const std = @import("std");

// ZIP file implementation
// See spec.txt.

const ZipFile = struct {
    allocator: std.mem.Allocator,
    is_zip_64: bool = false,
    end_of_central_directory_record: EndOfCentralDirectoryRecord,
    central_directory_headers: []CentralDirectoryHeader,
    fn from(allocator: std.mem.Allocator, file_or_stream: anytype) !ZipFile {
        // Find the EndOfCentralDirectoryRecord. It must be in the last 64k of the file
        const eocdr_search_width_max: usize = 64_000;
        const epos = try file_or_stream.getEndPos();
        const eocdr_search_width: usize = @min(epos, eocdr_search_width_max);
        const eocdr_seek_start: usize = epos - eocdr_search_width;
        try file_or_stream.seekTo(eocdr_seek_start);
        var reader = file_or_stream.reader();
        const needle = @byteSwap(EndOfCentralDirectoryRecord.SIG);
        var window: u32 = try reader.readIntLittle(u32);
        while (true) {
            if (window == needle) {
                try file_or_stream.seekBy(-4);
                break;
            }
            const nb = try reader.readByte();
            window <<= 8;
            window |= nb;
        } else {
            return error.EndOfCentralDirectoryRecordNotFound;
        }
        const eocdr = try EndOfCentralDirectoryRecord.read(allocator, file_or_stream);
        errdefer eocdr.deinit();
        if (eocdr.disk_number_this != 0 or eocdr.disk_number_central_dir_start != 0) return error.SpansNotSupported;
        if (eocdr.total_central_dir_entries != eocdr.total_central_dir_entries_on_this_disk) return error.SpansNotSupported;

        var central_directory_headers = try allocator.alloc(CentralDirectoryHeader, eocdr.total_central_dir_entries);
        errdefer allocator.free(central_directory_headers);
        try file_or_stream.seekTo(eocdr.central_dir_offset);
        for (0..eocdr.total_central_dir_entries) |i| {
            central_directory_headers[i] = try CentralDirectoryHeader.read(allocator, file_or_stream);
        }
        
        return ZipFile{
            .allocator = allocator,
            .end_of_central_directory_record = eocdr,
            .central_directory_headers = central_directory_headers,
        };
    }
    fn deinit(self: *ZipFile) void {
        self.end_of_central_directory_record.deinit();
        for (0..self.central_directory_headers.len) |i| {
            self.central_directory_headers[i].deinit();
        }
        self.allocator.free(self.central_directory_headers);
    }
    // [local file header 1]
    // [encryption header 1]
    // [file data 1]
    // [data descriptor 1]
    // .
    // .
    // .
    // [local file header n]
    // [encryption header n]
    // [file data n]
    // [data descriptor n]
    // [archive decryption header]
    // [archive extra data record]
    // [central directory header 1]
    // .
    // .
    // .
    // [central directory header n]
    // [zip64 end of central directory record]
    // [zip64 end of central directory locator]
    // [end of central directory record]
};

// const LocalFileHeader = struct {
//     const GPBF = packed struct(u16) {
//         encrypted: bool = false,
//     };
//     const SIG: [4]u8 = @bitCast(@as(u32, 0x04034b50));
//     sig: [4]u8 = SIG,
//     // version needed to extract       2 bytes
//     general_purpose_bit_flag: GPBF,
//     // compression method              2 bytes
//     // last mod file time              2 bytes
//     // last mod file date              2 bytes
//     // crc-32                          4 bytes
//     // compressed size                 4 bytes
//     // uncompressed size               4 bytes
//     // file name length                2 bytes
//     // extra field length              2 bytes
//     // file name (variable size)
//     // extra field (variable size)
// };

// const DataDescriptor = struct {
//     const SIG: [4]u8 = @bitCast(@as(u32, 0x08074b50));
//     sig: [4]u8 = SIG,
//     // crc-32                          4 bytes
//     // compressed size                 4 bytes
//     // uncompressed size               4 bytes
// };

