fix: Issues with stair exploration

This commit is a significant rewrite of stair-related aspects of travel.
Although qw doesn't get stuck often these days with the recent
improvements to exploration and travel, this case in Orc revealed that
it still has some blind spots. Specific qw got shafted from Orc:1,
partially explored Orc:2 to reveal two upstairs, and got stuck in a loop
between Orc:1 and Orc:2 when the upstairs it took lead to a disconnected
cell with no further stairs. In this case the necessary backtracking was
broken as a result of tight control travel has now over unexplored stair
searches.

The code to determine the next travel depth and associated direction was
relatively difficult to understand in terms of it repeating various bits
of logic several times in the relevant function. This commit refactors
and simplifies the logic into fewer functions with more general code. It
removes special state tracking for stairs searches that's made redundant
by aforementioned recent changes to stairs direction searches. We also
no longer use an explicit backtracking state variable, instead relying
on stair state resets and the backtracking plan to put us in a state
that has us search new stairs on the level to which we backtrack.

Author: gammafunk

source/gameplans.lua

@@ -754,127 +754,7 @@ function gameplan_options()
     return GAMEPLANS[plan]
 end
 
-function dir_key(dir)
-    return dir == DIR.DOWN and ">" or "<"
-end
-
--- Adjust depth for any backtracking, reversing to our previous level and
--- searching in the opposite direction. Otherwise we only set the dir if the
--- level is autoexplored.
-function final_depth_dir(branch, depth, dir, backtrack)
-    if backtrack then
-        return depth + dir, -dir
-    elseif autoexplored_level(branch, depth) then
-        return depth, dir
-    else
-        return depth
-    end
-end
-
-function finalize_exploration_depth(branch, depth)
-    if not autoexplored_level(branch, depth) then
-        return depth
-    end
-
-    -- We just backtracked from an adjacent level to this depth. We'll not
-    -- return to the final search depth we calculate, but rather try to reach
-    -- that search depth via unexplored stairs from the current depth.
-    local backtrack = backtracked_to == make_level(branch, depth)
-
-    function all_reachable(branch, depth, dir)
-        return count_stairs(branch, depth, dir, FEAT_LOS.REACHABLE)
-            == num_required_stairs(branch, depth, dir)
-    end
-
-    function all_explored(branch, depth, dir)
-        return count_stairs(branch, depth, dir, FEAT_LOS.REACHABLE)
-            == count_stairs(branch, depth, dir, FEAT_LOS.EXPLORED)
-    end
-
-    local up_depth = depth - 1
-    local up_unreach = true
-    local  depth_up_all_reachable, up_finished, up_lev
-    if up_depth >= 1 then
-        depth_up_all_reachable = all_reachable(branch, depth, DIR.UP)
-        up_lev = make_level(branch, up_depth)
-        up_unreach
-            = count_stairs(branch, depth, DIR.UP, FEAT_LOS.REACHABLE) == 0
-        up_finished = depth_up_all_reachable
-            or autoexplored_level(branch, up_depth)
-                and all_explored(branch, up_depth, DIR.DOWN)
-    end
-
-    depth_up_finished = depth_up_all_reachable
-        or all_explored(branch, depth, DIR.UP)
-
-    local down_depth = depth + 1
-    local down_unreach = true
-    local depth_down_all_reachable, down_finished, down_lev
-    if down_depth <= branch_depth(branch) then
-        depth_down_all_reachable = all_reachable(branch, depth, DIR.DOWN)
-        down_depth_lev = make_level(branch, down_depth)
-        down_unreach =
-            count_stairs(branch, depth, DIR.DOWN, FEAT_LOS.REACHABLE) == 0
-        down_finished = depth_down_all_reachable
-            or autoexplored_level(branch, down_depth)
-                and all_explored(branch, down_depth, DIR.UP)
-    end
-
-    depth_down_finished = depth_down_all_reachable
-        or all_explored(branch, depth, DIR.DOWN)
-
-    if up_unreach then
-        if depth_down_finished then
-            if down_unreach then
-                return depth
-            end
-
-            if down_finished then
-                level_stair_reset(branch, depth, DIR.DOWN)
-                level_stair_reset(branch, down_depth, DIR.UP)
-                return depth
-            end
-
-            return final_depth_dir(branch, down_depth, DIR.UP, backtrack)
-        end
-
-        return depth, DIR.DOWN
-    end
-
-    if up_finished then
-        if depth_up_finished then
-            if depth_down_finished then
-                if down_unreach then
-                    -- We don't try stair resets if we're still looking for the
-                    -- rune. This way we'll instead try branch-end-specific
-                    -- plans for e.g. Swamp.
-                    if have_branch_runes(branch)
-                            or depth < branch_rune_depth(branch) then
-                        level_stair_reset(branch, up_depth, DIR.DOWN)
-                        level_stair_reset(branch, depth, DIR.UP)
-                    end
-                    return depth
-                end
-
-                if down_finished then
-                    level_stair_reset(branch, up_depth, DIR.DOWN)
-                    level_stair_reset(branch, depth, DIR.UP)
-                    level_stair_reset(branch, depth, DIR.DOWN)
-                    level_stair_reset(branch, down_depth, DIR.UP)
-                    return depth
-                end
-            end
-
-            return final_depth_dir(branch, down_depth, DIR.UP, backtrack)
-        end
-
-        return depth, DIR.UP
-    end
-
-    return final_depth_dir(branch, up_depth, DIR.DOWN, backtrack)
-end
-
-function explore_next_range_depth(branch, min_depth, max_depth)
+function next_exploration_depth(branch, min_depth, max_depth)
     -- The earliest depth that either lacks autoexplore or doesn't have all
     -- stairs reachable.
     local branch_max = branch_depth(branch)
@@ -909,7 +789,7 @@ function set_gameplan(status, gameplan)
         gameplan_depth = where_depth
     elseif gameplan_branch then
         gameplan_depth
-            = explore_next_range_depth(gameplan_branch, min_depth, max_depth)
+            = next_exploration_depth(gameplan_branch, min_depth, max_depth)
 
