package handler

import "billit/internal/models"
import "billit/internal/view"
import (
	"billit/internal/database"
	"billit/internal/logic"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"math"
	"net/http"
	"strconv"
	"strings"

	"github.com/google/uuid"
	"github.com/labstack/echo/v4"
	qrcode "github.com/skip2/go-qrcode"
)

// numberToWords converts a number to Indian English words (supports up to crores)
func numberToWords(n float64) string {
	if n == 0 {
		return "Zero"
	}

	ones := []string{"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine",
		"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"}
	tens := []string{"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"}

	convertLessThanHundred := func(n int) string {
		if n < 20 {
			return ones[n]
		}
		if n%10 == 0 {
			return tens[n/10]
		}
		return tens[n/10] + " " + ones[n%10]
	}

	convertLessThanThousand := func(n int) string {
		if n < 100 {
			return convertLessThanHundred(n)
		}
		if n%100 == 0 {
			return ones[n/100] + " Hundred"
		}
		return ones[n/100] + " Hundred " + convertLessThanHundred(n%100)
	}
	// Split into rupees and paise
	rupees := int(math.Floor(n))
	paise := int(math.Round((n - float64(rupees)) * 100))

	var result string

	if rupees >= 10000000 { // Crores
		crores := rupees / 10000000
		rupees = rupees % 10000000
		result += convertLessThanThousand(crores) + " Crore "
	}
	if rupees >= 100000 { // Lakhs
		lakhs := rupees / 100000
		rupees = rupees % 100000
		result += convertLessThanHundred(lakhs) + " Lakh "
	}
	if rupees >= 1000 { // Thousands
		thousands := rupees / 1000
		rupees = rupees % 1000
		result += convertLessThanHundred(thousands) + " Thousand "
	}
	if rupees > 0 {
		result += convertLessThanThousand(rupees)
	}

	result = strings.TrimSpace(result)
	if result == "" {
		result = "Zero"
	}
	result += " Rupees"

	if paise > 0 {
		result += " and " + convertLessThanHundred(paise) + " Paise"
	}

	return result + " Only"
}

// BillingHandlers holds db reference for billing operations
type BillingHandlers struct {
	db database.Service
}

// NewBillingHandlers creates handlers with db access
func NewBillingHandlers(db database.Service) *BillingHandlers {
	return &BillingHandlers{db: db}
}

// BillingPageHandler renders the /billing page for creating bills
func (h *BillingHandlers) BillingPageHandler(c echo.Context) error {
	userID := getUserID(c)
	products, err := h.db.GetAllProducts(userID)
	if err != nil {
		products = []models.Product{}
	}
	buyers, err := h.db.GetAllBuyerDetails(userID)
	if err != nil {
		buyers = []models.BuyerDetails{}
	}
	return view.Render(c, view.BillingPage(products, buyers))
}

// CalculateBillHandler calculates the bill (HTMX endpoint)
func (h *BillingHandlers) CalculateBillHandler(c echo.Context) error {
	userID := getUserID(c)
	customerType := c.FormValue("customer_type")
	regionType := c.FormValue("region_type")
	includeConvenienceFee := c.FormValue("include_convenience_fee") == "yes"

	cType := logic.CustomerRetail
	if customerType == "wholesale" {
		cType = logic.CustomerWholesale
	}
	isInterState := regionType == "inter"

	calculator := logic.NewCalculator()
	var items []logic.LineItem
	var totalFee float64

	// Support up to 50 product slots for dynamic adding
	for i := 0; i < 50; i++ {
		sku := c.FormValue("product_sku_" + strconv.Itoa(i))
		qtyStr := c.FormValue("qty_" + strconv.Itoa(i))

		if sku == "" {
			continue
		}

		qty, err := strconv.Atoi(qtyStr)
		if err != nil || qty <= 0 {
			continue
		}

		// Get product from DB (user-scoped)
		dbProduct, err := h.db.GetProductBySKU(sku, userID)
		if err != nil || dbProduct == nil {
			continue
		}

