-- A pure SQL replacement for the `semver` PGXN extension.
--
-- The only reason `semver` was ever a dependency is that `fsm.statechart`
-- needs a version column that sorts correctly. `semver` is a C extension, so
-- depending on it means every user needs a compiler and the PostgreSQL server
-- headers just to install pg_statecharts.
--
-- An integer array gets that for free. Arrays compare element by element, so
-- `order by version desc` is correct with no helper function and no chance of
-- a caller getting it wrong: 1.10.0 outranks 1.9.0 because 10 > 9. The cost is
-- that the natural text form is '{1,10,0}' rather than '1.10.0'; use
-- fsm.semver_text() when a version is being shown to a person.
--
-- Everything lives in the fsm schema. That matters for more than tidiness:
-- the `semver` extension defines its own to_semver(text) in the schema it is
-- installed into, so an unqualified to_semver(text) here would collide with
-- it and make `create extension pg_statecharts` fail outright in any database
-- that happens to use `semver` for unrelated reasons. The only unqualified
-- object is the compatibility shim at the bottom of this file, and it is
-- skipped when the name is already taken.

-- The check is deliberately thorough. A CHECK that evaluates to NULL passes,
-- so `value[2] >= 0` alone would let array[1,null,3] through; and an array
-- with a lower bound other than 1 compares unequal to the same elements
-- starting at 1, which would let two rows that mean the same version both
-- into the unique index on (name, version).
--
-- The length test is cardinality(), not array_length(): for the empty array
-- '{}' array_ndims, array_lower and array_length are all NULL, so a check
-- built only from those is NULL for it and lets it through. cardinality('{}')
-- is 0, which makes that term FALSE and the whole conjunction with it.
create domain fsm.semver as integer[]
  check (array_ndims(value) = 1
         and array_lower(value, 1) = 1
         and cardinality(value) = 3
         and array_position(value, null) is null
         and value[1] >= 0
         and value[2] >= 0
         and value[3] >= 0);

comment on domain fsm.semver is $comment$
    A semantic version as a three element integer array: {major, minor, patch}.
    '1.10.0' is array[1, 10, 0].

    Stored as integers rather than text so that ordering is correct by default.
    Arrays compare element by element, so `order by version desc` ranks 1.10.0
    above 1.9.0 with no helper function involved.

    Build one with fsm.to_semver('1.10.0') and render one with
    fsm.semver_text(version). Casting to text gives the array form, '{1,10,0}'.

    Prerelease and build metadata suffixes (1.0.0-rc1, 1.0.0+build5) are not
    supported.
$comment$;

create or replace function fsm.to_semver(version text)
returns fsm.semver as
$$
  declare
    dot_count integer;
    padded text;
  begin
    if version is null then
      return null;
    end if;

    dot_count := length(version) - length(replace(version, '.', ''));

    if dot_count > 2 then
      raise exception 'invalid version %', quote_literal(version)
        using hint = 'expected at most three components, e.g. 1.2.3';
    end if;

    -- pads with '.0' if the provided value has fewer than two dots, so that
    -- both '1' and '1.2' are accepted and normalised to 1.0.0 and 1.2.0
    padded := version || repeat('.0', 2 - dot_count);

    if padded !~ '^\d+\.\d+\.\d+$' then
      raise exception 'invalid version %', quote_literal(version)
        using hint = 'expected digits separated by dots, e.g. 1.2.3';
    end if;

    return string_to_array(padded, '.')::integer[]::fsm.semver;
  end;
$$ language plpgsql immutable parallel safe;

comment on function fsm.to_semver(text) is $comment$
    Parses text into an fsm.semver, padding out omitted components so that '1'
    and '1.2' become 1.0.0 and 1.2.0.

    This is the canonical name. An unqualified to_semver(text) is also created
    when that name is free, for the benefit of statechart migrations generated
    against older versions of pg_statecharts.
$comment$;

create or replace function fsm.semver_text(version fsm.semver)
returns text as
$$
  select array_to_string(version, '.')
$$ language sql immutable strict parallel safe;

comment on function fsm.semver_text(fsm.semver) is $comment$
    Renders a version the way people write it: fsm.semver_text(array[1,10,0])
    is '1.10.0'. Casting to text instead gives the array form, '{1,10,0}'.
$comment$;

-- Compatibility shim.
--
-- Statechart migrations generated by pg_statecharts 0.0.0 call an unqualified
-- to_semver(...), which back then resolved to the `semver` extension's
-- function. Creating one here keeps those migrations deploying, reverting and
-- verifying unchanged.
--
-- It is conditional because that is exactly the name `semver` occupies. If
-- something else already provides to_semver(text) we leave it alone and carry
-- on: a database that uses `semver` for its own purposes can still install
-- pg_statecharts, it just does not get the shim. Note that in that case those
-- 0.0.0 migrations cannot work whatever we do here -- `semver`'s to_semver
-- returns its own type, which has no assignment cast to anything we could
-- store -- so they have to be regenerated. Migrations generated from 0.1.0
-- onwards call fsm.to_semver(...) and never needed the shim.
--
-- Objects created inside a DO block during CREATE EXTENSION are still
-- recorded as members of the extension, so this is dropped by DROP EXTENSION
-- like any other object here.
--
-- The skip is reported at WARNING rather than NOTICE deliberately: PostgreSQL
-- runs extension scripts with client_min_messages set to warning, so a NOTICE
-- here would never reach whoever ran CREATE EXTENSION.
do $shim$
  begin
    if exists (
      select 1
      from pg_proc p
      where p.proname = 'to_semver'
        and p.pronamespace = current_schema()::regnamespace
        and pg_get_function_identity_arguments(p.oid) = 'text'
    ) then
      raise warning 'to_semver(text) already exists in schema %, skipping the pg_statecharts compatibility shim', current_schema()
        using hint = 'use fsm.to_semver(text) instead; migrations generated by '
                     'pg_statecharts 0.0.0 will need regenerating';
      return;
    end if;

    create function to_semver(version text)
    returns fsm.semver as
    $body$
      select fsm.to_semver(version)
    $body$ language sql immutable parallel safe;

    comment on function to_semver(text) is $c$
    Deprecated alias for fsm.to_semver(text), kept so that statechart
    migrations generated by pg_statecharts 0.0.0 keep working. Not created if
    the name was already taken, so do not rely on it in new code.
    $c$;
  end;
$shim$;