const std = @import("std");
const log = std.log.scoped(.pgz);
const ByteArrayList = std.ArrayList(u8);
const ProtocolError = @import("main.zig").ProtocolError;
const ClientError = @import("main.zig").ClientError;
const enum_from_int = @import("main.zig").enum_from_int;

pub const Tag: u8 = 'D';

const DataRow = @This();

buf: ?[]const u8 = null, // owned
columns: [][]const u8, // also owned

pub fn read(a: std.mem.Allocator, b: []const u8) !DataRow {
    if (b.len < 2) return ProtocolError.InvalidMessageLength;
    var buf = try a.dupe(u8, b);
    var res: DataRow = undefined;
    res.buf  = buf;
    errdefer res.deinit(a);

    const n_columns = std.mem.readIntBig(u16, buf[0..2]);
    const columns = try a.alloc([]const u8, n_columns);
    errdefer a.free(columns);
    var pos: usize = 2;
    for (0..n_columns) |col| {
        const len = std.mem.readIntBig(u32, buf[pos..(pos+4)][0..4]); // second slice forces the slice size to be known at comptime and satisfy the type check on readIntBig!
        const data = if (len > 0) buf[(pos+4)..(pos+4+len)] else &[_]u8{};
        columns[col] = data;
        pos += (4+len);
    }
    res.columns = columns;
    return res;
}

pub fn write(self: DataRow, a: std.mem.Allocator, stream_writer: anytype) !void {
    try stream_writer.writeByte(Tag);
    var al = ByteArrayList.init(a);
    defer al.deinit();
    var cw = std.io.countingWriter(al.writer());
    var writer = cw.writer();
    try writer.writeIntBig(u32, 0); // length placeholder
    try writer.writeIntBig(u16, @as(u16, @intCast(self.columns.len)));
    for (self.columns) |column| {
        const len = @as(u32, @intCast(column.len));
        try writer.writeIntBig(u32, len);
        try writer.writeAll(column);
    }
    // Fixup the length and write to the original stream
    std.mem.writeIntBig(u32, al.items[0..4], @as(u32, @intCast(cw.bytes_written)));
    try stream_writer.writeAll(al.items);
}

pub fn deinit(self: *DataRow, a: std.mem.Allocator) void {
    if (self.buf != null) a.free(self.buf.?);
    a.free(self.columns);
}

test "round trip" {
    const allocator = std.testing.allocator;
    const columns = try allocator.alloc([]const u8, 3);
    columns[0] = "Hello";
    columns[1] = "FooBar";
    columns[2] = "";
    var sm = DataRow{
        .columns = columns,
    };
    defer sm.deinit(allocator);

    var bal = ByteArrayList.init(allocator);
    defer bal.deinit();
    try sm.write(allocator, bal.writer());

    var fbs = std.io.fixedBufferStream(bal.items);
    var reader = fbs.reader();
    const tag = try reader.readByte();
    try std.testing.expectEqual(Tag, tag);
    const len = try reader.readIntBig(u32);
    const buf = try allocator.alloc(u8, len - 4);
    defer allocator.free(buf);
    try reader.readNoEof(buf);
    var sm2 = try DataRow.read(allocator, buf);
    defer sm2.deinit(allocator);

    try std.testing.expectEqualStrings("Hello", sm2.columns[0]);
    try std.testing.expectEqualStrings("FooBar", sm2.columns[1]);
    try std.testing.expectEqualStrings("", sm2.columns[2]);
}