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core2026/docs/architecture/legacy-engine-items.md
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# Legacy Items, Traits, and Action Modules
This document summarizes the legacy action modules that supply modifiers and
triggers: items, specials, personalities, nation types, crew types, and
scenario effects. Primary references include `legacy/hwe/sammo/iAction.php`,
`legacy/hwe/sammo/BaseItem.php`, `legacy/hwe/sammo/BaseSpecial.php`,
and `legacy/hwe/sammo/Action*/` directories.
## Core Concept: `iAction`
All traits/items/effects implement `iAction` and are merged by
`General::getActionList()` (see `docs/architecture/legacy-engine-general.md`).
They can:
- Modify stats and command calculations (`onCalcStat`, `onCalcDomestic`, etc.).
- Provide triggers (`getPreTurnExecuteTriggerList`, battle init/phase triggers).
- Apply ad-hoc effects (`onArbitraryAction`).
`DefaultAction` provides no-op implementations for all hooks.
## Item System
- Base class: `BaseItem` implements `iAction` and exposes:
- `getCost()`, `isConsumable()`, `isBuyable()`, `getReqSecu()`.
- Stat items inherit `BaseStatItem` and apply a fixed stat bonus in
`onCalcStat()` based on class name tokens.
- Item instances live on the general (`General::getItem()`); items can also
insert battle triggers (see `ActionItem/`).
Items are configured via `GameConst::$allItems` and scenario overrides.
## Specials (Domestic / War)
- Base class: `BaseSpecial` (implements `iAction`).
- `ActionSpecialDomestic/*` modifies domestic outcomes
(`onCalcDomestic`), e.g., cost/success/score adjustments.
- `ActionSpecialWar/*` injects battle triggers or stat modifiers.
- Weighting and eligibility are managed by `SpecialityHelper`:
- Uses `selectWeight` + stat/arm constraints to choose specials.
- Deterministic RNG affects special selection for NPCs or resets.
## Personalities
- Stored in `ActionPersonality/*` and also implement `iAction`.
- Typically adjust core stats or apply small domestic bonuses.
## Nation Types
- `ActionNationType/*` extends `BaseNation`.
- Provide global modifiers to income and domestic outcomes.
- Injected per-nation via `buildNationTypeClass()`.
## Crew Types (Units as Actions)
- `ActionCrewType/*` defines per-crew `iAction` additions.
- Crew types can alter battle order, apply triggers, or modify war stats.
- For example, `che_성벽선제` forces city battle order to a high value.
## Scenario Effects
- `ActionScenarioEffect/*` provides scenario-wide modifiers
(e.g., attacker advantage, trigger overrides).
- Bound to `GameConst::$scenarioEffect` during scenario build.
## Interaction with Triggers
Action modules often construct trigger callers:
- Items and war specials can return `WarUnitTriggerCaller` with `BaseWarUnitTrigger`.
- Some item triggers use `raiseType` to allow coexistence with non-item versions.
See `docs/architecture/legacy-engine-triggers.md` for trigger execution rules.
## Open Questions / Follow-ups
- The precise selection rules for personalities and specials depend on
`SpecialityHelper` RNG thresholds and scenario overrides; capture those
when documenting specific rule packs.