package handlers

import (
	"errors"
	"net/http"
	"strings"
	"time"

	"github.com/celestia-trace/backend/models"
	"github.com/gin-gonic/gin"
	"gorm.io/gorm"
)

type SessionHandler struct {
	DB *gorm.DB
}

func sessionPreloads(db *gorm.DB) *gorm.DB {
	return db.Preload("Events", func(events *gorm.DB) *gorm.DB {
		return events.Order("relative_time_ms asc")
	}).Preload("Assets")
}

// GetSessions supports cursor-like incremental pulls with updatedAfter and can
// include deletion tombstones for multi-device reconciliation.
func (h *SessionHandler) GetSessions(c *gin.Context) {
	userID := c.GetString("userID")
	query := sessionPreloads(h.DB).Where("user_id = ?", userID)
	if c.Query("includeDeleted") != "true" {
		query = query.Where("deleted_at IS NULL")
	}
	if search := c.Query("search"); search != "" {
		query = query.Where("title ILIKE ?", "%"+search+"%")
	}
	if value := c.Query("updatedAfter"); value != "" {
		updatedAfter, err := time.Parse(time.RFC3339Nano, value)
		if err != nil {
			respondError(c, http.StatusBadRequest, 400, "invalid updatedAfter timestamp")
			return
		}
		query = query.Where("updated_at > ?", updatedAfter)
	}
	var sessions []models.CelestiaSession
	if err := query.Order("updated_at asc, id asc").Find(&sessions).Error; err != nil {
		respondError(c, http.StatusInternalServerError, 500, "failed to query field records")
		return
	}
	respondSuccess(c, sessions)
}

func (h *SessionHandler) GetSessionDetail(c *gin.Context) {
	userID := c.GetString("userID")
	var session models.CelestiaSession
	if err := sessionPreloads(h.DB).
		Where("id = ? AND user_id = ? AND deleted_at IS NULL", c.Param("id"), userID).
		First(&session).Error; err != nil {
		respondError(c, http.StatusNotFound, 404, "record not found")
		return
	}
	respondSuccess(c, session)
}

// CreateSession is an idempotent upsert keyed by (user_id, client_id).
func (h *SessionHandler) CreateSession(c *gin.Context) {
	userID := c.GetString("userID")
	var req models.CreateSessionRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		respondError(c, http.StatusBadRequest, 400, "invalid input data")
		return
	}

	var session models.CelestiaSession
	var conflictRevision int64
	var isConflict bool
	err := h.DB.Transaction(func(tx *gorm.DB) error {
		err := tx.Where("user_id = ? AND client_id = ?", userID, req.ClientID).First(&session).Error
		if errors.Is(err, gorm.ErrRecordNotFound) {
			clientID := req.ClientID
			session = models.CelestiaSession{
				UserID: userID, ClientID: &clientID, Revision: 1,
			}
		} else if err != nil {
			return err
		} else {
			// Optimistic locking: reject if client baseRevision doesn't match
			if req.BaseRevision != nil && *req.BaseRevision != session.Revision {
				conflictRevision = session.Revision
				isConflict = true
				return nil // exit transaction without error; handled below
			}
			session.Revision++
		}

		session.Title = req.Title
		session.StartTime = req.StartTime
		session.EndTime = req.EndTime
		session.DurationMs = req.DurationMs
		session.LocalAudioPath = ""
		session.IsSynced = true
		session.DeletedAt = nil
		session.PhotoCount, session.NoteCount = countEvents(req.Events)
		if session.ID == "" {
			if err := tx.Create(&session).Error; err != nil {
				return err
			}
		} else if err := tx.Save(&session).Error; err != nil {
			return err
		}

		for _, input := range req.Events {
			var event models.TimelineEvent
			err := tx.Where("session_id = ? AND client_id = ?", session.ID, input.ClientID).First(&event).Error
			if errors.Is(err, gorm.ErrRecordNotFound) {
				clientID := input.ClientID
				event = models.TimelineEvent{SessionID: session.ID, ClientID: &clientID}
			} else if err != nil {
				return err
			}
			event.RelativeTimeMs = input.RelativeTimeMs
			event.EventType = input.EventType
			event.TextContent = input.TextContent
			event.LocalFilePath = ""
			event.VoiceStartOffsetMs = input.VoiceStartOffsetMs
			event.VoiceEndOffsetMs = input.VoiceEndOffsetMs
			event.LocationName = input.LocationName
			event.LocationAddress = input.LocationAddress
			event.Latitude = input.Latitude
			event.Longitude = input.Longitude
			if event.ID == "" {
				if err := tx.Create(&event).Error; err != nil {
					return err
				}
			} else if err := tx.Save(&event).Error; err != nil {
				return err
			}
		}