		// Convert to logic.Product
		product := logic.Product{
			SKU:            dbProduct.SKU,
			Name:           dbProduct.Name,
			HSNCode:        dbProduct.HSNCode,
			BasePrice:      dbProduct.BasePrice,
			WholesalePrice: dbProduct.WholesalePrice,
			GSTRate:        logic.Rate(dbProduct.GSTRate),
			SmallOrderQty:  dbProduct.SmallOrderQty,
			SmallOrderFee:  dbProduct.SmallOrderFee,
			Unit:           dbProduct.Unit,
		}

		lineItem := calculator.CalculateLineItem(product, qty, cType, isInterState)
		items = append(items, lineItem)

		// Apply per-product convenience fee if quantity is below threshold and checkbox is checked
		if includeConvenienceFee && product.SmallOrderQty > 0 && qty < product.SmallOrderQty && product.SmallOrderFee > 0 {
			totalFee += product.SmallOrderFee
		}
	}

	invoice := calculator.CalculateInvoice(items, totalFee, isInterState)
	invoice.CustomerType = cType

	return view.Render(c, view.InvoiceSummary(invoice))
}

// GenerateBillHandler generates final invoice with UUID and persists to DB
func (h *BillingHandlers) GenerateBillHandler(c echo.Context) error {
	userID := getUserID(c)
	if userID == "" {
		return c.Redirect(http.StatusFound, "/")
	}

	customerType := c.FormValue("customer_type")
	regionType := c.FormValue("region_type")
	buyerID := c.FormValue("buyer_id")
	includeConvenienceFee := c.FormValue("include_convenience_fee") == "yes"

	cType := logic.CustomerRetail
	if customerType == "wholesale" {
		cType = logic.CustomerWholesale
	}
	isInterState := regionType == "inter"

	calculator := logic.NewCalculator()
	var items []logic.LineItem
	var totalFee float64

	for i := 0; i < 50; i++ {
		sku := c.FormValue("product_sku_" + strconv.Itoa(i))
		qtyStr := c.FormValue("qty_" + strconv.Itoa(i))

		if sku == "" {
			continue
		}

		qty, err := strconv.Atoi(qtyStr)
		if err != nil || qty <= 0 {
			continue
		}

		dbProduct, err := h.db.GetProductBySKU(sku, userID)
		if err != nil || dbProduct == nil {
			continue
		}

		product := logic.Product{
			SKU:            dbProduct.SKU,
			Name:           dbProduct.Name,
			HSNCode:        dbProduct.HSNCode,
			BasePrice:      dbProduct.BasePrice,
			WholesalePrice: dbProduct.WholesalePrice,
			GSTRate:        logic.Rate(dbProduct.GSTRate),
			SmallOrderQty:  dbProduct.SmallOrderQty,
			SmallOrderFee:  dbProduct.SmallOrderFee,
			Unit:           dbProduct.Unit,
		}

		lineItem := calculator.CalculateLineItem(product, qty, cType, isInterState)
		items = append(items, lineItem)

		// Apply per-product convenience fee if checkbox is checked
		if includeConvenienceFee && product.SmallOrderQty > 0 && qty < product.SmallOrderQty && product.SmallOrderFee > 0 {
			totalFee += product.SmallOrderFee
		}
	}

	if len(items) == 0 {
		return c.String(http.StatusBadRequest, "No products selected")
	}

	invoice := calculator.CalculateInvoice(items, totalFee, isInterState)
	invoice.CustomerType = cType

	// Get user's company and bank details
	user, err := h.db.GetUserByID(userID)
	if err == nil && user != nil {
		invoice.CompanyDetails = user.CompanyDetails
		invoice.BankDetails = user.BankDetails
	}

	// Get buyer details if selected
	if buyerID != "" {
		buyer, err := h.db.GetBuyerDetails(buyerID, userID)
		if err == nil && buyer != nil {
			invoice.BuyerName = buyer.Name
			invoice.BuyerDetails = buyer.Details
		}
	}

	// Generate UUID for invoice
	invoiceID := uuid.New().String()

	// Generate human-readable invoice ID
	humanReadableID, err := h.db.GetNextInvoiceNumber(userID)
	if err != nil {
		return c.String(http.StatusInternalServerError, "failed to generate invoice number")
	}

