/**
 * keeper.ts
 * ---------
 * The "Teams Status Keeper" behavior: the idle-watch loop plus the
 * per-sweep glue that ties a movement strategy to the execution driver.
 *
 * The mechanics are split across three seams so this file stays small and
 * the interesting parts stay testable:
 *   - `device.ts`     — the nut.js I/O boundary (injected here).
 *   - `strategies.ts` — pure "where to move" pattern generators.
 *   - `executor.ts`   — the "how to move" driver (on-screen reflection,
 *                       timing, interrupt detection, restore).
 *
 * `runKeeper` takes an optional `Device` so tests can drive the loop with a
 * fake; production supplies the nut.js device. Importing this module is
 * side-effect-free: nut.js isn't touched until `createNutDevice()` runs.
 *
 * Logging policy:
 *  - The startup banner in `runKeeper` is unconditional so the user always
 *    sees the process is alive.
 *  - Per-sweep / interrupt lines are gated by `config.verbose` (see
 *    `makeLogger`). Errors stay on `console.error`, raised by the entry
 *    point on unhandled rejection.
 */

import { createNutDevice, type Device, type Point } from "./device.ts";
import { executePath, type Logger, type SweepOutcome } from "./executor.ts";
import {
    createRandomPicker,
    DEFAULT_PATTERN,
    RANDOM_PATTERN,
    STRATEGIES,
    type MoveContext,
    type MovementStrategy,
} from "./strategies.ts";

import type { Config } from "./config.ts";

/**
 * Build a verbose-gated `Logger`. `info` is unconditional; `event` only
 * fires when the caller asked for verbose output. Returning a small object
 * keeps call sites free of `if (verbose)` noise at every log line.
 */
function makeLogger(verbose: boolean): Logger {
    return {
        info: (msg: string): void => {
            console.log(msg);
        },
        event: (msg: string): void => {
            if (verbose) console.log(msg);
        },
    };
}

/**
 * Perform synthetic mouse activity once the keeper decides the cursor is
 * idle.
 *
 * Snapshots the screen (re-read every call so monitor changes are handled)
 * and selects the configured strategy from the registry. An unknown
 * `config.pattern` falls back to the default strategy defensively; validation
 * at the CLI / config-file boundary should prevent that from ever happening.
 *
 * `pattern: "random"` isn't a registry key — it asks for a fresh pattern per
 * sweep, so `pickRandom` supplies one here. The pick happens once, before the
 * loop-mode branch below, which is what makes a random selection hold for an
 * entire loop run rather than changing under the user mid-run; the picker's
 * own no-repeat memory then spans sweeps, since the keeper holds one picker
 * for the life of the process. Because the pick is a real strategy, the log
 * lines below and in `executePath` name the concrete pattern, not "random".
 *
 * Single-sweep mode (`config.loop === false`) runs exactly one sweep via
 * `executePath`, which owns on-screen reflection, pacing, interrupt
 * detection, and restore-on-clean — unchanged from before loop mode existed.
 *
 * Loop mode (`config.loop === true`) keeps the cursor moving until the
 * user moves the mouse (or Ctrl+C). The cursor is never restored between
 * iterations (`restore: false`). Patterns that define an infinite `loopPath`
 * (`line`, `diagonal`) run it once and are stopped only by interruption; the
 * rest have their finite `path` chained, re-read from the cursor's current
 * position each cycle. Per-cycle event logs are suppressed to avoid unbounded
 * output — one line brackets the run at each end.
 */
async function simulateActivity(
    config: Config,
    log: Logger,
    device: Device,
    pickRandom: () => MovementStrategy,
): Promise<void> {
    const width: number = await device.width();
    const height: number = await device.height();
    const strategy: MovementStrategy =
        config.pattern === RANDOM_PATTERN
            ? pickRandom()
            : (STRATEGIES[config.pattern] ?? STRATEGIES[DEFAULT_PATTERN]!);

