// Package api implements palette's REST handlers and the HTTP router:
// pastes, cans, guess-language, rate limiting middleware, and the admin API.
package api

import (
	"context"
	"database/sql"
	"encoding/json"
	"fmt"
	"html/template"
	"net/http"
	"os"
	"strconv"
	"strings"
	"time"

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

	langpkg "palette/internal/lang"
	"palette/internal/store"
	"palette/internal/web"
)

type Config struct {
	Addr         string
	DBPath       string
	MaxTextBytes int64
	MaxItemBytes int64
}

type apiServer struct {
	store    *store.Store
	cfg      Config
	ui       *web.UI
	settings *settingsStore
	adminKey string
}

func NewServer(st *store.Store, cfg Config, ui *web.UI, ss *settingsStore, adminKey string) *apiServer {
	return &apiServer{store: st, cfg: cfg, ui: ui, settings: ss, adminKey: adminKey}
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(v)
}

func writeErr(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, map[string]string{"error": msg})
}

// Routes returns the HTTP handler for the server.
func (a *apiServer) Routes() http.Handler {
	return a.routes()
}

func (a *apiServer) routes() http.Handler {
	r := chi.NewRouter()
	r.Use(middleware.Recoverer)
	r.Use(middleware.Timeout(30 * time.Second))
	r.Use(a.limitRequestBody) // #68: hard server-side body cap -> 413
	r.Use(viewerCookieMiddleware)
	r.Use(web.SecurityHeaders) // #59: CSP + hardening headers on HTML pages

	// admin (#40): HTML page is open (key entry via form); API is key-guarded
	r.Get("/admin", a.ui.Handlers().HandleAdminPage)
	r.Get("/admin/api/settings", a.adminAuth(a.handleAdminGetSettings, a.adminKey))
	r.Post("/admin/api/settings", a.adminAuth(a.handleAdminPostSettings, a.adminKey))

	// API
	r.Route("/api", func(r chi.Router) {
		r.Post("/pastes", a.handleCreatePaste)
		r.Get("/pastes/{id}", a.handleGetPaste)
		r.Delete("/pastes/{id}", a.handleDeletePaste)
		r.Get("/mine", a.handleListMine)
		r.Delete("/pastes/{id}/redeem", a.handleRedeemDeletion)
		r.Get("/public", a.handleListPublic)
		r.Post("/guess-language", a.handleGuessLang)
		r.Post("/pastes/can", a.handleCreateCan)
		r.Get("/cans/{id}", a.handleGetCan)
		r.Delete("/cans/{id}", a.handleDeleteCan)
		r.Get("/cans/{id}/items/{item}", a.handleCanItem)
	})

	// can page (#4): GET renders, POST unlocks (same flow as pastes)
	r.Get("/can/{id}", a.handleCanPage)
	r.Post("/can/{id}", a.handleCanPage)

	// raw
	r.Get("/raw/{id}", a.handleRaw)

	// web pages
	r.Get("/", http.RedirectHandler("/history", http.StatusFound).ServeHTTP)
	r.Get("/new", a.ui.Handlers().HandleNewPage)
	r.Get("/history", a.ui.Handlers().HandleHistoryPage)
	r.Get("/settings", a.ui.Handlers().HandleSettingsPage)
	r.Get("/mine", a.ui.Handlers().HandleMinePage)
	r.Handle("/static/*", a.ui.StaticHandler())
	r.Get("/unlock/{id}", a.handlePasteView)
	r.Post("/unlock/{id}", a.handlePasteView)
	r.Get("/{id}", a.handlePasteView)
	r.Post("/{id}", a.handlePasteView)

	r.NotFound(func(w http.ResponseWriter, r *http.Request) {
		writeErr(w, 404, "not found")
	})
	return r
}

// viewerCookieMiddleware ensures every request carries an anonymous browser id
// cookie ("vwr"); sets one on the response if absent. Used by /mine (#37, #49).
func viewerCookieMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if c, err := r.Cookie("vwr"); err != nil || c.Value == "" {
			id := store.GenSlug(16)
			http.SetCookie(w, &http.Cookie{
				Name: "vwr", Value: id, Path: "/",
				MaxAge: 31536000, HttpOnly: true, SameSite: http.SameSiteLaxMode,
			})
			r.AddCookie(&http.Cookie{Name: "vwr", Value: id})
			// remember that this cookie was minted here, not sent by the client
			r = r.WithContext(context.WithValue(r.Context(), vwrMintedKey, true))
		}
		next.ServeHTTP(w, r)
	})
}

type vwrMintedKeyType struct{}

var vwrMintedKey vwrMintedKeyType

func currentViewerID(r *http.Request) string {
	if c, err := r.Cookie("vwr"); err == nil {
		return c.Value
	}
	return ""
}

