-- Migration 102: Fixed-Price Billing Periods
-- Tracks monthly usage and billing status per agreement
-- Structure compatible with future subscription_billing_periods table

CREATE TABLE IF NOT EXISTS fixed_price_billing_periods (
    id SERIAL PRIMARY KEY,
    agreement_id INTEGER NOT NULL REFERENCES customer_fixed_price_agreements(id) ON DELETE CASCADE,
    
    -- Period definition (compatible with future subscription_billing_periods)
    period_start DATE NOT NULL,
    period_end DATE NOT NULL,
    period_type VARCHAR(20) DEFAULT 'calendar_month',
    
    -- Usage tracking
    included_hours DECIMAL(8,2) NOT NULL,
    used_hours DECIMAL(8,2) DEFAULT 0,
    overtime_hours DECIMAL(8,2) GENERATED ALWAYS AS (
        CASE WHEN used_hours > included_hours THEN used_hours - included_hours ELSE 0 END
    ) STORED,
    remaining_hours DECIMAL(8,2) GENERATED ALWAYS AS (
        CASE WHEN used_hours < included_hours THEN included_hours - used_hours ELSE 0 END
    ) STORED,
    
    -- Billing amounts (v2: integrate with subscription_line_items)
    base_amount DECIMAL(12,2) NOT NULL,
    overtime_amount DECIMAL(12,2) DEFAULT 0,
    overtime_approved BOOLEAN DEFAULT false,
    
    -- Billing status (compatible with subscription billing workflow)
    status VARCHAR(20) DEFAULT 'active' CHECK (status IN (
        'active',           -- Currently accumulating usage
        'pending_approval', -- Overtime needs approval
        'ready_to_bill',    -- Approved, ready for invoice generation
        'billed',           -- Invoice created
        'cancelled'         -- Period cancelled (e.g. early termination)
    )),
    
    -- Invoice tracking
    billed_at TIMESTAMP,
    economic_invoice_number VARCHAR(50),
    invoice_id INTEGER,
    
    -- Metadata
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    
    UNIQUE(agreement_id, period_start)
);

-- Indexes
CREATE INDEX IF NOT EXISTS idx_fpbp_agreement ON fixed_price_billing_periods(agreement_id);
CREATE INDEX IF NOT EXISTS idx_fpbp_period ON fixed_price_billing_periods(period_start, period_end);
CREATE INDEX IF NOT EXISTS idx_fpbp_status ON fixed_price_billing_periods(status);

-- Update timestamp trigger
CREATE TRIGGER trigger_fpbp_updated_at
    BEFORE UPDATE ON fixed_price_billing_periods
    FOR EACH ROW
    EXECUTE FUNCTION update_updated_at_column();

COMMENT ON TABLE fixed_price_billing_periods IS 
    'Billing periods for fixed-price agreements. Structure compatible with future unified subscription_billing_periods table.';

COMMENT ON COLUMN fixed_price_billing_periods.overtime_approved IS 
    'Overtime must be approved before billing. Periods with unapproved overtime → status=pending_approval';