package web

import (
	"crypto/rand"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"time"

	"maisym.com/hsa/internal/receipt"
	"maisym.com/hsa/internal/storage"
)

const dateLayout = "2006-01-02"

type formView struct {
	Subject    string
	Categories []storage.Lookup
	People     []storage.Lookup
	Amount     string
	Date       string
	CategoryID string
	PersonID   string
	Errors     []string

	// ClassifyModel is the model that will read the receipt to pre-fill the form,
	// shown as a footnote. ClassifyEnabled is false when no API key is configured.
	ClassifyModel   string
	ClassifyEnabled bool

	// TagChips is the alphabetical tag picker: every known tag plus any unsaved
	// labels carried across an error re-render, each marked selected or not.
	TagChips []tagChip
}

// tagChip is one selectable tag in the upload form's picker.
type tagChip struct {
	Label    string
	Selected bool
}

func (s *Server) handleUploadForm(w http.ResponseWriter, r *http.Request) {
	sess := sessionFrom(r.Context())
	cats, people, err := s.lookups()
	if err != nil {
		s.serverError(w, "load lookups", err)
		return
	}
	s.renderForm(w, formView{
		Subject:    sess.Subject,
		Categories: cats,
		People:     people,
		Date:       time.Now().Format(dateLayout),
	})
}

func (s *Server) lookups() (cats, people []storage.Lookup, err error) {
	cats, err = s.store.ListCategories()
	if err != nil {
		return nil, nil, err
	}
	people, err = s.store.ListPeople()
	if err != nil {
		return nil, nil, err
	}
	return cats, people, nil
}

func (s *Server) renderForm(w http.ResponseWriter, v formView) {
	v.ClassifyModel = s.cfg.ClassifyModel
	v.ClassifyEnabled = s.classifier != nil
	if v.TagChips == nil { // callers that carry selected tags set this themselves
		if chips, err := s.tagChipsFor(nil); err == nil {
			v.TagChips = chips
		}
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := uploadPage.ExecuteTemplate(w, "base", v); err != nil {
		s.serverError(w, "render form", err)
	}
}

// tagChipsFor builds the upload form's tag picker: every known tag in alphabetical
// order, plus any selected labels that aren't saved tags yet (a chip the user
// created before an error re-render), with the selected ones marked.
func (s *Server) tagChipsFor(selected []string) ([]tagChip, error) {
	tags, err := s.store.ListTags()
	if err != nil {
		return nil, err
	}
	selSet := map[string]bool{}
	for _, l := range selected {
		if l = strings.TrimSpace(l); l != "" {
			selSet[strings.ToLower(l)] = true
		}
	}
	known := map[string]bool{}
	var chips []tagChip
	for _, t := range tags {
		key := strings.ToLower(t.Label)
		known[key] = true
		chips = append(chips, tagChip{Label: t.Label, Selected: selSet[key]})
	}
	for _, l := range selected { // pending labels not yet persisted
		l = strings.TrimSpace(l)
		key := strings.ToLower(l)
		if l == "" || known[key] {
			continue
		}
		known[key] = true
		chips = append(chips, tagChip{Label: l, Selected: true})
	}
	sort.Slice(chips, func(i, j int) bool {
		return strings.ToLower(chips[i].Label) < strings.ToLower(chips[j].Label)
	})
	return chips, nil
}

func (s *Server) handleUpload(w http.ResponseWriter, r *http.Request) {
	sess := sessionFrom(r.Context())
	cats, people, err := s.lookups()
	if err != nil {
		s.serverError(w, "load lookups", err)
		return
	}

	r.Body = http.MaxBytesReader(w, r.Body, s.cfg.MaxUploadBytes)
	if err := r.ParseMultipartForm(10 << 20); err != nil {
		s.renderForm(w, formView{
			Subject: sess.Subject, Categories: cats, People: people,
			Errors: []string{"Upload too large or malformed."},
		})
		return
	}

