// Package knowledge implements the RAG knowledge-base data source described in
// DevDocs/design/10-后台管理面板.md §3.12 (module 8 知识库 RAG) and the
// knowledge/memory separation in DevDocs/design/03-记忆.md §3 (③ 知识库 =
// 参考资料, 记忆 = 经历).
//
// It reads the project index (项目索引 → 项目描述 → 章节内容) as the set of knowledge
// documents and answers searches over it with line-level context. When a semantic
// retriever is wired, it also folds in project-linked long-term memories as
// semantic hits, ranked by the retriever's real keyword × semantic × decay path —
// so a configured vector index (pgvector / SQLite vector) is genuinely used and
// never a shell.
//
// The store is read-only for this milestone: upload/chunk/embed and delete land
// in M10. The write methods return ErrWriteUnsupported so the admin handler can
// answer honestly instead of fabricating a success.
package knowledge

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"strings"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/logger"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/memory"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/memory/projectindex"
)

// ErrWriteUnsupported is returned by the write operations. Upload/chunk/embed and
// delete are milestone M10; the admin handler maps it to a clear 501 so the
// frontend can explain rather than show a placeholder alert.
var ErrWriteUnsupported = errors.New("knowledge: write operations (upload/chunk/embed/delete) land in M10")

// defaultTopK bounds the semantic retrieval path.
const defaultTopK = 8

// Retriever is the subset of the memory retriever the knowledge store uses for
// semantic ranking. *memory.Retriever implements it; nil means no semantic path.
type Retriever interface {
	Retrieve(ctx context.Context, personaID, query string, topK int) ([]memory.Result, error)
}

// Doc is one knowledge-base document backing a project-index entry.
type Doc struct {
	// ID is the project index id.
	ID string
	// Name is the project title (the document's display name).
	Name string
	// Desc is the project description (layer 2 of the hierarchy).
	Desc string
	// Chunks is the number of chapters the document is split into.
	Chunks int
	// Embedded reports whether a persistent vector index is wired for this
	// deployment. This is the deployment-level semantic capability; per-document
	// embedding state is not tracked yet (M10).
	Embedded bool
}

// Hit is one retrieval result surfaced to the admin panel.
type Hit struct {
	// DocID is the owning project index id.
	DocID string
	// DocName is the owning project title.
	DocName string
	// Chapter is the chapter title that matched (empty for a semantic/memory hit).
	Chapter string
	// Text is the matched content: a chapter's located line(s) with context, or
	// the memory content for a semantic hit.
	Text string
	// Score is the relevance score (higher = more relevant).
	Score float64
	// Semantic reports whether the hit was ranked by the semantic/vector path.
	Semantic bool
}

// Deps carries the construction inputs. Every field is nil-tolerant so a store
// without a project index or retriever degrades to read-only empty answers.
type Deps struct {
	// Projects is the project index backing the document list and text search.
	// Optional; when nil the document list and text search return empty.
	Projects *projectindex.Store
	// Retriever ranks project-linked memories semantically. Optional; the
	// semantic path runs only when both Retriever and DefaultPersona are set.
	Retriever Retriever
	// DefaultPersona scopes semantic retrieval to one persona. Optional.
	DefaultPersona string
	// VectorOn reports whether a persistent vector index (pgvector / SQLite
	// vector) is wired, so Doc.Embedded is honest and never a shell.
	VectorOn bool
	// Log is the base logger. Nil uses a discard logger tagged with this package.
	Log *slog.Logger
}

// Store is the RAG data source. It is stateless and safe for concurrent use.
type Store struct {
	projects       *projectindex.Store
	retriever      Retriever
	defaultPersona string
	vectorOn       bool
	log            *slog.Logger
}

// New builds a Store. Availability degrades gracefully: a nil project index means
// no documents, a nil retriever means keyword/line search only.
func New(d Deps) *Store {
	log := d.Log
	if log == nil {
		log = slog.New(slog.NewTextHandler(io.Discard, nil))
	}
	return &Store{
		projects:       d.Projects,
		retriever:      d.Retriever,
		defaultPersona: strings.TrimSpace(d.DefaultPersona),
		vectorOn:       d.VectorOn,
		log:            logger.WithSource(log, "runtime/knowledge"),
	}
}

