// Package processor provides the main processing logic for GDELT timestamps.
// It uses parallel processing with bounded concurrency, structural validation,
// and existential validation via HEAD probing.
package processor

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"io"
	"net/url"
	"strings"
	"sync"
	"time"

	"gdelt-engine/internal/constants"
	"gdelt-engine/internal/downloader"
	"gdelt-engine/internal/parser"
	"gdelt-engine/internal/schema"

	"go.uber.org/zap"
)

// Storage defines the interface for database operations.
type Storage interface {
	IsTimestampCompleted(ctx context.Context, timestamp string) (bool, error)
	GetTimestampStatus(ctx context.Context, timestamp string) (*schema.CompletedTimestamp, error)
	MarkTimestampStarted(ctx context.Context, timestamp string) error
	MarkTimestampCompleted(ctx context.Context, ts *schema.CompletedTimestamp) error
	GetAllTimestamps(ctx context.Context) (completed []schema.CompletedTimestamp, processing []string, err error)
	MarkURLProcessed(ctx context.Context, url *schema.ProcessedURL) error
	GetProcessedURLs(ctx context.Context, timestamp string) ([]schema.ProcessedURL, error)
	BulkInsertArticles(ctx context.Context, articles []schema.Article) (int, error)
}

// ValidationResult represents the result of timestamp validation
type ValidationResult struct {
	Timestamp string
	Valid     bool
	Reason    string
	Status    schema.ProcessingStatus
}

// Task represents a single file processing task
type Task struct {
	Timestamp string
	URL       string
	FileType  string
}

// Result represents the result of processing a single file
type Result struct {
	Task         Task
	RowCount     int
	ArticleCount int
	Duration     time.Duration
	Err          error
}

// ProcessorOption is a functional option for Processor
type ProcessorOption func(*Processor)

func WithWorkers(n int) ProcessorOption {
	return func(p *Processor) { p.workers = n }
}

func WithTimeout(t time.Duration) ProcessorOption {
	return func(p *Processor) { p.timeout = t }
}

func WithBatchSize(n int) ProcessorOption {
	return func(p *Processor) { p.batchSize = n }
}

func WithMaxParallelTimestamps(n int) ProcessorOption {
	return func(p *Processor) { p.maxParallelTimestamps = n }
}

func WithFilterThemes(themes []string) ProcessorOption {
	return func(p *Processor) { p.filterThemes = themes }
}

func WithFilterLocations(locations []string) ProcessorOption {
	return func(p *Processor) { p.filterLocations = locations }
}

// Processor handles concurrent timestamp processing
type Processor struct {
	workers               int
	timeout               time.Duration
	batchSize             int
	maxParallelTimestamps int
	downloader            *downloader.StreamingDownloader
	parser                parser.StreamParser
	storage               Storage
	logger                *zap.Logger

	// Filters - if set, only articles matching these will be saved
	filterThemes    []string // e.g., ["ECON_", "TAX_"]
	filterLocations []string // e.g., ["US", "IN"]

	// Semaphore for limiting parallel timestamps
	semaphore chan struct{}

	// Track processing state
	mu         sync.RWMutex
	processing map[string]bool
}

// NewProcessor creates a new Processor with functional options
func NewProcessor(storage Storage, logger *zap.Logger, opts ...ProcessorOption) *Processor {
	p := &Processor{
		workers:               constants.DefaultWorkers,
		timeout:               constants.DefaultTimeout,
		batchSize:             constants.DefaultBatchSize,
		maxParallelTimestamps: constants.MaxParallelTimestamps,
		storage:               storage,
		logger:                logger,
		processing:            make(map[string]bool),
	}

	for _, opt := range opts {
		opt(p)
	}

	// Initialize semaphore for parallel timestamp limit
	p.semaphore = make(chan struct{}, p.maxParallelTimestamps)

	// Initialize downloader and parser
	p.downloader = downloader.NewStreamingDownloader(
		downloader.WithLogger(logger),
	)
	p.parser = parser.NewCSVStreamParser(
		parser.WithParserLogger(logger),
	)

	return p
}

// ValidateTimestampStructural performs structural validation (cheap, deterministic).
// Checks: length, parsable, minute ∈ {00,15,30,45}, not in future.
func ValidateTimestampStructural(ts string) *ValidationResult {
	result := &ValidationResult{Timestamp: ts}

