idx-cli/docs/DESIGN.md

System Design: idx-core and its frontends

Status: Accepted 2026-10-14. Released in v0.3.0; phases 0-5 done.

Goal

Turn idx-cli's data layer into idx-core, a library that is the single way this project retrieves Indonesian market, financial, and investor data. The CLI, an MCP server, and later an HTTP API become thin frontends over it.

Non-goals for now: new data sources, a hosted service, async rewrites of the provider clients.

Architecture

 Upstreams                 idx-core (library)                     Frontends
┌──────────────┐   ┌──────────────────────────────────────┐   ┌──────────────┐
│ MSN Finance  │──▶│ sources/    HTTP clients + parsers    │   │ idx-cli      │
│ Yahoo        │──▶│ cache/      TTL, offline, stale       │──▶│  clap, table │
│ IDX / KSEI   │──▶│ store/      ownership SQLite          │   ├──────────────┤
└──────────────┘   │ market/     quotes, history, screen   │──▶│ idx-mcp      │
                   │ financial/  fundamentals, reports     │   │  MCP tools   │
                   │ investor/   ownership queries + sync  │   ├──────────────┤
                   │ analysis/   technical, fundamental    │──▶│ idx-api      │
                   └──────────────────────────────────────┘   │  (later)     │
                                                              └──────────────┘

Rule: frontends parse input and render output. Every fetch, cache decision, filter, sort, and calculation lives in idx-core.

Data Domains

Domain	Data	Source today	Status
Market	quotes, OHLCV history, screener	MSN (default), Yahoo (OHLCV)	shipped
Market	IHSG index, breadth, movers, sectors	not chosen yet	ROADMAP.md
Financial	key ratios, statements, earnings, profile	MSN	shipped (single-period statements)
Financial	sentiment, insights, news	MSN	shipped
Investor	KSEI holders above 1%, entity holdings, changes, concentration, cross-holders, graph	IDX XLSX (legacy PDF), synced snapshot	shipped
Investor	institutional holders (Bing)	schema only	ingest unsupported
Analysis	technical signals, growth/valuation/risk	derived locally	shipped

Two access patterns, and the core API should keep them visibly separate:

• Live data (market, financial): fetched from upstreams, cached on disk by TTL.
• Local data (investor): read from a local SQLite database that is populated by sync or import. Queries never touch the network.

All upstreams are unofficial or scraped. They change without notice, rate limit datacenter IPs (Yahoo 429), and sit behind Cloudflare (IDX 403). The core must report which source and how fresh each result is, and must never present stale or fallback data as current.

idx-core API

A single entry point holds configuration, providers, cache, and the DB path. Domain methods hang off it.

let idx = Idx::new(CoreConfig::load()?)?;   // provider, TTLs, cache dir; no output settings
let policy = CachePolicy::Default;

// market
let quotes: Vec<Fetched<Quote>> = idx.market().quotes(&["BBCA", "BBRI"], policy)?;
let source = idx.market().history_source(None);   // which provider serves history
let candles: Fetched<Vec<Ohlc>> =
    idx.market().history("BBCA", &Period::ThreeMonths, &Interval::Day, source, policy)?;
let screen: Fetched<Vec<Quote>> = idx.market().screen(&ScreenQuery { filter, region, limit }, policy)?;

// financial
let report: Fetched<FinancialStatements> =
    idx.financial().statements("BBCA", &StatementFilter::all(), policy)?;
let earnings: Fetched<EarningsReport> =
    idx.financial().earnings("BBCA", EarningsFilter::default(), policy)?;

// analysis (fetches its own inputs through the same cache)
let tech: Fetched<TechnicalReport> = idx.analysis().technical("BBCA", source, policy)?;
let compared: Comparison = idx.analysis().compare(&["BBCA", "BBRI"], policy)?;

// investor (local DB)
let holders: TickerOwnership = idx.investor().ticker("BBCA")?;
let status: OwnershipStatus = idx.investor().status()?;      // releases, latest as-of, empty?
let sync: OwnershipSyncResult = idx.investor().sync(SyncOptions::default())?;

Key decisions:

• Blocking API. ureq and rusqlite are blocking, and so is the CLI. Async frontends (MCP, HTTP) call core through spawn_blocking. Revisit only if an HTTP API needs high concurrency.
• Fetched<T> envelope for live data: { data, source, fetched_at, stale }, so agents and API clients can see freshness. idx-core still emits the stale-cache warnings through runtime (which set_quiet silences) so CLI stderr stays identical.
• CachePolicy: Default | Offline | Refresh replaces the --offline / --no-cache flag handling now spread through cli/stocks.rs.
• Explicit configuration. CoreConfig::load() is the one place idx-core reads provider, exchange, and TTL settings from config.toml and IDX_*; other frontends and tests construct CoreConfig directly (cache_dir overrides the XDG default). Remaining environment hooks: XDG paths for the config file and ownership DB, IDX_CURL_IMPERSONATE_BIN, the IDX discovery URL overrides, and the testing-only mock variables.
• Mock provider behind a testing feature. Done: MockProvider and the embedded MSN fixtures compile only with idx-core's testing feature, which idx-cli enables as a dev-dependency.
• Typed inputs. Screener filters, regions, statement and earnings filters become enums with FromStr, so validation is identical across frontends.