	amountStr := strings.TrimSpace(r.FormValue("amount"))
	dateStr := strings.TrimSpace(r.FormValue("receipt_date"))
	categoryStr := strings.TrimSpace(r.FormValue("category_id"))
	personStr := strings.TrimSpace(r.FormValue("person_id"))

	view := formView{
		Subject: sess.Subject, Categories: cats, People: people,
		Amount: amountStr, Date: dateStr, CategoryID: categoryStr, PersonID: personStr,
	}

	var errs []string
	amountCents, err := receipt.ParseAmountCents(amountStr)
	if err != nil {
		errs = append(errs, "Enter a valid amount, e.g. 12.34")
	}
	receiptDate, err := time.Parse(dateLayout, dateStr)
	if err != nil {
		errs = append(errs, "Enter a valid date.")
	}

	categoryID, ok := parseLookupID(categoryStr, cats)
	if !ok {
		errs = append(errs, "Choose a category.")
	}

	var personID *int64
	if personStr != "" {
		pid, ok := parseLookupID(personStr, people)
		if !ok {
			errs = append(errs, "Choose a valid \"Who\" or leave it blank.")
		} else {
			personID = &pid
		}
	}

	file, header, err := r.FormFile("receipt")
	if err != nil {
		errs = append(errs, "Attach a receipt photo or PDF.")
	}
	var data []byte
	if file != nil {
		defer file.Close()
		data, err = io.ReadAll(file)
		if err != nil {
			errs = append(errs, "Could not read the uploaded file.")
		}
	}

	mimeType := ""
	if len(data) > 0 {
		mimeType = detectMime(data)
		if !allowedMime(mimeType) {
			errs = append(errs, "Only images and PDFs are allowed.")
		} else {
			data = normalizeOrientation(data, mimeType) // bake in EXIF rotation
		}
	}

	// Optional extra files attached in the same submission (item 10). Read and
	// validate them up front so a bad attachment re-renders the form before any
	// row is written. They are saved after the receipt row exists (see below).
	attachments, attErrs := readAttachments(r)
	errs = append(errs, attErrs...)

	// Selected tags (existing labels and/or newly-typed ones) ride along as repeated
	// "tags" fields. Resolved/created at save time so an abandoned upload adds none.
	var tagLabels []string
	if r.MultipartForm != nil {
		tagLabels = r.MultipartForm.Value["tags"]
	}

	if len(errs) > 0 {
		view.Errors = errs
		if chips, err := s.tagChipsFor(tagLabels); err == nil {
			view.TagChips = chips // keep the user's tag selection across the re-render
		}
		s.renderForm(w, view)
		return
	}

	// Dual-write: file on disk (dated, amount-tagged name) + blob in DB.
	id := newID()
	ext := extFor(header.Filename, mimeType)
	relPath, err := s.saveReceiptFile(receiptDate, amountCents, ext, data)
	if err != nil {
		s.serverError(w, "save file", err)
		return
	}

	rec := receipt.Receipt{
		ID:               id,
		UploadedBy:       sess.Subject,
		UploadedAt:       time.Now().UTC(),
		ReceiptDate:      receiptDate,
		AmountCents:      amountCents,
		CategoryID:       categoryID,
		PersonID:         personID,
		FilePath:         relPath,
		ImageData:        data,
		FileSizeBytes:    int64(len(data)),
		OriginalFilename: header.Filename,
		MimeType:         mimeType,
	}
	if err := s.store.Insert(rec); err != nil {
		s.serverError(w, "insert receipt", err)
		return
	}

	// Link tags now that the receipt id exists (create-if-missing by label).
	if len(tagLabels) > 0 {
		if err := s.store.SetReceiptTags(id, tagLabels); err != nil {
			s.serverError(w, "save tags", err)
			return
		}
	}

