-- Migration: 003_CreateEventSchemasTable
-- Description: Creates table for storing event schema versions and upcast relationships
-- Phase: 5 (Schema Evolution & Versioning)

-- Create event_schemas table
CREATE TABLE IF NOT EXISTS event_streaming.event_schemas
(
    event_type VARCHAR(500) NOT NULL,
    version INTEGER NOT NULL,
    clr_type_name TEXT NOT NULL,
    json_schema TEXT NULL,
    upcast_from_type TEXT NULL,
    upcast_from_version INTEGER NULL,
    registered_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),

    CONSTRAINT pk_event_schemas PRIMARY KEY (event_type, version),
    CONSTRAINT chk_version_positive CHECK (version > 0),
    CONSTRAINT chk_upcast_version_valid CHECK (
        (version = 1 AND upcast_from_type IS NULL AND upcast_from_version IS NULL) OR
        (version > 1 AND upcast_from_type IS NOT NULL AND upcast_from_version IS NOT NULL AND upcast_from_version = version - 1)
    )
);

-- Create index for getting latest version
CREATE INDEX IF NOT EXISTS idx_event_schemas_latest_version
    ON event_streaming.event_schemas (event_type, version DESC);

-- Create index for looking up by CLR type
CREATE INDEX IF NOT EXISTS idx_event_schemas_clr_type
    ON event_streaming.event_schemas (clr_type_name);

-- Add comment
COMMENT ON TABLE event_streaming.event_schemas IS
    'Stores event schema versions for automatic upcasting and schema evolution';

COMMENT ON COLUMN event_streaming.event_schemas.event_type IS
    'Logical event type name (e.g., UserCreatedEvent)';

COMMENT ON COLUMN event_streaming.event_schemas.version IS
    'Schema version number (starts at 1, increments sequentially)';

COMMENT ON COLUMN event_streaming.event_schemas.clr_type_name IS
    'Assembly-qualified CLR type name for deserialization';

COMMENT ON COLUMN event_streaming.event_schemas.json_schema IS
    'Optional JSON Schema (Draft 7) for external consumers';

COMMENT ON COLUMN event_streaming.event_schemas.upcast_from_type IS
    'CLR type of the previous version (null for version 1)';

COMMENT ON COLUMN event_streaming.event_schemas.upcast_from_version IS
    'Previous version number this can upcast from (null for version 1)';

COMMENT ON COLUMN event_streaming.event_schemas.registered_at IS
    'When this schema version was registered';