package controllers

import (
	"crypto/md5"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"hr_receiver/config"
	"hr_receiver/models"
	"io"
	"mime/multipart"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
	"gorm.io/gorm"
)

const (
	lessonPlanMaxSize     = 10 * 1024 * 1024
	lessonPlanStorageDir  = "storage/lesson_plans"
	lessonPlanFieldName   = "file"
	lessonPlanCleanupDays = 30
	shareCodeExpiry       = 5 * time.Minute
	shareCodeDigits       = 6
)

type LessonPlanController struct {
	DB *gorm.DB
}

type lessonPlanPaginationParams struct {
	PageNum  int `form:"pageNum,default=1"`
	PageSize int `form:"pageSize,default=10"`
}

type lessonPlanShareCodeResponse struct {
	Code      string `json:"code"`
	ExpiresAt int64  `json:"expiresAt"`
	FileID    uint   `json:"fileId"`
}

func NewLessonPlanController() *LessonPlanController {
	return &LessonPlanController{DB: config.DB}
}

func (lc *LessonPlanController) Upload(c *gin.Context) {
	fileHeader, err := c.FormFile(lessonPlanFieldName)
	if err != nil {
		writeError(c, http.StatusBadRequest, "missing file")
		return
	}
	if err := validateLessonPlanFileHeader(fileHeader); err != nil {
		writeError(c, http.StatusBadRequest, err.Error())
		return
	}

	uploaderID, uploaderName, ok := currentUser(c)
	if !ok {
		writeError(c, http.StatusUnauthorized, "invalid user context")
		return
	}

	src, err := fileHeader.Open()
	if err != nil {
		writeError(c, http.StatusInternalServerError, "failed to open upload")
		return
	}
	defer src.Close()

	if err := os.MkdirAll(lessonPlanStorageDir, 0o755); err != nil {
		writeError(c, http.StatusInternalServerError, "failed to initialize storage")
		return
	}

	tempFile, err := os.CreateTemp(lessonPlanStorageDir, "upload-*.docx")
	if err != nil {
		writeError(c, http.StatusInternalServerError, "failed to create temp file")
		return
	}
	tempPath := tempFile.Name()
	tempClosed := false
	defer func() {
		if !tempClosed {
			_ = tempFile.Close()
		}
		if _, statErr := os.Stat(tempPath); statErr == nil {
			_ = os.Remove(tempPath)
		}
	}()

	hasher := md5.New()
	size, err := io.Copy(io.MultiWriter(tempFile, hasher), src)
	if err != nil {
		writeError(c, http.StatusInternalServerError, "failed to save upload")
		return
	}
	if size > lessonPlanMaxSize {
		writeError(c, http.StatusBadRequest, "file exceeds 10MB limit")
		return
	}

	md5Value := hex.EncodeToString(hasher.Sum(nil))
	var existing models.AppFile
	if err := lc.DB.Where("md5 = ? AND file_type = ?", md5Value, models.AppFileTypeLessonPlan).First(&existing).Error; err == nil {
		writeSuccess(c, http.StatusConflict, "duplicate file", existing)
		return
	} else if !errors.Is(err, gorm.ErrRecordNotFound) {
		writeError(c, http.StatusInternalServerError, "failed to check duplicate file")
		return
	}

	storedFilename := buildStoredLessonPlanFilename(md5Value, fileHeader.Filename)
	finalPath := filepath.Join(lessonPlanStorageDir, storedFilename)
	if err := tempFile.Close(); err != nil {
		writeError(c, http.StatusInternalServerError, "failed to finalize upload")
		return
	}
	tempClosed = true
	if err := os.Rename(tempPath, finalPath); err != nil {
		writeError(c, http.StatusInternalServerError, "failed to finalize upload")
		return
	}

	record := models.AppFile{
		FileType:         models.AppFileTypeLessonPlan,
		OriginalFilename: fileHeader.Filename,
		StoredFilename:   storedFilename,
		FilePath:         finalPath,
		ContentType:      normalizeLessonPlanContentType(fileHeader.Header.Get("Content-Type")),
		FileSize:         size,
		MD5:              md5Value,
		UploaderID:       uploaderID,
		UploaderName:     uploaderName,
	}

