/**
 * config.ts
 * ---------
 * Runtime configuration types, defaults, the layered resolver, and the
 * default config-file path.
 *
 * The keeper is driven by a single `Config` object that carries every
 * tunable it cares about, including the `verbose` flag. Defaults live in
 * `DEFAULT_CONFIG`; CLI and config-file overrides are layered on top by
 * `resolveConfig` rather than mutating the defaults, so the defaults stay
 * genuinely constant and the resolved config stays structurally typed.
 *
 * All numeric `Config` fields are in their internal units (ms, pixels).
 * The CLI and config file expose the time-valued fields in seconds for
 * ergonomics; `resolveConfig` performs the seconds->ms conversion at the
 * boundary so downstream code never has to think about it.
 *
 * Layering precedence (highest wins):
 *   CLI overrides  >  file overrides  >  DEFAULT_CONFIG
 */

import { join } from "node:path";

/**
 * The shape of a resolved runtime configuration. `readonly` to make
 * accidental mutation a type error.
 *
 * - `moveInterval`  — how long the mouse must be idle (no real movement)
 *                     before a synthetic sweep is triggered. Milliseconds.
 * - `checkInterval` — cadence of the idleness poll in the main loop.
 *                     Milliseconds.
 * - `stepDelay`     — pause between individual synthetic mouse steps inside
 *                     a sweep. Also the window in which the user can
 *                     "interrupt" by moving the cursor. Milliseconds.
 * - `stepCount`     — number of pixel-steps in a single sweep. Pixels.
 * - `verbose`       — whether per-sweep / interrupt / bounds events are
 *                     logged. The startup banner is always printed.
 */
export interface Config {
    readonly moveInterval: number;
    readonly checkInterval: number;
    readonly stepDelay: number;
    readonly stepCount: number;
    readonly verbose: boolean;
}

/**
 * Built-in defaults used when neither the CLI nor the config file supplies
 * a value for a given field.
 */
export const DEFAULT_CONFIG: Config = {
    moveInterval: 4 * 60 * 1000, // 4 minutes in milliseconds
    checkInterval: 10 * 1000,    // Check every 10 seconds
    stepDelay: 50,               // ms between mouse steps
    stepCount: 250,              // pixels to move per sweep
    verbose: false,              // quiet by default; startup banner still prints
};

/**
 * Common shape for override layers (CLI args and config-file content).
 *
 * `undefined` means "this layer doesn't supply a value"; the next layer
 * down (file overrides, then DEFAULT_CONFIG) is consulted in that case.
 *
 * Numeric fields are in CLI / config-file units:
 *   moveInterval, checkInterval — seconds
 *   stepDelay                   — milliseconds
 *   stepCount                   — pixels
 *
 * `verbose` is `boolean | undefined` like the numeric fields, so all five
 * fields share the same "first defined value wins" precedence logic.
 *
 * For the CLI specifically, `verbose` is `undefined` when `-V/--verbose`
 * was not passed and `true` when it was. There is no CLI off-switch
 * today, so CLI `false` doesn't occur — a file-set `verbose: true` cannot
 * be overridden back to false from the command line (see the Configuration
 * section of the README).
 */
export interface ConfigOverrides {
    readonly moveInterval: number | undefined;
    readonly checkInterval: number | undefined;
    readonly stepDelay: number | undefined;
    readonly stepCount: number | undefined;
    readonly verbose: boolean | undefined;
}

/**
 * Resolve the default config-file path per the XDG Base Directory Spec.
 * Honors `$XDG_CONFIG_HOME` if set; otherwise falls back to
 * `$HOME/.config`. The file itself is always `move/config.json` under
 * that base.
 *
 * Computed at call time (not at module load) so tests can override
 * `XDG_CONFIG_HOME` after import.
 */
export function defaultConfigPath(): string {
    const xdg = process.env.XDG_CONFIG_HOME;
    if (xdg && xdg.length > 0) {
        return join(xdg, "move", "config.json");
    }
    const home = process.env.HOME ?? "";
    return join(home, ".config", "move", "config.json");
}

/**
 * Overlay file overrides (lowest priority) and CLI overrides (highest)
 * on top of `DEFAULT_CONFIG` and return a resolved `Config`. Time-valued
 * numeric inputs are in seconds; this is where they're converted to
 * milliseconds for internal use.
 *
 * For each field, the first layer that supplies a defined value wins:
 *   CLI -> file -> DEFAULT_CONFIG
 */
export function resolveConfig(file: ConfigOverrides | null, cli: ConfigOverrides): Config {
    const pickSeconds = (
        cliVal: number | undefined,
        fileVal: number | undefined,
        fallbackMs: number,
    ): number => {
        if (cliVal !== undefined) return cliVal * 1000;
        if (fileVal !== undefined) return fileVal * 1000;
        return fallbackMs;
    };

    const pickRaw = <T>(
        cliVal: T | undefined,
        fileVal: T | undefined,
        fallback: T,
    ): T => {
        if (cliVal !== undefined) return cliVal;
        if (fileVal !== undefined) return fileVal;
        return fallback;
    };

    return {
        moveInterval:  pickSeconds(cli.moveInterval,  file?.moveInterval,  DEFAULT_CONFIG.moveInterval),
        checkInterval: pickSeconds(cli.checkInterval, file?.checkInterval, DEFAULT_CONFIG.checkInterval),
        stepDelay:     pickRaw(cli.stepDelay,         file?.stepDelay,     DEFAULT_CONFIG.stepDelay),
        stepCount:     pickRaw(cli.stepCount,         file?.stepCount,     DEFAULT_CONFIG.stepCount),
        verbose:       pickRaw(cli.verbose,           file?.verbose,       DEFAULT_CONFIG.verbose),
    };
}