import type {
	ExtensionContext,
	NormalizedBuildSystemPromptOptions,
} from "@earendil-works/pi-coding-agent";
import { getAgentDir } from "@earendil-works/pi-coding-agent";
import { loadCursorSdkUserConfig, type CursorSdkConfig } from "./config.js";
import {
	isCursorModel,
	registerCursorModelLifecycle,
	type CursorModelLifecycleExtensionApi,
} from "./model.js";
import { cursorSettingSourcesIncludes, getEffectiveCursorSettingSources, resolveCursorSettingSources } from "./setting-sources.js";
import type { SettingSource } from "@cursor/sdk";

/** Opening tag prefix pi `buildSystemPrompt()` uses for each context file (path attribute only). */
export const PI_PROJECT_INSTRUCTIONS_OPEN_PREFIX = '<project_instructions path="';
const PI_PROJECT_INSTRUCTIONS_CLOSE = "</project_instructions>";
const PI_PROJECT_CONTEXT_OPEN = "\n\n<project_context>\nProject-specific instructions and guidelines:\n\n";
const PI_PROJECT_CONTEXT_CLOSE = "</project_context>\n";

function normalizeContextPath(filePath: string): string {
	return filePath.replace(/\\/g, "/");
}

function normalizeDirPath(dirPath: string): string {
	const normalized = normalizeContextPath(dirPath).replace(/\/+$/, "");
	return normalized || "/";
}

export type PiAgentsContextFile = {
	path: string;
	content: string;
};

/** Overlap classes for pi context files that Cursor also loads via `settingSources`. */
export type PiAgentsContextOverlap = "none" | "cursor-user-agents" | "cursor-project-rules";

/** Pi context filenames that can overlap Cursor project/user ambient rules. */
const CURSOR_OVERLAPPING_CONTEXT_BASE_NAMES = new Set(["agents.md", "claude.md"]);

export function getAgentsContextFileBaseName(filePath: string): string {
	const normalized = normalizeContextPath(filePath);
	return normalized.slice(normalized.lastIndexOf("/") + 1).toLowerCase();
}

function isPiAgentDirContextFilePath(
	filePath: string,
	fileName: "agents.md" | "claude.md",
	agentDir: string = getAgentDir(),
): boolean {
	const normalized = normalizeContextPath(filePath);
	const expectedPath = `${normalizeDirPath(agentDir)}/${fileName}`;
	return normalized.toLowerCase() === expectedPath.toLowerCase();
}

/** Actual pi agent dir `AGENTS.md` — overlaps Cursor `user` setting source (global agent instructions). */
export function isPiAgentDirAgentsMdPath(filePath: string, agentDir: string = getAgentDir()): boolean {
	return isPiAgentDirContextFilePath(filePath, "agents.md", agentDir);
}

/** Actual pi agent dir `CLAUDE.md` — kept because Cursor user rules use `~/.claude/CLAUDE.md`. */
export function isPiAgentDirClaudeMdPath(filePath: string, agentDir: string = getAgentDir()): boolean {
	return isPiAgentDirContextFilePath(filePath, "claude.md", agentDir);
}

/**
 * Classify whether a pi-loaded context file overlaps Cursor ambient rules.
 * Project/repo `AGENTS.md` and `CLAUDE.md` overlap Cursor `project` sources.
 * Only the actual pi agent dir `AGENTS.md` overlaps Cursor `user`; agent-dir `CLAUDE.md` is kept
 * because Cursor user rules use `~/.claude/CLAUDE.md`, not pi's agent dir path.
 */
export function classifyContextFileOverlap(
	filePath: string,
	agentDir: string = getAgentDir(),
): PiAgentsContextOverlap {
	const base = getAgentsContextFileBaseName(filePath);
	if (!CURSOR_OVERLAPPING_CONTEXT_BASE_NAMES.has(base)) return "none";
	if (base === "agents.md" && isPiAgentDirAgentsMdPath(filePath, agentDir)) return "cursor-user-agents";
	if (base === "claude.md" && isPiAgentDirClaudeMdPath(filePath, agentDir)) return "none";
	return "cursor-project-rules";
}

