-- Merchant onboarding: a prospective seller (personal 个人 or enterprise 企业)
-- applies once, a platform admin reviews it, and approval provisions the shop
-- and its dedicated shop_owner account in one transaction.

CREATE TYPE merchant_entity_type AS ENUM ('personal', 'enterprise');
CREATE TYPE merchant_application_status AS ENUM ('pending', 'approved', 'rejected');

CREATE TABLE merchant_applications (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    user_id UUID NOT NULL REFERENCES users (id) ON DELETE CASCADE,
    entity_type merchant_entity_type NOT NULL,
    -- Personal-kind entity information.
    real_name TEXT,
    -- Enterprise-kind entity information.
    company_name TEXT,
    business_license_no TEXT,
    -- Operating categories, one or more rows of the reference category tree.
    category_ids UUID[] NOT NULL DEFAULT '{}',
    -- Contact details, shared by both kinds.
    contact_name TEXT NOT NULL,
    contact_phone TEXT NOT NULL,
    contact_email TEXT NOT NULL,
    contact_address TEXT,
    -- Qualification materials are URLs only; no file storage in this MVP.
    identity_document_url TEXT,
    business_license_url TEXT,
    extra_materials JSONB NOT NULL DEFAULT '[]'::jsonb,
    status merchant_application_status NOT NULL DEFAULT 'pending',
    rejection_reason TEXT,
    reviewed_by UUID REFERENCES users (id),
    reviewed_at TIMESTAMPTZ,
    -- Shop created by approval; null until then.
    created_shop_id UUID REFERENCES shops (id),
    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
    updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
    -- Each kind carries its own required entity + qualification fields.
    CONSTRAINT merchant_applications_kind_fields CHECK (
        (
            entity_type = 'personal'
            AND real_name IS NOT NULL AND btrim(real_name) <> ''
            AND identity_document_url IS NOT NULL AND btrim(identity_document_url) <> ''
        )
        OR (
            entity_type = 'enterprise'
            AND company_name IS NOT NULL AND btrim(company_name) <> ''
            AND business_license_url IS NOT NULL AND btrim(business_license_url) <> ''
        )
    ),
    -- A pending row is unreviewed; terminal rows record who and when, and a
    -- rejection always carries its reason.
    CONSTRAINT merchant_applications_review_consistent CHECK (
        (status = 'pending' AND reviewed_by IS NULL AND reviewed_at IS NULL
            AND rejection_reason IS NULL AND created_shop_id IS NULL)
        OR (status = 'approved' AND reviewed_by IS NOT NULL AND reviewed_at IS NOT NULL
            AND rejection_reason IS NULL AND created_shop_id IS NOT NULL)
        OR (status = 'rejected' AND reviewed_by IS NOT NULL AND reviewed_at IS NOT NULL
            AND rejection_reason IS NOT NULL AND btrim(rejection_reason) <> ''
            AND created_shop_id IS NULL)
    ),
    CONSTRAINT merchant_applications_categories CHECK (cardinality(category_ids) >= 1)
);

-- At most one live application per user; rejected rows are free to retry.
CREATE UNIQUE INDEX merchant_applications_active_idx
    ON merchant_applications (user_id) WHERE status IN ('pending', 'approved');
CREATE INDEX merchant_applications_user_idx
    ON merchant_applications (user_id, created_at DESC);
CREATE INDEX merchant_applications_status_idx
    ON merchant_applications (status, created_at DESC);