package framework

import (
	"context"
	"errors"
	"strings"

	clusterv1alpha1 "github.com/karmada-io/karmada/pkg/apis/cluster/v1alpha1"
	policyv1alpha1 "github.com/karmada-io/karmada/pkg/apis/policy/v1alpha1"
	workv1alpha2 "github.com/karmada-io/karmada/pkg/apis/work/v1alpha2"
)

const (
	// MinClusterScore is the minimum score a Score plugin is expected to return.
	MinClusterScore int64 = 0

	// MaxClusterScore is the maximum score a Score plugin is expected to return.
	MaxClusterScore int64 = 100
)

// Framework manages the set of plugins in use by the scheduling framework.
// Configured plugins are called at specified points in a scheduling context.
type Framework interface {

	// RunFilterPlugins runs the set of configured Filter plugins for resources on
	// the given cluster.
	RunFilterPlugins(ctx context.Context, placement *policyv1alpha1.Placement, bindingSpec *workv1alpha2.ResourceBindingSpec, clusterv1alpha1 *clusterv1alpha1.Cluster) *Result

	// RunScorePlugins runs the set of configured Score plugins, it returns a map of plugin name to cores
	RunScorePlugins(ctx context.Context, placement *policyv1alpha1.Placement, spec *workv1alpha2.ResourceBindingSpec, clusters []*clusterv1alpha1.Cluster) (PluginToClusterScores, error)
}

// Plugin is the parent type for all the scheduling framework plugins.
type Plugin interface {
	Name() string
}

// FilterPlugin is an interface for filter plugins. These filters are used to filter out clusters
// that are not fit for the resource.
type FilterPlugin interface {
	Plugin
	// Filter is called by the scheduling framework.
	Filter(ctx context.Context, placement *policyv1alpha1.Placement, bindingSpec *workv1alpha2.ResourceBindingSpec, clusterv1alpha1 *clusterv1alpha1.Cluster) *Result
}

// Result indicates the result of running a plugin. It consists of a code, a
// message and (optionally) an error. When the status code is not `Success`,
// the reasons should explain why.
type Result struct {
	code    Code
	reasons []string
	err     error
}

// Code is the Status code/type which is returned from plugins.
type Code int

// These are predefined codes used in a Status.
const (
	// Success means that plugin ran correctly and found resource schedulable.
	// NOTE: A nil status is also considered as "Success".
	Success Code = iota
	// Unschedulable is used when a plugin finds the resource unschedulable.
	// The accompanying status message should explain why the it is unschedulable.
	Unschedulable
	// Error is used for internal plugin errors, unexpected input, etc.
	Error
)

// NewResult makes a result out of the given arguments and returns its pointer.
func NewResult(code Code, reasons ...string) *Result {
	s := &Result{
		code:    code,
		reasons: reasons,
	}
	if code == Error {
		s.err = errors.New(strings.Join(reasons, ","))
	}
	return s
}

// PluginToResult maps plugin name to Result.
type PluginToResult map[string]*Result

// Merge merges the statuses in the map into one. The resulting status code have the following
// precedence: Error, Unschedulable.
func (p PluginToResult) Merge() *Result {
	if len(p) == 0 {
		return nil
	}

	finalStatus := NewResult(Success)
	var hasUnschedulable bool
	for _, s := range p {
		if s.code == Error {
			finalStatus.err = s.err
		} else if s.code == Unschedulable {
			hasUnschedulable = true
		}
		finalStatus.code = s.code
		finalStatus.reasons = append(finalStatus.reasons, s.reasons...)
	}

	if finalStatus.err != nil {
		finalStatus.code = Error
	} else if hasUnschedulable {
		finalStatus.code = Unschedulable
	}
	return finalStatus
}

// IsSuccess returns true if and only if "Result" is nil or Code is "Success".
func (s *Result) IsSuccess() bool {
	return s == nil || s.code == Success
}

// AsError returns nil if the Result is a success; otherwise returns an "error" object
// with a concatenated message on reasons of the Result.
func (s *Result) AsError() error {
	if s.IsSuccess() {
		return nil
	}
	if s.err != nil {
		return s.err
	}
	return errors.New(strings.Join(s.reasons, ", "))
}

// ScorePlugin is an interface that must be implemented by "Score" plugins to rank
// clusters that passed the filtering phase.
type ScorePlugin interface {
	Plugin
	// Score is called on each filtered cluster. It must return success and an integer
	// indicating the rank of the cluster. All scoring plugins must return success or
	// the resource will be rejected.
	Score(ctx context.Context, placement *policyv1alpha1.Placement, spec *workv1alpha2.ResourceBindingSpec, cluster *clusterv1alpha1.Cluster) (int64, *Result)

	// ScoreExtensions returns a ScoreExtensions interface
	// if it implements one, or nil if does not.
	ScoreExtensions() ScoreExtensions
}

// ScoreExtensions is an interface for Score extended functionality.
type ScoreExtensions interface {
	// NormalizeScore is called for all cluster scores produced
	// by the same plugin's "Score"
	NormalizeScore(ctx context.Context, scores ClusterScoreList) *Result
}

// ClusterScore represent the cluster score.
type ClusterScore struct {
	Cluster *clusterv1alpha1.Cluster
	Score   int64
}

// ClusterScoreList declares a list of clusters and their scores.
type ClusterScoreList []ClusterScore

// PluginToClusterScores declares a map from plugin name to its ClusterScoreList.
type PluginToClusterScores map[string]ClusterScoreList