package tui

import (
	"fmt"
	"slices"
	"strings"
	"time"

	models "git.mlow.ca/mlow/lmcli/pkg/lmcli/model"
	"git.mlow.ca/mlow/lmcli/pkg/util"
	"github.com/charmbracelet/bubbles/viewport"
	tea "github.com/charmbracelet/bubbletea"
	"github.com/charmbracelet/lipgloss"
)

type loadedConversation struct {
	conv      models.Conversation
	lastReply models.Message
}

type (
	// sent when conversation list is loaded
	msgConversationsLoaded ([]loadedConversation)
	// sent when a conversation is selected
	msgConversationSelected models.Conversation
)

type conversationsModel struct {
	basemodel

	conversations []loadedConversation
	cursor        int   // index of the currently selected conversation
	itemOffsets   []int // keeps track of the viewport y offset of each rendered item

	content viewport.Model
}

func newConversationsModel(tui *model) conversationsModel {
	m := conversationsModel{
		basemodel: basemodel{
			opts:   tui.opts,
			ctx:    tui.ctx,
			views:  tui.views,
			width:  tui.width,
			height: tui.height,
		},
		content: viewport.New(0, 0),
	}
	return m
}

func (m *conversationsModel) handleInput(msg tea.KeyMsg) (bool, tea.Cmd) {
	switch msg.String() {
	case "enter":
		if len(m.conversations) > 0 && m.cursor < len(m.conversations) {
			return true, func() tea.Msg {
				return msgConversationSelected(m.conversations[m.cursor].conv)
			}
		}
	case "j", "down":
		if m.cursor < len(m.conversations)-1 {
			m.cursor++
			if m.cursor == len(m.conversations)-1 {
				// if last conversation, simply scroll to the bottom
				m.content.GotoBottom()
			} else {
				// this hack positions the *next* conversatoin slightly
				// *off* the screen, ensuring the entire m.cursor is shown,
				// even if its height may not be constant due to wrapping.
				scrollIntoView(&m.content, m.itemOffsets[m.cursor+1], -1)
			}
			m.content.SetContent(m.renderConversationList())
		} else {
			m.cursor = len(m.conversations) - 1
			m.content.GotoBottom()
		}
		return true, nil
	case "k", "up":
		if m.cursor > 0 {
			m.cursor--
			if m.cursor == 0 {
				m.content.GotoTop()
			} else {
				scrollIntoView(&m.content, m.itemOffsets[m.cursor], 1)
			}
			m.content.SetContent(m.renderConversationList())
		} else {
			m.cursor = 0
			m.content.GotoTop()
		}
		return true, nil
	case "n":
		// new conversation
	case "d":
		// show prompt to delete conversation
	case "c":
		// copy/clone conversation
	case "r":
		// show prompt to rename conversation
	case "shift+r":
		// show prompt to generate name for conversation
	}
	return false, nil
}

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

func (m *conversationsModel) handleResize(width, height int) {
	m.width, m.height = width, height
	m.content.Width = width
}

func (m conversationsModel) Update(msg tea.Msg) (conversationsModel, tea.Cmd) {
	var cmds []tea.Cmd
	switch msg := msg.(type) {
	case msgStateChange:
		cmds = append(cmds, m.loadConversations())
		m.content.SetContent(m.renderConversationList())
	case tea.WindowSizeMsg:
		m.handleResize(msg.Width, msg.Height)
		m.content.SetContent(m.renderConversationList())
	case msgConversationsLoaded:
		m.conversations = msg
		m.content.SetContent(m.renderConversationList())
	}

	var cmd tea.Cmd
	m.content, cmd = m.content.Update(msg)
	if cmd != nil {
		cmds = append(cmds, cmd)
	}

	if m.width > 0 {
		m.views.header = m.headerView()
		m.views.footer = "" // TODO: show /something/
		m.views.error = errorBanner(m.err, m.width)
		fixedHeight := height(m.views.header) + height(m.views.error) + height(m.views.footer)
		m.content.Height = m.height - fixedHeight
		m.views.content = m.content.View()
	}
	return m, tea.Batch(cmds...)
}