	// Persist to DB (user-scoped)
	if err := h.db.CreateInvoice(invoiceID, humanReadableID, invoice, userID); err != nil {
		return c.String(http.StatusInternalServerError, "failed to save invoice")
	}

	// Redirect to invoice view
	c.Response().Header().Set("HX-Redirect", fmt.Sprintf("/invoice/%s", invoiceID))
	return c.NoContent(http.StatusOK)
}

// ShowInvoiceHandler displays the invoice by UUID (requires auth)
func (h *BillingHandlers) ShowInvoiceHandler(c echo.Context) error {
	userID := getUserID(c)
	if userID == "" {
		return c.Redirect(http.StatusFound, "/")
	}

	invoiceID := c.Param("id")

	inv, err := h.db.GetInvoice(invoiceID, userID)
	if err != nil || inv == nil {
		return view.RenderNotFound(c, "Invoice not found or you don't have access to it.")
	}

	// Parse the JSON data back into Invoice struct
	var invoice logic.Invoice
	if err := json.Unmarshal([]byte(inv.Data), &invoice); err != nil {
		return c.String(http.StatusInternalServerError, "failed to parse invoice data")
	}

	// Generate QR code for invoice URL
	invoiceURL := fmt.Sprintf("%s://%s/invoice/%s", c.Scheme(), c.Request().Host, invoiceID)
	qrPNG, err := qrcode.Encode(invoiceURL, qrcode.Medium, 100)
	if err != nil {
		return c.String(http.StatusInternalServerError, "failed to generate QR code")
	}
	qrBase64 := base64.StdEncoding.EncodeToString(qrPNG)

	// Render printable invoice page with multi-page support
	c.Response().Header().Set(echo.HeaderContentType, echo.MIMETextHTML)
	w := c.Response().Writer
	fmt.Fprint(w, "<!doctype html><html><head><meta charset='utf-8'><meta name='viewport' content='width=device-width,initial-scale=1'><title>Invoice ")
	fmt.Fprintf(w, "%s</title>", invoiceID[:8])
	fmt.Fprint(w, "<link href='/assets/css/output.css' rel='stylesheet'>")
	fmt.Fprint(w, `<style type="text/css">
		@media print { 
			.no-print { display: none !important; }
			.page-break { page-break-before: always; }
			@page { margin: 1cm; size: A4; }
			body { background: white !important; }
			.invoice-table th { background: #e0e0e0 !important; color: black !important; -webkit-print-color-adjust: exact; print-color-adjust: exact; }
			.invoice-totals .row-total { background: #e0e0e0 !important; color: black !important; -webkit-print-color-adjust: exact; print-color-adjust: exact; }
		}
		.invoice-details-block { white-space: pre-wrap; font-size: 0.875rem; line-height: 1.4; }
		.invoice-footer-section { margin-top: 1.5rem; padding-top: 1rem; border-top: 1px solid #e0e0e0; }
	</style>`)
	fmt.Fprint(w, "</head><body>")
	fmt.Fprintf(w, `<div class="container page">
		<div class="no-print" style="display:flex;justify-content:space-between;align-items:center;margin-bottom:1.5rem;padding-bottom:1rem;border-bottom:1px solid #e0e0e0;">
			<a href="/invoice" class="text-accent">&larr; Back</a>
			<button onclick="window.print()" class="btn btn-primary">Print Invoice</button>
		</div>
		<div class="invoice">
			<div class="invoice-header">
				<div>
					<h1 class="invoice-title">Tax Invoice</h1>
				</div>
				<div class="invoice-meta">
					<p>Invoice ID: %s</p>
				</div>
				<div class="invoice-meta">
					<p>Date: %s</p>
				</div>
			</div>`, inv.HumanReadableID, strings.ReplaceAll(inv.CreatedAt, "T", " ")[0:10])

	// Display company details above the invoice table
	if invoice.CompanyDetails != "" {
		fmt.Fprintf(w, `<div class="invoice-details-block" style="margin-bottom:1rem;"><strong>From:</strong><br>%s</div>`, invoice.CompanyDetails)
	}

	if err := view.PrintableInvoice(invoice).Render(c.Request().Context(), w); err != nil {
		return err
	}

