# Architecture

## Principles

- Keep rules data-driven.
- Keep battle state independent from rendering.
- Build one complete vertical slice before expanding systems.
- Prefer simple Godot nodes and GDScript until a system proves it needs more structure.

## Current Layout

- `project.godot`: Godot 4 project configuration.
- `scenes/battle_scene.tscn`: Main playable battle scene.
- `scripts/core/data_catalog.gd`: JSON definition loader and deployment hydrator.
- `scripts/core/campaign_state.gd`: Thin campaign save state for gold, inventory, roster, completed scenarios, and campaign flags.
- `scripts/core/battle_state.gd`: Battle rules, unit state, turns, AI, and victory checks.
- `scripts/scenes/battle_scene.gd`: Rendering, input handling, and HUD wiring.
- `audio/bgm/*.wav` and `audio/sfx/*.wav`: Placeholder music loops and interface/action stingers.
- `art/portraits/*.png`, `art/units/*.png`, `art/items/*.png`, and `art/backgrounds/*.png`: Generated visual assets used by dialogue, battle HUD, board tokens, item buttons, and map backdrops.
- `data/campaign/campaign.json`: Campaign chapter ranges, scenario order, and scenario paths.
- `data/defs/*.json`: Officers, classes, terrain, items, and skills.
- `data/scenarios/*.json`: Scenario definitions.

## Data Files

- `data/defs/classes.json`: Class stats, movement types, skill access.
- `data/defs/officers.json`: Named officer base stats, growth, and default portrait paths.
- `data/defs/items.json`: Weapons, armor, accessories, and consumables.
- `data/defs/skills.json`: MP tactic definitions for damage, healing, support, status effects, target rules, and range.
- `data/defs/terrain.json`: Terrain colors, defense, avoid, and movement costs.
- `data/campaign/campaign.json`: Chapter ranges, scenario sequence, titles, and resource paths.
- `data/scenarios/*.json`: Dialogue, deployments, rewards, and branching flags.

## Battle Loop

1. Load battle data.
2. Hydrate deployments through `DataCatalog`.
3. Dispatch battle-start scenario events.
4. Show scenario briefing with the campaign chapter header, battle header, objective summary, chapter overview, selectable camp Talk conversations, manual checkpoint menu, and optional pre-battle shop, Armory, Roster, and Formation setup.
5. Player selects a unit.
6. Briefing completion dispatches battle-begin events, including opening dialogue.
7. Unit moves, attacks, chooses a tactic or consumable item from the side menu, changes equipment, counters, gains EXP, levels up, promotes at class thresholds, or waits. Tactic buttons show MP cost, kind, range, area radius, and power, support, debuff, movement modifier, accuracy/evasion modifier, damage-over-time, or action-lock effect. Physical attacks roll hit chance from unit agility and target terrain avoid, and equipped weapons can add small damage bonuses against matching target move types; misses give reduced EXP. The scene plays placeholder SFX, a short movement slide, a short attack motion, low-HP warning rings, hover target preview badges, area tactic overlays, an enemy threat overlay with physical damage and hostile tactic hints, selected/hover unit role, movement, terrain, status, and equipment details, and floating combat text for core action and UI feedback.
8. Player ends turn.
9. Enemy AI moves, picks physical attacks from damage, defeat, priority, and weapon-effectiveness scores, and can cast single-target or area damage, healing, support, debuff, movement-modifier, accuracy/evasion-modifier, damage-over-time, or action-lock tactics through the same combat and skill resolvers.
10. Battle checks scenario-defined defeat conditions first, including commander loss and turn limits, then victory conditions such as enemy defeat or reaching a marked destination tile.
11. Turn-start, movement-triggered, and unit-defeat scenario events run as phases change, units enter marked cells, or units fall, can wait for prerequisite events, and may update objectives with HUD notices, grant item or gold pickups, deploy reinforcements, withdraw units from the battlefield, or change AI target priorities.
12. On first-time victory, `CampaignState` snapshots player progression, battle inventory, and battle-only gold pickups, applies rewards once, advances `current_scenario_id`, and writes `user://campaign_save.json`.
13. If the scenario defines post-battle dialogue, it plays once before the victory result panel opens.
14. The victory result panel splits rewards, roster changes, saved player growth, campaign status, and pending choices into sections.
15. If the scenario defines post-battle choices, the result panel waits for the player to select one, previews choice rewards including officer join/leave effects, then saves the selected flags and optional choice rewards before enabling the next battle.
16. The result panel can load the next scenario, passing saved roster and inventory overlays back into `BattleState`.
17. Once all campaign scenarios are complete, the battle scene shows a campaign completion panel instead of loading another map.