func (m *conversationsModel) loadConversations() tea.Cmd {
	return func() tea.Msg {
		conversations, err := m.ctx.Store.Conversations()
		if err != nil {
			return msgError(fmt.Errorf("Could not load conversations: %v", err))
		}

		loaded := make([]loadedConversation, len(conversations))
		for i, c := range conversations {
			lastMessage, err := m.ctx.Store.LastMessage(&c)
			if err != nil {
				return msgError(err)
			}
			loaded[i].conv = c
			loaded[i].lastReply = *lastMessage
		}

		slices.SortFunc(loaded, func(a, b loadedConversation) int {
			return b.lastReply.CreatedAt.Compare(a.lastReply.CreatedAt)
		})

		return msgConversationsLoaded(loaded)
	}
}

func (m *conversationsModel) headerView() string {
	titleStyle := lipgloss.NewStyle().Bold(true)
	header := titleStyle.Render("Conversations")
	return headerStyle.Width(m.width).Render(header)
}

func (m *conversationsModel) renderConversationList() string {
	now := time.Now()
	midnight := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, now.Location())
	monthStart := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, now.Location())
	dayOfWeek := int(now.Weekday())
	categories := []struct {
		name   string
		cutoff time.Duration
	}{
		{"Today", now.Sub(midnight)},
		{"Yesterday", now.Sub(midnight.AddDate(0, 0, -1))},
		{"This week", now.Sub(midnight.AddDate(0, 0, -dayOfWeek))},
		{"Last week", now.Sub(midnight.AddDate(0, 0, -(dayOfWeek + 7)))},
		{"This month", now.Sub(monthStart)},
		{"Last month", now.Sub(monthStart.AddDate(0, -1, 0))},
		{"2 Months ago", now.Sub(monthStart.AddDate(0, -2, 0))},
		{"3 Months ago", now.Sub(monthStart.AddDate(0, -3, 0))},
		{"4 Months ago", now.Sub(monthStart.AddDate(0, -4, 0))},
		{"5 Months ago", now.Sub(monthStart.AddDate(0, -5, 0))},
		{"6 Months ago", now.Sub(monthStart.AddDate(0, -6, 0))},
		{"Older", now.Sub(time.Time{})},
	}

	categoryStyle := lipgloss.NewStyle().
		MarginBottom(1).
		Foreground(lipgloss.Color("12")).
		PaddingLeft(1).
		Bold(true)

	itemStyle := lipgloss.NewStyle().
		MarginBottom(1)

	ageStyle := lipgloss.NewStyle().Faint(true).SetString()
	titleStyle := lipgloss.NewStyle().Bold(true)
	untitledStyle := lipgloss.NewStyle().Faint(true).Italic(true)
	selectedStyle := lipgloss.NewStyle().Faint(true).Foreground(lipgloss.Color("6"))

	var (
		currentOffset   int
		currentCategory string
		sb              strings.Builder
	)

	m.itemOffsets = make([]int, len(m.conversations))
	sb.WriteRune('\n')
	currentOffset += 1

	for i, c := range m.conversations {
		lastReplyAge := now.Sub(c.lastReply.CreatedAt)

		var category string
		for _, g := range categories {
			if lastReplyAge < g.cutoff {
				category = g.name
				break
			}
		}

		// print the category
		if category != currentCategory {
			currentCategory = category
			heading := categoryStyle.Render(currentCategory)
			sb.WriteString(heading)
			currentOffset += height(heading)
			sb.WriteRune('\n')
		}

		tStyle := titleStyle.Copy()
		if c.conv.Title == "" {
			tStyle = tStyle.Inherit(untitledStyle).SetString("(untitled)")
		}
		if i == m.cursor {
			tStyle = tStyle.Inherit(selectedStyle)
		}

		title := tStyle.Width(m.width - 3).PaddingLeft(2).Render(c.conv.Title)
		if i == m.cursor {
			title = ">" + title[1:]
		}

		m.itemOffsets[i] = currentOffset
		item := itemStyle.Render(fmt.Sprintf(
			"%s\n  %s",
			title,
			ageStyle.Render(util.HumanTimeElapsedSince(lastReplyAge)),
		))
		sb.WriteString(item)
		currentOffset += height(item)
		if i < len(m.conversations)-1 {
			sb.WriteRune('\n')
		}
	}
	return sb.String()
}