package app

import (
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"
)

type exchangeRequest struct {
	Code             string `json:"code"`
	HostFingerprint  string `json:"host_fingerprint"`
	Hostname         string `json:"hostname"`
	RequestedAction  string `json:"requested_action,omitempty"`
	RequestedPackage string `json:"requested_package,omitempty"`
	InstallationID   string `json:"installation_id,omitempty"`
}

type exchangePackage struct {
	Slug        string `json:"slug"`
	DisplayName string `json:"display_name"`
	Version     string `json:"version"`
	SHA256      string `json:"sha256"`
	DownloadURL string `json:"download_url"`
}

type exchangeResponse struct {
	SessionToken string            `json:"session_token"`
	ExpiresAt    time.Time         `json:"expires_at"`
	Packages     []exchangePackage `json:"packages"`
	Actions      []string          `json:"actions"`
}

func (s *Server) handleExchange(w http.ResponseWriter, r *http.Request) {
	sourceIP := s.clientIP(r)
	limited, err := s.exchangeRateLimited(r, sourceIP)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "unable to validate request"})
		return
	}
	if limited {
		w.Header().Set("Retry-After", "600")
		writeJSON(w, http.StatusTooManyRequests, map[string]string{"error": "too many failed attempts; try again later"})
		return
	}

	r.Body = http.MaxBytesReader(w, r.Body, 32<<10)
	var request exchangeRequest
	if err := json.NewDecoder(r.Body).Decode(&request); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid request"})
		return
	}
	request.Code = normalizeCode(request.Code)
	request.HostFingerprint = strings.TrimSpace(request.HostFingerprint)
	request.Hostname = strings.TrimSpace(request.Hostname)
	request.RequestedAction = strings.TrimSpace(request.RequestedAction)
	request.RequestedPackage = strings.TrimSpace(request.RequestedPackage)
	request.InstallationID = strings.TrimSpace(request.InstallationID)
	if request.Code == "" || len(request.HostFingerprint) < 16 ||
		request.Hostname == "" || len(request.Hostname) > 255 ||
		(request.RequestedAction != "" && !validSlug(request.RequestedAction)) ||
		(request.RequestedPackage != "" && !validSlug(request.RequestedPackage)) {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "code and host identity are required"})
		return
	}

	response, authorizationID, err := s.exchangeDeploymentCode(r, request)
	if err != nil {
		status := http.StatusInternalServerError
		message := "unable to create download session"
		if errors.Is(err, errAuthorizationDenied) {
			status = http.StatusForbidden
			message = "authorization is invalid, expired, revoked, or at its host limit"
		}
		_ = s.audit(r.Context(), "code_exchange_failed", "", nil,
			request.Hostname, "", sourceIP, err.Error())
		writeJSON(w, status, map[string]string{"error": message})
		return
	}
	_ = s.audit(
		r.Context(),
		"code_exchanged",
		"",
		&authorizationID,
		request.Hostname,
		request.RequestedPackage,
		sourceIP,
		"requested_action="+request.RequestedAction,
	)
	s.verifyFleetInstallation(r.Context(), request.InstallationID)
	writeJSON(w, http.StatusOK, response)
}

func (s *Server) exchangeRateLimited(r *http.Request, sourceIP string) (bool, error) {
	var attempts int
	err := s.db.QueryRowContext(
		r.Context(),
		`SELECT COUNT(*)
		   FROM audit_events
		  WHERE event_type = 'code_exchange_failed'
		    AND source_ip = ?
		    AND created_at > datetime('now', '-10 minutes')`,
		sourceIP,
	).Scan(&attempts)
	return attempts >= 10, err
}

func (s *Server) exchangeDeploymentCode(
	r *http.Request,
	request exchangeRequest,
) (exchangeResponse, uint64, error) {
	var response exchangeResponse
	codeHash := hashValue(request.Code)
	fingerprintHash := hashValue(request.HostFingerprint)

	tx, err := s.db.BeginTx(r.Context(), &sql.TxOptions{Isolation: sql.LevelSerializable})
	if err != nil {
		return response, 0, err
	}
	defer tx.Rollback()

	var authorizationID uint64
	var hostLimit int
	var expiresAt time.Time
	err = tx.QueryRowContext(
		r.Context(),
		`SELECT id, host_limit, expires_at
		   FROM authorizations
		  WHERE code_hash = ?
		    AND revoked_at IS NULL
		    AND expires_at > CURRENT_TIMESTAMP`,
		codeHash[:],
	).Scan(&authorizationID, &hostLimit, &expiresAt)
	if errors.Is(err, sql.ErrNoRows) {
		return response, 0, errAuthorizationDenied
	}
	if err != nil {
		return response, 0, err
	}

