import fs from "node:fs";
import os from "node:os";
import path from "node:path";

import { resolveSessionTranscriptPath } from "../config/sessions.js";

export function readSessionMessages(
  sessionId: string,
  storePath: string | undefined,
  sessionFile?: string,
): unknown[] {
  const candidates = resolveSessionTranscriptCandidates(sessionId, storePath, sessionFile);

  const filePath = candidates.find((p) => fs.existsSync(p));
  if (!filePath) return [];

  const lines = fs.readFileSync(filePath, "utf-8").split(/\r?\n/);
  const messages: unknown[] = [];
  for (const line of lines) {
    if (!line.trim()) continue;
    try {
      const parsed = JSON.parse(line);
      if (parsed?.message) {
        messages.push(parsed.message);
      }
    } catch {
      // ignore bad lines
    }
  }
  return messages;
}

export function resolveSessionTranscriptCandidates(
  sessionId: string,
  storePath: string | undefined,
  sessionFile?: string,
  agentId?: string,
): string[] {
  const candidates: string[] = [];
  if (sessionFile) candidates.push(sessionFile);
  if (storePath) {
    const dir = path.dirname(storePath);
    candidates.push(path.join(dir, `${sessionId}.jsonl`));
  }
  if (agentId) {
    candidates.push(resolveSessionTranscriptPath(sessionId, agentId));
  }
  candidates.push(path.join(os.homedir(), ".clawdbot", "sessions", `${sessionId}.jsonl`));
  return candidates;
}

export function archiveFileOnDisk(filePath: string, reason: string): string {
  const ts = new Date().toISOString().replaceAll(":", "-");
  const archived = `${filePath}.${reason}.${ts}`;
  fs.renameSync(filePath, archived);
  return archived;
}

function jsonUtf8Bytes(value: unknown): number {
  try {
    return Buffer.byteLength(JSON.stringify(value), "utf8");
  } catch {
    return Buffer.byteLength(String(value), "utf8");
  }
}

export function capArrayByJsonBytes<T>(
  items: T[],
  maxBytes: number,
): { items: T[]; bytes: number } {
  if (items.length === 0) return { items, bytes: 2 };
  const parts = items.map((item) => jsonUtf8Bytes(item));
  let bytes = 2 + parts.reduce((a, b) => a + b, 0) + (items.length - 1);
  let start = 0;
  while (bytes > maxBytes && start < items.length - 1) {
    bytes -= parts[start] + 1;
    start += 1;
  }
  const next = start > 0 ? items.slice(start) : items;
  return { items: next, bytes };
}

const MAX_LINES_TO_SCAN = 10;

type TranscriptMessage = {
  role?: string;
  content?: string | Array<{ type: string; text?: string }>;
};

function extractTextFromContent(content: TranscriptMessage["content"]): string | null {
  if (typeof content === "string") return content.trim() || null;
  if (!Array.isArray(content)) return null;
  for (const part of content) {
    if (!part || typeof part.text !== "string") continue;
    if (part.type === "text" || part.type === "output_text" || part.type === "input_text") {
      const trimmed = part.text.trim();
      if (trimmed) return trimmed;
    }
  }
  return null;
}

export function readFirstUserMessageFromTranscript(
  sessionId: string,
  storePath: string | undefined,
  sessionFile?: string,
  agentId?: string,
): string | null {
  const candidates = resolveSessionTranscriptCandidates(sessionId, storePath, sessionFile, agentId);
  const filePath = candidates.find((p) => fs.existsSync(p));
  if (!filePath) return null;

  let fd: number | null = null;
  try {
    fd = fs.openSync(filePath, "r");
    const buf = Buffer.alloc(8192);
    const bytesRead = fs.readSync(fd, buf, 0, buf.length, 0);
    if (bytesRead === 0) return null;
    const chunk = buf.toString("utf-8", 0, bytesRead);
    const lines = chunk.split(/\r?\n/).slice(0, MAX_LINES_TO_SCAN);

    for (const line of lines) {
      if (!line.trim()) continue;
      try {
        const parsed = JSON.parse(line);
        const msg = parsed?.message as TranscriptMessage | undefined;
        if (msg?.role === "user") {
          const text = extractTextFromContent(msg.content);
          if (text) return text;
        }
      } catch {
        // skip malformed lines
      }
    }
  } catch {
    // file read error
  } finally {
    if (fd !== null) fs.closeSync(fd);
  }
  return null;
}

const LAST_MSG_MAX_BYTES = 16384;
const LAST_MSG_MAX_LINES = 20;

export function readLastMessagePreviewFromTranscript(
  sessionId: string,
  storePath: string | undefined,
  sessionFile?: string,
  agentId?: string,
): string | null {
  const candidates = resolveSessionTranscriptCandidates(sessionId, storePath, sessionFile, agentId);
  const filePath = candidates.find((p) => fs.existsSync(p));
  if (!filePath) return null;

  let fd: number | null = null;
  try {
    fd = fs.openSync(filePath, "r");
    const stat = fs.fstatSync(fd);
    const size = stat.size;
    if (size === 0) return null;

    const readStart = Math.max(0, size - LAST_MSG_MAX_BYTES);
    const readLen = Math.min(size, LAST_MSG_MAX_BYTES);
    const buf = Buffer.alloc(readLen);
    fs.readSync(fd, buf, 0, readLen, readStart);

    const chunk = buf.toString("utf-8");
    const lines = chunk.split(/\r?\n/).filter((l) => l.trim());
    const tailLines = lines.slice(-LAST_MSG_MAX_LINES);

    for (let i = tailLines.length - 1; i >= 0; i--) {
      const line = tailLines[i];
      try {
        const parsed = JSON.parse(line);
        const msg = parsed?.message as TranscriptMessage | undefined;
        if (msg?.role === "user" || msg?.role === "assistant") {
          const text = extractTextFromContent(msg.content);
          if (text) return text;
        }
      } catch {
        // skip malformed
      }
    }
  } catch {
    // file error
  } finally {
    if (fd !== null) fs.closeSync(fd);
  }
  return null;
}