// ListDocuments enumerates the knowledge-base documents (project-index entries).
// A nil project index returns an empty, non-nil slice.
func (s *Store) ListDocuments(ctx context.Context) ([]Doc, error) {
	out := make([]Doc, 0)
	if s.projects == nil {
		return out, nil
	}
	projects, err := s.projects.ListProjects(ctx)
	if err != nil {
		return nil, fmt.Errorf("knowledge: list projects: %w", err)
	}
	for i := range projects {
		chapters, cerr := s.projects.ListChapters(ctx, projects[i].ID)
		if cerr != nil {
			s.log.Error("list chapters", "project", projects[i].ID, "err", cerr)
			continue
		}
		out = append(out, Doc{
			ID:       projects[i].ID,
			Name:     projects[i].Title,
			Desc:     projects[i].Desc,
			Chunks:   len(chapters),
			Embedded: s.vectorOn,
		})
	}
	return out, nil
}

// Search runs the knowledge-base search over the project index (line-level,
// hierarchy-aware) and, when a semantic retriever is configured, folds in
// project-linked memories ranked by the real vector path. A blank query returns
// no hits.
func (s *Store) Search(ctx context.Context, query string) ([]Hit, error) {
	hits := make([]Hit, 0)
	if strings.TrimSpace(query) == "" {
		return hits, nil
	}
	if s.projects != nil {
		textHits, err := s.searchProjects(ctx, query)
		if err != nil {
			return nil, err
		}
		hits = append(hits, textHits...)
	}
	if s.retriever != nil && s.defaultPersona != "" {
		semHits, err := s.searchSemantic(ctx, query)
		if err != nil {
			s.log.Error("semantic search", "err", err)
		} else {
			hits = append(hits, semHits...)
		}
	}
	return hits, nil
}

// searchProjects walks every project and returns chapter/item hits via
// projectindex.Search (keyword + line context). A project deleted between the
// list and the search is skipped rather than failing the whole search.
func (s *Store) searchProjects(ctx context.Context, query string) ([]Hit, error) {
	projects, err := s.projects.ListProjects(ctx)
	if err != nil {
		return nil, fmt.Errorf("knowledge: list projects: %w", err)
	}
	hits := make([]Hit, 0)
	for i := range projects {
		res, err := s.projects.Search(ctx, projects[i].ID, query)
		if errors.Is(err, projectindex.ErrProjectNotFound) {
			continue
		}
		if err != nil {
			return nil, fmt.Errorf("knowledge: search project %q: %w", projects[i].ID, err)
		}
		if res.Project != nil {
			hits = append(hits, Hit{
				DocID:   res.Project.ID,
				DocName: res.Project.Title,
				Text:    describeProject(res.Project),
				Score:   float64(len(res.Chapters) + 1),
			})
		}
		for _, ch := range res.Chapters {
			hits = append(hits, chapterHit(projects[i], ch))
		}
	}
	return hits, nil
}

// searchSemantic ranks memories via the retriever's real retrieval path and maps
// each project-linked result to a Hit (marked Semantic so the panel can show it).
func (s *Store) searchSemantic(ctx context.Context, query string) ([]Hit, error) {
	results, err := s.retriever.Retrieve(ctx, s.defaultPersona, query, defaultTopK)
	if err != nil {
		return nil, fmt.Errorf("knowledge: retrieve: %w", err)
	}
	hits := make([]Hit, 0, len(results))
	for _, r := range results {
		if r.Project == nil {
			continue
		}
		hits = append(hits, Hit{
			DocID:    r.Project.ID,
			DocName:  r.Project.Title,
			Text:     r.Item.Content,
			Score:    r.Score,
			Semantic: true,
		})
	}
	return hits, nil
}

// chapterHit maps a matched chapter to a Hit. Text is the located line plus its
// surrounding context (projectindex.LineMatch.Context), and Score reflects how
// many lines in the chapter matched.
func chapterHit(p projectindex.Project, ch projectindex.ChapterHit) Hit {
	text := ""
	if len(ch.Matches) > 0 {
		text = ch.Matches[0].Context
	}
	return Hit{
		DocID:   p.ID,
		DocName: p.Title,
		Chapter: ch.Chapter.Title,
		Text:    text,
		Score:   float64(len(ch.Matches)),
	}
}

// describeProject summarizes a project-index hit (title/desc match) for the panel.
func describeProject(p *projectindex.Project) string {
	if p.Desc != "" {
		return p.Desc
	}
	return p.Title
}

// IndexDocument is not implemented in this milestone. It returns
// ErrWriteUnsupported so the handler answers honestly (upload/chunk/embed = M10).
func (s *Store) IndexDocument(_ context.Context, _ Doc) error {
	return ErrWriteUnsupported
}

// DeleteDocument is not implemented in this milestone. It returns
// ErrWriteUnsupported so the handler answers honestly (delete = M10).
func (s *Store) DeleteDocument(_ context.Context, _ string) error {
	return ErrWriteUnsupported
}