// Inbox rendering, the manual mail scan, and the classify action.
//
// Phase 3 groups messages by the live category list (FR-5) and shows the JEV
// recommended action plus confidence on each row. Phase 4 adds a bulk-select
// toolbar (FR-6) and folder views so a recoverable delete can be seen under the
// Delete folder and restored.
package server

import (
	"context"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"sort"
	"strings"
	"time"

	"gitea.lab.audasmedia.com.au/sam/email_agent/internal/classify"
	"gitea.lab.audasmedia.com.au/sam/email_agent/internal/mailfetch"
	"gitea.lab.audasmedia.com.au/sam/email_agent/internal/store"
)

// unclassifiedCategory is the bucket for messages JEV has not classified yet.
const unclassifiedCategory = store.UnclassifiedCategory

type messageRow struct {
	ID         int64
	From       string
	Subject    string
	SourceAddr string
	Action     string
	Confidence int
	Classified bool
	When       string
	// Restorable is true for a message outside the inbox, so the row offers a
	// Restore button (FR-9: deletes are recoverable).
	Restorable bool
}

type messageGroup struct {
	Name     string
	Messages []messageRow
}

type inboxData struct {
	Groups      []messageGroup
	Total       int
	Note        string
	Error       string
	CSRFToken   string
	Folder      string
	Category    string
	FolderLabel string
}

// loadInbox reads messages for the active folder/category filter and groups them
// by the live category list.
func (s *Server) loadInbox(ctx context.Context, f store.MessageFilter) (inboxData, error) {
	items, err := s.store.ListMessagesFiltered(ctx, f)
	if err != nil {
		return inboxData{}, err
	}
	categories, err := s.store.ListCategories(ctx)
	if err != nil {
		return inboxData{}, err
	}
	return inboxData{Groups: groupMessages(items, categories), Total: len(items)}, nil
}

// groupMessages buckets messages by category, ordering groups the way the
// category list is ordered in the UI. Unknown categories (for example a
// classification written before a rename) keep their own group; messages with
// no classification fall into "Unclassified" last.
func groupMessages(items []store.MessageListItem, categories []store.Category) []messageGroup {
	canonical := make(map[string]string, len(categories))
	order := make([]string, 0, len(categories))
	for _, c := range categories {
		canonical[strings.ToLower(c.Name)] = c.Name
		order = append(order, c.Name)
	}

	buckets := map[string][]messageRow{}
	for _, it := range items {
		raw := strings.TrimSpace(it.Category)
		key := ""
		if raw != "" {
			if name, ok := canonical[strings.ToLower(raw)]; ok {
				key = name
			} else {
				key = raw
			}
		}
		if key == "" {
			key = unclassifiedCategory
		}
		action := strings.TrimSpace(it.Action)
		if action == "" {
			action = "Review"
		}
		folder := strings.TrimSpace(it.Folder)
		if folder == "" {
			folder = store.FolderInbox
		}
		buckets[key] = append(buckets[key], messageRow{
			ID:         it.ID,
			From:       orDefault(it.FromAddr, "(unknown sender)"),
			Subject:    orDefault(it.Subject, "(no subject)"),
			SourceAddr: it.SourceAddress,
			Action:     action,
			Confidence: confidencePercent(it.Confidence),
			Classified: it.HasClassification,
			When:       formatWhen(it.DateSent, it.ReceivedAt),
			Restorable: folder != store.FolderInbox,
		})
	}

	var keys []string
	for _, name := range order {
		if _, ok := buckets[name]; ok {
			keys = append(keys, name)
		}
	}
	var unknown []string
	for k := range buckets {
		if k == unclassifiedCategory || contains(order, k) {
			continue
		}
		unknown = append(unknown, k)
	}
	sort.Strings(unknown)
	keys = append(keys, unknown...)
	if _, ok := buckets[unclassifiedCategory]; ok {
		keys = append(keys, unclassifiedCategory)
	}

	groups := make([]messageGroup, 0, len(keys))
	for _, k := range keys {
		groups = append(groups, messageGroup{Name: k, Messages: buckets[k]})
	}
	return groups
}

// inboxSelection reads the active folder/category from the query or the posted
// form, applying the inbox default and rejecting unknown values.
func inboxSelection(r *http.Request) (folder, category string) {
	folder = strings.TrimSpace(r.FormValue("folder"))
	category = strings.TrimSpace(r.FormValue("category"))
	if folder == "" {
		folder = store.FolderInbox
	}
	if folder != "all" && !store.ValidFolder(folder) {
		folder = store.FolderInbox
	}
	return folder, category
}

