package updates

import (
	"context"
	"os"
	"os/exec"
	"strings"
	"time"
)

// Ubuntu phases some -updates releases: a host is selected at random for each
// update, and until it is, apt lists the package as upgradable while an
// upgrade defers it. Reporting those as pending made a freshly patched host
// look unpatched, so they are flagged and left out of pending counts. The
// -security pocket is never phased.

// aptPhasedDeferred asks apt which upgrades it would defer, by simulating an
// upgrade. The simulation takes no lock and changes nothing. LC_ALL=C keeps
// the heading parsePhasedDeferred looks for in English. Any failure reports no
// phased packages: the update list is then exactly what it was before this
// existed, never shorter.
func aptPhasedDeferred() map[string]bool {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
	defer cancel()
	cmd := exec.CommandContext(ctx, "apt-get", "-s", "-o", "Debug::NoLocking=1", "upgrade")
	cmd.Env = append(os.Environ(), "LC_ALL=C", "DEBIAN_FRONTEND=noninteractive")
	out, err := cmd.Output()
	if err != nil {
		return nil
	}
	return parsePhasedDeferred(string(out))
}

// parsePhasedDeferred reads the package names apt lists under "The following
// upgrades have been deferred due to phasing:". The names follow on indented
// lines; the block ends at the first line that is not indented.
func parsePhasedDeferred(out string) map[string]bool {
	phased := map[string]bool{}
	in := false
	for _, line := range strings.Split(out, "\n") {
		if strings.Contains(line, "deferred due to phasing") {
			in = true
			continue
		}
		if !in {
			continue
		}
		if line == "" || (line[0] != ' ' && line[0] != '\t') {
			in = false
			continue
		}
		for _, name := range strings.Fields(line) {
			phased[name] = true
		}
	}
	return phased
}

// markPhased flags the updates apt would defer.
func markPhased(ups []PackageUpdate, phased map[string]bool) {
	for i := range ups {
		if phased[ups[i].Name] {
			ups[i].Phased = true
		}
	}
}

// CountInstallable is the number of updates an upgrade would actually install
// now: phased updates are pending but not yet installable.
func CountInstallable(ups []PackageUpdate) int {
	n := 0
	for _, u := range ups {
		if !u.Phased {
			n++
		}
	}
	return n
}