# Goal-Based Generator Unlocks - Technical Specification

## Document Status
- Version: 1.0
- Date: 2026-03-14
- Scope: Unlock generators when goal thresholds are reached using one or more currencies.
- Context sources: Amp threads `T-019ce93a-d410-70ad-aaa0-4697dafb0148` and `T-019c846f-2556-75bc-a1aa-fb26cd9ff52a`.

## Problem Statement
The project already supports generator state (`unlocked` + `available`) in `GameState`, but unlock 
transitions are currently configured only by static defaults (`starts_unlocked`, `starts_available`).

We need progression goals so that a locked generator becomes usable only after the player reaches
specific currency quantities. Goals must support one or more currencies per objective.

## Current Baseline
1. Generator state is persisted in `GameState.generator_states` with keys `owned`, `purchased_count`,
`unlocked`, `available`.
2. `CurrencyGenerator` already exposes `is_unlocked`, `is_available`, and `is_available_to_player()` 
and uses them to gate click, auto-production, and purchases.
3. `GeneratorContainer` listens to `GameState.generator_state_changed` and updates button enabled/disabled state.
4. Save/load sanitization already handles generator state schema evolution safely.

This means the unlock feature can be added without changing core purchase/production mechanics.

## Goals And Non-Goals

## Goals

1. Define unlock goals that depend on one or multiple currency thresholds.
2. Evaluate goals automatically when relevant currency values change.
3. Unlock and make target generator available exactly once when a goal is met.
4. Keep behavior deterministic after save/load.

## Non-Goals

1. Adding quests, timed objectives, or repeatable missions.
2. Adding reward types other than generator unlock/availability.
3. Rebalancing generator economy values in this feature.

## Functional Requirements

1. A goal targets exactly one generator (`target_generator_id`).
2. A goal contains one or more currency requirements (`requirements[]`).
3. Goal completion rule is logical AND across requirements (all thresholds must be met).
4. Supported currencies must map to existing `GameState.CurrencyType` values (`gold`, `gems`).
5. When completed, a goal sets both:
   - `GameState.set_generator_unlocked(target, true)`
   - `GameState.set_generator_available(target, true)`
6. Goal completion must be idempotent (re-evaluating does not re-apply side effects).
7. Goal checks must run:
   - at runtime on `currency_changed`
   - once at startup after loading save data
8. Invalid goal entries (unknown currency, missing target id, malformed amount) must be ignored with a warning,
not a crash.

## Data Model

## New Config File

Add a root JSON file:
- `res://generator_unlock_goals.json`

Schema (v1):

```json
{
  "version": 1,
  "goals": [
	{
	  "id": "unlock_gems_generator",
	  "target_generator_id": "Gems",
	  "requirements": [
		{
		  "currency": "gold",
		  "amount": { "m": 1.0, "e": 3 }
		}
	  ]
	}
  ]
}
```

Notes:
1. `amount` uses existing `BigNumber` serialization (`m`, `e`) to avoid float precision/overflow issues.
2. `id` must be unique and stable.
3. `requirements` must contain at least one entry.

## Runtime Structures (GDScript)

Recommended internal structs/classes:

1. `UnlockGoalRequirement`
   - `currency: GameState.CurrencyType`
   - `amount: BigNumber`
2. `UnlockGoal`
   - `id: StringName`
   - `target_generator_id: StringName`
   - `requirements: Array[UnlockGoalRequirement]`

No persistent `completed_goals` storage is required for v1 because completion is derived from generator unlock state.

## System Design

## New Runtime Component

Add a scene-level controller script (recommended name: `generator_unlock_system.gd`) responsible for:

1. Loading + validating `generator_unlock_goals.json`.
2. Subscribing to currency change signals.
3. Evaluating pending goals.
4. Triggering generator unlock transitions.

Placement options:

1. Attach to the main gameplay scene root (preferred for prototype).
2. Promote to autoload later if multiple gameplay scenes require shared unlock logic.

## Evaluation Flow

1. On `_ready()`:
   - load goals
   - connect to `GameState.currency_changed`
   - run `evaluate_all_goals()` once
2. On currency change:
   - run `evaluate_all_goals()` (or an optimized subset)
3. For each goal:
   - skip if target generator already unlocked and available
   - verify all requirement thresholds
   - if satisfied, unlock target generator and emit debug/info log

## Pseudocode

```gdscript
func _evaluate_goal(goal: UnlockGoal) -> bool:
	if GameState.is_generator_unlocked(goal.target_generator_id) and GameState.is_generator_available(goal.target_generator_id):
		return false

	for requirement in goal.requirements:
		var current: BigNumber = _get_currency_amount(requirement.currency)
		if current.is_less_than(requirement.amount):
			return false

	GameState.set_generator_unlocked(goal.target_generator_id, true)
	GameState.set_generator_available(goal.target_generator_id, true)
	return true
```

## UI/UX Behavior

1. Existing `GeneratorContainer` behavior already prevents interaction while locked.
2. Optional v1.1 enhancement: show a compact "Unlock requirement" line for locked generators.
3. On unlock, UI updates automatically through existing `generator_state_changed` signal path.

## Error Handling And Validation
1. File open failure: log warning and disable unlock processing for that session.
2. JSON parse failure or wrong root type: log warning and disable unlock processing.
3. Invalid goal entries: skip only invalid entries, continue loading valid ones.
4. Duplicate goal IDs: keep first entry, ignore duplicates with warning.
5. Unknown `target_generator_id`: allow config load, but warn when evaluation cannot find/resolve state.

## Save/Load Behavior

1. Unlock result persists naturally via existing generator state persistence.
2. On load, if a goal was completed previously, no duplicate effect occurs because state is already unlocked.
3. If config thresholds are reduced in future versions, startup evaluation can unlock additional generators from existing balances.

## Performance Considerations

1. v1 can safely evaluate all goals on every currency change (small goal count).
2. If goals scale up, add currency-to-goal index to evaluate only affected goals.
3. BigNumber comparisons are lightweight for this usage profile.

## Implementation Plan

1. Add `generator_unlock_goals.json` with initial goals.
2. Implement `generator_unlock_system.gd` loader/validator/evaluator.
3. Attach unlock system to gameplay scene (`generator_museum.tscn` or current active scene).
4. Configure at least one generator as initially locked (`starts_unlocked = false`, `starts_available = false`) in its `.tres` data.
5. Add runtime logs for unlock events and invalid config entries.
6. Run headless project parse smoke check.

## Acceptance Criteria

1. A locked generator becomes usable immediately after all configured currency thresholds are reached.
2. Goals with multiple requirements unlock only when every requirement is satisfied.
3. Unlock state persists after save/load and app restart.
4. No crashes occur when goals file is missing or malformed.
5. Existing generator purchase/production behavior is unchanged for already unlocked generators.

## Manual Test Cases

1. Start with a generator configured as locked; verify buy buttons are disabled.
2. Grant required currency via debug controls; verify automatic unlock and enabled buttons.
3. Save/restart; verify generator remains unlocked.
4. Use a multi-currency goal; verify partial progress does not unlock.
5. Corrupt one goal entry in JSON; verify warning is logged and other valid goals still work.