package console

import (
	"context"
	"errors"
	"log"
	"strings"
	"time"

	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/service/cloudwatch"
	"github.com/aws/aws-sdk-go-v2/service/cloudwatch/types"

	"github.com/carlosframework/platform/internal/rootaws"
)

// The AWS adapter of the eligible-capacity metric (region HA spec 2 §4,
// §25): CloudWatch, Carlos/Region EligibleBoxes, keyed by the placement
// code, in each region's own CloudWatch, where the region-host module's
// alarm reads it. Armed by CARLOS_REGION_METRICS=cloudwatch on the
// console. The platform box's role needs cloudwatch:PutMetricData on the
// Carlos/Region namespace: plan 2c grants it.

const (
	capacityNamespace = "Carlos/Region"
	capacityMetric    = "EligibleBoxes"
)

// capacityData is the exact PutMetricData input for one region's count.
func capacityData(c regionCapacity, now time.Time) *cloudwatch.PutMetricDataInput {
	return &cloudwatch.PutMetricDataInput{Namespace: aws.String(capacityNamespace), MetricData: []types.MetricDatum{{
		MetricName: aws.String(capacityMetric),
		Dimensions: []types.Dimension{{Name: aws.String("Region"), Value: aws.String(c.Placement)}},
		Timestamp:  aws.Time(now),
		Unit:       types.StandardUnitCount,
		Value:      aws.Float64(float64(c.Eligible)),
	}}}
}

// cloudWatchCapacity publishes each count to its region's CloudWatch.
type cloudWatchCapacity struct {
	put func(ctx context.Context, awsRegion string, in *cloudwatch.PutMetricDataInput) error
	now func() time.Time
}

func (c cloudWatchCapacity) PublishCapacity(ctx context.Context, counts []regionCapacity) error {
	var errs []error
	for _, n := range counts {
		errs = append(errs, c.put(ctx, n.AWSRegion, capacityData(n, c.now())))
	}
	return errors.Join(errs...)
}

// capacityPublisherFromEnv is the console's publisher: CloudWatch when
// CARLOS_REGION_METRICS is "cloudwatch", and nil otherwise, or when the
// AWS configuration cannot be loaded (logged).
func capacityPublisherFromEnv(ctx context.Context, getenv func(string) string) capacityPublisher {
	if strings.TrimSpace(getenv("CARLOS_REGION_METRICS")) != "cloudwatch" {
		return nil
	}
	cfg, err := rootaws.LoadDefaultConfig(ctx)
	if err != nil {
		log.Printf("console: eligible-capacity metric disabled: load aws config: %v", err)
		return nil
	}
	return cloudWatchCapacity{now: time.Now, put: func(ctx context.Context, awsRegion string, in *cloudwatch.PutMetricDataInput) error {
		_, err := cloudwatch.NewFromConfig(cfg, func(o *cloudwatch.Options) { o.Region = awsRegion }).PutMetricData(ctx, in)
		return err
	}}
}