// confidencePercent turns a 0–1 confidence into a whole percentage.
func confidencePercent(v float64) int {
	if v <= 0 {
		return 0
	}
	if v > 1 {
		v = 1
	}
	return int(v*100 + 0.5)
}

func (s *Server) renderInbox(w http.ResponseWriter, r *http.Request, note, errMsg string) {
	folder, category := inboxSelection(r)
	data, err := s.loadInbox(r.Context(), store.MessageFilter{
		Folder:       folder,
		Category:     category,
		Unclassified: strings.EqualFold(category, unclassifiedCategory),
		Limit:        200,
	})
	if err != nil {
		s.logger.Error("load inbox", "error", err)
		http.Error(w, "could not load messages", http.StatusInternalServerError)
		return
	}
	data.Note = note
	data.Error = errMsg
	data.CSRFToken = s.csrfToken(w, r)
	data.Folder = folder
	data.Category = category
	data.FolderLabel = folderLabel(folder)
	if category != "" {
		data.FolderLabel = orDefault(category, data.FolderLabel)
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := s.tmpl.ExecuteTemplate(w, "inbox.html", data); err != nil {
		s.logger.Error("render inbox partial", "error", err)
	}
}

// handleInboxPartial is the HTMX fragment for the centre list.
func (s *Server) handleInboxPartial(w http.ResponseWriter, r *http.Request) {
	s.renderInbox(w, r, "", "")
}

// handleFetchMail runs one IMAP scan, then returns the refreshed list. It is a
// POST because it changes stored state and must carry a CSRF token.
func (s *Server) handleFetchMail(w http.ResponseWriter, r *http.Request) {
	if !s.csrfOK(r) {
		http.Error(w, "invalid CSRF token", http.StatusForbidden)
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), 2*time.Minute)
	defer cancel()

	sum, err := s.fetcher.Fetch(ctx)
	switch {
	case err == nil:
		s.renderInbox(w, r, fmt.Sprintf("Scanned %d message(s); %d stored or refreshed.", sum.Fetched, sum.Stored), "")
	case errors.Is(err, mailfetch.ErrNoCredentials):
		s.renderInbox(w, r, "Mail is not connected yet: set GMAIL_USER and GMAIL_APP_PASSWORD.", "")
	case errors.Is(err, mailfetch.ErrAlreadyRunning):
		s.renderInbox(w, r, "A mail scan is already running.", "")
	default:
		s.logger.Error("mail scan failed", "error", err)
		s.renderInbox(w, r, "Mail scan failed: "+err.Error(), "")
	}
}

// handleClassify classifies pending messages (FR-3) and returns the refreshed
// list. A run can take minutes, so the write deadline is extended for this
// handler only.
func (s *Server) handleClassify(w http.ResponseWriter, r *http.Request) {
	s.runClassifier(w, r, false)
}

// handleReclassify re-runs the classifier over every stored message. It is how
// a category-list or rules edit is applied to mail that was already classified.
func (s *Server) handleReclassify(w http.ResponseWriter, r *http.Request) {
	s.runClassifier(w, r, true)
}

func (s *Server) runClassifier(w http.ResponseWriter, r *http.Request, all bool) {
	if !s.csrfOK(r) {
		http.Error(w, "invalid CSRF token", http.StatusForbidden)
		return
	}
	if rc := http.NewResponseController(w); rc != nil {
		_ = rc.SetWriteDeadline(time.Now().Add(15 * time.Minute))
	}

	ctx, cancel := context.WithTimeout(r.Context(), 15*time.Minute)
	defer cancel()

	var (
		sum classify.Summary
		err error
	)
	if all {
		sum, err = s.classifier.RunAll(ctx)
	} else {
		sum, err = s.classifier.Run(ctx)
	}
	switch {
	case err == nil:
		s.renderInbox(w, r, fmt.Sprintf(
			"Classified %d of %d message(s); %d failed; %d still unclassified.",
			sum.Classified, sum.Considered, sum.Failed, sum.Remaining), "")
	case errors.Is(err, classify.ErrNotConfigured):
		s.renderInbox(w, r, "Classification is not connected yet: set JEV_API_KEY.", "")
	default:
		s.logger.Error("classification run failed", "error", err)
		s.renderInbox(w, r, "Classification failed: "+err.Error(), "")
	}
}

func orDefault(v, def string) string {
	if strings.TrimSpace(v) == "" {
		return def
	}
	return strings.TrimSpace(v)
}

func contains(list []string, v string) bool {
	for _, x := range list {
		if x == v {
			return true
		}
	}
	return false
}

// formatWhen renders a compact, timezone-stable timestamp.
func formatWhen(sent, received time.Time) string {
	t := sent
	if t.IsZero() {
		t = received
	}
	if t.IsZero() {
		return ""
	}
	if t.Year() == time.Now().Year() {
		return t.Format("2 Jan 15:04")
	}
	return t.Format("2 Jan 2006")
}

// inboxURL builds the /partials/inbox URL for a folder/category view.
func inboxURL(folder, category string) string {
	q := url.Values{}
	if folder != "" {
		q.Set("folder", folder)
	}
	if category != "" {
		q.Set("category", category)
	}
	if len(q) == 0 {
		return "/partials/inbox"
	}
	return "/partials/inbox?" + q.Encode()
}