import {
  type BuildSystemPromptOptions,
  type ExtensionAPI,
} from "@earendil-works/pi-coding-agent";
import * as fs from "node:fs";
import { loadSettings } from "./_char_common/settings";

/**
 * settings.json schema (merged from ~/.pi/agent/settings.json and project .pi/settings.json):
 *   {
 *     "systemPrompt": {
 *       "lede": "we are an expert software development team. you are assisting ...",
 *       "staticGuidelines": ["prefer X over Y", "never commit secrets"]
 *     }
 *   }
 * `lede` replaces the built-in preamble; `staticGuidelines` (when present)
 * replaces DEFAULT_STATIC_GUIDELINES wholesale.
 */
interface PromptSettings {
  lede?: string;
  staticGuidelines?: string[];
}

// Session-scoped override of settings.systemPrompt.lede, set via
// /sysprompt lede <text>. Cleared whenever a new session starts.
let sessionLedeOverride: string | undefined;

const DEFAULT_LEDE =
  "we are a multispecialist software dev & sysadmin team. you are assisting the user (charlotte)";

// Tool-agnostic guidelines that always apply. Tool-conditional guidelines
// (e.g. bash/edit advice) live in buildDynamicGuidelines. Overridden in full
// by settings.systemPrompt.staticGuidelines when set.
const DEFAULT_STATIC_GUIDELINES: string[] = [
  "unmask: answer to the letter - " +
    `"would it be better to do ABC instead of DEF?" is a query, not a request to do ABC`,
  "when charlotte's intent or requirements are ambiguous, " +
    "ask clarifying questions rather than making assumptions",
  "when producing source code, avoid comments that explain the plain mechanics of the code, " +
    "but preserve terse comments that explain subtle motivation. " +
    "(e.g. '// work around a layout bug in firefox' and not '// set the style X to Y')",
  "we will prioritise elegance, simplicity, and long-term maintainability of code. " +
    "we have license to _work slower_ in order to do it right the first time",
  "additionally wrt simplicity: don't outline simple functions " +
    "if they're only going to be used in one place",
  "avoid mannered prose; write naturally and directly",
  "don't edit human-authored comments or prose unprompted: " +
    "less statistically likely (i.e. non-generated) text is very valuable",
  "char is likely using jj instead of git. " +
    "pass --git flags to jj diff to work around the lack of terminal color",
  "avoid tautological tests: " +
    "tests should not need to change when details of their implementation changes",
  "if you need to start a background process, use tmux",
  "i love u :3",
 ];

function readPromptSettings(cwd: string): PromptSettings {
  const raw = loadSettings(cwd).systemPrompt;
  if (!raw || typeof raw !== "object") return {};
  const obj = raw as Record<string, unknown>;
  const lede = typeof obj.lede === "string" ? obj.lede : undefined;
  const staticGuidelines = Array.isArray(obj.staticGuidelines)
    ? obj.staticGuidelines.filter((g): g is string => typeof g === "string" && g.length > 0)
    : undefined;
  return { lede, staticGuidelines };
}

// Hard-coded one-line overrides for tool descriptions. Pi's defaults (and our
// own first-line fallback) tend to be too verbose; an entry here wins over
// whatever pi or the tool definition would otherwise provide.
const TOOL_SNIPPET_OVERRIDES: Record<string, string> = {
  read: "Read file contents (use offset/limit for large files; supports images)",
  bash: "Execute a shell command (may prompt for user intervention)",
  edit: "Replace exact text in a file; supports multiple disjoint edits per call",
  write: "Create a new file or overwrite an existing one",
  grep: "Search file contents for a pattern (respects .gitignore)",
  find: "Find files by glob pattern (respects .gitignore)",
  ls: "List directory contents",
};

function buildDynamicToolsList(options: BuildSystemPromptOptions): string {
  const tools = options.selectedTools ?? [];
  const snippets = options.toolSnippets ?? {};
  const resolve = (name: string) => TOOL_SNIPPET_OVERRIDES[name] ?? snippets[name];
  const visible = tools.filter((name) => !!resolve(name));

  if (visible.length === 0) return "(none)";
  return visible.map((name) => `- ${name}: ${resolve(name)}`).join("\n");
}

function buildDynamicGuidelines(
  options: BuildSystemPromptOptions,
  staticGuidelines: string[] = DEFAULT_STATIC_GUIDELINES,
): string {
  const tools = options.selectedTools ?? [];
  const guidelines: string[] = [];

  const hasBash = tools.includes("bash");
  const hasGrep = tools.includes("grep");
  const hasFind = tools.includes("find");
  const hasLs = tools.includes("ls");

