// prompt-builders.ts — shared prompt builders + rules loader
//
// Provides buildGroupingPrompt and buildSingleMessagePrompt that wrap the
// existing prompt literals (byte-identical to upstream pi-committer) and
// optionally append rules from an external file pointed to by prompt_rules_path.
//
// Also provides loadCommitRules (cached, fail-graceful) and
// resetCommitRulesCache for session-lifecycle cache invalidation.
//
// Type-only import of CommitterConfig from config.ts (erased at runtime →
// safe for worker fork, no circular dependency).

import { readFileSync } from "node:fs";
import * as path from "node:path";

// ---------------------------------------------------------------------------
// Rules cache
// ---------------------------------------------------------------------------

/**
 * Module-level cache for loaded commit rules.
 * - undefined: not loaded yet
 * - null: no file / unreadable → returns ""
 * - string: cached content
 */
let cachedRules: string | null | undefined;
let cachedRulesPath: string | null | undefined; // resolved-path cache key; null = "no path"

/**
 * Load commit discipline rules from the file at `promptRulesPath`.
 *
 * - Returns "" when path is unset, empty, or unreadable (fail-graceful, no throw).
 * - Caches per-process (main: per-session; worker: per-fork).
 * - Relative paths resolved against process.cwd().
 */
export function loadCommitRules(promptRulesPath?: string): string {
	// Cache is keyed by the resolved path so calls with different paths do not
	// return a stale result (null = "no path" sentinel).
	const key =
		promptRulesPath && promptRulesPath.trim()
			? path.resolve(promptRulesPath)
			: null;
	if (cachedRulesPath === key && cachedRules !== undefined) {
		return cachedRules ?? "";
	}
	if (key === null) {
		cachedRulesPath = null;
		cachedRules = null;
		return "";
	}
	try {
		cachedRulesPath = key;
		cachedRules = readFileSync(key, "utf-8").trim();
		return cachedRules;
	} catch {
		cachedRules = null;
		return "";
	}
}

/**
 * Reset the rules cache. Called from /commit-config reload in the main process.
 * In the worker, each fork is a fresh process (no reset needed).
 */
export function resetCommitRulesCache(): void {
	cachedRules = undefined;
	cachedRulesPath = undefined;
}

// ---------------------------------------------------------------------------
// Grouping prompt builder
// ---------------------------------------------------------------------------

/**
 * Build the grouping-prompt string from the base literal (byte-identical to
 * upstream) with optional appended rules.
 *
 * The base literal is composed with the dynamic file list / diff stat / diff
 * content using the same assembly the inline code does. When rules are present,
 * they are appended as a distinct trailing section.
 */
export function buildGroupingPrompt(
	allFiles: string[],
	diffStat: string,
	truncatedDiff: string,
	rules: string,
): string {
	const fileListStr = allFiles.map((f) => `  - ${f}`).join("\n");

	const base = [
		"You are organizing a git commit. Given the diff below, split the changes into logical commit groups.",
		"",
		"Rules:",
		"- Group related changes together (same feature, same fix, same refactoring, same area of code)",
		"- Split unrelated changes into separate commits",
		"- Each commit must use conventional commit format: <type>(<scope>): <description>",
		"- Type must be one of: feat, fix, chore, docs, refactor, test, style, perf, ci, build, revert",
		"- Scope: use the single most-specific directory for each group (e.g. 'api', 'exposure', 'config'). NEVER comma-join multiple scopes. If files in a group span unrelated directories, OMIT scope.",
		"- Description: a SHORT imperative phrase summarizing what each group does. Be specific: 'add regression pipeline and tests', not 'update 27 modules'.",
		"- Max 72 chars per header line (type + scope + description combined).",
		"- Assign each file to EXACTLY ONE group",
		"- Cover ALL files listed below in your groups",
		"",
		`Changed files (${allFiles.length}):`,
		fileListStr,
		"",
		"Diff stat:",
		diffStat,
		"",
		"Diff content:",
		truncatedDiff,
		"",
		"Output format (replace N with group number):",
		"--- COMMIT GROUP 1 ---",
		"<type>(<scope>): <description>",
		"",
		"<body>",
		"Files: <file1>, <file2>",
		"",
		"--- COMMIT GROUP 2 ---",
		"...",
		"",
		"If all changes belong in one commit, output a single COMMIT GROUP.",
	].join("\n");

	if (rules && rules.trim()) {
		return `${base}\n\nAdditional commit discipline rules:\n${rules}`;
	}
	return base;
}

// ---------------------------------------------------------------------------
// Single-message prompt builder
// ---------------------------------------------------------------------------

/**
 * Build the single-message-prompt string from the base literal with optional
 * appended rules. Same composition pattern as buildGroupingPrompt.
 *
 * The base literal is byte-identical to upstream's inline literal at
 * index.ts:1238-1266 and async-commit-worker.ts:605-633.
 */
export function buildSingleMessagePrompt(
	diffStat: string,
	truncatedDiff: string,
	rules: string,
): string {
	const base = [
		"Generate a conventional commit message from this git diff.",
		"",
		"Format:",
		"<type>(<scope>): <short description>",
		"",
		"<detailed body explaining what changed and why>",
		"",
		"Rules:",
		"- Type must be one of: feat, fix, chore, docs, refactor, test, style, perf, ci, build, revert",
		"- Scope: use the single most-specific directory that groups the changes (e.g. 'api', 'config', 'exposure'). NEVER comma-join multiple scopes. If files span unrelated directories, OMIT scope entirely.",
		"- Description: a SHORT imperative phrase summarizing what was done. Be specific: 'add regression pipeline and tests', not 'update 27 modules'.",
		"- Max 72 chars for the header line (type + scope + description combined).",
		"- Body: a brief paragraph explaining what changed and why.",
		"- Output ONLY the commit message, nothing else.",
		"",
		"Diff stat:",
		diffStat,
		"",
		"Full diff:",
		truncatedDiff,
	].join("\n");

	if (rules && rules.trim()) {
		return `${base}\n\nAdditional commit discipline rules:\n${rules}`;
	}
	return base;
}