// Package handlers implements HTTP request handlers for ExpenseFlow.
//
// This file implements the event filing workflow — generating CSV or PDF
// expense reports and emailing them as attachments to a specified recipient.
package handlers

import (
	"archive/zip"
	"bytes"
	"database/sql"
	"encoding/csv"
	"fmt"
	"html/template"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/jung-kurt/gofpdf"

	"github.com/cclohmar/ReceiptNext/internal/database"
	"github.com/cclohmar/ReceiptNext/internal/email"
)

// ---------------------------------------------------------------------------
// FileHandler
// ---------------------------------------------------------------------------

// FileHandler handles the event filing workflow: generating expense reports
// in CSV or PDF format and emailing them to a specified address.
// It depends on a shared *sql.DB handle for database access and an
// *email.Sender for delivering the report as an email attachment.
type FileHandler struct {
	DB          *sql.DB
	EmailSender *email.Sender
}

// ---------------------------------------------------------------------------
// POST /events/{id}/file — FileEvent
// ---------------------------------------------------------------------------

// FileEvent generates an expense report (CSV or PDF) for a given event and
// emails it as an attachment to the specified recipient. On success the
// event status is updated to "closed" and the client is redirected to the
// dashboard via the HX-Redirect header.
//
// Flow:
//  1. Extract event ID from the URL via chi.URLParam
//  2. Parse the form for target email and report format
//  3. Verify the authenticated user owns this event
//  4. Fetch all expenses for the event from the database
//  5. Generate the report in the requested format (CSV or PDF)
//  6. Send the report as an email attachment
//  7. Update the event status to "closed"
//  8. Return an HX-Redirect header pointing to /dashboard
func (h *FileHandler) FileEvent(w http.ResponseWriter, r *http.Request) {
	// 1. Get event ID from the URL path parameter.
	eventID := chi.URLParam(r, "id")
	if eventID == "" {
		log.Printf("ERROR [%s] handlers: FileEvent: missing event ID in URL",
			time.Now().Format(time.RFC3339))
		renderFileError(w, "Missing event ID.")
		return
	}

	// 2. Parse form fields.
	if err := r.ParseForm(); err != nil {
		log.Printf("ERROR [%s] handlers: FileEvent: parse form: %v",
			time.Now().Format(time.RFC3339), err)
		renderFileError(w, "Cannot parse form data.")
		return
	}

	to := r.FormValue("email")
	format := r.FormValue("format")

	if to == "" {
		log.Printf("ERROR [%s] handlers: FileEvent: missing email field",
			time.Now().Format(time.RFC3339))
		renderFileError(w, "Email address is required.")
		return
	}
	if format != "csv" && format != "pdf" {
		log.Printf("ERROR [%s] handlers: FileEvent: invalid format %q",
			time.Now().Format(time.RFC3339), format)
		renderFileError(w, "Format must be 'csv' or 'pdf'.")
		return
	}

	// 3. Verify the authenticated user owns this event.
	userID := getUserID(r)
	if userID == "" {
		log.Printf("ERROR [%s] handlers: FileEvent: unauthenticated request",
			time.Now().Format(time.RFC3339))
		renderFileError(w, "Session expired. Please log in again.")
		return
	}

	event, err := database.GetEventByID(h.DB, eventID)
	if err != nil {
		log.Printf("ERROR [%s] handlers: FileEvent: GetEventByID(%s): %v",
			time.Now().Format(time.RFC3339), eventID, err)
		renderFileError(w, "Failed to retrieve event. Please try again.")
		return
	}
	if event == nil {
		log.Printf("ERROR [%s] handlers: FileEvent: event not found: %s",
			time.Now().Format(time.RFC3339), eventID)
		renderFileError(w, "Event not found.")
		return
	}
	if event.UserID != userID {
		log.Printf("ERROR [%s] handlers: FileEvent: user %s does not own event %s",
			time.Now().Format(time.RFC3339), userID, eventID)
		renderFileError(w, "You do not have permission to file this event.")
		return
	}

	// 4. Fetch all expenses for the event.
	expenses, err := database.GetExpensesByEvent(h.DB, eventID)
	if err != nil {
		log.Printf("ERROR [%s] handlers: FileEvent: GetExpensesByEvent(%s): %v",
			time.Now().Format(time.RFC3339), eventID, err)
		renderFileError(w, "Failed to retrieve expenses. Please try again.")
		return
	}

