package sync

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"sort"
	"strconv"
	"strings"
	"time"

	"git.jnss.me/joakim/opal/internal/engine"
	"github.com/google/uuid"
)

// Client represents a sync client for communicating with the API server
type Client struct {
	baseURL    string
	apiKey     string
	httpClient *http.Client
	clientID   string
}

// NewClient creates a new sync client
func NewClient(baseURL, apiKey, clientID string) *Client {
	return &Client{
		baseURL:    baseURL,
		apiKey:     apiKey,
		clientID:   clientID,
		httpClient: &http.Client{Timeout: 30 * time.Second},
	}
}

// testConnection checks if the server is reachable
func (c *Client) testConnection() bool {
	req, err := http.NewRequest("GET", c.baseURL+"/health", nil)
	if err != nil {
		return false
	}

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return false
	}
	defer resp.Body.Close()

	return resp.StatusCode == 200
}

// PullChanges retrieves changes from server since a given timestamp
func (c *Client) PullChanges(since int64) ([]ChangeLogEntry, error) {
	reqBody := map[string]interface{}{
		"since":     since,
		"client_id": c.clientID,
	}

	bodyBytes, err := json.Marshal(reqBody)
	if err != nil {
		return nil, fmt.Errorf("failed to marshal request: %w", err)
	}

	req, err := http.NewRequest("POST", c.baseURL+"/sync/changes", bytes.NewReader(bodyBytes))
	if err != nil {
		return nil, fmt.Errorf("failed to create request: %w", err)
	}

	req.Header.Set("Authorization", "Bearer "+c.apiKey)
	req.Header.Set("Content-Type", "application/json")

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("failed to send request: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != 200 {
		body, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("server returned %d: %s", resp.StatusCode, string(body))
	}

	var result struct {
		Success bool             `json:"success"`
		Data    []ChangeLogEntry `json:"data"`
		Error   string           `json:"error"`
	}

	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
		return nil, fmt.Errorf("failed to decode response: %w", err)
	}

	if !result.Success {
		return nil, fmt.Errorf("server error: %s", result.Error)
	}

	return result.Data, nil
}

// PushChanges sends local changes to the server
func (c *Client) PushChanges(tasks []*engine.Task) error {
	// Convert tasks to JSON
	var taskData []json.RawMessage
	for _, task := range tasks {
		data, err := json.Marshal(task)
		if err != nil {
			continue
		}
		taskData = append(taskData, data)
	}

	reqBody := map[string]interface{}{
		"tasks":     taskData,
		"client_id": c.clientID,
	}

	bodyBytes, err := json.Marshal(reqBody)
	if err != nil {
		return fmt.Errorf("failed to marshal request: %w", err)
	}

	req, err := http.NewRequest("POST", c.baseURL+"/sync/push", bytes.NewReader(bodyBytes))
	if err != nil {
		return fmt.Errorf("failed to create request: %w", err)
	}

	req.Header.Set("Authorization", "Bearer "+c.apiKey)
	req.Header.Set("Content-Type", "application/json")

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("failed to send request: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != 200 {
		body, _ := io.ReadAll(resp.Body)
		return fmt.Errorf("server returned %d: %s", resp.StatusCode, string(body))
	}

	return nil
}

// ChangeLogEntry represents a change from the server
type ChangeLogEntry struct {
	ID         int64  `json:"id"`
	TaskUUID   string `json:"task_uuid"`
	ChangeType string `json:"change_type"`
	ChangedAt  int64  `json:"changed_at"`
	Data       string `json:"data"`
}

// Sync performs a full bidirectional sync
func (c *Client) Sync(strategy ConflictResolution) (*SyncResult, error) {
	result := &SyncResult{}

	// Check if we have a queue with pending changes
	queue, err := NewQueue()
	if err != nil {
		return nil, fmt.Errorf("failed to load queue: %w", err)
	}

	// Test connection
	if !c.testConnection() {
		// Server offline - queue changes if any
		cfg, _ := engine.GetConfig()
		if cfg != nil && cfg.SyncQueueOffline {
			// Get local changes and queue them
			localChanges, _ := c.getLocalChanges(0)
			if len(localChanges) > 0 {
				_ = QueueLocalChanges(localChanges)
				result.QueuedOffline = len(localChanges)
			}
			result.QueuedOffline += queue.Size()
			return result, nil
		}
		return nil, fmt.Errorf("server unreachable")
	}

	// Server is online - process queue first if it has items
	if queue.Size() > 0 {
		if err := c.pushQueuedChanges(queue.GetPending()); err != nil {
			return nil, fmt.Errorf("failed to push queued changes: %w", err)
		}
		result.Pushed = queue.Size()
		queue.Clear()
	}

