pub const Diagnostics = struct {
    allocator: std.mem.Allocator,
    errors: std.ArrayListUnmanaged(Error) = .empty,

    entries: usize = 0,
    root_dir: []const u8 = "",

    pub const Error = union(enum) {
        unable_to_create_sym_link: struct {
            code: anyerror,
            file_name: []const u8,
            link_name: []const u8,
        },
        unable_to_create_file: struct {
            code: anyerror,
            file_name: []const u8,
        },
        unsupported_file_type: struct {
            file_name: []const u8,
            file_type: Header.Kind,
        },
        components_outside_stripped_prefix: struct {
            file_name: []const u8,
        },
    };

    fn findRoot(d: *Diagnostics, path: []const u8) !void {
        if (path.len == 0) return;

        d.entries += 1;
        const root_dir = rootDir(path);
        if (d.entries == 1) {
            d.root_dir = try d.allocator.dupe(u8, root_dir);
            return;
        }
        if (d.root_dir.len == 0 or std.mem.eql(u8, root_dir, d.root_dir))
            return;
        d.allocator.free(d.root_dir);
        d.root_dir = "";
    }

    // Returns root dir of the path, assumes non empty path.
    fn rootDir(path: []const u8) []const u8 {
        const start_index: usize = if (path[0] == '/') 1 else 0;
        const end_index: usize = if (path[path.len - 1] == '/') path.len - 1 else path.len;
        const buf = path[start_index..end_index];
        if (std.mem.indexOfScalarPos(u8, buf, 0, '/')) |idx| {
            return buf[0..idx];
        }
        return buf;
    }

    test rootDir {
        const expectEqualStrings = testing.expectEqualStrings;
        try expectEqualStrings("a", rootDir("a"));
        try expectEqualStrings("b", rootDir("b"));
        try expectEqualStrings("c", rootDir("/c"));
        try expectEqualStrings("d", rootDir("/d/"));
        try expectEqualStrings("a", rootDir("a/b"));
        try expectEqualStrings("a", rootDir("a/b/c"));
    }

    pub fn deinit(d: *Diagnostics) void {
        for (d.errors.items) |item| {
            switch (item) {
                .unable_to_create_sym_link => |info| {
                    d.allocator.free(info.file_name);
                    d.allocator.free(info.link_name);
                },
                .unable_to_create_file => |info| {
                    d.allocator.free(info.file_name);
                },
                .unsupported_file_type => |info| {
                    d.allocator.free(info.file_name);
                },
                .components_outside_stripped_prefix => |info| {
                    d.allocator.free(info.file_name);
                },
            }
        }
        d.errors.deinit(d.allocator);
        d.allocator.free(d.root_dir);
        d.* = undefined;
    }
}