// viewerSentCookie reports whether the client itself sent a vwr cookie
// (as opposed to the middleware minting one for this request).
func viewerSentCookie(r *http.Request) bool {
	if _, err := r.Cookie("vwr"); err != nil {
		return false
	}
	_, minted := r.Context().Value(vwrMintedKey).(bool)
	return !minted
}

func (a *apiServer) handleCreatePaste(w http.ResponseWriter, r *http.Request) {
	s := a.settings.get()
	setRateLimitHeaders(w, 1, 5)
	if !rateLimitCreate(r, s) {
		writeRateLimited(w, 1)
		return
	}
	var p store.Paste
	if err := json.NewDecoder(r.Body).Decode(&p); err != nil {
		if isBodyTooLarge(err) { // #68: body cut off by MaxBytesReader
			writeBodyTooLarge(w)
			return
		}
		writeErr(w, 400, "invalid json body")
		return
	}
	if status, msg := checkContent(p.Content, s.MaxContentBytes); status != 0 {
		writeErr(w, status, msg)
		return
	}
	// #86: bound free-form metadata at create time
	if p.Title != nil {
		t, err := checkTitle(*p.Title)
		if err != nil {
			writeErr(w, 400, err.Error())
			return
		}
		p.Title = &t
	}
	if p.Language != nil {
		l, err := checkLanguage(*p.Language)
		if err != nil {
			writeErr(w, 400, err.Error())
			return
		}
		if l == "" {
			p.Language = nil
		} else {
			p.Language = &l
		}
	}
	if p.BurnAfterReads != nil { // #68: reject negative read budgets
		if err := parseBurnAfterReads(*p.BurnAfterReads); err != nil {
			writeErr(w, 400, err.Error())
			return
		}
	}
	// #40: admin-configurable default expiry
	if (p.ExpiresIn == nil || *p.ExpiresIn == "") && s.DefaultExpiry != "" {
		def := s.DefaultExpiry
		p.ExpiresIn = &def
	}
	p.ViewerID = currentViewerID(r)
	created, err := a.store.CreatePaste(&p)
	if err != nil {
		writeErr(w, 400, err.Error())
		return
	}
	writeJSON(w, 201, map[string]any{
		"id":             created.ID,
		"deletion_token": created.DeletionToken,
		"url":            "/" + created.ID,
		"raw_url":        "/raw/" + created.ID,
		"api_url":        "/api/pastes/" + created.ID,
		"expires_at":     created.ExpiresAt,
		"created_at":     created.CreatedAt,
		"rate_limit":     map[string]int{"create_per_sec": 1, "burst": 5},
	})
}

func (a *apiServer) handleGetPaste(w http.ResponseWriter, r *http.Request) {
	id := chi.URLParam(r, "id")
	row, err := a.store.GetPaste(id)
	if err != nil {
		writeErr(w, 500, "db error")
		return
	}
	if row == nil {
		writeErr(w, 404, "paste not found")
		return
	}
	if row.ExpiresAt.Valid && row.ExpiresAt.Int64 < time.Now().Unix() {
		writeErr(w, 404, "paste expired")
		return
	}
	if row.Burned() { // #49: read budget exhausted
		writeErr(w, 404, "paste not found")
		return
	}
	if row.PasswordHash.Valid {
		// #81: every password verification (header, query param, or empty)
		// goes through the same per-IP+paste unlock limiter as the POST form
		// path, so brute-force via GET ?password= or X-Paste-Password gets 429.
		if !rateLimitUnlock(row.ID, r) {
			writeRateLimited(w, 60)
			return
		}
		// require password via header or query
		pw := r.Header.Get("X-Paste-Password")
		if pw == "" {
			pw = r.URL.Query().Get("password")
		}
		if pw == "" || !store.CheckPassword(row.PasswordHash.String, pw) {
			writeErr(w, 401, "password required")
			return
		}
	}
	// #58: only the reader that wins the atomic burn claim may see content.
	rem, admitted := a.store.RegisterRead(row, currentViewerID(r), a.burnViewerWindow())
	if !admitted {
		writeErr(w, 404, "paste not found")
		return
	}
	writeJSON(w, 200, map[string]any{
		"id": row.ID, "content": row.Content, "content_type": row.ContentType,
		"language": store.NullStrPtr(row.Language), "title": store.NullStrPtr(row.Title), "created_at": row.CreatedAt,
		"view_count": row.ViewCount, "visibility": row.Visibility,
		"reads_remaining": rem,
	})
}

