import type {
  BuildSystemPromptOptions,
  ExtensionContext,
  Skill,
} from "@earendil-works/pi-coding-agent";

function unescapeXml(text: string): string {
  return text
    .replace(/&lt;/g, "<")
    .replace(/&gt;/g, ">")
    .replace(/&quot;/g, '"')
    .replace(/&apos;/g, "'")
    .replace(/&amp;/g, "&");
}

function isLikelyContextFileHeading(value: string): boolean {
  return (
    value.includes("/") ||
    value.includes("\\") ||
    value.startsWith("~") ||
    /(?:^|\b)(?:AGENTS|CLAUDE|SYSTEM|APPEND_SYSTEM)\.md$/i.test(value)
  );
}

function deriveSkills(systemPrompt: string): Skill[] {
  const skills: Skill[] = [];
  const skillRegex =
    /<skill>\s*<name>([\s\S]*?)<\/name>\s*<description>([\s\S]*?)<\/description>\s*<location>([\s\S]*?)<\/location>\s*<\/skill>/g;

  for (const match of systemPrompt.matchAll(skillRegex)) {
    skills.push({
      name: unescapeXml(match[1].trim()),
      description: unescapeXml(match[2].trim()),
      filePath: unescapeXml(match[3].trim()),
    } as Skill);
  }

  return skills;
}

function sliceProjectContextSection(systemPrompt: string): string | null {
  const sectionMarker = "\n\n# Project Context\n\n";
  const projectContextStart = systemPrompt.indexOf(sectionMarker);
  if (projectContextStart < 0) {
    return null;
  }

  let projectContext = systemPrompt.slice(projectContextStart + sectionMarker.length);
  const intro = "Project-specific instructions and guidelines:\n\n";
  if (projectContext.startsWith(intro)) {
    projectContext = projectContext.slice(intro.length);
  }

  const skillsMarker =
    "\n\nThe following skills provide specialized instructions for specific tasks.";
  const skillsIndex = projectContext.indexOf(skillsMarker);
  if (skillsIndex >= 0) {
    projectContext = projectContext.slice(0, skillsIndex);
  }

  const dateIndex = projectContext.indexOf("\nCurrent date: ");
  if (dateIndex >= 0) {
    projectContext = projectContext.slice(0, dateIndex);
  }

  return projectContext;
}

function deriveContextFiles(systemPrompt: string): Array<{ path: string; content: string }> {
  const projectContext = sliceProjectContextSection(systemPrompt);
  if (!projectContext) {
    return [];
  }

  const contextFiles: Array<{ path: string; content: string }> = [];
  const headingRegex = /^##\s+(.+)$/gm;

  let match = headingRegex.exec(projectContext);
  while (match !== null) {
    const filePath = match[1].trim();
    const contentStart = match.index + match[0].length;

    const nextMatch = headingRegex.exec(projectContext);
    const contentEnd = nextMatch ? nextMatch.index : projectContext.length;

    let content = projectContext.slice(contentStart, contentEnd);
    if (content.startsWith("\n\n")) {
      content = content.slice(2);
    }
    if (content.endsWith("\n\n")) {
      content = content.slice(0, -2);
    }

    if (isLikelyContextFileHeading(filePath)) {
      contextFiles.push({ path: filePath, content });
    }

    match = nextMatch;
  }

  return contextFiles;
}

export function extractGuidelinesSection(systemPrompt: string): string | null {
  const marker = "\nGuidelines:\n";
  const start = systemPrompt.indexOf(marker);
  if (start < 0) {
    return null;
  }

  const afterStart = start + marker.length;
  const endMarkers = ["\n\nPi documentation", "\n\n# Project Context", "\nCurrent date: "];
  let end = systemPrompt.length;
  for (const endMarker of endMarkers) {
    const index = systemPrompt.indexOf(endMarker, afterStart);
    if (index >= 0) {
      end = Math.min(end, index);
    }
  }

  const section = systemPrompt.slice(afterStart, end).trim();
  return section.length > 0 ? section : null;
}

export function deriveOptionsFromSystemPrompt(
  ctx: ExtensionContext,
  cachedOptions: BuildSystemPromptOptions | undefined,
): BuildSystemPromptOptions | undefined {
  const systemPrompt = ctx.getSystemPrompt();
  const derivedFiles = deriveContextFiles(systemPrompt);
  const derivedSkills = deriveSkills(systemPrompt);

  if (cachedOptions) {
    const hasFiles = cachedOptions.contextFiles && cachedOptions.contextFiles.length > 0;
    const hasSkills = cachedOptions.skills && cachedOptions.skills.length > 0;
    if (hasFiles && hasSkills) {
      return cachedOptions;
    }
    return {
      ...cachedOptions,
      contextFiles: hasFiles ? cachedOptions.contextFiles : derivedFiles,
      skills: hasSkills ? cachedOptions.skills : derivedSkills,
    };
  }

  if (derivedFiles.length === 0 && derivedSkills.length === 0) {
    return undefined;
  }

  return {
    cwd: ctx.cwd,
    contextFiles: derivedFiles,
    skills: derivedSkills,
  };
}