ona/src/mem.zig

const std = @import("std");

///
/// State machine for lazily computing all components of [Spliterator.source] that match the pattern
/// in [Spliterator.delimiter].
///
pub fn Spliterator(comptime Element: type) type {
    return struct {
        source: []const Element,
        delimiter: []const Element,

        const Self = @This();

        ///
        /// Returns `true` if there is more data to be processed, otherwise `false`.
        ///
        pub fn hasNext(self: Self) bool {
            return (self.source.len != 0);
        }

        ///
        /// Iterates on `self` and returns the next view of [Spliterator.source] that matches
        /// [Spliterator.delimiter], or `null` if there is no more data to be processed.
        ///
        pub fn next(self: *Self) ?[]const Element {
            if (!self.hasNext()) return null;

            if (std.mem.indexOfPos(Element, self.source, 0, self.delimiter)) |index| {
                defer self.source = self.source[(index + self.delimiter.len) .. self.source.len];

                return self.source[0 .. index];
            }

            defer self.source = self.source[self.source.len .. self.source.len];

            return self.source;
        }
    };
}

test {
    const testing = std.testing;

    // Single-character delimiter.
    {
        var spliterator = Spliterator(u8){
            .source = "single.character.separated.hello.world",
            .delimiter = ".",
        };

        const components = [_][]const u8{"single", "character", "separated", "hello", "world"};
        var index = @as(usize, 0);

        while (spliterator.next()) |split| : (index += 1) {
            try testing.expect(std.mem.eql(u8, split, components[index]));
        }
    }

    // Multi-character delimiter.
    {
        var spliterator = Spliterator(u8){
            .source = "finding a needle in a needle stack",
            .delimiter = "needle",
        };

        const components = [_][]const u8{"finding a ", " in a ", " stack"};
        var index = @as(usize, 0);

        while (spliterator.next()) |split| : (index += 1) {
            try testing.expect(std.mem.eql(u8, split, components[index]));
        }
    }
}

///
/// Searches the slice of `Data` referenced by `data` for the first instance of `sought_datum`,
/// returning its index or `null` if it could not be found.
///
pub fn findFirst(comptime Data: type, data: []const Data, sought_datum: Data) ?usize {
    for (data) |datum, index| if (datum == sought_datum) return index;

    return null;
}

test {
    try std.testing.expectEqual(findFirst(u8, "1234567890", '7'), 6);
}