package client

import (
	"context"
	"errors"
	"fmt"

	computepb "google.golang.org/genproto/googleapis/cloud/compute/v1"
)

// GetScalingGroupImage returns the image URI of the scaling group.
func (c *Client) GetScalingGroupImage(ctx context.Context, scalingGroupID string) (string, error) {
	instanceTemplate, err := c.getScalingGroupTemplate(ctx, scalingGroupID)
	if err != nil {
		return "", err
	}
	return instanceTemplateSourceImage(instanceTemplate)
}

// SetScalingGroupImage sets the image URI of the scaling group.
func (c *Client) SetScalingGroupImage(ctx context.Context, scalingGroupID, imageURI string) error {
	project, zone, instanceGroupName, err := splitInstanceGroupID(scalingGroupID)
	if err != nil {
		return err
	}
	// get current template
	instanceTemplate, err := c.getScalingGroupTemplate(ctx, scalingGroupID)
	if err != nil {
		return err
	}
	// check if template already uses the same image
	oldImageURI, err := instanceTemplateSourceImage(instanceTemplate)
	if err != nil {
		return err
	}
	if oldImageURI == imageURI {
		return nil
	}

	// clone template with desired image
	if instanceTemplate.Name == nil {
		return fmt.Errorf("instance template of scaling group %q has no name", scalingGroupID)
	}
	instanceTemplate.Properties.Disks[0].InitializeParams.SourceImage = &imageURI
	newTemplateName, err := generateInstanceTemplateName(*instanceTemplate.Name)
	if err != nil {
		return err
	}
	instanceTemplate.Name = &newTemplateName
	op, err := c.instanceTemplateAPI.Insert(ctx, &computepb.InsertInstanceTemplateRequest{
		Project:                  project,
		InstanceTemplateResource: instanceTemplate,
	})
	if err != nil {
		return fmt.Errorf("cloning instance template: %w", err)
	}
	if err := op.Wait(ctx); err != nil {
		return fmt.Errorf("waiting for cloned instance template: %w", err)
	}

	newTemplateURI := joinInstanceTemplateURI(project, newTemplateName)
	// update instance group manager to use new template
	op, err = c.instanceGroupManagersAPI.SetInstanceTemplate(ctx, &computepb.SetInstanceTemplateInstanceGroupManagerRequest{
		InstanceGroupManager: instanceGroupName,
		Project:              project,
		Zone:                 zone,
		InstanceGroupManagersSetInstanceTemplateRequestResource: &computepb.InstanceGroupManagersSetInstanceTemplateRequest{
			InstanceTemplate: &newTemplateURI,
		},
	})
	if err != nil {
		return fmt.Errorf("setting instance template: %w", err)
	}
	if err := op.Wait(ctx); err != nil {
		return fmt.Errorf("waiting for setting instance template: %w", err)
	}
	return nil
}

func (c *Client) getScalingGroupTemplate(ctx context.Context, scalingGroupID string) (*computepb.InstanceTemplate, error) {
	project, zone, instanceGroupName, err := splitInstanceGroupID(scalingGroupID)
	if err != nil {
		return nil, err
	}
	instanceGroupManager, err := c.instanceGroupManagersAPI.Get(ctx, &computepb.GetInstanceGroupManagerRequest{
		InstanceGroupManager: instanceGroupName,
		Project:              project,
		Zone:                 zone,
	})
	if err != nil {
		return nil, fmt.Errorf("getting instance group manager %q: %w", instanceGroupName, err)
	}
	if instanceGroupManager.InstanceTemplate == nil {
		return nil, fmt.Errorf("instance group manager %q has no instance template", instanceGroupName)
	}
	instanceTemplateProject, instanceTemplateName, err := splitInstanceTemplateID(uriNormalize(*instanceGroupManager.InstanceTemplate))
	if err != nil {
		return nil, fmt.Errorf("splitting instance template name: %w", err)
	}
	instanceTemplate, err := c.instanceTemplateAPI.Get(ctx, &computepb.GetInstanceTemplateRequest{
		InstanceTemplate: instanceTemplateName,
		Project:          instanceTemplateProject,
	})
	if err != nil {
		return nil, fmt.Errorf("getting instance template %q: %w", instanceTemplateName, err)
	}
	return instanceTemplate, nil
}

func instanceTemplateSourceImage(instanceTemplate *computepb.InstanceTemplate) (string, error) {
	if instanceTemplate.Properties == nil ||
		len(instanceTemplate.Properties.Disks) == 0 ||
		instanceTemplate.Properties.Disks[0].InitializeParams == nil ||
		instanceTemplate.Properties.Disks[0].InitializeParams.SourceImage == nil {
		return "", errors.New("instance template has no source image")
	}
	return uriNormalize(*instanceTemplate.Properties.Disks[0].InitializeParams.SourceImage), nil
}