-- Invitation system for invite-only registration
-- Supports both platform-level and community-level invitations

CREATE TABLE invitations (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    
    -- Invitation code (unique, URL-safe)
    code VARCHAR(64) UNIQUE NOT NULL,
    
    -- Who created this invitation
    created_by UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    
    -- Optional: specific email this invite is for
    email VARCHAR(255),
    
    -- Optional: community-specific invite
    community_id UUID REFERENCES communities(id) ON DELETE CASCADE,
    
    -- Invitation metadata
    max_uses INTEGER DEFAULT 1,
    uses_count INTEGER DEFAULT 0,
    
    -- Expiration
    expires_at TIMESTAMPTZ,
    
    -- Status
    is_active BOOLEAN DEFAULT TRUE,
    
    -- Timestamps
    created_at TIMESTAMPTZ DEFAULT NOW(),
    
    -- Constraint: can't exceed max uses
    CONSTRAINT valid_uses CHECK (uses_count <= max_uses OR max_uses IS NULL)
);

-- Track invitation usage
CREATE TABLE invitation_uses (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    invitation_id UUID NOT NULL REFERENCES invitations(id) ON DELETE CASCADE,
    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    used_at TIMESTAMPTZ DEFAULT NOW(),
    
    UNIQUE(invitation_id, user_id)
);

-- Add invitation reference to users table
ALTER TABLE users ADD COLUMN IF NOT EXISTS invited_by UUID REFERENCES invitations(id);

-- Indexes
CREATE INDEX idx_invitations_code ON invitations(code);
CREATE INDEX idx_invitations_created_by ON invitations(created_by);
CREATE INDEX idx_invitations_community ON invitations(community_id);
CREATE INDEX idx_invitations_email ON invitations(email);
CREATE INDEX idx_invitations_active ON invitations(is_active) WHERE is_active = TRUE;

-- Function to generate secure invitation code
CREATE OR REPLACE FUNCTION generate_invitation_code() RETURNS VARCHAR(64) AS $$
DECLARE
    chars TEXT := 'ABCDEFGHJKLMNPQRSTUVWXYZabcdefghjkmnpqrstuvwxyz23456789';
    result VARCHAR(64) := '';
    i INTEGER;
BEGIN
    FOR i IN 1..16 LOOP
        result := result || substr(chars, floor(random() * length(chars) + 1)::integer, 1);
    END LOOP;
    RETURN result;
END;
$$ LANGUAGE plpgsql;

-- Function to validate and use an invitation
CREATE OR REPLACE FUNCTION use_invitation(
    p_code VARCHAR(64),
    p_user_id UUID,
    p_email VARCHAR(255) DEFAULT NULL
) RETURNS TABLE(
    success BOOLEAN,
    invitation_id UUID,
    community_id UUID,
    error_message TEXT
) AS $$
DECLARE
    v_invite invitations%ROWTYPE;
BEGIN
    -- Find the invitation
    SELECT * INTO v_invite 
    FROM invitations 
    WHERE code = p_code AND is_active = TRUE
    FOR UPDATE;
    
    IF NOT FOUND THEN
        RETURN QUERY SELECT FALSE, NULL::UUID, NULL::UUID, 'Invalid invitation code'::TEXT;
        RETURN;
    END IF;
    
    -- Check expiration
    IF v_invite.expires_at IS NOT NULL AND v_invite.expires_at < NOW() THEN
        UPDATE invitations SET is_active = FALSE WHERE id = v_invite.id;
        RETURN QUERY SELECT FALSE, NULL::UUID, NULL::UUID, 'Invitation has expired'::TEXT;
        RETURN;
    END IF;
    
    -- Check max uses
    IF v_invite.max_uses IS NOT NULL AND v_invite.uses_count >= v_invite.max_uses THEN
        UPDATE invitations SET is_active = FALSE WHERE id = v_invite.id;
        RETURN QUERY SELECT FALSE, NULL::UUID, NULL::UUID, 'Invitation has reached maximum uses'::TEXT;
        RETURN;
    END IF;
    
    -- Check email restriction
    IF v_invite.email IS NOT NULL AND v_invite.email != p_email THEN
        RETURN QUERY SELECT FALSE, NULL::UUID, NULL::UUID, 'This invitation is for a specific email address'::TEXT;
        RETURN;
    END IF;
    
    -- Record the use
    INSERT INTO invitation_uses (invitation_id, user_id) VALUES (v_invite.id, p_user_id);
    
    -- Increment uses count
    UPDATE invitations 
    SET uses_count = uses_count + 1,
        is_active = CASE 
            WHEN max_uses IS NOT NULL AND uses_count + 1 >= max_uses THEN FALSE 
            ELSE is_active 
        END
    WHERE id = v_invite.id;
    
    -- Update user's invited_by
    UPDATE users SET invited_by = v_invite.id WHERE id = p_user_id;
    
    RETURN QUERY SELECT TRUE, v_invite.id, v_invite.community_id, NULL::TEXT;
END;
$$ LANGUAGE plpgsql;