## Save Boundary

`BattleState` owns tactical runtime fields. `CampaignState` saves only campaign-facing data: completed scenario ids, gold, inventory counts, joined officers, campaign flags, and a player roster snapshot. It does not save map positions, pre-battle Roster/Formation choices, action flags, temporary status effects, or transient battle occupancy.

Joined officers gate whether `requires_joined` player deployments are loaded at all. Rewards and post-battle choices can add or remove joined officers without deleting their saved roster snapshot, so a later rejoin can preserve progression. When a save loads, `CampaignState` scans completed scenarios in campaign order and reapplies only officer join/leave transitions from rewards and the saved `applied_post_battle_choices` ledger, allowing added recruitment rewards to reach older saves without replaying gold or items. Old saves without the ledger can backfill a choice id only when exactly one completed scenario choice matches saved flags. Roster entries are keyed by `officer_id` when available, so future scenarios can deploy the same joined officer under different scenario-specific `unit_id` values. Saved progression overlays final battle stats for now; a later equipment refactor should split base stats from equipment bonuses before adding item leveling or stat recalculation. New battles currently start player units healed to their saved maximum HP/MP. Skill access is carried in roster snapshots, with class defaults still applied for old saves that do not include skills. Promoted class ids are saved in the roster, and the next battle rehydrates class-derived movement, growth, skills, and range from the saved class id before equipment range is recalculated.

