//! The .ZIP File Format Specification is found here:
//!    https://pkwaredownloads.blob.core.windows.net/pem/APPNOTE.txt
//!
//! Note that this file uses the abbreviation "cd" for "central directory"

const builtin = @import("builtin");
const std = @import("std");
const File = std.fs.File;
const is_le = builtin.target.cpu.arch.endian() == .little;
const Writer = std.Io.Writer;
const Reader = std.Io.Reader;
const flate = std.compress.flate;

pub const CompressionMethod = enum(u16) {
    store = 0,
    deflate = 8,
    _,
};

pub const central_file_header_sig = [4]u8{ 'P', 'K', 1, 2 };
pub const local_file_header_sig = [4]u8{ 'P', 'K', 3, 4 };
pub const end_record_sig = [4]u8{ 'P', 'K', 5, 6 };
pub const end_record64_sig = [4]u8{ 'P', 'K', 6, 6 };
pub const end_locator64_sig = [4]u8{ 'P', 'K', 6, 7 };
pub const ExtraHeader = enum(u16) {
    zip64_info = 0x1,
    _,
};

const GeneralPurposeFlags = packed struct(u16) {
    encrypted: bool,
    _: u15,
};

pub const LocalFileHeader = extern struct {
    signature: [4]u8 align(1),
    version_needed_to_extract: u16 align(1),
    flags: GeneralPurposeFlags align(1),
    compression_method: CompressionMethod align(1),
    last_modification_time: u16 align(1),
    last_modification_date: u16 align(1),
    crc32: u32 align(1),
    compressed_size: u32 align(1),
    uncompressed_size: u32 align(1),
    filename_len: u16 align(1),
    extra_len: u16 align(1),
};

pub const CentralDirectoryFileHeader = extern struct {
    signature: [4]u8 align(1),
    version_made_by: u16 align(1),
    version_needed_to_extract: u16 align(1),
    flags: GeneralPurposeFlags align(1),
    compression_method: CompressionMethod align(1),
    last_modification_time: u16 align(1),
    last_modification_date: u16 align(1),
    crc32: u32 align(1),
    compressed_size: u32 align(1),
    uncompressed_size: u32 align(1),
    filename_len: u16 align(1),
    extra_len: u16 align(1),
    comment_len: u16 align(1),
    disk_number: u16 align(1),
    internal_file_attributes: u16 align(1),
    external_file_attributes: u32 align(1),
    local_file_header_offset: u32 align(1),
};

pub const EndRecord64 = extern struct {
    signature: [4]u8 align(1),
    end_record_size: u64 align(1),
    version_made_by: u16 align(1),
    version_needed_to_extract: u16 align(1),
    disk_number: u32 align(1),
    central_directory_disk_number: u32 align(1),
    record_count_disk: u64 align(1),
    record_count_total: u64 align(1),
    central_directory_size: u64 align(1),
    central_directory_offset: u64 align(1),
};

pub const EndLocator64 = extern struct {
    signature: [4]u8 align(1),
    zip64_disk_count: u32 align(1),
    record_file_offset: u64 align(1),
    total_disk_count: u32 align(1),
};

pub const EndRecord = extern struct {
    signature: [4]u8 align(1),
    disk_number: u16 align(1),
    central_directory_disk_number: u16 align(1),
    record_count_disk: u16 align(1),
    record_count_total: u16 align(1),
    central_directory_size: u32 align(1),
    central_directory_offset: u32 align(1),
    comment_len: u16 align(1),

    pub fn need_zip64(self: EndRecord) bool {
        return isMaxInt(self.record_count_disk) or
            isMaxInt(self.record_count_total) or
            isMaxInt(self.central_directory_size) or
            isMaxInt(self.central_directory_offset);
    }

    pub const FindBufferError = error{ ZipNoEndRecord, ZipTruncated };

