package public

import (
	"context"
	"fmt"
	"strconv"
	"strings"
	"time"

	"velox-bot/internal/commands/schedule/shared"
	"velox-bot/internal/db/services"

	"github.com/bwmarrin/discordgo"
)

var Schedule = &discordgo.ApplicationCommand{
	Name:        "schedule",
	Description: "Schedule 1:1 sessions",
	Options: []*discordgo.ApplicationCommandOption{
		{
			Type:        discordgo.ApplicationCommandOptionSubCommand,
			Name:        "create",
			Description: "Create a new session with a user",
			Options: []*discordgo.ApplicationCommandOption{
				{
					Type:        discordgo.ApplicationCommandOptionUser,
					Name:        "user",
					Description: "User to invite",
					Required:    true,
				},
				{
					Type:        discordgo.ApplicationCommandOptionString,
					Name:        "datetime",
					Description: "When (UTC), format: 2006-01-02 15:04",
					Required:    true,
				},
				{
					Type:        discordgo.ApplicationCommandOptionString,
					Name:        "description",
					Description: "What is this session about? (optional)",
					Required:    false,
				},
			},
		},
		{
			Type:        discordgo.ApplicationCommandOptionSubCommand,
			Name:        "list",
			Description: "List your upcoming sessions",
		},
		{
			Type:        discordgo.ApplicationCommandOptionSubCommand,
			Name:        "reschedule",
			Description: "Reschedule an existing session",
			Options: []*discordgo.ApplicationCommandOption{
				{
					Type:        discordgo.ApplicationCommandOptionInteger,
					Name:        "id",
					Description: "ID of the session (from /schedule list)",
					Required:    true,
				},
				{
					Type:        discordgo.ApplicationCommandOptionString,
					Name:        "datetime",
					Description: "New datetime (UTC), format: 2006-01-02 15:04",
					Required:    true,
				},
			},
		},
	},
}

func ScheduleHandler(s *discordgo.Session, i *discordgo.InteractionCreate) {
	if !shared.RequireGuild(s, i) || !shared.RequireScheduleService(s, i) {
		return
	}

	data := i.ApplicationCommandData()
	if len(data.Options) == 0 {
		handleList(s, i)
		return
	}

	switch data.Options[0].Name {
	case "create":
		handleCreate(s, i)
	case "list":
		handleList(s, i)
	case "reschedule":
		handleReschedule(s, i)
	default:
		shared.RespondEphemeral(s, i, "Unknown subcommand.")
	}
}

func handleCreate(s *discordgo.Session, i *discordgo.InteractionCreate) {
	guildID, ok := shared.ParseGuildID(s, i)
	if !ok {
		return
	}
	if i.Member == nil || i.Member.User == nil {
		shared.RespondEphemeral(s, i, "Missing member info.")
		return
	}

	data := i.ApplicationCommandData()
	if len(data.Options) == 0 {
		shared.RespondEphemeral(s, i, "Missing options.")
		return
	}
	opt := data.Options[0]

	var (
		targetUser *discordgo.User
		whenStr    string
		desc       string
	)
	for _, o := range opt.Options {
		switch o.Name {
		case "user":
			targetUser = o.UserValue(s)
		case "datetime":
			whenStr = o.StringValue()
		case "description":
			desc = o.StringValue()
		}
	}

	if targetUser == nil {
		shared.RespondEphemeral(s, i, "Invalid user.")
		return
	}
	if targetUser.ID == i.Member.User.ID {
		shared.RespondEphemeral(s, i, "You cannot schedule a session with yourself.")
		return
	}

	whenStr = strings.TrimSpace(whenStr)
	if whenStr == "" {
		shared.RespondEphemeral(s, i, "Datetime cannot be empty.")
		return
	}

