Document search mechanics and tile depletion

doc/mechanics/README.md

@@ -3,6 +3,7 @@
 - [Global settings](globals.md)
 - [Background ticks](ticks.md)
 - [Hunger](hunger.md)
+- [Search](search.md)
 
 ## Configuration
 

doc/mechanics/search.md

@@ -0,0 +1,57 @@
+# Search
+
+## Searching algorithm
+
+- Get "loot table" from tile's terrain type
+- Update loot table according to current season
+  (some items have different find chances in different seasons)
+- Reduce find chances based on tile depletion (details below)
+- Calculate total chance to find anything
+- If total chance is zero then display system message and skip next steps
+- Pick a random number (0%-100%)
+- Compare the number with the loot table to determine if and what was found
+- If no item was found then display system message and skip next steps
+- Update character's inventory
+- Update tile depletion (details below)
+
+## Depletion in v2
+
+Depletion of tiles is stored in **HP** column.
+
+Each successful search has **15%** chance to reduce tile's **HP** by one point.
+
+Low HP reduces all chances in loot table:
+
+- When **HP > 2** then chances are not modified
+- If **HP equals 2** then chances are multiplied by **75%**
+- If **HP equals 1** then chances are multiplied by **50%**
+- If **HP equals 0** then chances are reduced to zero
+
+Each daily tick restores **1 HP**.
+
+## Depletion in v3
+
+The game stores total number of items found in a tile.
+These counters are reset on daily tick.
+
+High counter reduces chances in loot table:
+
+- When **searches < 6** then chances are not modified
+- If **searches between 6 and 11** then chances are multiplied by **75%**
+- If **searches between 12 and 17** then chances are multiplied by **50%**
+- If **searches >= 18** then chances are reduced to zero
+
+Additionally, some terrain types (forest, pine forest, grassland)
+are actually sets of terrain types, representing various levels of depletion.
+
+Forests and pine forests have **five** variants: the first three levels
+of depletion are displayed identically in game interface (as forest),
+heavy depletion is displayed as grass, and a complete depletion is displayed
+as dirt.
+
+Grassland has **two** levels of depletion, the depleted variant is displayed
+as dirt.
+
+After an item was found, a second random number is rolled, this time to check
+if tile transformed into a next depletion level. The chance for that
+transformation is equal to found item's find chance in calculated loop table.

doc/mechanics/ticks.md

@@ -149,13 +149,7 @@ if they executed no actions in the last **5 days**.
 
 ## Restore search odds
 
-Roll a dice for each tile, chance for restore is defined as **restore_odds**
-in terrain type.
-
-If a tile is restored and it is **dirt_track**
-then change it into **grassland** with **1 HP**.
-
-If a tile is restored and it is any other type, set **HP := min(HP+1, Max HP)**.
+This is documented on [search](search.md) page.
 
 ## Spawn animals