-- ADAPTIVE SAMPLING ESTIMATOR

-- adaptive_estimator data type (shell type)
CREATE TYPE adaptive_estimator;

-- get estimator size for the requested error rate / number of distinct items
CREATE FUNCTION adaptive_size(error_rate real, ndistinct int) RETURNS int
     AS '$libdir/adaptive_counter', 'adaptive_size'
     LANGUAGE C;

-- creates a new adaptive estimator with a given error / number of distinct items
CREATE FUNCTION adaptive_init(error_rate real, ndistinct int) RETURNS adaptive_estimator
     AS '$libdir/adaptive_counter', 'adaptive_init'
     LANGUAGE C;

-- merges the two estimators, creates a new one
CREATE FUNCTION adaptive_merge(estimator1 adaptive_estimator, estimator2 adaptive_estimator) RETURNS adaptive_estimator
     AS '$libdir/adaptive_counter', 'adaptive_merge_simple'
     LANGUAGE C;

-- merges the second estimator into the first one
CREATE FUNCTION adaptive_merge_agg(estimator1 adaptive_estimator, estimator2 adaptive_estimator) RETURNS adaptive_estimator
     AS '$libdir/adaptive_counter', 'adaptive_merge_agg'
     LANGUAGE C;

-- add an item to the estimator
CREATE FUNCTION adaptive_add_item(counter adaptive_estimator, item anyelement) RETURNS void
     AS '$libdir/adaptive_counter', 'adaptive_add_item'
     LANGUAGE C;

-- get error rate used when creating the estimator (as a real number)
CREATE FUNCTION adaptive_get_error(counter adaptive_estimator) RETURNS real
     AS '$libdir/adaptive_counter', 'adaptive_get_error'
     LANGUAGE C STRICT;

-- get expected number of distinct values used when creating the estimator (as integer)
CREATE FUNCTION adaptive_get_ndistinct(counter adaptive_estimator) RETURNS int
     AS '$libdir/adaptive_counter', 'adaptive_get_ndistinct'
     LANGUAGE C STRICT;

-- get number of distinct values used when creating the estimator (int)
CREATE FUNCTION adaptive_get_item_size(counter adaptive_estimator) RETURNS int
     AS '$libdir/adaptive_counter', 'adaptive_get_item_size'
     LANGUAGE C STRICT;

-- reset the estimator (start counting from the beginning)
CREATE FUNCTION adaptive_reset(counter adaptive_estimator) RETURNS void
     AS '$libdir/adaptive_counter', 'adaptive_reset'
     LANGUAGE C STRICT;

-- length of the estimator (about the same as adaptive_size with existing estimator)
CREATE FUNCTION length(counter adaptive_estimator) RETURNS int
     AS '$libdir/adaptive_counter', 'adaptive_length'
     LANGUAGE C STRICT;

-- get current estimate of the distinct values (as a real number)
CREATE FUNCTION adaptive_get_estimate(counter adaptive_estimator) RETURNS real
     AS '$libdir/adaptive_counter', 'adaptive_get_estimate'
     LANGUAGE C STRICT;

/* functions for the aggregates */
CREATE FUNCTION adaptive_add_item_agg(counter adaptive_estimator, item anyelement, error_rate real, ndistinct int) RETURNS adaptive_estimator
     AS '$libdir/adaptive_counter', 'adaptive_add_item_agg'
     LANGUAGE C;

CREATE FUNCTION adaptive_add_item_agg2(counter adaptive_estimator, item anyelement) RETURNS adaptive_estimator
     AS '$libdir/adaptive_counter', 'adaptive_add_item_agg2'
     LANGUAGE C;

/* input / output functions */
CREATE FUNCTION adaptive_in(value cstring) RETURNS adaptive_estimator
     AS '$libdir/adaptive_counter', 'adaptive_in'
     LANGUAGE C IMMUTABLE STRICT;

CREATE FUNCTION adaptive_out(counter adaptive_estimator) RETURNS cstring
     AS '$libdir/adaptive_counter', 'adaptive_out'
     LANGUAGE C IMMUTABLE STRICT;

-- data type for the adaptive-sampling based distinct estimator
CREATE TYPE adaptive_estimator (
    INPUT = adaptive_in,
    OUTPUT = adaptive_out,
    LIKE  = bytea
);

-- adaptive based aggregate (item, error rate, ndistinct)
CREATE AGGREGATE adaptive_distinct(anyelement, real, int)
(
    sfunc = adaptive_add_item_agg,
    stype = adaptive_estimator,
    finalfunc = adaptive_get_estimate
);

-- adaptive based aggregate (item)
CREATE AGGREGATE adaptive_distinct(anyelement)
(
    sfunc = adaptive_add_item_agg2,
    stype = adaptive_estimator,
    finalfunc = adaptive_get_estimate
);

-- build the counter(s), but does not perform the final estimation (i.e. can be used to pre-aggregate data)
-- parameters: item, error_rate, ndistinct
CREATE AGGREGATE adaptive_accum(anyelement, real, int)
(
    sfunc = adaptive_add_item_agg,
    stype = adaptive_estimator
);

-- parameters: item
CREATE AGGREGATE adaptive_accum(anyelement)
(
    sfunc = adaptive_add_item_agg2,
    stype = adaptive_estimator
);

-- merges all the counters into just a single one (e.g. after running adaptive_accum)
-- parameters: estimator
CREATE AGGREGATE adaptive_merge(adaptive_estimator)
(
    sfunc = adaptive_merge_agg,
    stype = adaptive_estimator
);

-- evaluates the estimate (for an estimator)
CREATE OPERATOR # (
    PROCEDURE = adaptive_get_estimate,
    RIGHTARG = adaptive_estimator
);

-- merges two estimators into a new one
CREATE OPERATOR || (
    PROCEDURE = adaptive_merge,
    LEFTARG  = adaptive_estimator,
    RIGHTARG = adaptive_estimator,
    COMMUTATOR = ||
);