import type { TranscriptContent, TranscriptMessage } from "./types.ts";
import { tailJsonlLines, type JsonlTailState } from "./jsonl-tail.ts";

export type PiStreamMessage = {
  role: "user" | "assistant" | "toolResult";
  content: unknown;
};

export function projectPiMessageToTranscript(msg: PiStreamMessage): TranscriptMessage {
  const rawContent: unknown = msg.content;
  const content: TranscriptContent[] = typeof rawContent === "string"
    ? [{ type: "text", text: rawContent }]
    : (rawContent as TranscriptContent[]);
  if (msg.role === "toolResult") {
    const tr = msg as any;
    return {
      role: "toolResult",
      content,
      toolCallId: tr.toolCallId,
      toolName: tr.toolName,
      isError: tr.isError,
    };
  }
  return { role: msg.role, content };
}

export type PiTailState = JsonlTailState;

// Compute the byte offset that skips past `tailStartLine` lines of the given
// session content. tailPiSessionEntries treats `state.offset` as a byte position
// passed to readSync, so a UTF-16 character count (e.g., from `string.length`)
// would land mid-character for any non-ASCII content and either skip valid
// entries or re-emit a partial line as garbage.
export function computePiTailResumeOffset(raw: string, tailStartLine: number): number {
  if (tailStartLine <= 0) return 0;
  const lines = raw.split("\n");
  const fileBytes = Buffer.byteLength(raw, "utf8");
  let bytesConsumed = 0;
  for (let i = 0; i < Math.min(tailStartLine, lines.length); i++) {
    bytesConsumed += Buffer.byteLength(lines[i], "utf8") + 1;
  }
  return Math.min(bytesConsumed, fileBytes);
}

export interface PiTailDelta {
  messages: PiStreamMessage[];
  assistantMessages: PiStreamMessage[];
}

// Incrementally reads bytes after `state.offset` from the session jsonl,
// avoiding repeated whole-file reads on each pane-watch tick. Truncation is
// detected via `stat.size < state.offset` and resets state to re-read from 0.
export function tailPiSessionEntries(sessionFile: string, state: PiTailState): PiTailDelta {
  const { lines } = tailJsonlLines(sessionFile, state);

  const messages: PiStreamMessage[] = [];
  const assistantMessages: PiStreamMessage[] = [];

  for (const line of lines) {
    if (line.trim() === "") continue;
    let entry: any;
    try { entry = JSON.parse(line); } catch { continue; }
    if (entry.type === "message" && entry.message) {
      const msg = entry.message as PiStreamMessage;
      messages.push(msg);
      if (msg.role === "assistant") {
        assistantMessages.push(entry.message);
      }
    }
  }

  return { messages, assistantMessages };
}