// Copyright 2016-2018, Pulumi Corporation.  All rights reserved.

package deploy

import (
	"crypto/sha256"
	"fmt"
	"time"

	"github.com/pkg/errors"

	"github.com/pulumi/pulumi/pkg/resource"
	"github.com/pulumi/pulumi/pkg/tokens"
	"github.com/pulumi/pulumi/pkg/workspace"
)

// Snapshot is a view of a collection of resources in an stack at a point in time.  It describes resources; their
// IDs, names, and properties; their dependencies; and more.  A snapshot is a diffable entity and can be used to create
// or apply an infrastructure deployment plan in order to make reality match the snapshot state.
type Snapshot struct {
	Stack     tokens.QName      // the stack being deployed into.
	Manifest  Manifest          // a deployment manifest of versions, checksums, and so on.
	Resources []*resource.State // fetches all resources and their associated states.
}

// Manifest captures versions for all binaries used to construct this snapshot.
type Manifest struct {
	Time    time.Time              // the time this snapshot was taken.
	Magic   string                 // a magic cookie.
	Version string                 // the pulumi command version.
	Plugins []workspace.PluginInfo // the plugin versions also loaded.
}

// NewMagic creates a magic cookie out of a manifest; this can be used to check for tampering.  This ignores
// any existing magic value already stored on the manifest.
func (m Manifest) NewMagic() string {
	if m.Version == "" {
		return ""
	}
	return fmt.Sprintf("%x", sha256.Sum256([]byte(m.Version)))
}

// NewSnapshot creates a snapshot from the given arguments.  The resources must be in topologically sorted order.
// This property is not checked; for verification, please refer to the VerifyIntegrity function below.
func NewSnapshot(stack tokens.QName, manifest Manifest, resources []*resource.State) *Snapshot {
	return &Snapshot{
		Stack:     stack,
		Manifest:  manifest,
		Resources: resources,
	}
}

// VerifyIntegrity checks a snapshot to ensure it is well-formed.  Because of the cost of this operation,
// integrity verification is only performed on demand, and not automatically during snapshot construction.
func (snap *Snapshot) VerifyIntegrity() error {
	if snap != nil {
		// Ensure the magic cookie checks out.
		if snap.Manifest.Magic != snap.Manifest.NewMagic() {
			return errors.Errorf("magic cookie mismatch; possible tampering/corruption detected")
		}

		// Now check the resources.  For now, we just verify that parents come before children, and that there aren't
		// any duplicate URNs.  Eventually, we will capture the full resource DAG (see
		// https://github.com/pulumi/pulumi/issues/624), on which we can then do additional verification.
		urns := make(map[resource.URN]*resource.State)
		for i, state := range snap.Resources {
			urn := state.URN
			if par := state.Parent; par != "" {
				if _, has := urns[par]; !has {
					// The parent isn't there; to give a good error message, see whether it's missing entirely, or
					// whether it comes later in the snapshot (neither of which should ever happen).
					for _, other := range snap.Resources[i+1:] {
						if other.URN == par {
							return errors.Errorf("child resource %s's parent %s comes after it", urn, par)
						}
					}
					return errors.Errorf("child resource %s refers to missing parent %s", urn, par)
				}
			}

			if _, has := urns[urn]; has && !state.Delete {
				// The only time we should have duplicate URNs is when all but one of them are marked for deletion.
				return errors.Errorf("duplicate resource %s (not marked for deletion)", urn)
			}

			urns[urn] = state
		}
	}

	return nil
}