package handler

import (
	"errors"
	"strconv"

	"accounting-app/pkg/api"
	"accounting-app/internal/models"
	"accounting-app/internal/service"

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

// CategoryHandler handles HTTP requests for category operations
type CategoryHandler struct {
	categoryService *service.CategoryService
}

// NewCategoryHandler creates a new CategoryHandler instance
func NewCategoryHandler(categoryService *service.CategoryService) *CategoryHandler {
	return &CategoryHandler{
		categoryService: categoryService,
	}
}

// CreateCategory handles POST /api/v1/categories
// Creates a new category with the provided data
func (h *CategoryHandler) CreateCategory(c *gin.Context) {
	var input service.CategoryInput
	if err := c.ShouldBindJSON(&input); err != nil {
		api.ValidationError(c, "Invalid request body: "+err.Error())
		return
	}

	userId, exists := c.Get("user_id")
	if !exists {
		api.Unauthorized(c, "User not authenticated")
		return
	}
	input.UserID = userId.(uint)

	category, err := h.categoryService.CreateCategory(input)
	if err != nil {
		if errors.Is(err, service.ErrInvalidParentCategory) {
			api.BadRequest(c, "Invalid parent category ID")
			return
		}
		if errors.Is(err, service.ErrParentTypeMismatch) {
			api.BadRequest(c, "Parent category type must match child category type")
			return
		}
		if errors.Is(err, service.ErrParentIsChild) {
			api.BadRequest(c, "Cannot set a child category as parent (only 2 levels allowed)")
			return
		}
		api.InternalError(c, "Failed to create category: "+err.Error())
		return
	}

	api.Created(c, category)
}

// GetCategories handles GET /api/v1/categories
// Returns a list of all categories, optionally filtered by type
func (h *CategoryHandler) GetCategories(c *gin.Context) {
	// Check for type filter
	categoryType := c.Query("type")
	tree := c.Query("tree") == "true"

	userId, exists := c.Get("user_id")
	if !exists {
		api.Unauthorized(c, "User not authenticated")
		return
	}

	var categories []models.Category
	var err error

	if tree {
		// Return hierarchical tree structure
		if categoryType != "" {
			categories, err = h.categoryService.GetCategoryTreeByType(userId.(uint), models.CategoryType(categoryType))
		} else {
			categories, err = h.categoryService.GetCategoryTree(userId.(uint))
		}
	} else {
		// Return flat list
		if categoryType != "" {
			categories, err = h.categoryService.GetCategoriesByType(userId.(uint), models.CategoryType(categoryType))
		} else {
			categories, err = h.categoryService.GetAllCategories(userId.(uint))
		}
	}

	if err != nil {
		api.InternalError(c, "Failed to get categories: "+err.Error())
		return
	}

	api.Success(c, categories)
}

// GetCategory handles GET /api/v1/categories/:id
// Returns a single category by ID
func (h *CategoryHandler) GetCategory(c *gin.Context) {
	id, err := strconv.ParseUint(c.Param("id"), 10, 32)
	if err != nil {
		api.BadRequest(c, "Invalid category ID")
		return
	}

	// Check if children should be included
	withChildren := c.Query("children") == "true"

	userId, exists := c.Get("user_id")
	if !exists {
		api.Unauthorized(c, "User not authenticated")
		return
	}

	var category *models.Category
	if withChildren {
		category, err = h.categoryService.GetCategoryWithChildren(userId.(uint), uint(id))
	} else {
		category, err = h.categoryService.GetCategory(userId.(uint), uint(id))
	}

	if err != nil {
		if errors.Is(err, service.ErrCategoryNotFound) {
			api.NotFound(c, "Category not found")
			return
		}
		api.InternalError(c, "Failed to get category: "+err.Error())
		return
	}

	api.Success(c, category)
}

// GetCategoryChildren handles GET /api/v1/categories/:id/children
// Returns all child categories of a given parent
func (h *CategoryHandler) GetCategoryChildren(c *gin.Context) {
	id, err := strconv.ParseUint(c.Param("id"), 10, 32)
	if err != nil {
		api.BadRequest(c, "Invalid category ID")
		return
	}