         if gameplan == zot_end and not gameplan_depth then
             gameplan_depth = branch_depth("Zot")

source/plans-explore.lua

@@ -1,10 +1,5 @@
 function plan_autoexplore()
-    if disable_autoexplore
-            -- Autoexplore will try to take us near any runed doors. We don't
-            -- even attempt it if doing a stairs search, since it would move us
-            -- off our map travel destination.
-            or stairs_search
-            or free_inventory_slots() == 0 then
+    if disable_autoexplore or free_inventory_slots() == 0 then
         return false
     end
 
@@ -231,8 +226,8 @@ function set_plan_explore2()
         {plan_go_to_pan_downstairs, "try_go_to_pan_downstairs"},
         {plan_enter_abyss, "enter_abyss"},
         {plan_go_to_abyss_portal, "try_go_to_abyss_portal"},
+        {plan_take_unexplored_stairs, "take_unexplored_stairs"},
         {plan_go_to_unexplored_stairs, "try_go_to_unexplored_stairs"},
-        {plan_take_unexplored_stairs, "try_take_unexplored_stairs"},
         {plan_shopping_spree, "try_shopping_spree"},
         {plan_go_to_orb, "try_go_to_orb"},
         {plan_go_command, "try_go_command"},

source/plans-stairs.lua

@@ -1,18 +1,11 @@
 function plan_go_to_unexplored_stairs()
     if not can_waypoint
-            or stairs_search
             or not stairs_search_dir
             or where_branch ~= travel_branch
             or where_depth ~= travel_depth then
         return false
     end
 
-    -- No point in trying if we don't have unexplored stairs.
-    if have_all_stairs(where_branch, where_depth, stairs_search_dir,
-            FEAT_LOS.EXPLORED) then
-        return false
-    end
-
     if map_search_attempts == 1 then
         map_search_attempts = 0
         disable_autoexplore = false
@@ -92,26 +85,35 @@ function plan_transporter_orient_exit()
 end
 
 function plan_take_unexplored_stairs()
-    if not stairs_search then
+    if not stairs_search_dir then
         return false
     end
 
-    local dir = stone_stair_type(stairs_search)
+    local dir, num
+    dir, num = stone_stair_type(view.feature_at(0, 0))
+    if not dir or dir ~= stairs_search_dir
+            or stairs_state(where_branch, where_depth, dir, num)
+                >= FEAT_LOS.EXPLORED then
+        return false
+    end
 
     -- Ensure that we autoexplore any new area we arrive in, otherwise, if we
     -- have completed autoexplore at least once, we may immediately leave once
     -- we see we've found the last missing staircase.
-    local level = make_level(where_branch, where_depth + dir)
-    c_persist.autoexplore[level] = AUTOEXP.NEEDED
+    c_persist.autoexplore[make_level(where_branch, where_depth + dir)]
+        = AUTOEXP.NEEDED
 
     magic("G" .. dir_key(dir))
     return true
 end
 
 -- Backtrack to the previous level if we're trying to explore stairs on a
--- travel or gameplan destination level yet have no further accessible
--- unexplored stairs. We require a travel or gameplan stairs search direction
--- to know whether to attempt this and what direction we should backtrack.
+-- destination level yet have no further accessible unexplored stairs. We
+-- require a travel stairs search direction to know whether to attempt this and
+-- what direction we should backtrack. Stairs are reset in the relevant
+-- directions on both levels so after we explore the pair of stairs used to
+-- return to the previous level, we'll take a different set of stairs from that
+-- level via a new travel stairs search direction.
 function plan_unexplored_stairs_backtrack()
     if not stairs_search_dir
             or where_branch ~= travel_branch
@@ -123,7 +125,7 @@ function plan_unexplored_stairs_backtrack()
     local next_depth = where_depth + stairs_search_dir
     level_stair_reset(where_branch, where_depth, stairs_search_dir)
     level_stair_reset(where_branch, next_depth, -stairs_search_dir)
-    backtracked_to = make_level(where_branch, next_depth)
+    want_gameplan_update = true
     send_travel(where_branch, next_depth)
     return true
 end

source/stairs.lua

@@ -47,6 +47,10 @@ function set_stairs(branch, depth, dir, feat_los, min_feat_los)
     end
 end
 
+function dir_key(dir)
+    return dir == DIR.DOWN and ">" or "<"
+end
+
 function level_stair_reset(branch, depth, dir)
     set_stairs(branch, depth, dir, FEAT_LOS.REACHABLE)
 
@@ -63,18 +67,6 @@ function level_stair_reset(branch, depth, dir)
     end
 end
 
-function check_stairs_search(feat)
-    local dir, num
-    dir, num = stone_stair_type(feat)
-    if not dir then
-        return
-    end
-
-    if stairs_state(where_branch, where_depth, dir, num) < FEAT_LOS.EXPLORED then
-        stairs_search = feat
-    end
-end
-
 function stairs_state(branch, depth, dir, num)
     local level = make_level(branch, depth)
     if dir == DIR.UP then
@@ -296,7 +288,6 @@ function update_level_map(num)
         if feat_uses_map_key(map_search_key, feat) then
             record_map_search(num, map_search_key, map_search_pos,
                 map_search_count, 100 * dx + dy)
-            check_stairs_search(feat)
         end
         map_search_key = nil
         map_search_pos = nil