-- Session Events table (Event Sourcing pattern - insert only, never update)
-- This provides an immutable audit trail of all session state changes
-- The current session state can be derived by replaying events

CREATE TABLE session_events (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    session_id UUID NOT NULL,
    username VARCHAR(255) NOT NULL,              -- The user this session belongs to
    event_type VARCHAR(50) NOT NULL,             -- Event type: created, joined, ready, completed, failed, expired
    session_type VARCHAR(20) NOT NULL,           -- 'keygen' or 'sign'

    -- Event payload (immutable snapshot at event time)
    threshold_n INTEGER,
    threshold_t INTEGER,
    party_id VARCHAR(255),                       -- For party-specific events (joined, ready, completed)
    party_index INTEGER,
    message_hash BYTEA,                          -- For sign sessions
    public_key BYTEA,                            -- Result of keygen
    signature BYTEA,                             -- Result of sign
    error_message TEXT,                          -- For failed events

    -- Metadata
    metadata JSONB,                              -- Additional event-specific data
    created_at TIMESTAMP NOT NULL DEFAULT NOW(),

    -- Constraints
    CONSTRAINT chk_session_event_type CHECK (event_type IN (
        'session_created',      -- Session initiated
        'party_joined',         -- A party joined the session
        'party_ready',          -- A party is ready to start MPC
        'round_started',        -- MPC round started
        'round_completed',      -- MPC round completed
        'session_completed',    -- Session completed successfully
        'session_failed',       -- Session failed
        'session_expired',      -- Session expired
        'delegate_share_sent',  -- Delegate share sent to user
        'signing_config_set',   -- Signing parties configured
        'signing_config_cleared' -- Signing parties cleared
    )),
    CONSTRAINT chk_session_event_session_type CHECK (session_type IN ('keygen', 'sign'))
);

-- Indexes for efficient querying
CREATE INDEX idx_session_events_session_id ON session_events(session_id);
CREATE INDEX idx_session_events_username ON session_events(username);
CREATE INDEX idx_session_events_created_at ON session_events(created_at);
CREATE INDEX idx_session_events_event_type ON session_events(event_type);
CREATE INDEX idx_session_events_session_type ON session_events(session_type);

-- Composite index for common queries
CREATE INDEX idx_session_events_session_timeline ON session_events(session_id, created_at);
CREATE INDEX idx_session_events_user_sessions ON session_events(username, session_type, created_at DESC);

-- Comments
COMMENT ON TABLE session_events IS 'Immutable event log for MPC sessions - append only, never update or delete';
COMMENT ON COLUMN session_events.username IS 'The unique user identifier that links all MPC operations';
COMMENT ON COLUMN session_events.event_type IS 'Type of event that occurred';
COMMENT ON COLUMN session_events.metadata IS 'Additional JSON data specific to the event type';

-- View to get current session state by replaying events
CREATE OR REPLACE VIEW session_current_state AS
SELECT DISTINCT ON (session_id)
    session_id,
    username,
    session_type,
    threshold_n,
    threshold_t,
    event_type as current_status,
    public_key,
    signature,
    error_message,
    created_at as last_event_at,
    (SELECT MIN(created_at) FROM session_events e2 WHERE e2.session_id = session_events.session_id) as started_at
FROM session_events
ORDER BY session_id, created_at DESC;

COMMENT ON VIEW session_current_state IS 'Derived view showing current state of each session from event log';