package viewer

import (
	"errors"
	"fmt"
	"io"
	"mime"
	"net/http"
	"strings"

	"reanimator/chart/web"
)

type HandlerOptions struct {
	Title      string
	Standalone bool
}

func NewHandler(opts HandlerOptions) http.Handler {
	opts.Standalone = false
	return newHandler(opts)
}

func NewStandaloneHandler(opts HandlerOptions) http.Handler {
	opts.Standalone = true
	return newHandler(opts)
}

func newHandler(opts HandlerOptions) http.Handler {
	title := strings.TrimSpace(opts.Title)
	if title == "" {
		title = "Reanimator Chart"
	}

	mux := http.NewServeMux()
	mux.Handle("GET /static/", http.StripPrefix("/static/", web.Static()))
	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
		_, _ = w.Write([]byte("ok"))
	})
	mux.HandleFunc("GET /", func(w http.ResponseWriter, r *http.Request) {
		var (
			html []byte
			err  error
		)
		if opts.Standalone {
			html, err = web.RenderUpload(pageData{Title: title})
		} else {
			html, err = RenderHTML(nil, title)
		}
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		_, _ = w.Write(html)
	})
	mux.HandleFunc("POST /render", func(w http.ResponseWriter, r *http.Request) {
		payload, err := readSnapshotPayload(r)
		if err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}

		page, err := buildPageData([]byte(payload), title)
		if err != nil {
			if opts.Standalone {
				html, renderErr := web.RenderUpload(pageData{
					Title: title,
					Error: err.Error(),
				})
				if renderErr != nil {
					http.Error(w, renderErr.Error(), http.StatusInternalServerError)
					return
				}
				w.Header().Set("Content-Type", "text/html; charset=utf-8")
				_, _ = w.Write(html)
				return
			}
			page = pageData{Title: title, Error: err.Error()}
		}

		html, renderErr := web.Render(page)
		if renderErr != nil {
			http.Error(w, renderErr.Error(), http.StatusInternalServerError)
			return
		}
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		_, _ = w.Write(html)
	})
	return mux
}

func readSnapshotPayload(r *http.Request) (string, error) {
	mediaType, _, err := mime.ParseMediaType(r.Header.Get("Content-Type"))
	if err != nil {
		return "", fmt.Errorf("parse content type: %w", err)
	}

	switch mediaType {
	case "application/json":
		body, err := io.ReadAll(r.Body)
		if err != nil {
			return "", fmt.Errorf("read request body: %w", err)
		}
		return string(body), nil
	case "multipart/form-data":
		if err := r.ParseMultipartForm(32 << 20); err != nil {
			return "", fmt.Errorf("parse multipart form: %w", err)
		}

		payload, err := readSnapshotFile(r, "snapshot_file")
		if err == nil && strings.TrimSpace(payload) != "" {
			return payload, nil
		}
		if err != nil && !errors.Is(err, http.ErrMissingFile) {
			return "", err
		}
		return r.FormValue("snapshot"), nil
	default:
		if err := r.ParseForm(); err != nil {
			return "", fmt.Errorf("parse form: %w", err)
		}
		return r.FormValue("snapshot"), nil
	}
}

func readSnapshotFile(r *http.Request, field string) (string, error) {
	file, _, err := r.FormFile(field)
	if err != nil {
		return "", fmt.Errorf("read uploaded file: %w", err)
	}
	defer file.Close()

	body, err := io.ReadAll(file)
	if err != nil {
		return "", fmt.Errorf("read uploaded file contents: %w", err)
	}
	return string(body), nil
}