/**
 * Configuration loading for matrix-welcome.
 *
 * Users must never have to edit the installed source: `omp plugin install`
 * replaces the package tree on every upgrade. Settings therefore live in a JSON
 * file outside the package.
 *
 * Search order, first existing file wins:
 *   1. <cwd>/.omp/matrix-welcome.json          (project)
 *   2. <agent dir>/matrix-welcome.json         (user)
 *
 * The agent directory is `$PI_CODING_AGENT_DIR` when set, otherwise
 * `~/.omp/agent`, matching how omp resolves its own state directory.
 */
import { existsSync, readFileSync } from "node:fs";
import { homedir } from "node:os";
import { join } from "node:path";

export type AnimationCharset = "katakana" | "ascii";

export interface WelcomeConfig {
	/** Seconds before the screen dismisses itself. 0 = wait for a keypress. */
	countdown: number;
	/** Milliseconds between animation frames. Lower = faster rain. */
	frameDelayMs: number;
	/** Rows the screen occupies. "full" uses the whole terminal height. */
	height: "full" | number;
	/** Rain glyphs. "katakana" is classic, "ascii" is safest on odd terminals. */
	charset: AnimationCharset;
	/** How many recent sessions to list. */
	maxSessions: number;
	/** Chance per frame that a banner cell flickers into a rain glyph. */
	bannerFlicker: number;
	/** Rain density: fraction of columns carrying a drop at any time. */
	density: number;
	/** Text rendered in the block banner. Unsupported characters are skipped. */
	bannerText: string;
}

export const DEFAULT_CONFIG: WelcomeConfig = {
	countdown: 8,
	frameDelayMs: 70,
	height: "full",
	charset: "katakana",
	maxSessions: 4,
	bannerFlicker: 0.012,
	density: 0.9,
	bannerText: "OH-MY-PI",
};

export const CONFIG_FILENAME = "matrix-welcome.json";

export interface LoadedConfig {
	config: WelcomeConfig;
	/** Absolute path the config came from, or undefined when using defaults. */
	source?: string;
	/** Human-readable problems. Every entry means one field fell back. */
	warnings: string[];
}

export function getConfigCandidates(cwd: string): string[] {
	const agentDir =
		process.env.PI_CODING_AGENT_DIR?.trim() ||
		join(process.env.HOME ?? homedir(), ".omp", "agent");
	return [
		join(cwd, ".omp", CONFIG_FILENAME),
		join(agentDir, CONFIG_FILENAME),
	];
}

/** Reads one key without asserting a shape the compiler never checked. */
function readEntry(source: object, key: string): unknown {
	return key in source ? Reflect.get(source, key) : undefined;
}

function readNumber(
	source: object,
	key: string,
	min: number,
	max: number,
	warnings: string[],
): number | undefined {
	const value = readEntry(source, key);
	if (value === undefined) return undefined;
	if (typeof value !== "number" || !Number.isFinite(value)) {
		warnings.push(`${key}: expected a number, got ${JSON.stringify(value)}`);
		return undefined;
	}
	if (value < min || value > max) {
		warnings.push(`${key}: ${value} is outside ${min}..${max}`);
		return undefined;
	}
	return value;
}

export function applyOverrides(
	source: object,
	warnings: string[],
): WelcomeConfig {
	const config: WelcomeConfig = { ...DEFAULT_CONFIG };

	const countdown = readNumber(source, "countdown", 0, 600, warnings);
	if (countdown !== undefined) config.countdown = Math.round(countdown);

	const frameDelayMs = readNumber(source, "frameDelayMs", 16, 1000, warnings);
	if (frameDelayMs !== undefined) config.frameDelayMs = Math.round(frameDelayMs);

	const maxSessions = readNumber(source, "maxSessions", 0, 20, warnings);
	if (maxSessions !== undefined) config.maxSessions = Math.round(maxSessions);

	const bannerFlicker = readNumber(source, "bannerFlicker", 0, 1, warnings);
	if (bannerFlicker !== undefined) config.bannerFlicker = bannerFlicker;

	const density = readNumber(source, "density", 0, 1, warnings);
	if (density !== undefined) config.density = density;

	const height = readEntry(source, "height");
	if (height !== undefined) {
		if (height === "full") {
			config.height = "full";
		} else if (typeof height === "number" && Number.isFinite(height) && height >= 8) {
			config.height = Math.round(height);
		} else {
			warnings.push(`height: expected "full" or a number >= 8, got ${JSON.stringify(height)}`);
		}
	}

	const charset = readEntry(source, "charset");
	if (charset !== undefined) {
		if (charset === "katakana" || charset === "ascii") {
			config.charset = charset;
		} else {
			warnings.push(`charset: expected "katakana" or "ascii", got ${JSON.stringify(charset)}`);
		}
	}

	const bannerText = readEntry(source, "bannerText");
	if (bannerText !== undefined) {
		if (typeof bannerText === "string" && bannerText.length > 0 && bannerText.length <= 16) {
			config.bannerText = bannerText;
		} else {
			warnings.push(`bannerText: expected a string of 1..16 characters, got ${JSON.stringify(bannerText)}`);
		}
	}

	return config;
}

/**
 * Never throws and never returns a partial config: on any failure the defaults
 * stand and the reason is reported in `warnings`.
 */
export function loadConfig(cwd: string = process.cwd()): LoadedConfig {
	const warnings: string[] = [];

	for (const path of getConfigCandidates(cwd)) {
		if (!existsSync(path)) continue;

		let text: string;
		try {
			text = readFileSync(path, "utf8");
		} catch (error) {
			warnings.push(`${path}: unreadable (${String(error)})`);
			continue;
		}

		let parsed: unknown;
		try {
			parsed = JSON.parse(text);
		} catch (error) {
			warnings.push(`${path}: invalid JSON (${String(error)})`);
			continue;
		}

		if (typeof parsed !== "object" || parsed === null || Array.isArray(parsed)) {
			warnings.push(`${path}: expected a JSON object at the top level`);
			continue;
		}

		return { config: applyOverrides(parsed, warnings), source: path, warnings };
	}

	return { config: { ...DEFAULT_CONFIG }, warnings };
}