	if request.RequestedAction != "" {
		var authorized int
		if err := tx.QueryRowContext(
			r.Context(),
			`SELECT COUNT(*)
			   FROM authorization_actions aa
			   JOIN installer_actions ia ON ia.slug = aa.action_slug
			  WHERE aa.authorization_id = ?
			    AND aa.action_slug = ?
			    AND ia.enabled = TRUE`,
			authorizationID, request.RequestedAction,
		).Scan(&authorized); err != nil {
			return response, 0, err
		}
		if authorized != 1 {
			return response, 0, errAuthorizationDenied
		}
	}
	if request.RequestedPackage != "" {
		var authorized int
		if err := tx.QueryRowContext(
			r.Context(),
			`SELECT COUNT(*)
			   FROM authorization_packages ap
			   JOIN packages p ON p.id = ap.package_id
			  WHERE ap.authorization_id = ?
			    AND p.slug = ?
			    AND p.enabled = TRUE`,
			authorizationID, request.RequestedPackage,
		).Scan(&authorized); err != nil {
			return response, 0, err
		}
		if authorized != 1 {
			return response, 0, errAuthorizationDenied
		}
	}

	var hostID uint64
	err = tx.QueryRowContext(
		r.Context(),
		`SELECT id FROM authorization_hosts
		  WHERE authorization_id = ? AND host_fingerprint = ?`,
		authorizationID, fingerprintHash[:],
	).Scan(&hostID)
	if errors.Is(err, sql.ErrNoRows) {
		var hostCount int
		if err := tx.QueryRowContext(
			r.Context(),
			`SELECT COUNT(*) FROM authorization_hosts WHERE authorization_id = ?`,
			authorizationID,
		).Scan(&hostCount); err != nil {
			return response, 0, err
		}
		if hostCount >= hostLimit {
			return response, 0, errAuthorizationDenied
		}
		result, err := tx.ExecContext(
			r.Context(),
			`INSERT INTO authorization_hosts
				(authorization_id, host_fingerprint, hostname)
			 VALUES (?, ?, ?)`,
			authorizationID, fingerprintHash[:], request.Hostname,
		)
		if err != nil {
			return response, 0, err
		}
		insertedID, _ := result.LastInsertId()
		hostID = uint64(insertedID)
	} else if err != nil {
		return response, 0, err
	} else {
		_, err = tx.ExecContext(
			r.Context(),
			`UPDATE authorization_hosts
			    SET hostname = ?,
			        last_seen_at = CURRENT_TIMESTAMP
			  WHERE id = ?`,
			request.Hostname, hostID,
		)
		if err != nil {
			return response, 0, err
		}
	}

	sessionToken, err := randomToken(32)
	if err != nil {
		return response, 0, err
	}
	sessionHash := hashValue(sessionToken)
	_, err = tx.ExecContext(
		r.Context(),
		`INSERT INTO download_sessions
			(token_hash, authorization_id, authorization_host_id, expires_at)
		 VALUES (?, ?, ?, ?)`,
		sessionHash[:], authorizationID, hostID, expiresAt,
	)
	if err != nil {
		return response, 0, err
	}

	rows, err := tx.QueryContext(
		r.Context(),
		`SELECT p.slug, p.display_name, p.package_version, p.sha256
		   FROM authorization_packages ap
		   JOIN packages p ON p.id = ap.package_id
		  WHERE ap.authorization_id = ? AND p.enabled = TRUE
		  ORDER BY p.display_name`,
		authorizationID,
	)
	if err != nil {
		return response, 0, err
	}
	defer rows.Close()
	for rows.Next() {
		var record exchangePackage
		if err := rows.Scan(
			&record.Slug,
			&record.DisplayName,
			&record.Version,
			&record.SHA256,
		); err != nil {
			return response, 0, err
		}
		record.DownloadURL = strings.TrimRight(s.cfg.PublicURL.String(), "/") +
			"/api/v1/packages/" + url.PathEscape(record.Slug)
		response.Packages = append(response.Packages, record)
	}
	if err := rows.Err(); err != nil {
		return response, 0, err
	}
	if err := rows.Close(); err != nil {
		return response, 0, err
	}
	actionRows, err := tx.QueryContext(
		r.Context(),
		`SELECT ia.slug
		   FROM authorization_actions aa
		   JOIN installer_actions ia ON ia.slug = aa.action_slug
		  WHERE aa.authorization_id = ? AND ia.enabled = TRUE
		  ORDER BY ia.sort_order, ia.display_name`,
		authorizationID,
	)
	if err != nil {
		return response, 0, err
	}
	defer actionRows.Close()
	for actionRows.Next() {
		var slug string
		if err := actionRows.Scan(&slug); err != nil {
			return response, 0, err
		}
		response.Actions = append(response.Actions, slug)
	}
	if err := actionRows.Err(); err != nil {
		return response, 0, err
	}
	if err := actionRows.Close(); err != nil {
		return response, 0, err
	}
	if len(response.Packages) == 0 && len(response.Actions) == 0 {
		return response, 0, errAuthorizationDenied
	}

