package main

import (
	"bytes"
	"context"
	"encoding/csv"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"github.com/wailsapp/wails/v2/pkg/runtime"
)

// CSVData represents the CSV data passed between Go and the frontend.
type CSVData struct {
	Headers  []string   `json:"Headers"`
	Rows     [][]string `json:"Rows"`
	FilePath string     `json:"FilePath"`
}

// App struct holds the application state.
type App struct {
	ctx         context.Context
	headers     []string
	rows        [][]string
	currentFile string
}

// NewApp creates a new App application struct.
func NewApp() *App {
	return &App{}
}

// startup is called when the app starts. The context is saved
// so we can call the runtime methods.
func (a *App) startup(ctx context.Context) {
	a.ctx = ctx

	// Set up file drop handler
	runtime.OnFileDrop(ctx, func(x, y int, paths []string) {
		if len(paths) > 0 {
			runtime.EventsEmit(ctx, "file-dropped", paths[0])
		}
	})
}

// domReady is called after the front-end DOM is ready.
func (a *App) domReady(ctx context.Context) {
	// placeholder for any post-DOM-ready initialisation
}

// LoadCSV reads a CSV file and returns its data. The first row is treated as headers.
func (a *App) LoadCSV(filePath string) (*CSVData, error) {
	data, err := os.ReadFile(filePath)
	if err != nil {
		return nil, fmt.Errorf("failed to read file: %w", err)
	}

	reader := csv.NewReader(bytes.NewReader(data))
	reader.FieldsPerRecord = -1 // allow variable field counts

	records, err := reader.ReadAll()
	if err != nil {
		return nil, fmt.Errorf("failed to parse CSV: %w", err)
	}

	if len(records) == 0 {
		a.headers = []string{}
		a.rows = [][]string{}
		a.currentFile = filePath
		a.updateWindowTitle()
		return &CSVData{Headers: a.headers, Rows: a.rows, FilePath: filePath}, nil
	}

	a.headers = records[0]
	if len(records) > 1 {
		a.rows = records[1:]
	} else {
		a.rows = [][]string{}
	}
	a.currentFile = filePath
	a.updateWindowTitle()

	return &CSVData{Headers: a.headers, Rows: a.rows, FilePath: filePath}, nil
}

// SaveCSV writes headers and rows to the given file path as CSV.
func (a *App) SaveCSV(filePath string, headers []string, rows [][]string) error {
	f, err := os.Create(filePath)
	if err != nil {
		return fmt.Errorf("failed to create file: %w", err)
	}
	defer f.Close()

	writer := csv.NewWriter(f)
	defer writer.Flush()

	if err := writer.Write(headers); err != nil {
		return fmt.Errorf("failed to write headers: %w", err)
	}
	for _, row := range rows {
		if err := writer.Write(row); err != nil {
			return fmt.Errorf("failed to write row: %w", err)
		}
	}

	a.headers = headers
	a.rows = rows
	a.currentFile = filePath
	a.updateWindowTitle()

	return nil
}

// SaveCurrentFile saves to the currently open file.
func (a *App) SaveCurrentFile(headers []string, rows [][]string) error {
	if a.currentFile == "" {
		return fmt.Errorf("no file is currently open")
	}
	return a.SaveCSV(a.currentFile, headers, rows)
}

// GetTableData returns the current CSV state.
func (a *App) GetTableData() *CSVData {
	return &CSVData{
		Headers:  a.headers,
		Rows:     a.rows,
		FilePath: a.currentFile,
	}
}

// SetTableData updates the in-memory state from the frontend.
func (a *App) SetTableData(headers []string, rows [][]string) {
	a.headers = headers
	a.rows = rows
}

// OpenFileDialog shows a native open dialog filtered for CSV files.
func (a *App) OpenFileDialog() (string, error) {
	return runtime.OpenFileDialog(a.ctx, runtime.OpenDialogOptions{
		Title: "Open CSV File",
		Filters: []runtime.FileFilter{
			{
				DisplayName: "CSV Files (*.csv)",
				Pattern:     "*.csv",
			},
			{
				DisplayName: "All Files (*.*)",
				Pattern:     "*.*",
			},
		},
	})
}

// SaveFileDialog shows a native save dialog.
func (a *App) SaveFileDialog() (string, error) {
	return runtime.SaveFileDialog(a.ctx, runtime.SaveDialogOptions{
		Title:           "Save CSV File",
		DefaultFilename: "untitled.csv",
		Filters: []runtime.FileFilter{
			{
				DisplayName: "CSV Files (*.csv)",
				Pattern:     "*.csv",
			},
			{
				DisplayName: "All Files (*.*)",
				Pattern:     "*.*",
			},
		},
	})
}