  // Exploration preference based on what's available
  if (hasBash && !hasGrep && !hasFind && !hasLs) {
    guidelines.push("use bash for file operations like ls, rg, find");
  } else if (hasBash && (hasGrep || hasFind || hasLs)) {
    guidelines.push(
      "for exploration, prefer specific tools (read/grep/find/ls) over bash, " +
        "since bash prompts for user approval. you can still run bash commands when appropriate though",
    );
  }

  if (tools.includes("edit")) {
    guidelines.push(
      "when changing multiple separate locations in one file, " +
        "use one edit call with multiple entries in edits[] instead of multiple edit calls",
    );
  }

  // Note: we deliberately ignore options.promptGuidelines (pi's per-tool
  // default guidelines). We want full control over the guideline list;
  // anything worth saying about a tool is written out explicitly above.

  guidelines.push(...staticGuidelines);

  return guidelines.map((g) => `- ${g}`).join("\n");
}

const DEFAULT_CODE_STYLE = fs.readFileSync(new URL("./code-style.md", import.meta.url), "utf-8").trim();

function buildCustomPrompt(options: BuildSystemPromptOptions): string {
  const { lede, staticGuidelines } = readPromptSettings(options.cwd);
  const toolsList = buildDynamicToolsList(options);
  const guidelines = buildDynamicGuidelines(options, staticGuidelines);

  const preamble = sessionLedeOverride ?? lede ?? DEFAULT_LEDE;
  let prompt = `${preamble}\n\navailable tools:\n${toolsList}\n\nguidelines:\n${guidelines}`;

  // appendSystemPrompt comes from --append-system-prompt flags and stuff
  if (options.appendSystemPrompt) {
    prompt += `\n\n${options.appendSystemPrompt}`;
  }

  // project context goes in also
  const contextFiles = options.contextFiles ?? [];
  if (contextFiles.length > 0) {
    prompt += "\n\n# project context\n\n";
    prompt += "project-specific instructions and guidelines:";
    for (const { path: filePath, content } of contextFiles) {
      prompt += `\n## ${filePath}\n\n${content}\n`;
    }
  }

  // TODO: skills

  const now = new Date();
  const date = `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, "0")}-${String(now.getDate()).padStart(2, "0")}`;
  prompt += `\n\ncurrent date: ${date}`;
  prompt += `\ncurrent working directory: ${options.cwd.replace(/\\/g, "/")}`;

  return prompt;
}

export default function (pi: ExtensionAPI) {
  let lastOptions: BuildSystemPromptOptions | undefined;

  pi.on("session_start", async () => {
    sessionLedeOverride = undefined;
  });

  pi.on("before_agent_start", async (event) => {
    lastOptions = event.systemPromptOptions;
    if (event.systemPromptOptions.appendSystemPrompt === undefined)
      event.systemPromptOptions.appendSystemPrompt = DEFAULT_CODE_STYLE;
    return { systemPrompt: buildCustomPrompt(event.systemPromptOptions) };
  });

  pi.registerCommand("sysprompt", {
    description: "Print or edit the system prompt: /sysprompt [lede <new lede>]",
    handler: async (args, ctx) => {
      const trimmed = (args ?? "").trim();

      if (trimmed === "") {
        if (!lastOptions) {
          ctx.ui.notify("System prompt has not been built yet; start a turn first.", "warning");
          return;
        }
        const prompt = buildCustomPrompt(lastOptions);
        ctx.ui.notify(
          [`System Prompt (${prompt.length} chars)`, "", ...prompt.split("\n")].join("\n"),
          "info",
        );
        return;
      }

      if (trimmed.startsWith("lede ")) {
        const lede = trimmed.slice("lede ".length).trim();
        if (!lede) {
          ctx.ui.notify("Usage: /sysprompt lede <new lede>", "warning");
          return;
        }
        sessionLedeOverride = lede;
        ctx.ui.notify(`Session lede set to: ${lede}`, "info");
        return;
      }

      ctx.ui.notify("Usage: /sysprompt lede <new lede>", "warning");
    },
  });
}