package environment

import (
	"github.com/kubernetes/helm/pkg/engine"
	"github.com/kubernetes/helm/pkg/proto/hapi/chart"
	"github.com/kubernetes/helm/pkg/proto/hapi/release"
	"github.com/kubernetes/helm/pkg/storage"
)

// GoTplEngine is the name of the Go template engine, as registered in the EngineYard.
const GoTplEngine = "gotpl"

// DefaultEngine points to the engine that the EngineYard should treat as the
// default. A chart that does not specify an engine may be run through the
// default engine.
var DefaultEngine = GoTplEngine

// EngineYard maps engine names to engine implementations.
type EngineYard map[string]Engine

// Get retrieves a template engine by name.
//
// If no matching template engine is found, the second return value will
// be false.
func (y EngineYard) Get(k string) (Engine, bool) {
	e, ok := y[k]
	return e, ok
}

// Default returns the default template engine.
//
// The default is specified by DefaultEngine.
//
// If the default template engine cannot be found, this panics.
func (y EngineYard) Default() Engine {
	d, ok := y[DefaultEngine]
	if !ok {
		// This is a developer error!
		panic("Default template engine does not exist")
	}
	return d
}

// Engine represents a template engine that can render templates.
//
// For some engines, "rendering" includes both compiling and executing. (Other
// engines do not distinguish between phases.)
//
// The engine returns a map where the key is the named output entity (usually
// a file name) and the value is the rendered content of the template.
//
// An Engine must be capable of executing multiple concurrent requests, but
// without tainting one request's environment with data from another request.
type Engine interface {
	Render(*chart.Chart, *chart.Config) (map[string]string, error)
}

// ReleaseStorage represents a storage engine for a Release.
//
// Release storage must be concurrency safe.
type ReleaseStorage interface {

	// Create stores a release in the storage.
	//
	// If a release with the same name exists, this returns an error.
	//
	// It may return other errors in cases where it cannot write to storage.
	Create(*release.Release) error
	// Read takes a name and returns a release that has that name.
	//
	// It will only return releases that are not deleted and not superseded.
	//
	// It will return an error if no relevant release can be found, or if storage
	// is not properly functioning.
	Read(name string) (*release.Release, error)

	// Update looks for a release with the same name and updates it with the
	// present release contents.
	//
	// For immutable storage backends, this may result in a new release record
	// being created, and the previous release being marked as superseded.
	//
	// It will return an error if a previous release is not found. It may also
	// return an error if the storage backend encounters an error.
	Update(*release.Release) error

	// Delete marks a Release as deleted.
	//
	// It returns the deleted record. If the record is not found or if the
	// underlying storage encounters an error, this will return an error.
	Delete(name string) (*release.Release, error)

	// List lists all active (non-deleted, non-superseded) releases.
	//
	// To get deleted or superseded releases, use Query.
	List() ([]*release.Release, error)

	// Query takes a map of labels and returns any releases that match.
	//
	// Query will search all releases, including deleted and superseded ones.
	// The provided map will be used to filter results.
	Query(map[string]string) ([]*release.Release, error)
}

// KubeClient represents a client capable of communicating with the Kubernetes API.
//
// A KubeClient must be concurrency safe.
type KubeClient interface {
	// Install takes a map where the key is a "file name" (read: unique relational
	// id) and the value is a Kubernetes manifest containing one or more resource
	// definitions.
	//
	// TODO: Can these be in YAML or JSON, or must they be in one particular
	// format?
	Install(manifests map[string]string) error
}

// Environment provides the context for executing a client request.
//
// All services in a context are concurrency safe.
type Environment struct {
	// EngineYard provides access to the known template engines.
	EngineYard EngineYard
	// Releases stores records of releases.
	Releases ReleaseStorage
	// KubeClient is a Kubernetes API client.
	KubeClient KubeClient
}

// New returns an environment initialized with the defaults.
func New() *Environment {
	e := engine.New()
	var ey EngineYard = map[string]Engine{
		// Currently, the only template engine we support is the GoTpl one. But
		// we can easily add some here.
		GoTplEngine: e,
	}
	return &Environment{
		EngineYard: ey,
		Releases:   storage.NewMemory(),
	}
}