Unify custom_boost_factor, custom_score and custom_filters_score

[brwe]

Unify custom scores

The custom boost factor, custom script boost and the filters function query all do the same thing: They take a query and for each found document compute a new score based on the query score and some script, come custom boost factor or a combination of these two. However, the json format for these three functionalities is very different. This makes it hard to add new functions.

It would be nice to consolidate the three custom scores under the keyword function_score.

The new format should provide the same functionality as before that is: compute a new score with one function:

"function_score": {
    "(query|filter)": {},
    "boost": "boost for the whole query",
    "function": {}
} 

or allow to combine the newly computed scores

"function_score": {
    "(query|filter)": {},
    "boost": "boost for the whole query",
    "functions": [
        {
            "filter": {},
            "function": {}
        },
        {
            "function": {}
        }
    ],
    "score_mode": "(mult|max|...)"
}

function here can be either

"script_score": {
    "lang": "lang",
    "params": {
        "param1": "value1",
        "param2": "value2"
     },
    "script": "some script"
}

or

"boost_factor" : number

Changes

The custom boost factor query

"custom_boost_factor" : {
    "query" : {
        ....
    },
    "boost_factor" : 5.2
}

would become

"function_score" : {
    "query" : {
        ....
    },
    "boost_factor" : 5.2
}

The custom script score

"custom_score" : {
    "query" : {
        ....
    },
    "params" : {
        "param1" : 2,
        "param2" : 3.1
    },
    "script" : "_score * doc['my_numeric_field'].value / pow(param1, param2)"
}

would become

"function_score" : {
    "query" : {
        ....
    },
    "script_score" : {

        "params" : {
            "param1" : 2,
            "param2" : 3.1
        },
        "script" : "_score * doc['my_numeric_field'].value / pow(param1, param2)"
    }
}

and the custom filters score query

"custom_filters_score" : {
    "query" : {
        "match_all" : {}
     },
    "filters" : [
        {
            "filter" : { "range" : { "age" : {"from" : 0, "to" : 10} } },
            "boost" : "3"
        },
        {
            "filter" : { "range" : { "age" : {"from" : 10, "to" : 20} } },
            "script" : "_score * doc['my_numeric_field'].value / pow(param1, param2)"
        }
    ],
    "score_mode" : "first",
    "params" : {
        "param1" : 2,
        "param2" : 3.1
    }
    "score_mode" : "first"
}       

becomes:

"function_score" : {
    "query" : {
        "match_all" : {}
    },
    "functions" : [
        {
            "filter" : { "range" : { "age" : {"from" : 0, "to" : 10} } },
            "boost" : "3"
        },
        {
            "filter" : { "range" : { "age" : {"from" : 10, "to" : 20} } },
            "script_score" : { 
                "script" : "_score * doc['my_numeric_field'].value / pow(param1, param2)",
                "params" : {
                    "param1" : 2,
                    "param2" : 3.1
                }

            }
        }
    ],
    "score_mode" : "first",     
}       

[brwe]

replaced by issue #3423