/**
 * POST /follow - Follow a user
 * DELETE /follow - Unfollow a user
 *
 * Design intent:
 * - Following is explicit and intentional
 * - Mutual follow enables conversation
 * - Cannot follow if blocked
 */

import { serve } from 'https://deno.land/std@0.177.0/http/server.ts';
import { createSupabaseClient } from '../_shared/supabase-client.ts';
import { validateUUID, ValidationError } from '../_shared/validation.ts';

interface FollowRequest {
  user_id: string; // the user to follow/unfollow
}

serve(async (req) => {
  if (req.method === 'OPTIONS') {
    return new Response(null, {
      headers: {
        'Access-Control-Allow-Origin': '*',
        'Access-Control-Allow-Methods': 'POST, DELETE',
        'Access-Control-Allow-Headers': 'authorization, x-client-info, apikey, content-type',
      },
    });
  }

  try {
    const authHeader = req.headers.get('Authorization');
    if (!authHeader) {
      return new Response(JSON.stringify({ error: 'Missing authorization header' }), {
        status: 401,
        headers: { 'Content-Type': 'application/json' },
      });
    }

    const supabase = createSupabaseClient(authHeader);
    const {
      data: { user },
      error: authError,
    } = await supabase.auth.getUser();

    if (authError || !user) {
      return new Response(JSON.stringify({ error: 'Unauthorized' }), {
        status: 401,
        headers: { 'Content-Type': 'application/json' },
      });
    }

    let { user_id: following_id } = (await req.json()) as FollowRequest;
    validateUUID(following_id, 'user_id');
    following_id = following_id.toLowerCase();

    if (following_id === user.id.toLowerCase()) {
      return new Response(
        JSON.stringify({ error: 'Cannot follow yourself' }),
        { status: 400, headers: { 'Content-Type': 'application/json' } }
      );
    }

    // Handle unfollow
    if (req.method === 'DELETE') {
      const { error: deleteError } = await supabase
        .from('follows')
        .delete()
        .eq('follower_id', user.id)
        .eq('following_id', following_id);

      if (deleteError) {
        console.error('Error unfollowing:', deleteError);
        return new Response(JSON.stringify({ error: 'Failed to unfollow' }), {
          status: 500,
          headers: { 'Content-Type': 'application/json' },
        });
      }

      return new Response(JSON.stringify({ success: true, message: 'Unfollowed' }), {
        status: 200,
        headers: { 'Content-Type': 'application/json' },
      });
    }

    // Handle follow (POST) via request_follow
    const { data: status, error: followError } = await supabase
      .rpc('request_follow', { target_id: following_id });

    if (followError) {
      if (followError.message?.includes('Cannot follow') || followError.code === '23514') {
        return new Response(
          JSON.stringify({ error: 'Cannot follow this user' }),
          { status: 403, headers: { 'Content-Type': 'application/json' } }
        );
      }

      console.error('Error following:', followError);
      return new Response(JSON.stringify({ error: 'Failed to follow' }), {
        status: 500,
        headers: { 'Content-Type': 'application/json' },
      });
    }

    const followStatus = status as string | null;
    const message =
      followStatus === 'pending'
        ? 'Request sent.'
        : 'Followed. Mutual follow enables conversation.';

    return new Response(
      JSON.stringify({
        success: true,
        status: followStatus,
        message,
      }),
      {
        status: 200,
        headers: { 'Content-Type': 'application/json' },
      }
    );
  } catch (error) {
    if (error instanceof ValidationError) {
      return new Response(
        JSON.stringify({ error: 'Validation error', message: error.message }),
        { status: 400, headers: { 'Content-Type': 'application/json' } }
      );
    }

    console.error('Unexpected error:', error);
    return new Response(JSON.stringify({ error: 'Internal server error' }), {
      status: 500,
      headers: { 'Content-Type': 'application/json' },
    });
  }
});