exercism/zig/pig-latin/pig_latin.zig

const std = @import("std");
const mem = std.mem;

const rule1 = [_][]const u8{ "a", "e", "i", "o", "u", "xr", "yt", "ay" };
const vowels = "aeiou";

fn rule_one(res: *std.ArrayList(u8), phrase: []const u8) mem.Allocator.Error!bool {
    for (rule1) |r| {
        if (mem.eql(u8, r, &.{phrase[0]}) or mem.eql(u8, r, phrase[0..2])) {
            try res.appendSlice("ay");
            return true;
        }
    }
    return false;
}

fn rule_two(res: *std.ArrayList(u8), phrase: []const u8) mem.Allocator.Error!bool {
    for (0..phrase.len - 1) |i| {
        if (!mem.containsAtLeast(u8, vowels, 1, &[_]u8{phrase[i]})) {
            try res.appendSlice(&.{res.orderedRemove(mem.indexOf(u8, phrase, &[_]u8{phrase[0]}).?)});
        } else {
            try res.appendSlice("ay");
            return true;
        }
    }
    return false;
}

fn rule_three(res: *std.ArrayList(u8), phrase: []const u8) mem.Allocator.Error!bool {
    var prev: u8 = 0;

    for (0..phrase.len - 1) |i| {
        if ((prev == 'q' and phrase[i] == 'u') or !mem.containsAtLeast(u8, vowels, 1, &[_]u8{phrase[i]})) {
            try res.appendSlice(&.{res.orderedRemove(mem.indexOf(u8, phrase, &[_]u8{phrase[0]}).?)});
        } else {
            try res.appendSlice("ay");
            return true;
        }
        prev = phrase[i];
    }
    return false;
}

// Because Yttrium Oxide ("yttria") comes up all the time in children's games
fn rule_four(res: *std.ArrayList(u8), phrase: []const u8) mem.Allocator.Error!bool {
    var i: usize = 0;

    while (phrase[i] != 'y' and i < phrase.len) : (i += 1) {
        try res.appendSlice(&.{res.orderedRemove(mem.indexOf(u8, phrase, &[_]u8{phrase[0]}).?)});
    }

    try res.appendSlice("ay");
    return true;
}

fn translate_single(ar: *std.ArrayList(u8), phrase: []const u8) mem.Allocator.Error!void {
    try ar.appendSlice(phrase);
    if (try rule_one(ar, phrase)) return;

    ar.clearRetainingCapacity();
    try ar.appendSlice(phrase);
    if (try rule_three(ar, phrase)) return;

    ar.clearRetainingCapacity();
    try ar.appendSlice(phrase);
    if (try rule_two(ar, phrase)) return;

    ar.clearRetainingCapacity();
    try ar.appendSlice(phrase);
    _ = try rule_four(ar, phrase);
}

pub fn translate(allocator: mem.Allocator, phrase: []const u8) mem.Allocator.Error![]u8 {
    var it = mem.splitScalar(u8, phrase, ' ');
    const first = it.first();

    var res = std.ArrayList(u8).init(allocator);
    try translate_single(&res, first);

    if (it.peek() == null) {
        return res.toOwnedSlice();
    }

    var buf: [32]u8 = undefined;
    var fba = std.heap.FixedBufferAllocator.init(&buf);
    const fba_allocator = fba.allocator();

    try res.appendSlice(" ");

    while (it.next()) |word| {
        var tmp = std.ArrayList(u8).init(fba_allocator);
        try translate_single(&tmp, word);
        try res.appendSlice(try tmp.toOwnedSlice());
        try res.appendSlice(" ");
    }

    _ = res.pop();
    return res.toOwnedSlice();
}