    /// TODO audit this logic
    pub fn findBuffer(buffer: []const u8) FindBufferError!EndRecord {
        const pos = std.mem.lastIndexOf(u8, buffer, &end_record_sig) orelse return error.ZipNoEndRecord;
        if (pos + @sizeOf(EndRecord) > buffer.len) return error.EndOfStream;
        const record_ptr: *EndRecord = @ptrCast(buffer[pos..][0..@sizeOf(EndRecord)]);
        var record = record_ptr.*;
        if (!is_le) std.mem.byteSwapAllFields(EndRecord, &record);
        return record;
    }

    pub const FindFileError = File.GetEndPosError || File.SeekError || File.ReadError || error{
        ZipNoEndRecord,
        EndOfStream,
        ReadFailed,
    };

    pub fn findFile(fr: *File.Reader) FindFileError!EndRecord {
        const end_pos = try fr.getSize();

        var buf: [@sizeOf(EndRecord) + std.math.maxInt(u16)]u8 = undefined;
        const record_len_max = @min(end_pos, buf.len);
        var loaded_len: u32 = 0;
        var comment_len: u16 = 0;
        while (true) {
            const record_len: u32 = @as(u32, comment_len) + @sizeOf(EndRecord);
            if (record_len > record_len_max)
                return error.ZipNoEndRecord;

            if (record_len > loaded_len) {
                const new_loaded_len = @min(loaded_len + 300, record_len_max);
                const read_len = new_loaded_len - loaded_len;

                try fr.seekTo(end_pos - @as(u64, new_loaded_len));
                const read_buf: []u8 = buf[buf.len - new_loaded_len ..][0..read_len];
                fr.interface.readSliceAll(read_buf) catch |err| switch (err) {
                    error.ReadFailed => return fr.err.?,
                    error.EndOfStream => return error.EndOfStream,
                };
                loaded_len = new_loaded_len;
            }

            const record_bytes = buf[buf.len - record_len ..][0..@sizeOf(EndRecord)];
            if (std.mem.eql(u8, record_bytes[0..4], &end_record_sig) and
                std.mem.readInt(u16, record_bytes[20..22], .little) == comment_len)
            {
                const record: *align(1) EndRecord = @ptrCast(record_bytes.ptr);
                if (!is_le) std.mem.byteSwapAllFields(EndRecord, record);
                return record.*;
            }

            if (comment_len == std.math.maxInt(u16))
                return error.ZipNoEndRecord;
            comment_len += 1;
        }
    }
};

pub const Decompress = struct {
    interface: Reader,
    state: union {
        inflate: flate.Decompress,
        store: *Reader,
    },

    pub fn init(reader: *Reader, method: CompressionMethod, buffer: []u8) Reader {
        return switch (method) {
            .store => .{
                .state = .{ .store = reader },
                .interface = .{
                    .context = undefined,
                    .vtable = &.{ .stream = streamStore },
                    .buffer = buffer,
                    .end = 0,
                    .seek = 0,
                },
            },
            .deflate => .{
                .state = .{ .inflate = .init(reader, .raw) },
                .interface = .{
                    .context = undefined,
                    .vtable = &.{ .stream = streamDeflate },
                    .buffer = buffer,
                    .end = 0,
                    .seek = 0,
                },
            },
            else => unreachable,
        };
    }

    fn streamStore(r: *Reader, w: *Writer, limit: std.io.Limit) Reader.StreamError!usize {
        const d: *Decompress = @fieldParentPtr("interface", r);
        return d.store.read(w, limit);
    }

    fn streamDeflate(r: *Reader, w: *Writer, limit: std.io.Limit) Reader.StreamError!usize {
        const d: *Decompress = @fieldParentPtr("interface", r);
        return flate.Decompress.read(&d.inflate, w, limit);
    }
};

fn isBadFilename(filename: []const u8) bool {
    if (filename.len == 0 or filename[0] == '/')
        return true;

    var it = std.mem.splitScalar(u8, filename, '/');
    while (it.next()) |part| {
        if (std.mem.eql(u8, part, ".."))
            return true;
    }

    return false;
}

fn isMaxInt(uint: anytype) bool {
    return uint == std.math.maxInt(@TypeOf(uint));
}

const FileExtents = struct {
    uncompressed_size: u64,
    compressed_size: u64,
    local_file_header_offset: u64,
};