What Moves Out of crates/idx-cli/src/cli/

From	To
fetch_with_cache, cache_bucket, offline/stale handling (cli/stocks.rs)	idx-core cache layer, behind CachePolicy
build_technical_report, fetch_fundamental_analysis_report	analysis
filter_financial_statements, filter_earnings_report	financial
screener_filter_key, screener_region_key, sort_screener_quotes, full-list fetch	market::screen
ownership command orchestration (cli/ownership.rs)	investor
IdxConfig.output, no_color	stay in idx-cli

Done in phase 3: cli/stocks.rs and cli/ownership.rs are argument parsing, one idx-core call, and rendering.

Error Model

IdxError and its stable codes (SYMBOLNOTFOUND, NOMARKETDATA, RATELIMITED, UNSUPPORTED, INVALIDINPUT, OFFLINE, CACHEMISS, HTTP, ...) live in core. Each frontend maps them once:

Frontend	Mapping
CLI	unchanged: stderr, JSON {error, code, message} in JSON mode, non-zero exit
MCP	tool result with isError: true and the same {code, message} body
HTTP	status by class (INVALIDINPUT 400, SYMBOLNOTFOUND 404, RATELIMITED 429, upstream failures 502) plus the same body

Agent-Native CLI Output

Agents mostly drive the CLI through a shell and compose it with jq, grep, sed, Python, and other commands. The CLI should be a well-behaved Unix filter first and a pretty terminal tool second.

Output resolution

-o flag > IDX_OUTPUT > config.toml > auto. Auto picks:

• stdout is a terminal: table
• stdout is a pipe, file, or captured by a harness: json

idx cannot tell whether an agent is calling it, only whether stdout is a terminal (std::io::IsTerminal). Agent harnesses capture output, so they get JSON with no flag. Two edge cases, both handled by the explicit overrides:

• a human piping to less or grep gets JSON; use -o table
• a harness that runs commands inside a pseudo-terminal gets tables; set IDX_OUTPUT=json in its environment

Formats

Format	Shape	Use
table	human-readable	terminals
json	one document; pretty on a terminal, compact otherwise	default for pipes; jq, json.load
jsonl	list results: one record per line; single objects: one line	head, grep, streaming, pandas.read_json(..., lines=True)

Measured on fixtures, table output is 2-5x the bytes of JSON, and compact JSON is another 20-30% smaller than pretty JSON.

Composability contract

• stdout carries only data; diagnostics and warnings go to stderr. Already true.

• Errors in json/jsonl mode are one JSON object on stderr with stdout empty. Already true.

• No ANSI color when stdout is not a terminal. Today some table headers emit bold codes even when piped.

• stocks quote and stocks compare accept - to read symbols from stdin, separated by whitespace or commas: idx stocks screen --filter low-pe | jq -r '.[].symbol' | idx stocks compare -

• Exit codes by error class (today every error exits 1):

  Exit	Meaning	Codes
  0	success, including partial compare results
  1	other failure	IO, DATABASEERROR, PARSEERROR, ...
  2	invalid usage or input	clap errors, INVALIDINPUT, CONFIGERROR
  3	not found or no data	SYMBOLNOTFOUND, NOMARKETDATA, CACHEMISS
  4	upstream unavailable or blocked, retry later	HTTP, RATELIMITED, PROVIDERUNAVAILABLE, OFFLINE, AUTHERROR, UPSTREAMBLOCKED
  5	unsupported	UNSUPPORTED

• JSON keeps today's top-level shape: no {data, meta} wrapper, so jq paths stay short and JSONL works per record. Freshness metadata (Fetched<T>) is exposed by MCP and the API; the CLI keeps its stderr stale-cache warning.

• Field names, units (basis points, whole IDR, WIB timestamps), and nullability are part of the contract and documented in docs/ARCHITECTURE.md.

Examples:

idx stocks quote BBCA BBRI | jq -r '.[] | "\(.symbol) \(.price)"'
idx -o jsonl stocks history BBCA --period 1y | tail -5
idx ownership ticker BBCA | jq '.holders | map(select(.percentage_bps > 500))'
idx -o jsonl stocks screen --filter top-performers \
  | python -c 'import sys, json; [print(json.loads(l)["symbol"]) for l in sys.stdin]'

This is a breaking change for anyone parsing table output from a pipe. Ship it in a minor version with a release note; general.output = "table" restores the old default.

Frontend: idx-mcp

Stdio transport first, using the rmcp crate. Read-only by default.

