package classes

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"regexp"
	"slices"
	"strconv"
	"strings"

	"git.golem15.com/golem15/summercms/modules/backpack"
	"git.golem15.com/golem15/summercms/modules/beachcomber"
	"git.golem15.com/golem15/summercms/modules/beachcomber/typesense"
	"git.golem15.com/golem15/summercms/modules/diary"
	"git.golem15.com/golem15/summercms/modules/lagoon"
	"git.golem15.com/jakub/sm-bm-plugin/models"
	"gorm.io/gorm"
)

// materialSearchKey marks a context whose syncs belong to jz.bm.
type materialSearchKey struct{}

// MarkMaterialSearch returns ctx marked as a jz.bm material sync. The
// app-wide beachcomber Gate (MaterialSearchGate) is on only for a marked
// context, so every jz.bm Sync or Remove passes one.
func MarkMaterialSearch(ctx context.Context) context.Context {
	if ctx == nil {
		ctx = context.Background()
	}
	return context.WithValue(ctx, materialSearchKey{}, true)
}

// MaterialSearchGate is the app-wide beachcomber Gate jz.bm installs. The
// Gate sees only (ctx, db), not the model, so it is on only for a context
// marked by MarkMaterialSearch: golem15.chatchannels syncs its messages
// with unmarked contexts, and chat messages and DMs never reach the index.
// The automatic callbacks of material writes are off as well; every jz.bm
// write path syncs explicitly.
func MaterialSearchGate() beachcomber.Gate {
	return beachcomber.GateFunc(func(ctx context.Context, _ *gorm.DB) bool {
		return ctx != nil && ctx.Value(materialSearchKey{}) != nil
	})
}

// MaterialSearchWindow is how many engine candidates one search re-gates in
// SQL. The list counts and pages over the gated rows, so a page never
// depends on how the engine paged.
const MaterialSearchWindow = typesense.MaxPerPage

// MaterialQueryBy are the document fields a query is matched against, and
// MaterialQueryWeights their weights in the same order: the title over the
// tags, the source and the course, then the body, the link and file text.
var (
	MaterialQueryBy      = []string{"title", "tags", "source", "course", "url", "body", "file_texts"}
	MaterialQueryWeights = []int{6, 4, 3, 3, 1, 2, 1}
)

// materialHighlightFields are the fields snippets are cut from.
var materialHighlightFields = []string{"body", "file_texts"}

// ErrSearchUnavailable is returned by Search when the engine is not
// configured or the search failed. The API answers it with a 503.
var ErrSearchUnavailable = errors.New("jz.bm: search is unavailable")

// MaterialSearch is one material search: the query text and the validated
// filters of the list.
type MaterialSearch struct {
	Q         string
	CourseID  uint
	MeetingID uint
	Type      string
	Tag       string
}

// MaterialCandidates are the engine's answer: the candidate ids in rank
// order and the Hit of each. Both are candidates only: the caller re-gates
// the ids in SQL and reads the Hit of a row only once SQL returned it.
// Highlights reports whether the engine was asked for snippets.
type MaterialCandidates struct {
	IDs        []uint
	Hits       map[uint]beachcomber.Hit
	Highlights bool
}

// MaterialIndexer searches the materials index and keeps it current. A nil
// *MaterialIndexer is valid: Search answers ErrSearchUnavailable and the
// syncs do nothing.
type MaterialIndexer struct {
	// Service returns the app's beachcomber service, or nil.
	Service func() *beachcomber.Service
	// Log is where failures are logged; nil means slog.Default.
	Log *slog.Logger
}

// NewMaterialIndexer returns the indexer of app. The service is resolved on
// each call, so it may be built after the indexer.
func NewMaterialIndexer(app *backpack.App) *MaterialIndexer {
	return &MaterialIndexer{
		Service: func() *beachcomber.Service {
			if app == nil {
				return nil
			}
			svc, err := beachcomber.From(app)
			if err != nil {
				return nil
			}
			return svc
		},
		Log: diary.For("jz.bm"),
	}
}

func (ix *MaterialIndexer) service() *beachcomber.Service {
	if ix == nil || ix.Service == nil {
		return nil
	}
	return ix.Service()
}

func (ix *MaterialIndexer) log() *slog.Logger {
	if ix == nil || ix.Log == nil {
		return slog.Default()
	}
	return ix.Log
}

