<?php

class PaymentBillingManager {

    private PDO $pdo;
    private int $company_id;

    public function __construct(PDO $pdo, int $company_id) {
        $this->pdo = $pdo;
        $this->company_id = $company_id;
    }

    private function generateBillingNumber(): string
    {
        $prefix = 'PB-' . date('Ymd') . '-';
        $sth = $this->pdo->prepare(
            "SELECT billing_number FROM td_payment_billing
             WHERE company_id = :company_id
               AND billing_number LIKE :prefix
             ORDER BY billing_number DESC
             LIMIT 1"
        );
        $sth->execute([
            ':company_id' => $this->company_id,
            ':prefix'     => $prefix . '%',
        ]);
        $last = $sth->fetchColumn();
        $seq = $last ? ((int)substr($last, -4) + 1) : 1;
        return $prefix . str_pad($seq, 4, '0', STR_PAD_LEFT);
    }

    private function unavailableDocumentAmount(int $invoice_id): float
    {
        $sth = $this->pdo->prepare(
            "SELECT COALESCE(billed.billed_amount, 0) + COALESCE(direct.paid_amount, 0)
             FROM (
                SELECT :company_id AS company_id, :invoice_id AS invoice_id
             ) doc
             LEFT JOIN (
                SELECT ba.company_id, ba.invoice_id, SUM(ba.amount) AS billed_amount
                FROM td_payment_billing_item ba
                JOIN td_payment_billing b
                  ON b.company_id = ba.company_id
                 AND b.id = ba.billing_id
                WHERE ba.company_id = :company_id_billed
                  AND ba.invoice_id = :invoice_id_billed
                  AND b.status IN (1, 2, 3)
                GROUP BY ba.company_id, ba.invoice_id
             ) billed
               ON billed.company_id = doc.company_id
              AND billed.invoice_id = doc.invoice_id
             LEFT JOIN (
                SELECT ra.company_id, ra.invoice_id, SUM(ra.amount) AS paid_amount
                FROM td_payment_item ra
                JOIN td_payment r
                  ON r.company_id = ra.company_id
                 AND r.id = ra.payment_id
                WHERE ra.company_id = :company_id_direct
                  AND ra.invoice_id = :invoice_id_direct
                  AND r.status = 1
                  AND r.payment_billing_id = 0
                GROUP BY ra.company_id, ra.invoice_id
             ) direct
               ON direct.company_id = doc.company_id
              AND direct.invoice_id = doc.invoice_id"
        );
        $sth->execute([
            ':company_id'          => $this->company_id,
            ':invoice_id'          => $invoice_id,
            ':company_id_billed'   => $this->company_id,
            ':invoice_id_billed'   => $invoice_id,
            ':company_id_direct'   => $this->company_id,
            ':invoice_id_direct'   => $invoice_id,
        ]);
        return (float)$sth->fetchColumn();
    }

    public function getBillableDocuments(int $contact_id = 0): array
    {
        $where = [
            "i.company_id = :company_id",
            "i.doc_type IN ('purchase_invoice', 'supplier_credit_note')",
            "i.status = 1"
        ];
        $params = [':company_id' => $this->company_id];

        $where[] = 'i.contact_id = :contact_id';
        $params[':contact_id'] = $contact_id;

        $sth = $this->pdo->prepare(
            "SELECT i.*,
                    COALESCE(c.contact_name, '') AS contact_name,
                    po.po_number AS order_number,
                    COALESCE(payment.paid_amount, 0) AS paid_amount,
                    COALESCE(billed.billed_amount, 0) AS billed_amount
             FROM td_invoice i
             LEFT JOIN md_contact c
               ON c.company_id = i.company_id
              AND c.id = i.contact_id
             LEFT JOIN td_purchase_order po
               ON po.company_id = i.company_id
              AND po.id = i.source_id
              AND i.source = 'po'
             LEFT JOIN (
                SELECT ra.company_id, ra.invoice_id, SUM(ra.amount) AS paid_amount
                FROM td_payment_item ra
                JOIN td_payment r
                  ON r.company_id = ra.company_id
                 AND r.id = ra.payment_id
                WHERE r.status = 1
                  AND r.payment_billing_id = 0
                GROUP BY ra.company_id, ra.invoice_id
             ) payment
               ON payment.company_id = i.company_id
              AND payment.invoice_id = i.id
             LEFT JOIN (
                SELECT ba.company_id, ba.invoice_id, SUM(ba.amount) AS billed_amount
                FROM td_payment_billing_item ba
                JOIN td_payment_billing b
                  ON b.company_id = ba.company_id
                 AND b.id = ba.billing_id
                WHERE b.status IN (1, 2, 3)
                GROUP BY ba.company_id, ba.invoice_id
             ) billed
               ON billed.company_id = i.company_id
              AND billed.invoice_id = i.id
             WHERE " . implode(' AND ', $where) . "
             ORDER BY i.issued_date ASC, i.id ASC"
        );
        $sth->execute($params);

