package game

import (
	"encoding/gob"
	"errors"
	"fmt"
	"os"
)

// save.c + state.c — game persistence. The hand-written, XOR-encrypted C
// serializer becomes a gob snapshot; what remains hand-written is exactly
// what state.c's rs_fix_thing did: pointers that alias other structures
// (equipment, chase targets, room membership) are encoded as indices.

// saveFormatVersion identifies the snapshot layout; it changes whenever a
// field rename or retype would make gob silently mis-decode an older
// save ("go2": Object.Type became Kind ObjectKind; "go3": Object.Arm split
// into ArmorClass/Charges/GoldValue/Bonus, damage strings became
// DiceSpec).
const saveFormatVersion = Release + "-go3"

// destRef encodes a monster's chase target (state.c rs_write_thing's
// (kind, index) pairs).
type destRef struct {
	Kind int // 0 none, 1 hero, 2 monster index, 3 level-object index, 4 room gold
	Idx  int
}

// savedCreature is the pointer-free image of a Creature.
type savedCreature struct {
	Pos      Coord
	Turn     bool
	Type     byte
	Disguise byte
	OldCh    byte
	Flags    CreatureFlags
	Stats    Stats
	RoomIdx  int // 0..MaxRooms-1; 100+i for passages; -1 none
	Pack     []Object
}

// savedPlayer adds the player-only state. The creature half is a named
// field, not an embedded one: gob drops embedded fields of unexported
// types silently.
type savedPlayer struct {
	Body        savedCreature
	CurArmor    int // pack indices; -1 = none
	CurWeapon   int
	CurRing     [2]int
	PackUsed    [26]bool
	Inpack      int
	Purse       int
	FoodLeft    int
	HungryState int
	NoFood      int
	MaxStats    Stats
	VfHit       int
}

// savedPlace is one map cell without its monster pointer.
type savedPlace struct {
	Ch    byte
	Flags PlaceFlags
}

// SaveState is the complete serialized game (the field list mirrors
// state.c rs_save_file).
type SaveState struct {
	Version string

	Seed   int32
	Dnum   int
	Whoami string
	Fruit  string
	Home   string
	Wizard bool

	Player savedPlayer

	Depth      int
	MaxDepth   int
	HasAmulet  bool
	SeenStairs bool

	Places    []savedPlace
	Rooms     [MaxRooms]Room
	Passages  [MaxPass]Room
	Objects   []Object
	Monsters  []savedCreature
	Dests     []destRef // parallel to Monsters
	Stairs    Coord
	TrapCount int

	After     bool
	Again     bool
	NoScoreF  bool
	Count     int
	NoCommand int
	NoMove    int
	Quiet     int
	Running   bool
	RunCh     byte
	DoorStop  bool
	Firstmove bool
	MoveOn    bool
	ToDeath   bool
	Kamikaze  bool
	MaxHit    int
	Take      byte
	Delta     Coord
	DirCh     byte
	LastComm  byte
	LastDir   byte
	LastPick  int // pack index, -1
	Oldpos    Coord
	OldrpIdx  int

	Daemons  DaemonList
	Options  Options
	Items    ItemLore
	Bestiary [26]MonsterKind
	Huh      string

	LastScore int
	AllScore  bool

	Screen []byte // the visible map (Std window contents)
}

// roomIdx encodes a room pointer as an index (state.c find_room_coord).
func (g *RogueGame) roomIdx(rp *Room) int {
	if rp == nil {
		return -1
	}

	for i := range g.Level.Rooms {
		if rp == &g.Level.Rooms[i] {
			return i
		}
	}

	for i := range g.Level.Passages {
		if rp == &g.Level.Passages[i] {
			return 100 + i
		}
	}

	return -1
}

// roomAt decodes a room index.
func (g *RogueGame) roomAt(i int) *Room {
	switch {
	case i >= 100:
		return &g.Level.Passages[i-100]
	case i >= 0:
		return &g.Level.Rooms[i]
	}