func (a *apiServer) handleDeletePaste(w http.ResponseWriter, r *http.Request) {
	id := chi.URLParam(r, "id")
	row, err := a.store.GetPaste(id)
	if err != nil || row == nil {
		writeErr(w, 404, "paste not found")
		return
	}
	// #63: deletion requires authorization. Either the deletion token issued
	// at create time (Authorization header or ?token= query param, matching
	// the create response's "deletion_token" field), or the creator browser
	// itself (client-sent vwr cookie matching the paste's viewer, #37).
	if !a.deletionAuthorized(r, row) {
		writeErr(w, 403, "deletion token required")
		return
	}
	if _, err := a.store.SoftDelete(row.ID); err != nil {
		writeErr(w, 500, "db error")
		return
	}
	writeJSON(w, 200, map[string]string{"status": "soft-deleted"})
}

// deletionAuthorization extracts the deletion token from the request: the
// Authorization header ("Bearer <t>", "Token <t>", or a bare token) or the
// token query parameter. Returns "" when absent.
func deletionAuthorization(r *http.Request) string {
	if h := r.Header.Get("Authorization"); h != "" {
		for _, prefix := range []string{"Bearer ", "Token "} {
			if len(h) > len(prefix) && strings.EqualFold(h[:len(prefix)], prefix) {
				return strings.TrimSpace(h[len(prefix):])
			}
		}
		return strings.TrimSpace(h)
	}
	return r.URL.Query().Get("token")
}

// deletionAuthorized reports whether the request may soft-delete the paste:
// a valid constant-time-matched deletion token, or the creator browser's
// viewer cookie (#37). Plain API clients with no token get false.
func (a *apiServer) deletionAuthorized(r *http.Request, row *store.PasteRow) bool {
	if tok := deletionAuthorization(r); tok != "" {
		return row.DeletionToken.Valid && row.DeletionToken.String != "" &&
			store.DeletionTokenEqual(row.DeletionToken.String, tok)
	}
	// viewer-cookie delete enforcement (#37): only the browser that created
	// the paste (matching vwr) may delete it via this endpoint. Requests with
	// no client-sent vwr cookie (plain API clients) are unaffected.
	vid := currentViewerID(r)
	return vid != "" && viewerSentCookie(r) && row.ViewerID.Valid &&
		row.ViewerID.String != "" && row.ViewerID.String == vid
}

// handleListMine serves /api/mine: pastes created from this browser (#37).
func (a *apiServer) handleListMine(w http.ResponseWriter, r *http.Request) {
	vid := currentViewerID(r)
	if vid == "" {
		writeJSON(w, 200, map[string]any{"total": 0, "items": []any{}})
		return
	}
	limit := parseLimit(r, 50, 100)
	offset := parseOffset(r)
	rows, total, err := a.store.ListMine(vid, limit, offset)
	if err != nil {
		writeErr(w, 500, "db error")
		return
	}
	items := make([]map[string]any, 0, len(rows))
	for _, row := range rows {
		lang, title := store.NullStrPtr(row.Language), store.NullStrPtr(row.Title)
		items = append(items, map[string]any{
			"id": row.ID, "title": title, "language": lang,
			"created_at": row.CreatedAt, "view_count": row.ViewCount, "size": row.Size,
			"custom_slug": store.NullStrPtr(row.CustomSlug), "visibility": row.Visibility,
			"is_can": row.IsCan,
		})
	}
	writeJSON(w, 200, map[string]any{"total": total, "limit": limit, "offset": offset, "items": items})
}