	// Persist the AI suggestion the browser round-tripped, so misreads can be
	// reviewed later (best-effort, diagnostic — never block the upload on it).
	if blob := strings.TrimSpace(r.FormValue("classify_json")); blob != "" {
		var cr classifyResponse
		_ = json.Unmarshal([]byte(blob), &cr) // model only; blob stored verbatim
		if err := s.store.InsertClassification(id, cr.Model, blob, time.Now().UTC()); err != nil {
			log.Printf("warning: store classification for %s: %v", id, err)
		}
	}

	// Save each attachment now that the parent receipt id exists, keyed to the
	// receipt's date+amount so the files sort alongside it.
	var attachmentNames []string
	for _, a := range attachments {
		relPath, err := s.saveAttachmentFile(receiptDate, amountCents, a.ext, a.data)
		if err != nil {
			s.serverError(w, "save attachment", err)
			return
		}
		if err := s.store.InsertAttachment(receipt.Attachment{
			ID:               newID(),
			ReceiptID:        id,
			UploadedBy:       sess.Subject,
			UploadedAt:       time.Now().UTC(),
			FilePath:         relPath,
			ImageData:        a.data,
			FileSizeBytes:    int64(len(a.data)),
			OriginalFilename: a.filename,
			MimeType:         a.mimeType,
		}); err != nil {
			s.serverError(w, "insert attachment", err)
			return
		}
		attachmentNames = append(attachmentNames, a.filename)
	}

	savedTags, _ := s.store.ListReceiptTags(id)

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	_ = confirmPage.ExecuteTemplate(w, "base", confirmView{
		Category:    labelFor(categoryID, cats),
		Who:         whoLabel(personID, people),
		Amount:      fmt.Sprintf("%d.%02d", amountCents/100, amountCents%100),
		Date:        dateStr,
		Filename:    header.Filename,
		Attachments: attachmentNames,
		Tags:        savedTags,
	})
}

// confirmView is the data for the post-save confirmation page.
type confirmView struct {
	Category    string
	Who         string
	Amount      string
	Date        string
	Filename    string
	Attachments []string
	Tags        []string
}

// pendingAttachment is a validated extra file waiting to be saved with its receipt.
type pendingAttachment struct {
	data     []byte
	mimeType string
	ext      string
	filename string
}

// readAttachments reads and validates the optional "attachments" multi-file field.
// Empty parts are skipped; invalid types accumulate into errs (and the upload is
// re-rendered, so nothing is written).
func readAttachments(r *http.Request) (out []pendingAttachment, errs []string) {
	if r.MultipartForm == nil {
		return nil, nil
	}
	for _, fh := range r.MultipartForm.File["attachments"] {
		af, err := fh.Open()
		if err != nil {
			errs = append(errs, "Could not read an attachment.")
			continue
		}
		adata, err := io.ReadAll(af)
		af.Close()
		if err != nil {
			errs = append(errs, "Could not read an attachment.")
			continue
		}
		if len(adata) == 0 {
			continue
		}
		amime := detectMime(adata)
		if !allowedMime(amime) {
			errs = append(errs, "Attachments must be images or PDFs.")
			continue
		}
		adata = normalizeOrientation(adata, amime) // bake in EXIF rotation
		out = append(out, pendingAttachment{
			data:     adata,
			mimeType: amime,
			ext:      extFor(fh.Filename, amime),
			filename: fh.Filename,
		})
	}
	return out, errs
}

// parseLookupID parses s as an int64 and confirms it exists in the given set.
func parseLookupID(s string, set []storage.Lookup) (int64, bool) {
	id, err := strconv.ParseInt(s, 10, 64)
	if err != nil {
		return 0, false
	}
	for _, l := range set {
		if l.ID == id {
			return id, true
		}
	}
	return 0, false
}

func labelFor(id int64, set []storage.Lookup) string {
	for _, l := range set {
		if l.ID == id {
			return l.Label
		}
	}
	return ""
}

func whoLabel(id *int64, set []storage.Lookup) string {
	if id == nil {
		return ""
	}
	return labelFor(*id, set)
}

