package service

import (
	"axolotl/models"
	"axolotl/store"
	"maps"
	"regexp"
	"slices"
	"time"
)

type nodeServiceImpl struct {
	store  store.Store
	userID string
}

var mentionRegex = regexp.MustCompile(`@([a-z0-9_]+)`)

func mentions(t string) []string {
	seen := make(map[string]bool)
	for _, m := range mentionRegex.FindAllStringSubmatch(t, -1) {
		seen[m[1]] = true
	}
	return slices.Collect(maps.Keys(seen))
}

func (s *nodeServiceImpl) GetByID(id string) (*models.Node, error) {
	return s.store.GetNode(id)
}

func (s *nodeServiceImpl) Exists(id string) (bool, error) {
	return s.store.NodeExists(id)
}

func (s *nodeServiceImpl) Delete(id string) error {
	return s.store.DeleteNode(id)
}

func (s *nodeServiceImpl) CanClose(id string) (bool, []string, error) {
	node, err := s.store.GetNode(id)
	if err != nil {
		return false, nil, err
	}
	blockerIDs := node.Relations()[string(models.RelBlocks)]
	var blocking []string
	for _, bID := range blockerIDs {
		blocker, err := s.store.GetNode(bID)
		if err != nil {
			return false, nil, err
		}
		if blocker.GetProperty("status") == "open" {
			blocking = append(blocking, bID)
		}
	}
	return len(blocking) == 0, blocking, nil
}

func (s *nodeServiceImpl) List(opts ...ListOption) ([]*models.Node, error) {
	f := &listFilter{}
	for _, opt := range opts {
		opt(f)
	}

	// Resolve rel filter targets from names to node IDs (read-only, no auto-creation).
	resolvedRels := make([]*models.Rel, 0, len(f.relPrefixes))
	for _, rel := range f.relPrefixes {
		resolvedID, ok := s.lookupRelTarget(rel.Type, rel.Target)
		if !ok {
			return nil, nil // target doesn't exist; no nodes can match
		}
		resolvedRels = append(resolvedRels, &models.Rel{Type: rel.Type, Target: resolvedID})
	}

	return s.store.FindNodes(f.tagPrefixes, resolvedRels)
}

// lookupRelTarget resolves a rel filter target (name or ID) to a node ID without
// creating anything. Returns (id, false) when the target doesn't exist in the store.
func (s *nodeServiceImpl) lookupRelTarget(relType models.RelType, target string) (string, bool) {
	if exists, _ := s.store.NodeExists(target); exists {
		return target, true
	}
	var nodeType string
	switch relType {
	case models.RelAssignee, models.RelCreated, models.RelMentions:
		nodeType = "user"
	case models.RelInNamespace:
		nodeType = "namespace"
	default:
		return target, true // other rel types expect a raw node ID
	}
	id, err := s.resolveIDByNameAndType(s.store, target, nodeType)
	if err != nil || id == "" {
		return "", false
	}
	return id, true
}

func (s *nodeServiceImpl) Create(title, content, dueDate string, tags []string, rels map[models.RelType][]string) (*models.Node, error) {
	id, err := s.store.GenerateID()
	if err != nil {
		return nil, err
	}

	err = s.store.Transaction(func(st store.Store) error {
		now := time.Now().UTC().Format(time.RFC3339)
		if err := st.AddNode(id, title, content, dueDate, now, now); err != nil {
			return err
		}

		for _, m := range mentions(title + " " + content) {
			userID, err := s.resolveUserRef(st, m)
			if err != nil {
				return err
			}
			if err := st.AddEdge(id, userID, models.RelMentions); err != nil {
				return err
			}
		}

		for _, t := range tags {
			if err := st.AddTag(id, t); err != nil {
				return err
			}
		}

		hasCreated := false
		for rt, tgts := range rels {
			for _, tgt := range tgts {
				if rt == models.RelCreated {
					hasCreated = true
				}
				if rt == models.RelAssignee || rt == models.RelCreated {
					var err error
					if tgt, err = s.resolveUserRef(st, tgt); err != nil {
						return err
					}
				}
				if rt == models.RelInNamespace {
					var err error
					if tgt, err = s.resolveNamespaceRef(st, tgt); err != nil {
						return err
					}
				}
				if err := st.AddEdge(id, tgt, rt); err != nil {
					return err
				}
			}
		}

		if !hasCreated {
			userID, err := s.resolveUserRef(st, s.userID)
			if err != nil {
				return err
			}
			if err := st.AddEdge(id, userID, models.RelCreated); err != nil {
				return err
			}
		}

		return nil
	})
	if err != nil {
		return nil, err
	}
	return s.store.GetNode(id)
}

func (s *nodeServiceImpl) Update(node *models.Node) error {
	current, err := s.store.GetNode(node.ID)
	if err != nil {
		return err
	}

	return s.store.Transaction(func(st store.Store) error {
		// Update scalar fields if changed.
		if node.Title != current.Title || node.Content != current.Content || node.DueDate != current.DueDate {
			updatedAt := time.Now().UTC().Format(time.RFC3339)
			if err := st.UpdateNode(node.ID, node.Title, node.Content, node.DueDate, updatedAt); err != nil {
				return err
			}
		}

