Add getting monster spells to clua m:spells() (#8737)

[Committer's note: squashed two commits. The second commit's message
 was:

changed clua moninfo:spells() to return book sets/string tables like
describe.cc monster_info has_spells based on mostly on spellbooks.
describe and clua moninfo:spells's shared code moves to
mon-book.h/mon-util.cc

-neil]

1 files changed, 37 insertions, 0 deletions

diff --git a/crawl-ref/source/mon-util.cc b/crawl-ref/source/mon-util.cc
index 8b6cfd753f..b102e0473b 100644
--- a/crawl-ref/source/mon-util.cc
+++ b/crawl-ref/source/mon-util.cc
@@ -2303,6 +2303,43 @@ vector<mon_spellbook_type> get_spellbooks(const monster_info &mon)
     return books;
 }
 
+// get a list of unique spells from a monster's preset spellbooks
+// or in the case of ghosts their actual spells.
+unique_books get_unique_spells(const monster_info &mi)
+{
+    const vector<mon_spellbook_type> books = get_spellbooks(mi);
+    const size_t num_books = books.size();
+
+    unique_books result;
+    for (size_t i = 0; i < num_books; ++i)
+    {
+        mon_spellbook_type book = books[i];
+        vector<spell_type> spells;
+
+        for (int j = 0; j < NUM_MONSTER_SPELL_SLOTS; ++j)
+        {
+            spell_type spell;
+            if (book == MST_GHOST)
+                spell = mi.spells[j];
+            else
+                spell = mspell_list[book].spells[j];
+
+            bool match = false;
+
+            for (size_t k = 0; k < spells.size(); ++k)
+                if (spell == spells[k])
+                    match = true;
+
+            if (!match && spell != SPELL_NO_SPELL && spell != SPELL_MELEE)
+                spells.push_back(spell);
+        }
+
+        result.push_back(spells);
+    }
+
+    return result;
+}
+
 static void _mons_load_spells(monster* mon)
 {
     vector<mon_spellbook_type> books = _mons_spellbook_list(mon->type);