	if err := lc.DB.Create(&record).Error; err != nil {
		_ = os.Remove(finalPath)
		writeError(c, http.StatusInternalServerError, "failed to persist file metadata")
		return
	}

	writeSuccess(c, http.StatusCreated, "upload success", record)
}

func (lc *LessonPlanController) List(c *gin.Context) {
	var records []models.AppFile
	if err := lc.DB.Where("file_type = ?", models.AppFileTypeLessonPlan).Order("created_at DESC").Find(&records).Error; err != nil {
		writeError(c, http.StatusInternalServerError, "failed to list lesson plans")
		return
	}
	writeSuccess(c, http.StatusOK, "query success", records)
}

func (lc *LessonPlanController) Page(c *gin.Context) {
	var params lessonPlanPaginationParams
	if err := c.ShouldBindQuery(&params); err != nil {
		writeError(c, http.StatusBadRequest, err.Error())
		return
	}
	if params.PageNum < 1 {
		params.PageNum = 1
	}
	if params.PageSize < 1 || params.PageSize > 100 {
		params.PageSize = 10
	}
	offset := (params.PageNum - 1) * params.PageSize

	var total int64
	var records []models.AppFile
	query := lc.DB.Model(&models.AppFile{}).Where("file_type = ?", models.AppFileTypeLessonPlan)
	if err := query.Count(&total).Error; err != nil {
		writeError(c, http.StatusInternalServerError, "failed to count lesson plans")
		return
	}
	if err := query.Order("created_at DESC").Offset(offset).Limit(params.PageSize).Find(&records).Error; err != nil {
		writeError(c, http.StatusInternalServerError, "failed to query lesson plans")
		return
	}

	writeSuccess(c, http.StatusOK, "query success", gin.H{
		"list": records,
		"pagination": gin.H{
			"currentPage": params.PageNum,
			"pageSize":    params.PageSize,
			"totalList":   total,
			"totalPage":   int((total + int64(params.PageSize) - 1) / int64(params.PageSize)),
		},
	})
}

func (lc *LessonPlanController) Download(c *gin.Context) {
	record, err := lc.findLessonPlan(c.Param("id"))
	if err != nil {
		respondLessonPlanLookupError(c, err)
		return
	}

	userID, _, ok := currentUser(c)
	if !ok {
		writeError(c, http.StatusUnauthorized, "invalid user context")
		return
	}
	role := currentUserRole(c)
	if !canAccessLessonPlan(record, userID, role) {
		writeError(c, http.StatusForbidden, "permission denied")
		return
	}

	now := time.Now().UnixMilli()
	if err := lc.DB.Model(&models.AppFile{}).
		Where("id = ?", record.ID).
		Updates(map[string]interface{}{
			"download_count":   gorm.Expr("download_count + 1"),
			"last_download_at": now,
		}).Error; err != nil {
		writeError(c, http.StatusInternalServerError, "failed to update download stats")
		return
	}

	c.FileAttachment(record.FilePath, record.OriginalFilename)
}

func (lc *LessonPlanController) GenerateShareCode(c *gin.Context) {
	record, err := lc.findLessonPlan(c.Param("id"))
	if err != nil {
		respondLessonPlanLookupError(c, err)
		return
	}

	userID, username, ok := currentUser(c)
	if !ok {
		writeError(c, http.StatusUnauthorized, "invalid user context")
		return
	}
	role := currentUserRole(c)
	if !canAccessLessonPlan(record, userID, role) {
		writeError(c, http.StatusForbidden, "permission denied")
		return
	}

	now := time.Now()
	expiresAt := now.Add(shareCodeExpiry).UnixMilli()
	var created models.AppFileShareCode

	if err := lc.DB.Transaction(func(tx *gorm.DB) error {
		if err := tx.Model(&models.AppFileShareCode{}).
			Where("app_file_id = ? AND is_active = ?", record.ID, true).
			Update("is_active", false).Error; err != nil {
			return err
		}

		shareCode, err := generateUniqueShareCode(tx, now.UnixMilli())
		if err != nil {
			return err
		}

