// Session-grain usage from the CLI's own transcripts (novox/hq ADR 0054). The mature implementation
// reads `~/.claude/projects/<projDir>/<sessionId>.jsonl` and sums the token counts each assistant
// message reports; this ports the token extraction and DROPS the per-message account-attribution
// timeline — the nox (node,module) session has a fixed licence binding (port map "don't-map" #3), so
// there is nothing to attribute per message.
//
// The fields are ported from the port map: assistant lines carry
// `message.usage.{input_tokens,cache_creation_input_tokens,cache_read_input_tokens,output_tokens}`,
// `costUSD`, `message.model`, `timestamp`; user lines carry `cwd`, `gitBranch`.

import { createInterface } from "node:readline";
import { createReadStream } from "node:fs";

/** One session's totals — the session-grain usage row ADR 0054 fixes. */
export interface SessionUsage {
  sessionId: string;
  model: string | null;
  gitBranch: string | null;
  cwd: string | null;
  turns: number;
  inputTokens: number;
  cacheCreationTokens: number;
  cacheReadTokens: number;
  outputTokens: number;
  costUSD: number;
  startedAt: string | null;
  lastActive: string | null;
}

interface Line {
  type?: string;
  timestamp?: string;
  cwd?: string;
  gitBranch?: string;
  costUSD?: number;
  message?: {
    model?: string;
    usage?: {
      input_tokens?: number;
      cache_creation_input_tokens?: number;
      cache_read_input_tokens?: number;
      output_tokens?: number;
    };
  };
}

function empty(sessionId: string): SessionUsage {
  return {
    sessionId,
    model: null,
    gitBranch: null,
    cwd: null,
    turns: 0,
    inputTokens: 0,
    cacheCreationTokens: 0,
    cacheReadTokens: 0,
    outputTokens: 0,
    costUSD: 0,
    startedAt: null,
    lastActive: null,
  };
}

/** Fold one transcript line into a session's running totals. Pure, so it is tested on fixtures. */
export function foldLine(acc: SessionUsage, raw: string): SessionUsage {
  const line = parse(raw);
  if (!line) return acc;

  if (line.timestamp) {
    if (!acc.startedAt || line.timestamp < acc.startedAt) acc.startedAt = line.timestamp;
    if (!acc.lastActive || line.timestamp > acc.lastActive) acc.lastActive = line.timestamp;
  }
  if (line.type === "user") {
    if (line.cwd) acc.cwd = line.cwd;
    if (line.gitBranch) acc.gitBranch = line.gitBranch;
  }
  if (line.type === "assistant") {
    acc.turns += 1;
    const u = line.message?.usage ?? {};
    acc.inputTokens += u.input_tokens ?? 0;
    acc.cacheCreationTokens += u.cache_creation_input_tokens ?? 0;
    acc.cacheReadTokens += u.cache_read_input_tokens ?? 0;
    acc.outputTokens += u.output_tokens ?? 0;
    acc.costUSD += line.costUSD ?? 0;
    if (!acc.model && line.message?.model) acc.model = line.message.model;
  }
  return acc;
}

function parse(raw: string): Line | null {
  const trimmed = raw.trim();
  if (!trimmed) return null;
  try {
    return JSON.parse(trimmed) as Line;
  } catch {
    // A malformed line is skipped, never fatal: a transcript is an append-only log the CLI owns, and
    // a half-written last line is ordinary.
    return null;
  }
}

/** Sum a whole transcript string into one session's usage — the tested core of the streaming read. */
export function foldTranscript(sessionId: string, text: string): SessionUsage {
  return text.split("\n").reduce(foldLine, empty(sessionId));
}

/** Stream one `<sessionId>.jsonl` file line by line, so a large transcript never loads whole. */
export async function readSessionFile(path: string, sessionId: string): Promise<SessionUsage> {
  const acc = empty(sessionId);
  const rl = createInterface({ input: createReadStream(path), crlfDelay: Infinity });
  for await (const line of rl) foldLine(acc, line);
  return acc;
}