	// Expect layout "2006-01-02 15:04" in UTC.
	when, err := time.ParseInLocation("2006-01-02 15:04", whenStr, time.UTC)
	if err != nil {
		shared.RespondEphemeral(s, i, "Invalid datetime format. Use `2006-01-02 15:04` in UTC.")
		return
	}

	requesterID, err := strconv.ParseInt(i.Member.User.ID, 10, 64)
	if err != nil {
		shared.RespondEphemeral(s, i, "Invalid user ID.")
		return
	}
	inviteeID, err := strconv.ParseInt(targetUser.ID, 10, 64)
	if err != nil {
		shared.RespondEphemeral(s, i, "Invalid target user ID.")
		return
	}

	ctx := context.Background()
	scheduleID, err := services.Global.Schedule.CreateSchedule(ctx, guildID, requesterID, inviteeID, when, desc)
	if err != nil {
		shared.RespondEphemeral(s, i, "Failed to create schedule.")
		return
	}

	// Send DM to invitee.
	dmCh, err := s.UserChannelCreate(targetUser.ID)
	if err != nil {
		shared.RespondEphemeral(s, i, "Failed to DM the invited user (are DMs disabled?).")
		return
	}

	embed := &discordgo.MessageEmbed{
		Title:       "New session request",
		Description: fmt.Sprintf("You have been invited to a session by <@%s>.", i.Member.User.ID),
		Color:       0x4caf50,
		Fields: []*discordgo.MessageEmbedField{
			{
				Name:  "When (UTC)",
				Value: when.Format("2006-01-02 15:04"),
			},
		},
	}
	if desc != "" {
		embed.Fields = append(embed.Fields, &discordgo.MessageEmbedField{
			Name:  "Description",
			Value: desc,
		})
	}

	msg, err := s.ChannelMessageSendComplex(dmCh.ID, &discordgo.MessageSend{
		Content: "React with ✅ to accept, ❌ to decline, or 🔁 to request rescheduling.",
		Embed:   embed,
	})
	if err != nil {
		shared.RespondEphemeral(s, i, "Failed to DM the invited user.")
		return
	}

	// Add reactions for interaction.
	for _, emoji := range []string{"✅", "❌", "🔁"} {
		_ = s.MessageReactionAdd(dmCh.ID, msg.ID, emoji)
	}

	// Store linkage between message and schedule.
	msgID64, _ := strconv.ParseInt(msg.ID, 10, 64)
	chID64, _ := strconv.ParseInt(dmCh.ID, 10, 64)
	_ = services.Global.Schedule.AddMessage(ctx, scheduleID, msgID64, chID64, true)

	shared.RespondEphemeral(s, i, "Session request created and sent to "+targetUser.Mention()+".")
}

func handleList(s *discordgo.Session, i *discordgo.InteractionCreate) {
	guildID, ok := shared.ParseGuildID(s, i)
	if !ok {
		return
	}
	if i.Member == nil || i.Member.User == nil {
		shared.RespondEphemeral(s, i, "Missing member info.")
		return
	}

	userID, err := strconv.ParseInt(i.Member.User.ID, 10, 64)
	if err != nil {
		shared.RespondEphemeral(s, i, "Invalid user ID.")
		return
	}

	const limit = 10
	items, err := services.Global.Schedule.ListForUser(context.Background(), guildID, userID, limit)
	if err != nil {
		shared.RespondEphemeral(s, i, "Failed to load your sessions.")
		return
	}
	if len(items) == 0 {
		shared.RespondEphemeral(s, i, "You have no upcoming sessions.")
		return
	}

	var b strings.Builder
	for _, sch := range items {
		role := "Requester"
		otherID := sch.InviteeID
		if sch.InviteeID == userID {
			role = "Invitee"
			otherID = sch.RequesterID
		}
		status := string(sch.Status)
		whenStr := sch.ScheduledAt.UTC().Format("2006-01-02 15:04")
		line := fmt.Sprintf("ID `%d` • %s with <@%d> at %s UTC (%s)\n", sch.ID, role, otherID, whenStr, status)
		if sch.Description != "" {
			line += "  " + sch.Description + "\n"
		}
		b.WriteString(line)
	}

	shared.RespondEphemeral(s, i, b.String())
}

func handleReschedule(s *discordgo.Session, i *discordgo.InteractionCreate) {
	guildID, ok := shared.ParseGuildID(s, i)
	if !ok {
		return
	}
	if i.Member == nil || i.Member.User == nil {
		shared.RespondEphemeral(s, i, "Missing member info.")
		return
	}

	data := i.ApplicationCommandData()
	if len(data.Options) == 0 {
		shared.RespondEphemeral(s, i, "Missing options.")
		return
	}
	opt := data.Options[0]

