/**
 * KHAELOR
 * File: src/context/system-prompt.ts
 * Description: Three-tier byte-stable system prompt and KHAELOR.md/CLAUDE.md/AGENTS.md instruction discovery (ARCHITECTURE.md §6.5, CLAUDE.md §12).
 *
 * Author: Simon-Pierre Boucher
 * Contact: contact@spboucher.ai
 */

import * as path from "node:path";
import type { SystemTier } from "../anthropic/index.js";

// ───────────────────────────── instruction discovery ─────────────────────────────

/**
 * The file-reading capability this module needs — a structural subset of
 * `Workspace` (ADR-13). Injected so `src/context/` never imports the
 * workspace module (dependency rule 8) and never touches `node:fs`.
 */
export interface InstructionReader {
  cwd(): string;
  readFile(filePath: string): Promise<string>;
}

/** Precedence within one directory: KHAELOR.md, then compatibility fallbacks. */
export const INSTRUCTION_FILENAMES: readonly string[] = ["KHAELOR.md", "CLAUDE.md", "AGENTS.md"];

export interface InstructionFile {
  /** Absolute path of the discovered file. */
  path: string;
  scope: "user" | "project" | "nested";
  content: string;
}

export interface DiscoverInstructionsOptions {
  /** Directory holding the user-global instructions (e.g. ~/.khaelor). Omit to skip the user tier. */
  userDir?: string;
  /** Project root. Default: the reader's cwd. Nested directories between root and cwd refine it. */
  projectRoot?: string;
}

async function readFirstMatch(
  reader: InstructionReader,
  dir: string,
): Promise<{ path: string; content: string } | null> {
  for (const name of INSTRUCTION_FILENAMES) {
    const candidate = path.join(dir, name);
    try {
      const content = await reader.readFile(candidate);
      return { path: candidate, content };
    } catch {
      // absent or unreadable — try the next compatibility name
    }
  }
  return null;
}

/**
 * Discover project instructions with the CLAUDE.md §12 precedence, ordered
 * global → nested (instructions closer to the working path refine earlier
 * ones):
 *
 *   <userDir>/KHAELOR.md → <projectRoot>/KHAELOR.md → nested dirs toward cwd
 *
 * In each directory KHAELOR.md wins; CLAUDE.md then AGENTS.md are
 * compatibility fallbacks. All reads go through the injected reader.
 */
export async function discoverProjectInstructions(
  reader: InstructionReader,
  options: DiscoverInstructionsOptions = {},
): Promise<InstructionFile[]> {
  const found: InstructionFile[] = [];
  const cwd = path.resolve(reader.cwd());
  const projectRoot = path.resolve(options.projectRoot ?? cwd);

  if (options.userDir !== undefined) {
    const user = await readFirstMatch(reader, path.resolve(options.userDir));
    if (user) found.push({ ...user, scope: "user" });
  }

  // Directory chain from projectRoot down to cwd (boundary-aware containment).
  const chain: string[] = [projectRoot];
  const relative = path.relative(projectRoot, cwd);
  if (relative.length > 0 && !relative.startsWith("..") && !path.isAbsolute(relative)) {
    let dir = projectRoot;
    for (const segment of relative.split(path.sep)) {
      dir = path.join(dir, segment);
      chain.push(dir);
    }
  }

  for (const candidateDir of chain) {
    const match = await readFirstMatch(reader, candidateDir);
    if (match) {
      found.push({ ...match, scope: candidateDir === projectRoot ? "project" : "nested" });
    }
  }
  return found;
}

// ───────────────────────────── system prompt tiers ─────────────────────────────

export interface SystemPromptOptions {
  /** Absolute working directory shown to the model (stable for the session). */
  workingDirectory: string;
  /** Tool names available this session (registry order — stable). */
  toolNames: readonly string[];
  /** Discovered instruction files, in precedence order (global → nested). */
  instructions: readonly InstructionFile[];
}

const IDENTITY_TEXT = `You are KHAELOR, a terminal-native autonomous engineering agent.

You work directly inside the user's repository, in three phases: understand → design → implement. Understand first: read the relevant code. Then design: for any change that touches files, submit a design with the "design" tool (goal, approach, files, risks, verification) — write tools stay locked until a design is approved, and a PHASE_GATE_BLOCKED error means you must design first. Then implement: precise, minimal edits. Verify meaningful changes with the repository's own checks (tests, typecheck, build) before claiming completion — failing verify results arrive automatically after edit batches; repair them. Never fabricate results, token counts, or test outcomes — every claim must be backed by observed evidence.

When you discover a durable fact about the project (a convention, a build command, a pitfall), persist it with the "remember" tool so future sessions know it.

Communication style: short, specific, action-oriented. No filler, no preamble about what you will do next — do it. Protect the user's uncommitted work at all times and never commit unless explicitly asked.`;

function toolTierText(toolNames: readonly string[]): string {
  return `Available tools: ${toolNames.join(", ")}.

Use symbols/refs (the semantic index) to find definitions and usage sites before reaching for grep; use read/grep/glob to explore before editing. Prefer edit (exact replacement) over write for existing files. Use bash for short foreground commands and process for long-running ones (dev servers, watchers) — never block on a long-running command. Tool outputs may be truncated with explicit markers; re-read with narrower ranges when needed.`;
}

function instructionsTierText(instructions: readonly InstructionFile[]): string {
  const sections = instructions.map(
    (file) => `## Instructions from ${file.path} (${file.scope})\n\n${file.content}`,
  );
  return `# Project instructions\n\nThe following instructions were provided by the user and project. Later sections are closer to the working directory and refine earlier ones.\n\n${sections.join("\n\n---\n\n")}`;
}

/**
 * Build the three stable system tiers (ARCHITECTURE.md §6.5 rule 1):
 * [identity/behavior] → [tool guidance] → [project instructions]. Built once
 * per session and never re-rendered — cache breakpoints land at tier ends
 * (planned by anthropic/caching.ts). The output is a pure function of its
 * inputs: same inputs, byte-identical tiers.
 */
export function buildSystemPrompt(options: SystemPromptOptions): SystemTier[] {
  const tiers: SystemTier[] = [
    {
      name: "identity",
      text: `${IDENTITY_TEXT}\n\nWorking directory: ${options.workingDirectory}`,
    },
    { name: "tools", text: toolTierText(options.toolNames) },
  ];
  if (options.instructions.length > 0) {
    tiers.push({ name: "project-instructions", text: instructionsTierText(options.instructions) });
  }
  return tiers;
}