	// 5. Generate the report in the requested format.
	var reportAttachment *email.Attachment
	switch format {
	case "csv":
		reportAttachment, err = generateCSV(event.Name, expenses)
	case "pdf":
		reportAttachment, err = generatePDF(event.Name, expenses)
	}
	if err != nil {
		log.Printf("ERROR [%s] handlers: FileEvent: generate %s report: %v",
			time.Now().Format(time.RFC3339), format, err)
		renderFileError(w, "Failed to generate report. Please try again.")
		return
	}

	// 6. Create a ZIP of all receipt images.
	zipAttachment, zipErr := createReceiptZip(event.Name, expenses)

	// 7. Build the list of attachments (report + ZIP if available).
	attachments := []*email.Attachment{reportAttachment}
	if zipErr == nil && zipAttachment != nil {
		attachments = append(attachments, zipAttachment)
	} else if zipErr != nil {
		log.Printf("WARN  [%s] handlers: FileEvent: receipt zip failed: %v",
			time.Now().Format(time.RFC3339), zipErr)
	}

	// 8. Send the email with all attachments.
	if h.EmailSender == nil {
		log.Printf("ERROR [%s] handlers: FileEvent: SMTP not configured, cannot send email",
			time.Now().Format(time.RFC3339))
		renderFileError(w, "SMTP not configured. Please contact the administrator.")
		return
	}
	subject := "Expense report for event " + event.Name
	body := "Please find attached the expense report and receipt images."
	if err := h.EmailSender.SendReport(to, subject, body, attachments); err != nil {
		log.Printf("ERROR [%s] handlers: FileEvent: SendReport(%s): %v",
			time.Now().Format(time.RFC3339), to, err)
		renderFileError(w, "Failed to send report: "+err.Error())
		return
	}

	// 7. Update the event status to "closed".
	if err := database.UpdateEventStatus(h.DB, eventID, "closed"); err != nil {
		log.Printf("ERROR [%s] handlers: FileEvent: UpdateEventStatus(%s): %v",
			time.Now().Format(time.RFC3339), eventID, err)
		renderFileError(w, "Report sent but failed to close the event. Please try again.")
		return
	}

	// 8. Redirect to the dashboard via HTMX.
	w.Header().Set("HX-Redirect", "/dashboard")
	w.WriteHeader(http.StatusOK)
}

// ---------------------------------------------------------------------------
// Report generation helpers
// ---------------------------------------------------------------------------

// generateCSV creates a CSV attachment from the provided expenses.
// The CSV includes a header row and one data row per expense.
// If the expenses use a different currency than the base currency, both
// original and converted amounts are included.
func generateCSV(eventName string, expenses []database.Expense) (*email.Attachment, error) {
	var buf bytes.Buffer
	writer := csv.NewWriter(&buf)

	// Determine if we need conversion columns.
	hasConversion := false
	for _, exp := range expenses {
		if exp.ConvertedAmount > 0 && exp.BaseCurrency != "" && exp.BaseCurrency != exp.Currency {
			hasConversion = true
			break
		}
	}

	// Write header row.
	var header []string
	if hasConversion {
		header = []string{"#", "Date", "Merchant", "Amount", "Currency", "Converted", "Claim Currency", "Category", "Description"}
	} else {
		header = []string{"#", "Date", "Merchant", "Amount", "Currency", "Category", "Description"}
	}
	if err := writer.Write(header); err != nil {
		return nil, fmt.Errorf("write CSV header: %w", err)
	}

	// Write one data row per expense with item number.
	totalOrig := 0.0
	totalConv := 0.0
	for i, exp := range expenses {
		itemNum := i + 1
		var row []string
		if hasConversion {
			row = []string{
				fmt.Sprintf("%d", itemNum),
				exp.Date,
				exp.Merchant,
				fmt.Sprintf("%.2f", exp.Amount),
				exp.Currency,
				fmt.Sprintf("%.2f", exp.ConvertedAmount),
				exp.BaseCurrency,
				exp.Category,
				exp.Description,
			}
		} else {
			row = []string{
				fmt.Sprintf("%d", itemNum),
				exp.Date,
				exp.Merchant,
				fmt.Sprintf("%.2f", exp.Amount),
				exp.Currency,
				exp.Category,
				exp.Description,
			}
		}
		if err := writer.Write(row); err != nil {
			return nil, fmt.Errorf("write CSV row: %w", err)
		}
		totalOrig += exp.Amount
		totalConv += exp.ConvertedAmount
	}

