CREATE OR REPLACE VIEW water_z0 AS (
    SELECT geom FROM ne_110m_ocean
    UNION ALL
    SELECT geom FROM ne_110m_lakes
);

CREATE OR REPLACE VIEW water_z1 AS (
    SELECT geom FROM ne_110m_ocean
    UNION ALL
    SELECT geom FROM ne_110m_lakes
);

CREATE OR REPLACE VIEW water_z2 AS (
    SELECT geom FROM ne_50m_ocean
    UNION ALL
    SELECT geom FROM ne_110m_lakes
);

CREATE OR REPLACE VIEW water_z3 AS (
    SELECT geom FROM ne_50m_ocean
    UNION ALL
    SELECT geom FROM ne_110m_lakes
    UNION ALL
    SELECT geom FROM ne_110m_rivers_lake_centerlines
    WHERE featurecla = 'River'
);

CREATE OR REPLACE VIEW water_z4 AS (
    SELECT geom FROM ne_50m_ocean
    UNION ALL
    SELECT geom FROM ne_50m_lakes
    UNION ALL
    SELECT geom FROM ne_50m_rivers_lake_centerlines
    WHERE featurecla = 'River'
);

CREATE OR REPLACE VIEW water_z5 AS (
    SELECT geom FROM ne_10m_ocean
    UNION ALL
    SELECT geom FROM ne_10m_lakes
    UNION ALL
    SELECT geom FROM ne_50m_rivers_lake_centerlines
    WHERE featurecla = 'River'
);

CREATE OR REPLACE VIEW water_z6 AS (
    SELECT geom FROM ne_10m_ocean
    UNION ALL
    SELECT geom FROM ne_10m_lakes
    UNION ALL
    SELECT geom FROM ne_10m_rivers_lake_centerlines
    WHERE featurecla = 'River'
);

CREATE TABLE IF NOT EXISTS water_z8 AS (
    SELECT geom FROM ne_10m_ocean
    UNION ALL
    SELECT ST_SimplifyPreserveTopology(way, 200) AS geom FROM water_areas
    WHERE way_area > 1000000
    UNION ALL
    SELECT ST_Simplify(way, 200) AS geom FROM waterways
    WHERE waterway IN ('river') AND ST_Length(way) > 10000
);
CREATE INDEX IF NOT EXISTS water_z8_geom_idx ON water_z8 USING gist(geom);

CREATE TABLE IF NOT EXISTS water_z9 AS (
    SELECT ST_SimplifyPreserveTopology(way, 100) AS geom FROM water_areas
    WHERE way_area > 500000
    UNION ALL
    SELECT ST_Simplify(way,100) AS geom FROM waterways
    WHERE waterway IN ('river') AND ST_Length(way) > 5000
);
CREATE INDEX IF NOT EXISTS water_z9_geom_idx ON water_z9 USING gist(geom);

CREATE OR REPLACE VIEW water_z11 AS (
    SELECT way AS geom FROM water_areas
    WHERE way_area > 50000
    UNION ALL
    SELECT way AS geom FROM waterways
    WHERE waterway IN ('river')
);

CREATE OR REPLACE VIEW water_z12 AS (
    SELECT way AS geom FROM water_areas
    WHERE way_area > 40000
    UNION ALL
    SELECT way AS geom FROM waterways
    WHERE waterway IN ('river', 'canal', 'stream')
);

CREATE OR REPLACE VIEW water_z13 AS (
    SELECT way AS geom FROM water_areas
    WHERE way_area > 2000
    UNION ALL
    SELECT way AS geom FROM waterways
    WHERE waterway IN ('river', 'canal', 'stream', 'drain', 'ditch')
);

CREATE OR REPLACE VIEW water_z14 AS (
    SELECT way AS geom FROM water_areas
    UNION ALL
    SELECT way AS geom FROM waterways
);

CREATE OR REPLACE FUNCTION layer_water (bbox geometry, zoom_level int)
RETURNS TABLE(geom geometry) AS $$
    SELECT geom FROM (
        SELECT * FROM water_z0
        WHERE zoom_level = 0
        UNION ALL
        SELECT * FROM water_z1
        WHERE zoom_level = 1
        UNION ALL
        SELECT * FROM water_z2
        WHERE zoom_level = 2
        UNION ALL
        SELECT * FROM water_z3
        WHERE zoom_level = 3
        UNION ALL
        SELECT * FROM water_z4
        WHERE zoom_level = 4
        UNION ALL
        SELECT * FROM water_z5
        WHERE zoom_level = 5
        UNION ALL
        SELECT * FROM water_z6
        WHERE zoom_level BETWEEN 6 AND 7
        UNION ALL
        SELECT geom FROM water_z8
        WHERE zoom_level = 8
        UNION ALL
        SELECT geom FROM water_z9
        WHERE zoom_level BETWEEN 9 AND 10
        UNION ALL
        SELECT * FROM water_z11
        WHERE zoom_level = 11
        UNION ALL
        SELECT * FROM water_z12
        WHERE zoom_level = 12
        UNION ALL
        SELECT * FROM water_z13
        WHERE zoom_level = 13
        UNION ALL
        SELECT * FROM water_z14
        WHERE zoom_level >= 14
    ) AS zoom_levels
    WHERE geom && bbox;
$$ LANGUAGE SQL IMMUTABLE;