	return nil
}

// packIdx finds an object in the player's pack (state.c find_list_ptr).
func (g *RogueGame) packIdx(obj *Object) int {
	if obj == nil {
		return -1
	}

	for i, o := range g.Player.Pack {
		if o == obj {
			return i
		}
	}

	return -1
}

// snapshot captures the complete game state.
func (g *RogueGame) snapshot() *SaveState {
	p := &g.Player
	st := &SaveState{
		Version:    saveFormatVersion,
		Seed:       g.Rng.Seed,
		Dnum:       g.Dnum,
		Whoami:     g.Whoami,
		Fruit:      g.Fruit,
		Home:       g.Home,
		Wizard:     g.Wizard,
		Depth:      g.Depth,
		MaxDepth:   g.MaxDepth,
		HasAmulet:  g.HasAmulet,
		SeenStairs: g.SeenStairs,
		Rooms:      g.Level.Rooms,
		Passages:   g.Level.Passages,
		Stairs:     g.Level.Stairs,
		TrapCount:  g.Level.TrapCount,
		After:      g.After,
		Again:      g.Again,
		NoScoreF:   g.NoScore,
		Count:      g.Count,
		NoCommand:  g.NoCommand,
		NoMove:     g.NoMove,
		Quiet:      g.Quiet,
		Running:    g.Running,
		RunCh:      g.RunCh,
		DoorStop:   g.DoorStop,
		Firstmove:  g.Firstmove,
		MoveOn:     g.MoveOn,
		ToDeath:    g.ToDeath,
		Kamikaze:   g.Kamikaze,
		MaxHit:     g.MaxHit,
		Take:       g.Take,
		Delta:      g.Delta,
		DirCh:      g.DirCh,
		LastComm:   g.LastComm,
		LastDir:    g.LastDir,
		LastPick:   g.packIdx(g.LastPick),
		Oldpos:     g.Oldpos,
		OldrpIdx:   g.roomIdx(g.Oldrp),
		Daemons:    g.Daemons,
		Options:    g.Options,
		Items:      g.Items,
		Bestiary:   g.Monsters,
		Huh:        g.Msgs.Huh,
		LastScore:  g.LastScore,
		AllScore:   g.AllScore,
		Screen:     g.scr.Std.Contents(),
	}

	// the map, sans monster pointers (rebuilt on load)
	st.Places = make([]savedPlace, len(g.Level.Places))
	for i := range g.Level.Places {
		st.Places[i] = savedPlace{
			Ch:    g.Level.Places[i].Ch,
			Flags: g.Level.Places[i].Flags,
		}
	}

	// level objects by value; remember their pointers for dest encoding
	objAt := make(map[*Object]int, len(g.Level.Objects))
	for i, o := range g.Level.Objects {
		st.Objects = append(st.Objects, *o)
		objAt[o] = i
	}

	// the player
	st.Player = savedPlayer{
		Body: savedCreature{
			Pos: p.Pos, Turn: p.Turn, Type: p.Type, Disguise: p.Disguise,
			OldCh: p.OldCh, Flags: p.Flags, Stats: p.Stats,
			RoomIdx: g.roomIdx(p.Room),
		},
		CurArmor:  g.packIdx(p.CurArmor),
		CurWeapon: g.packIdx(p.CurWeapon),
		CurRing: [2]int{
			g.packIdx(p.CurRing[Left]), g.packIdx(p.CurRing[Right]),
		},
		PackUsed: p.PackUsed, Inpack: p.Inpack, Purse: p.Purse,
		FoodLeft: p.FoodLeft, HungryState: p.HungryState, NoFood: p.NoFood,
		MaxStats: p.MaxStats, VfHit: p.VfHit,
	}
	for _, o := range p.Pack {
		st.Player.Body.Pack = append(st.Player.Body.Pack, *o)
	}