fn readZip64FileExtents(comptime T: type, header: T, extents: *FileExtents, data: []u8) !void {
    var data_offset: usize = 0;
    if (isMaxInt(header.uncompressed_size)) {
        if (data_offset + 8 > data.len)
            return error.ZipBadCd64Size;
        extents.uncompressed_size = std.mem.readInt(u64, data[data_offset..][0..8], .little);
        data_offset += 8;
    }
    if (isMaxInt(header.compressed_size)) {
        if (data_offset + 8 > data.len)
            return error.ZipBadCd64Size;
        extents.compressed_size = std.mem.readInt(u64, data[data_offset..][0..8], .little);
        data_offset += 8;
    }

    switch (T) {
        CentralDirectoryFileHeader => {
            if (isMaxInt(header.local_file_header_offset)) {
                if (data_offset + 8 > data.len)
                    return error.ZipBadCd64Size;
                extents.local_file_header_offset = std.mem.readInt(u64, data[data_offset..][0..8], .little);
                data_offset += 8;
            }
            if (isMaxInt(header.disk_number)) {
                if (data_offset + 4 > data.len)
                    return error.ZipInvalid;
                const disk_number = std.mem.readInt(u32, data[data_offset..][0..4], .little);
                if (disk_number != 0)
                    return error.ZipMultiDiskUnsupported;
                data_offset += 4;
            }
            if (data_offset > data.len)
                return error.ZipBadCd64Size;
        },
        else => {},
    }
}

pub const Iterator = struct {
    input: *File.Reader,

    cd_record_count: u64,
    cd_zip_offset: u64,
    cd_size: u64,

    cd_record_index: u64 = 0,
    cd_record_offset: u64 = 0,

    pub fn init(input: *File.Reader) !Iterator {
        const end_record = try EndRecord.findFile(input);

        if (!isMaxInt(end_record.record_count_disk) and end_record.record_count_disk > end_record.record_count_total)
            return error.ZipDiskRecordCountTooLarge;

        if (end_record.disk_number != 0 or end_record.central_directory_disk_number != 0)
            return error.ZipMultiDiskUnsupported;

        {
            const counts_valid = !isMaxInt(end_record.record_count_disk) and !isMaxInt(end_record.record_count_total);
            if (counts_valid and end_record.record_count_disk != end_record.record_count_total)
                return error.ZipMultiDiskUnsupported;
        }

        var result: Iterator = .{
            .input = input,
            .cd_record_count = end_record.record_count_total,
            .cd_zip_offset = end_record.central_directory_offset,
            .cd_size = end_record.central_directory_size,
        };
        if (!end_record.need_zip64()) return result;

        const locator_end_offset: u64 = @as(u64, end_record.comment_len) + @sizeOf(EndRecord) + @sizeOf(EndLocator64);
        const stream_len = try input.getSize();

        if (locator_end_offset > stream_len)
            return error.ZipTruncated;
        try input.seekTo(stream_len - locator_end_offset);
        const locator = input.interface.takeStruct(EndLocator64, .little) catch |err| switch (err) {
            error.ReadFailed => return input.err.?,
            error.EndOfStream => return error.EndOfStream,
        };
        if (!std.mem.eql(u8, &locator.signature, &end_locator64_sig))
            return error.ZipBadLocatorSig;
        if (locator.zip64_disk_count != 0)
            return error.ZipUnsupportedZip64DiskCount;
        if (locator.total_disk_count != 1)
            return error.ZipMultiDiskUnsupported;

        try input.seekTo(locator.record_file_offset);

        const record64 = input.interface.takeStruct(EndRecord64, .little) catch |err| switch (err) {
            error.ReadFailed => return input.err.?,
            error.EndOfStream => return error.EndOfStream,
        };

        if (!std.mem.eql(u8, &record64.signature, &end_record64_sig))
            return error.ZipBadEndRecord64Sig;

        if (record64.end_record_size < @sizeOf(EndRecord64) - 12)
            return error.ZipEndRecord64SizeTooSmall;
        if (record64.end_record_size > @sizeOf(EndRecord64) - 12)
            return error.ZipEndRecord64UnhandledExtraData;

        if (record64.version_needed_to_extract > 45)
            return error.ZipUnsupportedVersion;

