package snake

import (
	"encoding/json"
	"time"

	"github.com/ryanhamamura/games/player"
)

// SubjectPrefix is the NATS subject namespace for snake games.
const SubjectPrefix = "snake"

// GameSubject returns the NATS subject for game state updates.
func GameSubject(gameID string) string { return SubjectPrefix + "." + gameID }

// ChatSubject returns the NATS subject for chat messages.
func ChatSubject(gameID string) string { return SubjectPrefix + ".chat." + gameID }

type Direction int

const (
	DirUp Direction = iota
	DirDown
	DirLeft
	DirRight
)

type GameMode int

const (
	ModeMultiplayer  GameMode = iota // Default (0) - backward compatible
	ModeSinglePlayer                 // Single player survival mode
)

// Opposite returns true if a and b are 180-degree reversals.
func (d Direction) Opposite(other Direction) bool {
	switch d {
	case DirUp:
		return other == DirDown
	case DirDown:
		return other == DirUp
	case DirLeft:
		return other == DirRight
	case DirRight:
		return other == DirLeft
	}
	return false
}

type Point struct {
	X int `json:"x"`
	Y int `json:"y"`
}

type Snake struct {
	Body    []Point   `json:"body"`
	Dir     Direction `json:"dir"`
	Alive   bool      `json:"alive"`
	Growing bool      `json:"growing"`
	Color   int       `json:"color"` // 1-8
}

type GameState struct {
	Width  int      `json:"width"`
	Height int      `json:"height"`
	Snakes []*Snake `json:"snakes"`
	Food   []Point  `json:"food"`
}

func (gs *GameState) ToJSON() string {
	data, _ := json.Marshal(gs)
	return string(data)
}

func GameStateFromJSON(data string) (*GameState, error) {
	var gs GameState
	if err := json.Unmarshal([]byte(data), &gs); err != nil {
		return nil, err
	}
	return &gs, nil
}

type Status int

const (
	StatusWaitingForPlayers Status = iota
	StatusCountdown
	StatusInProgress
	StatusFinished
)

type Player struct {
	ID       player.ID
	UserID   *string
	Nickname string
	Slot     int // 0-7
}

type SnakeGame struct {
	ID            string
	State         *GameState
	Players       []*Player // up to 8
	Status        Status
	Winner        *Player   // nil if draw
	CountdownEnd  time.Time // when countdown reaches 0
	RematchGameID *string
	Mode          GameMode // ModeMultiplayer or ModeSinglePlayer
	Score         int      // tracks food eaten in single player
	Speed         int      // cells per second
}

// SpeedPreset defines a named speed option for the snake game.
type SpeedPreset struct {
	Name  string
	Speed int
}

var SpeedPresets = []SpeedPreset{
	{Name: "Slow", Speed: 5},
	{Name: "Normal", Speed: 7},
	{Name: "Fast", Speed: 10},
	{Name: "Insane", Speed: 15},
}

const DefaultSpeed = 7

func (sg *SnakeGame) IsFinished() bool {
	return sg.Status == StatusFinished
}

func (sg *SnakeGame) PlayerCount() int {
	count := 0
	for _, p := range sg.Players {
		if p != nil {
			count++
		}
	}
	return count
}

// GridPreset defines a named grid size option for the snake game.
type GridPreset struct {
	Name   string
	Width  int
	Height int
}

var GridPresets = []GridPreset{
	{Name: "Tiny", Width: 15, Height: 15},
	{Name: "Small", Width: 20, Height: 20},
	{Name: "Medium", Width: 30, Height: 20},
	{Name: "Large", Width: 40, Height: 20},
	{Name: "XL", Width: 50, Height: 30},
}

// snapshot returns a shallow copy of the game safe for reading outside the lock.
// Slices and pointers are shared but the top-level struct is copied.
func (sg *SnakeGame) snapshot() *SnakeGame {
	cp := *sg
	if sg.State != nil {
		stateCp := *sg.State
		// Copy slices so the caller's iteration is safe
		stateCp.Snakes = make([]*Snake, len(sg.State.Snakes))
		copy(stateCp.Snakes, sg.State.Snakes)
		stateCp.Food = make([]Point, len(sg.State.Food))
		copy(stateCp.Food, sg.State.Food)
		cp.State = &stateCp
	}
	cp.Players = make([]*Player, len(sg.Players))
	copy(cp.Players, sg.Players)
	// Mode and Score are value types, already copied by *sg
	return &cp
}

// SnakeColors are hex color values for CSS, indexed by player slot.
var SnakeColors = []string{
	"#00b894", // 1: Green
	"#e17055", // 2: Orange
	"#0984e3", // 3: Blue
	"#6c5ce7", // 4: Purple
	"#fd79a8", // 5: Pink
	"#00cec9", // 6: Cyan
	"#d63031", // 7: Red
	"#fdcb6e", // 8: Yellow
}