class ExerciseGenerator {

// ----------
constructor(collection) {
    this.collection = collection;

    // console.log(this.collection);
    this.used_exercise_ids = new Array;

    this.ex_nxt;
    this.ex_last = null;
}

// ----------
exercise_id_used(ex) {
    return (this.used_exercise_ids.filter(function(v) { return (v == ex.id) }).length > 0);
}

// ----------
exercise_related_to(ex) {
    let related = false;
    let gen = this;

    if (gen.ex_last == null) {
        return related;
    }

    ex.focus.forEach(function(e) {
        related |= gen.ex_last.focus.includes(e);
    });

    return related;
}

// ----------
get_next_exercise() {
    let scope = this.collection.exercises;
    let gen = this;

    scope = this.collection.exercises.filter(function(e) {
        let pick = true;

        // Pick if exercise is not already used
        pick &= (gen.exercise_id_used(e) == false);

        // Pick if nor related to the previous one
        pick &= (gen.exercise_related_to(e) == false);

        return pick
    });
    gen.shuffle_exercise_array(scope);
    // gen.show_exercise_array(scope);

    return scope[0];
}

// ----------
show_exercise_array(arr) {
    let gen = this;

    arr.map(function(it) {
        gen.show_exercise(it);
    });
}

// ----------
show_exercise(ex) {
    console.log(`${ex.id} : ${ex.name} [` + ex.focus.join(", ") + ']');
}

// ----------
// From answer on https://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array
shuffle_exercise_array(arr) {
    let currentIndex = arr.length;

    // While there remain elements to shuffle...
    while (currentIndex != 0) {
        // Pick a remaining element...
        let randomIndex = Math.floor(Math.random() * currentIndex);
        currentIndex--;

        // And swap it with the current element.
        [arr[currentIndex], arr[randomIndex]] = [
            arr[randomIndex], arr[currentIndex]];
    }
}

// ----------
generate_set(size) {
    let set_exercises = Array();
    let lim = size;

    this.ex_last = null;

    do {
        this.ex_nxt = this.get_next_exercise();
        if (this.ex_nxt == null) {
            break;
        }
        this.used_exercise_ids.push(this.ex_nxt.id);
        set_exercises.push(this.ex_nxt);
        this.ex_last = this.ex_nxt;
        lim--;
    } while ((this.ex_nxt != null) && (lim > 0));

    this.show_exercise_array(set_exercises);
    console.log(this.used_exercise_ids);

    return set_exercises;
}

// ----------
generate_build_and_burn(sets, exercises, reps) {
    let wo_plan = {
        "name": "Daily Build and Burn",
        "set": [
        ]
    }

    for (let i = 1; i <= sets; i ++) {
        let set = {
            "name": `Set ${i}`,
            "count": reps,
            "exercise": this.generate_set(exercises)
        }
        wo_plan.set.push(set);
    }

    return wo_plan;
}

}