// package api implements public HTTP endpoints for the launcher and website.
package api

import (
	"crypto/sha1"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"strconv"

	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/auth"
	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/config"
	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/database"
)

// Handler serves public API endpoints.
type Handler struct {
	db  *database.DB
	cfg *config.Config
}

// NewHandler creates a new API handler.
func NewHandler(db *database.DB, cfg *config.Config) *Handler {
	return &Handler{db: db, cfg: cfg}
}

// RegisterRoutes mounts the API endpoints.
func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
	// Website endpoints.
	mux.HandleFunc("POST /api/web/register", h.register)
	mux.HandleFunc("POST /api/web/login", h.webLogin)
	mux.HandleFunc("POST /api/web/profile/skin", h.uploadSkin)

	// Launcher endpoints.
	mux.HandleFunc("GET /api/launcher/latest", h.launcherLatest)
	mux.HandleFunc("GET /api/servers.json", h.serversList)
	mux.HandleFunc("GET /api/instances/{slug}/manifest.json", h.instanceManifest)

	// Skin serving.
	mux.HandleFunc("GET /skins/{hash}.png", h.serveSkin)
}

// ── Request / Response types ──────────────────────────────────

type registerRequest struct {
	Username string `json:"username"`
	Email    string `json:"email"`
	Password string `json:"password"`
}

type registerResponse struct {
	UUID string `json:"uuid"`
}

type webLoginRequest struct {
	Username string `json:"username"`
	Password string `json:"password"`
}

type webLoginResponse struct {
	Token    string `json:"token"`
	UUID     string `json:"uuid"`
	Username string `json:"username"`
}

type serversResponse struct {
	Servers []serverInfo `json:"servers"`
}

type serverInfo struct {
	Slug    string `json:"slug"`
	Name    string `json:"name"`
	Version string `json:"version"`
	IP      string `json:"ip"`
}

type launcherLatestResponse struct {
	Version    string            `json:"version"`
	Downloads  map[string]string `json:"downloads"` // os+arch -> url
	SHA256     string            `json:"sha256"`
	IsMandatory bool             `json:"is_mandatory"`
}

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

// ── Handlers ──────────────────────────────────────────────────

func (h *Handler) register(w http.ResponseWriter, r *http.Request) {
	body, err := io.ReadAll(r.Body)
	if err != nil {
		writeError(w, http.StatusBadRequest, "Cannot read body")
		return
	}

	var req registerRequest
	if err := json.Unmarshal(body, &req); err != nil {
		writeError(w, http.StatusBadRequest, "Invalid JSON")
		return
	}

	if req.Username == "" || req.Email == "" || req.Password == "" {
		writeError(w, http.StatusBadRequest, "Username, email and password are required")
		return
	}

	// Check uniqueness.
	var exists int
	err = h.db.Pool().QueryRow(r.Context(),
		`SELECT COUNT(*) FROM users WHERE username = $1 OR email = $2`,
		req.Username, req.Email,
	).Scan(&exists)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Database error")
		return
	}
	if exists > 0 {
		writeError(w, http.StatusConflict, "Username or email already taken")
		return
	}

	uuid := auth.GenerateUUID()
	passwordHash := auth.HashPassword(req.Password)

	_, err = h.db.Pool().Exec(r.Context(),
		`INSERT INTO users (username, email, password_hash, uuid, role)
		 VALUES ($1, $2, $3, $4, 'user')`,
		req.Username, req.Email, passwordHash, uuid,
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Failed to create user")
		return
	}

	writeJSON(w, http.StatusCreated, registerResponse{UUID: uuid})
}

func (h *Handler) webLogin(w http.ResponseWriter, r *http.Request) {
	body, err := io.ReadAll(r.Body)
	if err != nil {
		writeError(w, http.StatusBadRequest, "Cannot read body")
		return
	}

	var req webLoginRequest
	if err := json.Unmarshal(body, &req); err != nil {
		writeError(w, http.StatusBadRequest, "Invalid JSON")
		return
	}

	var user database.User
	err = h.db.Pool().QueryRow(r.Context(),
		`SELECT id, username, password_hash, uuid FROM users
		 WHERE username = $1 OR email = $1`,
		req.Username,
	).Scan(&user.ID, &user.Username, &user.PasswordHash, &user.UUID)

	if err != nil || !verifyPassword(req.Password, user.PasswordHash) {
		writeError(w, http.StatusUnauthorized, "Invalid credentials")
		return
	}

	// Generate a simple session token (for web; launcher uses Yggdrasil).
	token := auth.GenerateToken()

	_, err = h.db.Pool().Exec(r.Context(),
		`INSERT INTO yggdrasil_sessions (client_token, access_token, user_id, expires_at)
		 VALUES ($1, $2, $3, NOW() + INTERVAL '7 days')`,
		token, token, user.ID,
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Failed to create session")
		return
	}

	writeJSON(w, http.StatusOK, webLoginResponse{
		Token:    token,
		UUID:     user.UUID,
		Username: user.Username,
	})
}

func (h *Handler) uploadSkin(w http.ResponseWriter, r *http.Request) {
	// TODO: authenticate via session token from header.
	// For now, accept user_id from form (to be replaced with proper auth).
	userID, err := strconv.Atoi(r.FormValue("user_id"))
	if err != nil || userID == 0 {
		writeError(w, http.StatusUnauthorized, "Authentication required")
		return
	}

	file, _, err := r.FormFile("skin")
	if err != nil {
		writeError(w, http.StatusBadRequest, "No skin file provided")
		return
	}
	defer file.Close()

	data, err := io.ReadAll(file)
	if err != nil {
		writeError(w, http.StatusBadRequest, "Cannot read skin file")
		return
	}