    if (!config.loop) {
        const start: Point = await device.getPosition();
        const ctx: MoveContext = { start, width, height, rng: Math.random };
        await executePath(strategy, ctx, device, log, config);
        return;
    }

    log.event(`Loop mode (${strategy.name}); repeating until you move the mouse.`);
    const cycleLog: Logger = { info: log.info, event: (): void => {} };
    const loopOpts = { restore: false, loop: true };

    let cycles = 0;
    let outcome: SweepOutcome;
    do {
        const start: Point = await device.getPosition();
        const ctx: MoveContext = { start, width, height, rng: Math.random };
        outcome = await executePath(strategy, ctx, device, cycleLog, config, loopOpts);
        cycles++;
        // Spin guard for the chained-repeat path: a finite strategy that
        // yielded nothing would otherwise return "completed" instantly in a
        // tight loop. Sleeping one stepDelay makes that harmless. An infinite
        // loopPath never returns "completed", so this branch is skipped there.
        if (outcome === "completed") await device.sleep(config.stepDelay);
    } while (outcome === "completed");

    log.event(`Loop run ended after ${cycles} cycle(s): ${outcome}.`);
}

/**
 * Main idle-watch loop. Runs forever; exits only on `Ctrl+C` (SIGINT) or
 * an unhandled rejection caught by the entry point.
 *
 * Algorithm:
 *  - Track the last known cursor position (`lastPos`) and the timestamp of
 *    the last observed real user movement (`lastActivity`).
 *  - Every `config.checkInterval`:
 *      * If the cursor moved since the last check, that's real user
 *        activity: reset `lastActivity` and `lastPos`, skip the rest.
 *      * Otherwise, if it's been at least `config.moveInterval` since the
 *        last real activity, fire a synthetic sweep, then reset the
 *        idleness clock so we wait another full `moveInterval` before
 *        firing again.
 *
 * `simulateActivity` (via `executePath`) is designed so its own synthetic
 * movement never counts as real activity: on a clean sweep it restores the
 * cursor, and on a user-interrupted sweep the next iteration sees the
 * user's new position and correctly resets the clock.
 *
 * @param config     - Resolved runtime config.
 * @param device     - I/O device; defaults to the production nut.js device.
 * @param pickRandom - Supplies a strategy when `config.pattern` is `random`.
 *                     Created once here (not per sweep) so its no-repeat
 *                     memory spans the whole run; injectable so tests can
 *                     drive a deterministic sequence.
 */
export async function runKeeper(
    config: Config,
    device?: Device,
    pickRandom: () => MovementStrategy = createRandomPicker(),
): Promise<void> {
    const dev: Device = device ?? (await createNutDevice());

    const log = makeLogger(config.verbose);
    log.info("Teams Status Keeper started. Press Ctrl+C to stop.");

    let lastPos: Point = await dev.getPosition();
    let lastActivity: number = Date.now();

    while (true) {
        await dev.sleep(config.checkInterval);
        const pos: Point = await dev.getPosition();
        const now: number = Date.now();

        if (pos.x !== lastPos.x || pos.y !== lastPos.y) {
            // Real user activity since the last check; reset the idleness clock.
            lastActivity = now;
            lastPos = pos;
            continue;
        }

        if (now - lastActivity >= config.moveInterval) {
            await simulateActivity(config, log, dev, pickRandom);
            // The sweep either restored the cursor to its start (clean) or
            // left it where the user moved it (interrupt). Either way, reset
            // the clock and require another full moveInterval of inactivity
            // before firing again.
            lastActivity = Date.now();
            // Re-sync lastPos to where the cursor actually ended. After a
            // clean sweep this is a no-op (it was restored to start). After
            // an interrupt it snaps lastPos to the user's position, so the
            // next poll doesn't re-read that same displacement and count it a
            // second time as fresh activity.
            lastPos = await dev.getPosition();
        }
    }
}