        {
            const is_multidisk = record64.disk_number != 0 or
                record64.central_directory_disk_number != 0 or
                record64.record_count_disk != record64.record_count_total;
            if (is_multidisk)
                return error.ZipMultiDiskUnsupported;
        }

        if (isMaxInt(end_record.record_count_total)) {
            result.cd_record_count = record64.record_count_total;
        } else if (end_record.record_count_total != record64.record_count_total)
            return error.Zip64RecordCountTotalMismatch;

        if (isMaxInt(end_record.central_directory_offset)) {
            result.cd_zip_offset = record64.central_directory_offset;
        } else if (end_record.central_directory_offset != record64.central_directory_offset)
            return error.Zip64CentralDirectoryOffsetMismatch;

        if (isMaxInt(end_record.central_directory_size)) {
            result.cd_size = record64.central_directory_size;
        } else if (end_record.central_directory_size != record64.central_directory_size)
            return error.Zip64CentralDirectorySizeMismatch;

        return result;
    }

    pub fn next(self: *Iterator) !?Entry {
        if (self.cd_record_index == self.cd_record_count) {
            if (self.cd_record_offset != self.cd_size)
                return if (self.cd_size > self.cd_record_offset)
                    error.ZipCdOversized
                else
                    error.ZipCdUndersized;

            return null;
        }

        const header_zip_offset = self.cd_zip_offset + self.cd_record_offset;
        const input = self.input;
        try input.seekTo(header_zip_offset);
        const header = input.interface.takeStruct(CentralDirectoryFileHeader, .little) catch |err| switch (err) {
            error.ReadFailed => return input.err.?,
            error.EndOfStream => return error.EndOfStream,
        };
        if (!std.mem.eql(u8, &header.signature, &central_file_header_sig))
            return error.ZipBadCdOffset;

        self.cd_record_index += 1;
        self.cd_record_offset += @sizeOf(CentralDirectoryFileHeader) + header.filename_len + header.extra_len + header.comment_len;

        // Note: checking the version_needed_to_extract doesn't seem to be helpful, i.e. the zip file
        // at https://github.com/ninja-build/ninja/releases/download/v1.12.0/ninja-linux.zip
        // has an undocumented version 788 but extracts just fine.

        if (header.flags.encrypted)
            return error.ZipEncryptionUnsupported;
        // TODO: check/verify more flags
        if (header.disk_number != 0)
            return error.ZipMultiDiskUnsupported;

        var extents: FileExtents = .{
            .uncompressed_size = header.uncompressed_size,
            .compressed_size = header.compressed_size,
            .local_file_header_offset = header.local_file_header_offset,
        };

        if (header.extra_len > 0) {
            var extra_buf: [std.math.maxInt(u16)]u8 = undefined;
            const extra = extra_buf[0..header.extra_len];

            try input.seekTo(header_zip_offset + @sizeOf(CentralDirectoryFileHeader) + header.filename_len);
            input.interface.readSliceAll(extra) catch |err| switch (err) {
                error.ReadFailed => return input.err.?,
                error.EndOfStream => return error.EndOfStream,
            };

            var extra_offset: usize = 0;
            while (extra_offset + 4 <= extra.len) {
                const header_id = std.mem.readInt(u16, extra[extra_offset..][0..2], .little);
                const data_size = std.mem.readInt(u16, extra[extra_offset..][2..4], .little);
                const end = extra_offset + 4 + data_size;
                if (end > extra.len)
                    return error.ZipBadExtraFieldSize;
                const data = extra[extra_offset + 4 .. end];
                switch (@as(ExtraHeader, @enumFromInt(header_id))) {
                    .zip64_info => try readZip64FileExtents(CentralDirectoryFileHeader, header, &extents, data),
                    else => {}, // ignore
                }
                extra_offset = end;
            }
        }

        return .{
            .version_needed_to_extract = header.version_needed_to_extract,
            .flags = header.flags,
            .compression_method = header.compression_method,
            .last_modification_time = header.last_modification_time,
            .last_modification_date = header.last_modification_date,
            .header_zip_offset = header_zip_offset,
            .crc32 = header.crc32,
            .filename_len = header.filename_len,
            .compressed_size = extents.compressed_size,
            .uncompressed_size = extents.uncompressed_size,
            .file_offset = extents.local_file_header_offset,
        };
    }