export function shouldRemovePiAgentsContextFile(
	file: PiAgentsContextFile,
	settingSources: SettingSource[] | undefined,
	agentDir?: string,
): boolean {
	switch (classifyContextFileOverlap(file.path, agentDir)) {
		case "cursor-user-agents":
			return cursorSettingSourcesIncludes(settingSources, "user");
		case "cursor-project-rules":
			return cursorSettingSourcesIncludes(settingSources, "project");
		default:
			return false;
	}
}

export function shouldSuppressPiAgentsContext(
	model: ExtensionContext["model"],
	contextFiles: readonly PiAgentsContextFile[],
	settingSources: SettingSource[] | undefined,
	agentDir?: string,
	config: CursorSdkConfig = loadCursorSdkUserConfig(),
): boolean {
	if (!isCursorModel(model)) return false;
	if (config.local?.preservePiAgentsContext === true) return false;
	if (contextFiles.length === 0) return false;
	return contextFiles.some((file) => shouldRemovePiAgentsContextFile(file, settingSources, agentDir));
}

/** Exact pi `buildSystemPrompt()` serialization for one context file block (including trailing blank line). */
export function serializePiProjectInstructionsBlock(file: PiAgentsContextFile): string {
	return `${PI_PROJECT_INSTRUCTIONS_OPEN_PREFIX}${file.path}">\n${file.content}\n${PI_PROJECT_INSTRUCTIONS_CLOSE}\n\n`;
}

/** Exact pi `buildSystemPrompt()` serialization for the full project context section. */
export function serializePiProjectContextSection(contextFiles: readonly PiAgentsContextFile[]): string {
	if (contextFiles.length === 0) return "";
	const blocks = contextFiles
		.map(serializePiProjectInstructionsBlock)
		.join("")
		.replace(/\n$/, "");
	return `${PI_PROJECT_CONTEXT_OPEN}${blocks}${PI_PROJECT_CONTEXT_CLOSE}`;
}

/** Remove pi context blocks that overlap Cursor setting sources. */
export function removePiAgentsContextFromSystemPrompt(
	systemPrompt: string,
	contextFiles: readonly PiAgentsContextFile[],
	settingSources: SettingSource[] | undefined,
	agentDir?: string,
): string {
	const retainedContextFiles: PiAgentsContextFile[] = [];
	let removedAny = false;
	for (const file of contextFiles) {
		if (shouldRemovePiAgentsContextFile(file, settingSources, agentDir)) {
			removedAny = true;
			continue;
		}
		retainedContextFiles.push(file);
	}
	if (!removedAny) return systemPrompt;

	const originalSection = serializePiProjectContextSection(contextFiles);
	const start = systemPrompt.indexOf(originalSection);
	if (start < 0) return systemPrompt;

	const replacementSection = serializePiProjectContextSection(retainedContextFiles);
	return systemPrompt.slice(0, start) + replacementSection + systemPrompt.slice(start + originalSection.length);
}

export function resolveCursorFacingSystemPrompt(
	systemPrompt: string,
	model: ExtensionContext["model"],
	systemPromptOptions?: NormalizedBuildSystemPromptOptions,
	settingSourcesRaw?: string,
	agentDir?: string,
	config: CursorSdkConfig = loadCursorSdkUserConfig(),
): string {
	if (!systemPromptOptions) return systemPrompt;
	const contextFiles = systemPromptOptions.contextFiles ?? [];
	const settingSources = settingSourcesRaw === undefined
		? getEffectiveCursorSettingSources(config)
		: resolveCursorSettingSources(settingSourcesRaw);
	if (!shouldSuppressPiAgentsContext(model, contextFiles, settingSources, agentDir, config)) {
		return systemPrompt;
	}
	return removePiAgentsContextFromSystemPrompt(systemPrompt, contextFiles, settingSources, agentDir);
}

export type CursorAgentsContextExtensionApi = CursorModelLifecycleExtensionApi;

export function registerCursorAgentsContextDedup(
	pi: CursorAgentsContextExtensionApi,
	config: CursorSdkConfig = loadCursorSdkUserConfig(),
): void {
	registerCursorModelLifecycle(pi, {
		beforeAgentStart: (event, ctx) => {
			if (!isCursorModel(ctx.model)) return undefined;
			const resolved = resolveCursorFacingSystemPrompt(
				event.systemPrompt,
				ctx.model,
				event.systemPromptOptions,
				undefined,
				undefined,
				config,
			);
			if (resolved === event.systemPrompt) return undefined;
			return { systemPrompt: resolved };
		},
	});
}