Add support of method bucket_id()

Patch adds a method bucket_id() that calculates a bucket id using
sharding function specified in DDL schema or in _ddl_sharding_func space
and passed sharding key.

Closes #76

Author: ligurio

CHANGELOG.md

@@ -10,6 +10,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - Added integration with service coveralls.io.
 - Allow specifying `sharding_func` for space.
+- Add a method `bucket_id` that calculate bucket id using sharding function
+  specified in DDL schema.
 
 ## [1.5.0] - 2021-08-09
 

README.md

@@ -84,6 +84,13 @@ bucket identifier (number)
 
     Return values: table with space's schemas (see "Schema example")
 
+### Get bucket id
+    `ddl.bucket_id(space_name, sharding_key)`
+    - Calculate bucket id for a specified space and sharding key.
+    Method uses sharding function specified in DDL schema.
+
+    Return values: bucket_id if no error, otherwise return `nil, err`
+
 ## Input data format
 
 ```lua

ddl.lua

@@ -163,8 +163,29 @@ local function get_schema()
     }
 end
 
+local function bucket_id(space_name, sharding_key)
+    if type(space_name) ~= 'string' then
+        return nil, string.format(
+            "Invalid space name (string expected, got %s)", type(space_name)
+        )
+    end
+    if sharding_key == nil then
+        return nil, string.format(
+            "Sharding key specified for space (%s) is nil", space_name)
+    end
+
+    local bucket_id, err = ddl_get.internal.bucket_id(
+        space_name, sharding_key)
+    if err ~= nil then
+        return nil, err
+    end
+
+    return bucket_id
+end
+
 return {
     check_schema = check_schema,
     set_schema = set_schema,
     get_schema = get_schema,
+    bucket_id = bucket_id,
 }

ddl/check.lua

@@ -1030,5 +1030,8 @@ return {
     check_index_part = check_index_part,
     check_index_parts = check_index_parts,
     check_index = check_index,
-    check_field = check_field
+    check_field = check_field,
+    internal = {
+        is_callable = is_callable,
+    }
 }

ddl/get.lua

@@ -1,3 +1,6 @@
+local utils = require('ddl.utils')
+local ddl_check = require('ddl.check')
+
 local function _get_index_field_path(space, index_part)
     local space_field = space:format()[index_part.fieldno]
 
@@ -111,6 +114,56 @@ local function get_space_schema(space_name)
     return space_ddl
 end
 
+local function prepare_sharding_func_for_call(space_name, sharding_func_def)
+    if type(sharding_func_def) == 'string' then
+        local sharding_func = utils.get_G_function(sharding_func_def)
+        if sharding_func ~= nil and
+           ddl_check.internal.is_callable(sharding_func) == true then
+            return sharding_func
+        end
+    end
+
+    if type(sharding_func_def) == 'table' then
+        local sharding_func, err = loadstring('return ' .. sharding_func_def.body)
+        if sharding_func == nil then
+            return nil, string.format(
+                "Body is incorrect in sharding_func for space (%s): %s", space_name, err)
+        end
+        return sharding_func()
+    end
+
+    return nil, string.format(
+        "Wrong sharding function specified in DDL schema of space (%s)", space_name
+    )
+end
+
+local function bucket_id(space_name, sharding_key)
+    local sharding_func_def = get_sharding_func(space_name)
+    if sharding_func_def == nil then
+        return nil, string.format(
+            "No sharding function specified in DDL schema of space (%s)", space_name
+        )
+    end
+    local sharding_func, err =
+        prepare_sharding_func_for_call(space_name, sharding_func_def)
+    if err ~= nil then
+        return nil, err
+    end
+
+    local ok, id = pcall(sharding_func, sharding_key)
+    if not ok then
+        return nil, string.format(
+            "Failed to execute sharding function for space name (%s): %s",
+            space_name, id
+        )
+    end
+
+    return id
+end
+
 return {
     get_space_schema = get_space_schema,
+    internal = {
+        bucket_id = bucket_id,
+    }
 }