	// monsters, with chase targets as (kind, index) references
	for _, m := range g.Level.Monsters {
		sc := savedCreature{
			Pos: m.Pos, Turn: m.Turn, Type: m.Type, Disguise: m.Disguise,
			OldCh: m.OldCh, Flags: m.Flags, Stats: m.Stats,
			RoomIdx: g.roomIdx(m.Room),
		}
		for _, o := range m.Pack {
			sc.Pack = append(sc.Pack, *o)
		}

		st.Monsters = append(st.Monsters, sc)
		st.Dests = append(st.Dests, g.destRefFor(m, objAt))
	}

	return st
}

// destRefFor encodes a monster's chase target as a (kind, index)
// reference: the hero, another monster, a level object, or room gold
// (state.c rs_write_thing).
func (g *RogueGame) destRefFor(m *Monster, objAt map[*Object]int) destRef {
	switch {
	case m.Dest == nil:
		return destRef{}
	case m.Dest == &g.Player.Pos:
		return destRef{Kind: 1}
	}

	for mi, om := range g.Level.Monsters {
		if m.Dest == &om.Pos {
			return destRef{Kind: 2, Idx: mi}
		}
	}

	for _, oo := range g.Level.Objects {
		if m.Dest == &oo.Pos {
			return destRef{Kind: 3, Idx: objAt[oo]}
		}
	}

	for ri := range g.Level.Rooms {
		if m.Dest == &g.Level.Rooms[ri].Gold {
			return destRef{Kind: 4, Idx: ri}
		}
	}

	return destRef{}
}

// applySnapshot rebuilds live game state from a snapshot.
func (g *RogueGame) applySnapshot(st *SaveState) {
	p := &g.Player
	g.Rng.Seed = st.Seed
	g.Dnum = st.Dnum
	g.Whoami = st.Whoami
	g.Fruit = st.Fruit
	g.Home = st.Home
	g.Wizard = st.Wizard
	g.Depth = st.Depth
	g.MaxDepth = st.MaxDepth
	g.HasAmulet = st.HasAmulet
	g.SeenStairs = st.SeenStairs
	g.Level.Rooms = st.Rooms
	g.Level.Passages = st.Passages
	g.Level.Stairs = st.Stairs
	g.Level.TrapCount = st.TrapCount
	g.After = st.After
	g.Again = st.Again
	g.NoScore = st.NoScoreF
	g.Count = st.Count
	g.NoCommand = st.NoCommand
	g.NoMove = st.NoMove
	g.Quiet = st.Quiet
	g.Running = st.Running
	g.RunCh = st.RunCh
	g.DoorStop = st.DoorStop
	g.Firstmove = st.Firstmove
	g.MoveOn = st.MoveOn
	g.ToDeath = st.ToDeath
	g.Kamikaze = st.Kamikaze
	g.MaxHit = st.MaxHit
	g.Take = st.Take
	g.Delta = st.Delta
	g.DirCh = st.DirCh
	g.LastComm = st.LastComm
	g.LastDir = st.LastDir
	g.Oldpos = st.Oldpos
	g.Oldrp = g.roomAt(st.OldrpIdx)
	g.Daemons = st.Daemons
	g.Options = st.Options
	g.Items = st.Items
	g.Monsters = st.Bestiary
	g.Msgs.Huh = st.Huh
	g.LastScore = st.LastScore
	g.AllScore = st.AllScore
	g.Playing = true

	for i := range g.Level.Places {
		g.Level.Places[i] = Place{
			Ch:    st.Places[i].Ch,
			Flags: st.Places[i].Flags,
		}
	}

	// level objects
	g.Level.Objects = nil
	for i := range st.Objects {
		o := st.Objects[i]
		g.Level.Objects = append(g.Level.Objects, &o)
	}

