-- All tables with the original data rows must be renamed, because it is not
-- possible to remove existing foreign keys. The tables will be recreated with
-- a new column measured_value_id which reference on the primary key of the
-- table measured values.
--
-- More about why it is not possible to delete a foreign key is described here:
-- https://stackoverflow.com/a/1884893/7652996
ALTER TABLE humidities
RENAME TO humidities_backup;

CREATE TABLE humidities (
  id                      CHAR(36)                                                  NOT NULL,
  value                   NUMERIC(10,3)                                             NOT NULL,
  date                    TIMESTAMP                                                 NOT NULL,
  sensor_id               CHAR(36)                                                  NOT NULL,
  creation_date           TIMESTAMP       DEFAULT (datetime('now', 'localtime'))    NOT NULL,
  update_date             TIMESTAMP,
  CONSTRAINT pk_humidities PRIMARY KEY(id),
  CONSTRAINT fk_humidities_sensor_id FOREIGN KEY(sensor_id) REFERENCES sensors(sensor_id) ON DELETE CASCADE ON UPDATE CASCADE
);

ALTER TABLE pressures
RENAME TO pressures_backup;

CREATE TABLE pressures (
  id                      CHAR(36)                                                  NOT NULL,
  value                   NUMERIC(10,3)                                             NOT NULL,
  date                    TIMESTAMP                                                 NOT NULL,
  sensor_id               CHAR(36)                                                  NOT NULL,
  creation_date           TIMESTAMP       DEFAULT (datetime('now', 'localtime'))    NOT NULL,
  update_date             TIMESTAMP,
  CONSTRAINT pk_pressures PRIMARY KEY(id),
  CONSTRAINT fk_pressures_sensor_id FOREIGN KEY(sensor_id) REFERENCES sensors(sensor_id) ON DELETE CASCADE ON UPDATE CASCADE
);

ALTER TABLE temperatures
RENAME TO temperatures_backup;

CREATE TABLE temperatures (
  id                      CHAR(36)                                                  NOT NULL,
  value                   NUMERIC(10,3)                                             NOT NULL,
  date                    TIMESTAMP                                                 NOT NULL,
  sensor_id               CHAR(36)                                                  NOT NULL,
  creation_date           TIMESTAMP       DEFAULT (datetime('now', 'localtime'))    NOT NULL,
  update_date             TIMESTAMP,
  CONSTRAINT pk_temperatures PRIMARY KEY(id),
  CONSTRAINT fk_temperatures_id FOREIGN KEY(sensor_id) REFERENCES sensors(sensor_id) ON DELETE CASCADE ON UPDATE CASCADE
);

-- Filling tables humidities, pressures and temperatures with the data from the
-- backup table.
INSERT INTO humidities
SELECT
  h.id,
  h.value,
  h.date,
  m.sensor_id,
  h.creation_date,
  h.update_date
FROM humidities_backup h
  INNER JOIN measured_values m ON (m.id = h.measured_value_id);

INSERT INTO pressures
SELECT
  p.id,
  p.value,
  p.date,
  m.sensor_id,
  p.creation_date,
  p.update_date
FROM pressures_backup p
  INNER JOIN measured_values m ON (m.id = p.measured_value_id);

INSERT INTO temperatures
SELECT
  t.id,
  t.value,
  t.date,
  m.sensor_id,
  t.creation_date,
  t.update_date
FROM temperatures_backup t
  INNER JOIN measured_values m ON (m.id = t.measured_value_id);

-- The remaining tables, which were only necessary for the migration,
-- are now removed.
DROP TABLE humidities_backup;
DROP TABLE pressures_backup;
DROP TABLE temperatures_backup;
DROP TABLE measured_values;