// Package consumers holds the queue-driven half of the service: work that
// arrives on a queue rather than as an HTTP request. It is to SQS what
// internal/handlers is to HTTP — it decodes a message, calls repositories, and
// decides what the message's fate is — so the same seams apply, and no SQL
// lives here.
package consumers

import (
	"context"
	"encoding/json"
	"errors"
	"log"
	"thamanyah/cms/v2/internal/db/repositories"
	"thamanyah/cms/v2/internal/models"
	"thamanyah/cms/v2/internal/services"
	"time"
)

// receiveBackoff is how long the loop waits after a failed receive, so a queue
// that is unreachable produces a slow trickle of log lines rather than a spin.
const receiveBackoff = 5 * time.Second

// jobStateChange is the EventBridge event MediaConvert emits on every job
// state transition. The subscription delivers it raw, so this is the whole
// message body — there is no SNS envelope to unwrap. Only the members this
// service acts on are modelled; AWS sends a good deal more.
type jobStateChange struct {
	Source     string `json:"source"`
	DetailType string `json:"detail-type"`
	Detail     struct {
		JobID  string `json:"jobId"`
		Status string `json:"status"`
	} `json:"detail"`
}

// statusForJobState maps MediaConvert's job states onto the catalogue's. The
// second return is false for states that are not an outcome — the job is still
// running, and the record should stay where it is rather than being rewritten
// with what it already says.
func statusForJobState(state string) (models.VideoStatus, bool) {
	switch state {
	case "COMPLETE":
		return models.VideoStatusReady, true
	case "ERROR", "CANCELED":
		return models.VideoStatusFailed, true
	default:
		return "", false
	}
}

// RunMediaConvertEvents consumes job state changes until ctx is cancelled. It
// is meant to be run in its own goroutine for the lifetime of the process.
func RunMediaConvertEvents(ctx context.Context) {
	log.Println("mediaconvert job events consumer started")

	for {
		if ctx.Err() != nil {
			log.Println("mediaconvert job events consumer stopped")
			return
		}

		messages, err := services.SQSClient.ReceiveMessages(ctx)
		if err != nil {
			if ctx.Err() != nil {
				log.Println("mediaconvert job events consumer stopped")
				return
			}
			log.Printf("Something Went Wrong Receiving Job Events: %s", err)
			time.Sleep(receiveBackoff)
			continue
		}

		for _, message := range messages {
			if !handleJobEvent(ctx, message.Body) {
				// Left on the queue on purpose: it becomes visible again when
				// the visibility timeout expires, and reaches the dead-letter
				// queue if it keeps failing.
				continue
			}

			if err := services.SQSClient.DeleteMessage(ctx, message.ReceiptHandle); err != nil {
				log.Printf("Something Went Wrong Acknowledging A Job Event: %s", err)
			}
		}
	}
}

// handleJobEvent processes one message and reports whether it is finished
// with — that is, whether it should be deleted from the queue. It returns
// false only when a retry could plausibly succeed. Anything a retry cannot fix
// (a body that will never parse, an event for a job nobody has) is finished
// with, however little it accomplished: leaving it on the queue would only
// stall the events behind it.
func handleJobEvent(ctx context.Context, body string) bool {
	var event jobStateChange
	if err := json.Unmarshal([]byte(body), &event); err != nil {
		log.Printf("Discarding A Job Event That Is Not JSON: %s", err)
		return true
	}

	if event.Source != "aws.mediaconvert" || event.DetailType != "MediaConvert Job State Change" {
		log.Printf("Discarding An Event That Is Not A MediaConvert Job State Change: source=%q detail-type=%q",
			event.Source, event.DetailType)
		return true
	}

	if event.Detail.JobID == "" {
		log.Printf("Discarding A Job Event That Names No Job")
		return true
	}

	status, isOutcome := statusForJobState(event.Detail.Status)
	if !isOutcome {
		// SUBMITTED, PROGRESSING and STATUS_UPDATE say the job is still
		// running, which is what "processing" already records.
		return true
	}

	err := repositories.VideoRepo.UpdateVideoStatusByJobID(ctx, event.Detail.JobID, status)
	if errors.Is(err, repositories.ErrVideoNotFound) {
		// Not a fault: the topic carries every job in the account, including
		// ones this service never submitted.
		log.Printf("Ignoring A Job Event For A Job No Video Has: job=%q status=%q",
			event.Detail.JobID, event.Detail.Status)
		return true
	}
	if err != nil {
		log.Printf("Something Went Wrong Recording A Job Outcome: job=%q status=%q: %s",
			event.Detail.JobID, event.Detail.Status, err)
		return false
	}

	log.Printf("Recorded A Job Outcome: job=%q status=%q", event.Detail.JobID, status)
	return true
}