	// the player
	sp := &st.Player
	p.Pos = sp.Body.Pos
	p.Turn = sp.Body.Turn
	p.Type = sp.Body.Type
	p.Disguise = sp.Body.Disguise
	p.OldCh = sp.Body.OldCh
	p.Flags = sp.Body.Flags
	p.Stats = sp.Body.Stats
	p.Room = g.roomAt(sp.Body.RoomIdx)

	p.Pack = nil
	for i := range sp.Body.Pack {
		o := sp.Body.Pack[i]
		p.Pack = append(p.Pack, &o)
	}

	pick := func(i int) *Object {
		if i < 0 || i >= len(p.Pack) {
			return nil
		}

		return p.Pack[i]
	}
	p.CurArmor = pick(sp.CurArmor)
	p.CurWeapon = pick(sp.CurWeapon)
	p.CurRing[Left] = pick(sp.CurRing[0])
	p.CurRing[Right] = pick(sp.CurRing[1])
	g.LastPick = pick(st.LastPick)
	p.PackUsed = sp.PackUsed
	p.Inpack = sp.Inpack
	p.Purse = sp.Purse
	p.FoodLeft = sp.FoodLeft
	p.HungryState = sp.HungryState
	p.NoFood = sp.NoFood
	p.MaxStats = sp.MaxStats
	p.VfHit = sp.VfHit

	g.applyMonsters(st)
	g.applyDests(st)

	g.scr.Std.SetContents(st.Screen)
}

// applyMonsters rebuilds the monster list and its map index from a
// snapshot (the monster half of applySnapshot).
func (g *RogueGame) applyMonsters(st *SaveState) {
	g.Level.Monsters = nil
	for i := range st.Monsters {
		sc := &st.Monsters[i]

		m := &Monster{Creature: Creature{
			Pos: sc.Pos, Turn: sc.Turn, Type: sc.Type, Disguise: sc.Disguise,
			OldCh: sc.OldCh, Flags: sc.Flags, Stats: sc.Stats,
			Room: g.roomAt(sc.RoomIdx),
		}}
		for j := range sc.Pack {
			o := sc.Pack[j]
			m.Pack = append(m.Pack, &o)
		}

		g.Level.Monsters = append(g.Level.Monsters, m)
		g.Level.SetMonsterAt(m.Pos.Y, m.Pos.X, m)
	}
}

// applyDests re-aims the monsters' chase targets from their (kind,
// index) references (the fixup half of applySnapshot).
func (g *RogueGame) applyDests(st *SaveState) {
	for i, ref := range st.Dests {
		m := g.Level.Monsters[i]

		switch ref.Kind {
		case 1:
			m.Dest = &g.Player.Pos
		case 2:
			m.Dest = &g.Level.Monsters[ref.Idx].Pos
		case 3:
			m.Dest = &g.Level.Objects[ref.Idx].Pos
		case 4:
			m.Dest = &g.Level.Rooms[ref.Idx].Gold
		}
	}
}

// saveAnswer is a yes/no/escape prompt result in the save-game flow.
type saveAnswer int

// The saveGame prompt outcomes.
const (
	saveYes saveAnswer = iota
	saveNo
	saveAbort
)

// saveGame implements the "save game" command (save.c save_game). The
// labeled prompt loop stands in for the C goto over/gotfile flow.
func (g *RogueGame) saveGame() {
	g.Msgs.Mpos = 0

prompt:
	for {
		useDefault := false

		if g.FileName != "" {
			a := g.askDefaultSave()
			if a == saveAbort {
				return
			}

			useDefault = a == saveYes
		}

		for {
			buf, ok := g.saveFileName(useDefault)
			if !ok {
				return
			}

			useDefault = false

			a := g.saveCheckOverwrite(buf)
			if a == saveAbort {
				return
			}

			if a == saveNo {
				continue prompt // the C goto over: start again
			}

			g.FileName = buf

			if err := g.saveFile(g.FileName); err != nil {
				g.msg("%s", err.Error())

				continue
			}

			break prompt
		}
	}

	g.myExit()
}

// askDefaultSave asks whether to save to the current file name (save.c
// save_game).
func (g *RogueGame) askDefaultSave() saveAnswer {
	for {
		g.msg("save file (%s)? ", g.FileName)
		c := g.readchar()

		g.Msgs.Mpos = 0

		switch c {
		case Escape:
			g.msg("")

			return saveAbort
		case 'y', 'Y':
			g.addstr("Yes\n")
			g.refresh()

