const std = @import("../std.zig");
const builtin = @import("builtin");
const os = std.os;
const io = std.io;
const mem = std.mem;
const math = std.math;
const assert = std.debug.assert;
const windows = os.windows;
const Os = builtin.Os;
const maxInt = std.math.maxInt;
const need_async_thread = std.fs.need_async_thread;

pub const File = struct {
    /// The OS-specific file descriptor or file handle.
    handle: os.fd_t,

    /// On some systems, such as Linux, file system file descriptors are incapable of non-blocking I/O.
    /// This forces us to perform asynchronous I/O on a dedicated thread, to achieve non-blocking
    /// file-system I/O. To do this, `File` must be aware of whether it is a file system file descriptor,
    /// or, more specifically, whether the I/O is blocking.
    io_mode: io.Mode,

    /// Even when std.io.mode is async, it is still sometimes desirable to perform blocking I/O, although
    /// not by default. For example, when printing a stack trace to stderr.
    async_block_allowed: @TypeOf(async_block_allowed_no) = async_block_allowed_no,

    pub const async_block_allowed_yes = if (io.is_async) true else {};
    pub const async_block_allowed_no = if (io.is_async) false else {};

    pub const Mode = os.mode_t;

    pub const default_mode = switch (builtin.os) {
        .windows => 0,
        else => 0o666,
    };

    pub const OpenError = windows.CreateFileError || os.OpenError;

    /// TODO https://github.com/ziglang/zig/issues/3802
    pub const OpenFlags = struct {
        read: bool = true,
        write: bool = false,
    };

    /// TODO https://github.com/ziglang/zig/issues/3802
    pub const CreateFlags = struct {
        /// Whether the file will be created with read access.
        read: bool = false,

        /// If the file already exists, and is a regular file, and the access
        /// mode allows writing, it will be truncated to length 0.
        truncate: bool = true,

        /// Ensures that this open call creates the file, otherwise causes
        /// `error.FileAlreadyExists` to be returned.
        exclusive: bool = false,

        /// For POSIX systems this is the file system mode the file will
        /// be created with.
        mode: Mode = default_mode,
    };

    /// Upon success, the stream is in an uninitialized state. To continue using it,
    /// you must use the open() function.
    pub fn close(self: File) void {
        if (need_async_thread and self.io_mode == .blocking and !self.async_block_allowed) {
            std.event.Loop.instance.?.close(self.handle);
        } else {
            return os.close(self.handle);
        }
    }

    /// Test whether the file refers to a terminal.
    /// See also `supportsAnsiEscapeCodes`.
    pub fn isTty(self: File) bool {
        return os.isatty(self.handle);
    }

    /// Test whether ANSI escape codes will be treated as such.
    pub fn supportsAnsiEscapeCodes(self: File) bool {
        if (builtin.os == .windows) {
            return os.isCygwinPty(self.handle);
        }
        if (self.isTty()) {
            if (self.handle == os.STDOUT_FILENO or self.handle == os.STDERR_FILENO) {
                // Use getenvC to workaround https://github.com/ziglang/zig/issues/3511
                if (os.getenvC("TERM")) |term| {
                    if (std.mem.eql(u8, term, "dumb"))
                        return false;
                }
            }
            return true;
        }
        return false;
    }

    pub const SeekError = os.SeekError;

    /// Repositions read/write file offset relative to the current offset.
    /// TODO: integrate with async I/O
    pub fn seekBy(self: File, offset: i64) SeekError!void {
        return os.lseek_CUR(self.handle, offset);
    }

    /// Repositions read/write file offset relative to the end.
    /// TODO: integrate with async I/O
    pub fn seekFromEnd(self: File, offset: i64) SeekError!void {
        return os.lseek_END(self.handle, offset);
    }

    /// Repositions read/write file offset relative to the beginning.
    /// TODO: integrate with async I/O
    pub fn seekTo(self: File, offset: u64) SeekError!void {
        return os.lseek_SET(self.handle, offset);
    }

    pub const GetPosError = os.SeekError || os.FStatError;

    /// TODO: integrate with async I/O
    pub fn getPos(self: File) GetPosError!u64 {
        return os.lseek_CUR_get(self.handle);
    }

    /// TODO: integrate with async I/O
    pub fn getEndPos(self: File) GetPosError!u64 {
        if (builtin.os == .windows) {
            return windows.GetFileSizeEx(self.handle);
        }
        return (try self.stat()).size;
    }

    pub const ModeError = os.FStatError;

