package redisstate

import (
	"context"
	"errors"
	"fmt"
	"sort"

	"galaxy/lobby/internal/domain/common"
	"galaxy/lobby/internal/ports"

	"github.com/redis/go-redis/v9"
)

// saveInitialPlayerStatsScript stores the JSON aggregate under the primary
// key only when no aggregate exists yet for the user. The script also
// records the user id in the per-game lookup set so Load and Delete avoid
// scanning the keyspace. Inputs:
//
//	KEYS[1] — primary aggregate key
//	KEYS[2] — per-game lookup set key
//	ARGV[1] — user id stored in the lookup set
//	ARGV[2] — JSON payload to store on first observation
//
// Returns 1 when the script wrote the payload and 0 when the user already
// had an aggregate.
const saveInitialPlayerStatsScript = `
local primaryKey = KEYS[1]
local byGameKey = KEYS[2]
local userID = ARGV[1]
local payload = ARGV[2]

local existing = redis.call('GET', primaryKey)
if existing then
  return 0
end
redis.call('SET', primaryKey, payload)
redis.call('SADD', byGameKey, userID)
return 1
`

// updateMaxPlayerStatsScript updates the running maxima for the user in
// place. When no aggregate exists yet the script seeds one whose initial
// fields and max fields both equal the observation. The script always
// keeps the max fields monotonically non-decreasing. Inputs:
//
//	KEYS[1] — primary aggregate key
//	KEYS[2] — per-game lookup set key
//	ARGV[1] — user id stored in the lookup set
//	ARGV[2] — observed planets
//	ARGV[3] — observed population
//	ARGV[4] — observed ships built
//	ARGV[5] — JSON payload to seed when no aggregate exists yet
//
// Returns 1 when a new aggregate was created and 0 otherwise.
const updateMaxPlayerStatsScript = `
local primaryKey = KEYS[1]
local byGameKey = KEYS[2]
local userID = ARGV[1]
local newPlanets = tonumber(ARGV[2])
local newPopulation = tonumber(ARGV[3])
local newShipsBuilt = tonumber(ARGV[4])
local freshPayload = ARGV[5]

local existing = redis.call('GET', primaryKey)
if not existing then
  redis.call('SET', primaryKey, freshPayload)
  redis.call('SADD', byGameKey, userID)
  return 1
end

local data = cjson.decode(existing)
local changed = false
if newPlanets > data.max_planets then
  data.max_planets = newPlanets
  changed = true
end
if newPopulation > data.max_population then
  data.max_population = newPopulation
  changed = true
end
if newShipsBuilt > data.max_ships_built then
  data.max_ships_built = newShipsBuilt
  changed = true
end
if changed then
  redis.call('SET', primaryKey, cjson.encode(data))
end
return 0
`

// GameTurnStatsStore is the Redis-backed implementation of
// ports.GameTurnStatsStore. It keeps one JSON aggregate per (game, user)
// at the GameTurnStat key and indexes the user ids in a per-game set so
// Load and Delete reach every entry without scanning the full keyspace.
type GameTurnStatsStore struct {
	client          *redis.Client
	keys            Keyspace
	saveInitialLua  *redis.Script
	updateMaxLua    *redis.Script
}

// NewGameTurnStatsStore constructs one Redis-backed GameTurnStatsStore.
func NewGameTurnStatsStore(client *redis.Client) (*GameTurnStatsStore, error) {
	if client == nil {
		return nil, errors.New("new game turn stats store: nil redis client")
	}
	return &GameTurnStatsStore{
		client:         client,
		keys:           Keyspace{},
		saveInitialLua: redis.NewScript(saveInitialPlayerStatsScript),
		updateMaxLua:   redis.NewScript(updateMaxPlayerStatsScript),
	}, nil
}

// SaveInitial freezes the initial fields for every user in stats. The
// script in Redis enforces the «first observation wins» invariant per
// user; later calls observe an existing aggregate and return without
// writes.
func (store *GameTurnStatsStore) SaveInitial(ctx context.Context, gameID common.GameID, stats []ports.PlayerInitialStats) error {
	if store == nil || store.client == nil {
		return errors.New("save initial player stats: nil store")
	}
	if ctx == nil {
		return errors.New("save initial player stats: nil context")
	}
	if err := gameID.Validate(); err != nil {
		return fmt.Errorf("save initial player stats: %w", err)
	}
	for _, line := range stats {
		if err := line.Validate(); err != nil {
			return fmt.Errorf("save initial player stats: %w", err)
		}
	}

	byGameKey := store.keys.GameTurnStatsByGame(gameID)
	for _, line := range stats {
		primaryKey := store.keys.GameTurnStat(gameID, line.UserID)
		payload, err := MarshalPlayerStats(ports.PlayerStatsAggregate{
			UserID:            line.UserID,
			InitialPlanets:    line.Planets,
			InitialPopulation: line.Population,
			InitialShipsBuilt: line.ShipsBuilt,
			MaxPlanets:        line.Planets,
			MaxPopulation:     line.Population,
			MaxShipsBuilt:     line.ShipsBuilt,
		})
		if err != nil {
			return fmt.Errorf("save initial player stats: %w", err)
		}
		if _, err := store.saveInitialLua.Run(
			ctx, store.client,
			[]string{primaryKey, byGameKey},
			line.UserID, string(payload),
		).Result(); err != nil {
			return fmt.Errorf("save initial player stats: %w", err)
		}
	}
	return nil
}