    pub const Entry = struct {
        version_needed_to_extract: u16,
        flags: GeneralPurposeFlags,
        compression_method: CompressionMethod,
        last_modification_time: u16,
        last_modification_date: u16,
        header_zip_offset: u64,
        crc32: u32,
        filename_len: u32,
        compressed_size: u64,
        uncompressed_size: u64,
        file_offset: u64,

        pub fn extract(
            self: Entry,
            stream: *File.Reader,
            options: ExtractOptions,
            filename_buf: []u8,
            dest: std.fs.Dir,
        ) !void {
            if (filename_buf.len < self.filename_len)
                return error.ZipInsufficientBuffer;
            switch (self.compression_method) {
                .store, .deflate => {},
                else => return error.UnsupportedCompressionMethod,
            }
            const filename = filename_buf[0..self.filename_len];
            {
                try stream.seekTo(self.header_zip_offset + @sizeOf(CentralDirectoryFileHeader));
                try stream.interface.readSliceAll(filename);
            }

            const local_data_header_offset: u64 = local_data_header_offset: {
                const local_header = blk: {
                    try stream.seekTo(self.file_offset);
                    break :blk try stream.interface.takeStruct(LocalFileHeader, .little);
                };
                if (!std.mem.eql(u8, &local_header.signature, &local_file_header_sig))
                    return error.ZipBadFileOffset;
                if (local_header.version_needed_to_extract != self.version_needed_to_extract)
                    return error.ZipMismatchVersionNeeded;
                if (local_header.last_modification_time != self.last_modification_time)
                    return error.ZipMismatchModTime;
                if (local_header.last_modification_date != self.last_modification_date)
                    return error.ZipMismatchModDate;

                if (@as(u16, @bitCast(local_header.flags)) != @as(u16, @bitCast(self.flags)))
                    return error.ZipMismatchFlags;
                if (local_header.crc32 != 0 and local_header.crc32 != self.crc32)
                    return error.ZipMismatchCrc32;
                var extents: FileExtents = .{
                    .uncompressed_size = local_header.uncompressed_size,
                    .compressed_size = local_header.compressed_size,
                    .local_file_header_offset = 0,
                };
                if (local_header.extra_len > 0) {
                    var extra_buf: [std.math.maxInt(u16)]u8 = undefined;
                    const extra = extra_buf[0..local_header.extra_len];

                    {
                        try stream.seekTo(self.file_offset + @sizeOf(LocalFileHeader) + local_header.filename_len);
                        try stream.interface.readSliceAll(extra);
                    }

                    var extra_offset: usize = 0;
                    while (extra_offset + 4 <= local_header.extra_len) {
                        const header_id = std.mem.readInt(u16, extra[extra_offset..][0..2], .little);
                        const data_size = std.mem.readInt(u16, extra[extra_offset..][2..4], .little);
                        const end = extra_offset + 4 + data_size;
                        if (end > local_header.extra_len)
                            return error.ZipBadExtraFieldSize;
                        const data = extra[extra_offset + 4 .. end];
                        switch (@as(ExtraHeader, @enumFromInt(header_id))) {
                            .zip64_info => try readZip64FileExtents(LocalFileHeader, local_header, &extents, data),
                            else => {}, // ignore
                        }
                        extra_offset = end;
                    }
                }

                if (extents.compressed_size != 0 and
                    extents.compressed_size != self.compressed_size)
                    return error.ZipMismatchCompLen;
                if (extents.uncompressed_size != 0 and
                    extents.uncompressed_size != self.uncompressed_size)
                    return error.ZipMismatchUncompLen;

                if (local_header.filename_len != self.filename_len)
                    return error.ZipMismatchFilenameLen;

                break :local_data_header_offset @as(u64, local_header.filename_len) +
                    @as(u64, local_header.extra_len);
            };

            if (isBadFilename(filename))
                return error.ZipBadFilename;

            if (options.allow_backslashes) {
                std.mem.replaceScalar(u8, filename, '\\', '/');
            } else {
                if (std.mem.indexOfScalar(u8, filename, '\\')) |_|
                    return error.ZipFilenameHasBackslash;
            }

