-- PCSA SAMPLING ESTIMATOR

-- PCSA counter (shell type)
CREATE TYPE pcsa_estimator;

-- get estimator size for the requested number of bitmaps / key size
CREATE FUNCTION pcsa_size(nbitmaps int, keysize int) RETURNS int
     AS '$libdir/pcsa_counter', 'pcsa_size'
     LANGUAGE C;

-- creates a new pcsa estimator with a given number of bitmaps / key size
-- an estimator with 32 bitmaps and keysize 3 usually gives reasonable results
CREATE FUNCTION pcsa_init(nbitmaps int, keysize int) RETURNS pcsa_estimator
     AS '$libdir/pcsa_counter', 'pcsa_init'
     LANGUAGE C;

-- merges the second estimator into the first one
CREATE FUNCTION pcsa_merge(estimator1 pcsa_estimator, estimator2 pcsa_estimator) RETURNS pcsa_estimator
     AS '$libdir/pcsa_counter', 'pcsa_merge_simple'
     LANGUAGE C;

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

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

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

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

-- length of the estimator (about the same as pcsa_size with existing estimator)
CREATE FUNCTION length(counter pcsa_estimator) RETURNS int
     AS '$libdir/pcsa_counter', 'pcsa_length'
     LANGUAGE C STRICT;

/* functions for aggregate functions */

CREATE FUNCTION pcsa_add_item_agg(counter pcsa_estimator, item anyelement, nbitmaps integer, keysize integer) RETURNS pcsa_estimator
     AS '$libdir/pcsa_counter', 'pcsa_add_item_agg'
     LANGUAGE C;

CREATE FUNCTION pcsa_add_item_agg2(counter pcsa_estimator, item anyelement) RETURNS pcsa_estimator
     AS '$libdir/pcsa_counter', 'pcsa_add_item_agg2'
     LANGUAGE C;

/* input/output functions */

CREATE FUNCTION pcsa_in(value cstring) RETURNS pcsa_estimator
     AS '$libdir/pcsa_counter', 'pcsa_in'
     LANGUAGE C IMMUTABLE STRICT;

CREATE FUNCTION pcsa_out(counter pcsa_estimator) RETURNS cstring
     AS '$libdir/pcsa_counter', 'pcsa_out'
     LANGUAGE C IMMUTABLE STRICT;

-- actual PCSA counter data type
CREATE TYPE pcsa_estimator (
    INPUT = pcsa_in,
    OUTPUT = pcsa_out,
    LIKE  = bytea
);

-- pcsa based aggregate (item, nbitmaps, keysize)
CREATE AGGREGATE pcsa_distinct(anyelement, int, int)
(
    sfunc = pcsa_add_item_agg,
    stype = pcsa_estimator,
    finalfunc = pcsa_get_estimate
);

-- pcsa based aggregate (item)
CREATE AGGREGATE pcsa_distinct(anyelement)
(
    sfunc = pcsa_add_item_agg2,
    stype = pcsa_estimator,
    finalfunc = pcsa_get_estimate
);

-- build the counter(s), but does not perform the final estimation (i.e. can be used to pre-aggregate data)
-- parameters: item, nbitmaps, keysize
CREATE AGGREGATE pcsa_accum(anyelement, int, int)
(
    sfunc = pcsa_add_item_agg,
    stype = pcsa_estimator
);

-- parameters: item
CREATE AGGREGATE pcsa_accum(anyelement)
(
    sfunc = pcsa_add_item_agg2,
    stype = pcsa_estimator
);

-- merges all the counters into just a single one (e.g. after running pcsa_accum)
-- parameters: estimator
CREATE AGGREGATE pcsa_merge(pcsa_estimator)
(
    sfunc = pcsa_merge_agg,
    stype = pcsa_estimator
);

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

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