	// Get last sync time
	lastSync := c.getLastSyncTime()

	// Pull changes from server
	changes, err := c.PullChanges(lastSync)
	if err != nil {
		return nil, fmt.Errorf("failed to pull changes: %w", err)
	}

	// Convert changes to tasks
	remoteTasks, err := c.parseChanges(changes)
	if err != nil {
		return nil, fmt.Errorf("failed to parse changes: %w", err)
	}

	// Sort: parent tasks before children (ensures parent exists when child is saved)
	sort.Slice(remoteTasks, func(i, j int) bool {
		// Tasks without ParentUUID come first
		iHasParent := remoteTasks[i].ParentUUID != nil
		jHasParent := remoteTasks[j].ParentUUID != nil

		if !iHasParent && jHasParent {
			return true // i (no parent) before j (has parent)
		}
		if iHasParent && !jHasParent {
			return false // j (no parent) before i (has parent)
		}
		return false // maintain original order
	})

	result.Pulled = len(remoteTasks)

	// Get local changes since last sync
	localChanges, err := c.getLocalChanges(lastSync)
	if err != nil {
		return nil, fmt.Errorf("failed to get local changes: %w", err)
	}

	// Merge
	merged, conflicts, err := MergeTasks(localChanges, remoteTasks, strategy)
	if err != nil {
		return nil, fmt.Errorf("failed to merge tasks: %w", err)
	}

	result.ConflictsResolved = conflicts

	// Apply merged tasks locally
	for _, task := range merged {
		if err := task.Save(); err != nil {
			result.Errors = append(result.Errors, fmt.Sprintf("failed to save task %s: %v", task.UUID, err))
			continue
		}

		// Reload task to ensure we have the database ID
		savedTask, err := engine.GetTask(task.UUID)
		if err != nil {
			result.Errors = append(result.Errors, fmt.Sprintf("failed to reload task %s: %v", task.UUID, err))
			continue
		}

		// Sync tags: task.Tags contains the desired tag list (from parsing or local)
		// Get current tags from database
		currentTags, _ := savedTask.GetTags()

		// Build sets for comparison
		currentSet := make(map[string]bool)
		for _, tag := range currentTags {
			currentSet[tag] = true
		}
		desiredSet := make(map[string]bool)
		for _, tag := range task.Tags {
			desiredSet[tag] = true
		}

		// Remove tags no longer present
		for tag := range currentSet {
			if !desiredSet[tag] {
				savedTask.RemoveTag(tag)
			}
		}

		// Add new tags
		for tag := range desiredSet {
			if !currentSet[tag] {
				savedTask.AddTag(tag)
			}
		}
	}

	// Push local changes to server
	if len(localChanges) > 0 {
		if err := c.PushChanges(localChanges); err != nil {
			result.Errors = append(result.Errors, fmt.Sprintf("failed to push changes: %v", err))
		} else {
			result.Pushed += len(localChanges)
		}
	}

	// Update last sync time
	c.updateLastSyncTime(time.Now().Unix())

	return result, nil
}

// getLastSyncTime retrieves the last sync timestamp from database
func (c *Client) getLastSyncTime() int64 {
	db := engine.GetDB()
	if db == nil {
		return 0
	}

	var lastSync int64
	err := db.QueryRow("SELECT last_sync FROM sync_state WHERE client_id = ?", c.clientID).Scan(&lastSync)
	if err != nil {
		return 0
	}

	return lastSync
}

// updateLastSyncTime updates the last sync timestamp
func (c *Client) updateLastSyncTime(timestamp int64) {
	db := engine.GetDB()
	if db == nil {
		return
	}

	_, _ = db.Exec(`
		INSERT OR REPLACE INTO sync_state (client_id, last_sync, last_change_id)
		VALUES (?, ?, 0)
	`, c.clientID, timestamp)
}

// getLocalChanges retrieves local changes since a timestamp
func (c *Client) getLocalChanges(since int64) ([]*engine.Task, error) {
	db := engine.GetDB()
	if db == nil {
		return nil, fmt.Errorf("database not initialized")
	}

	rows, err := db.Query(`
		SELECT DISTINCT task_uuid
		FROM change_log
		WHERE changed_at > ?
		ORDER BY changed_at ASC
	`, since)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var tasks []*engine.Task
	for rows.Next() {
		var uuidStr string
		if err := rows.Scan(&uuidStr); err != nil {
			continue
		}

