#!/usr/bin/env php
<?php

/**
 * Dalanga Transparency Chain Verification Tool
 *
 * A standalone, zero-dependency PHP script that verifies the integrity of a
 * downloaded Dalanga system chain export file.
 *
 * Requirements: PHP 8.0+ with JSON and hash extensions (standard in all PHP installs).
 * No Composer, no autoloader, no framework dependencies.
 *
 * Usage:
 *   php verify-chain.php <path-to-export.json>
 *
 * Examples:
 *   php verify-chain.php system-chain-export.json
 *   php verify-chain.php /tmp/chain-export.json
 *
 * What it verifies:
 *   1. Consecutive sequence numbers starting from 0
 *   2. Hash linking: each block's previous_hash matches the preceding block's hash
 *   3. Hash recomputation: re-hashes each block's hash_input and compares to stored hash
 *   4. Genesis block validation: sequence 0 must have previous_hash = null
 *   5. Draw fairness: for draw.revealed events, re-derives the winner using the
 *      algorithm_version from event_data and confirms the recorded winner matches
 *
 * Exit codes:
 *   0 = Chain is valid (all checks passed)
 *   1 = Chain is invalid (one or more checks failed)
 *   2 = Usage error (missing file, invalid JSON, etc.)
 */

// ANSI color codes
define('GREEN', "\033[32m");
define('RED', "\033[31m");
define('RESET', "\033[0m");
define('BOLD', "\033[1m");

function success(string $message): void
{
    echo GREEN.'✓'.RESET.' '.$message.PHP_EOL;
}

function failure(string $message): void
{
    echo RED.'✗'.RESET.' '.$message.PHP_EOL;
}

function canonical_json_encode(mixed $data): string
{
    return json_encode(sort_keys_recursive($data), JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
}

function sort_keys_recursive(mixed $data): mixed
{
    if (! is_array($data)) {
        return $data;
    }

    if (array_is_list($data)) {
        return array_map('sort_keys_recursive', $data);
    }

    ksort($data);

    return array_map('sort_keys_recursive', $data);
}

// ─── Input Validation ────────────────────────────────────────────────

if ($argc < 2) {
    echo 'Dalanga Transparency Chain Verification Tool'.PHP_EOL;
    echo PHP_EOL;
    echo 'Usage: php '.basename($argv[0]).' <path-to-export.json>'.PHP_EOL;
    echo PHP_EOL;
    echo 'Verifies the cryptographic integrity of a chain export file.'.PHP_EOL;
    echo 'For draw events, re-derives the winner to confirm fairness.'.PHP_EOL;
    exit(2);
}

$path = $argv[1];

if (! file_exists($path)) {
    failure("File not found: {$path}");
    exit(2);
}

$content = file_get_contents($path);
$data = json_decode($content, true);

if ($data === null) {
    failure('Invalid JSON: '.json_last_error_msg());
    exit(2);
}

if (! isset($data['blocks']) || ! is_array($data['blocks'])) {
    failure('Invalid export format: missing "blocks" array');
    exit(2);
}

// ─── Chain Verification ──────────────────────────────────────────────

$blocks = $data['blocks'];
$blockCount = count($blocks);
$errors = 0;

echo BOLD.'Dalanga Transparency Chain Verifier'.RESET.PHP_EOL;

if (isset($data['chain'])) {
    echo 'Chain: '.$data['chain'].PHP_EOL;
}

if (isset($data['exported_at'])) {
    echo 'Exported: '.$data['exported_at'].PHP_EOL;
}

echo 'Blocks: '.$blockCount.PHP_EOL;
echo PHP_EOL;

if ($blockCount === 0) {
    success('Chain is empty (0 blocks)');
    exit(0);
}

// Chain integrity checks
for ($i = 0; $i < $blockCount; $i++) {
    $block = $blocks[$i];

    // Check consecutive sequences
    if ($block['sequence'] !== $i) {
        failure("Block {$i}: expected sequence {$i}, got {$block['sequence']}");
        $errors++;

        continue;
    }

    // Genesis block validation
    if ($i === 0 && $block['previous_hash'] !== null) {
        failure('Block 0: genesis block must have previous_hash = null');
        $errors++;
    }