    /// TODO: integrate with async I/O
    pub fn mode(self: File) ModeError!Mode {
        if (builtin.os == .windows) {
            return {};
        }
        return (try self.stat()).mode;
    }

    pub const Stat = struct {
        size: u64,
        mode: Mode,

        /// access time in nanoseconds
        atime: i64,

        /// last modification time in nanoseconds
        mtime: i64,

        /// creation time in nanoseconds
        ctime: i64,
    };

    pub const StatError = os.FStatError;

    /// TODO: integrate with async I/O
    pub fn stat(self: File) StatError!Stat {
        if (builtin.os == .windows) {
            var io_status_block: windows.IO_STATUS_BLOCK = undefined;
            var info: windows.FILE_ALL_INFORMATION = undefined;
            const rc = windows.ntdll.NtQueryInformationFile(self.handle, &io_status_block, &info, @sizeOf(windows.FILE_ALL_INFORMATION), .FileAllInformation);
            switch (rc) {
                .SUCCESS => {},
                .BUFFER_OVERFLOW => {},
                .INVALID_PARAMETER => unreachable,
                .ACCESS_DENIED => return error.AccessDenied,
                else => return windows.unexpectedStatus(rc),
            }
            return Stat{
                .size = @bitCast(u64, info.StandardInformation.EndOfFile),
                .mode = 0,
                .atime = windows.fromSysTime(info.BasicInformation.LastAccessTime),
                .mtime = windows.fromSysTime(info.BasicInformation.LastWriteTime),
                .ctime = windows.fromSysTime(info.BasicInformation.CreationTime),
            };
        }

        const st = try os.fstat(self.handle);
        const atime = st.atime();
        const mtime = st.mtime();
        const ctime = st.ctime();
        return Stat{
            .size = @bitCast(u64, st.size),
            .mode = st.mode,
            .atime = @as(i64, atime.tv_sec) * std.time.ns_per_s + atime.tv_nsec,
            .mtime = @as(i64, mtime.tv_sec) * std.time.ns_per_s + mtime.tv_nsec,
            .ctime = @as(i64, ctime.tv_sec) * std.time.ns_per_s + ctime.tv_nsec,
        };
    }

    pub const UpdateTimesError = os.FutimensError || windows.SetFileTimeError;

    /// The underlying file system may have a different granularity than nanoseconds,
    /// and therefore this function cannot guarantee any precision will be stored.
    /// Further, the maximum value is limited by the system ABI. When a value is provided
    /// that exceeds this range, the value is clamped to the maximum.
    /// TODO: integrate with async I/O
    pub fn updateTimes(
        self: File,
        /// access timestamp in nanoseconds
        atime: i64,
        /// last modification timestamp in nanoseconds
        mtime: i64,
    ) UpdateTimesError!void {
        if (builtin.os == .windows) {
            const atime_ft = windows.nanoSecondsToFileTime(atime);
            const mtime_ft = windows.nanoSecondsToFileTime(mtime);
            return windows.SetFileTime(self.handle, null, &atime_ft, &mtime_ft);
        }
        const times = [2]os.timespec{
            os.timespec{
                .tv_sec = math.cast(isize, @divFloor(atime, std.time.ns_per_s)) catch maxInt(isize),
                .tv_nsec = math.cast(isize, @mod(atime, std.time.ns_per_s)) catch maxInt(isize),
            },
            os.timespec{
                .tv_sec = math.cast(isize, @divFloor(mtime, std.time.ns_per_s)) catch maxInt(isize),
                .tv_nsec = math.cast(isize, @mod(mtime, std.time.ns_per_s)) catch maxInt(isize),
            },
        };
        try os.futimens(self.handle, &times);
    }

    pub const ReadError = os.ReadError;

    pub fn read(self: File, buffer: []u8) ReadError!usize {
        if (need_async_thread and self.io_mode == .blocking and !self.async_block_allowed) {
            return std.event.Loop.instance.?.read(self.handle, buffer);
        }
        return os.read(self.handle, buffer);
    }

    pub fn pread(self: File, buffer: []u8, offset: u64) ReadError!usize {
        if (need_async_thread and self.io_mode == .blocking and !self.async_block_allowed) {
            return std.event.Loop.instance.?.pread(self.handle, buffer);
        }
        return os.pread(self.handle, buffer, offset);
    }

