package main

import (
	"fmt"
	"os"
	"time"

	tea "github.com/charmbracelet/bubbletea"
	"github.com/charmbracelet/lipgloss"
)

const (
	numRows = 6 // Max possible rows in a calendar month view
	numCols = 7 // Days in a week
	cellW   = 10
	cellH   = 1
)

var (
	cellStyle       = lipgloss.NewStyle().Width(cellW).Height(cellH).Align(lipgloss.Center)
	selectedStyle   = cellStyle.Copy().Bold(true).Background(lipgloss.Color("12")).Foreground(lipgloss.Color("15"))
	unselectedStyle = cellStyle.Copy().Background(lipgloss.Color("236")).Foreground(lipgloss.Color("250"))
	headerStyle     = lipgloss.NewStyle().Width(numCols * cellW).Align(lipgloss.Center).Bold(true)
	daysOfWeekStyle = lipgloss.NewStyle().Width(cellW).Align(lipgloss.Center).Bold(true)
)

type model struct {
	cursorRow  int
	cursorCol  int
	monthIndex int
	year       int
}

func (m model) Init() tea.Cmd {
	return nil
}

func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
	switch msg := msg.(type) {
	case tea.KeyMsg:
		switch msg.String() {
		case "ctrl+c", "q":
			return m, tea.Quit
		case "up":
			if m.cursorRow > 0 {
				m.cursorRow--
			}
		case "down":
			if m.cursorRow < numRows-1 {
				m.cursorRow++
			}
		case "left":
			if m.cursorCol > 0 {
				m.cursorCol--
			}
		case "right":
			if m.cursorCol < numCols-1 {
				m.cursorCol++
			}
		case "a": // Previous month
			if m.monthIndex == 0 {
				m.monthIndex = 11
				m.year--
			} else {
				m.monthIndex--
			}
		case "d": // Next month
			if m.monthIndex == 11 {
				m.monthIndex = 0
				m.year++
			} else {
				m.monthIndex++
			}
		}
	}
	return m, nil
}

func (m model) View() string {
	var out string

	// Header
	monthTime := time.Date(m.year, time.Month(m.monthIndex+1), 1, 0, 0, 0, 0, time.UTC)
	header := headerStyle.Render(monthTime.Format("January 2006"))
	out += header + "\n"

	// Days of the week header
	weekdays := []string{"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"}
	for _, day := range weekdays {
		out += daysOfWeekStyle.Render(day)
	}
	out += "\n"

	// First weekday and number of days
	firstDay := time.Date(m.year, time.Month(m.monthIndex+1), 1, 0, 0, 0, 0, time.UTC)
	startWeekday := int(firstDay.Weekday())
	daysInMonth := time.Date(m.year, time.Month(m.monthIndex+2), 0, 0, 0, 0, 0, time.UTC).Day()

	// Calendar grid
	day := 1
	for r := 0; r < numRows; r++ {
		for c := 0; c < numCols; c++ {
			cellNum := r*numCols + c
			var content string

			if cellNum >= startWeekday && day <= daysInMonth {
				content = fmt.Sprintf("%2d", day)
				if r == m.cursorRow && c == m.cursorCol {
					out += selectedStyle.Render(content)
				} else {
					out += unselectedStyle.Render(content)
				}
				day++
			} else {
				out += cellStyle.Render("") // Empty cell
			}
		}
		out += "\n"
	}

	out += "\n[a]/[d] to change month, arrows to move, q to quit."
	return out
}

func main() {
	now := time.Now()
	p := tea.NewProgram(model{
		year:       now.Year(),
		monthIndex: int(now.Month()) - 1,
	})
	if err := p.Start(); err != nil {
		fmt.Fprintf(os.Stderr, "error: %v", err)
		os.Exit(1)
	}
}