class_name CharacterStore
extends RefCounted
## Server-side persistence for accounts and their characters.
##
## JSON on disk, because the shape is small, the write rate is low (a level-up
## or a death, not a tick), and a save file you can open in a text editor is
## worth a great deal while a game is still being built. If this ever becomes a
## bottleneck the interface is narrow enough to put a database behind.
##
## Keyed by account id -- a 64-bit integer, deliberately the same shape as a
## SteamID64 so swapping [AuthProvider] for a real Steam one needs no migration.

const SAVE_PATH := "user://characters.json"
const FORMAT_VERSION := 1
## Live characters an account may hold at once. Retired ones do not count: a
## player who has died five times must not be locked out of their own account.
const MAX_ACTIVE := 5

## account_id -> { "characters": Array[Character], "last_played": String }
var _accounts: Dictionary[int, Dictionary] = {}
var _path: String = SAVE_PATH
var _rng := RandomNumberGenerator.new()


func _init(path: String = SAVE_PATH) -> void:
	_path = path
	_rng.randomize()


# --- Queries ----------------------------------------------------------------

func characters_for(account_id: int) -> Array[Character]:
	var entry: Dictionary = _accounts.get(account_id, {})
	var out: Array[Character] = []
	for c in entry.get("characters", []):
		out.append(c)
	return out


func active_characters(account_id: int) -> Array[Character]:
	var out: Array[Character] = []
	for c in characters_for(account_id):
		if c.active:
			out.append(c)
	return out


func get_character(account_id: int, character_id: String) -> Character:
	for c in characters_for(account_id):
		if c.id == character_id:
			return c
	return null


## The character to select on login: the last one played if it is still alive,
## otherwise the newest living one, otherwise nothing.
func last_played(account_id: int) -> Character:
	var entry: Dictionary = _accounts.get(account_id, {})
	var wanted := String(entry.get("last_played", ""))
	var c := get_character(account_id, wanted)
	if c != null and c.active:
		return c
	var living := active_characters(account_id)
	if living.is_empty():
		return null
	var newest: Character = living[0]
	for candidate in living:
		if candidate.created_unix > newest.created_unix:
			newest = candidate
	return newest


func can_create(account_id: int) -> bool:
	return active_characters(account_id).size() < MAX_ACTIVE


# --- Mutations --------------------------------------------------------------

## Returns null when the account is already at its living-character limit.
func create_character(account_id: int, character_name: String) -> Character:
	if not can_create(account_id):
		return null
	var c := Character.create(character_name, _rng)
	var entry: Dictionary = _accounts.get(account_id, {"characters": [], "last_played": ""})
	entry["characters"].append(c)
	entry["last_played"] = c.id
	_accounts[account_id] = entry
	save()
	return c


func set_last_played(account_id: int, character_id: String) -> void:
	var entry: Dictionary = _accounts.get(account_id, {"characters": [], "last_played": ""})
	entry["last_played"] = character_id
	_accounts[account_id] = entry
	save()


## Death. The record stays; only its active flag changes.
func retire_character(account_id: int, character_id: String) -> void:
	var c := get_character(account_id, character_id)
	if c == null or not c.active:
		return
	c.retire()
	save()


## Write a character's carried items back to disk. Separate from grant_xp
## rather than folded into a general "save this character", so the one caller
## reads as what it is.
func set_inventory(account_id: int, character_id: String, items: Array[StringName]) -> void:
	var c := get_character(account_id, character_id)
	if c == null:
		return
	c.set_inventory(items)
	save()


## Award level-up choices and, if nothing is on the table yet, roll one.
##
## The offer is rolled HERE and stored, not generated on demand when the screen
## opens: an offer that regenerated per request would be a free reroll, and a
## player would simply close and reopen until a legendary appeared.
func grant_choices(account_id: int, character_id: String, count: int) -> void:
	var c := get_character(account_id, character_id)
	if c == null or count <= 0:
		return
	c.pending_choices += count
	_refresh_offer(c)
	save()


## Spend one choice on [param index] of the character's current offer. Returns
## the upgrade taken, or an empty id if the choice was not available -- the
## caller is the server, and "not available" is a refusal, not an error.
func take_upgrade(account_id: int, character_id: String, index: int) -> StringName:
	var c := get_character(account_id, character_id)
	if c == null or not c.active or c.pending_choices <= 0:
		return &""
	if index < 0 or index >= c.offer.size():
		return &""
	var chosen := c.offer[index]
	c.upgrades.append(chosen)
	c.pending_choices -= 1
	# Cleared before re-rolling, so the next choice is a fresh three rather than
	# the two that were passed over.
	c.offer.clear()
	_refresh_offer(c)
	save()
	return chosen


func _refresh_offer(c: Character) -> void:
	if c.pending_choices > 0 and c.offer.is_empty():
		c.offer = Upgrades.roll_offer(_rng, SimConfig.UPGRADE_CHOICES)
	elif c.pending_choices <= 0:
		c.offer.clear()


func grant_xp(account_id: int, character_id: String, amount: int) -> int:
	var c := get_character(account_id, character_id)
	if c == null:
		return 0
	var gained := c.grant_xp(amount)
	if gained > 0:
		save()
	return gained


# --- Persistence ------------------------------------------------------------

func save() -> void:
	var accounts := {}
	for account_id in _accounts:
		var entry: Dictionary = _accounts[account_id]
		var chars := []
		for c in entry["characters"]:
			chars.append(c.to_dict())
		# JSON object keys are strings; account ids are 64-bit and would lose
		# precision as JSON numbers, so they are written as decimal strings.
		accounts[str(account_id)] = {
			"characters": chars,
			"last_played": entry.get("last_played", ""),
		}
	var f := FileAccess.open(_path, FileAccess.WRITE)
	if f == null:
		GameLog.error("store", "cannot write %s (error %d)" % [_path, FileAccess.get_open_error()])
		return
	f.store_string(JSON.stringify({"version": FORMAT_VERSION, "accounts": accounts}, "\t"))
	f.close()


## A missing file is a new server, not an error. A corrupt one is refused
## loudly and left alone rather than silently overwritten -- losing every
## character to a stray byte would be far worse than refusing to start.
func load_from_disk() -> bool:
	_accounts.clear()
	if not FileAccess.file_exists(_path):
		return true
	var f := FileAccess.open(_path, FileAccess.READ)
	if f == null:
		GameLog.error("store", "cannot read %s" % _path)
		return false
	var text := f.get_as_text()
	f.close()
	# JSON.new().parse() rather than JSON.parse_string(): it reports where the
	# file is malformed instead of just returning null, which is the difference
	# between a usable error and a mystery when someone's save will not load.
	var json := JSON.new()
	if json.parse(text) != OK or typeof(json.data) != TYPE_DICTIONARY:
		GameLog.error("store", "%s is not valid JSON (line %d: %s); refusing to overwrite it"
			% [_path, json.get_error_line(), json.get_error_message()])
		return false
	var data: Dictionary = json.data
	var accounts: Dictionary = data.get("accounts", {})
	for key in accounts:
		var account_id := int(str(key))
		var entry: Dictionary = accounts[key]
		var chars: Array[Character] = []
		for raw in entry.get("characters", []):
			chars.append(Character.from_dict(raw))
		_accounts[account_id] = {
			"characters": chars,
			"last_played": String(entry.get("last_played", "")),
		}
	GameLog.info("store", "loaded %d account(s) from %s" % [_accounts.size(), _path])
	return true