	// Check length
	if len(ts) != constants.TimestampLength {
		result.Valid = false
		result.Reason = fmt.Sprintf("invalid length: expected %d, got %d", constants.TimestampLength, len(ts))
		result.Status = schema.StatusFailed
		return result
	}

	// Parse as time
	t, err := time.Parse(constants.TimestampFormat, ts)
	if err != nil {
		result.Valid = false
		result.Reason = fmt.Sprintf("invalid format: %v", err)
		result.Status = schema.StatusFailed
		return result
	}

	// Check minute is valid GDELT interval (00, 15, 30, 45)
	m := t.Minute()
	if m%15 != 0 {
		result.Valid = false
		result.Reason = fmt.Sprintf("invalid minute %d: must be 00, 15, 30, or 45", m)
		result.Status = schema.StatusFailed
		return result
	}

	// Check not in future
	if t.After(time.Now().UTC()) {
		result.Valid = false
		result.Reason = "timestamp is in the future"
		result.Status = schema.StatusFailed
		return result
	}

	result.Valid = true
	return result
}

// isWithinGraceWindow checks if timestamp is within the grace window for recent data
func isWithinGraceWindow(ts string) bool {
	t, err := time.Parse(constants.TimestampFormat, ts)
	if err != nil {
		return false
	}
	graceTime := time.Now().UTC().Add(-time.Duration(constants.GraceWindowMinutes) * time.Minute)
	return t.After(graceTime)
}

// QueueTimestamps validates and queues timestamps for processing.
// Returns per-timestamp validation results.
func (p *Processor) QueueTimestamps(ctx context.Context, timestamps []string) (queued []string, rejected []ValidationResult) {
	p.mu.Lock()
	defer p.mu.Unlock()

	for _, ts := range timestamps {
		// Layer 1: Structural validation
		validation := ValidateTimestampStructural(ts)
		if !validation.Valid {
			rejected = append(rejected, *validation)
			p.logger.Debug("Rejected invalid timestamp",
				zap.String("timestamp", ts),
				zap.String("reason", validation.Reason),
			)
			continue
		}

		// Check if already processing
		if p.processing[ts] {
			rejected = append(rejected, ValidationResult{
				Timestamp: ts,
				Valid:     false,
				Reason:    "already processing",
				Status:    schema.StatusProcessing,
			})
			continue
		}

		// Check if already completed
		completed, err := p.storage.IsTimestampCompleted(ctx, ts)
		if err != nil {
			p.logger.Error("Failed to check timestamp status", zap.String("timestamp", ts), zap.Error(err))
			continue
		}
		if completed {
			rejected = append(rejected, ValidationResult{
				Timestamp: ts,
				Valid:     false,
				Reason:    "already completed",
				Status:    schema.StatusCompleted,
			})
			continue
		}

		// Mark as processing
		p.processing[ts] = true
		queued = append(queued, ts)
	}

	// Start background processing for queued timestamps
	if len(queued) > 0 {
		go p.processTimestampsParallel(context.Background(), queued)
	}

	return queued, rejected
}

// processTimestampsParallel processes multiple timestamps in parallel with bounded concurrency.
func (p *Processor) processTimestampsParallel(ctx context.Context, timestamps []string) {
	var wg sync.WaitGroup

	for _, ts := range timestamps {
		wg.Add(1)
		go func(timestamp string) {
			defer wg.Done()

			// Acquire semaphore (limit parallel timestamps)
			p.semaphore <- struct{}{}
			defer func() { <-p.semaphore }()

			p.processTimestamp(ctx, timestamp)
		}(ts)
	}

	wg.Wait()
}

// processTimestamp processes a single timestamp with existential validation
func (p *Processor) processTimestamp(ctx context.Context, timestamp string) {
	start := time.Now()

	p.logger.Info("Processing timestamp", zap.String("timestamp", timestamp))

	// Mark as started in database
	if err := p.storage.MarkTimestampStarted(ctx, timestamp); err != nil {
		p.logger.Error("Failed to mark timestamp started", zap.Error(err))
	}

	// Create timeout context
	ctx, cancel := context.WithTimeout(ctx, p.timeout)
	defer cancel()

	// Generate tasks for all 3 files
	tasks := p.generateTasks(timestamp)