    // Hash linking
    if ($i > 0 && $block['previous_hash'] !== $blocks[$i - 1]['hash']) {
        failure("Block {$i}: previous_hash does not match preceding block's hash");
        $errors++;
    }

    // Hash recomputation
    $recomputedHash = hash('sha256', $block['hash_input']);

    if ($block['hash'] !== $recomputedHash) {
        failure("Block {$i}: hash does not match recomputed hash from hash_input");
        $errors++;
    } else {
        $eventType = $block['event_type'] ?? 'unknown';
        success("Block {$i}: hash valid ({$eventType})");
    }
}

// ─── Payload Hash Verification ──────────────────────────────────────

$hasPayloadHashes = false;

foreach ($blocks as $block) {
    if (isset($block['payload_hash'])) {
        $hasPayloadHashes = true;

        break;
    }
}

if ($hasPayloadHashes) {
    echo PHP_EOL;
    echo BOLD.'Payload Hash Verification'.RESET.PHP_EOL;
    $payloadChecked = 0;
    $payloadSkipped = 0;

    foreach ($blocks as $block) {
        if (! isset($block['payload_hash'])) {
            continue;
        }

        if (! isset($block['payload'])) {
            $payloadSkipped++;

            continue;
        }

        $payloadChecked++;
        $recomputedPayloadHash = hash('sha256', canonical_json_encode($block['payload']));

        if ($block['payload_hash'] !== $recomputedPayloadHash) {
            failure("Block {$block['sequence']}: payload_hash does not match recomputed hash from payload");
            $errors++;
        } else {
            success("Block {$block['sequence']}: payload hash valid ({$block['event_type']})");
        }
    }

    if ($payloadSkipped > 0) {
        echo "(Skipped {$payloadSkipped} block(s) without payload data — blocks-only export)".PHP_EOL;
    }

    echo "Payload hashes checked: {$payloadChecked}, skipped: {$payloadSkipped}".PHP_EOL;
}

// ─── Anchor Event Verification ───────────────────────────────────────

$anchorConfiguredCount = 0;
$anchoredBlocks = [];

foreach ($blocks as $block) {
    $eventType = $block['event_type'] ?? null;

    if ($eventType === 'chain.anchor_configured') {
        $anchorConfiguredCount++;
        $eventData = $block['event_data'] ?? [];

        if (! isset($eventData['anchor_service'])) {
            failure("Block {$block['sequence']}: chain.anchor_configured missing anchor_service");
            $errors++;
        } else {
            success("Block {$block['sequence']}: anchor configured ({$eventData['anchor_service']})");
        }

        if ($anchorConfiguredCount > 1) {
            failure("Block {$block['sequence']}: duplicate chain.anchor_configured (expected at most 1)");
            $errors++;
        }
    }

    if ($eventType === 'chain.anchored') {
        $eventData = $block['event_data'] ?? [];

        if (! isset($eventData['anchor_service'])) {
            failure("Block {$block['sequence']}: chain.anchored missing anchor_service");
            $errors++;
        }

        if (! isset($eventData['anchor_reference'])) {
            failure("Block {$block['sequence']}: chain.anchored missing anchor_reference");
            $errors++;
        }

        if (! isset($eventData['chain_state_hash'])) {
            failure("Block {$block['sequence']}: chain.anchored missing chain_state_hash");
            $errors++;
        }

        if (! isset($eventData['block_count'])) {
            failure("Block {$block['sequence']}: chain.anchored missing block_count");
            $errors++;
        }

        if (! isset($eventData['block_sequence'])) {
            failure("Block {$block['sequence']}: chain.anchored missing block_sequence");
            $errors++;
        } else {
            // anchor's block_sequence must reference a block that exists before this anchor block
            if ($eventData['block_sequence'] >= $block['sequence']) {
                failure("Block {$block['sequence']}: chain.anchored references block_sequence {$eventData['block_sequence']} which is not before this block");
                $errors++;
            } else {
                success("Block {$block['sequence']}: anchor record valid ({$eventData['anchor_service']} @ seq {$eventData['block_sequence']})");
            }
        }

