Decompose remaining effects-file hot spots (refactor step 7)

drain gains drainReaches; zapSpeed gains hasteTarget/slowTarget;
readHoldMonster gains holdMonstersNear; readCreateMonster gains
createMonsterSpot; revealSpot splits into revealChar/revealWall/
revealSolid/revealFloor; turnSee gains showSensed. potions.go,
scrolls.go, and sticks.go are complexity-clean. Behavior and RNG call
order unchanged.

game/scrolls.go

@@ -59,6 +59,31 @@ func (g *RogueGame) readEnchantArmor(*Object) {
 func (g *RogueGame) readHoldMonster(*Object) {
 	// Hold monster scroll.  Stop all monsters within two spaces from
 	// chasing after the hero.
+	held := g.holdMonstersNear()
+
+	if held > 0 {
+		g.addmsgf("the monster")
+
+		if held > 1 {
+			g.addmsgf("s around you")
+		}
+
+		g.addmsgf(" freeze")
+
+		if held == 1 {
+			g.addmsgf("s")
+		}
+
+		g.endmsg()
+		g.Items.Scrolls[ScrollHoldMonster].Know = true
+	} else {
+		g.msg("you feel a strange sense of loss")
+	}
+}
+
+// holdMonstersNear freezes every awake monster within two spaces of the
+// hero and reports how many froze (the scan of the C S_HOLD case).
+func (g *RogueGame) holdMonstersNear() int {
 	p := &g.Player
 	held := 0
 
@@ -81,24 +106,7 @@ func (g *RogueGame) readHoldMonster(*Object) {
 		}
 	}
 
-	if held > 0 {
-		g.addmsgf("the monster")
-
-		if held > 1 {
-			g.addmsgf("s around you")
-		}
-
-		g.addmsgf(" freeze")
-
-		if held == 1 {
-			g.addmsgf("s")
-		}
-
-		g.endmsg()
-		g.Items.Scrolls[ScrollHoldMonster].Know = true
-	} else {
-		g.msg("you feel a strange sense of loss")
-	}
+	return held
 }
 
 func (g *RogueGame) readSleep(*Object) {
@@ -113,6 +121,19 @@ func (g *RogueGame) readSleep(*Object) {
 func (g *RogueGame) readCreateMonster(*Object) {
 	// Create a monster: first look in a circle around him, next try
 	// his room, otherwise give up
+	mp, ok := g.createMonsterSpot()
+	if !ok {
+		g.msg("you hear a faint cry of anguish in the distance")
+	} else {
+		tp := &Monster{}
+		g.newMonster(tp, g.randMonster(false), mp)
+	}
+}
+
+// createMonsterSpot reservoir-samples a legal spot around the hero for a
+// created monster; ok is false when every neighbor is blocked (the scan
+// of the C S_CREATE case).
+func (g *RogueGame) createMonsterSpot() (Coord, bool) {
 	p := &g.Player
 	i := 0
 
@@ -139,12 +160,7 @@ func (g *RogueGame) readCreateMonster(*Object) {
 		}
 	}
 
-	if i == 0 {
-		g.msg("you hear a faint cry of anguish in the distance")
-	} else {
-		tp := &Monster{}
-		g.newMonster(tp, g.randMonster(false), mp)
-	}
+	return mp, i != 0
 }
 
 func (g *RogueGame) readIdentify(obj *Object) {
@@ -166,45 +182,41 @@ func (g *RogueGame) readMagicMapping(*Object) {
 	}
 }
 
-// revealSpot uncovers one map cell for magic mapping: secret doors and
-// passages become real, hidden traps show, and the visible character is
-// drawn (the loop body of the C SCR_MAP case).
+// revealSpot uncovers one map cell for magic mapping and draws it (the
+// loop body of the C SCR_MAP case).
 func (g *RogueGame) revealSpot(y, x int) {
 	pp := g.Level.At(y, x)
+
+	ch := revealChar(pp)
+	if ch != ' ' {
+		if tp := pp.Monst; tp != nil {
+			tp.OldCh = ch
+			if !g.Player.On(SenseMonsters) {
+				g.mvaddch(y, x, ch)
+			}
+		} else {
+			g.mvaddch(y, x, ch)
+		}
+	}
+}
+
+// revealChar decides what magic mapping shows at a cell, making secret
+// doors, hidden passages, and hidden traps real as a side effect; ' '
+// means show nothing (the switch of the C SCR_MAP loop).
+func revealChar(pp *Place) byte {
 	ch := pp.Ch
 	pass := false
 
 	switch ch {
 	case Door, Stairs:
 	case '-', '|':
-		if !pp.Flags.Has(FReal) {
-			ch = Door
-			pp.Ch = Door
-			pp.Flags.Set(FReal)
-		}
+		ch = revealWall(pp)
 	case ' ':
-		if pp.Flags.Has(FReal) {
-			// def: hidden things in walls stay hidden
-			if pp.Flags.Has(FPassage) {
-				pass = true
-			} else {
-				ch = ' '
-			}
-		} else {
-			pp.Flags.Set(FReal)
-			pp.Ch = Passage
-			pass = true
-		}
+		pass = revealSolid(pp)
 	case Passage:
 		pass = true
 	case Floor:
-		if pp.Flags.Has(FReal) {
-			ch = ' '
-		} else {
-			ch = Trap
-			pp.Ch = Trap
-			pp.Flags.Set(FSeen | FReal)
-		}
+		ch = revealFloor(pp)
 	default:
 		if pp.Flags.Has(FPassage) {
 			pass = true
@@ -223,16 +235,47 @@ func (g *RogueGame) revealSpot(y, x int) {
 		ch = Passage
 	}
 
-	if ch != ' ' {
-		if tp := pp.Monst; tp != nil {
-			tp.OldCh = ch
-			if !g.Player.On(SenseMonsters) {
-				g.mvaddch(y, x, ch)
-			}
-		} else {
-			g.mvaddch(y, x, ch)
-		}
+	return ch
+}
+
+// revealWall handles a wall cell for magic mapping: a secret door
+// becomes a real door (the '-'/'|' arm).
+func revealWall(pp *Place) byte {
+	if !pp.Flags.Has(FReal) {
+		pp.Ch = Door
+		pp.Flags.Set(FReal)
+
+		return Door
 	}
+
+	return pp.Ch
+}
+
+// revealSolid handles a blank cell for magic mapping, reporting whether
+// it is passage: hidden passages become real; hidden things in walls
+// stay hidden (the ' ' arm).
+func revealSolid(pp *Place) bool {
+	if pp.Flags.Has(FReal) {
+		return pp.Flags.Has(FPassage)
+	}
+
+	pp.Flags.Set(FReal)
+	pp.Ch = Passage
+
+	return true
+}
+
+// revealFloor handles a floor cell for magic mapping: a hidden trap
+// becomes a real, seen trap; real floor shows nothing (the FLOOR arm).
+func revealFloor(pp *Place) byte {
+	if pp.Flags.Has(FReal) {
+		return ' '
+	}
+
+	pp.Ch = Trap
+	pp.Flags.Set(FSeen | FReal)
+
+	return Trap
 }
 
 func (g *RogueGame) readFoodDetection(*Object) {