package util

import (
	"errors"
	"fmt"
	"os"
	"strconv"
	"syscall"

	logging "github.com/ipfs/go-log"
)

var log = logging.Logger("ulimit")

var (
	supportsFDManagement = false

	// getlimit returns the soft and hard limits of file descriptors counts
	getLimit func() (uint64, uint64, error)
	// set limit sets the soft and hard limits of file descriptors counts
	setLimit func(uint64, uint64) error
)

// maxFds is the maximum number of file descriptors that go-ipfs
// can use. The default value is 2048. This can be overwritten by the
// IPFS_FD_MAX env variable
var maxFds = uint64(2048)

// setMaxFds sets the maxFds value from IPFS_FD_MAX
// env variable if it's present on the system
func setMaxFds() {
	// check if the IPFS_FD_MAX is set up and if it does
	// not have a valid fds number notify the user
	if val := os.Getenv("IPFS_FD_MAX"); val != "" {

		fds, err := strconv.ParseUint(val, 10, 64)
		if err != nil {
			log.Errorf("bad value for IPFS_FD_MAX: %s", err)
			return
		}

		maxFds = fds
	}
}

// ManageFdLimit raise the current max file descriptor count
// of the process based on the IPFS_FD_MAX value
func ManageFdLimit() (changed bool, newLimit uint64, err error) {
	if !supportsFDManagement {
		return false, 0, nil
	}

	setMaxFds()
	soft, hard, err := getLimit()
	if err != nil {
		return false, 0, err
	}

	if maxFds <= soft {
		return false, 0, nil
	}

	// the soft limit is the value that the kernel enforces for the
	// corresponding resource
	// the hard limit acts as a ceiling for the soft limit
	// an unprivileged process may only set it's soft limit to a
	// alue in the range from 0 up to the hard limit
	if err = setLimit(maxFds, maxFds); err != nil {
		if err != syscall.EPERM {
			return false, 0, fmt.Errorf("error setting: ulimit: %s", err)
		}

		// the process does not have permission so we should only
		// set the soft value
		if maxFds > hard {
			return false, 0, errors.New(
				"cannot set rlimit, IPFS_FD_MAX is larger than the hard limit",
			)
		}

		if err = setLimit(maxFds, hard); err != nil {
			return false, 0, fmt.Errorf("error setting ulimit wihout hard limit: %s", err)
		}
	}

	return true, maxFds, nil
}