// receiptStem returns the dated, amount-tagged base name (no extension) shared by
// a receipt and its attachments, e.g. "06_08_42.50".
func receiptStem(date time.Time, amountCents int64) string {
	return fmt.Sprintf("%02d_%02d_%d.%02d", int(date.Month()), date.Day(), amountCents/100, amountCents%100)
}

// saveReceiptFile writes the receipt bytes under
// <StorageDir>/receipts/<YYYY>/<MM>_<DD>_<dollars>.<cents><ext>.
func (s *Server) saveReceiptFile(date time.Time, amountCents int64, ext string, data []byte) (string, error) {
	return s.saveBlobFile("receipts", fmt.Sprintf("%04d", date.Year()), receiptStem(date, amountCents), ext, data)
}

// saveAttachmentFile writes an attachment's bytes under
// <StorageDir>/attachments/<YYYY>/<MM>_<DD>_<dollars>.<cents>_att<ext>, keyed to
// the PARENT receipt's date and amount so an expense's files sort together.
func (s *Server) saveAttachmentFile(date time.Time, amountCents int64, ext string, data []byte) (string, error) {
	return s.saveBlobFile("attachments", fmt.Sprintf("%04d", date.Year()), receiptStem(date, amountCents)+"_att", ext, data)
}

// saveBlobFile writes data to <StorageDir>/<subdir>/<year>/<stem><ext>, adding a
// _1, _2, … suffix on the stem when the name is taken (legitimately possible —
// duplicates can be approved, and a receipt can have several attachments).
// Exclusive create avoids two concurrent uploads racing onto the same name.
// Returns the storage-relative path actually written (forward-slash separated).
func (s *Server) saveBlobFile(subdir, year, stem, ext string, data []byte) (string, error) {
	if err := os.MkdirAll(filepath.Join(s.cfg.StorageDir, subdir, year), 0o700); err != nil {
		return "", err
	}
	for i := 0; i < 10000; i++ {
		name := stem
		if i > 0 {
			name += "_" + strconv.Itoa(i)
		}
		name += ext
		rel := filepath.Join(subdir, year, name)
		f, err := os.OpenFile(filepath.Join(s.cfg.StorageDir, rel), os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o600)
		if os.IsExist(err) {
			continue // name taken — try the next suffix
		}
		if err != nil {
			return "", err
		}
		_, werr := f.Write(data)
		cerr := f.Close()
		if werr != nil {
			return "", werr
		}
		if cerr != nil {
			return "", cerr
		}
		return filepath.ToSlash(rel), nil
	}
	return "", fmt.Errorf("could not find a free filename for %s", stem)
}

func detectMime(data []byte) string {
	n := min(len(data), 512)
	ct := http.DetectContentType(data[:n])
	if i := strings.IndexByte(ct, ';'); i >= 0 {
		ct = ct[:i]
	}
	return strings.TrimSpace(ct)
}

func allowedMime(mime string) bool {
	return strings.HasPrefix(mime, "image/") || mime == "application/pdf"
}

func extFor(filename, mimeType string) string {
	if ext := strings.ToLower(filepath.Ext(filename)); ext != "" && len(ext) <= 5 {
		return ext
	}
	switch mimeType {
	case "image/jpeg":
		return ".jpg"
	case "image/png":
		return ".png"
	case "image/gif":
		return ".gif"
	case "image/webp":
		return ".webp"
	case "application/pdf":
		return ".pdf"
	default:
		return ".bin"
	}
}

// newID returns a random UUIDv4 string.
func newID() string {
	var b [16]byte
	_, _ = rand.Read(b[:])
	b[6] = (b[6] & 0x0f) | 0x40
	b[8] = (b[8] & 0x3f) | 0x80
	return fmt.Sprintf("%x-%x-%x-%x-%x", b[0:4], b[4:6], b[6:8], b[8:10], b[10:16])
}