    pub fn readv(self: File, iovecs: []const os.iovec) ReadError!usize {
        if (need_async_thread and self.io_mode == .blocking and !self.async_block_allowed) {
            return std.event.Loop.instance.?.readv(self.handle, iovecs);
        }
        return os.readv(self.handle, iovecs);
    }

    pub fn preadv(self: File, iovecs: []const os.iovec, offset: u64) ReadError!usize {
        if (need_async_thread and self.io_mode == .blocking and !self.async_block_allowed) {
            return std.event.Loop.instance.?.preadv(self.handle, iovecs, offset);
        }
        return os.preadv(self.handle, iovecs, offset);
    }

    pub const WriteError = os.WriteError;

    pub fn write(self: File, bytes: []const u8) WriteError!void {
        if (need_async_thread and self.io_mode == .blocking and !self.async_block_allowed) {
            return std.event.Loop.instance.?.write(self.handle, bytes);
        }
        return os.write(self.handle, bytes);
    }

    pub fn pwrite(self: File, bytes: []const u8, offset: u64) WriteError!void {
        if (need_async_thread and self.io_mode == .blocking and !self.async_block_allowed) {
            return std.event.Loop.instance.?.pwrite(self.handle, bytes, offset);
        }
        return os.pwrite(self.handle, bytes, offset);
    }

    pub fn writev(self: File, iovecs: []const os.iovec_const) WriteError!void {
        if (need_async_thread and self.io_mode == .blocking and !self.async_block_allowed) {
            return std.event.Loop.instance.?.writev(self.handle, iovecs);
        }
        return os.writev(self.handle, iovecs);
    }

    pub fn pwritev(self: File, iovecs: []const os.iovec_const, offset: usize) WriteError!void {
        if (need_async_thread and self.io_mode == .blocking and !self.async_block_allowed) {
            return std.event.Loop.instance.?.pwritev(self.handle, iovecs);
        }
        return os.pwritev(self.handle, iovecs);
    }

    pub fn inStream(file: File) InStream {
        return InStream{
            .file = file,
            .stream = InStream.Stream{ .readFn = InStream.readFn },
        };
    }

    pub fn outStream(file: File) OutStream {
        return OutStream{
            .file = file,
            .stream = OutStream.Stream{ .writeFn = OutStream.writeFn },
        };
    }

    pub fn seekableStream(file: File) SeekableStream {
        return SeekableStream{
            .file = file,
            .stream = SeekableStream.Stream{
                .seekToFn = SeekableStream.seekToFn,
                .seekByFn = SeekableStream.seekByFn,
                .getPosFn = SeekableStream.getPosFn,
                .getEndPosFn = SeekableStream.getEndPosFn,
            },
        };
    }

    /// Implementation of io.InStream trait for File
    pub const InStream = struct {
        file: File,
        stream: Stream,

        pub const Error = ReadError;
        pub const Stream = io.InStream(Error);

        fn readFn(in_stream: *Stream, buffer: []u8) Error!usize {
            const self = @fieldParentPtr(InStream, "stream", in_stream);
            return self.file.read(buffer);
        }
    };

    /// Implementation of io.OutStream trait for File
    pub const OutStream = struct {
        file: File,
        stream: Stream,

        pub const Error = WriteError;
        pub const Stream = io.OutStream(Error);

        fn writeFn(out_stream: *Stream, bytes: []const u8) Error!void {
            const self = @fieldParentPtr(OutStream, "stream", out_stream);
            return self.file.write(bytes);
        }
    };

    /// Implementation of io.SeekableStream trait for File
    pub const SeekableStream = struct {
        file: File,
        stream: Stream,

        pub const Stream = io.SeekableStream(SeekError, GetPosError);

        pub fn seekToFn(seekable_stream: *Stream, pos: u64) SeekError!void {
            const self = @fieldParentPtr(SeekableStream, "stream", seekable_stream);
            return self.file.seekTo(pos);
        }

        pub fn seekByFn(seekable_stream: *Stream, amt: i64) SeekError!void {
            const self = @fieldParentPtr(SeekableStream, "stream", seekable_stream);
            return self.file.seekBy(amt);
        }

        pub fn getEndPosFn(seekable_stream: *Stream) GetPosError!u64 {
            const self = @fieldParentPtr(SeekableStream, "stream", seekable_stream);
            return self.file.getEndPos();
        }

        pub fn getPosFn(seekable_stream: *Stream) GetPosError!u64 {
            const self = @fieldParentPtr(SeekableStream, "stream", seekable_stream);
            return self.file.getPos();
        }
    };
};