// SPDX-License-Identifier: AGPL-3.0-or-later

package handler

import (
	"encoding/csv"
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"strings"

	"kode.naiv.no/olemd/favoritter/internal/middleware"
	"kode.naiv.no/olemd/favoritter/internal/render"
)

const maxExportFaves = 100000

// ExportFave is the JSON representation for export/import.
type ExportFave struct {
	Description string   `json:"description"`
	URL         string   `json:"url,omitempty"`
	Notes       string   `json:"notes,omitempty"`
	Privacy     string   `json:"privacy"`
	Tags        []string `json:"tags,omitempty"`
	CreatedAt   string   `json:"created_at"`
}

// handleExportPage shows the export options page.
func (h *Handler) handleExportPage(w http.ResponseWriter, r *http.Request) {
	h.deps.Renderer.Page(w, r, "export", render.PageData{
		Title: "Eksporter favoritter",
	})
}

// handleExportJSON exports the user's faves as JSON.
func (h *Handler) handleExportJSON(w http.ResponseWriter, r *http.Request) {
	user := middleware.UserFromContext(r.Context())

	faves, _, err := h.deps.Faves.ListByUser(user.ID, maxExportFaves, 0)
	if err != nil {
		slog.Error("export: list faves error", "error", err)
		http.Error(w, "Internal error", http.StatusInternalServerError)
		return
	}

	if err := h.deps.Faves.LoadTags(faves); err != nil {
		slog.Error("export: load tags error", "error", err)
	}

	export := make([]ExportFave, len(faves))
	for i, f := range faves {
		tags := make([]string, len(f.Tags))
		for j, t := range f.Tags {
			tags[j] = t.Name
		}
		export[i] = ExportFave{
			Description: f.Description,
			URL:         f.URL,
			Notes:       f.Notes,
			Privacy:     f.Privacy,
			Tags:        tags,
			CreatedAt:   f.CreatedAt.Format("2006-01-02T15:04:05Z"),
		}
	}

	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Content-Disposition", "attachment; filename=favoritter.json")
	enc := json.NewEncoder(w)
	enc.SetIndent("", "  ")
	enc.Encode(export)
}

// handleExportCSV exports the user's faves as CSV.
func (h *Handler) handleExportCSV(w http.ResponseWriter, r *http.Request) {
	user := middleware.UserFromContext(r.Context())

	faves, _, err := h.deps.Faves.ListByUser(user.ID, maxExportFaves, 0)
	if err != nil {
		slog.Error("export: list faves error", "error", err)
		http.Error(w, "Internal error", http.StatusInternalServerError)
		return
	}

	if err := h.deps.Faves.LoadTags(faves); err != nil {
		slog.Error("export: load tags error", "error", err)
	}

	w.Header().Set("Content-Type", "text/csv; charset=utf-8")
	w.Header().Set("Content-Disposition", "attachment; filename=favoritter.csv")

	cw := csv.NewWriter(w)
	cw.Write([]string{"description", "url", "notes", "privacy", "tags", "created_at"})

	for _, f := range faves {
		tags := make([]string, len(f.Tags))
		for j, t := range f.Tags {
			tags[j] = t.Name
		}
		cw.Write([]string{
			f.Description,
			f.URL,
			f.Notes,
			f.Privacy,
			strings.Join(tags, ","),
			f.CreatedAt.Format("2006-01-02T15:04:05Z"),
		})
	}
	cw.Flush()
}

// handleImportPage shows the import page.
func (h *Handler) handleImportPage(w http.ResponseWriter, r *http.Request) {
	h.deps.Renderer.Page(w, r, "import", render.PageData{
		Title: "Importer favoritter",
	})
}

// handleImportPost processes an uploaded JSON or CSV file.
func (h *Handler) handleImportPost(w http.ResponseWriter, r *http.Request) {
	user := middleware.UserFromContext(r.Context())

	if err := r.ParseMultipartForm(h.deps.Config.MaxUploadSize); err != nil {
		h.flash(w, r, "import", "Filen er for stor.", "error", nil)
		return
	}

	file, header, err := r.FormFile("file")
	if err != nil {
		h.flash(w, r, "import", "Velg en fil å importere.", "error", nil)
		return
	}
	defer file.Close()

	var faves []ExportFave
	filename := strings.ToLower(header.Filename)

	switch {
	case strings.HasSuffix(filename, ".json"):
		faves, err = parseImportJSON(file)
	case strings.HasSuffix(filename, ".csv"):
		faves, err = parseImportCSV(file)
	default:
		h.flash(w, r, "import", "Ugyldig filformat. Bruk JSON eller CSV.", "error", nil)
		return
	}

	if err != nil {
		slog.Error("import parse error", "error", err)
		h.flash(w, r, "import", "Kunne ikke lese filen. Sjekk formatet.", "error", nil)
		return
	}

	imported := 0
	for _, ef := range faves {
		if ef.Description == "" {
			continue
		}
		privacy := ef.Privacy
		if privacy != "public" && privacy != "private" {
			privacy = user.DefaultFavePrivacy
		}

		fave, err := h.deps.Faves.Create(user.ID, ef.Description, ef.URL, "", ef.Notes, privacy)
		if err != nil {
			slog.Error("import: create fave error", "error", err)
			continue
		}

		if len(ef.Tags) > 0 {
			if err := h.deps.Tags.SetFaveTags(fave.ID, ef.Tags); err != nil {
				slog.Error("import: set tags error", "error", err)
			}
		}
		imported++
	}

	h.flash(w, r, "import",
		fmt.Sprintf("Importert %d av %d favoritter.", imported, len(faves)),
		"success", nil)
}

func parseImportJSON(r io.Reader) ([]ExportFave, error) {
	var faves []ExportFave
	if err := json.NewDecoder(r).Decode(&faves); err != nil {
		return nil, err
	}
	return faves, nil
}

func parseImportCSV(r io.Reader) ([]ExportFave, error) {
	cr := csv.NewReader(r)
	records, err := cr.ReadAll()
	if err != nil {
		return nil, err
	}

	if len(records) < 2 {
		return nil, nil
	}

	// Find column indices from header row.
	header := records[0]
	colMap := make(map[string]int)
	for i, col := range header {
		colMap[strings.ToLower(strings.TrimSpace(col))] = i
	}

	var faves []ExportFave
	for _, row := range records[1:] {
		f := ExportFave{}
		if idx, ok := colMap["description"]; ok && idx < len(row) {
			f.Description = row[idx]
		}
		if idx, ok := colMap["url"]; ok && idx < len(row) {
			f.URL = row[idx]
		}
		if idx, ok := colMap["notes"]; ok && idx < len(row) {
			f.Notes = row[idx]
		}
		if idx, ok := colMap["privacy"]; ok && idx < len(row) {
			f.Privacy = row[idx]
		}
		if idx, ok := colMap["tags"]; ok && idx < len(row) && row[idx] != "" {
			f.Tags = strings.Split(row[idx], ",")
			for i := range f.Tags {
				f.Tags[i] = strings.TrimSpace(f.Tags[i])
			}
		}
		if idx, ok := colMap["created_at"]; ok && idx < len(row) {
			f.CreatedAt = row[idx]
		}
		faves = append(faves, f)
	}
	return faves, nil
}