concept iteration

docs/concept.md

@@ -25,8 +25,9 @@ A single-player asymmetric game inspired by DOTA's wave/tower structure, combine
 - Buildings are placed in a queue and constructed one at a time; each building takes time to complete.
 - The crafting/production tree is defined in a config file so it can be extended later without code changes.
 - The factory is simpler than Factorio in depth but follows the same production-chain principle.
+- Materials are transported between buildings manually using **belts**.
 
-## Resources
+## Resources & Building Blocks
 
 Two sources feed the same production tree:
 
@@ -35,6 +36,13 @@ Two sources feed the same production tree:
   - Scrap can be smelted into the same basic materials as mined ores.
   - A dedicated **Reprocessing Plant** building can extract higher-level intermediate products from scrap (with fixed probabilities per product type), bypassing parts of the normal crafting chain.
 
+**Building Blocks** are the one globally shared resource:
+
+- An assembler recipe turns input materials into building blocks.
+- Building blocks are transported via belts into the HQ, where they are added to the global building blocks stock.
+- The global building blocks stock is the only global inventory; all other materials exist only in buildings and on belts.
+- Building blocks are spent to place new factory buildings and to unlock new asteroid columns (see Asteroid Expansion).
+
 ## Ships & Shipyards
 
 - Shipyards are built at the edge of the asteroid.
@@ -46,22 +54,30 @@ Two sources feed the same production tree:
   - **Repair ships** — fly out and repair damaged player defence stations and other player ships in the field.
 - If the player's ships are all destroyed, enemy ships advance unhindered toward the player's defence stations and then the asteroid.
 
-## Enemy Waves
+## Enemy Waves & Difficulty Scaling
 
 - Waves spawn continuously over a period of several seconds, then there is a gap before the next wave begins spawning.
 - The previous wave may still be in transit or fighting during the gap — there is no hard "wave cleared" state.
-- The number and strength of enemies increases over time.
+- Difficulty scales multiplicatively from two independent sources:
+  - **Time scaling** — enemy strength increases gradually over elapsed game time.
+  - **Push scaling** — each time the player destroys a set of enemy defence stations, enemy strength is multiplied by a configurable factor (e.g. 1.5×). This factor also determines the strength of the replacement defence stations.
+- Both scaling factors stack multiplicatively.
 
 ## Push Mechanic (Enemy Defence Stations)
 
 - The enemy owns a pair of defence stations positioned just beyond the scrollable area boundary.
 - The player is **not** forced to push — purely defensive play is valid.
-- If the player's fleet becomes strong enough that incoming waves are trivial, pushing to destroy enemy defence stations provides a new challenge: destroying them **doubles the enemy threat level** starting with the next wave, extends the scrollable area, and places a new pair of stations (twice as strong) at the new boundary.
+- If the player's fleet becomes strong enough that incoming waves are trivial, pushing to destroy enemy defence stations provides a new challenge: destroying them multiplies the enemy threat level by the configurable push scaling factor (starting with the next wave), extends the scrollable area, and places a new pair of stations (scaled by the same factor) at the new boundary.
 - Destroyed enemy defence stations drop loot: primarily **ship blueprints** that unlock new ship types at shipyards.
 
+## Starting Conditions
+
+- The player starts with the **HQ** pre-placed and a stock of building blocks.
+- Enemy waves do not begin immediately; there is a grace period at the start to allow initial factory setup.
+
 ## Game Over Condition
 
-- There is a **Headquarters** building at the edge of the asteroid (the last line of defence).
+- There is a **Headquarters (HQ)** building at the asteroid edge, through which building blocks enter the global stock via belts.
 - If enemy ships breach the asteroid — all player ships and defence stations destroyed — they attack the HQ.
 - The game is lost when the HQ is destroyed.
 - Individual factory buildings are **not** targeted or destroyed by enemies.
@@ -72,6 +88,8 @@ Two sources feed the same production tree:
 - Elapsed time is always displayed.
 - New ship blueprints are unlocked by destroying enemy defence stations.
 
-## Open Questions / TODO
+## Asteroid Expansion
 
-- How does the player unlock additional asteroid tiles for building?
+- The asteroid has a fixed number of columns, configurable at game start.
+- Additional columns can be unlocked by spending building blocks from the global stock.
+- Each unlocked column costs a fixed amount of building blocks (value to be tuned).