rdev/internal/adapter/postgres/work_queue.go

// Package postgres provides PostgreSQL-based implementations of port interfaces.
package postgres

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"

	"github.com/orchard9/rdev/internal/domain"
	"github.com/orchard9/rdev/internal/port"
)

// WorkQueueRepository implements port.WorkQueue using PostgreSQL.
type WorkQueueRepository struct {
	db *sql.DB
}

// NewWorkQueueRepository creates a new PostgreSQL work queue repository.
func NewWorkQueueRepository(db *sql.DB) *WorkQueueRepository {
	return &WorkQueueRepository{db: db}
}

// Ensure WorkQueueRepository implements port.WorkQueue at compile time.
var _ port.WorkQueue = (*WorkQueueRepository)(nil)

// Enqueue adds a task to the queue.
func (r *WorkQueueRepository) Enqueue(ctx context.Context, task *domain.WorkTask) (string, error) {
	specJSON, err := json.Marshal(task.Spec)
	if err != nil {
		return "", fmt.Errorf("marshal task spec: %w", err)
	}

	var id string
	err = r.db.QueryRowContext(ctx, `
		INSERT INTO work_queue (project_id, task_type, task_spec, priority, callback_url, max_retries)
		VALUES ($1, $2, $3, $4, $5, $6)
		RETURNING id
	`, task.ProjectID, string(task.Type), specJSON, task.Priority, nullString(task.CallbackURL), task.MaxRetries).Scan(&id)

	if err != nil {
		return "", fmt.Errorf("enqueue work task: %w", err)
	}

	return id, nil
}

// Dequeue atomically claims the next available task for a worker.
func (r *WorkQueueRepository) Dequeue(ctx context.Context, workerID string) (*domain.WorkTask, error) {
	// Use a single UPDATE ... RETURNING with subquery for atomic claim
	// This avoids explicit transaction management while still being safe
	var task domain.WorkTask
	var taskType string
	var specJSON []byte
	var status string
	var callbackURL sql.NullString
	var startedAt sql.NullTime
	var completedAt sql.NullTime
	var resultJSON []byte
	var errorMsg sql.NullString

	err := r.db.QueryRowContext(ctx, `
		UPDATE work_queue
		SET status = 'running', worker_id = $1, started_at = NOW()
		WHERE id = (
			SELECT id FROM work_queue
			WHERE status = 'pending'
			ORDER BY priority DESC, created_at ASC
			LIMIT 1
			FOR UPDATE SKIP LOCKED
		)
		RETURNING id, project_id, task_type, task_spec, status, priority, worker_id,
		          callback_url, created_at, started_at, completed_at, result, error,
		          retry_count, max_retries
	`, workerID).Scan(
		&task.ID,
		&task.ProjectID,
		&taskType,
		&specJSON,
		&status,
		&task.Priority,
		&task.WorkerID,
		&callbackURL,
		&task.CreatedAt,
		&startedAt,
		&completedAt,
		&resultJSON,
		&errorMsg,
		&task.RetryCount,
		&task.MaxRetries,
	)

	if errors.Is(err, sql.ErrNoRows) {
		return nil, nil // No pending tasks
	}
	if err != nil {
		return nil, fmt.Errorf("dequeue work task: %w", err)
	}

	task.Type = domain.WorkTaskType(taskType)
	task.Status = domain.WorkTaskStatus(status)

	if callbackURL.Valid {
		task.CallbackURL = callbackURL.String
	}
	if startedAt.Valid {
		task.StartedAt = &startedAt.Time
	}
	if completedAt.Valid {
		task.CompletedAt = &completedAt.Time
	}
	if errorMsg.Valid {
		task.Error = errorMsg.String
	}

	// Parse task spec
	if len(specJSON) > 0 {
		if err := json.Unmarshal(specJSON, &task.Spec); err != nil {
			return nil, fmt.Errorf("unmarshal task spec: %w", err)
		}
	}

	// Parse result
	if len(resultJSON) > 0 {
		task.Result = &domain.WorkResult{}
		if err := json.Unmarshal(resultJSON, task.Result); err != nil {
			return nil, fmt.Errorf("unmarshal task result: %w", err)
		}
	}

	return &task, nil
}

// Complete marks a task as successfully completed with results.
func (r *WorkQueueRepository) Complete(ctx context.Context, taskID string, result *domain.WorkResult) error {
	var resultJSON []byte
	var err error

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

	res, err := r.db.ExecContext(ctx, `
		UPDATE work_queue
		SET status = 'completed', completed_at = NOW(), result = $1
		WHERE id = $2 AND status = 'running'
	`, resultJSON, taskID)
	if err != nil {
		return fmt.Errorf("complete work task: %w", err)
	}

	rows, err := res.RowsAffected()
	if err != nil {
		return fmt.Errorf("rows affected: %w", err)
	}
	if rows == 0 {
		return domain.ErrWorkTaskNotFound
	}

	return nil
}

// Fail marks a task as failed with an error message.
// Uses a single atomic UPDATE to avoid race conditions between SELECT and UPDATE.
func (r *WorkQueueRepository) Fail(ctx context.Context, taskID string, errMsg string) error {
	// Use a single atomic query that handles both retry and permanent failure cases
	result, err := r.db.ExecContext(ctx, `
		UPDATE work_queue
		SET
			status = CASE
				WHEN retry_count < max_retries THEN 'pending'
				ELSE 'failed'
			END,
			worker_id = CASE
				WHEN retry_count < max_retries THEN NULL
				ELSE worker_id
			END,
			started_at = CASE
				WHEN retry_count < max_retries THEN NULL
				ELSE started_at
			END,
			completed_at = CASE
				WHEN retry_count >= max_retries THEN NOW()
				ELSE completed_at
			END,
			retry_count = CASE
				WHEN retry_count < max_retries THEN retry_count + 1
				ELSE retry_count
			END,
			error = $1
		WHERE id = $2
	`, errMsg, taskID)

	if err != nil {
		return fmt.Errorf("fail work task: %w", err)
	}

	rows, err := result.RowsAffected()
	if err != nil {
		return fmt.Errorf("rows affected: %w", err)
	}
	if rows == 0 {
		return domain.ErrWorkTaskNotFound
	}

	return nil
}

// Cancel marks a pending task as cancelled.
func (r *WorkQueueRepository) Cancel(ctx context.Context, taskID string) error {
	result, err := r.db.ExecContext(ctx, `
		UPDATE work_queue
		SET status = 'cancelled', completed_at = NOW()
		WHERE id = $1 AND status = 'pending'
	`, taskID)
	if err != nil {
		return fmt.Errorf("cancel work task: %w", err)
	}

	rows, err := result.RowsAffected()
	if err != nil {
		return fmt.Errorf("rows affected: %w", err)
	}

	if rows == 0 {
		// Check if task exists
		var exists bool
		err := r.db.QueryRowContext(ctx, `SELECT EXISTS(SELECT 1 FROM work_queue WHERE id = $1)`, taskID).Scan(&exists)
		if err != nil {
			return fmt.Errorf("check exists: %w", err)
		}
		if !exists {
			return domain.ErrWorkTaskNotFound
		}
		return fmt.Errorf("task is not in pending state")
	}

	return nil
}