package queue

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

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

	"git.threesix.ai/jordan/sp4-verify-1770325799/pkg/logging"
)

const (
	// RedisQueueKey is the sorted set key for the job queue
	RedisQueueKey = "jobs:queue"
	// RedisJobPrefix is the prefix for job data hash keys
	RedisJobPrefix = "jobs:data:"
	// RedisRunningKey is the set of currently running job IDs
	RedisRunningKey = "jobs:running"
)

// RedisQueue implements Producer and Consumer using Redis.
// Uses sorted sets for priority ordering and lists for atomic dequeue.
type RedisQueue struct {
	client *redis.Client
	logger *logging.Logger
}

// Ensure RedisQueue implements Queue at compile time.
var _ Queue = (*RedisQueue)(nil)

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

// Enqueue adds a job to the queue with default options.
func (q *RedisQueue) Enqueue(ctx context.Context, jobType string, payload map[string]any) (string, error) {
	return q.EnqueueWithOptions(ctx, Job{
		Type:       jobType,
		Payload:    payload,
		Priority:   0,
		MaxRetries: 3,
	})
}

// EnqueueWithOptions adds a job with custom configuration.
func (q *RedisQueue) EnqueueWithOptions(ctx context.Context, job Job) (string, error) {
	if job.Type == "" {
		return "", fmt.Errorf("job type is required")
	}

	job.ID = uuid.New().String()
	job.Status = StatusPending
	job.CreatedAt = time.Now().UTC()

	if job.MaxRetries == 0 {
		job.MaxRetries = 3
	}
	if job.MaxRetries > 100 {
		job.MaxRetries = 100
	}
	if job.Payload == nil {
		job.Payload = make(map[string]any)
	}

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

	// Use a pipeline for atomic operations
	pipe := q.client.Pipeline()

	// Store job data
	jobKey := RedisJobPrefix + job.ID
	pipe.Set(ctx, jobKey, data, 0)

	// Add to sorted set with score = -priority (higher priority = lower score = first out)
	// Secondary sort by timestamp for FIFO within same priority
	score := float64(-job.Priority) + float64(job.CreatedAt.UnixNano())/1e18
	pipe.ZAdd(ctx, RedisQueueKey, redis.Z{
		Score:  score,
		Member: job.ID,
	})

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

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

// Dequeue atomically claims the next pending job.
func (q *RedisQueue) Dequeue(ctx context.Context, workerID string) (*Job, error) {
	// Pop the highest priority job (lowest score) atomically
	result, err := q.client.ZPopMin(ctx, RedisQueueKey, 1).Result()
	if err != nil {
		return nil, fmt.Errorf("dequeue job: %w", err)
	}

	if len(result) == 0 {
		return nil, ErrNoJob
	}

	jobID := result[0].Member.(string)
	jobKey := RedisJobPrefix + jobID

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

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

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

	// Save updated job and add to running set
	updatedData, err := json.Marshal(job)
	if err != nil {
		return nil, fmt.Errorf("marshal updated job: %w", err)
	}

	pipe := q.client.Pipeline()
	pipe.Set(ctx, jobKey, updatedData, 0)
	pipe.SAdd(ctx, RedisRunningKey, jobID)
	_, err = pipe.Exec(ctx)
	if err != nil {
		return nil, fmt.Errorf("update job status: %w", err)
	}

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

// Ack marks a job as successfully completed.
func (q *RedisQueue) Ack(ctx context.Context, jobID string) error {
	jobKey := RedisJobPrefix + jobID

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

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

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

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

	pipe := q.client.Pipeline()
	pipe.Set(ctx, jobKey, updatedData, 24*time.Hour) // Keep completed jobs for 24h
	pipe.SRem(ctx, RedisRunningKey, jobID)
	_, err = pipe.Exec(ctx)
	if err != nil {
		return fmt.Errorf("ack job: %w", err)
	}