        $open = [];
        foreach ($sth->fetchAll(PDO::FETCH_ASSOC) as $row) {
            $total = abs((float)$row['grand_total']);
            $used = (float)$row['paid_amount'] + (float)$row['billed_amount'];
            $balance = max(0, $total - $used);
            if ($balance <= 0.0001) continue;
            $row['document_total'] = $total;
            $row['balance_amount'] = $balance;
            $open[] = $row;
        }

        return $open;
    }

    public function getBillingList(): array
    {
        $sth = $this->pdo->prepare(
            "SELECT b.*,
                    COALESCE(c.contact_name, '') AS contact_name,
                    COALESCE(SUM(CASE WHEN r.status = 1 THEN r.amount ELSE 0 END), 0) AS paid_amount
             FROM td_payment_billing b
             LEFT JOIN md_contact c
               ON c.company_id = b.company_id
              AND c.id = b.contact_id
             LEFT JOIN td_payment r
               ON r.company_id = b.company_id
              AND r.payment_billing_id = b.id
             WHERE b.company_id = :company_id
             GROUP BY b.id
             ORDER BY b.id DESC"
        );
        $sth->execute([':company_id' => $this->company_id]);
        $rows = $sth->fetchAll(PDO::FETCH_ASSOC);

        foreach ($rows as &$row) {
            $row['balance_amount'] = max(0, (float)$row['amount'] - (float)$row['paid_amount']);
        }
        return $rows;
    }

    public function getOpenBillingList(int $contact_id = 0): array
    {
        $rows = $this->getBillingList();
        return array_values(array_filter($rows, function($row) use ($contact_id) {
            if ((int)$row['status'] === 4) return false;
            if ((int)$row['contact_id'] !== $contact_id) return false;
            return (float)$row['balance_amount'] > 0.0001;
        }));
    }

    public function getBillingById(int $billing_id): array
    {
        $sth = $this->pdo->prepare(
            "SELECT b.*,
                    COALESCE(c.contact_name, '') AS contact_name,
                    COALESCE(SUM(CASE WHEN r.status = 1 THEN r.amount ELSE 0 END), 0) AS paid_amount
             FROM td_payment_billing b
             LEFT JOIN md_contact c
               ON c.company_id = b.company_id
              AND c.id = b.contact_id
             LEFT JOIN td_payment r
               ON r.company_id = b.company_id
              AND r.payment_billing_id = b.id
             WHERE b.company_id = :company_id
               AND b.id = :id
             GROUP BY b.id"
        );
        $sth->execute([':company_id' => $this->company_id, ':id' => $billing_id]);
        $billing = $sth->fetch(PDO::FETCH_ASSOC);
        if (!$billing) throw new Exception("Payment billing not found.");

        $sth = $this->pdo->prepare(
            "SELECT a.*,
                    i.invoice_number,
                    i.order_id,
                    i.department_id,
                    i.grand_total,
                    i.status AS invoice_status,
                    COALESCE(SUM(CASE WHEN r.status = 1 THEN ra.amount ELSE 0 END), 0) AS paid_line_amount,
                    po.po_number AS order_number
             FROM td_payment_billing_item a
             JOIN td_invoice i
               ON i.company_id = a.company_id
              AND i.id = a.invoice_id
             LEFT JOIN td_payment_item ra
               ON ra.company_id = a.company_id
              AND ra.invoice_id = a.invoice_id
             LEFT JOIN td_payment r
               ON r.company_id = ra.company_id
              AND r.id = ra.payment_id
              AND r.payment_billing_id = a.billing_id
             LEFT JOIN td_purchase_order po
               ON po.company_id = i.company_id
              AND po.id = i.source_id
              AND i.source = 'po'
             WHERE a.company_id = :company_id
               AND a.billing_id = :billing_id
             GROUP BY a.id
             ORDER BY a.id ASC"
        );
        $sth->execute([':company_id' => $this->company_id, ':billing_id' => $billing_id]);
        $allocations = $sth->fetchAll(PDO::FETCH_ASSOC);
        foreach ($allocations as &$line) {
            $line['balance_amount'] = max(0, (float)$line['amount'] - (float)$line['paid_line_amount']);
        }
        $billing['allocations'] = $allocations;
        $billing['balance_amount'] = max(0, (float)$billing['amount'] - (float)$billing['paid_amount']);

        return $billing;
    }

    public function refreshBillingStatus(int $billing_id): void
    {
        $billing = $this->getBillingById($billing_id);
        if ((int)$billing['status'] === 4) return;
        if ((float)$billing['balance_amount'] <= 0.0001) {
            $new_status = 2;
        } elseif ((float)$billing['paid_amount'] > 0.0001) {
            $new_status = 3;
        } else {
            $new_status = 1;
        }
        $this->pdo->prepare(
            "UPDATE td_payment_billing
             SET status = :status
             WHERE company_id = :company_id
               AND id = :id"
        )->execute([
            ':status'     => $new_status,
            ':company_id' => $this->company_id,
            ':id'         => $billing_id,
        ]);
    }

    public function createBilling(array $data, array $logging): int
    {
        $contact_id = (int)($data['contact_id'] ?? 0);
        $billing_date = $data['billing_date'] ?? date('Y-m-d');
        $notes = trim((string)($data['notes'] ?? ''));
        $allocations = $data['allocations'] ?? [];

        if (is_string($allocations)) {
            $allocations = json_decode($allocations, true) ?: [];
        }

        if ($contact_id <= 0) throw new Exception("Supplier is required.");
        if (!$allocations) throw new Exception("Payment billing requires at least one document.");

