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// Burton Computer Corporation
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package org.javimmutable.collections.array;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.util.Arrays;

class TrieArrayBuilder
{
    private final LeafBuilder leafBuilder = new LeafBuilder<>();

    synchronized void clear()
    {
        leafBuilder.clear();
    }
    
    synchronized int size()
    {
        return leafBuilder.index;
    }

    synchronized void add(T value)
    {
        leafBuilder.add(value);
    }

    @Nonnull
    synchronized TrieNode build()
    {
        return leafBuilder.build();
    }

    private static class LeafBuilder
    {
        private final TrieNode[] leaves;
        private int offset;
        private int index;
        private BranchBuilder next;

        @SuppressWarnings("unchecked")
        private LeafBuilder()
        {
            leaves = new LeafTrieNode[32];
        }

        private void clear()
        {
            Arrays.fill(leaves, null);
            offset = 0;
            index = 0;
            next = null;
        }
        
        private void add(T value)
        {
            leaves[offset] = LeafTrieNode.of(index, value);
            index += 1;
            offset += 1;
            if (offset == 32) {
                push();
            }
        }

        private void push()
        {
            assert offset == 32;
            TrieNode branch = new FullBranchTrieNode<>(0, TrieNode.computeValueCount(leaves), leaves.clone());
            if (next == null) {
                next = new BranchBuilder<>(5);
            }
            next.add(branch);
            offset = 0;
        }

        private TrieNode build()
        {
            assert offset < 32;
            TrieNode node = branchForBuild(leaves, offset, 0);
            return resultForBuild(next, node);
        }
    }

    private static class BranchBuilder
    {
        private final TrieNode[] nodes;
        private final int shift;
        private int offset;
        private BranchBuilder next;

        @SuppressWarnings("unchecked")
        private BranchBuilder(int shift)
        {
            nodes = new TrieNode[32];
            this.shift = shift;
        }

        private void add(TrieNode node)
        {
            nodes[offset] = node;
            offset += 1;
            if (offset == 32) {
                push();
            }
        }

        private void push()
        {
            assert offset == 32;
            TrieNode branch = new FullBranchTrieNode<>(shift, TrieNode.computeValueCount(nodes), nodes.clone());
            if (next == null) {
                next = new BranchBuilder<>(shift + 5);
            }
            next.add(branch);
            offset = 0;
        }

        private TrieNode build(@Nullable TrieNode extra)
        {
            assert offset < 32;
            int length;
            if (extra != null) {
                nodes[offset] = extra;
                length = offset + 1;
            } else {
                length = offset;
            }
            TrieNode node = branchForBuild(nodes, length, shift);
            return resultForBuild(next, node);
        }
    }

    private static  TrieNode branchForBuild(@Nonnull TrieNode[] nodes,
                                                  int length,
                                                  int shift)
    {
        TrieNode branch;
        switch (length) {
            case 0:
                branch = null;
                break;
            case 1:
                branch = SingleBranchTrieNode.forBranchIndex(shift, 0, nodes[0]);
                break;
            case 32:
                branch = new FullBranchTrieNode<>(shift, TrieNode.computeValueCount(nodes), nodes.clone());
                break;
            default:
                branch = MultiBranchTrieNode.forEntries(shift, nodes, length);
                break;
        }
        return branch;
    }

    private static  TrieNode resultForBuild(@Nullable BranchBuilder next,
                                                  @Nullable TrieNode node)
    {
        if (next != null) {
            return next.build(node);
        } else if (node == null) {
            return EmptyTrieNode.of();
        } else {
            return node;
        }
    }
}