		// Sync mention edges when title or content changed.
		if node.Title != current.Title || node.Content != current.Content {
			newMentions := mentions(node.Title + " " + node.Content)

			existingMentionIDs := make(map[string]bool)
			for _, uid := range current.Relations()[string(models.RelMentions)] {
				existingMentionIDs[uid] = true
			}

			mentionedUserIDs := make(map[string]bool)
			for _, m := range newMentions {
				userID, err := s.resolveUserRef(st, m)
				if err != nil {
					return err
				}
				mentionedUserIDs[userID] = true
				if !existingMentionIDs[userID] {
					if err := st.AddEdge(node.ID, userID, models.RelMentions); err != nil {
						return err
					}
				}
			}
			for uid := range existingMentionIDs {
				if !mentionedUserIDs[uid] {
					if err := st.RemoveEdge(node.ID, uid, models.RelMentions); err != nil {
						return err
					}
				}
			}
		}

		// Sync tags.
		currentTags := current.Tags()
		nodeTags := node.Tags()
		for _, t := range currentTags {
			if !slices.Contains(nodeTags, t) {
				if err := st.RemoveTag(node.ID, t); err != nil {
					return err
				}
			}
		}
		for _, t := range nodeTags {
			if !slices.Contains(currentTags, t) {
				if err := st.AddTag(node.ID, t); err != nil {
					return err
				}
			}
		}

		// Sync edges (excluding mention edges, already handled above).
		currentRels := current.Relations()
		nodeRels := node.Relations()
		for rt, tgts := range currentRels {
			if rt == string(models.RelMentions) {
				continue
			}
			for _, tgt := range tgts {
				if nodeRels[rt] == nil || !slices.Contains(nodeRels[rt], tgt) {
					if err := st.RemoveEdge(node.ID, tgt, models.RelType(rt)); err != nil {
						return err
					}
				}
			}
		}
		for rt, tgts := range nodeRels {
			if rt == string(models.RelMentions) {
				continue
			}
			for _, tgt := range tgts {
				if currentRels[rt] == nil || !slices.Contains(currentRels[rt], tgt) {
					resolvedTgt := tgt
					if models.RelType(rt) == models.RelAssignee || models.RelType(rt) == models.RelCreated {
						var err error
						if resolvedTgt, err = s.resolveUserRef(st, tgt); err != nil {
							return err
						}
					}
					if models.RelType(rt) == models.RelInNamespace {
						var err error
						if resolvedTgt, err = s.resolveNamespaceRef(st, tgt); err != nil {
							return err
						}
					}
					if err := st.AddEdge(node.ID, resolvedTgt, models.RelType(rt)); err != nil {
						return err
					}
				}
			}
		}

		return nil
	})
}

// resolveIDByNameAndType finds a node by title and _type tag.
// Loads all nodes of that type and filters in-memory (few users/namespaces expected).
func (s *nodeServiceImpl) resolveIDByNameAndType(st store.Store, title, nodeType string) (string, error) {
	nodes, err := st.FindNodes([]string{"_type::" + nodeType}, nil)
	if err != nil {
		return "", err
	}
	for _, n := range nodes {
		if n.Title == title {
			return n.ID, nil
		}
	}
	return "", nil
}

func (s *nodeServiceImpl) resolveUserRef(st store.Store, ref string) (string, error) {
	if exists, _ := st.NodeExists(ref); exists {
		return ref, nil
	}
	return s.ensureUser(st, ref)
}

func (s *nodeServiceImpl) ensureUser(st store.Store, username string) (string, error) {
	userID, err := s.resolveIDByNameAndType(st, username, "user")
	if err != nil {
		return "", err
	}
	if userID != "" {
		return userID, nil
	}

	id, err := st.GenerateID()
	if err != nil {
		return "", err
	}
	now := time.Now().UTC().Format(time.RFC3339)
	if err := st.AddNode(id, username, "", "", now, now); err != nil {
		return "", err
	}
	if err := st.AddTag(id, "_type::user"); err != nil {
		return "", err
	}
	return id, nil
}

func (s *nodeServiceImpl) resolveNamespaceRef(st store.Store, ref string) (string, error) {
	if exists, _ := st.NodeExists(ref); exists {
		return ref, nil
	}
	return s.ensureNamespace(st, ref)
}

func (s *nodeServiceImpl) ensureNamespace(st store.Store, name string) (string, error) {
	nsID, err := s.resolveIDByNameAndType(st, name, "namespace")
	if err != nil {
		return "", err
	}
	if nsID != "" {
		return nsID, nil
	}

	id, err := st.GenerateID()
	if err != nil {
		return "", err
	}
	now := time.Now().UTC().Format(time.RFC3339)
	if err := st.AddNode(id, name, "", "", now, now); err != nil {
		return "", err
	}
	if err := st.AddTag(id, "_type::namespace"); err != nil {
		return "", err
	}
	if err := st.AddEdge(id, id, models.RelInNamespace); err != nil {
		return "", err
	}
	userID, err := s.resolveUserRef(st, s.userID)
	if err != nil {
		return "", err
	}
	if err := st.AddEdge(id, userID, models.RelCreated); err != nil {
		return "", err
	}
	return id, nil
}