import { readFile } from "node:fs/promises";
import { dirname } from "node:path";
import { stripFrontmatter, type ExtensionAPI } from "@earendil-works/pi-coding-agent";
import type { AutocompleteProvider } from "@earendil-works/pi-tui";
import { completionPrefix, findMentions } from "./mentions.ts";

export interface Skill {
  name: string;
  description?: string;
  path: string;
}

function getSkills(pi: ExtensionAPI): Skill[] {
  return pi.getCommands()
    .filter((command) => command.source === "skill" && command.name.startsWith("skill:"))
    .map((command) => ({
      name: command.name.slice(6),
      description: command.description,
      path: command.sourceInfo.path,
    }));
}

function escapeAttribute(value: string): string {
  return value.replaceAll("&", "&").replaceAll('"', """)
    .replaceAll("<", "&lt;").replaceAll(">", "&gt;");
}

export async function expandSkills(text: string, skills: Skill[]) {
  const byName = new Map(skills.map((skill) => [skill.name, skill]));
  const names = [...new Set(findMentions(text).map((mention) => mention.name))];
  const blocks: string[] = [];
  const errors: string[] = [];
  for (const name of names) {
    const skill = byName.get(name);
    if (!skill) continue;
    try {
      const body = stripFrontmatter(await readFile(skill.path, "utf8")).trim();
      blocks.push(`<skill name="${escapeAttribute(name)}" location="${escapeAttribute(skill.path)}">\nReferences are relative to ${dirname(skill.path)}.\n\n${body}\n</skill>`);
    } catch (error) {
      errors.push(`Could not load $${name}: ${error instanceof Error ? error.message : String(error)}`);
    }
  }
  if (!blocks.length && !errors.length) return { text, errors };
  // Keep the original prompt, including $name and its arguments, intact for
  // other input hooks (e.g. skill-specific mode guards) and the model.
  const context = [
    ...blocks,
    ...errors.map((error) => `[pi-dollar-skills: ${error}]`),
  ].join("\n\n");
  return { text: `${text}\n\n${context}`, errors };
}

export function skillAutocomplete(current: AutocompleteProvider, skills: () => Skill[]): AutocompleteProvider {
  return {
    triggerCharacters: [...new Set([...(current.triggerCharacters ?? []), "$"])],
    async getSuggestions(lines, line, col, options) {
      const prefix = completionPrefix(lines, line, col);
      if (prefix === undefined) return current.getSuggestions(lines, line, col, options);
      const query = prefix.slice(1).toLowerCase();
      const items = skills()
        .filter((skill) => skill.name.toLowerCase().startsWith(query))
        .sort((a, b) => a.name.localeCompare(b.name))
        .map((skill) => ({ value: `$${skill.name}`, label: `$${skill.name}`, description: skill.description }));
      return items.length ? { prefix, items } : null;
    },
    applyCompletion(lines, line, col, item, prefix) {
      if (!prefix.startsWith("$") || !item.value.startsWith("$")) {
        return current.applyCompletion(lines, line, col, item, prefix);
      }
      const updated = [...lines];
      const original = lines[line] ?? "";
      const insertion = `${item.value} `;
      updated[line] = original.slice(0, col - prefix.length) + insertion + original.slice(col);
      return { lines: updated, cursorLine: line, cursorCol: col - prefix.length + insertion.length };
    },
    shouldTriggerFileCompletion(lines, line, col) {
      if (completionPrefix(lines, line, col) !== undefined) return false;
      return current.shouldTriggerFileCompletion?.(lines, line, col) ?? true;
    },
  };
}

export default function dollarSkills(pi: ExtensionAPI): void {
  pi.on("session_start", (_event, ctx) => {
    if (ctx.mode === "tui") {
      ctx.ui.addAutocompleteProvider((current) => skillAutocomplete(current, () => getSkills(pi)));
    }
  });

  pi.on("input", async (event, ctx) => {
    // Don't recursively expand messages generated by extensions or turn shell
    // commands into prompts. Ordinary Pi slash-command dispatch is unchanged.
    if (event.source === "extension" || event.text.trimStart().startsWith("!")) {
      return { action: "continue" };
    }
    const result = await expandSkills(event.text, getSkills(pi));
    if (ctx.hasUI) {
      for (const error of result.errors) ctx.ui.notify(error, "error");
    }
    if (result.text === event.text) return { action: "continue" };
    // Transform in place: Pi retains images and steer/followUp delivery semantics.
    return { action: "transform", text: result.text };
  });
}