	// Write totals row.
	if hasConversion {
		writer.Write([]string{"TOTAL", "", "", fmt.Sprintf("%.2f", totalOrig), "", fmt.Sprintf("%.2f", totalConv), "", "", ""})
	} else {
		writer.Write([]string{"TOTAL", "", "", fmt.Sprintf("%.2f", totalOrig), "", "", "", ""})
	}

	writer.Flush()
	if err := writer.Error(); err != nil {
		return nil, fmt.Errorf("CSV writer flush: %w", err)
	}

	filename := fmt.Sprintf("expense-%s-report.csv", sanitiseFilename(eventName))
	return &email.Attachment{
		Filename: filename,
		Content:  buf.Bytes(),
	}, nil
}

// generatePDF creates a PDF attachment from the provided expenses using gofpdf.
// The PDF contains a title row, a header row, and one data row per expense.
// If the expenses use a different currency than the base currency, both
// original and converted amounts are included.
func generatePDF(eventName string, expenses []database.Expense) (*email.Attachment, error) {
	pdf := gofpdf.New("P", "mm", "A4", "")
	pdf.AddPage()

	// Title: "Expense Report: <event name>"
	pdf.SetFont("Helvetica", "B", 16)
	pdf.Cell(0, 10, "Expense Report: "+eventName)
	pdf.Ln(15)

	// Determine if we need conversion columns.
	hasConversion := false
	for _, exp := range expenses {
		if exp.ConvertedAmount > 0 && exp.BaseCurrency != "" && exp.BaseCurrency != exp.Currency {
			hasConversion = true
			break
		}
	}

	// Table header row with item number.
	pdf.SetFont("Helvetica", "B", 10)
	var headers []string
	var colWidths []float64
	if hasConversion {
		headers = []string{"#", "Date", "Merchant", "Amount", "Curr.", "Converted", "Claim", "Category"}
		colWidths = []float64{8, 22, 38, 18, 12, 20, 14, 30}
	} else {
		headers = []string{"#", "Date", "Merchant", "Amount", "Currency", "Category"}
		colWidths = []float64{10, 28, 48, 22, 18, 40}
	}
	for i, h := range headers {
		pdf.Cell(colWidths[i], 8, h)
	}
	pdf.Ln(8)

	// Table data rows with item numbers and automatic page breaks.
	pdf.SetFont("Helvetica", "", 9)
	marginBottom := 20.0 // mm margin from bottom before page break
	for i, exp := range expenses {
		// Check if we need a page break (A4 = 297mm height).
		if pdf.GetY() > 297-marginBottom {
			pdf.AddPage()
			// Re-draw header row on new page.
			pdf.SetFont("Helvetica", "B", 9)
			for j, h := range headers {
				pdf.Cell(colWidths[j], 8, h)
			}
			pdf.Ln(8)
			pdf.SetFont("Helvetica", "", 9)
		}
		itemNum := i + 1
		if hasConversion {
			pdf.Cell(colWidths[0], 8, fmt.Sprintf("%d", itemNum))
			pdf.Cell(colWidths[1], 8, exp.Date)
			pdf.Cell(colWidths[2], 8, truncateString(exp.Merchant, 18))
			pdf.Cell(colWidths[3], 8, fmt.Sprintf("%.2f", exp.Amount))
			pdf.Cell(colWidths[4], 8, exp.Currency)
			pdf.Cell(colWidths[5], 8, fmt.Sprintf("%.2f", exp.ConvertedAmount))
			pdf.Cell(colWidths[6], 8, exp.BaseCurrency)
			pdf.Cell(colWidths[7], 8, truncateString(exp.Category, 12))
		} else {
			pdf.Cell(colWidths[0], 8, fmt.Sprintf("%d", itemNum))
			pdf.Cell(colWidths[1], 8, exp.Date)
			pdf.Cell(colWidths[2], 8, truncateString(exp.Merchant, 20))
			pdf.Cell(colWidths[3], 8, fmt.Sprintf("%.2f", exp.Amount))
			pdf.Cell(colWidths[4], 8, exp.Currency)
			pdf.Cell(colWidths[5], 8, truncateString(exp.Category, 20))
		}
		pdf.Ln(8)
	}

