// WRONG — these macros/attributes don't exist
#[spacetimedb::table]           // Use #[table] after importing
#[spacetimedb::reducer]         // Use #[reducer] after importing
#[derive(Table)]                // Tables use #[table] attribute, not derive
#[derive(Reducer)]              // Reducers use #[reducer] attribute

// WRONG — SpacetimeType on tables
#[derive(SpacetimeType)]        // DO NOT use on #[table] structs!
#[table(name = my_table)]
pub struct MyTable { ... }

// WRONG — mutable context
pub fn my_reducer(ctx: &mut ReducerContext, ...) { }  // Should be &ReducerContext

// WRONG — table access without parentheses
ctx.db.player                   // Should be ctx.db.player()
ctx.db.player.find(id)          // Should be ctx.db.player().id().find(&id)

// CORRECT IMPORTS
use spacetimedb::{table, reducer, Table, ReducerContext, Identity, Timestamp};
use spacetimedb::SpacetimeType;  // Only for custom types, NOT tables

// CORRECT TABLE — no SpacetimeType derive!
#[table(name = player, public)]
pub struct Player {
    #[primary_key]
    pub id: u64,
    pub name: String,
}

// CORRECT REDUCER — immutable context reference
#[reducer]
pub fn create_player(ctx: &ReducerContext, name: String) {
    ctx.db.player().insert(Player { id: 0, name });
}

// CORRECT TABLE ACCESS — methods with parentheses
let player = ctx.db.player().id().find(&player_id);

[package]
name = "my-module"
version = "0.1.0"
edition = "2021"

[lib]
crate-type = ["cdylib"]

[dependencies]
spacetimedb = "1.0"
log = "0.4"

use spacetimedb::{ReducerContext, Table};

use spacetimedb::{Identity, Timestamp, ConnectionId, ScheduleAt};
use spacetimedb::sats::{i256, u256};  // For 256-bit integers

#[spacetimedb::table(name = player, public)]
pub struct Player {
    #[primary_key]
    #[auto_inc]
    id: u64,
    name: String,
    score: u32,
}

// Insert and get the auto-generated ID
let row = ctx.db.task().insert(Task {
    id: 0,  // Placeholder for auto_inc
    owner_id: ctx.sender,
    title: "New task".to_string(),
    created_at: ctx.timestamp,
});
let new_id = row.id;  // Get the actual ID

// No public flag — only server can read
#[table(name = secret_data)]
pub struct SecretData { ... }

// Use row-level security for per-user visibility
#[table(name = player_data, public)]
#[rls(filter = |ctx, row| row.owner_id == ctx.sender)]
pub struct PlayerData {
    #[primary_key]
    pub id: u64,
    pub owner_id: Identity,
    pub data: String,
}

#[spacetimedb::reducer]
pub fn create_player(ctx: &ReducerContext, name: String) -> Result<(), String> {
    if name.is_empty() {
        return Err("Name cannot be empty".to_string());
    }

    ctx.db.player().insert(Player {
        id: 0,  // auto_inc assigns the value
        name,
        score: 0,
    });

    Ok(())
}

#[spacetimedb::reducer]
pub fn example(ctx: &ReducerContext) {
    // Database access
    let _table = ctx.db.player();

    // Caller identity (always present)
    let caller: Identity = ctx.sender;

    // Connection ID (None for scheduled/system reducers)
    let conn: Option<ConnectionId> = ctx.connection_id;

    // Invocation timestamp
    let when: Timestamp = ctx.timestamp;

    // Module's own identity
    let module_id: Identity = ctx.identity();

    // Random number generation (deterministic)
    let random_val: u32 = ctx.random();

    // UUID generation
    let uuid = ctx.new_uuid_v4().unwrap();  // Random UUID
    let uuid = ctx.new_uuid_v7().unwrap();  // Timestamp-based UUID

    // Check if caller is internal (scheduled reducer)
    if ctx.sender_auth().is_internal() {
        // Called by scheduler, not external client
    }
}

// Insert returns the row with auto_inc values populated
let player = ctx.db.player().insert(Player {
    id: 0,  // auto_inc fills this
    name: "Alice".to_string(),
    score: 100,
});
log::info!("Created player with id: {}", player.id);

// find() returns Option<RowType>
if let Some(player) = ctx.db.player().id().find(123) {
    log::info!("Found: {}", player.name);
}

// filter() returns an iterator
for player in ctx.db.player().name().filter("Alice") {
    log::info!("Player {}: score {}", player.id, player.score);
}

// Range queries (Rust range syntax)
for player in ctx.db.player().score().filter(50..=100) {
    log::info!("{} has score {}", player.name, player.score);
}

if let Some(mut player) = ctx.db.player().id().find(123) {
    player.score += 10;
    ctx.db.player().id().update(player);
}

// Delete by unique key
ctx.db.player().id().delete(&123);

// Delete by indexed column (returns count)
let deleted = ctx.db.player().name().delete("Alice");
log::info!("Deleted {} rows", deleted);

// Delete by range
ctx.db.player().score().delete(..50);  // Delete all with score < 50

for player in ctx.db.player().iter() {
    log::info!("{}: {}", player.name, player.score);
}

// Count rows
let total = ctx.db.player().count();

#[spacetimedb::table(name = player, public)]
pub struct Player {
    #[primary_key]
    id: u64,
    #[index(btree)]
    level: u32,
    name: String,
}

#[spacetimedb::table(
    name = score,
    public,
    index(name = by_player_level, btree(columns = [player_id, level]))
)]
pub struct Score {
    player_id: u32,
    level: u32,
    points: i64,
}

// Prefix match (first column only)
for score in ctx.db.score().by_player_level().filter(&123u32) {
    log::info!("Level {}: {} points", score.level, score.points);
}

