package org.shedlang.compiler.backends;

import org.pcollections.Empty;
import org.pcollections.PSet;

import java.util.Optional;
import java.util.function.Predicate;

public record NameAllocator<TPrefix>(PSet<String> existingNames) {
    public static <TPrefix> NameAllocator<TPrefix> empty() {
        return new NameAllocator<>(Empty.set());
    }

    public Result<TPrefix> allocateName(
        TPrefix prefix,
        Optional<String> name
    ) {
        var fullName = allocateName(existingNames::contains, prefix, name);
        var newAllocator = new NameAllocator<TPrefix>(existingNames.plus(fullName));
        return new Result<>(fullName, newAllocator);
    }

    public Result<TPrefix> allocateFixedName(TPrefix prefix, String name) {
        var fullName = allocateFixedName(existingNames::contains, prefix, name);
        var newAllocator = new NameAllocator<TPrefix>(existingNames.plus(fullName));
        return new Result<>(fullName, newAllocator);
    }

    public static <TPrefix> String allocateName(
        Predicate<String> isUsed,
        TPrefix prefix,
        Optional<String> name
    ) {
        var fullPrefix = prefix.toString();
        if (name.isPresent()) {
            fullPrefix += "__" + name.get();
        }

        var index = 0;
        while (true) {
            var fullName = fullPrefix + "__" + index;
            if (isUsed.test(fullName)) {
                index++;
            } else {
                return fullName;
            }
        }
    }

    public static <TPrefix> String allocateFixedName(Predicate<String> isUsed, TPrefix prefix, String name) {
        var fullName = prefix + "__" + name;

        if (isUsed.test(fullName)) {
            throw new RuntimeException("name is already allocated: " + fullName);
        }

        return fullName;
    }

    public record Result<TPrefix>(String name, NameAllocator<TPrefix> allocator) {
    }
}