// Search asks the engine for up to MaterialSearchWindow candidates of req.
// It answers ErrSearchUnavailable (wrapping the cause) when the service or
// its engine is missing, the engine is not configured or the call fails.
// The query text is never logged.
func (ix *MaterialIndexer) Search(ctx context.Context, req MaterialSearch) (MaterialCandidates, error) {
	svc := ix.service()
	if svc == nil {
		return MaterialCandidates{}, fmt.Errorf("%w: no search service", ErrSearchUnavailable)
	}
	engine := svc.Engine()
	if engine == nil || !engine.Configured() {
		return MaterialCandidates{}, fmt.Errorf("%w: the search engine is not configured", ErrSearchUnavailable)
	}
	q := beachcomber.Query{
		Q:              req.Q,
		QueryBy:        MaterialQueryBy,
		QueryByWeights: MaterialQueryWeights,
		FilterBy:       materialFilterBy(req),
		SortBy:         "_text_match:desc,published_at:desc",
		Page:           1,
		PerPage:        MaterialSearchWindow,
		ExcludeFields:  []string{"body", "file_texts"},
	}
	highlights := beachcomber.SupportsHighlights(engine)
	if highlights {
		q.Highlight = &beachcomber.Highlight{Fields: materialHighlightFields, AffixTokens: 12, MaxSnippetsPerArray: 1}
	}
	res, err := beachcomber.SearchPage(ctx, engine, svc.IndexName(&models.Material{}), q)
	if err != nil {
		ix.log().Warn("jz.bm: material search failed", "err", err)
		return MaterialCandidates{}, fmt.Errorf("%w: %w", ErrSearchUnavailable, err)
	}
	out := MaterialCandidates{IDs: make([]uint, 0, len(res.IDs)), Hits: make(map[uint]beachcomber.Hit, len(res.IDs)), Highlights: highlights}
	for i, raw := range res.IDs {
		n, err := strconv.ParseUint(raw, 10, 64)
		if err != nil || n == 0 {
			continue
		}
		id := uint(n)
		if _, seen := out.Hits[id]; seen {
			continue
		}
		out.IDs = append(out.IDs, id)
		hit := beachcomber.Hit{ID: raw}
		if i < len(res.Hits) {
			hit = res.Hits[i]
		}
		out.Hits[id] = hit
	}
	return out, nil
}

// materialTagSlug is the shape of a tag slug the engine filter may carry.
var materialTagSlug = regexp.MustCompile(`^[a-z0-9-]{1,100}$`)

// materialFilterBy narrows the engine's candidates to the list filters. It
// is built only from parsed integers, an enumerated type and a tag that is
// a plain slug; any other value is left out and applied by SQL alone, which
// applies every filter anyway.
func materialFilterBy(req MaterialSearch) string {
	var parts []string
	if req.CourseID != 0 {
		parts = append(parts, "course_id:="+strconv.FormatUint(uint64(req.CourseID), 10))
	}
	if req.MeetingID != 0 {
		parts = append(parts, "meeting_id:="+strconv.FormatUint(uint64(req.MeetingID), 10))
	}
	if slices.Contains(models.MaterialTypes, req.Type) {
		parts = append(parts, "type:=`"+req.Type+"`")
	}
	if materialTagSlug.MatchString(req.Tag) {
		parts = append(parts, "tag_slugs:=`"+req.Tag+"`")
	}
	return strings.Join(parts, " && ")
}

// Sync upserts the document of material id now. A failure is logged with
// the id and never returned: a write never fails because of the index.
func (ix *MaterialIndexer) Sync(ctx context.Context, db *gorm.DB, id uint) {
	ix.run(ctx, db, id, false)
}

// Remove deletes the document of material id now, logging a failure like
// Sync.
func (ix *MaterialIndexer) Remove(ctx context.Context, db *gorm.DB, id uint) {
	ix.run(ctx, db, id, true)
}

// SyncAfterCommit runs Sync once tx commits; with a nil tx, or outside a
// transaction, it runs at once.
func (ix *MaterialIndexer) SyncAfterCommit(ctx context.Context, tx *gorm.DB, id uint) {
	ix.afterCommit(ctx, tx, id, false)
}

// RemoveAfterCommit runs Remove once tx commits, like SyncAfterCommit.
func (ix *MaterialIndexer) RemoveAfterCommit(ctx context.Context, tx *gorm.DB, id uint) {
	ix.afterCommit(ctx, tx, id, true)
}

func (ix *MaterialIndexer) afterCommit(ctx context.Context, tx *gorm.DB, id uint, remove bool) {
	if ix == nil || id == 0 {
		return
	}
	if tx == nil {
		ix.run(ctx, nil, id, remove)
		return
	}
	lagoon.AfterCommit(ctx, tx, func(ctx context.Context, db *gorm.DB) {
		ix.run(ctx, db, id, remove)
	})
}

func (ix *MaterialIndexer) run(ctx context.Context, db *gorm.DB, id uint, remove bool) {
	svc := ix.service()
	if svc == nil || id == 0 {
		return
	}
	ctx = MarkMaterialSearch(ctx)
	var err error
	if remove {
		err = svc.Remove(ctx, db, &models.Material{ID: id})
	} else {
		err = svc.Sync(ctx, db, &models.Material{ID: id})
	}
	if err != nil {
		ix.log().Warn("jz.bm: material index sync failed", "material_id", id, "remove", remove, "err", err)
	}
}