package conditions

import (
	"reflect"

	"github.com/google/go-cmp/cmp"
	"github.com/pkg/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

// Patch defines a list of operations to change a list of conditions into another.
type Patch []PatchOperation

// PatchOperation define an operation that changes a single condition.
type PatchOperation struct {
	Before *metav1.Condition
	After  *metav1.Condition
	Op     PatchOperationType
}

// PatchOperationType defines patch operation types.
type PatchOperationType string

const (
	// AddConditionPatch defines an add condition patch operation.
	AddConditionPatch PatchOperationType = "Add"

	// ChangeConditionPatch defines an change condition patch operation.
	ChangeConditionPatch PatchOperationType = "Change"

	// RemoveConditionPatch defines a remove condition patch operation.
	RemoveConditionPatch PatchOperationType = "Remove"
)

// NewPatch returns the list of Patch required to align source conditions to after conditions.
func NewPatch(before Getter, after Getter) Patch {
	var patch Patch

	// Identify AddCondition and ModifyCondition changes.
	targetConditions := after.GetConditions()
	for i := range targetConditions {
		targetCondition := targetConditions[i]
		currentCondition := Get(before, targetCondition.Type)
		if currentCondition == nil {
			patch = append(patch, PatchOperation{Op: AddConditionPatch, After: &targetCondition})
			continue
		}

		if !reflect.DeepEqual(&targetCondition, currentCondition) {
			patch = append(patch, PatchOperation{Op: ChangeConditionPatch, After: &targetCondition, Before: currentCondition})
		}
	}

	// Identify RemoveCondition changes.
	baseConditions := before.GetConditions()
	for i := range baseConditions {
		baseCondition := baseConditions[i]
		targetCondition := Get(after, baseCondition.Type)
		if targetCondition == nil {
			patch = append(patch, PatchOperation{Op: RemoveConditionPatch, Before: &baseCondition})
		}
	}
	return patch
}

// applyOptions allows to set strategies for patch apply.
type applyOptions struct {
	ownedConditions []string
	forceOverwrite  bool
}

func (o *applyOptions) isOwnedCondition(t string) bool {
	for _, i := range o.ownedConditions {
		if i == t {
			return true
		}
	}
	return false
}

// ApplyOption defines an option for applying a condition patch.
type ApplyOption func(*applyOptions)

// WithOwnedConditions allows to define condition types owned by the controller.
// In case of conflicts for the owned conditions, the patch helper will always use the value provided by the controller.
func WithOwnedConditions(t ...string) ApplyOption {
	return func(c *applyOptions) {
		c.ownedConditions = t
	}
}

// WithForceOverwrite instructs the patch helper to always use the value provided by the controller in case of conflicts
// for the owned conditions.
func WithForceOverwrite(v bool) ApplyOption {
	return func(c *applyOptions) {
		c.forceOverwrite = v
	}
}

// Apply executes a three-way merge of a list of Patch.
// When merge conflicts are detected (latest deviated from before in an incompatible way), an error is returned.
func (p Patch) Apply(latest Setter, options ...ApplyOption) error {
	if len(p) == 0 {
		return nil
	}

	applyOpt := &applyOptions{}
	for _, o := range options {
		o(applyOpt)
	}

	for _, conditionPatch := range p {
		switch conditionPatch.Op {
		case AddConditionPatch:
			// If the conditions is owned, always keep the after value.
			if applyOpt.forceOverwrite || applyOpt.isOwnedCondition(conditionPatch.After.Type) {
				Set(latest, conditionPatch.After)
				continue
			}

			// If the condition is already on latest, check if latest and after agree on the change; if not, this is a conflict.
			if latestCondition := Get(latest, conditionPatch.After.Type); latestCondition != nil {
				// If latest and after agree on the change, then it is a conflict.
				if !hasSameState(latestCondition, conditionPatch.After) {
					return errors.Errorf("error patching conditions: The condition %q was modified by a different process and this caused a merge/AddCondition conflict: %v", conditionPatch.After.Type, cmp.Diff(latestCondition, conditionPatch.After))
				}
				// otherwise, the latest is already as intended.
				// NOTE: We are preserving LastTransitionTime from the latest in order to avoid altering the existing value.
				continue
			}
			// If the condition does not exist on the latest, add the new after condition.
			Set(latest, conditionPatch.After)

		case ChangeConditionPatch:
			// If the conditions is owned, always keep the after value.
			if applyOpt.forceOverwrite || applyOpt.isOwnedCondition(conditionPatch.After.Type) {
				Set(latest, conditionPatch.After)
				continue
			}

			latestCondition := Get(latest, conditionPatch.After.Type)

			// If the condition does not exist anymore on the latest, this is a conflict.
			if latestCondition == nil {
				return errors.Errorf("error patching conditions: The condition %q was deleted by a different process and this caused a merge/ChangeCondition conflict", conditionPatch.After.Type)
			}

			// If the condition on the latest is different from the base condition, check if
			// the after state corresponds to the desired value. If not this is a conflict (unless we should ignore conflicts for this condition type).
			if !reflect.DeepEqual(latestCondition, conditionPatch.Before) {
				if !hasSameState(latestCondition, conditionPatch.After) {
					return errors.Errorf("error patching conditions: The condition %q was modified by a different process and this caused a merge/ChangeCondition conflict: %v", conditionPatch.After.Type, cmp.Diff(latestCondition, conditionPatch.After))
				}
				// Otherwise the latest is already as intended.
				// NOTE: We are preserving LastTransitionTime from the latest in order to avoid altering the existing value.
				continue
			}
			// Otherwise apply the new after condition.
			Set(latest, conditionPatch.After)

		case RemoveConditionPatch:
			// If the conditions is owned, always keep the after value (condition should be deleted).
			if applyOpt.forceOverwrite || applyOpt.isOwnedCondition(conditionPatch.Before.Type) {
				Delete(latest, conditionPatch.Before.Type)
				continue
			}

			// If the condition is still on the latest, check if it is changed in the meantime;
			// if so then this is a conflict.
			if latestCondition := Get(latest, conditionPatch.Before.Type); latestCondition != nil {
				if !hasSameState(latestCondition, conditionPatch.Before) {
					return errors.Errorf("error patching conditions: The condition %q was modified by a different process and this caused a merge/RemoveCondition conflict: %v", conditionPatch.Before.Type, cmp.Diff(latestCondition, conditionPatch.Before))
				}
			}
			// Otherwise the latest and after agreed on the delete operation, so there's nothing to change.
			Delete(latest, conditionPatch.Before.Type)
		}
	}
	return nil
}

// IsZero returns true if the patch has no changes.
func (p Patch) IsZero() bool {
	return len(p) == 0
}