import { sidebar as defaultSidebar } from '@/docs.config';
import type { Sidebar, SupportedFramework } from '@/types/docs';
import { DEFAULT_FRAMEWORK, isValidFramework } from '@/types/docs';
import { findFirstGuide, findGuideBySlug, getValidFrameworksForGuide } from './sidebar';

/**
 * Build a docs URL from framework and guide slug components.
 */
export function buildDocsUrl(framework: SupportedFramework, guideSlug: string): string {
  return `/docs/framework/${framework}/${guideSlug}`;
}

/**
 * Input for resolveIndexRedirect
 */
export interface IndexRedirectInput {
  preferences: {
    framework: string | null;
  };
  params: {
    framework?: string;
  };
}

/**
 * Output from resolveIndexRedirect
 */
export interface IndexRedirectResult {
  url: string;
  selectedFramework: SupportedFramework;
  selectedSlug: string;
  reason: string;
}

/**
 * Resolve redirect for index pages (/docs, /docs/framework/X).
 * Nothing is pinned - we must select framework AND slug.
 *
 * Logic:
 * 1. If params.framework → validate → find first guide
 * 2. If no param → get from preferences or defaults → find first guide
 *
 * @param input - The input containing preferences and params
 * @param sidebar - Optional sidebar to search (defaults to main sidebar config)
 */
export function resolveIndexRedirect(
  input: IndexRedirectInput,
  sidebar: Sidebar = defaultSidebar
): IndexRedirectResult {
  const { preferences, params } = input;

  let selectedFramework: SupportedFramework;
  let reason: string;

  if (params.framework) {
    // Framework in params - validate it
    if (!isValidFramework(params.framework)) {
      throw new Error(`Invalid framework param: ${params.framework}`);
    }
    selectedFramework = params.framework;
    reason = 'Using validated params.framework';
  } else {
    // No params - use preferences or defaults
    if (preferences.framework && isValidFramework(preferences.framework)) {
      selectedFramework = preferences.framework;
      reason = 'Using preferences.framework';
    } else {
      // Use all defaults
      selectedFramework = DEFAULT_FRAMEWORK;
      reason = 'Using default framework (no valid preferences)';
    }
  }

  // Find the first guide for the selected framework
  const selectedSlug = findFirstGuide(selectedFramework, sidebar);
  const url = buildDocsUrl(selectedFramework, selectedSlug);

  return {
    url,
    selectedFramework,
    selectedSlug,
    reason,
  };
}

/**
 * Input for resolveFrameworkChange
 */
export interface FrameworkChangeInput {
  currentFramework: SupportedFramework;
  currentSlug: string;
  newFramework: SupportedFramework;
}

/**
 * Output from resolveFrameworkChange
 */
export interface FrameworkChangeResult {
  url: string;
  shouldReplace: boolean;
  selectedFramework: SupportedFramework;
  selectedSlug: string;
  slugChanged: boolean;
  reason: string;
}

/**
 * Resolve URL when user changes framework selector.
 * newFramework is PINNED (must keep), slug MAY change if not visible.
 *
 * Logic:
 * 1. framework = newFramework (PINNED)
 * 2. If currentSlug visible in newFramework → slug = currentSlug, shouldReplace = true
 *    Else → slug = first guide in newFramework, shouldReplace = false
 *
 * @param input - The input containing current state and new framework
 * @param sidebar - Optional sidebar to search (defaults to main sidebar config)
 */
export function resolveFrameworkChange(
  input: FrameworkChangeInput,
  sidebar: Sidebar = defaultSidebar
): FrameworkChangeResult {
  const { currentSlug, newFramework } = input;

  if (!isValidFramework(newFramework)) {
    throw new Error(`Invalid framework: ${newFramework}`);
  }

  const selectedFramework = newFramework; // PINNED

  // Determine the slug to use
  let selectedSlug: string;
  let shouldReplace: boolean;
  let slugChanged: boolean;
  let reason: string;

  const guide = findGuideBySlug(currentSlug, sidebar);
  const validFrameworks = guide ? getValidFrameworksForGuide(guide, sidebar) : [];
  if (guide && validFrameworks.includes(selectedFramework)) {
    // Current slug is visible in the new framework
    selectedSlug = currentSlug;
    shouldReplace = true;
    slugChanged = false;
    reason = 'Changed framework, kept slug (visible in new framework)';
  } else {
    // Current slug is not visible, find first guide
    selectedSlug = findFirstGuide(selectedFramework, sidebar);
    shouldReplace = false;
    slugChanged = true;
    reason = 'Changed framework, changed slug (slug not visible in new framework)';
  }

  const url = buildDocsUrl(selectedFramework, selectedSlug);

  return {
    url,
    shouldReplace,
    selectedFramework,
    selectedSlug,
    slugChanged,
    reason,
  };
}

/**
 * Input for resolveDocsLinkUrl
 */
export interface DocsLinkInput {
  targetSlug: string;
  contextFramework: SupportedFramework;
}

/**
 * Output from resolveDocsLinkUrl
 */
export interface DocsLinkResult {
  url: string;
  selectedFramework: SupportedFramework;
  selectedSlug: string;
  priorityLevel: 1 | 2;
  reason: string;
}

/**
 * Resolve the best URL for a guide slug link given current context.
 * targetSlug is PINNED (must keep), framework MAY change.
 *
 * Logic (2-level priority cascade):
 * 1. slug = targetSlug (PINNED)
 * 2. Try to find best framework that supports targetSlug:
 *    - Priority 1: If targetSlug visible in contextFramework → use it (best UX)
 *    - Priority 2: Use guide's first valid framework
 *
 * @param input - The input containing target slug and context
 * @param sidebar - Optional sidebar to search (defaults to main sidebar config)
 */
export function resolveDocsLinkUrl(input: DocsLinkInput, sidebar: Sidebar = defaultSidebar): DocsLinkResult {
  const { targetSlug, contextFramework } = input;

  const guide = findGuideBySlug(targetSlug, sidebar);
  if (!guide) {
    throw new Error(`No guide found with slug "${targetSlug}"`);
  }

  if (!isValidFramework(contextFramework)) {
    throw new Error(`Invalid context framework: ${contextFramework}`);
  }

  const selectedSlug = targetSlug; // PINNED
  let selectedFramework: SupportedFramework;
  let priorityLevel: 1 | 2;
  let reason: string;

  // Priority 1: Try current framework
  const validFrameworks = getValidFrameworksForGuide(guide, sidebar);
  if (validFrameworks.includes(contextFramework)) {
    selectedFramework = contextFramework;
    priorityLevel = 1;
    reason = 'Priority 1: Kept framework (slug visible in current context)';
  } else {
    // Priority 2: Fallback to guide's first valid framework
    selectedFramework = validFrameworks[0];
    priorityLevel = 2;
    reason = 'Priority 2: Changed framework (slug not visible in current context)';
  }

  const url = buildDocsUrl(selectedFramework, selectedSlug);

  return {
    url,
    selectedFramework,
    selectedSlug,
    priorityLevel,
    reason,
  };
}