// const ArchiveExtraDataRecord = struct {
//     const SIG: [4]u8 = @bitCast(@as(u32, 0x08064b50));
//     sig: [4]u8 = SIG,
//     // extra field length              4 bytes
//     // extra field data                (variable size)

// };

const CentralDirectoryHeader = struct {
    const SIG: u32 = @as(u32, 0x02014b50);
    allocator: std.mem.Allocator,
    version_made_by: u16,
    version_needed_to_extract: u16,
    general_purpose_bit_flag: u16,
    compression_method: u16,
    last_mod_file_time: u16,
    last_mod_file_date: u16,
    crc32: u32,
    compressed_size: u32,
    uncompressed_size: u32,
    file_name_length: u16,
    extra_field_length: u16,
    file_comment_length: u16,
    disk_number_start: u16,
    internal_file_attributes: u16,
    external_file_attributes: u32,
    relative_offset_of_local_header: u32,
    file_name: []const u8,
    extra_field: []const u8,
    file_comment: []const u8,

    fn read(allocator: std.mem.Allocator, stream_or_file: anytype) !CentralDirectoryHeader {
        var reader = stream_or_file.reader();
        const sig = try reader.readIntLittle(u32);
        if (sig != CentralDirectoryHeader.SIG) {
            std.log.err("invalid signature expected {x} got {x}", .{CentralDirectoryHeader.SIG, sig});
            return error.InvalidSignature;
        }
        const version_made_by = try reader.readIntLittle(u16);
        const version_needed_to_extract = try reader.readIntLittle(u16);
        const general_purpose_bit_flag = try reader.readIntLittle(u16);
        const compression_method = try reader.readIntLittle(u16);
        const last_mod_file_time = try reader.readIntLittle(u16);
        const last_mod_file_date = try reader.readIntLittle(u16);
        const crc32 = try reader.readIntLittle(u32);
        const compressed_size = try reader.readIntLittle(u32);
        const uncompressed_size = try reader.readIntLittle(u32);
        const file_name_length = try reader.readIntLittle(u16);
        const extra_field_length = try reader.readIntLittle(u16);
        const file_comment_length = try reader.readIntLittle(u16);
        const disk_number_start = try reader.readIntLittle(u16);
        const internal_file_attributes = try reader.readIntLittle(u16);
        const external_file_attributes = try reader.readIntLittle(u32);
        const relative_offset_of_local_header = try reader.readIntLittle(u32);
        const file_name = try allocator.alloc(u8, file_name_length);
        errdefer allocator.free(file_name);
        _ = try reader.readAll(file_name);
        const extra_field = try allocator.alloc(u8, extra_field_length);
        errdefer allocator.free(extra_field);
        _ = try reader.readAll(extra_field);

        const file_comment = try allocator.alloc(u8, file_comment_length);
        errdefer allocator.free(file_comment);
        _ = try reader.readAll(file_comment);
        return CentralDirectoryHeader{
            .allocator = allocator,
            .version_made_by = version_made_by,
            .version_needed_to_extract = version_needed_to_extract,
            .general_purpose_bit_flag = general_purpose_bit_flag,
            .compression_method = compression_method,
            .last_mod_file_time = last_mod_file_time,
            .last_mod_file_date = last_mod_file_date,
            .crc32 = crc32,
            .compressed_size = compressed_size,
            .uncompressed_size = uncompressed_size,
            .file_name_length = file_name_length,
            .extra_field_length = extra_field_length,
            .file_comment_length = file_comment_length,
            .disk_number_start = disk_number_start,
            .internal_file_attributes = internal_file_attributes,
            .external_file_attributes = external_file_attributes,
            .relative_offset_of_local_header = relative_offset_of_local_header,
            .file_name = file_name, 
            .extra_field = extra_field,
            .file_comment = file_comment,
        };
    }
    fn deinit(self: *CentralDirectoryHeader) void {
        self.allocator.free(self.file_name);
        self.allocator.free(self.extra_field);
        self.allocator.free(self.file_comment);
    }
};

