package handler

import (
	"errors"
	"strconv"

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

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

// ReimbursementServiceInterface defines the interface for reimbursement operations
type ReimbursementServiceInterface interface {
	ApplyReimbursement(userID uint, transactionID uint, amount float64) (*models.Transaction, error)
	ConfirmReimbursement(userID uint, transactionID uint) (*models.Transaction, error)
	CancelReimbursement(userID uint, transactionID uint) (*models.Transaction, error)
}

// ReimbursementHandler handles HTTP requests for reimbursement operations
// Feature: accounting-feature-upgrade
// Validates: Requirements 8.1-8.9
type ReimbursementHandler struct {
	reimbursementService ReimbursementServiceInterface
}

// NewReimbursementHandler creates a new ReimbursementHandler instance
func NewReimbursementHandler(reimbursementService ReimbursementServiceInterface) *ReimbursementHandler {
	return &ReimbursementHandler{
		reimbursementService: reimbursementService,
	}
}

// ApplyReimbursementInput represents the input for applying for reimbursement
type ApplyReimbursementInput struct {
	Amount float64 `json:"amount" binding:"required,gt=0"`
}

// ApplyReimbursement handles PUT /api/v1/transactions/:id/reimbursement
// Applies for reimbursement on an expense transaction
// Feature: accounting-feature-upgrade
// Validates: Requirements 8.2, 8.3, 8.4
func (h *ReimbursementHandler) ApplyReimbursement(c *gin.Context) {
	userId, exists := c.Get("user_id")
	if !exists {
		api.Unauthorized(c, "User not authenticated")
		return
	}

	id, err := strconv.ParseUint(c.Param("id"), 10, 32)
	if err != nil {
		api.BadRequest(c, "Invalid transaction ID")
		return
	}

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

	transaction, err := h.reimbursementService.ApplyReimbursement(userId.(uint), uint(id), input.Amount)
	if err != nil {
		if errors.Is(err, service.ErrTransactionNotFound) {
			api.NotFound(c, "Transaction not found")
			return
		}
		if errors.Is(err, service.ErrNotExpenseTransaction) {
			api.BadRequest(c, "Only expense transactions can be reimbursed")
			return
		}
		if errors.Is(err, service.ErrAlreadyReimbursed) {
			api.BadRequest(c, "Transaction is already reimbursed")
			return
		}
		if errors.Is(err, service.ErrInvalidReimbursementAmount) {
			api.BadRequest(c, "Reimbursement amount must be greater than 0 and not exceed original amount")
			return
		}
		api.InternalError(c, "Failed to apply reimbursement: "+err.Error())
		return
	}

	api.Success(c, transaction)
}

// ConfirmReimbursement handles PUT /api/v1/transactions/:id/reimbursement/confirm
// Confirms a pending reimbursement and creates the income record
// Feature: accounting-feature-upgrade
// Validates: Requirements 8.5, 8.6, 8.28
func (h *ReimbursementHandler) ConfirmReimbursement(c *gin.Context) {
	userId, exists := c.Get("user_id")
	if !exists {
		api.Unauthorized(c, "User not authenticated")
		return
	}

	id, err := strconv.ParseUint(c.Param("id"), 10, 32)
	if err != nil {
		api.BadRequest(c, "Invalid transaction ID")
		return
	}

	reimbursementIncome, err := h.reimbursementService.ConfirmReimbursement(userId.(uint), uint(id))
	if err != nil {
		if errors.Is(err, service.ErrTransactionNotFound) {
			api.NotFound(c, "Transaction not found")
			return
		}
		if errors.Is(err, service.ErrNotPendingReimbursement) {
			api.BadRequest(c, "Transaction is not in pending reimbursement status")
			return
		}
		if errors.Is(err, service.ErrReimbursementCategoryNotFound) {
			api.InternalError(c, "Reimbursement system category not found. Please run database migrations.")
			return
		}
		api.InternalError(c, "Failed to confirm reimbursement: "+err.Error())
		return
	}

	api.Success(c, reimbursementIncome)
}

// CancelReimbursement handles PUT /api/v1/transactions/:id/reimbursement/cancel
// Cancels a pending reimbursement
// Feature: accounting-feature-upgrade
// Validates: Requirements 8.9
func (h *ReimbursementHandler) CancelReimbursement(c *gin.Context) {
	userId, exists := c.Get("user_id")
	if !exists {
		api.Unauthorized(c, "User not authenticated")
		return
	}

	id, err := strconv.ParseUint(c.Param("id"), 10, 32)
	if err != nil {
		api.BadRequest(c, "Invalid transaction ID")
		return
	}

	transaction, err := h.reimbursementService.CancelReimbursement(userId.(uint), uint(id))
	if err != nil {
		if errors.Is(err, service.ErrTransactionNotFound) {
			api.NotFound(c, "Transaction not found")
			return
		}
		if errors.Is(err, service.ErrNotPendingReimbursement) {
			api.BadRequest(c, "Transaction is not in pending reimbursement status")
			return
		}
		api.InternalError(c, "Failed to cancel reimbursement: "+err.Error())
		return
	}

	api.Success(c, transaction)
}

// RegisterRoutes registers all reimbursement routes to the given router group
func (h *ReimbursementHandler) RegisterRoutes(rg *gin.RouterGroup) {
	transactions := rg.Group("/transactions")
	{
		transactions.PUT("/:id/reimbursement", h.ApplyReimbursement)
		transactions.PUT("/:id/reimbursement/confirm", h.ConfirmReimbursement)
		transactions.PUT("/:id/reimbursement/cancel", h.CancelReimbursement)
	}
}