Tools are grouped by question rather than mirroring every CLI command, which keeps the tool list short for agents:

Tool	Inputs	Backed by
get_quotes	symbols[]	market().quotes
get_price_history	symbol, period, interval	market().history
screen_stocks	filter, region, limit	market().screen
get_company	symbol, sections[] (profile, financials, earnings, sentiment, insights, news)	financial()
analyze_stock	symbol, kinds[] (technical, growth, valuation, risk)	analysis()
compare_stocks	symbols[]	analysis()
get_shareholders	ticker	investor().ticker
get_investor_holdings	entity	investor().entity
search_investors	query	investor().search
get_ownership_changes	from, to, ticker?	investor().changes
ownership_status	none	investor().status

Ownership bootstrap: if the local DB is empty, investor tools return a NOMARKETDATA error telling the agent to call ownership_sync. That tool is listed only when the server runs with --allow-sync, because it downloads several MB.

As built (phase 4):

• Live tools return Fetched<T> objects; get_quotes wraps its list as {quotes}. get_company and analyze_stock return one key per section (default: all) and list failed sections under errors, failing only if every section fails.
• get_ownership_changes returns at most limit rows (default 200) with the full count in total.
• Each call runs on a blocking thread with a fresh Idx, so tools share the CLI's config, cache, and database. With a shared cache, tool data equals the CLI's JSON value for value (checked live for every tool); object keys come out sorted.
• crates/idx-mcp/tests/mcp.rs drives the binary over stdio JSON-RPC with the mock provider; nix flake check also smoke-tests the packaged server.

Frontend: idx-api (later)

An HTTP server over the same core, e.g. GET /v1/stocks/{symbol}/quote. Before building it, decide whether it is self-hosted only. Publicly re-serving MSN, Yahoo, or IDX data raises terms-of-use and rate-limit questions that a local CLI does not.

Packaging

Cargo workspace (this repo)
├── crates/idx-core   library, published to crates.io
├── crates/idx-cli    binary `idx`  (package name unchanged)
├── crates/idx-mcp    binary `idx-mcp`
npm/
├── idx-cli           existing wrapper
└── idx-mcp           same postinstall download + SHA256SUMS

• One version for every crate and npm package, released from one vX.Y.Z tag. Release assets add idx-mcp-<platform> next to the existing idx-<platform>.
• Nix: packages.default (idx) and packages.idx-mcp; both run through nix flake check.
• The names idx-core, idx-mcp, and idx-api were free on crates.io and npm on 2026-10-14.
• Bundling later is a packaging choice: an idx mcp subcommand behind a Cargo feature, or an npm package that installs both binaries.

Parity and Verification

The refactor must keep every shipped command's output identical. Two gates enforce that, and neither may be skipped or weakened to make a change pass.

Golden output tests (offline, in nix flake check)

Before any refactor code lands, capture the current CLI as golden files:

• every stocks, ownership, config, cache, version, and completions command, in both table and json, against the mock provider fixtures and a fixture-built ownership DB
• the documented error cases (invalid input, unsupported provider, offline without cache, empty ownership DB)
• cases listed in tests/golden/cases.toml; each result stored as tests/golden/<case>.<format>.golden (exit code, stdout, stderr) and compared byte for byte by one data-driven test in tests/golden.rs

Regenerating goldens (UPDATE_GOLDEN=1) is only allowed for an intentional, reviewed output change, and the diff must be in the same commit with the reason in the message. Phases 2-4 must not change any golden file. Phase 1 changes only what it documents: default format resolution, JSON whitespace when piped, ANSI color when piped (table output emits bold headers into pipes today), and exit codes; JSON content and table text stay identical.

tests/cli.rs stays the behavioral suite and must keep passing unchanged.

Live A/B check (opt-in, before merging the refactor)

Fixtures cannot show that the new code still talks to real upstreams correctly. scripts/live-smoke.sh --compare <old-idx> runs every command with the pre-refactor binary and the new binary back to back against live MSN, Yahoo, and IDX, then compares:

• exit codes and JSON structure (keys and types) for every command
• values for slow-moving data (profile, financials, earnings, ownership)
• volatile fields (price, change, volume, news items) for type only

Any coding agent that changes CLI behavior must run the live check and report its summary before calling the work done. IDX ownership cases need a network that Cloudflare does not block; when they return 403, report that explicitly instead of treating it as a pass.

Migration Plan

Work happens on the refactor/idx-core branch. Each phase is its own commit series with nix flake check -L green; main receives the branch only after every phase passes both parity gates.

0. Golden baseline. Add tests/golden.rs and the golden files from the current main, plus live-smoke.sh --compare. No source changes.
1. Agent-native output. auto output, compact JSON, jsonl, stdin -, and exit-code classes. Touches only config.rs, output/, and main.rs.
2. Workspace split, no behavior change. Move code into crates/idx-core and crates/idx-cli.
3. Pull logic into core. Move the table above into core, add CachePolicy, Fetched<T>, CoreConfig, and typed filter enums.
4. idx-mcp. Implement the tool table over stdio, with fixture-backed tests.
5. Release. Workspace publishing, npm idx-mcp, release assets, flake package.

Open Questions

1. Are the exit-code classes right, and should compare with partial results still exit 0?
2. Which source should back IHSG index, breadth, and sector data?
3. Is idx-api self-hosted only?