	// Display buyer details and total amount in same section (50-50 split or 100% if no buyer)
	totalGST := invoice.TotalCGST + invoice.TotalSGST + invoice.TotalIGST
	hasBuyerInfo := invoice.BuyerName != "" || invoice.BuyerDetails != ""

	if hasBuyerInfo {
		fmt.Fprint(w, `<div class="invoice-footer-section" style="display:flex;justify-content:space-between;gap:2rem;">`)
		// Left side: Billed To (50%)
		fmt.Fprint(w, `<div style="flex:1;"><strong>Billed To:</strong><br>`)
		if invoice.BuyerName != "" {
			fmt.Fprintf(w, `<span class="invoice-details-block">%s</span>`, invoice.BuyerName)
		}
		if invoice.BuyerDetails != "" {
			fmt.Fprintf(w, `<br><span class="invoice-details-block">%s</span>`, invoice.BuyerDetails)
		}
		fmt.Fprint(w, `</div>`)
		// Right side: Total Amount (50%)
		fmt.Fprintf(w, `<div style="flex:1;">
			<p style="margin: 0.5rem 0;"><strong>Total Amount (before GST):</strong><br>%s</p>
			<p style="margin: 0.5rem 0;"><strong>GST Amount:</strong><br>%s</p>
		</div>`, numberToWords(invoice.SubTotal), numberToWords(totalGST))
	} else {
		fmt.Fprint(w, `<div class="invoice-footer-section">`)
		// Total Amount takes 100%
		fmt.Fprintf(w, `<div>
			<p style="margin: 0.5rem 0;"><strong>Total Amount (before GST):</strong><br>%s</p>
			<p style="margin: 0.5rem 0;"><strong>GST Amount:</strong><br>%s</p>
		</div>`, numberToWords(invoice.SubTotal), numberToWords(totalGST))
	}

	fmt.Fprint(w, `</div>`)

	// Bank details (left) and QR code (right) in the same section
	fmt.Fprint(w, `<div class="invoice-footer-section" style="display:flex;justify-content:space-between;align-items:flex-start;">`)
	if invoice.BankDetails != "" {
		fmt.Fprintf(w, `<div style="flex:1;"><strong>Bank Details:</strong><br><span class="invoice-details-block">%s</span></div>`, invoice.BankDetails)
	} else {
		fmt.Fprint(w, `<div style="flex:1;"></div>`)
	}
	fmt.Fprintf(w, `<div style="margin-left:1rem;"><img src="data:image/png;base64,%s" alt="QR Code" style="width:80px;height:80px;"></div>`, qrBase64)
	fmt.Fprint(w, `</div>`)

	fmt.Fprint(w, "</div>")

	fmt.Fprint(w, "</div></body></html>")
	return nil
}

// AddProductRowHandler returns HTML for a new product row (HTMX endpoint)
func (h *BillingHandlers) AddProductRowHandler(c echo.Context) error {
	userID := getUserID(c)
	indexStr := c.QueryParam("index")
	index, err := strconv.Atoi(indexStr)
	if err != nil {
		index = 0
	}

	products, _ := h.db.GetAllProducts(userID)

	// Build product options HTML
	productOptions := `<option value="">-- Select Product --</option>`
	for _, p := range products {
		productOptions += fmt.Sprintf(`<option value="%s">%s (₹%.2f)</option>`, p.SKU, p.Name, p.BasePrice)
	}

	rowHTML := fmt.Sprintf(`
		<div class="product-row">
			<div class="product-row-grid">
				<div class="form-group" style="margin:0;">
					<label class="form-label">Product</label>
					<select name="product_sku_%d" class="form-select">%s</select>
				</div>
				<div class="form-group" style="margin:0;">
					<label class="form-label">Qty</label>
					<input type="number" name="qty_%d" value="1" min="0" class="form-input">
				</div>
				<div style="padding-top:20px;">
					<button type="button" onclick="this.closest('.product-row').remove()" class="btn btn-danger btn-sm">×</button>
				</div>
			</div>
		</div>`, index, productOptions, index)

	return c.HTML(http.StatusOK, rowHTML)
}