// vectord is the vector-search service. HNSW indexes keyed by
// string IDs with optional opaque JSON metadata. Wraps
// github.com/coder/hnsw (pure Go, no cgo).
//
// G1 + persistence: indexes are persisted to storaged at
// _vectors/<name>.{json,hnsw} and rehydrated on startup. Setting
// [vectord].storaged_url empty disables persistence (dev mode).
package main

import (
	"context"
	"encoding/json"
	"errors"
	"flag"
	"log/slog"
	"net/http"
	"os"
	"strconv"
	"strings"
	"time"

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

	"git.agentview.dev/profit/golangLAKEHOUSE/internal/shared"
	"git.agentview.dev/profit/golangLAKEHOUSE/internal/storeclient"
	"git.agentview.dev/profit/golangLAKEHOUSE/internal/vectord"
)

const (
	maxRequestBytes = 64 << 20 // 64 MiB cap for batched Add payloads
	defaultK        = 10
	maxK            = 1000
)

func main() {
	configPath := flag.String("config", "lakehouse.toml", "path to TOML config")
	flag.Parse()

	cfg, err := shared.LoadConfig(*configPath)
	if err != nil {
		slog.Error("config", "err", err)
		os.Exit(1)
	}

	h := &handlers{reg: vectord.NewRegistry()}

	// Persistence is optional — empty StoragedURL = dev/ephemeral mode.
	if cfg.Vectord.StoragedURL != "" {
		h.persist = vectord.NewPersistor(storeclient.New(cfg.Vectord.StoragedURL))

		// Rehydrate any persisted indexes at startup. Failures are
		// logged-not-fatal: storaged might be coming up after vectord,
		// and an index that failed to load is still recoverable by
		// re-ingesting on top of an empty registry.
		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
		n, err := h.rehydrate(ctx)
		cancel()
		if err != nil {
			slog.Warn("rehydrate", "err", err, "loaded", n)
		} else {
			slog.Info("rehydrated", "indexes", n)
		}
	}

	if err := shared.Run("vectord", cfg.Vectord.Bind, h.register); err != nil {
		slog.Error("server", "err", err)
		os.Exit(1)
	}
}

type handlers struct {
	reg     *vectord.Registry
	persist *vectord.Persistor // nil when persistence is disabled
}

// rehydrate enumerates persisted indexes and loads each into the
// registry. Returns the count of successfully loaded indexes plus
// the first error (if any) — caller decides fatality.
func (h *handlers) rehydrate(ctx context.Context) (int, error) {
	if h.persist == nil {
		return 0, nil
	}
	names, err := h.persist.List(ctx)
	if err != nil {
		return 0, err
	}
	loaded := 0
	for _, name := range names {
		idx, err := h.persist.Load(ctx, name)
		if err != nil {
			slog.Warn("rehydrate skip", "name", name, "err", err)
			continue
		}
		// The registry's Create rebuilds an empty Index from params;
		// we want the LOADED one (with vectors). Bypass via a
		// helper that registers a pre-built Index.
		if err := h.reg.RegisterPrebuilt(idx); err != nil {
			slog.Warn("rehydrate register", "name", name, "err", err)
			continue
		}
		loaded++
	}
	return loaded, nil
}

// saveAfter is the post-write persistence hook. Logs-not-fatal:
// in-memory state is the source of truth in flight; a failed save
// gets re-attempted on the next mutation, and the operator log
// shows the storaged outage.
func (h *handlers) saveAfter(idx *vectord.Index) {
	if h.persist == nil {
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()
	if err := h.persist.Save(ctx, idx); err != nil {
		slog.Warn("persist save", "name", idx.Params().Name, "err", err)
	}
}