            // All entries that end in '/' are directories
            if (filename[filename.len - 1] == '/') {
                if (self.uncompressed_size != 0)
                    return error.ZipBadDirectorySize;
                try dest.makePath(filename[0 .. filename.len - 1]);
                return;
            }

            const out_file = blk: {
                if (std.fs.path.dirname(filename)) |dirname| {
                    var parent_dir = try dest.makeOpenPath(dirname, .{});
                    defer parent_dir.close();

                    const basename = std.fs.path.basename(filename);
                    break :blk try parent_dir.createFile(basename, .{ .exclusive = true });
                }
                break :blk try dest.createFile(filename, .{ .exclusive = true });
            };
            defer out_file.close();
            var out_file_buffer: [1024]u8 = undefined;
            var file_writer = out_file.writer(&out_file_buffer);
            const local_data_file_offset: u64 =
                @as(u64, self.file_offset) +
                @as(u64, @sizeOf(LocalFileHeader)) +
                local_data_header_offset;
            try stream.seekTo(local_data_file_offset);

            // TODO limit based on self.compressed_size

            switch (self.compression_method) {
                .store => {
                    stream.interface.streamExact64(&file_writer.interface, self.uncompressed_size) catch |err| switch (err) {
                        error.ReadFailed => return stream.err.?,
                        error.WriteFailed => return file_writer.err.?,
                        error.EndOfStream => return error.ZipDecompressTruncated,
                    };
                },
                .deflate => {
                    var flate_buffer: [flate.max_window_len]u8 = undefined;
                    var decompress: flate.Decompress = .init(&stream.interface, .raw, &flate_buffer);
                    decompress.reader.streamExact64(&file_writer.interface, self.uncompressed_size) catch |err| switch (err) {
                        error.ReadFailed => return stream.err.?,
                        error.WriteFailed => return file_writer.err orelse decompress.err.?,
                        error.EndOfStream => return error.ZipDecompressTruncated,
                    };
                },
                else => return error.UnsupportedCompressionMethod,
            }
            try file_writer.end();
        }
    };
};

// returns true if `filename` starts with `root` followed by a forward slash
fn filenameInRoot(filename: []const u8, root: []const u8) bool {
    return (filename.len >= root.len + 1) and
        (filename[root.len] == '/') and
        std.mem.eql(u8, filename[0..root.len], root);
}

pub const Diagnostics = struct {
    allocator: std.mem.Allocator,

    /// The common root directory for all extracted files if there is one.
    root_dir: []const u8 = "",

    saw_first_file: bool = false,

    pub fn deinit(self: *Diagnostics) void {
        self.allocator.free(self.root_dir);
        self.* = undefined;
    }

    // This function assumes name is a filename from a zip file which has already been verified to
    // not start with a slash, backslashes have been normalized to forward slashes, and directories
    // always end in a slash.
    pub fn nextFilename(self: *Diagnostics, name: []const u8) error{OutOfMemory}!void {
        if (!self.saw_first_file) {
            self.saw_first_file = true;
            std.debug.assert(self.root_dir.len == 0);
            const root_len = std.mem.indexOfScalar(u8, name, '/') orelse return;
            std.debug.assert(root_len > 0);
            self.root_dir = try self.allocator.dupe(u8, name[0..root_len]);
        } else if (self.root_dir.len > 0) {
            if (!filenameInRoot(name, self.root_dir)) {
                self.allocator.free(self.root_dir);
                self.root_dir = "";
            }
        }
    }
};

pub const ExtractOptions = struct {
    /// Allow filenames within the zip to use backslashes.  Back slashes are normalized
    /// to forward slashes before forwarding them to platform APIs.
    allow_backslashes: bool = false,
    diagnostics: ?*Diagnostics = null,
    verify_checksums: bool = false,
};

/// Extract the zipped files to the given `dest` directory.
pub fn extract(dest: std.fs.Dir, fr: *File.Reader, options: ExtractOptions) !void {
    if (options.verify_checksums) @panic("TODO unimplemented");

    var iter = try Iterator.init(fr);

    var filename_buf: [std.fs.max_path_bytes]u8 = undefined;
    while (try iter.next()) |entry| {
        try entry.extract(fr, options, &filename_buf, dest);
        if (options.diagnostics) |d| {
            try d.nextFilename(filename_buf[0..entry.filename_len]);
        }
    }
}
