package web

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"strings"

	"github.com/go-chi/chi/v5"

	"plumber/internal/store"
)

// handleCreatePost creates either a root question or a reply. Replies are
// limited to the root author and admins, and cannot be added to hidden threads.
func (s *Server) handleCreatePost(w http.ResponseWriter, r *http.Request) {
	if !s.requireCSRF(w, r) {
		return
	}
	user := currentUser(r)
	if user == nil {
		http.Error(w, "authentication required", http.StatusUnauthorized)
		return
	}

	parentID := strings.TrimSpace(r.PostFormValue("parent_id"))
	body := strings.TrimSpace(r.PostFormValue("body"))
	if body == "" {
		http.Error(w, "post body required", http.StatusBadRequest)
		return
	}

	post := &store.Post{
		AuthorID: user.ID,
		Body:     truncateRunes(body, 12000),
	}
	var root *store.Post
	if parentID == "" {
		post.Title = truncateRunes(strings.TrimSpace(r.PostFormValue("title")), 120)
		post.City = truncateRunes(strings.TrimSpace(r.PostFormValue("city")), 80)
		if post.Title == "" {
			http.Error(w, "post title required", http.StatusBadRequest)
			return
		}
	} else {
		parent, threadRoot, err := s.postAndRoot(r.Context(), parentID)
		if err != nil {
			if errors.Is(err, sql.ErrNoRows) {
				http.NotFound(w, r)
				return
			}
			http.Error(w, "could not load thread", http.StatusInternalServerError)
			return
		}
		if threadRoot.PostState == store.PostStateHidden {
			http.NotFound(w, r)
			return
		}
		if !canReplyToThread(user, threadRoot) {
			http.Error(w, "forbidden", http.StatusForbidden)
			return
		}
		post.ParentID = &parent.ID
		root = threadRoot
	}

	if err := s.store.CreatePost(r.Context(), post); err != nil {
		if errors.Is(err, store.ErrInvalidPost) {
			http.Error(w, "invalid post", http.StatusBadRequest)
			return
		}
		http.Error(w, "could not save post", http.StatusInternalServerError)
		return
	}
	if root == nil {
		root = post
	}
	http.Redirect(
		w,
		r,
		"/questions/"+url.PathEscape(root.ID)+"#post-"+url.PathEscape(post.ID),
		http.StatusSeeOther,
	)
}

// handleEditPost updates only a post's body after verifying that the current
// homeowner owns it or that an admin is editing an admin-authored post.
func (s *Server) handleEditPost(w http.ResponseWriter, r *http.Request) {
	if !s.requireCSRF(w, r) {
		return
	}
	user := currentUser(r)
	if user == nil {
		http.Error(w, "authentication required", http.StatusUnauthorized)
		return
	}

	post, root, err := s.postAndRoot(r.Context(), chi.URLParam(r, "id"))
	if err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			http.NotFound(w, r)
			return
		}
		http.Error(w, "could not load post", http.StatusInternalServerError)
		return
	}
	if !canEditPost(user, post) {
		http.Error(w, "forbidden", http.StatusForbidden)
		return
	}

	body := strings.TrimSpace(r.PostFormValue("body"))
	if body == "" {
		http.Error(w, "post body required", http.StatusBadRequest)
		return
	}
	post.Body = truncateRunes(body, 12000)
	if err := s.store.UpdatePost(r.Context(), post); err != nil {
		if errors.Is(err, store.ErrInvalidPost) {
			http.Error(w, "invalid post", http.StatusBadRequest)
			return
		}
		if errors.Is(err, sql.ErrNoRows) {
			http.NotFound(w, r)
			return
		}
		http.Error(w, "could not save post", http.StatusInternalServerError)
		return
	}
	http.Redirect(
		w,
		r,
		"/questions/"+url.PathEscape(root.ID)+"#post-"+url.PathEscape(post.ID),
		http.StatusSeeOther,
	)
}

// postAndRoot loads a post and follows its immutable parent chain to the root.
// It returns both so callers can authorize against the thread and redirect to it.
func (s *Server) postAndRoot(ctx context.Context, postID string) (*store.Post, *store.Post, error) {
	postID = strings.TrimSpace(postID)
	if postID == "" {
		return nil, nil, sql.ErrNoRows
	}
	post, err := s.store.GetPost(ctx, postID)
	if err != nil {
		return nil, nil, err
	}
	current := post
	seen := map[string]bool{}
	for current.ParentID != nil {
		if seen[current.ID] {
			return nil, nil, fmt.Errorf("post ancestry cycle at %s", current.ID)
		}
		seen[current.ID] = true
		current, err = s.store.GetPost(ctx, *current.ParentID)
		if err != nil {
			return nil, nil, err
		}
	}
	return post, current, nil
}

// canEditPost keeps homeowner posts owner-only while allowing admins to edit
// posts authored by an admin.
func canEditPost(user *store.User, post *store.Post) bool {
	if user == nil || post == nil {
		return false
	}
	if post.AuthorRole == store.RoleAdmin {
		return user.Admin()
	}
	return user.ID == post.AuthorID
}

func canReplyToThread(user *store.User, root *store.Post) bool {
	return user != nil &&
		root != nil &&
		root.PostState != store.PostStateHidden &&
		(user.Admin() || user.ID == root.AuthorID)
}

func postLabel(post *store.Post) string {
	if post == nil {
		return ""
	}
	if post.ParentID == nil {
		return "Question"
	}
	if post.AuthorRole == store.RoleAdmin {
		return "Shop response"
	}
	return "Homeowner"
}

func postDepthClass(depth int) string {
	switch depth {
	case 0:
		return "root"
	case 1:
		return "branch"
	default:
		return "deep"
	}
}

func postPointers(posts []store.Post) []*store.Post {
	out := make([]*store.Post, len(posts))
	for i := range posts {
		out[i] = &posts[i]
	}
	return out
}