<?php

namespace app\serializers;

class Serializer
{
    /* ========= 规则存储 ========= */

    protected array $handlerTrie = [];
    protected array $removeTrie  = [];
    protected array $appendRules = [];

    public function __construct(
        protected array|null $source = null
    ) {}

    /* ========= API ========= */

    public function handle(string $path, callable $fn): static
    {
        $this->insertTrie($this->handlerTrie, explode('.', $path), $fn);
        return $this;
    }

    public function remove(string $path): static
    {
        $this->insertTrie($this->removeTrie, explode('.', $path), true);
        return $this;
    }

    /**
     * 节点级追加（path 指向节点）
     */
    public function append(string $path, callable $fn): static
    {
        $this->appendRules[] = [
            'path' => explode('.', $path),
            'fn'   => $fn,
        ];
        return $this;
    }

    /* ========= 执行 ========= */

    public function serialize(): array
    {
        $data = $this->source ?? [];

        // Phase 1：字段级（Trie）
        $this->walkTrie($data, $this->handlerTrie, $this->removeTrie);

        // Phase 2：节点级（append）
        $this->applyAppend($data);

        return $data;
    }

    /* ========= Phase 1 ========= */

    protected function walkTrie(
        &$node,
        array $handlerNode,
        array $removeNode
    ): void {
        if (!is_array($node)) return;

        foreach ($node as $key => &$value) {

            // list：不消费 trie
            if (is_int($key)) {
                $this->walkTrie($value, $handlerNode, $removeNode);
                continue;
            }

            $nextHandler = $handlerNode[$key] ?? [];
            $nextRemove  = $removeNode[$key]  ?? [];

            // 删除优先
            if (isset($nextRemove['_end'])) {
                unset($node[$key]);
                continue;
            }

            // 修改字段
            if (isset($nextHandler['_fn'])) {
                $value = ($nextHandler['_fn'])($value);
            }

            if (is_array($value)) {
                $this->walkTrie($value, $nextHandler, $nextRemove);
            }
        }
    }

    /* ========= Phase 2 ========= */

    protected function applyAppend(array &$data): void
    {
        foreach ($this->appendRules as $rule) {
            $this->walkAppend($data, $rule['path'], $rule['fn']);
        }
    }

    protected function walkAppend(
        &$node,
        array $path,
        callable $fn
    ): void {
        if (!is_array($node)) return;

        // 命中节点
        if (empty($path)) {
            if (!$this->isList($node)) {
                $fn($node);
            }
            return;
        }

        $key = array_shift($path);

        if ($this->isList($node)) {
            foreach ($node as &$item) {
                $this->walkAppend($item, array_merge([$key], $path), $fn);
            }
            return;
        }

        if (isset($node[$key])) {
            $this->walkAppend($node[$key], $path, $fn);
        }
    }

    /* ========= Trie ========= */

    protected function insertTrie(array &$trie, array $path, $value): void
    {
        $node = &$trie;

        foreach ($path as $segment) {
            if (!isset($node[$segment])) {
                $node[$segment] = [];
            }
            $node = &$node[$segment];
        }

        if (is_callable($value)) {
            $node['_fn'] = $value;
        } else {
            $node['_end'] = true;
        }
    }

    protected function isList(array $arr): bool
    {
        return array_keys($arr) === range(0, count($arr) - 1);
    }
}