	var (
		idVal   int64
		whenStr string
	)
	for _, o := range opt.Options {
		switch o.Name {
		case "id":
			idVal = o.IntValue()
		case "datetime":
			whenStr = o.StringValue()
		}
	}
	if idVal <= 0 {
		shared.RespondEphemeral(s, i, "Invalid session ID.")
		return
	}
	whenStr = strings.TrimSpace(whenStr)
	if whenStr == "" {
		shared.RespondEphemeral(s, i, "Datetime cannot be empty.")
		return
	}

	when, err := time.ParseInLocation("2006-01-02 15:04", whenStr, time.UTC)
	if err != nil {
		shared.RespondEphemeral(s, i, "Invalid datetime format. Use `2006-01-02 15:04` in UTC.")
		return
	}

	userID, err := strconv.ParseInt(i.Member.User.ID, 10, 64)
	if err != nil {
		shared.RespondEphemeral(s, i, "Invalid user ID.")
		return
	}

	ctx := context.Background()
	sch, err := services.Global.Schedule.GetByID(ctx, idVal)
	if err != nil || sch == nil {
		shared.RespondEphemeral(s, i, "Session not found.")
		return
	}
	if sch.GuildID != guildID {
		shared.RespondEphemeral(s, i, "This session belongs to another server.")
		return
	}
	if userID != sch.RequesterID && userID != sch.InviteeID {
		shared.RespondEphemeral(s, i, "You are not part of this session.")
		return
	}

	if err := services.Global.Schedule.Reschedule(ctx, sch.ID, when); err != nil {
		shared.RespondEphemeral(s, i, "Failed to reschedule session.")
		return
	}

	// Notify participants via DM and send new request DM to invitee.
	whenFmt := when.Format("2006-01-02 15:04")

	otherID := sch.InviteeID
	if userID == sch.InviteeID {
		otherID = sch.RequesterID
	}

	// DM both about the change
	msg := fmt.Sprintf("Session `%d` has been rescheduled to %s UTC with <@%d>.", sch.ID, whenFmt, otherID)
	if sch.Description != "" {
		msg += "\nTopic: " + sch.Description
	}
	for _, uid := range []int64{sch.RequesterID, sch.InviteeID} {
		ch, err := s.UserChannelCreate(strconv.FormatInt(uid, 10))
		if err != nil {
			continue
		}
		_, _ = s.ChannelMessageSend(ch.ID, msg)
	}

	// Send new "request" DM to invitee with reactions again.
	inviteeStr := strconv.FormatInt(sch.InviteeID, 10)
	inviteeUser, err := s.User(inviteeStr)
	if err == nil && inviteeUser != nil {
		dmCh, err := s.UserChannelCreate(inviteeStr)
		if err == nil {
			embed := &discordgo.MessageEmbed{
				Title:       "Rescheduled session",
				Description: fmt.Sprintf("Session `%d` has been rescheduled by <@%s>.", sch.ID, i.Member.User.ID),
				Color:       0xffc107,
				Fields: []*discordgo.MessageEmbedField{
					{
						Name:  "When (UTC)",
						Value: whenFmt,
					},
				},
			}
			if sch.Description != "" {
				embed.Fields = append(embed.Fields, &discordgo.MessageEmbedField{
					Name:  "Description",
					Value: sch.Description,
				})
			}
			msgObj, err := s.ChannelMessageSendComplex(dmCh.ID, &discordgo.MessageSend{
				Content: "React with ✅ to accept, ❌ to decline, or 🔁 to request another reschedule.",
				Embed:   embed,
			})
			if err == nil && msgObj != nil {
				for _, emoji := range []string{"✅", "❌", "🔁"} {
					_ = s.MessageReactionAdd(dmCh.ID, msgObj.ID, emoji)
				}
				msgID64, _ := strconv.ParseInt(msgObj.ID, 10, 64)
				chID64, _ := strconv.ParseInt(dmCh.ID, 10, 64)
				_ = services.Global.Schedule.AddMessage(ctx, sch.ID, msgID64, chID64, true)
			}
		}
	}

	shared.RespondEphemeral(s, i, "Session rescheduled to "+whenFmt+" UTC.")
}