// Full match
for score in ctx.db.score().by_player_level().filter((123u32, 5u32)) {
    log::info!("Points: {}", score.points);
}

// Prefix with range on second column
for score in ctx.db.score().by_player_level().filter((123u32, 1u32..=10u32)) {
    log::info!("Level {}: {} points", score.level, score.points);
}

#[spacetimedb::table(name = user_profile, public)]
pub struct UserProfile {
    #[primary_key]
    identity: Identity,
    display_name: String,
    created_at: Timestamp,
}

#[spacetimedb::reducer]
pub fn create_profile(ctx: &ReducerContext, display_name: String) -> Result<(), String> {
    // Check if profile already exists
    if ctx.db.user_profile().identity().find(ctx.sender).is_some() {
        return Err("Profile already exists".to_string());
    }

    ctx.db.user_profile().insert(UserProfile {
        identity: ctx.sender,
        display_name,
        created_at: ctx.timestamp,
    });

    Ok(())
}

#[spacetimedb::reducer]
pub fn update_my_profile(ctx: &ReducerContext, new_name: String) -> Result<(), String> {
    // Only allow users to update their own profile
    if let Some(mut profile) = ctx.db.user_profile().identity().find(ctx.sender) {
        profile.display_name = new_name;
        ctx.db.user_profile().identity().update(profile);
        Ok(())
    } else {
        Err("Profile not found".to_string())
    }
}

#[spacetimedb::reducer(init)]
pub fn init(ctx: &ReducerContext) -> Result<(), String> {
    log::info!("Database initializing...");

    // Set up default data
    if ctx.db.config().count() == 0 {
        ctx.db.config().insert(Config {
            key: "version".to_string(),
            value: "1.0.0".to_string(),
        });
    }

    Ok(())
}

#[spacetimedb::reducer(client_connected)]
pub fn on_connect(ctx: &ReducerContext) -> Result<(), String> {
    log::info!("Client connected: {}", ctx.sender);

    // connection_id is guaranteed to be Some
    let conn_id = ctx.connection_id.unwrap();

    // Create or update user session
    if let Some(user) = ctx.db.user().identity().find(ctx.sender) {
        ctx.db.user().identity().update(User { online: true, ..user });
    } else {
        ctx.db.user().insert(User {
            identity: ctx.sender,
            online: true,
            name: None,
        });
    }

    Ok(())
}

#[spacetimedb::reducer(client_disconnected)]
pub fn on_disconnect(ctx: &ReducerContext) -> Result<(), String> {
    log::info!("Client disconnected: {}", ctx.sender);

    if let Some(user) = ctx.db.user().identity().find(ctx.sender) {
        ctx.db.user().identity().update(User { online: false, ..user });
    }

    Ok(())
}

use spacetimedb::ScheduleAt;
use std::time::Duration;

#[spacetimedb::table(name = game_tick_schedule, scheduled(game_tick))]
pub struct GameTickSchedule {
    #[primary_key]
    #[auto_inc]
    scheduled_id: u64,
    scheduled_at: ScheduleAt,
}

#[spacetimedb::reducer]
fn game_tick(ctx: &ReducerContext, schedule: GameTickSchedule) {
    // Verify this is an internal call (from scheduler)
    if !ctx.sender_auth().is_internal() {
        log::warn!("External call to scheduled reducer rejected");
        return;
    }

    // Game logic here
    log::info!("Game tick at {:?}", ctx.timestamp);
}

#[spacetimedb::reducer]
fn start_game_loop(ctx: &ReducerContext) {
    // Schedule game tick every 100ms
    ctx.db.game_tick_schedule().insert(GameTickSchedule {
        scheduled_id: 0,
        scheduled_at: ScheduleAt::Interval(Duration::from_millis(100).into()),
    });
}

#[spacetimedb::reducer]
fn schedule_reminder(ctx: &ReducerContext, delay_secs: u64) {
    let run_at = ctx.timestamp + Duration::from_secs(delay_secs);

    ctx.db.reminder_schedule().insert(ReminderSchedule {
        scheduled_id: 0,
        scheduled_at: ScheduleAt::Time(run_at),
        message: "Time's up!".to_string(),
    });
}

undefined

```rust
use spacetimedb::{procedure, ProcedureContext};

// Simple procedure
#[procedure]
fn add_numbers(_ctx: &mut ProcedureContext, a: u32, b: u32) -> u64 {
    a as u64 + b as u64
}

// Procedure with database access
#[procedure]
fn save_external_data(ctx: &mut ProcedureContext, url: String) -> Result<(), String> {
    // HTTP request (allowed in procedures, not reducers)
    let data = fetch_from_url(&url)?;

    // Database access requires explicit transaction
    ctx.try_with_tx(|tx| {
        tx.db.external_data().insert(ExternalData {
            id: 0,
            content: data,
        });
        Ok(())
    })?;

    Ok(())
}

#[spacetimedb::reducer]
pub fn transfer_credits(
    ctx: &ReducerContext,
    to_user: Identity,
    amount: u32,
) -> Result<(), String> {
    let sender = ctx.db.user().identity().find(ctx.sender)
        .ok_or("Sender not found")?;

    if sender.credits < amount {
        return Err("Insufficient credits".to_string());
    }

    // Perform transfer...
    Ok(())
}

#[spacetimedb::reducer]
pub fn process_data(ctx: &ReducerContext, data: Vec<u8>) {
    // This should never happen - indicates a bug
    assert!(!data.is_empty(), "Unexpected empty data");

    // Use expect for operations that should always succeed
    let parsed = parse_data(&data).expect("Failed to parse data");
}