func (a *apiServer) handleListPublic(w http.ResponseWriter, r *http.Request) {
	limit := parseLimit(r, 25, 100)
	offset := parseOffset(r)
	rows, total, err := a.store.ListPublic(limit, offset)
	if err != nil {
		writeErr(w, 500, "db error")
		return
	}
	items := make([]map[string]any, 0, len(rows))
	for _, row := range rows {
		lang, title := store.NullStrPtr(row.Language), store.NullStrPtr(row.Title)
		items = append(items, map[string]any{
			"id": row.ID, "title": title, "language": lang,
			"created_at": row.CreatedAt, "view_count": row.ViewCount, "size": row.Size,
			"custom_slug": store.NullStrPtr(row.CustomSlug),
			"is_can":      row.IsCan,
		})
	}
	writeJSON(w, 200, map[string]any{"total": total, "limit": limit, "offset": offset, "items": items})
}

func (a *apiServer) handleRaw(w http.ResponseWriter, r *http.Request) {
	id := chi.URLParam(r, "id")
	row, err := a.store.GetPaste(id)
	if err != nil || row == nil {
		http.Error(w, "not found", 404)
		return
	}
	if row.ExpiresAt.Valid && row.ExpiresAt.Int64 < time.Now().Unix() {
		http.Error(w, "paste expired", 404)
		return
	}
	if row.PasswordHash.Valid {
		http.Error(w, "password required", 401)
		return
	}
	if row.Burned() { // #49: read budget exhausted
		http.Error(w, "not found", 404)
		return
	}
	// #49 decision: raw reads count against the read budget too, with the
	// same per-viewer dedupe window as page views. #58: a reader that loses
	// the burn claim must not receive the content.
	_, admitted := a.store.RegisterRead(row, currentViewerID(r), a.burnViewerWindow())
	if !admitted {
		http.Error(w, "not found", 404)
		return
	}
	// #34: content_type is attacker-controlled via the create API. Serving it
	// verbatim let a paste be stored with text/html (or image/svg+xml) and
	// render as active content on this origin when fetched from /raw —
	// stored XSS. Only pass through a fixed safe set; anything else is
	// served as plain text with nosniff.
	ct := row.ContentType
	if !safeRawContentType(ct) {
		ct = "text/plain; charset=utf-8"
	}
	w.Header().Set("Content-Type", ct)
	w.Header().Set("X-Content-Type-Options", "nosniff")
	a.store.IncrementViews(row.ID, "", 0) // raw views always count (#49/#95)
	w.Write([]byte(row.Content))
}

// safeRawContentType reports whether ct is in the fixed set of types that are
// safe to serve verbatim on /raw (no active-content execution contexts).
func safeRawContentType(ct string) bool {
	base := ct
	if i := strings.IndexByte(ct, ';'); i >= 0 {
		base = ct[:i]
	}
	base = strings.ToLower(strings.TrimSpace(base))
	switch base {
	case "text/plain", "text/markdown", "text/x-markdown",
		"application/json", "application/pdf",
		"image/png", "image/jpeg", "image/gif", "image/webp",
		"application/octet-stream":
		return true
	}
	return false
}

func (a *apiServer) handleCanPage(w http.ResponseWriter, r *http.Request) {
	id := chi.URLParam(r, "id")
	can, err := a.store.GetCan(id)
	if err != nil || can == nil {
		http.NotFound(w, r)
		return
	}
	if can.ExpiresAt.Valid && can.ExpiresAt.Int64 < time.Now().Unix() {
		http.NotFound(w, r)
		return
	}
	// #4: password-protected cans go through the same unlock flow as pastes:
	// the pw_<id> cookie carries an HMAC token bound to this can id. Items
	// inherit the protection (handleCanItem checks the same cookie).
	if can.PasswordHash.Valid {
		h := a.webHandlers()
		if r.Method == http.MethodPost {
			if !rateLimitUnlock(can.ID, r) {
				h.WriteRateLimited(w, 60)
				return
			}
			r.ParseForm()
			pw := r.FormValue("password")
			if pw != "" && store.CheckPassword(can.PasswordHash.String, pw) {
				http.SetCookie(w, &http.Cookie{
					Name: "pw_" + can.ID, Value: web.UnlockToken(can.ID), Path: "/",
					MaxAge: 3600, HttpOnly: true, SameSite: http.SameSiteLaxMode,
				})
				a.renderCan(w, can)
				return
			}
			h.RenderPage(w, "unlock.html", map[string]any{
				"Page": "unlock", "ID": can.ID, "Wrong": true,
				"CreatedAgo": web.AgoString(can.CreatedAt), "CreatedAtUnix": can.CreatedAt,
			})
			return
		}
		c, err := r.Cookie("pw_" + can.ID)
		if err != nil || c.Value != web.UnlockToken(can.ID) {
			h.RenderPage(w, "unlock.html", map[string]any{
				"Page": "unlock", "ID": can.ID, "Wrong": false,
				"CreatedAgo": web.AgoString(can.CreatedAt), "CreatedAtUnix": can.CreatedAt,
			})
			return
		}
	}
	a.renderCan(w, can)
}

