CREATE TABLE IF NOT EXISTS invitation_codes (
  id BIGINT NOT NULL AUTO_INCREMENT,
  code_hash CHAR(64) NOT NULL,
  code_prefix VARCHAR(20) NOT NULL,
  max_uses INT UNSIGNED NOT NULL DEFAULT 1,
  used_count INT UNSIGNED NOT NULL DEFAULT 0,
  expires_at DATETIME NULL,
  status ENUM('active','revoked') NOT NULL DEFAULT 'active',
  note VARCHAR(255) NULL,
  created_by BIGINT NULL,
  created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (id), UNIQUE KEY uq_invitation_codes_hash (code_hash), KEY idx_invitation_codes_created_at (created_at)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

CREATE TABLE IF NOT EXISTS invitation_code_usages (
  id BIGINT NOT NULL AUTO_INCREMENT,
  invitation_code_id BIGINT NOT NULL,
  user_id BIGINT NOT NULL,
  email VARCHAR(100) NOT NULL,
  used_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (id), UNIQUE KEY uq_invitation_usage_code_user (invitation_code_id, user_id),
  KEY idx_invitation_usage_user (user_id),
  CONSTRAINT fk_invitation_usage_code FOREIGN KEY (invitation_code_id) REFERENCES invitation_codes(id),
  CONSTRAINT fk_invitation_usage_user FOREIGN KEY (user_id) REFERENCES users(id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;