// const DigitalSignature = struct {
//     const SIG: [4]u8 = @bitCast(@as(u32, 0x05054b50));
//     sig: [4]u8 = SIG,
//     // size of data                    2 bytes
//     // signature data (variable size)
// };

// const Zip64EndOfCentralDirectoryRecord = struct {
//     const SIG: [4]u8 = @bitCast(@as(u32, 0x06064b50));
//     sig: [4]u8 = SIG,
//     // size of zip64 end of central
//     // directory record                8 bytes
//     // version made by                 2 bytes
//     // version needed to extract       2 bytes
//     // number of this disk             4 bytes
//     // number of the disk with the
//     // start of the central directory  4 bytes
//     // total number of entries in the
//     // central directory on this disk  8 bytes
//     // total number of entries in the
//     // central directory               8 bytes
//     // size of the central directory   8 bytes
//     // offset of start of central
//     // directory with respect to
//     // the starting disk number        8 bytes
//     // zip64 extensible data sector    (variable size)
// };

// const Zip64EndOfCentralDirectoryLocator = struct {
//     const SIG: [4]u8 = @bitCast(@as(u32, 0x07064b50));
//     sig: [4]u8 = SIG,
//     // number of the disk with the
//     // start of the zip64 end of
//     // central directory               4 bytes
//     // relative offset of the zip64
//     // end of central directory record 8 bytes
//     // total number of disks           4 bytes
// };

const EndOfCentralDirectoryRecord = struct {
    const SIG: u32 = @as(u32, 0x06054b50);
    allocator: std.mem.Allocator,
    disk_number_this: u16,
    disk_number_central_dir_start: u16,
    total_central_dir_entries_on_this_disk: u16,
    total_central_dir_entries: u16,
    size_of_central_dir: u32,
    central_dir_offset: u32,
    comment_length: u16,
    comment: []const u8,

    fn read(allocator: std.mem.Allocator, file_or_stream: anytype) !EndOfCentralDirectoryRecord {
        var reader = file_or_stream.reader();
        const sig = try reader.readIntLittle(u32);
        if (sig != EndOfCentralDirectoryRecord.SIG) {
            std.log.err("invalid signature expected {x} got {x}", .{EndOfCentralDirectoryRecord.SIG, sig});
            return error.InvalidSignature;
        }
        const disk_number_this = try reader.readIntLittle(u16);
        const disk_number_central_dir_start = try reader.readIntLittle(u16);
        const total_central_dir_entries_on_this_disk = try reader.readIntLittle(u16);
        const total_central_dir_entries = try reader.readIntLittle(u16);
        const size_of_central_dir = try reader.readIntLittle(u32);        
        const central_dir_offset = try reader.readIntLittle(u32);
        const comment_length = try reader.readIntLittle(u16);
        var comment = try allocator.alloc(u8, comment_length);
        _ = try reader.readAll(comment);
        return EndOfCentralDirectoryRecord{
            .allocator = allocator,
            .disk_number_this = disk_number_this,
            .disk_number_central_dir_start = disk_number_central_dir_start,
            .total_central_dir_entries_on_this_disk = total_central_dir_entries_on_this_disk,
            .total_central_dir_entries = total_central_dir_entries,
            .size_of_central_dir = size_of_central_dir,
            .central_dir_offset = central_dir_offset,
            .comment_length = comment_length,
            .comment = comment,
        };
    }

    fn deinit(self: *EndOfCentralDirectoryRecord) void {
        self.allocator.free(self.comment);
    }
};

test "foo" {
    const test_zip = @embedFile("hello.zip");
    var fbs = std.io.fixedBufferStream(test_zip);
    var zf = try ZipFile.from(std.testing.allocator, &fbs);
    defer zf.deinit();
    try std.testing.expectEqual(zf.central_directory_headers.len, 2);
    try std.testing.expectEqualStrings(zf.central_directory_headers[0].file_name, "hello.txt");
    try std.testing.expectEqualStrings(zf.central_directory_headers[1].file_name, "foo.txt");
}