-- Create measures_values table.
-- This table represent a collection of different measured values, because it
-- can be possible, that a sensor returns multiple measured values. For example
-- the BME280 semsor returns humidity, pressure and temperature values.
CREATE TABLE measured_values (
  id                      CHAR(36)                                                NOT NULL,
  sensor_id               CHAR(36)                                                NOT NULL,
  creation_date           TIMESTAMP WITH TIME ZONE    DEFAULT CURRENT_TIMESTAMP   NOT NULL,
  update_date             TIMESTAMP WITH TIME ZONE,
  CONSTRAINT pk_measured_value PRIMARY KEY(id),
  CONSTRAINT pk_measured_value_sensor_id FOREIGN KEY(sensor_id) REFERENCES sensors(sensor_id) ON DELETE CASCADE ON UPDATE CASCADE
);

-- 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,
  measured_value_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_measured_value_id FOREIGN KEY(measured_value_id) REFERENCES measured_values(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,
  measured_value_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_measured_value_id FOREIGN KEY(measured_value_id) REFERENCES measured_values(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,
  measured_value_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_measured_value_id FOREIGN KEY(measured_value_id) REFERENCES measured_values(id) ON DELETE CASCADE ON UPDATE CASCADE
);

-- The following two views are necessary to create a FULL OUTER JOIN via the
-- tables humidities, pressures and temperatures, as this is not supported in
-- SQLite. More about this here:
--
-- https://stackoverflow.com/questions/12759087/full-outer-join-in-sqlite-on-4-tables
CREATE VIEW humidities_pressures AS
SELECT
  h.id AS humidity_id,
  h.value AS humidity_value,
  h.date AS humidity_date,
  h.sensor_id AS humidity_sensor_id,
  h.creation_date AS humidity_creation_date,
  h.update_date AS humidity_update_date,
  p.id AS pressure_id,
  p.value AS pressure_value,
  p.date AS pressure_date,
  p.sensor_id AS pressure_sensor_id,
  p.creation_date AS pressure_creation_date,
  p.update_date AS pressure_update_date
FROM humidities_backup h
  LEFT JOIN pressures_backup p ON (h.date = p.date AND h.sensor_id = p.sensor_id)
UNION ALL
SELECT
  h.id AS humidity_id,
  h.value AS humidity_value,
  h.date AS humidity_date,
  h.sensor_id AS humidity_sensor_id,
  h.creation_date AS humidity_creation_date,
  h.update_date AS humidity_update_date,
  p.id AS pressure_id,
  p.value AS pressure_value,
  p.date AS pressure_date,
  p.sensor_id AS pressure_sensor_id,
  p.creation_date AS pressure_creation_date,
  p.update_date AS pressure_update_date
FROM pressures_backup p
  LEFT JOIN humidities_backup h ON (p.date = h.date AND p.sensor_id = h.sensor_id)
WHERE h.date IS NULL
AND h.sensor_id IS NULL;

CREATE VIEW joined_values AS
SELECT
  hp.*,
  t.id AS temperature_id,
  t.value AS temperature_value,
  t.date AS temperature_date,
  t.sensor_id AS temperature_sensor_id,
  t.creation_date AS temperature_creation_date,
  t.update_date AS temperature_update_date
FROM temperatures_backup t
  LEFT JOIN humidities_pressures hp ON (t.date = hp.pressure_date AND t.sensor_id = hp.pressure_sensor_id)
UNION ALL
SELECT
  hp.*,
  t.id AS temperature_id,
  t.value AS temperature_value,
  t.date AS temperature_date,
  t.sensor_id AS temperature_sensor_id,
  t.creation_date AS temperature_creation_date,
  t.update_date AS temperature_update_date
FROM humidities_pressures hp
  LEFT JOIN temperatures_backup t ON (t.date = hp.pressure_date  AND t.sensor_id = hp.pressure_sensor_id)
WHERE t.date IS NULL
AND t.sensor_id IS NULL;

-- The date and the SensorID are used as primary key between the tables
-- humidities, pressures and temperatures. Based on this information, a
-- MeasuredValueID is generated. The data records are then inserted into the
-- table.
INSERT INTO measured_values (id, creation_date, sensor_id)
SELECT
  LOWER(HEX(RANDOMBLOB(4)) || '-' || HEX(RANDOMBLOB(2)) || '-' || '4' || SUBSTR(HEX(RANDOMBLOB(2)), 2) || '-' || SUBSTR('AB89', 1 + (ABS(random()) % 4) , 1) || SUBSTR(HEX(RANDOMBLOB(2)), 2) || '-' || HEX(RANDOMBLOB(6))) AS measured_value_id,
  CASE WHEN humidity_date IS NOT NULL THEN humidity_date
    WHEN pressure_date IS NOT NULL THEN pressure_date
    WHEN temperature_date IS NOT NULL THEN temperature_date
    ELSE NULL
  END date,
	CASE WHEN humidity_sensor_id IS NOT NULL THEN humidity_sensor_id
      WHEN pressure_sensor_id IS NOT NULL THEN pressure_sensor_id
      WHEN temperature_sensor_id IS NOT NULL THEN temperature_sensor_id
      ELSE NULL
  END sensor_id
FROM joined_values;

-- In the following, the original data records from the backup are restored with
-- the difference that the MeasuredValueID is added as a foreign key based on
-- the date and the SensorID.
INSERT INTO humidities (id, value, date, measured_value_id, creation_date, update_date)
SELECT
	jv.humidity_id,
	jv.humidity_value,
	jv.humidity_date,
	(SELECT mv.id FROM measured_values mv WHERE mv.creation_date = jv.humidity_date AND mv.sensor_id = jv.humidity_sensor_id) AS measured_value,
  jv.humidity_creation_date,
  jv.humidity_update_date
FROM joined_values jv
WHERE humidity_id IS NOT NULL;

INSERT INTO pressures (id, value, date, measured_value_id, creation_date, update_date)
SELECT
	jv.pressure_id,
	jv.pressure_value,
	jv.pressure_date,
	(SELECT mv.id FROM measured_values mv WHERE mv.creation_date = jv.pressure_date AND mv.sensor_id = jv.pressure_sensor_id) AS measured_value,
  jv.pressure_creation_date,
  jv.pressure_update_date
FROM joined_values jv
WHERE pressure_id IS NOT NULL;

INSERT INTO temperatures (id, value, date, measured_value_id, creation_date, update_date)
SELECT
	jv.temperature_id,
	jv.temperature_value,
	jv.temperature_date,
	(SELECT mv.id FROM measured_values mv WHERE mv.creation_date = jv.temperature_date AND mv.sensor_id = jv.temperature_sensor_id) AS measured_value,
  jv.temperature_creation_date,
  jv.temperature_update_date
FROM joined_values jv
WHERE temperature_id IS NOT NULL;

-- The remaining views and tables, which were only necessary for the migration,
-- are now removed.
DROP VIEW humidities_pressures;
DROP VIEW joined_values;
DROP TABLE humidities_backup;
DROP TABLE pressures_backup;
DROP TABLE temperatures_backup;