// UpdateMax updates the per-user max fields by per-component maximum. New
// users observed for the first time receive an aggregate whose initial
// fields and max fields both equal the observation, so callers never need
// to invoke SaveInitial first to keep state consistent.
func (store *GameTurnStatsStore) UpdateMax(ctx context.Context, gameID common.GameID, stats []ports.PlayerObservedStats) error {
	if store == nil || store.client == nil {
		return errors.New("update max player stats: nil store")
	}
	if ctx == nil {
		return errors.New("update max player stats: nil context")
	}
	if err := gameID.Validate(); err != nil {
		return fmt.Errorf("update max player stats: %w", err)
	}
	for _, line := range stats {
		if err := line.Validate(); err != nil {
			return fmt.Errorf("update max player stats: %w", err)
		}
	}

	byGameKey := store.keys.GameTurnStatsByGame(gameID)
	for _, line := range stats {
		primaryKey := store.keys.GameTurnStat(gameID, line.UserID)
		freshPayload, err := MarshalPlayerStats(ports.PlayerStatsAggregate{
			UserID:            line.UserID,
			InitialPlanets:    line.Planets,
			InitialPopulation: line.Population,
			InitialShipsBuilt: line.ShipsBuilt,
			MaxPlanets:        line.Planets,
			MaxPopulation:     line.Population,
			MaxShipsBuilt:     line.ShipsBuilt,
		})
		if err != nil {
			return fmt.Errorf("update max player stats: %w", err)
		}
		if _, err := store.updateMaxLua.Run(
			ctx, store.client,
			[]string{primaryKey, byGameKey},
			line.UserID,
			line.Planets,
			line.Population,
			line.ShipsBuilt,
			string(freshPayload),
		).Result(); err != nil {
			return fmt.Errorf("update max player stats: %w", err)
		}
	}
	return nil
}

// Load returns the GameTurnStatsAggregate for gameID. The Players slice is
// sorted by UserID ascending so capability evaluation produces
// deterministic side-effect order on replay.
func (store *GameTurnStatsStore) Load(ctx context.Context, gameID common.GameID) (ports.GameTurnStatsAggregate, error) {
	if store == nil || store.client == nil {
		return ports.GameTurnStatsAggregate{}, errors.New("load player stats: nil store")
	}
	if ctx == nil {
		return ports.GameTurnStatsAggregate{}, errors.New("load player stats: nil context")
	}
	if err := gameID.Validate(); err != nil {
		return ports.GameTurnStatsAggregate{}, fmt.Errorf("load player stats: %w", err)
	}

	byGameKey := store.keys.GameTurnStatsByGame(gameID)
	userIDs, err := store.client.SMembers(ctx, byGameKey).Result()
	if err != nil {
		return ports.GameTurnStatsAggregate{}, fmt.Errorf("load player stats: %w", err)
	}
	if len(userIDs) == 0 {
		return ports.GameTurnStatsAggregate{GameID: gameID}, nil
	}
	sort.Strings(userIDs)

	keys := make([]string, 0, len(userIDs))
	for _, userID := range userIDs {
		keys = append(keys, store.keys.GameTurnStat(gameID, userID))
	}
	payloads, err := store.client.MGet(ctx, keys...).Result()
	if err != nil {
		return ports.GameTurnStatsAggregate{}, fmt.Errorf("load player stats: %w", err)
	}

	players := make([]ports.PlayerStatsAggregate, 0, len(payloads))
	for index, raw := range payloads {
		if raw == nil {
			continue
		}
		text, ok := raw.(string)
		if !ok {
			return ports.GameTurnStatsAggregate{}, fmt.Errorf("load player stats: unexpected payload type for %s", userIDs[index])
		}
		aggregate, err := UnmarshalPlayerStats([]byte(text))
		if err != nil {
			return ports.GameTurnStatsAggregate{}, fmt.Errorf("load player stats: %w", err)
		}
		players = append(players, aggregate)
	}
	return ports.GameTurnStatsAggregate{GameID: gameID, Players: players}, nil
}

// Delete removes every aggregate entry for gameID and the per-game lookup
// set itself. It is a no-op when no entries exist.
func (store *GameTurnStatsStore) Delete(ctx context.Context, gameID common.GameID) error {
	if store == nil || store.client == nil {
		return errors.New("delete player stats: nil store")
	}
	if ctx == nil {
		return errors.New("delete player stats: nil context")
	}
	if err := gameID.Validate(); err != nil {
		return fmt.Errorf("delete player stats: %w", err)
	}

	byGameKey := store.keys.GameTurnStatsByGame(gameID)
	userIDs, err := store.client.SMembers(ctx, byGameKey).Result()
	if err != nil {
		return fmt.Errorf("delete player stats: %w", err)
	}

	pipeline := store.client.Pipeline()
	for _, userID := range userIDs {
		pipeline.Del(ctx, store.keys.GameTurnStat(gameID, userID))
	}
	pipeline.Del(ctx, byGameKey)
	if _, err := pipeline.Exec(ctx); err != nil {
		return fmt.Errorf("delete player stats: %w", err)
	}
	return nil
}

// Compile-time interface assertion.
var _ ports.GameTurnStatsStore = (*GameTurnStatsStore)(nil)