// renderCan renders the can view page: title/description and items as cards.
// Text items expand inline; files link to download.
func (a *apiServer) renderCan(w http.ResponseWriter, can *store.CanRow) {
	h := a.webHandlers()
	items, err := a.store.ListCanItems(can.ID)
	if err != nil {
		http.Error(w, "db error", 500)
		return
	}
	type canItem struct {
		ID          string
		Title       string
		ContentType string
		Size        string
		IsFile      bool
		Content     string
		ContentHTML template.HTML
		Language    string
	}
	cards := make([]canItem, 0, len(items))
	totalSize := 0
	for _, it := range items {
		totalSize += len(it.Content)
		isFile := it.ContentType != "text/plain" && !strings.HasPrefix(it.ContentType, "text/")
		ci := canItem{
			ID:          it.ID,
			Title:       nullStrOr(it.Title, it.ID),
			ContentType: it.ContentType,
			Size:        web.HumanSize(len(it.Content)),
			IsFile:      isFile,
			Language:    it.Language.String,
		}
		if !isFile {
			ci.ContentHTML = template.HTML(langpkg.HighlightCode(it.Content, it.Language.String))
		}
		cards = append(cards, ci)
	}
	h.RenderPage(w, "can.html", map[string]any{
		"Page":          "can",
		"ID":            can.ID,
		"Title":         nullStrOr(can.Title, "Untitled can"),
		"Description":   can.Description.String,
		"HasDescription": can.Description.Valid && can.Description.String != "",
		"HasPassword":   can.PasswordHash.Valid,
		"Items":         cards,
		"ItemCount":     len(cards),
		"SizeHuman":     web.HumanSize(totalSize),
		"CreatedAgo":    web.AgoString(can.CreatedAt),
		"CreatedAtUnix": can.CreatedAt,
		"ExpiresAt":     can.ExpiresAt.Valid,
		"ExpiresIn":     expiryStringIfValid(can.ExpiresAt),
	})
}

// expiryStringIfValid formats remaining time for a valid expiry, "" otherwise.
func expiryStringIfValid(ns sql.NullInt64) string {
	if !ns.Valid {
		return ""
	}
	remaining := ns.Int64 - time.Now().Unix()
	s := remaining
	switch {
	case s < 3600:
		return fmt.Sprintf("%dm", s/60)
	case s < 86400:
		return fmt.Sprintf("%dh", s/3600)
	default:
		return fmt.Sprintf("%dd", s/86400)
	}
}

func templateEsc(s string) string {
	r := strings.NewReplacer("&", "&amp;", "<", "&lt;", ">", "&gt;")
	return r.Replace(s)
}

func (a *apiServer) handlePasteView(w http.ResponseWriter, r *http.Request) {
	h := a.webHandlers()
	// unlock POST rate limiting is wired through h.RateLimitOK
	h.HandlePasteView(w, r)
}

func (a *apiServer) webHandlers() *web.Handlers {
	return &web.Handlers{
		UI:            a.ui,
		Store:         a.store,
		ViewerID:      currentViewerID,
		BurnWindowMin: a.burnViewerWindow,
		RateLimitOK:   func(id string, r *http.Request) bool { return rateLimitUnlock(id, r) },
	}
}

func envOr(k, d string) string {
	if v := os.Getenv(k); v != "" {
		return v
	}
	return d
}

func envIntOr(k string, d int) int {
	if v := os.Getenv(k); v != "" {
		if n, err := strconv.Atoi(v); err == nil {
			return n
		}
	}
	return d
}

func nullStrOr(ns sql.NullString, def string) string {
	if ns.Valid {
		return ns.String
	}
	return def
}

// EnvOr returns the env var value or default.
func EnvOr(k, d string) string { return envOr(k, d) }

// EnvIntOr returns the env int value or default.
func EnvIntOr(k string, d int) int { return envIntOr(k, d) }