		// Delete events that were removed on the client
		if len(req.DeletedEventClientIds) > 0 {
			if err := tx.Where("session_id = ? AND client_id IN ?", session.ID, req.DeletedEventClientIds).
				Delete(&models.TimelineEvent{}).Error; err != nil {
				return err
			}
			// Recalculate counts from the remaining DB events
			var remaining []models.TimelineEvent
			if err := tx.Where("session_id = ?", session.ID).Find(&remaining).Error; err != nil {
				return err
			}
			session.PhotoCount, session.NoteCount = countPersistedEvents(remaining)
			if err := tx.Save(&session).Error; err != nil {
				return err
			}
		}

		return nil
	})
	if isConflict {
		c.JSON(http.StatusConflict, gin.H{
			"code": 409, "message": "version conflict",
			"data": gin.H{"serverRevision": conflictRevision},
		})
		return
	}
	if err != nil {
		respondError(c, http.StatusInternalServerError, 500, "failed to save record")
		return
	}
	if err := sessionPreloads(h.DB).First(&session, "id = ?", session.ID).Error; err != nil {
		respondError(c, http.StatusInternalServerError, 500, "failed to reload record")
		return
	}
	respondSuccess(c, session)
}

func countEvents(events []models.CreateEventSubSchema) (photoCount, noteCount int) {
	for _, event := range events {
		switch event.EventType {
		case "PHOTO":
			photoCount++
		case "NOTE":
			noteCount++
		case "MARKER":
			// Exclude continuation markers (e.g. "续录时间：...") from note count
			if !strings.HasPrefix(event.TextContent, "续录时间：") {
				noteCount++
			}
		case "CONTINUATION":
			// Dedicated continuation type, not counted as a note
		}
	}
	return
}

// countPersistedEvents recalculates counts from persisted TimelineEvent rows
// (used after event deletion to keep counts accurate).
func countPersistedEvents(events []models.TimelineEvent) (photoCount, noteCount int) {
	for _, event := range events {
		switch event.EventType {
		case "PHOTO":
			photoCount++
		case "NOTE":
			noteCount++
		case "MARKER":
			if !strings.HasPrefix(event.TextContent, "续录时间：") {
				noteCount++
			}
		case "CONTINUATION":
			// Not counted
		}
	}
	return
}

func (h *SessionHandler) AddEventToSession(c *gin.Context) {
	userID := c.GetString("userID")
	sessionID := c.Param("id")
	var session models.CelestiaSession
	if err := h.DB.Where("id = ? AND user_id = ? AND deleted_at IS NULL", sessionID, userID).First(&session).Error; err != nil {
		respondError(c, http.StatusNotFound, 404, "record not found")
		return
	}
	var req models.CreateEventRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		respondError(c, http.StatusBadRequest, 400, "invalid event payload")
		return
	}
	clientID := req.ClientID
	event := models.TimelineEvent{
		SessionID: session.ID, ClientID: &clientID,
		RelativeTimeMs: req.RelativeTimeMs, EventType: req.EventType,
		TextContent: req.TextContent, VoiceStartOffsetMs: req.VoiceStartOffsetMs,
		VoiceEndOffsetMs: req.VoiceEndOffsetMs,
		LocationName:     req.LocationName, LocationAddress: req.LocationAddress,
		Latitude: req.Latitude, Longitude: req.Longitude,
	}
	if err := h.DB.Where("session_id = ? AND client_id = ?", session.ID, req.ClientID).
		Assign(event).FirstOrCreate(&event).Error; err != nil {
		respondError(c, http.StatusInternalServerError, 500, "failed to add event")
		return
	}
	h.DB.Model(&session).Updates(map[string]interface{}{"revision": gorm.Expr("revision + 1")})
	respondSuccess(c, event)
}

// DeleteSession creates a tombstone rather than hard deleting cloud data.
func (h *SessionHandler) DeleteSession(c *gin.Context) {
	userID := c.GetString("userID")
	sessionID := c.Param("id")
	now := time.Now().UTC()
	result := h.DB.Model(&models.CelestiaSession{}).
		Where("id = ? AND user_id = ? AND deleted_at IS NULL", sessionID, userID).
		Updates(map[string]interface{}{"deleted_at": &now, "revision": gorm.Expr("revision + 1")})
	if result.Error != nil {
		respondError(c, http.StatusInternalServerError, 500, "failed to delete record")
		return
	}
	if result.RowsAffected == 0 {
		respondError(c, http.StatusNotFound, 404, "record not found")
		return
	}
	respondSuccess(c, gin.H{"deletedId": sessionID, "deletedAt": now})
}