		created = models.AppFileShareCode{
			AppFileID:       record.ID,
			ShareCode:       shareCode,
			GeneratedByID:   userID,
			GeneratedByName: username,
			ExpiresAt:       expiresAt,
			IsActive:        true,
		}
		return tx.Create(&created).Error
	}); err != nil {
		writeError(c, http.StatusInternalServerError, "failed to generate share code")
		return
	}

	writeSuccess(c, http.StatusOK, "share code generated", lessonPlanShareCodeResponse{
		Code:      created.ShareCode,
		ExpiresAt: created.ExpiresAt,
		FileID:    record.ID,
	})
}

func (lc *LessonPlanController) DownloadByShareCode(c *gin.Context) {
	shareCode := strings.TrimSpace(c.Param("code"))
	if len(shareCode) != shareCodeDigits {
		writeError(c, http.StatusBadRequest, "invalid share code")
		return
	}

	now := time.Now().UnixMilli()
	var share models.AppFileShareCode
	if err := lc.DB.
		Where("share_code = ? AND is_active = ? AND expires_at > ?", shareCode, true, now).
		Order("id DESC").
		First(&share).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			writeError(c, http.StatusNotFound, "share code expired or not found")
			return
		}
		writeError(c, http.StatusInternalServerError, "failed to query share code")
		return
	}

	var record models.AppFile
	if err := lc.DB.Where("id = ? AND file_type = ?", share.AppFileID, models.AppFileTypeLessonPlan).First(&record).Error; err != nil {
		respondLessonPlanLookupError(c, err)
		return
	}

	if err := lc.DB.Model(&models.AppFile{}).
		Where("id = ?", record.ID).
		Updates(map[string]interface{}{
			"download_count":   gorm.Expr("download_count + 1"),
			"last_download_at": now,
		}).Error; err != nil {
		writeError(c, http.StatusInternalServerError, "failed to update download stats")
		return
	}

	c.FileAttachment(record.FilePath, record.OriginalFilename)
}

func (lc *LessonPlanController) Delete(c *gin.Context) {
	record, err := lc.findLessonPlan(c.Param("id"))
	if err != nil {
		respondLessonPlanLookupError(c, err)
		return
	}

	userID, _, ok := currentUser(c)
	if !ok {
		writeError(c, http.StatusUnauthorized, "invalid user context")
		return
	}
	role := currentUserRole(c)
	if !canAccessLessonPlan(record, userID, role) {
		writeError(c, http.StatusForbidden, "permission denied")
		return
	}

	if err := deleteLessonPlanRecord(lc.DB, &record); err != nil {
		writeError(c, http.StatusInternalServerError, err.Error())
		return
	}

	writeSuccess(c, http.StatusOK, "delete success", nil)
}

func (lc *LessonPlanController) CleanupExpiredFiles() error {
	cutoffMillis := time.Now().AddDate(0, 0, -lessonPlanCleanupDays).UnixMilli()
	cutoffTime := time.Now().AddDate(0, 0, -lessonPlanCleanupDays)
	var records []models.AppFile
	if err := lc.DB.
		Where("file_type = ?", models.AppFileTypeLessonPlan).
		Where("(last_download_at IS NOT NULL AND last_download_at < ?) OR (last_download_at IS NULL AND created_at < ?)", cutoffMillis, cutoffTime).
		Find(&records).Error; err != nil {
		return err
	}
	for i := range records {
		if err := deleteLessonPlanRecord(lc.DB, &records[i]); err != nil {
			return err
		}
	}
	return nil
}

func StartLessonPlanCleanupJob(db *gorm.DB) {
	controller := &LessonPlanController{DB: db}
	go func() {
		runCleanup := func() {
			if err := controller.CleanupExpiredFiles(); err != nil {
				fmt.Printf("lesson plan cleanup failed: %v\n", err)
			}
		}
		runCleanup()
		ticker := time.NewTicker(24 * time.Hour)
		defer ticker.Stop()
		for range ticker.C {
			runCleanup()
		}
	}()
}