Inventory and campaign flags are copied from `CampaignState` into `BattleState` when a scenario starts. The pre-battle Chapters overview reads `CampaignState` chapter progress and can load completed or current battles without mutating the save. Briefings preview first-clear rewards, can expose `briefing.camp_conversations` through a selectable Talk menu with `briefing.camp_dialogue` as a fallback, and show completed replay rewards as already claimed. The pre-battle Save menu can write the current campaign state to `user://campaign_manual_save.json`, and loading that checkpoint restores it into `user://campaign_save.json` before re-entering the same pending-choice, completion, or current-briefing branch as startup. Pre-battle shop stock comes from the loaded scenario's `shop.items` list plus matching `shop.conditional_items` blocks, with optional finite limits from item entries or `stock` maps, and `shop.merchant` lines are presentation-only camp flavor. Shop purchases and 50% sell-back are campaign transactions: they update saved gold, unequipped inventory, and finite-stock purchase counts immediately, write the save file, and refresh the already-loaded battle inventory before the player begins the battle. Pre-battle Armory equipment changes use the same equipment rules as battle HUD equipment changes, then immediately save merged roster equipment/stat snapshots and inventory stock. Pre-battle Roster uses scenario `roster.max_units`, `roster.required_officers`, and `roster.required_units` to mark optional player deployments as sortie or reserve; reserve units remain in the candidate list but are excluded from board occupancy, drawing, selection, AI targeting, and living-unit victory checks. Non-controllable player units can act as protected escort targets: enemies can attack them and conditions can reference them, but they are skipped by player selection, Armory, Formation, counterattacks, and campaign roster progression snapshots when `persist_progression` is false. Scenario `ai_target_priority` nudges enemy movement and damage-skill scoring toward important targets such as envoys without overriding defeat bonuses or range checks, and `set_ai_target_priority` events can retune that battle-only pressure after an ambush, gate closure, or escort exposure. Pre-battle Formation uses the loaded scenario's `formation.cells` and only mutates current battle unit positions before battle-begin events fire. Destination victory cells from `unit_reaches_tile` conditions are exposed to the scene for objective overlays and tile info, and can be expressed as one `pos` or a multi-cell `cells` list; gated victory conditions can also expose the `unit_reaches_tile` event that unlocks them as the next visible objective marker. Movement-triggered `unit_reaches_tile` events receive the unit that just moved, so ambushes and pickup events fire on entry rather than from units already standing on a marker; `unit_defeated` events receive the fallen unit before final victory/defeat checks, allowing named-officer reactions and last-moment reinforcements. Briefing data can append matching `briefing.conditional_lines`, and scenario events can use `when.campaign_flags` to branch dialogue, objective changes, item and gold pickups, AI target-priority shifts, and reinforcements from saved campaign choices or `when.after_event` to wait for earlier scenario beats. Consumable use can restore HP or MP, cure matching poison/seal/snare/disarm statuses, or cleanse negative stat debuffs, and in-battle item use, event pickup grants, event gold pickups, plus equipment swaps mutate only the battle copy until victory; defeats and restarts do not spend saved items, keep picked-up items or gold, or preserve in-battle gear changes. Post-battle choices write campaign `flags` only after the result-panel button is pressed; if the player reloads after rewards are saved but before selecting, the pending scenario id restores the victory choice panel without replaying rewards. The next battle button stays locked until the campaign choice save succeeds. Equipment rewards share the same `item_id -> count` inventory stock, cover weapon, armor, and accessory slots, can be equipped from the side HUD before the selected unit moves or acts, and do not appear in the consumable action menu. Named equipment currently uses the same stock model with a presentation-only rarity tag rather than unique item instances. Already completed scenarios can be replayed without granting duplicate rewards, choices, replay inventory consumption, event gold pickups, save writes, current-scenario advancement, or finite-stock purchases; pre-battle Shop, Armory, Roster, Formation, and Save are disabled on completed-scenario replays to avoid side effects.

The battle scene owns presentation feedback: briefing and result states use menu BGM, briefing headers combine `CampaignState` chapter ranges, campaign order, and title data with `BattleState` briefing, objective text, condition-progress text, and defeat-risk text, active battles use battle BGM and show an objective/progress/risk panel fed by `BattleState`, objective-update signals show a short HUD notice and refresh the objective panel immediately, dialogue lines can show optional cached portrait textures or speaker-initial fallback panels in an expanded visual-novel-style panel, can place the portrait on the left or right side of that panel, and expose progress plus previous-line controls while a sequence is open, the side HUD reuses cached officer portrait textures or class sprites for the selected unit or hovered unit and formats focus text with role, movement type, current terrain move cost, defense/avoid bonuses, core stats, status effects, and gear, board maps can draw a scenario background texture under translucent terrain overlays and terrain detail patterns, board units render class sprite tokens, team rings, class badges, low-HP warning rings, HP bar color states, and active support/debuff/poison/seal/snare/disarm status pips from battle state fields, item buttons can show optional cached item icons, hover previews are rendered as target badges from existing `BattleState` forecast APIs, equipment option menus show stat/range/effect deltas, result and inventory summaries show named equipment with compact rarity tags, selected area tactics highlight their affected cells, the Threat toggle overlays enemy physical and hostile tactic reach while tile info names threat sources, estimates physical damage, and summarizes hostile tactic damage or status effects against occupied cells, log/result hooks trigger placeholder SFX, support, debuff, poison, seal, snare, disarm, objective updates, AI target-focus changes, and item/gold pickup effects use distinct feedback, `BattleState.unit_motion_requested` asks the scene to interpolate a unit's draw position during movement, `BattleState.unit_action_motion_requested` asks the scene to render a short attack motion, and `BattleState.combat_feedback_requested` asks the scene to draw transient floating combat text without changing battle rules.

The `New Campaign` button clears `user://campaign_save.json`, resets campaign state to the first scenario, and reloads the opening briefing.
