package web

import (
	"encoding/json"
	"fmt"
	"html/template"
	"io"
	"mime"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"

	"cpu-benchmark-server/lib/model"
	"cpu-benchmark-server/lib/store"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
)

const maxSubmissionBytes = 4 << 20

type App struct {
	store     *store.Store
	templates *template.Template
	pageSize  int
}

type indexPageData struct {
	Submissions []model.Submission
	QueryText   string
	QueryCPU    string
	Page        int
	TotalPages  int
	TotalCount  int
	ShowingFrom int
	ShowingTo   int
	PrevURL     string
	NextURL     string
}

type jsonSubmissionEnvelope struct {
	Submitter string                 `json:"submitter"`
	Benchmark *model.BenchmarkResult `json:"benchmark"`
	Result    *model.BenchmarkResult `json:"result"`
	Data      *model.BenchmarkResult `json:"data"`
}

type flatSubmissionEnvelope struct {
	Submitter string `json:"submitter"`
	model.BenchmarkResult
}

type errorResponse struct {
	Error string `json:"error"`
}

func New(store *store.Store, pageSize int) (*App, error) {
	funcs := template.FuncMap{
		"formatInt64": formatInt64,
		"formatFloat": formatFloat,
		"formatTime":  formatTime,
		"modeLabel":   model.ThreadModeLabel,
	}

	templates, err := template.New("index.html").Funcs(funcs).ParseFiles("templates/index.html")
	if err != nil {
		return nil, err
	}

	return &App{
		store:     store,
		templates: templates,
		pageSize:  pageSize,
	}, nil
}

func (a *App) Routes() http.Handler {
	router := chi.NewRouter()
	router.Use(middleware.RequestID)
	router.Use(middleware.RealIP)
	router.Use(middleware.Logger)
	router.Use(middleware.Recoverer)
	router.Use(middleware.Timeout(30 * time.Second))

	router.Get("/", a.handleIndex)
	router.Get("/healthz", a.handleHealth)
	router.Get("/api/search", a.handleSearch)
	router.Post("/api/submit", a.handleSubmit)

	return router
}

func (a *App) handleIndex(w http.ResponseWriter, r *http.Request) {
	page := parsePositiveInt(r.URL.Query().Get("page"), 1)
	text := strings.TrimSpace(r.URL.Query().Get("text"))
	cpu := strings.TrimSpace(r.URL.Query().Get("cpu"))

	var (
		submissions []model.Submission
		totalCount  int
	)

	if text != "" || cpu != "" {
		matches := a.store.SearchSubmissions(text, cpu)
		totalCount = len(matches)
		start, end, normalizedPage := pageBounds(page, a.pageSize, totalCount)
		page = normalizedPage
		submissions = matches[start:end]
	} else {
		var count int
		submissions, count = a.store.ListSubmissions(page, a.pageSize)
		totalCount = count
		_, _, page = pageBounds(page, a.pageSize, totalCount)
	}

	totalPageCount := totalPages(totalCount, a.pageSize)
	showingFrom, showingTo := visibleBounds(page, a.pageSize, len(submissions), totalCount)

	data := indexPageData{
		Submissions: submissions,
		QueryText:   text,
		QueryCPU:    cpu,
		Page:        page,
		TotalPages:  totalPageCount,
		TotalCount:  totalCount,
		ShowingFrom: showingFrom,
		ShowingTo:   showingTo,
		PrevURL:     buildIndexURL(max(1, page-1), text, cpu),
		NextURL:     buildIndexURL(max(1, min(totalPageCount, page+1)), text, cpu),
	}

	if err := a.templates.ExecuteTemplate(w, "index.html", data); err != nil {
		http.Error(w, fmt.Sprintf("render template: %v", err), http.StatusInternalServerError)
	}
}

func (a *App) handleHealth(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]any{
		"status":      "ok",
		"submissions": a.store.Count(),
	})
}

func (a *App) handleSearch(w http.ResponseWriter, r *http.Request) {
	results := a.store.SearchSubmissions(r.URL.Query().Get("text"), r.URL.Query().Get("cpu"))
	writeJSON(w, http.StatusOK, results)
}

func (a *App) handleSubmit(w http.ResponseWriter, r *http.Request) {
	r.Body = http.MaxBytesReader(w, r.Body, maxSubmissionBytes)

	result, submitter, err := parseSubmissionRequest(r)
	if err != nil {
		writeJSON(w, http.StatusBadRequest, errorResponse{Error: err.Error()})
		return
	}

	if err := result.Validate(); err != nil {
		writeJSON(w, http.StatusBadRequest, errorResponse{Error: err.Error()})
		return
	}

	submission, err := a.store.SaveSubmission(result, submitter)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, errorResponse{Error: fmt.Sprintf("store submission: %v", err)})
		return
	}

	writeJSON(w, http.StatusCreated, map[string]any{
		"success":      true,
		"submissionID": submission.SubmissionID,
		"submitter":    submission.Submitter,
		"submittedAt":  submission.SubmittedAt,
	})
}