func validateLessonPlanFileHeader(fileHeader *multipart.FileHeader) error {
	if fileHeader.Size > lessonPlanMaxSize {
		return fmt.Errorf("file exceeds 10MB limit")
	}
	if !strings.EqualFold(filepath.Ext(fileHeader.Filename), ".docx") {
		return fmt.Errorf("only .docx files are allowed")
	}
	contentType := strings.ToLower(strings.TrimSpace(fileHeader.Header.Get("Content-Type")))
	if contentType != "" && contentType != "application/vnd.openxmlformats-officedocument.wordprocessingml.document" {
		return fmt.Errorf("content-type must be .docx")
	}
	return nil
}

func buildStoredLessonPlanFilename(md5Value, originalName string) string {
	return fmt.Sprintf("%d_%s%s", time.Now().UnixNano(), md5Value, strings.ToLower(filepath.Ext(originalName)))
}

func normalizeLessonPlanContentType(contentType string) string {
	if strings.TrimSpace(contentType) == "" {
		return "application/vnd.openxmlformats-officedocument.wordprocessingml.document"
	}
	return contentType
}

func currentUser(c *gin.Context) (uint, string, bool) {
	userIDValue, idExists := c.Get("userID")
	usernameValue, usernameExists := c.Get("username")
	if !idExists || !usernameExists {
		return 0, "", false
	}
	userID, ok := userIDValue.(uint)
	if !ok {
		return 0, "", false
	}
	username, ok := usernameValue.(string)
	if !ok {
		return 0, "", false
	}
	return userID, username, true
}

func currentUserRole(c *gin.Context) models.UserRole {
	roleValue, exists := c.Get("role")
	if !exists {
		return ""
	}
	role, _ := roleValue.(models.UserRole)
	return role
}

func canAccessLessonPlan(record models.AppFile, userID uint, role models.UserRole) bool {
	if record.UploaderID == userID {
		return true
	}
	return role == models.UserRoleSuperAdmin || role == models.UserRoleRegionAdmin
}

func deleteLessonPlanRecord(db *gorm.DB, record *models.AppFile) error {
	if err := db.Where("app_file_id = ?", record.ID).Delete(&models.AppFileShareCode{}).Error; err != nil {
		return fmt.Errorf("failed to delete share codes: %w", err)
	}
	if err := os.Remove(record.FilePath); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("failed to remove file: %w", err)
	}
	if err := db.Unscoped().Delete(&models.AppFile{}, record.ID).Error; err != nil {
		return fmt.Errorf("failed to delete metadata: %w", err)
	}
	return nil
}

func (lc *LessonPlanController) findLessonPlan(id string) (models.AppFile, error) {
	var record models.AppFile
	if err := lc.DB.Where("id = ? AND file_type = ?", id, models.AppFileTypeLessonPlan).First(&record).Error; err != nil {
		return record, err
	}
	return record, nil
}

func respondLessonPlanLookupError(c *gin.Context, err error) {
	if errors.Is(err, gorm.ErrRecordNotFound) {
		writeError(c, http.StatusNotFound, "lesson plan not found")
		return
	}
	writeError(c, http.StatusInternalServerError, "failed to query lesson plan")
}

func generateUniqueShareCode(db *gorm.DB, nowMillis int64) (string, error) {
	for i := 0; i < 10; i++ {
		shareCode, err := randomNumericCode(shareCodeDigits)
		if err != nil {
			return "", err
		}
		var count int64
		if err := db.Model(&models.AppFileShareCode{}).
			Where("share_code = ? AND is_active = ? AND expires_at > ?", shareCode, true, nowMillis).
			Count(&count).Error; err != nil {
			return "", err
		}
		if count == 0 {
			return shareCode, nil
		}
	}
	return "", fmt.Errorf("failed to allocate unique share code")
}

func randomNumericCode(length int) (string, error) {
	if length <= 0 {
		return "", fmt.Errorf("invalid code length")
	}
	buffer := make([]byte, length)
	if _, err := rand.Read(buffer); err != nil {
		return "", err
	}
	digits := make([]byte, length)
	for i, value := range buffer {
		digits[i] = byte('0' + (value % 10))
	}
	return string(digits), nil
}