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

// Fail marks a job as failed, requeuing if retries remain.
func (q *RedisQueue) Fail(ctx context.Context, jobID string, errMsg string) error {
	jobKey := RedisJobPrefix + jobID

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

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

	job.RetryCount++
	job.Error = errMsg

	pipe := q.client.Pipeline()
	pipe.SRem(ctx, RedisRunningKey, jobID)

	if job.RetryCount >= job.MaxRetries {
		// Exhausted retries - mark as failed
		now := time.Now().UTC()
		job.Status = StatusFailed
		job.CompletedAt = &now

		updatedData, err := json.Marshal(job)
		if err != nil {
			return fmt.Errorf("marshal job: %w", err)
		}
		pipe.Set(ctx, jobKey, updatedData, 24*time.Hour) // Keep failed jobs for 24h
	} else {
		// Requeue for retry
		job.Status = StatusPending
		job.StartedAt = nil
		job.WorkerID = ""

		updatedData, err := json.Marshal(job)
		if err != nil {
			return fmt.Errorf("marshal job: %w", err)
		}
		pipe.Set(ctx, jobKey, updatedData, 0)

		// Re-add to queue with original priority
		score := float64(-job.Priority) + float64(job.CreatedAt.UnixNano())/1e18
		pipe.ZAdd(ctx, RedisQueueKey, redis.Z{
			Score:  score,
			Member: jobID,
		})
	}

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

	logErrMsg := errMsg
	if len(logErrMsg) > 500 {
		logErrMsg = logErrMsg[:497] + "..."
	}
	q.logger.Debug("job failed", "job_id", jobID, "retry_count", job.RetryCount, "max_retries", job.MaxRetries, "error", logErrMsg)
	return nil
}

// Heartbeat extends the job's visibility timeout (no-op for Redis implementation).
func (q *RedisQueue) Heartbeat(ctx context.Context, jobID string) error {
	// For Redis, we track running jobs in a set but don't have visibility timeout.
	// This could be extended to use Redis EXPIRE on job keys if needed.
	return nil
}

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

	data, err := q.client.Get(ctx, jobKey).Bytes()
	if err != nil {
		if errors.Is(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
}

// QueueLength returns the number of pending jobs.
func (q *RedisQueue) QueueLength(ctx context.Context) (int64, error) {
	return q.client.ZCard(ctx, RedisQueueKey).Result()
}

// RequeueStale requeues jobs that have been running too long.
func (q *RedisQueue) RequeueStale(ctx context.Context, timeout time.Duration) (int64, error) {
	// Get all running job IDs
	runningIDs, err := q.client.SMembers(ctx, RedisRunningKey).Result()
	if err != nil {
		return 0, fmt.Errorf("get running jobs: %w", err)
	}

	cutoff := time.Now().UTC().Add(-timeout)
	var requeued int64

	for _, jobID := range runningIDs {
		job, err := q.GetJob(ctx, jobID)
		if err != nil {
			continue // Job may have been deleted
		}

		if job.StartedAt != nil && job.StartedAt.Before(cutoff) {
			// Requeue stale job
			job.Status = StatusPending
			job.StartedAt = nil
			job.WorkerID = ""

			data, err := json.Marshal(job)
			if err != nil {
				continue
			}

			pipe := q.client.Pipeline()
			pipe.Set(ctx, RedisJobPrefix+jobID, data, 0)
			pipe.SRem(ctx, RedisRunningKey, jobID)
			score := float64(-job.Priority) + float64(job.CreatedAt.UnixNano())/1e18
			pipe.ZAdd(ctx, RedisQueueKey, redis.Z{
				Score:  score,
				Member: jobID,
			})
			_, err = pipe.Exec(ctx)
			if err == nil {
				requeued++
			}
		}
	}

	if requeued > 0 {
		q.logger.Info("requeued stale jobs", "count", requeued, "timeout", timeout)
	}
	return requeued, nil
}