// ParseCSVString parses CSV text content and returns structured data.
func (a *App) ParseCSVString(content string) (*CSVData, error) {
	reader := csv.NewReader(strings.NewReader(content))
	reader.FieldsPerRecord = -1

	records, err := reader.ReadAll()
	if err != nil {
		return nil, fmt.Errorf("failed to parse CSV string: %w", err)
	}

	if len(records) == 0 {
		return &CSVData{Headers: []string{}, Rows: [][]string{}}, nil
	}

	headers := records[0]
	var rows [][]string
	if len(records) > 1 {
		rows = records[1:]
	} else {
		rows = [][]string{}
	}

	return &CSVData{Headers: headers, Rows: rows}, nil
}

// FormatAsCSV formats headers and rows as a CSV string.
func (a *App) FormatAsCSV(headers []string, rows [][]string) string {
	var buf bytes.Buffer
	writer := csv.NewWriter(&buf)

	_ = writer.Write(headers)
	for _, row := range rows {
		_ = writer.Write(row)
	}
	writer.Flush()

	return buf.String()
}

// FormatRowsAsCSV formats just the rows (no headers) as CSV text.
func (a *App) FormatRowsAsCSV(rows [][]string) string {
	var buf bytes.Buffer
	writer := csv.NewWriter(&buf)
	for _, row := range rows {
		_ = writer.Write(row)
	}
	writer.Flush()
	return buf.String()
}

// FormatAsMarkdown formats headers and rows as a Markdown table.
func (a *App) FormatAsMarkdown(headers []string, rows [][]string) string {
	if len(headers) == 0 {
		return ""
	}

	var sb strings.Builder

	// Header row
	sb.WriteString("| ")
	sb.WriteString(strings.Join(headers, " | "))
	sb.WriteString(" |\n")

	// Separator row
	separators := make([]string, len(headers))
	for i := range separators {
		separators[i] = "---"
	}
	sb.WriteString("| ")
	sb.WriteString(strings.Join(separators, " | "))
	sb.WriteString(" |\n")

	// Data rows
	for _, row := range rows {
		padded := padRow(row, len(headers))
		sb.WriteString("| ")
		sb.WriteString(strings.Join(padded, " | "))
		sb.WriteString(" |\n")
	}

	return sb.String()
}

// FormatAsJira formats headers and rows as Jira table markup.
func (a *App) FormatAsJira(headers []string, rows [][]string) string {
	if len(headers) == 0 {
		return ""
	}

	var sb strings.Builder

	// Header row: || Header1 || Header2 ||
	sb.WriteString("|| ")
	sb.WriteString(strings.Join(headers, " || "))
	sb.WriteString(" ||\n")

	// Data rows: | val1 | val2 |
	for _, row := range rows {
		padded := padRow(row, len(headers))
		sb.WriteString("| ")
		sb.WriteString(strings.Join(padded, " | "))
		sb.WriteString(" |\n")
	}

	return sb.String()
}

// FormatAsSingleColumn formats a single column of data as newline-separated lines.
func (a *App) FormatAsSingleColumn(rows [][]string) string {
	var lines []string
	for _, row := range rows {
		if len(row) > 0 {
			lines = append(lines, row[0])
		} else {
			lines = append(lines, "")
		}
	}
	return strings.Join(lines, "\n")
}

// SetWindowTitle sets the window title. If title is empty, resets to default.
func (a *App) SetWindowTitle(title string) {
	if title == "" {
		runtime.WindowSetTitle(a.ctx, "CSV Tool")
	} else {
		runtime.WindowSetTitle(a.ctx, title+" - CSV Tool")
	}
}

// updateWindowTitle sets the window title based on the current file.
func (a *App) updateWindowTitle() {
	if a.currentFile == "" {
		runtime.WindowSetTitle(a.ctx, "CSV Tool")
	} else {
		name := filepath.Base(a.currentFile)
		runtime.WindowSetTitle(a.ctx, name+" - CSV Tool")
	}
}

// padRow ensures a row has exactly n columns, padding with empty strings if needed.
func padRow(row []string, n int) []string {
	if len(row) >= n {
		return row[:n]
	}
	padded := make([]string, n)
	copy(padded, row)
	return padded
}