WIP: expressions: analyze for suitable indexes

Author: Totktonada

graphql/find_expr_index.lua

@@ -0,0 +1,83 @@
+--[[
+
+Temporary notes
+---------------
+
+Task: got result using index lookup(s) that are superset of the needed result.
+
+- pattern matchers (match only what that is suitable for index lookup)
+- support >, < and so on in find_index
+- unit tests for find_index, try to make it reusable
+- glue them all
+- ----
+- each node: suitable index parts: {index,field_no,iterator(=,!=,>,<,>=,<=),key}
+- each node: suitable indexes: {index,iterator,key,full_match}
+- each node: suitable index-sets: {{suitable indexes},full_match}
+- construction:
+  - index: // note: should be based on child index-sets, not indexes
+    - and:
+    - or:
+  - index-set:
+    - and:
+    - or:
+- full_match can be superseded with
+  - for index: weight = covered child nodes / child nodes
+  - for index-set: weight = index weights sum / child nodes
+  - the above is wrong weights: it should not be about which part of an
+    expr are covered, but about which fraction of the result we covered
+- ----
+- idea: doing all boolean arithmetic on parts, don't introduce
+  index/index-set until end
+- idea: we can construct DNF of parts (corr. to CNF of expr ops) during
+  tree traversal by expanding and of ors / or of ands and passing negation
+  down
+- ----
+- provide an iterator that merges several iterator results
+- ----
+- idea: construct DNF structure, where some conjuncts can be just expr, but
+  some are saturated with index parts info
+- it worth to support ranges: (x > V1 && x < V2) and so on; set index and stop
+  key for it
+
+]]--
+
+--local expressions = require('graphql.expressions')
+
+local find_expr_index = {}
+
+--[[
+local cmp_op_to_iterator_type = {
+    ['=='] = 'EQ',
+    ['!='] = 'NE', -- discarded after all NOT ops processing
+    ['>']  = 'GT',
+    ['>='] = 'GE',
+    ['<']  = 'LT',
+    ['<='] = 'LE',
+}
+
+-- 42 > x => x < 42
+local reverse_iterator_type = {
+    ['EQ'] = 'EQ',
+    ['NE'] = 'NE',
+    ['GT'] = 'LT',
+    ['GE'] = 'LE',
+    ['LT'] = 'GT',
+    ['LE'] = 'GE',
+}
+
+-- !(x < 42) => x >= 42
+local negate_iterator_type = {
+    ['EQ'] = 'NE',
+    ['NE'] = 'EQ',
+    ['GT'] = 'LE',
+    ['GE'] = 'LT',
+    ['LT'] = 'GE',
+    ['LE'] = 'GT',
+}
+
+local function is_cmp_op(op)
+    return cmp_op_to_iterator_type[op] ~= nil
+end
+]]--
+
+return find_expr_index