-- Migration 063: Phasen und parallele Streams pro Trainingseinheit (Grundlage Breakout).
-- Bestehende Sektionen werden einer Default-whole_group-Phase zugeordnet.
-- UNIQUE (training_unit_id, order_index) auf Sektionen entfällt zugunsten
-- eindeutiger order_index je Phase bzw. je parallel_stream.

-- ── Phasen ───────────────────────────────────────────────────────────────
CREATE TABLE IF NOT EXISTS training_unit_phases (
    id SERIAL PRIMARY KEY,
    training_unit_id INT NOT NULL REFERENCES training_units(id) ON DELETE CASCADE,
    order_index INT NOT NULL,
    phase_kind VARCHAR(20) NOT NULL CHECK (phase_kind IN ('whole_group', 'parallel')),
    title VARCHAR(200),
    guidance_notes TEXT,
    UNIQUE (training_unit_id, order_index)
);

CREATE INDEX IF NOT EXISTS idx_training_unit_phases_unit ON training_unit_phases(training_unit_id);

-- ── Streams innerhalb einer Parallelphase ──────────────────────────────────
CREATE TABLE IF NOT EXISTS training_unit_parallel_streams (
    id SERIAL PRIMARY KEY,
    phase_id INT NOT NULL REFERENCES training_unit_phases(id) ON DELETE CASCADE,
    order_index INT NOT NULL,
    title VARCHAR(200),
    notes TEXT,
    assigned_trainer_profile_ids JSONB,
    UNIQUE (phase_id, order_index)
);

CREATE INDEX IF NOT EXISTS idx_training_unit_parallel_streams_phase
    ON training_unit_parallel_streams(phase_id);

COMMENT ON COLUMN training_unit_parallel_streams.assigned_trainer_profile_ids IS
    'Optionale Co-Trainer-IDs (JSON-Array von Profil-IDs) für diese Teilstrecke; MVP+';

-- ── Sektionen: Zuordnung zu Phase (gemeinsam) oder Stream (parallel) ─────
ALTER TABLE training_unit_sections
    ADD COLUMN IF NOT EXISTS phase_id INT REFERENCES training_unit_phases(id) ON DELETE CASCADE,
    ADD COLUMN IF NOT EXISTS parallel_stream_id INT REFERENCES training_unit_parallel_streams(id) ON DELETE CASCADE;

-- Backfill: je Einheit mit Sektionen eine whole_group-Phase, alle Sektionen dorthin
INSERT INTO training_unit_phases (training_unit_id, order_index, phase_kind, title)
SELECT tu.id, 0, 'whole_group', NULL
FROM training_units tu
WHERE EXISTS (SELECT 1 FROM training_unit_sections s WHERE s.training_unit_id = tu.id)
  AND NOT EXISTS (
    SELECT 1 FROM training_unit_phases p
    WHERE p.training_unit_id = tu.id AND p.order_index = 0 AND p.phase_kind = 'whole_group'
);

UPDATE training_unit_sections tus
SET phase_id = p.id
FROM training_unit_phases p
WHERE tus.phase_id IS NULL
  AND p.training_unit_id = tus.training_unit_id
  AND p.order_index = 0
  AND p.phase_kind = 'whole_group';

-- Alte globale Reihenfolge-Eindeutigkeit pro Einheit entfernen
ALTER TABLE training_unit_sections
    DROP CONSTRAINT IF EXISTS training_unit_sections_training_unit_id_order_index_key;

-- Genau eine Zielspalte gesetzt: gemeinsame Phase ODER paralleler Stream
ALTER TABLE training_unit_sections
    DROP CONSTRAINT IF EXISTS training_unit_sections_phase_or_stream_chk;

ALTER TABLE training_unit_sections
    ADD CONSTRAINT training_unit_sections_phase_or_stream_chk CHECK (
        (phase_id IS NOT NULL AND parallel_stream_id IS NULL)
        OR (phase_id IS NULL AND parallel_stream_id IS NOT NULL)
    );

CREATE UNIQUE INDEX IF NOT EXISTS uq_training_unit_sections_phase_order
    ON training_unit_sections (phase_id, order_index)
    WHERE phase_id IS NOT NULL;

CREATE UNIQUE INDEX IF NOT EXISTS uq_training_unit_sections_stream_order
    ON training_unit_sections (parallel_stream_id, order_index)
    WHERE parallel_stream_id IS NOT NULL;

CREATE INDEX IF NOT EXISTS idx_training_unit_sections_phase
    ON training_unit_sections(phase_id) WHERE phase_id IS NOT NULL;

CREATE INDEX IF NOT EXISTS idx_training_unit_sections_parallel_stream
    ON training_unit_sections(parallel_stream_id) WHERE parallel_stream_id IS NOT NULL;