<?php

function check_obsidian_project($bytes) {
    $HEADERS_LENGTH = 51;
    $MIN_SECTION_SIZE = 2;

    if (strlen($bytes) <= $HEADERS_LENGTH) {
        return false;
    }

    $unpackString = "a4magic/nversion/A10type";
    $unpackString .= "/CmetadataFormat/NmetadataOffset/NmetadataLength";
    $unpackString .= "/CprojectFormat/NprojectOffset/NprojectLength";
    $unpackString .= "/CblobIndexFormat/NblobIndexOffset/NblobIndexLength";
    $unpackString .= "/NblobsOffset/NblobsLength";
    $data = unpack($unpackString, $bytes);

    // magic
    if ($data["magic"] != "WPRJ") {
        return false;
    }

    // metadata*
    if ($data["metadataFormat"] != 0 && $data["metadataFormat"] != 1) {
        return false;
    }
    if ($data["metadataOffset"] != $HEADERS_LENGTH) {
        return false;
    }
    if ($data["metadataLength"] < $MIN_SECTION_SIZE) {
        return false;
    }

    // project*
    if ($data["projectFormat"] != 0 && $data["projectFormat"] != 1) {
        return false;
    }
    if ($data["projectOffset"] != $data["metadataOffset"] + $data["metadataLength"]) {
        return false;
    }
    if ($data["projectLength"] < $MIN_SECTION_SIZE) {
        return false;
    }

    // blobIndex*
    if ($data["blobIndexFormat"] != 0 && $data["blobIndexFormat"] != 1) {
        return false;
    }
    if ($data["blobIndexOffset"] != $data["projectOffset"] + $data["projectLength"]) {
        return false;
    }
    if ($data["blobIndexLength"] < $MIN_SECTION_SIZE) {
        return false;
    }

    // blobs*
    if ($data["blobsOffset"] != $data["blobIndexOffset"] + $data["blobIndexLength"]) {
        return false;
    }

    // Check that the file size is coherent
    if (strlen($bytes) != $HEADERS_LENGTH + $data["metadataLength"] + $data["projectLength"] + $data["blobIndexLength"] + $data["blobsLength"]) {
        return false;
    }

    return true;
}

function check_obsidian_project_from_file($path) {
    $handle = fopen($path, "rb");
    $fsize = filesize($path);
    $bytes = fread($handle, $fsize);
    return check_obsidian_project($bytes);
}