<?php

declare(strict_types=1);

namespace Sarcio\WordPress\Assistant;

/**
 * The conversation as it goes to Sarcio, trimmed to what one turn needs: at
 * most MAX_MESSAGES (the first thing the owner asked always stays unless a
 * summary of the earlier part travels instead), and no result larger than
 * MAX_OUTPUT_CHARS once encoded. Past MAX_MESSAGES the oldest part is
 * summarised and only the newest KEEP_MESSAGES stay as they were said.
 */
final class Transcript
{
    public const KEEP_MESSAGES = 20;
    public const MAX_MESSAGES = 40;
    public const MAX_OUTPUT_CHARS = 12000;
    public const MAX_SUMMARY_CHARS = 6000;
    public const MAX_TEXT_CHARS = 8000;

    /**
     * @param array<int,mixed> $messages
     * @return array<int,array<string,mixed>>
     */
    public static function prepare(array $messages, bool $summarised = false): array
    {
        $clean = [];
        foreach ($messages as $message) {
            $one = self::message($message);
            if ($one !== null) {
                $clean[] = $one;
            }
        }
        if (count($clean) <= self::MAX_MESSAGES) {
            return $clean;
        }
        if ($summarised) {
            $rest = array_slice($clean, count($clean) - self::MAX_MESSAGES);
            while ($rest !== [] && $rest[0]['role'] !== 'user') {
                array_shift($rest);
            }
            return $rest;
        }
        $first = $clean[0];
        $rest = array_slice($clean, 1);
        $rest = array_slice($rest, count($rest) - (self::MAX_MESSAGES - 1));
        while ($rest !== [] && $rest[0]['role'] !== 'user') {
            array_shift($rest);
        }
        return array_merge([$first], $rest);
    }

    /**
     * Where to cut when the conversation outgrows MAX_MESSAGES: everything up
     * to the start of the newest KEEP_MESSAGES (moved back to a person's
     * message, so a reply never travels without what it answered) is the part
     * to summarise. Counted on the messages as the browser holds them, so the
     * browser can drop the same ones.
     *
     * @param array<int,mixed> $messages
     * @return array{0:array<int,mixed>,1:array<int,mixed>} the old part and the part to keep
     */
    public static function split(array $messages): array
    {
        $messages = array_values($messages);
        $cut = max(0, count($messages) - self::KEEP_MESSAGES);
        while ($cut > 0 && $cut < count($messages) && !(is_array($messages[$cut]) && ($messages[$cut]['role'] ?? '') === 'user')) {
            $cut -= 1;
        }
        return [array_slice($messages, 0, $cut), array_slice($messages, $cut)];
    }

    /** @return array<string,mixed> */
    public static function capOutput(array $output): array
    {
        $encoded = (string) wp_json_encode($output);
        if (strlen($encoded) <= self::MAX_OUTPUT_CHARS) {
            return $output;
        }
        $budget = self::MAX_OUTPUT_CHARS;
        $capped = self::shrink($output, $budget);
        $capped['truncated'] = true;
        return $capped;
    }

    /** @return array<string,mixed>|null */
    private static function message(mixed $message): ?array
    {
        if (!is_array($message) || !is_string($message['role'] ?? null)) {
            return null;
        }
        switch ($message['role']) {
            case 'user':
                $text = is_string($message['text'] ?? null) ? mb_substr($message['text'], 0, self::MAX_TEXT_CHARS) : '';
                return $text === '' ? null : ['role' => 'user', 'text' => $text];
            case 'assistant':
                $calls = [];
                foreach ((array) ($message['calls'] ?? []) as $call) {
                    if (is_array($call) && is_string($call['id'] ?? null) && is_string($call['ability'] ?? null)) {
                        $calls[] = [
                            'ability' => $call['ability'],
                            'args' => is_array($call['args'] ?? null) && $call['args'] !== [] ? $call['args'] : new \stdClass(),
                            'id' => mb_substr($call['id'], 0, 40),
                            'why' => is_string($call['why'] ?? null) ? mb_substr($call['why'], 0, 500) : '',
                        ];
                    }
                }
                return [
                    'calls' => $calls,
                    'role' => 'assistant',
                    'text' => is_string($message['text'] ?? null) ? mb_substr($message['text'], 0, self::MAX_TEXT_CHARS) : '',
                ];
            case 'result':
                $results = [];
                foreach ((array) ($message['results'] ?? []) as $result) {
                    if (!is_array($result) || !is_string($result['id'] ?? null)) {
                        continue;
                    }
                    $one = ['id' => mb_substr($result['id'], 0, 40), 'ok' => (bool) ($result['ok'] ?? false)];
                    if (!empty($result['skipped'])) {
                        $one['skipped'] = true;
                    } elseif ($one['ok']) {
                        $output = self::capOutput(is_array($result['output'] ?? null) ? $result['output'] : []);
                        $one['output'] = $output === [] ? new \stdClass() : $output;
                    } else {
                        $one['error'] = is_string($result['error'] ?? null) ? mb_substr($result['error'], 0, 1000) : 'Failed';
                    }
                    $results[] = $one;
                }
                return ['results' => $results, 'role' => 'result'];
            default:
                return null;
        }
    }

    /** @param array<mixed> $value */
    private static function shrink(array $value, int &$budget): array
    {
        $out = [];
        foreach ($value as $key => $item) {
            if ($budget <= 0) {
                break;
            }
            if (is_array($item)) {
                $item = self::shrink($item, $budget);
            } elseif (is_string($item)) {
                $keep = max(0, min(mb_strlen($item), (int) ($budget / 2)));
                $item = $keep < mb_strlen($item) ? mb_substr($item, 0, $keep) . '…' : $item;
            }
            $out[$key] = $item;
            $budget -= strlen((string) wp_json_encode($item)) + strlen((string) $key) + 4;
        }
        return $out;
    }
}