// deleteAfter mirrors saveAfter for the Delete path.
func (h *handlers) deleteAfter(name string) {
	if h.persist == nil {
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()
	if err := h.persist.Delete(ctx, name); err != nil {
		slog.Warn("persist delete", "name", name, "err", err)
	}
}

func (h *handlers) register(r chi.Router) {
	r.Post("/vectors/index", h.handleCreate)
	r.Get("/vectors/index", h.handleList)
	r.Get("/vectors/index/{name}", h.handleGetIndex)
	r.Delete("/vectors/index/{name}", h.handleDelete)
	r.Post("/vectors/index/{name}/add", h.handleAdd)
	r.Post("/vectors/index/{name}/search", h.handleSearch)
}

// createRequest mirrors POST /vectors/index body.
type createRequest struct {
	Name      string `json:"name"`
	Dimension int    `json:"dimension"`
	M         int    `json:"m,omitempty"`
	EfSearch  int    `json:"ef_search,omitempty"`
	Distance  string `json:"distance,omitempty"`
}

// indexInfo is the GET /vectors/index/{name} response shape.
type indexInfo struct {
	Params vectord.IndexParams `json:"params"`
	Length int                 `json:"length"`
}

// addRequest is the body for POST /vectors/index/{name}/add. Items
// are batched so callers can amortize HTTP overhead — the smoke
// inserts hundreds of vectors per request.
type addRequest struct {
	Items []addItem `json:"items"`
}

type addItem struct {
	ID       string          `json:"id"`
	Vector   []float32       `json:"vector"`
	Metadata json.RawMessage `json:"metadata,omitempty"`
}

// searchRequest is the body for POST /vectors/index/{name}/search.
type searchRequest struct {
	Vector []float32 `json:"vector"`
	K      int       `json:"k,omitempty"`
}

type searchResponse struct {
	Results []vectord.Result `json:"results"`
}

func (h *handlers) handleCreate(w http.ResponseWriter, r *http.Request) {
	var req createRequest
	if !decodeJSON(w, r, &req) {
		return
	}
	idx, err := h.reg.Create(vectord.IndexParams{
		Name:      req.Name,
		Dimension: req.Dimension,
		M:         req.M,
		EfSearch:  req.EfSearch,
		Distance:  req.Distance,
	})
	if errors.Is(err, vectord.ErrIndexAlreadyExists) {
		http.Error(w, err.Error(), http.StatusConflict)
		return
	}
	if errors.Is(err, vectord.ErrInvalidParams) || errors.Is(err, vectord.ErrUnknownDistance) {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	if err != nil {
		slog.Error("create index", "name", req.Name, "err", err)
		http.Error(w, "internal", http.StatusInternalServerError)
		return
	}
	h.saveAfter(idx)
	writeJSON(w, http.StatusCreated, indexInfo{Params: idx.Params(), Length: idx.Len()})
}

func (h *handlers) handleList(w http.ResponseWriter, _ *http.Request) {
	names := h.reg.Names()
	writeJSON(w, http.StatusOK, map[string]any{"names": names, "count": len(names)})
}

func (h *handlers) handleGetIndex(w http.ResponseWriter, r *http.Request) {
	name := chi.URLParam(r, "name")
	idx, err := h.reg.Get(name)
	if errors.Is(err, vectord.ErrIndexNotFound) {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}
	if err != nil {
		http.Error(w, "internal", http.StatusInternalServerError)
		return
	}
	writeJSON(w, http.StatusOK, indexInfo{Params: idx.Params(), Length: idx.Len()})
}

func (h *handlers) handleDelete(w http.ResponseWriter, r *http.Request) {
	name := chi.URLParam(r, "name")
	if err := h.reg.Delete(name); errors.Is(err, vectord.ErrIndexNotFound) {
		http.Error(w, "not found", http.StatusNotFound)
		return
	} else if err != nil {
		http.Error(w, "internal", http.StatusInternalServerError)
		return
	}
	h.deleteAfter(name)
	w.WriteHeader(http.StatusNoContent)
}

