package game

import (
	"errors"

	"git.sunturtle.xyz/studio/shotgun/player"
	"git.sunturtle.xyz/studio/shotgun/serve"
)

type Game struct {
	rng     RNG
	players [2]Player
	shells  []bool
	round   uint
	group   uint
	turn    uint
	hp      int8
	damage  int8
	reveal  bool
	prev    *bool

	// Backing storage for shells.
	shellArray [8]bool
}

// New creates a new game started at round 1.
func New(dealer, challenger player.ID) *Game {
	g := &Game{
		rng: NewRNG(),
		players: [2]Player{
			{id: dealer},
			{id: challenger},
		},
	}
	g.StartRound()
	return g
}

// StartRound starts the next round of a game.
func (g *Game) StartRound() {
	g.hp = int8(g.rng.Intn(3) + 2)
	g.players[0].StartRound(g.hp)
	g.players[1].StartRound(g.hp)
	g.round++
	g.group = 0
	g.StartGroup()
}

// StartGroup starts the next shell group of a round.
func (g *Game) StartGroup() {
	items := g.rng.Intn(4) + 1
	g.players[0].StartGroup(&g.rng, items)
	g.players[1].StartGroup(&g.rng, items)
	shells := g.rng.Intn(6) + 2
	for i := 0; i < shells/2; i++ {
		g.shellArray[i] = true
	}
	for i := shells / 2; i < shells; i++ {
		g.shellArray[i] = false
	}
	g.shells = g.shellArray[:shells]
	ShuffleSlice(&g.rng, g.shells)
	g.group++
	g.turn = 0
	g.prev = nil
	g.NextTurn()
}

// NextTurn advances the turn.
func (g *Game) NextTurn() {
	g.turn++
	g.damage = 1
	g.reveal = false
	cur := g.CurrentPlayer()
	skip := cur.cuffs == CuffedSkip
	cur.cuffs = cur.cuffs.NextState()
	if skip {
		g.NextTurn()
	}
}

// CurrentPlayer gets the index of the current player, either 0 or 1.
func (g *Game) CurrentPlayer() *Player {
	return &g.players[g.turn%2]
}

// Opponent returns the player who is not the current player.
func (g *Game) Opponent() *Player {
	return &g.players[g.turn%2^1]
}

// Apply uses an item by index for the current player.
// This may cause the group to end.
// Returns ErrWrongTurn if id does not correspond to the current player.
func (g *Game) Apply(id player.ID, item int) error {
	cur := g.CurrentPlayer()
	if cur.id != id {
		return ErrWrongTurn
	}
	if item < 0 || item >= len(cur.items) {
		return errors.New("item index out of bounds")
	}
	if cur.items[item].Apply(g) {
		cur.items[item] = ItemNone
	}
	return nil
}

// PopShell removes a shell from the shotgun.
// This may cause the shotgun to be empty, but does not start the next group
// if so.
func (g *Game) PopShell() bool {
	g.prev = &g.shells[0]
	g.shells = g.shells[1:]
	return *g.prev
}

// Peek returns the current turn's shell if it is revealed for the player with
// the given ID, or nil otherwise.
func (g *Game) Peek(id player.ID) *bool {
	if len(g.shells) == 0 || id != g.CurrentPlayer().id || !g.reveal {
		return nil
	}
	return &g.shells[0]
}

// Empty returns whether the shotgun is empty.
func (g *Game) Empty() bool {
	return len(g.shells) == 0
}

// Winner returns the player who won, or nil if the round is not over.
func (g *Game) Winner() *Player {
	if g.players[0].hp <= 0 {
		return &g.players[1]
	}
	if g.players[1].hp <= 0 {
		return &g.players[0]
	}
	return nil
}

// Shoot fires the shotgun, at the opponent if self is false and at the current
// player if self is true. Afterward, the round may be over, or the shotgun may
// be empty.
// Returns ErrWrongTurn if id does not correspond to the current player.
func (g *Game) Shoot(id player.ID, self bool) error {
	cur := g.CurrentPlayer()
	if cur.id != id {
		return ErrWrongTurn
	}
	target := g.Opponent()
	if self {
		target = g.CurrentPlayer()
	}
	live := g.PopShell()
	if live {
		target.hp -= g.damage
		g.NextTurn()
	} else if !self {
		g.NextTurn()
	}
	return nil
}

// DTO returns the current game state as viewed by the given player.
func (g *Game) DTO(id player.ID) serve.Game {
	return serve.Game{
		Players: [2]serve.Player{
			g.players[0].DTO(),
			g.players[1].DTO(),
		},
		Round:    g.round,
		Damage:   g.damage,
		Shell:    g.Peek(id),
		Previous: g.prev,
	}
}

// ShellCounts returns the number of live and blank shells.
func (g *Game) ShellCounts() serve.ShellCounts {
	var counts serve.ShellCounts
	for _, s := range g.shells {
		if s {
			counts.Live++
		} else {
			counts.Blank++
		}
	}
	return counts
}

var ErrWrongTurn = errors.New("not your turn")