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//! The state document and its fold: where the game is, not what the
//! scene is (spec/state.md). A save game is base + state declaration +
//! a player's session log — the fold below is the arithmetic.
use std::collections::BTreeMap;
use serde::{Deserialize, Serialize};
use serde_json::Value;
use crate::oplog::OpLogEntry;
use crate::session::SessionOp;
/// `state.json` — the world's declared state and its initial values.
#[derive(Debug, Clone, Default, Serialize, Deserialize)]
pub struct StateDoc {
/// The state document's own version.
pub format_version: u32,
/// The declared fields: dotted name → `{type, initial}`.
pub fields: BTreeMap<String, StateField>,
}
/// One declared field.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct StateField {
/// The field's type: int, float, bool, string, map, list, json.
#[serde(rename = "type")]
pub kind: String,
/// The initial value; absent means the type's zero (or null for json).
#[serde(default, skip_serializing_if = "Option::is_none")]
pub initial: Option<Value>,
}
impl StateField {
/// The value a reset returns to: the declared initial, else the
/// type's zero.
pub fn initial_value(&self) -> Value {
self.initial
.clone()
.unwrap_or_else(|| match self.kind.as_str() {
"int" | "float" => Value::from(0),
"bool" => Value::from(false),
"string" => Value::from(""),
"map" => serde_json::json!({}),
"list" => serde_json::json!([]),
_ => Value::Null,
})
}
}
/// A state fold's result.
#[derive(Debug, Clone, Default, PartialEq)]
pub struct StateFold {
/// The values at the last entry.
pub values: BTreeMap<String, Value>,
/// Keys no declaration covers — carried, and said so, because
/// history must never break the fold.
pub undeclared: Vec<String>,
}
/// Fold a session log's `state` ops over a state document: the values at
/// the last entry. Separate from the document fold — state ops never
/// touch entities — and equally tolerant.
///
/// The rules (spec/state.md): a key naming a declared field sets it,
/// and `null` resets it to its initial; a key *under* a declared `map`
/// field sets or removes that entry; a key declaring nothing is carried
/// and reported.
pub fn fold_state(state_doc: &StateDoc, entries: &[OpLogEntry]) -> StateFold {
let mut values: BTreeMap<String, Value> = state_doc
.fields
.iter()
.map(|(name, field)| (name.clone(), field.initial_value()))
.collect();
let mut undeclared: Vec<String> = Vec::new();
for entry in entries {
for op in &entry.ops {
let SessionOp::State(record) = op else {
continue;
};
for (key, value) in &record.state {
if state_doc.fields.contains_key(key) {
match value {
Value::Null => {
values.insert(key.clone(), state_doc.fields[key].initial_value());
}
v => {
values.insert(key.clone(), v.clone());
}
}
continue;
}
if let Some((base, inner)) = key.split_once('.')
&& state_doc.fields.get(base).map(|f| f.kind.as_str()) == Some("map")
&& let Some(Value::Object(map)) = values.get_mut(base)
{
match value {
Value::Null => {
map.remove(inner);
}
v => {
map.insert(inner.to_string(), v.clone());
}
}
continue;
}
match value {
Value::Null => {
values.remove(key);
}
v => {
values.insert(key.clone(), v.clone());
if !undeclared.contains(key) {
undeclared.push(key.clone());
}
}
}
}
}
}
StateFold { values, undeclared }
}
#[cfg(test)]
mod tests {
use super::*;
use crate::session::StateRecord;
fn entry(state: &[(&str, Value)]) -> OpLogEntry {
OpLogEntry {
revision: 1,
author: crate::author::Author {
peer: None,
name: "t".into(),
},
ops: vec![SessionOp::State(StateRecord {
state: state
.iter()
.map(|(k, v)| (k.to_string(), v.clone()))
.collect(),
})],
timestamp_ms: 0,
id: None,
parent: None,
message: None,
}
}
/// spec/state.md: if a declared field exactly matches a dotted key,
/// the declared field ALWAYS takes precedence over map sub-keys.
/// Declaring both `inventory` (a map) and `inventory.rope` (an int)
/// is the whole game.
#[test]
fn a_declared_field_beats_the_map_subkey_it_resembles() {
let state_doc = StateDoc {
format_version: 1,
fields: BTreeMap::from([
(
"inventory".to_string(),
StateField {
kind: "map".into(),
initial: Some(serde_json::json!({})),
},
),
(
"inventory.rope".to_string(),
StateField {
kind: "int".into(),
initial: Some(serde_json::json!(0)),
},
),
]),
};
let folded = fold_state(
&state_doc,
&[entry(&[("inventory.rope", serde_json::json!(5))])],
);
assert_eq!(folded.values["inventory.rope"], serde_json::json!(5));
// The map kept its initial emptiness: not a sub-key hit.
assert_eq!(folded.values["inventory"], serde_json::json!({}));
assert!(folded.undeclared.is_empty());
// And a null on the declared field resets it, rather than
// deleting an inventory entry.
let folded = fold_state(&state_doc, &[entry(&[("inventory.rope", Value::Null)])]);
assert_eq!(folded.values["inventory.rope"], serde_json::json!(0));
}
#[test]
fn map_subkeys_still_work_without_a_shadowing_declaration() {
let state_doc = StateDoc {
format_version: 1,
fields: BTreeMap::from([(
"inventory".to_string(),
StateField {
kind: "map".into(),
initial: Some(serde_json::json!({})),
},
)]),
};
let folded = fold_state(
&state_doc,
&[entry(&[
("inventory.rope", serde_json::json!(1)),
("inventory.torch", serde_json::json!(2)),
("inventory.rope", Value::Null),
])],
);
assert_eq!(folded.values["inventory"], serde_json::json!({"torch": 2}));
}
}