import { basename, dirname, relative, resolve } from "path";
import { existsSync, readFileSync } from "fs";
import { parsePackageMap } from "./format.js";
import {
	discoverProject,
	generateDirectoryArtifacts,
	buildDirectoryContext,
	getAncestorEntries,
} from "./init.js";
import type { DirectoryEntry } from "./discover.js";
import type { LLMClient } from "./llm/llm-client.js";
import { loadConfig } from "./config.js";

export type PatchMode = "auto" | "small" | "structural";

export interface PatchOptions {
	patchMode?: PatchMode;
	rootPath?: string;
}

const SMALL_CHANGE_FILE_WINDOW = 3;
const STRUCTURAL_FILE_HINT =
	/(^|\b)(index|config|cli|command|init|format|discover|patch|validate)(\b|\.)/i;

export async function patchFile(
	filePath: string,
	llmClient?: LLMClient,
	cacheDir?: string,
	options: PatchOptions = {},
): Promise<void> {
	const rootPath = resolve(options.rootPath ?? cacheDir ?? process.cwd());
	const absFilePath = resolve(rootPath, filePath);
	const dirPath = dirname(absFilePath);
	const relDir = normalizeRelativePath(relative(rootPath, dirPath));
	const entries = discoverProject(rootPath);
	const entry = entries.find((candidate) => candidate.relativePath === relDir);

	if (!entry) {
		console.warn(`No discovered directory entry found for ${relDir}`);
		return;
	}

	const config = loadConfig(rootPath);
	const routingOpts = {
		tagCap: config.tagCap,
		workflowHintCap: config.workflowHintCap,
	};
	const mode = determinePatchMode(
		entry,
		absFilePath,
		rootPath,
		options.patchMode,
	);
	const changedCtx = buildDirectoryContext(entries, entry);
	await generateDirectoryArtifacts(
		entry,
		changedCtx,
		llmClient,
		cacheDir,
		undefined,
		routingOpts,
		"both",
	);

	for (const ancestor of getAncestorEntries(entries, changedCtx, entry)) {
		const ancestorCtx = buildDirectoryContext(entries, ancestor);
		await generateDirectoryArtifacts(
			ancestor,
			ancestorCtx,
			llmClient,
			cacheDir,
			undefined,
			routingOpts,
			mode === "small" ? "index" : "both",
		);
	}

	console.log(
		`Patched ${joinArtifactPath(relDir, ".pi-map.md")} (patchMode: ${mode})`,
	);
}

function determinePatchMode(
	entry: DirectoryEntry,
	absFilePath: string,
	rootPath: string,
	explicitMode: PatchMode = "auto",
): Exclude<PatchMode, "auto"> {
	if (explicitMode !== "auto") {
		return explicitMode;
	}

	const existingMapPath = resolve(entry.dirPath, ".pi-map.md");
	const fileName = basename(absFilePath);
	const childCount =
		entry.relativePath === "."
			? 0
			: countDirectChildren(rootPath, entry.relativePath);

	if (childCount > 0) {
		return "structural";
	}

	if (entry.files.length > SMALL_CHANGE_FILE_WINDOW) {
		return "structural";
	}

	if (STRUCTURAL_FILE_HINT.test(fileName)) {
		return "structural";
	}

	if (existsSync(existingMapPath)) {
		const existing = parsePackageMap(readFileSync(existingMapPath, "utf8"));
		const existingFile = existing.files.find(
			(candidate) => candidate.name === fileName,
		);
		if (!existingFile) {
			return "structural";
		}
	}

	return "small";
}

function countDirectChildren(rootPath: string, relDir: string): number {
	const entries = discoverProject(rootPath);
	return entries.filter((entry) => {
		if (entry.relativePath === "." || entry.relativePath === relDir)
			return false;
		const parent = normalizeRelativePath(
			entry.relativePath.split("/").slice(0, -1).join("/"),
		);
		return parent === relDir;
	}).length;
}

function normalizeRelativePath(relPath: string): string {
	if (!relPath || relPath === ".") return ".";
	return relPath.replace(/\\/g, "/");
}

function joinArtifactPath(relDir: string, artifactName: string): string {
	return relDir === "." ? artifactName : `${relDir}/${artifactName}`;
}