	// Write the PDF document to a memory buffer.
	var buf bytes.Buffer
	if err := pdf.Output(&buf); err != nil {
		return nil, fmt.Errorf("PDF output: %w", err)
	}

	filename := fmt.Sprintf("expense-%s-report.pdf", sanitiseFilename(eventName))
	return &email.Attachment{
		Filename: filename,
		Content:  buf.Bytes(),
	}, nil
}

// createReceiptZip creates a ZIP archive containing all receipt images from the
// given expenses. Each image is named {event-name}-{index}.{ext} inside the ZIP.
// Returns nil if there are no expenses with images, or if all image files are
// missing from disk.
func createReceiptZip(eventName string, expenses []database.Expense) (*email.Attachment, error) {
	safeName := sanitiseFilename(eventName)
	if safeName == "" {
		safeName = "event"
	}

	var buf bytes.Buffer
	zw := zip.NewWriter(&buf)
	added := 0

	for i, exp := range expenses {
		if exp.ImagePath == "" {
			continue
		}

		// Normalize path (strip legacy "storage/" prefix if present),
		// then construct the full path safely within the storage directory.
		// filepath.Base prevents path traversal by extracting only the filename.
		normPath := normalizeImagePath(exp.ImagePath)
		safePath := filepath.Join("storage", filepath.Base(normPath))

		// Read the image file from disk.
		data, err := os.ReadFile(safePath)
		if err != nil {
			log.Printf("WARN  [%s] handlers: createReceiptZip: reading %q: %v",
				time.Now().Format(time.RFC3339), safePath, err)
			continue
		}

		// Determine file extension from the image path.
		ext := filepath.Ext(exp.ImagePath)
		if ext == "" {
			ext = ".jpg"
		}

		filename := fmt.Sprintf("%s-%d%s", safeName, i+1, ext)
		f, err := zw.Create(filename)
		if err != nil {
			log.Printf("WARN  [%s] handlers: createReceiptZip: creating entry %q: %v",
				time.Now().Format(time.RFC3339), filename, err)
			continue
		}
		if _, err := f.Write(data); err != nil {
			log.Printf("WARN  [%s] handlers: createReceiptZip: writing %q: %v",
				time.Now().Format(time.RFC3339), filename, err)
			continue
		}
		added++
	}

	if err := zw.Close(); err != nil {
		return nil, fmt.Errorf("closing zip: %w", err)
	}

	if added == 0 {
		log.Printf("INFO  [%s] handlers: createReceiptZip: no receipt images found for event %q",
			time.Now().Format(time.RFC3339), eventName)
		return nil, nil
	}

	return &email.Attachment{
		Filename: fmt.Sprintf("expense-%s-images.zip", safeName),
		Content:  buf.Bytes(),
	}, nil
}

// renderFileError writes an HTMX-compatible error fragment targeted at the
// #submit-error container on the event expenses page. Using a 200 status
// ensures HTMX always swaps the content (HTMX skips 4xx/5xx by default).
func renderFileError(w http.ResponseWriter, message string) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.Header().Set("HX-Retarget", "#submit-error")
	w.WriteHeader(http.StatusOK)
	fmt.Fprintf(w, `<div id="submit-error" style="background: #450a0a; border: 1px solid #7f1d1d; color: #fca5a5; padding: 0.75rem; border-radius: 0.5rem; margin-bottom: 1rem;">%s</div>`,
		template.HTMLEscapeString(message))
}

// truncateString truncates a string to the given maximum length, appending "…"
// if the string was shortened.
func truncateString(s string, maxLen int) string {
	if len(s) <= maxLen {
		return s
	}
	return s[:maxLen-1] + "…"
}

// sanitiseFilename converts a string into a safe filename (alphanumerics,
// hyphens, underscores only — no spaces or special characters).
func sanitiseFilename(s string) string {
	var result []rune
	for _, r := range s {
		if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || r == '-' || r == '_' {
			result = append(result, r)
		} else if r == ' ' || r == '.' {
			result = append(result, '-')
		}
	}
	if len(result) == 0 {
		return "expenses"
	}
	return strings.Trim(string(result), "-")
}