package redisqueue

import (
	"context"
	"encoding/json"
	"fmt"
	"time"

	"github.com/google/uuid"
	"github.com/redis/go-redis/v9"

	"git.threesix.ai/jordan/sp2-verify-1770324794/pkg/logging"
)

const (
	// queueKey is the Redis list key for pending job IDs.
	queueKey = "jobs:queue"

	// jobKeyPrefix is the prefix for job data keys.
	jobKeyPrefix = "jobs:data:"

	// defaultJobTTL is the TTL for completed/failed jobs.
	defaultJobTTL = 24 * time.Hour
)

// RedisQueue implements a job queue backed by Redis.
type RedisQueue struct {
	client *redis.Client
	logger *logging.Logger
}

// NewRedisQueue creates a new Redis-backed job queue.
func NewRedisQueue(client *redis.Client, logger *logging.Logger) *RedisQueue {
	return &RedisQueue{
		client: client,
		logger: logger.WithComponent("redisqueue"),
	}
}

// Enqueue adds a job to the queue.
// The job ID is generated automatically if not set.
func (q *RedisQueue) Enqueue(ctx context.Context, jobType string, payload map[string]any) (*Job, error) {
	if jobType == "" {
		return nil, fmt.Errorf("job type is required")
	}

	job := &Job{
		ID:        uuid.New().String(),
		Type:      jobType,
		Payload:   payload,
		Status:    StatusPending,
		CreatedAt: time.Now().UTC(),
	}

	if job.Payload == nil {
		job.Payload = make(map[string]any)
	}

	// Store job data
	data, err := json.Marshal(job)
	if err != nil {
		return nil, fmt.Errorf("marshal job: %w", err)
	}

	jobKey := jobKeyPrefix + job.ID

	// Use transaction to ensure atomicity
	pipe := q.client.TxPipeline()
	pipe.Set(ctx, jobKey, data, 0) // No TTL for pending jobs
	pipe.RPush(ctx, queueKey, job.ID)

	if _, err := pipe.Exec(ctx); err != nil {
		return nil, fmt.Errorf("enqueue job: %w", err)
	}

	q.logger.Debug("job enqueued", "job_id", job.ID, "type", job.Type)
	return job, nil
}

// GetJob retrieves a job by ID.
func (q *RedisQueue) GetJob(ctx context.Context, jobID string) (*Job, error) {
	jobKey := jobKeyPrefix + jobID

	data, err := q.client.Get(ctx, jobKey).Bytes()
	if err != nil {
		if err == redis.Nil {
			return nil, ErrJobNotFound
		}
		return nil, fmt.Errorf("get job: %w", err)
	}

	var job Job
	if err := json.Unmarshal(data, &job); err != nil {
		return nil, fmt.Errorf("unmarshal job: %w", err)
	}

	return &job, nil
}

// Dequeue retrieves the next pending job from the queue.
// Blocks until a job is available or the timeout expires.
// Returns ErrNoJob if timeout expires with no job available.
func (q *RedisQueue) Dequeue(ctx context.Context, timeout time.Duration) (*Job, error) {
	// BLPOP blocks until a job is available or timeout
	result, err := q.client.BLPop(ctx, timeout, queueKey).Result()
	if err != nil {
		if err == redis.Nil {
			return nil, ErrNoJob
		}
		return nil, fmt.Errorf("dequeue job: %w", err)
	}

	// result[0] is the key, result[1] is the value (job ID)
	if len(result) < 2 {
		return nil, ErrNoJob
	}
	jobID := result[1]

	// Get job data
	job, err := q.GetJob(ctx, jobID)
	if err != nil {
		return nil, err
	}

	// Update status to running
	now := time.Now().UTC()
	job.Status = StatusRunning
	job.StartedAt = &now

	if err := q.saveJob(ctx, job); err != nil {
		// Re-queue the job on save failure
		q.client.LPush(ctx, queueKey, jobID)
		return nil, fmt.Errorf("update job status: %w", err)
	}

	q.logger.Debug("job dequeued", "job_id", job.ID, "type", job.Type)
	return job, nil
}

// Complete marks a job as completed.
func (q *RedisQueue) Complete(ctx context.Context, jobID string) error {
	job, err := q.GetJob(ctx, jobID)
	if err != nil {
		return err
	}

	now := time.Now().UTC()
	job.Status = StatusCompleted
	job.CompletedAt = &now

	if err := q.saveJobWithTTL(ctx, job, defaultJobTTL); err != nil {
		return fmt.Errorf("complete job: %w", err)
	}

	q.logger.Debug("job completed", "job_id", jobID)
	return nil
}

// Fail marks a job as failed with an error message.
func (q *RedisQueue) Fail(ctx context.Context, jobID string, errMsg string) error {
	job, err := q.GetJob(ctx, jobID)
	if err != nil {
		return err
	}

	now := time.Now().UTC()
	job.Status = StatusFailed
	job.CompletedAt = &now
	job.Error = errMsg

	if err := q.saveJobWithTTL(ctx, job, defaultJobTTL); err != nil {
		return fmt.Errorf("fail job: %w", err)
	}

	q.logger.Debug("job failed", "job_id", jobID, "error", errMsg)
	return nil
}

// saveJob saves a job to Redis without TTL.
func (q *RedisQueue) saveJob(ctx context.Context, job *Job) error {
	return q.saveJobWithTTL(ctx, job, 0)
}

// saveJobWithTTL saves a job to Redis with optional TTL.
func (q *RedisQueue) saveJobWithTTL(ctx context.Context, job *Job, ttl time.Duration) error {
	data, err := json.Marshal(job)
	if err != nil {
		return fmt.Errorf("marshal job: %w", err)
	}

	jobKey := jobKeyPrefix + job.ID
	return q.client.Set(ctx, jobKey, data, ttl).Err()
}

// HealthCheck verifies Redis connectivity.
func (q *RedisQueue) HealthCheck(ctx context.Context) error {
	return q.client.Ping(ctx).Err()
}