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;
const FormatCode = @import("main.zig").FormatCode;

pub const Tag: u8 = 'T';

const RowDescription = @This();

buf: ?[]const u8 = null, // owned
fields: ?[]Field = null, // owned

pub const Field = struct {
    name: []const u8,
    table_oid: u32,
    attr_no: u16,
    data_type_oid: u32,
    data_type_size: i16,
    data_type_modifier: u32,
    format_code: FormatCode,
};

pub fn read(a: std.mem.Allocator, b: []const u8) !RowDescription {
    var res: RowDescription = undefined;
    res.buf = try a.dupe(u8, b);
    errdefer res.deinit(a);
    var fbs = std.io.fixedBufferStream(res.buf.?);
    var reader = fbs.reader();
    const n_fields = try reader.readIntBig(u16);
    res.fields = try a.alloc(Field, n_fields);
    for (0..n_fields) |i| {
        const name_start = fbs.pos;
        try reader.skipUntilDelimiterOrEof(0);
        const name_end = fbs.pos-1;
        const name = res.buf.?[name_start..name_end];
        const field = Field{
            .name = name,
            .table_oid = try reader.readIntBig(u32),
            .attr_no = try reader.readIntBig(u16),
            .data_type_oid = try reader.readIntBig(u32),
            .data_type_size = try reader.readIntBig(i16),
            .data_type_modifier = try reader.readIntBig(u32),
            .format_code = enum_from_int(FormatCode, try reader.readIntBig(u16)) orelse return ProtocolError.InvalidFormatCode,
        };
        res.fields.?[i] = field;
    }
    return res;
}

pub fn write(self: RowDescription, 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.fields.?.len)));
    for (self.fields.?) |field| {
        try writer.writeAll(field.name);
        try writer.writeByte(0);
        try writer.writeIntBig(u32, field.table_oid);
        try writer.writeIntBig(u16, field.attr_no);
        try writer.writeIntBig(u32, field.data_type_oid);
        try writer.writeIntBig(i16, field.data_type_size);
        try writer.writeIntBig(u32, field.data_type_modifier);
        try writer.writeIntBig(u16, @intFromEnum(field.format_code));
    }
    std.mem.writeIntBig(u32, al.items[0..4], @as(u32, @intCast(cw.bytes_written)));
    try stream_writer.writeAll(al.items);
}

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

test "round trip" {
    const allocator = std.testing.allocator;
    var fields = try allocator.alloc(Field, 3);
    fields[0] = .{
        .name = "foo",
        .table_oid = 1,
        .attr_no = 2,
        .data_type_oid = 3,
        .data_type_size = 4,
        .data_type_modifier = 5,
        .format_code = .Binary,
    };
    fields[1] = .{
        .name = "bar",
        .table_oid = 1,
        .attr_no = 2,
        .data_type_oid = 3,
        .data_type_size = 4,
        .data_type_modifier = 5,
        .format_code = .Binary,
    };
    fields[2] = .{
        .name = "BAZZZZZ",
        .table_oid = 99,
        .attr_no = 98,
        .data_type_oid = 97,
        .data_type_size = 96,
        .data_type_modifier = 95,
        .format_code = .Text,
    };
    var f0 = fields[0];
    var f1 = fields[1];
    var f2 = fields[2];
    var sm = RowDescription{
        .fields = fields,
    };
    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 RowDescription.read(allocator, buf);
    defer sm2.deinit(allocator);

    try std.testing.expectEqualDeep(f0, sm2.fields.?[0]);
    try std.testing.expectEqualDeep(f1, sm2.fields.?[1]);
    try std.testing.expectEqualDeep(f2, sm2.fields.?[2]);
}