	if err := tx.Commit(); err != nil {
		return response, 0, err
	}
	response.SessionToken = sessionToken
	response.ExpiresAt = expiresAt
	return response, authorizationID, nil
}

func (s *Server) handlePackageDownload(w http.ResponseWriter, r *http.Request) {
	const bearerPrefix = "Bearer "
	authorization := r.Header.Get("Authorization")
	if !strings.HasPrefix(authorization, bearerPrefix) {
		writeJSON(w, http.StatusUnauthorized, map[string]string{"error": "bearer token required"})
		return
	}
	sessionToken := strings.TrimSpace(strings.TrimPrefix(authorization, bearerPrefix))
	if sessionToken == "" {
		writeJSON(w, http.StatusUnauthorized, map[string]string{"error": "bearer token required"})
		return
	}
	slug := r.PathValue("slug")
	sessionHash := hashValue(sessionToken)

	var packageInfo packageRecord
	var authorizationID uint64
	var hostname string
	err := s.db.QueryRowContext(
		r.Context(),
		`SELECT p.id, p.slug, p.display_name, p.package_name,
		        p.package_version, p.file_name, p.sha256, p.enabled,
		        ds.authorization_id, ah.hostname
		   FROM download_sessions ds
		   JOIN authorizations a ON a.id = ds.authorization_id
		   JOIN authorization_hosts ah ON ah.id = ds.authorization_host_id
		   JOIN authorization_packages ap ON ap.authorization_id = a.id
		   JOIN packages p ON p.id = ap.package_id
		  WHERE ds.token_hash = ?
		    AND ds.revoked_at IS NULL
		    AND ds.expires_at > CURRENT_TIMESTAMP
		    AND a.revoked_at IS NULL
		    AND a.expires_at > CURRENT_TIMESTAMP
		    AND p.slug = ?
		    AND p.enabled = TRUE`,
		sessionHash[:], slug,
	).Scan(
		&packageInfo.ID,
		&packageInfo.Slug,
		&packageInfo.DisplayName,
		&packageInfo.PackageName,
		&packageInfo.PackageVersion,
		&packageInfo.FileName,
		&packageInfo.SHA256,
		&packageInfo.Enabled,
		&authorizationID,
		&hostname,
	)
	if errors.Is(err, sql.ErrNoRows) {
		writeJSON(w, http.StatusForbidden, map[string]string{"error": "package is not authorized"})
		return
	}
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "unable to authorize package"})
		return
	}

	registryURL := joinURL(
		s.cfg.GiteaURL,
		fmt.Sprintf(
			"/api/packages/%s/generic/%s/%s/%s",
			url.PathEscape(s.cfg.GiteaPackageOwner),
			url.PathEscape(packageInfo.PackageName),
			url.PathEscape(packageInfo.PackageVersion),
			url.PathEscape(packageInfo.FileName),
		),
	)
	upstreamRequest, err := http.NewRequestWithContext(r.Context(), http.MethodGet, registryURL, nil)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "unable to request package"})
		return
	}
	upstreamRequest.SetBasicAuth(s.cfg.GiteaPackageUser, s.cfg.GiteaPackageToken)
	upstreamResponse, err := s.packageClient.Do(upstreamRequest)
	if err != nil {
		_ = s.audit(r.Context(), "package_download_failed", "",
			&authorizationID, hostname, slug, s.clientIP(r), err.Error())
		writeJSON(w, http.StatusBadGateway, map[string]string{"error": "package registry is unavailable"})
		return
	}
	defer upstreamResponse.Body.Close()
	if upstreamResponse.StatusCode != http.StatusOK {
		_ = s.audit(r.Context(), "package_download_failed", "",
			&authorizationID, hostname, slug, s.clientIP(r), upstreamResponse.Status)
		writeJSON(w, http.StatusBadGateway, map[string]string{"error": "package registry rejected the request"})
		return
	}

	w.Header().Set("Content-Type", "application/octet-stream")
	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=%q", packageInfo.FileName))
	w.Header().Set("X-TAPM-SHA256", packageInfo.SHA256)
	w.Header().Set("Cache-Control", "no-store")
	w.WriteHeader(http.StatusOK)
	if _, err := io.Copy(w, upstreamResponse.Body); err != nil {
		_ = s.audit(r.Context(), "package_download_failed", "",
			&authorizationID, hostname, slug, s.clientIP(r), err.Error())
		return
	}
	_ = s.audit(r.Context(), "package_downloaded", "",
		&authorizationID, hostname, slug, s.clientIP(r), "")
}