func (h *handlers) handleAdd(w http.ResponseWriter, r *http.Request) {
	name := chi.URLParam(r, "name")
	idx, err := h.reg.Get(name)
	if errors.Is(err, vectord.ErrIndexNotFound) {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}
	var req addRequest
	if !decodeJSON(w, r, &req) {
		return
	}
	if len(req.Items) == 0 {
		http.Error(w, "items must be non-empty", http.StatusBadRequest)
		return
	}
	// Per scrum O-W4 (Opus, D5): pre-validate all items before any
	// Add, so a bad item at position N doesn't leave items 0..N-1
	// committed and item N rejected. Per scrum O-I3 (Opus, G1P):
	// extend pre-validation to cover NaN/Inf and zero-norm — these
	// were caught inside idx.Add but only after partial commits.
	params := idx.Params()
	dim := params.Dimension
	for j, it := range req.Items {
		if it.ID == "" {
			http.Error(w, "items["+strconv.Itoa(j)+"]: empty id", http.StatusBadRequest)
			return
		}
		if len(it.Vector) != dim {
			http.Error(w, "items["+strconv.Itoa(j)+"]: dim mismatch (index="+strconv.Itoa(dim)+", got="+strconv.Itoa(len(it.Vector))+")", http.StatusBadRequest)
			return
		}
		if err := vectord.ValidateVector(it.Vector, params.Distance); err != nil {
			http.Error(w, "items["+strconv.Itoa(j)+"]: "+err.Error(), http.StatusBadRequest)
			return
		}
	}
	for j, it := range req.Items {
		if err := idx.Add(it.ID, it.Vector, it.Metadata); err != nil {
			// Vector-validation errors (NaN/Inf, zero-norm under
			// cosine) only surface here; pre-validation is intentional
			// minimal scope (id + dim only).
			if errors.Is(err, vectord.ErrDimensionMismatch) ||
				strings.Contains(err.Error(), "non-finite") ||
				strings.Contains(err.Error(), "zero-norm") {
				http.Error(w, "items["+strconv.Itoa(j)+"]: "+err.Error(), http.StatusBadRequest)
				return
			}
			slog.Error("add", "name", name, "id", it.ID, "err", err)
			http.Error(w, "internal", http.StatusInternalServerError)
			return
		}
	}
	// One save per batch (post-loop), not per item. Per scrum
	// O-W4-style discipline: HTTP-batch boundary is the natural unit.
	h.saveAfter(idx)
	writeJSON(w, http.StatusOK, map[string]any{"added": len(req.Items), "length": idx.Len()})
}

func (h *handlers) handleSearch(w http.ResponseWriter, r *http.Request) {
	name := chi.URLParam(r, "name")
	idx, err := h.reg.Get(name)
	if errors.Is(err, vectord.ErrIndexNotFound) {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}
	var req searchRequest
	if !decodeJSON(w, r, &req) {
		return
	}
	k := req.K
	if k <= 0 {
		k = defaultK
	}
	if k > maxK {
		k = maxK
	}
	hits, err := idx.Search(req.Vector, k)
	if errors.Is(err, vectord.ErrDimensionMismatch) {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	if err != nil {
		slog.Error("search", "name", name, "err", err)
		http.Error(w, "internal", http.StatusInternalServerError)
		return
	}
	writeJSON(w, http.StatusOK, searchResponse{Results: hits})
}

// decodeJSON reads + decodes a JSON body with a body-size cap.
// Returns false (and writes the error response) on failure.
func decodeJSON(w http.ResponseWriter, r *http.Request, v any) bool {
	defer r.Body.Close()
	r.Body = http.MaxBytesReader(w, r.Body, maxRequestBytes)
	if err := json.NewDecoder(r.Body).Decode(v); err != nil {
		var maxErr *http.MaxBytesError
		if errors.As(err, &maxErr) || strings.Contains(err.Error(), "http: request body too large") {
			http.Error(w, "body too large", http.StatusRequestEntityTooLarge)
			return false
		}
		http.Error(w, "decode body: "+err.Error(), http.StatusBadRequest)
		return false
	}
	return true
}

func writeJSON(w http.ResponseWriter, code int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(code)
	if err := json.NewEncoder(w).Encode(v); err != nil {
		slog.Warn("write json", "err", err)
	}
}