Christmas Tree Generator, PostgreSQL

Christmas Tree Generator

WITH
params AS(
	SELECT 
		--- tree params
		30 as _p_halfwidth, -- max half width of the tree 
		4 as _p_height,  -- heigt of single tree block
		5 as _p_num_blocks,  -- number of tree blocks
		1.1 as _p_scale_inter,  -- inter scale of block widening
		1.15 as _p_scale_outer,   --- outer scale of blocks

---- the look of tree
		'.'::text as _p_tree_char,
		'X'::text as _p_star_char,
		'x'::text as _p_chain_char,
		'O'::text as _p_decor1_char,
		'8'::text as _p_decor2_char,

--- density and location of decors :

3 as _p_chain_start,
		0 as _p_decor1_start,
		0 as _p_decor2_start,
		
		2 as _p_chain_helicity,
		1 as _p_decor1_helicity,
		1 as _p_decor2_helicity,
		
		8 as _p_chain_step,
		5 as _p_decor1_step,
		7 as _p_decor2_step,
		
		0.99 as _p_chain_prob, -- chain sometimes ends...
		0.1 as _p_decor1_prob,
		0.1 as _p_decor2_prob	
	),
christmas_tree as (
        ---- build a table of float numbers b in blocks_
	WITH  RECURSIVE tree(b, pos,l, lv) AS ( 
		(WITH RECURSIVE t(b,pos, l) AS (
			SELECT 
				1 -(abs(generate_series(-_p_halfwidth, _p_halfwidth, 1)))::float8 /(_p_halfwidth) b, -- to draw tree
				generate_series (0, 2*_p_halfwidth, 1) as  pos, -- to find positions of decorations
				0 as l from params
			UNION ALL
			SELECT (b *_p_scale_inter), pos, l + 1 FROM t,params WHERE l < _p_height-1
		)
		select b, pos, l, 1 AS lv from t order by l asc
	)
	UNION ALL
	SELECT b * _p_scale_outer, pos, l + (lv * (2*_p_halfwidth+1)) AS l, lv + 1
	FROM tree,params
	WHERE lv < _p_num_blocks
	)

select l,array_to_string(array_agg(
		(CASE 
			WHEN b>=1 THEN 
			CASE
				WHEN l=0 THEN _p_star_char
				ELSE
					CASE
						WHEN mod(pos+_p_chain_helicity*l + _p_chain_start,_p_chain_step)=0 and random()<_p_chain_prob  THEN _p_chain_char
						WHEN mod(pos+_p_decor1_helicity*l + _p_decor1_start,_p_decor1_step)=0 and random()<_p_decor1_prob  THEN _p_decor1_char
						WHEN mod(pos+_p_decor2_helicity*l + _p_decor2_start,_p_decor2_step)=0 and random()<_p_decor2_prob THEN _p_decor2_char				
					ELSE _p_tree_char
					END 
			END
		ELSE ' ' 
		END)::text), ''
	) AS "Merry Christmas"
	from tree,params
	group by l
	order by l asc
)
select "Merry Christmas" from christmas_tree
order by l


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