package web

import (
	"crypto/rand"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"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
}

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
	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)
	}
}

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.")
		}
	}

	if len(errs) > 0 {
		view.Errors = errs
		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
	}

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

// 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)
}

// saveReceiptFile writes the bytes under
//
//	<StorageDir>/<YYYY>/<MM>_<DD>_<dollars>.<cents><ext>
//
// using the receipt date and amount. When a file with the same date+amount+ext
// already exists (legitimately possible — duplicates can be approved), a _1, _2, …
// suffix is added to the stem. Exclusive create avoids two concurrent uploads
// racing onto the same name. Returns the storage-relative path actually written
// (forward-slash separated, as stored in receipts.file_path).
func (s *Server) saveReceiptFile(date time.Time, amountCents int64, ext string, data []byte) (string, error) {
	yearDir := fmt.Sprintf("%04d", date.Year())
	if err := os.MkdirAll(filepath.Join(s.cfg.StorageDir, yearDir), 0o700); err != nil {
		return "", err
	}
	stem := fmt.Sprintf("%02d_%02d_%d.%02d", int(date.Month()), date.Day(), amountCents/100, amountCents%100)

	for i := 0; i < 10000; i++ {
		name := stem
		if i > 0 {
			name += "_" + strconv.Itoa(i)
		}
		name += ext
		rel := filepath.Join(yearDir, 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])
}