		taskUUID, err := uuid.Parse(uuidStr)
		if err != nil {
			continue
		}

		task, err := engine.GetTask(taskUUID)
		if err != nil {
			continue
		}

		tasks = append(tasks, task)
	}

	return tasks, nil
}

// parseChanges converts change log entries to tasks
func (c *Client) parseChanges(changes []ChangeLogEntry) ([]*engine.Task, error) {
	// Sort changes by timestamp (primary) and ID (secondary) to ensure correct order
	// This handles same-second updates (e.g., CREATE followed by UPDATE with tags)
	sort.Slice(changes, func(i, j int) bool {
		if changes[i].ChangedAt != changes[j].ChangedAt {
			return changes[i].ChangedAt < changes[j].ChangedAt
		}
		// Same timestamp: use ID as tiebreaker (higher ID = later change)
		return changes[i].ID < changes[j].ID
	})

	// Group changes by UUID - last one wins (latest by timestamp+ID)
	taskMap := make(map[string]ChangeLogEntry)

	for _, change := range changes {
		// Since changes are sorted, we can simply overwrite
		// (later entries will overwrite earlier ones)
		taskMap[change.TaskUUID] = change
	}

	// Parse tasks from change data (key:value format)
	var tasks []*engine.Task

	for uuidStr, change := range taskMap {
		// Handle deletions
		if change.ChangeType == "delete" {
			taskUUID, err := uuid.Parse(uuidStr)
			if err != nil {
				continue
			}

			// Delete locally if exists
			if task, err := engine.GetTask(taskUUID); err == nil {
				task.Delete(false) // Soft delete
			}
			continue
		}

		// Parse the key:value data
		fields, err := engine.ParseKeyValueFormat(change.Data, false) // no comments in change log
		if err != nil {
			fmt.Fprintf(os.Stderr, "Warning: skipping task %s - failed to parse change data: %v\n", uuidStr, err)
			continue
		}

		// Get or create task
		taskUUID, err := uuid.Parse(uuidStr)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Warning: skipping task - invalid UUID %s: %v\n", uuidStr, err)
			continue
		}

		task, err := engine.GetTask(taskUUID)
		if err != nil {
			// Task doesn't exist locally - create new
			task = &engine.Task{
				UUID: taskUUID,
				Tags: []string{},
			}
		}

		// Apply parsed change data to task
		if err := applyChangeDataToTask(task, fields); err != nil {
			fmt.Fprintf(os.Stderr, "Warning: skipping task %s - failed to apply changes: %v\n", uuidStr, err)
			continue
		}

		tasks = append(tasks, task)
	}

	return tasks, nil
}

// applyChangeDataToTask applies parsed change log data to a task
// Expects fields from ParseKeyValueFormat with sync data (Unix timestamps, etc.)
func applyChangeDataToTask(task *engine.Task, fields map[string]string) error {
	// UUID (required)
	if uuidStr, ok := fields["uuid"]; ok && uuidStr != "" {
		parsed, err := uuid.Parse(uuidStr)
		if err != nil {
			return fmt.Errorf("invalid uuid '%s': %w", uuidStr, err)
		}
		task.UUID = parsed
	}

	// Description (required, non-empty)
	if desc, ok := fields["description"]; ok {
		if strings.TrimSpace(desc) == "" {
			return fmt.Errorf("description cannot be empty")
		}
		task.Description = desc
	}

	// Status
	if statusStr, ok := fields["status"]; ok && statusStr != "" {
		task.Status = parseStatusFromChangeLog(statusStr)
	}

	// Priority
	if priStr, ok := fields["priority"]; ok && priStr != "" {
		task.Priority = parsePriorityFromChangeLog(priStr)
	}

	// Project (nullable)
	if proj, ok := fields["project"]; ok {
		if proj == "" {
			task.Project = nil
		} else {
			task.Project = &proj
		}
	}

	// Created timestamp
	if createdStr, ok := fields["created"]; ok && createdStr != "" {
		ts, err := strconv.ParseInt(createdStr, 10, 64)
		if err != nil {
			return fmt.Errorf("invalid created timestamp '%s': %w", createdStr, err)
		}
		task.Created = time.Unix(ts, 0)
	}

	// Modified timestamp
	if modStr, ok := fields["modified"]; ok && modStr != "" {
		ts, err := strconv.ParseInt(modStr, 10, 64)
		if err != nil {
			return fmt.Errorf("invalid modified timestamp '%s': %w", modStr, err)
		}
		task.Modified = time.Unix(ts, 0)
	}