	// Validate PNG.
	if len(data) < 8 || string(data[:8]) != "\x89PNG\r\n\x1a\n" {
		writeError(w, http.StatusBadRequest, "Invalid PNG file")
		return
	}

	// Compute SHA-1 hash.
	hash := sha1Hex(data)

	// Store in CAS.
	destDir := filepath.Join(h.cfg.SkinsDir, hash[:2])
	if err := os.MkdirAll(destDir, 0o755); err != nil {
		writeError(w, http.StatusInternalServerError, "Failed to store skin")
		return
	}
	dest := filepath.Join(destDir, hash+".png")
	if err := os.WriteFile(dest, data, 0o644); err != nil {
		writeError(w, http.StatusInternalServerError, "Failed to write skin")
		return
	}

	// Update user profile.
	_, err = h.db.Pool().Exec(r.Context(),
		`INSERT INTO player_textures (user_id, skin_hash)
		 VALUES ($1, $2)
		 ON CONFLICT (user_id) DO UPDATE SET skin_hash = $2`,
		userID, hash,
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Failed to update profile")
		return
	}

	writeJSON(w, http.StatusOK, map[string]string{"hash": hash})
}

func (h *Handler) launcherLatest(w http.ResponseWriter, r *http.Request) {
	osParam := r.URL.Query().Get("os")
	archParam := r.URL.Query().Get("arch")

	if osParam == "" || archParam == "" {
		writeError(w, http.StatusBadRequest, "os and arch query parameters are required")
		return
	}

	var release database.LauncherRelease
	err := h.db.Pool().QueryRow(r.Context(),
		`SELECT version, file_path, sha256, is_mandatory FROM launcher_releases
		 WHERE os = $1 AND arch = $2 AND is_active = true
		 ORDER BY created_at DESC LIMIT 1`,
		osParam, archParam,
	).Scan(&release.Version, &release.FilePath, &release.SHA256, &release.IsMandatory)

	if err != nil {
		writeError(w, http.StatusNotFound, "No release found for this platform")
		return
	}

	downloadURL := fmt.Sprintf("%s/files/launcher/%s/%s/%s",
		h.cfg.BaseURL, osParam, archParam, filepath.Base(release.FilePath))

	writeJSON(w, http.StatusOK, launcherLatestResponse{
		Version:     release.Version,
		Downloads:   map[string]string{osParam + "_" + archParam: downloadURL},
		SHA256:      release.SHA256,
		IsMandatory: release.IsMandatory,
	})
}

func (h *Handler) serversList(w http.ResponseWriter, r *http.Request) {
	rows, err := h.db.Pool().Query(r.Context(),
		`SELECT slug, name, minecraft_version, server_ip FROM modpacks
		 WHERE is_active = true ORDER BY created_at DESC`)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Database error")
		return
	}
	defer rows.Close()

	var servers []serverInfo
	for rows.Next() {
		var s serverInfo
		if err := rows.Scan(&s.Slug, &s.Name, &s.Version, &s.IP); err != nil {
			continue
		}
		servers = append(servers, s)
	}

	writeJSON(w, http.StatusOK, serversResponse{Servers: servers})
}

func (h *Handler) instanceManifest(w http.ResponseWriter, r *http.Request) {
	slug := r.PathValue("slug")
	if slug == "" {
		writeError(w, http.StatusBadRequest, "Instance slug is required")
		return
	}

	// Check modpack exists.
	var exists bool
	err := h.db.Pool().QueryRow(r.Context(),
		`SELECT EXISTS(SELECT 1 FROM modpacks WHERE slug = $1 AND is_active = true)`,
		slug,
	).Scan(&exists)
	if err != nil || !exists {
		writeError(w, http.StatusNotFound, "Instance not found")
		return
	}

	// Read manifest file.
	manifestPath := filepath.Join(h.cfg.CASDir, "..", "manifests", slug, "manifest.json")
	data, err := os.ReadFile(manifestPath)
	if err != nil {
		writeError(w, http.StatusNotFound, "Manifest not found")
		return
	}

	w.Header().Set("Content-Type", "application/json")
	w.Write(data)
}

func (h *Handler) serveSkin(w http.ResponseWriter, r *http.Request) {
	hash := r.PathValue("hash")
	if hash == "" {
		http.NotFound(w, r)
		return
	}

	// Sanitize: only hex chars.
	for _, c := range hash {
		if !((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f')) {
			http.NotFound(w, r)
			return
		}
	}

	path := filepath.Join(h.cfg.SkinsDir, hash[:2], hash+".png")
	data, err := os.ReadFile(path)
	if err != nil {
		http.NotFound(w, r)
		return
	}

	w.Header().Set("Content-Type", "image/png")
	w.Header().Set("Cache-Control", "public, max-age=3600")
	w.Write(data)
}

// ── Helpers ───────────────────────────────────────────────────

func verifyPassword(password, hash string) bool {
	h := sha256.Sum256([]byte(password))
	return subtle.ConstantTimeCompare([]byte(hex.EncodeToString(h[:])), []byte(hash)) == 1
}

func sha1Hex(data []byte) string {
	h := sha1.Sum(data)
	return hex.EncodeToString(h[:])
}

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 writeError(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, errorResponse{Error: msg})
}