import { SecretsManagerClient, GetSecretValueCommand } from '@aws-sdk/client-secrets-manager';
import {
  BedrockAgentRuntimeClient,
  InvokeAgentCommand,
} from '@aws-sdk/client-bedrock-agent-runtime';
import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocumentClient, PutCommand, QueryCommand } from '@aws-sdk/lib-dynamodb';

const secretsClient = new SecretsManagerClient({});
const bedrockClient = new BedrockAgentRuntimeClient({ region: process.env.REGION! });
const ddb = DynamoDBDocumentClient.from(new DynamoDBClient({}));

interface SlackCredentials {
  botToken: string;
  signingSecret: string;
}

interface ProcessorEvent {
  userId: string;
  channelId: string;
  text: string;
  ts: string;
  threadTs?: string;
}

// Cache the secret across warm invocations
let cachedCredentials: SlackCredentials | undefined;

async function getSlackCredentials(): Promise<SlackCredentials> {
  if (!cachedCredentials) {
    const res = await secretsClient.send(
      new GetSecretValueCommand({ SecretId: process.env.SLACK_SECRET_ARN! }),
    );
    cachedCredentials = JSON.parse(res.SecretString!) as SlackCredentials;
  }
  return cachedCredentials;
}

async function postToSlack(
  token: string,
  channel: string,
  text: string,
  threadTs?: string,
): Promise<void> {
  const body: Record<string, string> = { channel, text };
  if (threadTs) body.thread_ts = threadTs;

  const res = await fetch('https://slack.com/api/chat.postMessage', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: `Bearer ${token}`,
    },
    body: JSON.stringify(body),
  });

  if (!res.ok) throw new Error(`Slack HTTP error ${res.status}`);
  const data = (await res.json()) as { ok: boolean; error?: string };
  if (!data.ok) throw new Error(`Slack API error: ${data.error}`);
}

// Reuse the most recent Bedrock session if there's been activity in the last 30 minutes.
// This enables multi-turn conversation without re-introducing context each message.
async function resolveSessionId(userId: string): Promise<string> {
  const cutoff = new Date(Date.now() - 30 * 60 * 1000).toISOString();

  const result = await ddb.send(
    new QueryCommand({
      TableName: process.env.CONVERSATION_TABLE!,
      KeyConditionExpression: 'userId = :uid AND #ts > :cutoff',
      ExpressionAttributeNames: { '#ts': 'timestamp' },
      ExpressionAttributeValues: { ':uid': userId, ':cutoff': cutoff },
      Limit: 1,
      ScanIndexForward: false,
      ProjectionExpression: 'sessionId',
    }),
  );

  if (result.Items?.length && result.Items[0].sessionId) {
    return result.Items[0].sessionId as string;
  }

  return `${userId}-${Date.now()}`;
}

async function invokeAgent(sessionId: string, inputText: string): Promise<string> {
  const res = await bedrockClient.send(
    new InvokeAgentCommand({
      agentId: process.env.AGENT_ID!,
      agentAliasId: process.env.AGENT_ALIAS_ID!,
      sessionId,
      inputText,
    }),
  );

  let answer = '';
  if (res.completion) {
    for await (const event of res.completion) {
      if (event.chunk?.bytes) {
        answer += Buffer.from(event.chunk.bytes).toString('utf-8');
      }
    }
  }

  return answer.trim() || 'I was unable to generate a response. Please try again.';
}

export const handler = async (event: ProcessorEvent): Promise<void> => {
  const { userId, channelId, text, ts, threadTs } = event;

  const [credentials, sessionId] = await Promise.all([
    getSlackCredentials(),
    resolveSessionId(userId),
  ]);

  let answer: string;
  try {
    answer = await invokeAgent(sessionId, text);
  } catch (err) {
    console.error('Bedrock agent invocation failed:', err);
    answer = 'Sorry, I encountered an error processing your request. Please try again in a moment.';
  }

  await postToSlack(credentials.botToken, channelId, answer, threadTs ?? ts);

  const now = new Date().toISOString();
  const ttl = Math.floor(Date.now() / 1000) + 90 * 24 * 60 * 60; // 90-day TTL

  await ddb.send(
    new PutCommand({
      TableName: process.env.CONVERSATION_TABLE!,
      Item: {
        userId,
        timestamp: now,
        sessionId,
        question: text,
        answer,
        channelId,
        messageTs: ts,
        ttl,
      },
    }),
  );
};