	userId, exists := c.Get("user_id")
	if !exists {
		api.Unauthorized(c, "User not authenticated")
		return
	}

	children, err := h.categoryService.GetChildCategories(userId.(uint), uint(id))
	if err != nil {
		if errors.Is(err, service.ErrCategoryNotFound) {
			api.NotFound(c, "Category not found")
			return
		}
		api.InternalError(c, "Failed to get child categories: "+err.Error())
		return
	}

	api.Success(c, children)
}

// UpdateCategory handles PUT /api/v1/categories/:id
// Updates an existing category with the provided data
func (h *CategoryHandler) UpdateCategory(c *gin.Context) {
	id, err := strconv.ParseUint(c.Param("id"), 10, 32)
	if err != nil {
		api.BadRequest(c, "Invalid category ID")
		return
	}

	var input service.CategoryInput
	if err := c.ShouldBindJSON(&input); err != nil {
		api.ValidationError(c, "Invalid request body: "+err.Error())
		return
	}

	userId, exists := c.Get("user_id")
	if !exists {
		api.Unauthorized(c, "User not authenticated")
		return
	}
	input.UserID = userId.(uint)

	category, err := h.categoryService.UpdateCategory(userId.(uint), uint(id), input)
	if err != nil {
		if errors.Is(err, service.ErrCategoryNotFound) {
			api.NotFound(c, "Category not found")
			return
		}
		if errors.Is(err, service.ErrInvalidParentCategory) {
			api.BadRequest(c, "Invalid parent category ID")
			return
		}
		if errors.Is(err, service.ErrParentTypeMismatch) {
			api.BadRequest(c, "Parent category type must match child category type")
			return
		}
		if errors.Is(err, service.ErrCircularReference) {
			api.BadRequest(c, "Cannot create circular reference in category hierarchy")
			return
		}
		if errors.Is(err, service.ErrParentIsChild) {
			api.BadRequest(c, "Cannot set a child category as parent (only 2 levels allowed)")
			return
		}
		api.InternalError(c, "Failed to update category: "+err.Error())
		return
	}

	api.Success(c, category)
}

// DeleteCategory handles DELETE /api/v1/categories/:id
// Deletes a category by ID
func (h *CategoryHandler) DeleteCategory(c *gin.Context) {
	id, err := strconv.ParseUint(c.Param("id"), 10, 32)
	if err != nil {
		api.BadRequest(c, "Invalid category ID")
		return
	}

	userId, exists := c.Get("user_id")
	if !exists {
		api.Unauthorized(c, "User not authenticated")
		return
	}

	err = h.categoryService.DeleteCategory(userId.(uint), uint(id))
	if err != nil {
		if errors.Is(err, service.ErrCategoryNotFound) {
			api.NotFound(c, "Category not found")
			return
		}
		if errors.Is(err, service.ErrCategoryInUse) {
			api.Conflict(c, "Category is in use and cannot be deleted. Please remove associated transactions first.")
			return
		}
		if errors.Is(err, service.ErrCategoryHasChildren) {
			api.Conflict(c, "Category has child categories and cannot be deleted. Please remove child categories first.")
			return
		}
		api.InternalError(c, "Failed to delete category: "+err.Error())
		return
	}

	api.NoContent(c)
}

// RegisterRoutes registers all category routes to the given router group
func (h *CategoryHandler) RegisterRoutes(rg *gin.RouterGroup) {
	categories := rg.Group("/categories")
	{
		categories.POST("", h.CreateCategory)
		categories.GET("", h.GetCategories)
		categories.GET("/:id", h.GetCategory)
		categories.GET("/:id/children", h.GetCategoryChildren)
		categories.PUT("/:id", h.UpdateCategory)
		categories.DELETE("/:id", h.DeleteCategory)
	}
}