	// Layer 2: Existential validation via HEAD probing
	// Check if at least the export file exists
	exportURL := fmt.Sprintf(constants.ExportURLTemplate, timestamp)
	headResult, err := p.downloader.HeadCheck(ctx, exportURL)

	if headResult == downloader.HeadNotFound {
		// Check if within grace window
		if isWithinGraceWindow(timestamp) {
			p.logger.Info("Timestamp not yet published, within grace window",
				zap.String("timestamp", timestamp),
			)
			p.markTimestampResult(ctx, timestamp, start, schema.StatusPending,
				"GDELT file not yet published (within grace window)", 0, 0, 0)
		} else {
			p.logger.Warn("Timestamp does not exist on GDELT",
				zap.String("timestamp", timestamp),
			)
			p.markTimestampResult(ctx, timestamp, start, schema.StatusFailed,
				"GDELT file does not exist", 0, 0, 0)
		}
		p.removeFromProcessing(timestamp)
		return
	}

	if headResult == downloader.HeadError && err != nil {
		p.logger.Error("HEAD check failed", zap.String("timestamp", timestamp), zap.Error(err))
		p.markTimestampResult(ctx, timestamp, start, schema.StatusFailed,
			fmt.Sprintf("HEAD check failed: %v", err), 0, 0, 0)
		p.removeFromProcessing(timestamp)
		return
	}

	// Process files in parallel with batching
	results := p.processFilesParallel(ctx, tasks)

	// Aggregate results
	var totalRows, totalArticles, filesProcessed int
	var lastError error

	for result := range results {
		if result.Err != nil {
			p.logger.Error("Task failed",
				zap.String("file_type", result.Task.FileType),
				zap.Error(result.Err),
			)
			lastError = result.Err
			continue
		}

		filesProcessed++
		totalRows += result.RowCount
		totalArticles += result.ArticleCount

		p.logger.Info("File processed",
			zap.String("file_type", result.Task.FileType),
			zap.Int("rows", result.RowCount),
			zap.Int("articles", result.ArticleCount),
			zap.Duration("duration", result.Duration),
		)
	}

	// Mark completion
	status := schema.StatusCompleted
	errMsg := ""
	if lastError != nil {
		status = schema.StatusFailed
		errMsg = lastError.Error()
	}

	p.markTimestampResult(ctx, timestamp, start, status, errMsg, filesProcessed, totalRows, totalArticles)
	p.removeFromProcessing(timestamp)

	p.logger.Info("Timestamp completed",
		zap.String("timestamp", timestamp),
		zap.Int("files", filesProcessed),
		zap.Int("rows", totalRows),
		zap.Int("articles", totalArticles),
		zap.Duration("duration", time.Since(start)),
	)
}

// processFilesParallel processes multiple files in parallel with batching
func (p *Processor) processFilesParallel(ctx context.Context, tasks []Task) <-chan Result {
	results := make(chan Result, len(tasks))
	var wg sync.WaitGroup

	// Process all files in parallel (limited by constants.MaxParallelFiles)
	fileSemaphore := make(chan struct{}, constants.MaxParallelFiles)

	for _, task := range tasks {
		wg.Add(1)
		go func(t Task) {
			defer wg.Done()

			// Acquire file semaphore
			fileSemaphore <- struct{}{}
			defer func() { <-fileSemaphore }()

			result := p.processTask(ctx, t)
			results <- result
		}(task)
	}

	go func() {
		wg.Wait()
		close(results)
	}()

	return results
}

// markTimestampResult saves the timestamp processing result to database
func (p *Processor) markTimestampResult(ctx context.Context, timestamp string, start time.Time,
	status schema.ProcessingStatus, errMsg string, filesProcessed, totalRows, totalArticles int) {

	completedAt := time.Now()
	ts := &schema.CompletedTimestamp{
		Timestamp:      timestamp,
		Status:         status,
		StartedAt:      start,
		CompletedAt:    &completedAt,
		FilesTotal:     constants.FilesPerTimestamp,
		FilesProcessed: filesProcessed,
		ArticlesCount:  totalArticles,
		TotalRows:      totalRows,
		DurationMs:     time.Since(start).Milliseconds(),
		Error:          errMsg,
	}

	if err := p.storage.MarkTimestampCompleted(ctx, ts); err != nil {
		p.logger.Error("Failed to mark timestamp result", zap.Error(err))
	}
}

// removeFromProcessing removes a timestamp from the processing map
func (p *Processor) removeFromProcessing(timestamp string) {
	p.mu.Lock()
	delete(p.processing, timestamp)
	p.mu.Unlock()
}

