-- This is Free Software under GNU Affero General Public License v >= 3.0
-- without warranty, see README.md and license for details.

-- SPDX-License-Identifier: AGPL-3.0-or-later
-- License-Filename: LICENSES/AGPL-3.0.txt

-- Copyright (C) 2018, 2019 by via donau
--   – Österreichische Wasserstraßen-Gesellschaft mbH
-- Software engineering by Intevation GmbH

-- Author(s):
--  * Tom Gottfried <tom@intevation.de>
--  * Sascha Wilde <wilde@intevation.de>

CREATE OR REPLACE FUNCTION best_utm(stretch isrsrange) RETURNS integer
AS $$
    SELECT best_utm(ST_Collect(geom::geometry))
        FROM waterway.distance_marks_virtual
        WHERE location_code IN (lower(stretch), upper(stretch))
    $$
    LANGUAGE sql
    STABLE PARALLEL SAFE;

-- Clip waterway axis to a stretch given by a pair of ISRS location codes.
-- Uses the table waterway.distance_marks_virtual to map ISRS location codes
-- to their geo-location.
-- Distance marks are assumed to be near the axis.
CREATE OR REPLACE FUNCTION ISRSrange_axis(stretch isrsrange) RETURNS geometry
AS $$
    WITH RECURSIVE
        -- Get coordinates of location codes
        points_geog AS (
            SELECT geom FROM waterway.distance_marks_virtual
                WHERE location_code = lower(stretch)
                    OR location_code = upper(stretch)),
        utm_zone AS (
            -- Find best matchting UTM zone
            SELECT best_utm(stretch) AS z),
        axis AS (
            SELECT id, ST_Transform(wtwaxs::geometry, z) AS wtwaxs
                FROM waterway.waterway_axis, utm_zone),
        -- In order to guarantee the following ST_Covers to work,
        -- snap distance mark coordinates to axis
        points AS (
            SELECT ST_ClosestPoint(
                    wtwaxs,
                    ST_Transform(points_geog.geom::geometry, z)) AS geom
                FROM points_geog, utm_zone, (
                    SELECT ST_Collect(wtwaxs) AS wtwaxs
                        FROM axis) AS ax),
        axis_snapped AS (
            -- Iteratively connect non-contiguous axis chunks
            -- to find the contiguous axis on which given distance marks lie
            (SELECT ARRAY[id] AS ids, wtwaxs
                FROM axis, points
                WHERE ST_Intersects(
                    ST_Buffer(axis.wtwaxs, 0.0001), points.geom)
                FETCH FIRST ROW ONLY)
            UNION
            -- Connect endpoint of next linestring with closest
            -- endpoint of merged linestring until a contiguous
            -- linestring connecting both distance marks is build up
            (SELECT refids || id,
                    ST_LineMerge(ST_Collect(ARRAY(
                        -- Linestring build up so far
                        SELECT refgeom
                        UNION
                        -- Fill eventual gap
                        SELECT ST_ShortestLine(
                                ST_Boundary(refgeom), ST_Boundary(geom))
                        UNION
                        -- Linestring to be added
                        SELECT geom)))
                FROM axis_snapped AS axis_snapped (refids, refgeom),
                    axis AS axis (id, geom),
                    (SELECT ST_Collect(points.geom) AS pts
                        FROM points) AS points
                WHERE id <> ALL(refids)
                    AND NOT ST_Covers(ST_Buffer(refgeom, 0.0001), points.pts)
                ORDER BY ST_Distance(ST_Boundary(refgeom), ST_Boundary(geom))
                FETCH FIRST ROW ONLY)),
        axis_segment AS (
            -- Fetch end result from snapping
            SELECT wtwaxs AS line
                FROM axis_snapped
                WHERE array_length(ids, 1) = (
                    SELECT max(array_length(ids, 1)) FROM axis_snapped))
        -- Use linear referencing to clip axis between distance marks.
        -- Simplification is used to work-around the problem, that
        -- ST_LineSubstring might generate very small line segments at an
        -- end of the resulting linestring, that significantly differ from
        -- the direction of the input linestring due to finite precision
        -- of the calculation. The generated small segment of the
        -- resulting line leads to unexpected results of the buffer with
        -- endcap=flat in the CTE below.
        SELECT ST_SimplifyPreserveTopology(ST_LineSubstring(
                    axis_segment.line, min(fractions.f), max(fractions.f)),
                0.0001) AS line
        FROM axis_segment, LATERAL (
            SELECT ST_LineLocatePoint(axis_segment.line, points.geom) AS f
                FROM points) AS fractions
        GROUP BY axis_segment.line
    $$
    LANGUAGE sql
    STABLE PARALLEL SAFE;

-- Clip an area to a stretch given by a pair of ISRS location codes.
-- Uses ISRSrange_axis() to retrieve the respective clipped axis used to find
-- perpendicular direction at geo-locations of ISRS codes.
-- The area passed as argument is assumed to intersect with the axis
-- (use e.g. waterway area or fairway dimensions).
-- If a multipolygon is passed, the union of the polygons intersecting with the
-- relevant part of the axis is used for clipping.
CREATE OR REPLACE FUNCTION ISRSrange_area(
    stretch isrsrange,
    area geometry
) RETURNS geometry
AS $$
    WITH
        axis_substring AS (
            SELECT ISRSrange_axis(stretch) AS line),
        utm_zone AS (
            SELECT best_utm(stretch) AS z),
        area_subset AS (
            -- In case area is a multipolygon, process the union of those
            -- polygons, which intersect with the axis. The union is to avoid
            -- problems with invalid/self-intersecting multipolygons
            SELECT ST_Union(a_dmp.geom) AS area
                FROM axis_substring, utm_zone, LATERAL (
                    SELECT ST_MakeValid(ST_Transform(geom, z)) AS geom
                        FROM ST_Dump(area)) AS a_dmp
                WHERE ST_Intersects(a_dmp.geom, axis_substring.line)
            ),
        rotated_ends AS (
            SELECT ST_Collect(ST_Scale(
                    ST_Translate(e,
                        (ST_X(p1) - ST_X(p2)) / 2,
                        (ST_Y(p1) - ST_Y(p2)) / 2),
                    ST_Point(d, d), p1)) AS blade
                FROM axis_substring, area_subset,
                    LATERAL (SELECT i, ST_PointN(line, i) AS p1
                        FROM (VALUES (1), (-1)) AS idx (i)) AS ep,
                    ST_Rotate(ST_PointN(line, i*2), pi()/2, p1) AS ep2 (p2),
                    ST_Makeline(p1, p2) AS e (e),
                    LATERAL (SELECT (ST_MaxDistance(p1, area) / ST_Length(e))
                            * 2) AS d (d)),
        range_area AS (
            -- Split area by orthogonal lines at the ends of the clipped axis
            SELECT (ST_Dump(ST_CollectionExtract(
                    ST_Split(area, blade), 3))).geom
                FROM area_subset, rotated_ends)
        -- From the polygons returned by the last CTE, select only those
        -- around the clipped axis
        SELECT ST_Multi(ST_Transform(ST_Union(range_area.geom), ST_SRID(area)))
            FROM axis_substring, range_area
            WHERE ST_Intersects(ST_Buffer(range_area.geom, -0.0001),
                axis_substring.line)
    $$
    LANGUAGE sql;