	// Date fields (nullable Unix timestamps)
	dateFields := map[string]**time.Time{
		"start":     &task.Start,
		"end":       &task.End,
		"due":       &task.Due,
		"scheduled": &task.Scheduled,
		"wait":      &task.Wait,
		"until":     &task.Until,
	}

	for fieldName, taskField := range dateFields {
		if dateStr, ok := fields[fieldName]; ok {
			if dateStr == "" {
				*taskField = nil
			} else {
				ts, err := strconv.ParseInt(dateStr, 10, 64)
				if err != nil {
					return fmt.Errorf("invalid %s timestamp '%s': %w", fieldName, dateStr, err)
				}
				t := time.Unix(ts, 0)
				*taskField = &t
			}
		}
	}

	// Recurrence duration (nullable, int64 nanoseconds)
	if recurStr, ok := fields["recurrence"]; ok {
		if recurStr == "" {
			task.RecurrenceDuration = nil
		} else {
			nanos, err := strconv.ParseInt(recurStr, 10, 64)
			if err != nil {
				return fmt.Errorf("invalid recurrence '%s': %w", recurStr, err)
			}
			// Validate: not negative, not unreasonably large (max 100 years)
			if nanos < 0 {
				return fmt.Errorf("recurrence cannot be negative: %d", nanos)
			}
			maxNanos := int64(time.Hour * 24 * 365 * 100)
			if nanos > maxNanos {
				return fmt.Errorf("recurrence too large (max 100 years): %d", nanos)
			}
			duration := time.Duration(nanos)
			task.RecurrenceDuration = &duration
		}
	}

	// Parent UUID (nullable)
	if parentStr, ok := fields["parent_uuid"]; ok {
		if parentStr == "" {
			task.ParentUUID = nil
		} else {
			parsed, err := uuid.Parse(parentStr)
			if err != nil {
				return fmt.Errorf("invalid parent_uuid '%s': %w", parentStr, err)
			}
			task.ParentUUID = &parsed
		}
	}

	// Tags (comma-separated, sorted)
	if tagsStr, ok := fields["tags"]; ok {
		task.Tags = parseTagsFromChangeLog(tagsStr)
	}

	return nil
}

// parseStatusFromChangeLog parses status from change log string
func parseStatusFromChangeLog(s string) engine.Status {
	switch s {
	case "pending":
		return engine.StatusPending
	case "completed":
		return engine.StatusCompleted
	case "deleted":
		return engine.StatusDeleted
	case "recurring":
		return engine.StatusRecurring
	default:
		return engine.StatusPending
	}
}

// parsePriorityFromChangeLog parses priority from change log string
func parsePriorityFromChangeLog(s string) engine.Priority {
	switch s {
	case "L":
		return engine.PriorityLow
	case "D":
		return engine.PriorityDefault
	case "M":
		return engine.PriorityMedium
	case "H":
		return engine.PriorityHigh
	default:
		return engine.PriorityDefault
	}
}

// parseTagsFromChangeLog parses and sorts tags from change log
func parseTagsFromChangeLog(s string) []string {
	if s == "" {
		return []string{}
	}
	parts := strings.Split(s, ",")
	tags := make([]string, 0, len(parts))
	for _, tag := range parts {
		tag = strings.TrimSpace(tag)
		if tag != "" {
			tags = append(tags, tag)
		}
	}
	sort.Strings(tags) // Sort alphabetically for consistency
	return tags
}

// pushQueuedChanges sends queued changes to server
func (c *Client) pushQueuedChanges(changes []QueuedChange) error {
	var tasks []*engine.Task

	for _, change := range changes {
		var task engine.Task
		if err := json.Unmarshal(change.Data, &task); err != nil {
			continue
		}
		tasks = append(tasks, &task)
	}

	return c.PushChanges(tasks)
}

// SyncResult represents the result of a sync operation
type SyncResult struct {
	Pulled            int
	Pushed            int
	ConflictsResolved int
	QueuedOffline     int
	Errors            []string
}

// Display prints the sync result
func (r *SyncResult) Display() {
	if r.QueuedOffline > 0 {
		fmt.Printf("⚠️  Server unreachable. %d changes queued.\n", r.QueuedOffline)
		return
	}

	fmt.Println("✓ Sync completed")
	if r.Pulled > 0 {
		fmt.Printf("  ↓ Pulled %d changes from server\n", r.Pulled)
	}
	if r.Pushed > 0 {
		fmt.Printf("  ↑ Pushed %d changes to server\n", r.Pushed)
	}
	if r.ConflictsResolved > 0 {
		fmt.Printf("  ⚠️  Auto-resolved %d conflicts (last-write-wins)\n", r.ConflictsResolved)
		fmt.Println("     Run 'opal sync log' to see details")
	}
	if len(r.Errors) > 0 {
		fmt.Println("  ✗ Errors:")
		for _, err := range r.Errors {
			fmt.Printf("    - %s\n", err)
		}
	}
}