resource list, keeping track of which
	// URNs refer to at least one physical resource at each point in the list, and remove any dependencies that refer
	// to URNs that do not refer to any physical resources. This process produces the following final list:
	//
	//     [ (B, 0, []), (A, 1, []), (C, 0, [A]) ]
	//
	// Note that the correctness of this process depends on the fact that the list of resources is a topological sort
	// of its corresponding dependency graph, so a resource always appears in the list after any resources on which it
	// may depend.
	resources := make([]*resource.State, 0, len(prev.Resources))
	referenceable := make(map[resource.URN]bool)
	olds := make(map[resource.URN]*resource.State)
	for _, s := range steps {
		new := s.New()
		if new == nil {
			contract.Assert(s.Old().Custom)
			contract.Assert(!providers.IsProviderType(s.Old().Type))
			continue
		}

		// Remove any deleted resources from this resource's dependency list.
		if len(new.Dependencies) != 0 {
			deps := make([]resource.URN, 0, len(new.Dependencies))
			for _, d := range new.Dependencies {
				if referenceable[d] {
					deps = append(deps, d)
				}
			}
			new.Dependencies = deps
		}

		// Add this resource to the resource list and mark it as referenceable.
		resources = append(resources, new)
		referenceable[new.URN] = true

		// Do not record resources that are pending deletion in the "olds" lookup table.
		if !new.Delete {
			olds[new.URN] = new
		}
	}
	pe.plan.prev.Resources = resources
	pe.plan.olds, pe.plan.depGraph = olds, graph.NewDependencyGraph(resources)

	// NOTE: we use the presence of an error in the caller context in order to distinguish caller-initiated
	// cancellation from internally-initiated cancellation.
	canceled := callerCtx.Err() != nil

	if stepExec.Errored() {
		pe.reportExecResult("failed", preview)
		return result.Bail()
	} else if canceled {
		pe.reportExecResult("canceled", preview)
		return result.Bail()
	}
	return nil
}