const std = @import("std");

pub const Version = packed struct {
    major: u8,
    minor: u8,

    pub fn format(self: @This(), writer: *std.Io.Writer) !void {
        try writer.print("v{}.{}", .{self.major, self.minor});
    }
};

pub const Unit = enum(u8) {
    none = 0,
    pixels_per_inch = 1,
    pixels_per_cm = 2,
};

const Self = @This();

version: Version,
unit: Unit,
density: struct { x: u16, y: u16 },
thumbnail: struct { x: u8, y: u8 },

const identifier: []const u8 = "JFIF\x00";

pub fn read(reader: *std.Io.Reader) !Self {
    const ident = try reader.peekArray(identifier.len);

    if (!std.mem.eql(u8, ident, identifier)) {
        return error.WrongIdentifier;
    }
    reader.toss(identifier.len);

    var self: Self = undefined;
    self.version.major = try reader.takeByte();
    self.version.minor = try reader.takeByte();

    self.unit = @enumFromInt(try reader.takeByte());

    self.density.x = try reader.takeInt(u16, .big);
    self.density.y = try reader.takeInt(u16, .big);

    self.thumbnail.x = try reader.takeInt(u8, .big);
    self.thumbnail.y = try reader.takeInt(u8, .big);

    // WARNING: we do not decode the thumbnail yet.
    const size = 3 * self.thumbnail.x * self.thumbnail.y;
    reader.toss(size);

    return self;
}