        $anchoredBlocks[] = $block;
    }
}

if ($anchoredBlocks !== []) {
    echo PHP_EOL;
    echo BOLD.'Anchor History'.RESET.PHP_EOL;
    echo 'Anchor configuration events: '.$anchorConfiguredCount.PHP_EOL;
    echo 'Anchor records on-chain: '.count($anchoredBlocks).PHP_EOL;

    foreach ($anchoredBlocks as $ab) {
        $ed = $ab['event_data'] ?? [];
        $service = $ed['anchor_service'] ?? '?';
        $ref = $ed['anchor_reference'] ?? '';
        $seq = $ed['block_sequence'] ?? '?';
        echo "  [{$service}] seq {$seq} → {$ref}".PHP_EOL;
    }
}

// ─── Draw Event Verification ─────────────────────────────────────────

$committedBlocks = [];

foreach ($blocks as $block) {
    if (($block['event_type'] ?? null) === 'draw.committed') {
        $committedBlocks[] = $block;
    }
}

foreach ($blocks as $block) {
    if (($block['event_type'] ?? null) !== 'draw.revealed') {
        continue;
    }

    $eventData = $block['event_data'] ?? [];
    $algorithmVersion = $eventData['algorithm_version'] ?? null;

    if ($algorithmVersion === null) {
        failure("Block {$block['sequence']}: draw.revealed missing algorithm_version");
        $errors++;

        continue;
    }

    if ($algorithmVersion !== 'sha256-modulo-v1') {
        failure("Block {$block['sequence']}: unknown algorithm version '{$algorithmVersion}'");
        $errors++;

        continue;
    }

    // Find matching draw.committed block
    $committed = null;

    foreach ($committedBlocks as $cb) {
        $cbData = $cb['event_data'] ?? [];
        if (isset($cbData['eligible_tickets_snapshot'])) {
            $committed = $cb;
        }
    }

    if ($committed === null) {
        failure("Block {$block['sequence']}: draw.revealed but no matching draw.committed found");
        $errors++;

        continue;
    }

    $committedData = $committed['event_data'];
    $seed = $eventData['seed'];
    $eligibleTickets = $committedData['eligible_tickets_snapshot'];
    $totalEligible = count($eligibleTickets);

    // Re-derive winner using sha256-modulo-v1
    $winnerIndex = hexdec(substr(hash('sha256', $seed), 0, 12)) % $totalEligible;
    $winnerTicketNumber = $eligibleTickets[$winnerIndex];

    if ($winnerIndex !== $eventData['winner_index']) {
        failure("Block {$block['sequence']}: draw winner_index mismatch (expected {$winnerIndex}, got {$eventData['winner_index']})");
        $errors++;
    } elseif ($winnerTicketNumber !== $eventData['winner_ticket_number']) {
        failure("Block {$block['sequence']}: draw winner_ticket_number mismatch (expected {$winnerTicketNumber}, got {$eventData['winner_ticket_number']})");
        $errors++;
    } else {
        success("Block {$block['sequence']}: draw winner independently verified (sha256-modulo-v1)");
    }

    // Verify commitment hash
    $commitmentHash = $committedData['commitment_hash'] ?? null;

    if ($commitmentHash !== null) {
        $recomputedCommitment = hash('sha256', $seed.json_encode($eligibleTickets));

        if ($commitmentHash !== $recomputedCommitment) {
            failure("Block {$committed['sequence']}: commitment hash mismatch");
            $errors++;
        } else {
            success("Block {$committed['sequence']}: commitment hash verified");
        }
    }
}

// ─── Summary ─────────────────────────────────────────────────────────

echo PHP_EOL;

if ($errors === 0) {
    echo GREEN."Chain valid: {$blockCount} blocks verified, 0 errors".RESET.PHP_EOL;
    exit(0);
}

echo RED."Chain INVALID: {$blockCount} blocks verified, {$errors} error(s)".RESET.PHP_EOL;
exit(1);