        $validated = [];
        $purchase_invoice_total = 0.0;
        $credit_total = 0.0;

        foreach ($allocations as $line) {
            $invoice_id = (int)($line['invoice_id'] ?? 0);
            $amount = (float)($line['amount'] ?? 0);
            if ($invoice_id <= 0 || $amount <= 0) continue;

            $sth = $this->pdo->prepare(
                "SELECT id, doc_type, invoice_number, contact_id, department_id, grand_total, status
                 FROM td_invoice
                 WHERE company_id = :company_id AND id = :id
                 FOR UPDATE"
            );
            $sth->execute([':company_id' => $this->company_id, ':id' => $invoice_id]);
            $doc = $sth->fetch(PDO::FETCH_ASSOC);

            if (!$doc) throw new Exception("Document not found.");
            if ((int)$doc['contact_id'] !== $contact_id) {
                throw new Exception("All billing documents must belong to the selected contact.");
            }
            if (!in_array($doc['doc_type'], ['purchase_invoice', 'supplier_credit_note'], true)) {
                throw new Exception("Payment billing can only include purchase invoices and supplier credit notes.");
            }
            if ((int)$doc['status'] !== 1) {
                throw new Exception($doc['invoice_number'] . " is not open for billing.");
            }

            $balance = abs((float)$doc['grand_total']) - $this->unavailableDocumentAmount($invoice_id);
            if ($amount - $balance > 0.0001) {
                throw new Exception($doc['invoice_number'] . " allocation exceeds remaining billable balance.");
            }

            if ($doc['doc_type'] === 'supplier_credit_note') $credit_total += $amount;
            else $purchase_invoice_total += $amount;

            $validated[] = [
                'invoice_id'     => $invoice_id,
                'doc_type'       => $doc['doc_type'],
                'department_id'  => (int)($doc['department_id'] ?? 0),
                'amount'         => round($amount, 4),
            ];
        }

        if (!$validated) throw new Exception("Payment billing requires at least one valid document.");
        $net_amount = round($purchase_invoice_total - $credit_total, 4);
        if ($net_amount <= 0.0001) {
            throw new Exception("Payment billing amount must be greater than zero.");
        }

        $log = [array_merge($logging, ['action' => 'create_payment_billing'])];
        $this->pdo->prepare(
            "INSERT INTO td_payment_billing
                (company_id, uuid, billing_number, contact_id, billing_date,
                 amount, status, notes, `log`, created_at)
             VALUES
                (:company_id, :uuid, :billing_number, :contact_id, :billing_date,
                 :amount, 1, :notes, :log, :created_at)"
        )->execute([
            ':company_id'     => $this->company_id,
            ':uuid'           => bin2hex(random_bytes(16)),
            ':billing_number' => $this->generateBillingNumber(),
            ':contact_id'     => $contact_id,
            ':billing_date'   => $billing_date,
            ':amount'         => $net_amount,
            ':notes'          => $notes,
            ':log'            => json_encode($log),
            ':created_at'     => date('Y-m-d H:i:s'),
        ]);

        $billing_id = (int)$this->pdo->lastInsertId();

        foreach ($validated as $line) {
            $this->pdo->prepare(
                "INSERT INTO td_payment_billing_item
                    (company_id, billing_id, invoice_id, doc_type, amount)
                 VALUES
                    (:company_id, :billing_id, :invoice_id, :doc_type, :amount)"
            )->execute([
                ':company_id' => $this->company_id,
                ':billing_id' => $billing_id,
                ':invoice_id' => $line['invoice_id'],
                ':doc_type'   => $line['doc_type'],
                ':amount'     => $line['amount'],
            ]);
        }

        return $billing_id;
    }

    public function voidBilling(int $billing_id, array $logging): void
    {
        $billing = $this->getBillingById($billing_id);
        if ((int)$billing['status'] === 4) throw new Exception("Payment billing is already void.");
        if ((float)$billing['paid_amount'] > 0.0001) {
            throw new Exception("Cannot void a payment billing with posted payments.");
        }

        $log = json_decode($billing['log'] ?: '[]', true);
        if (!is_array($log)) $log = [];
        $log[] = array_merge($logging, ['action' => 'void_payment_billing']);

        $this->pdo->prepare(
            "UPDATE td_payment_billing
             SET status = 4, `log` = :log
             WHERE company_id = :company_id
               AND id = :id"
        )->execute([
            ':log'        => json_encode($log),
            ':company_id' => $this->company_id,
            ':id'         => $billing_id,
        ]);
    }
}
?>