import { SOURCE_PRIORITY } from "./rules/constants.js";
import { defaultConfig } from "./rules/engine.js";
import type { PiRulesConfig, RuleSource } from "./rules/types.js";

export function configFromEnvironment(env: NodeJS.ProcessEnv = process.env): PiRulesConfig {
	const config = defaultConfig();
	const disableBundledRules = isTruthy(firstEnv(env, "CODEX_RULES_DISABLE_BUNDLED", "PI_RULES_DISABLE_BUNDLED"));
	config.disabled = isTruthy(firstEnv(env, "CODEX_RULES_DISABLED", "PI_RULES_DISABLED"));
	config.mode = parseMode(firstEnv(env, "CODEX_RULES_MODE", "PI_RULES_MODE")) ?? config.mode;
	config.maxRuleChars =
		parsePositiveInteger(firstEnv(env, "CODEX_RULES_MAX_RULE_CHARS", "PI_RULES_MAX_RULE_CHARS")) ??
		config.maxRuleChars;
	config.maxResultChars =
		parsePositiveInteger(firstEnv(env, "CODEX_RULES_MAX_RESULT_CHARS", "PI_RULES_MAX_RESULT_CHARS")) ??
		config.maxResultChars;
	config.postCompactMaxRuleChars =
		parsePositiveInteger(
			firstEnv(env, "CODEX_RULES_POST_COMPACT_MAX_RULE_CHARS", "PI_RULES_POST_COMPACT_MAX_RULE_CHARS"),
		) ?? config.postCompactMaxRuleChars;
	config.postCompactMaxResultChars =
		parsePositiveInteger(
			firstEnv(env, "CODEX_RULES_POST_COMPACT_MAX_RESULT_CHARS", "PI_RULES_POST_COMPACT_MAX_RESULT_CHARS"),
		) ?? config.postCompactMaxResultChars;
	config.enabledSources = parseEnabledSources(
		firstEnv(env, "CODEX_RULES_ENABLED_SOURCES", "PI_RULES_ENABLED_SOURCES"),
		disableBundledRules,
	);
	return config;
}

function firstEnv(env: NodeJS.ProcessEnv, ...names: string[]): string | undefined {
	for (const name of names) {
		const value = env[name];
		if (typeof value === "string" && value.trim().length > 0) {
			return value;
		}
	}
	return undefined;
}

function isTruthy(value: string | undefined): boolean {
	if (value === undefined) return false;
	return ["1", "true", "yes", "on"].includes(value.trim().toLowerCase());
}

function parseMode(value: string | undefined): PiRulesConfig["mode"] | undefined {
	if (value === undefined) return undefined;
	const normalized = value.trim().toLowerCase();
	switch (normalized) {
		case "static":
		case "dynamic":
		case "both":
		case "off":
			return normalized;
		default:
			return undefined;
	}
}

function parsePositiveInteger(value: string | undefined): number | undefined {
	if (value === undefined) return undefined;
	const parsed = Number.parseInt(value.trim(), 10);
	return Number.isSafeInteger(parsed) && parsed > 0 ? parsed : undefined;
}

function parseEnabledSources(value: string | undefined, disableBundledRules: boolean): RuleSource[] | "auto" {
	if (value === undefined || value.trim().toLowerCase() === "auto") {
		return disableBundledRules ? sourcesWithoutBundledRules() : "auto";
	}

	const sources: RuleSource[] = [];
	for (const rawSource of value.split(",")) {
		const source = toRuleSource(rawSource.trim());
		if (source === null) {
			continue;
		}
		sources.push(source);
	}
	const enabledSources = disableBundledRules ? sources.filter((source) => source !== "plugin-bundled") : sources;
	return enabledSources;
}

function sourcesWithoutBundledRules(): RuleSource[] {
	return [...SOURCE_PRIORITY.keys()].filter((source) => source !== "plugin-bundled");
}

function toRuleSource(value: string): RuleSource | null {
	switch (value) {
		case ".omo/rules":
		case ".claude/rules":
		case ".cursor/rules":
		case ".github/instructions":
		case ".github/copilot-instructions.md":
		case "CONTEXT.md":
		case "plugin-bundled":
		case "~/.omo/rules":
		case "~/.opencode/rules":
		case "~/.claude/rules":
			return value;
		default:
			return null;
	}
}