// processTask handles a single file download and processing
func (p *Processor) processTask(ctx context.Context, task Task) Result {
	start := time.Now()

	// Download stream
	reader, _, err := p.downloader.StreamDownload(ctx, task.URL)
	if err != nil {
		return Result{Task: task, Err: fmt.Errorf("download: %w", err)}
	}
	defer reader.Close()

	// Read ZIP content (required for zip.NewReader)
	zipData, err := io.ReadAll(reader)
	if err != nil {
		return Result{Task: task, Err: fmt.Errorf("read zip: %w", err)}
	}

	// Parse ZIP stream
	records := p.parser.ParseZipStream(ctx, zipData, task.FileType, task.Timestamp)

	// Collect and extract articles
	articles := make(map[string]*schema.Article)
	var rowCount int

	for result := range records {
		if result.Err != nil {
			if result.Err == context.Canceled || result.Err == context.DeadlineExceeded {
				return Result{Task: task, Err: result.Err}
			}
			continue
		}

		rowCount++

		// Extract URL based on record type
		url := p.extractURL(result.Record, task.FileType)
		if url == "" {
			continue
		}

		// Apply filters when processing GKG files (only GKG has theme/location data)
		// When filters are set and we're processing GKG, check if record matches
		if p.hasFilters() && task.FileType == constants.FileTypeGKG {
			if !p.matchesFilters(result.Record) {
				continue // Skip articles that don't match filters
			}
		} else if p.hasFilters() && task.FileType != constants.FileTypeGKG {
			// When filters are set, only process GKG (has theme/location data)
			continue
		}

		// Create or update article
		normalized := normalizeURL(url)
		if normalized == "" {
			continue
		}

		id := hashURL(normalized)
		if _, ok := articles[id]; ok {
			// Article already seen, refresh expiration time
			articles[id].ExpiresAt = time.Now().Add(time.Duration(schema.ArticleTTLDays) * 24 * time.Hour)
		} else {
			article := &schema.Article{
				ID:        id,
				URL:       url,
				ExpiresAt: time.Now().Add(time.Duration(schema.ArticleTTLDays) * 24 * time.Hour),
			}
			articles[id] = article
		}
	}

	// Save articles in batches
	articleSlice := make([]schema.Article, 0, len(articles))
	for _, a := range articles {
		articleSlice = append(articleSlice, *a)
	}

	insertedCount := 0
	if len(articleSlice) > 0 {
		inserted, err := p.storage.BulkInsertArticles(ctx, articleSlice)
		if err != nil {
			p.logger.Error("Failed to insert articles", zap.Error(err))
		}
		insertedCount = inserted
	}

	// Mark URL as processed
	processedURL := &schema.ProcessedURL{
		URL:               task.URL,
		Timestamp:         task.Timestamp,
		FileType:          task.FileType,
		Status:            schema.StatusCompleted,
		ProcessedAt:       time.Now(),
		RowCount:          rowCount,
		ArticlesExtracted: len(articles),
		DurationMs:        time.Since(start).Milliseconds(),
	}
	if err := p.storage.MarkURLProcessed(ctx, processedURL); err != nil {
		p.logger.Error("Failed to mark URL processed", zap.Error(err))
	}

	return Result{
		Task:         task,
		RowCount:     rowCount,
		ArticleCount: insertedCount,
		Duration:     time.Since(start),
	}
}

// generateTasks creates Task objects for all 3 GDELT files for a timestamp
func (p *Processor) generateTasks(timestamp string) []Task {
	return []Task{
		{Timestamp: timestamp, URL: fmt.Sprintf(constants.ExportURLTemplate, timestamp), FileType: constants.FileTypeExport},
		{Timestamp: timestamp, URL: fmt.Sprintf(constants.MentionsURLTemplate, timestamp), FileType: constants.FileTypeMentions},
		{Timestamp: timestamp, URL: fmt.Sprintf(constants.GKGURLTemplate, timestamp), FileType: constants.FileTypeGKG},
	}
}

// extractURL extracts the article URL from a parsed record
func (p *Processor) extractURL(record interface{}, fileType string) string {
	switch fileType {
	case constants.FileTypeExport:
		if event, ok := record.(*schema.Event); ok {
			return event.SourceURL
		}
	case constants.FileTypeMentions:
		if mention, ok := record.(*schema.Mention); ok {
			return mention.MentionIdentifier
		}
	case constants.FileTypeGKG:
		if gkg, ok := record.(*schema.GKG); ok {
			return gkg.DocumentIdentifier
		}
	}
	return ""
}