			return saveYes
		case 'n', 'N':
			return saveNo
		}

		g.msg("please answer Y or N")
	}
}

// saveFileName picks the save path: the default, or a prompted one; ok
// is false when the player quit the prompt (save.c save_game).
func (g *RogueGame) saveFileName(useDefault bool) (string, bool) {
	if useDefault {
		return g.FileName, true
	}

	g.Msgs.Mpos = 0
	g.msg("file name: ")

	buf := ""
	if g.getStr(&buf, g.scr.Std) == Quit {
		g.msg("")

		return "", false
	}

	g.Msgs.Mpos = 0

	return buf, true
}

// saveCheckOverwrite guards an existing file: saveNo restarts the whole
// prompt, saveAbort quits (save.c save_game).
func (g *RogueGame) saveCheckOverwrite(buf string) saveAnswer {
	// test to see if the file exists
	if _, statErr := os.Stat(buf); statErr != nil {
		return saveYes
	}

	answer := g.askOverwrite()
	if answer != saveYes {
		return answer
	}

	g.msg("file name: %s", buf)
	_ = os.Remove(g.FileName) // best effort, as in C (md_unlink)

	return saveYes
}

// askOverwrite asks whether to overwrite the existing file (save.c
// save_game).
func (g *RogueGame) askOverwrite() saveAnswer {
	for {
		g.msg("File exists.  Do you wish to overwrite it?")
		g.Msgs.Mpos = 0

		switch g.readchar() {
		case Escape:
			g.msg("")

			return saveAbort
		case 'y', 'Y':
			return saveYes
		case 'n', 'N':
			return saveNo
		}

		g.msg("Please answer Y or N")
	}
}

// saveFile writes the saved game (save.c save_file). A failed write means
// a corrupt save, so the file is removed before reporting the error.
func (g *RogueGame) saveFile(path string) error {
	f, err := os.OpenFile(path, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o400) //nolint:gosec,lll // G304: user-chosen save path
	if err != nil {
		return err
	}

	encErr := gob.NewEncoder(f).Encode(g.snapshot())
	closeErr := f.Close()

	if encErr != nil || closeErr != nil {
		_ = os.Remove(path) // don't leave a corrupt save behind

		if encErr != nil {
			return encErr
		}

		return closeErr
	}

	return os.Chmod(path, 0o400)
}

// AutoSave silently saves to the current file name; used on SIGHUP/SIGTERM
// (save.c auto_save). Best effort by design: it runs on the way out of a
// dying process.
func (g *RogueGame) AutoSave() {
	if g.FileName != "" {
		_ = os.Remove(g.FileName)
		_ = g.saveFile(g.FileName)
	}
}

// ErrSaveOutOfDate reports a save file from an incompatible version.
var ErrSaveOutOfDate = errors.New("sorry, saved game is out of date")

// Restore restores a saved game from a file (save.c restore). The file is
// deleted, as in C, to defeat restarting from the same save.
func Restore(path string, cfg Config) (*RogueGame, error) {
	f, err := os.Open(path) //nolint:gosec // G304: the save path is user-chosen by design
	if err != nil {
		return nil, err
	}
	defer func() { _ = f.Close() }() // read-only handle

	var st SaveState

	decErr := gob.NewDecoder(f).Decode(&st)
	if decErr != nil {
		return nil, fmt.Errorf("%s: corrupt or incompatible save file: %w",
			path, decErr)
	}

	if st.Version != saveFormatVersion {
		return nil, ErrSaveOutOfDate
	}

	g := &RogueGame{
		data:      newGameData(),
		Rng:       &Rng{},
		Playing:   true,
		ScorePath: cfg.ScorePath,
		FileName:  path,
		rogueOpts: cfg.RogueOpts,
		restored:  true,
	}
	g.scr = NewScreen(cfg.Term)
	g.Msgs.attach(g.scr, g.look, g.readchar)
	g.applySnapshot(&st)

	// defeat multiple restarting from the same place
	rmErr := os.Remove(path)
	if rmErr != nil {
		return nil, fmt.Errorf("cannot unlink file: %w", rmErr)
	}

	return g, nil
}