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

	switch mediaType {
	case "", "application/json":
		return parseJSONSubmission(r)
	case "multipart/form-data":
		return parseMultipartSubmission(r)
	default:
		return model.BenchmarkResult{}, "", fmt.Errorf("unsupported content type %q", mediaType)
	}
}

func parseJSONSubmission(r *http.Request) (model.BenchmarkResult, string, error) {
	body, err := io.ReadAll(r.Body)
	if err != nil {
		return model.BenchmarkResult{}, "", fmt.Errorf("read request body: %w", err)
	}

	submitter := firstNonEmpty(
		r.URL.Query().Get("submitter"),
		r.Header.Get("X-Submitter"),
	)

	var nested jsonSubmissionEnvelope
	if err := json.Unmarshal(body, &nested); err == nil {
		submitter = firstNonEmpty(nested.Submitter, submitter)
		for _, candidate := range []*model.BenchmarkResult{nested.Benchmark, nested.Result, nested.Data} {
			if candidate != nil {
				return *candidate, submitter, nil
			}
		}
	}

	var flat flatSubmissionEnvelope
	if err := json.Unmarshal(body, &flat); err != nil {
		return model.BenchmarkResult{}, "", fmt.Errorf("decode benchmark JSON: %w", err)
	}

	return flat.BenchmarkResult, firstNonEmpty(flat.Submitter, submitter), nil
}

func parseMultipartSubmission(r *http.Request) (model.BenchmarkResult, string, error) {
	if err := r.ParseMultipartForm(maxSubmissionBytes); err != nil {
		return model.BenchmarkResult{}, "", fmt.Errorf("parse multipart form: %w", err)
	}

	payload, err := readMultipartPayload(r)
	if err != nil {
		return model.BenchmarkResult{}, "", err
	}

	var result model.BenchmarkResult
	if err := json.Unmarshal(payload, &result); err != nil {
		return model.BenchmarkResult{}, "", fmt.Errorf("decode benchmark JSON: %w", err)
	}

	return result, r.FormValue("submitter"), nil
}

func readMultipartPayload(r *http.Request) ([]byte, error) {
	for _, field := range []string{"benchmark", "file", "benchmarkFile"} {
		file, _, err := r.FormFile(field)
		if err == nil {
			defer file.Close()
			payload, readErr := io.ReadAll(file)
			if readErr != nil {
				return nil, fmt.Errorf("read multipart benchmark file: %w", readErr)
			}

			return payload, nil
		}

		if err != http.ErrMissingFile {
			return nil, fmt.Errorf("read multipart benchmark file: %w", err)
		}
	}

	for _, field := range []string{"benchmark", "payload", "result", "data"} {
		if value := strings.TrimSpace(r.FormValue(field)); value != "" {
			return []byte(value), nil
		}
	}

	return nil, fmt.Errorf("multipart request must include benchmark JSON in a file field or text field named benchmark")
}

func parsePositiveInt(raw string, fallback int) int {
	if raw == "" {
		return fallback
	}

	value, err := strconv.Atoi(raw)
	if err != nil || value <= 0 {
		return fallback
	}

	return value
}

func pageBounds(page, pageSize, total int) (int, int, int) {
	if pageSize <= 0 {
		pageSize = 50
	}

	totalPages := totalPages(total, pageSize)
	if totalPages == 0 {
		return 0, 0, 1
	}

	if page < 1 {
		page = 1
	}

	if page > totalPages {
		page = totalPages
	}

	start := (page - 1) * pageSize
	end := min(total, start+pageSize)
	return start, end, page
}

func totalPages(total, pageSize int) int {
	if total == 0 || pageSize <= 0 {
		return 0
	}

	pages := total / pageSize
	if total%pageSize != 0 {
		pages++
	}

	return pages
}

func visibleBounds(page, pageSize, visibleCount, total int) (int, int) {
	if total == 0 || visibleCount == 0 {
		return 0, 0
	}

	from := (page-1)*pageSize + 1
	to := from + visibleCount - 1
	return from, to
}

func buildIndexURL(page int, text, cpu string) string {
	if page < 1 {
		page = 1
	}

	values := url.Values{}
	values.Set("page", strconv.Itoa(page))
	if strings.TrimSpace(text) != "" {
		values.Set("text", text)
	}
	if strings.TrimSpace(cpu) != "" {
		values.Set("cpu", cpu)
	}

	return "/?" + values.Encode()
}

func writeJSON(w http.ResponseWriter, status int, payload any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	encoder := json.NewEncoder(w)
	encoder.SetIndent("", "  ")
	_ = encoder.Encode(payload)
}

func firstNonEmpty(values ...string) string {
	for _, value := range values {
		if trimmed := strings.TrimSpace(value); trimmed != "" {
			return trimmed
		}
	}

	return ""
}

func formatInt64(value int64) string {
	negative := value < 0
	if negative {
		value = -value
	}

	digits := strconv.FormatInt(value, 10)
	if len(digits) <= 3 {
		if negative {
			return "-" + digits
		}
		return digits
	}

	var builder strings.Builder
	if negative {
		builder.WriteByte('-')
	}

	pre := len(digits) % 3
	if pre > 0 {
		builder.WriteString(digits[:pre])
		if len(digits) > pre {
			builder.WriteByte(',')
		}
	}

	for i := pre; i < len(digits); i += 3 {
		builder.WriteString(digits[i : i+3])
		if i+3 < len(digits) {
			builder.WriteByte(',')
		}
	}

	return builder.String()
}

func formatFloat(value float64) string {
	return fmt.Sprintf("%.2f", value)
}

func formatTime(value time.Time) string {
	if value.IsZero() {
		return "-"
	}

	return value.Format("2006-01-02 15:04:05 MST")
}

func min(a, b int) int {
	if a < b {
		return a
	}

	return b
}

func max(a, b int) int {
	if a > b {
		return a
	}

	return b
}