// hasFilters returns true if any filters are configured
func (p *Processor) hasFilters() bool {
	return len(p.filterThemes) > 0 || len(p.filterLocations) > 0
}

// matchesFilters checks if a GKG record matches the configured filters
// Returns true if record matches any theme OR location filter (OR logic)
func (p *Processor) matchesFilters(record interface{}) bool {
	gkg, ok := record.(*schema.GKG)
	if !ok {
		return false
	}

	// Check theme filters (prefix match)
	if len(p.filterThemes) > 0 {
		allThemes := append(gkg.Themes, gkg.V2Themes...)
		for _, filterTheme := range p.filterThemes {
			for _, theme := range allThemes {
				if strings.HasPrefix(strings.ToUpper(theme), strings.ToUpper(filterTheme)) {
					return true
				}
			}
		}
	}

	// Check location filters (prefix match on location string)
	if len(p.filterLocations) > 0 {
		allLocations := append(gkg.Locations, gkg.V2Locations...)
		for _, filterLoc := range p.filterLocations {
			for _, loc := range allLocations {
				if strings.HasPrefix(strings.ToUpper(loc), strings.ToUpper(filterLoc)) {
					return true
				}
			}
		}
	}

	// If themes filter is set but didn't match, and no location filter or didn't match
	return false
}

// GetTimestampStatus returns the processing status for a timestamp
func (p *Processor) GetTimestampStatus(ctx context.Context, timestamp string) (interface{}, error) {
	p.mu.RLock()
	isProcessing := p.processing[timestamp]
	p.mu.RUnlock()

	if isProcessing {
		return map[string]interface{}{
			"timestamp": timestamp,
			"status":    "processing",
		}, nil
	}

	ts, err := p.storage.GetTimestampStatus(ctx, timestamp)
	if err != nil {
		return nil, err
	}

	if ts == nil {
		return map[string]interface{}{
			"timestamp": timestamp,
			"status":    "not_found",
			"message":   "Timestamp not queued for processing",
		}, nil
	}

	return ts, nil
}

// GetAllTimestamps returns all completed and processing timestamps
func (p *Processor) GetAllTimestamps(ctx context.Context) (interface{}, error) {
	completed, processing, err := p.storage.GetAllTimestamps(ctx)
	if err != nil {
		return nil, err
	}

	p.mu.RLock()
	for ts := range p.processing {
		if !containsString(processing, ts) {
			processing = append(processing, ts)
		}
	}
	p.mu.RUnlock()

	return map[string]interface{}{
		"completed":        completed,
		"processing":       processing,
		"total_completed":  len(completed),
		"total_processing": len(processing),
	}, nil
}

// Helper functions

func normalizeURL(rawURL string) string {
	if rawURL == "" {
		return ""
	}
	u, err := url.Parse(rawURL)
	if err != nil {
		return ""
	}
	if u.Scheme == "" {
		u.Scheme = "http"
	}
	u.Host = strings.ToLower(u.Host)
	u.Host = strings.TrimPrefix(u.Host, "www.")
	q := u.Query()
	for _, param := range constants.TrackingParams {
		q.Del(param)
	}
	u.RawQuery = q.Encode()
	u.Fragment = ""
	u.Path = strings.TrimSuffix(u.Path, "/")
	return u.String()
}

func hashURL(normalizedURL string) string {
	hash := sha256.Sum256([]byte(normalizedURL))
	return hex.EncodeToString(hash[:])
}

func contains(slice []string, item string) bool {
	for _, s := range slice {
		if s == item {
			return true
		}
	}
	return false
}

func containsString(slice []string, item string) bool {
	return contains(slice, item)
}

func mergeUnique(a, b []string) []string {
	seen := make(map[string]bool)
	for _, s := range a {
		seen[s] = true
	}
	for _, s := range b {
		if !seen[s] {
			a = append(a, s)
			seen[s] = true
		}
	}
	return a
}

// ValidateTimestamp is exported for use by API handlers
func ValidateTimestamp(timestamp string) error {
	result := ValidateTimestampStructural(timestamp)
	if !result.Valid {
		return fmt.Errorf(result.Reason)
	}
	return nil
}