package apply

import (
	"context"
	"fmt"
	"strings"

	"github.com/novox/mesh-host/internal/declaration"
	"github.com/novox/mesh-host/internal/store"
	"github.com/novox/mesh-host/internal/system"
)

// An account's groups, from any module (novox/hq ADR 0252, issue 247).
//
// **A module that needs the account in a group declares the account with that group, and nothing else
// of it.** The shell's module sets the account's shell; the lighting daemon's module puts the same
// account in `openrazer`; the container runtime's in `docker`. A shell is one value and stays one
// module's (the controller refuses two); a group is added, so several modules' groups never contradict.
//
// **The mesh takes back only what it gave.** A group the account was in before is the machine's or the
// operator's, and stays when every resource that named it goes. A group the mesh put the account in is
// recorded on the resource that put it there, and given back when that resource stops asking for it —
// unless another declared resource still asks for the same group, which keeps it.
//
// **A group takes effect at the next login.** The machine's group database changes at once; every
// process already running, the account's own service manager and everything it started included, keeps
// the groups it started with. So the outcome says a new login is needed, and the node-engine's account
// judge (internal/accounts) says so on every look until the account's running manager has the group.

// Wanted is every group a declaration asks an account to be in, and which resources ask: account →
// group → resource ids.
type Wanted map[string]map[string][]string

// groupsWanted reads every user resource's groups from a declaration.
func groupsWanted(resources []declaration.Resource) Wanted {
	w := Wanted{}
	for _, r := range resources {
		u, ok := r.(*declaration.User)
		if !ok || u.Name == "" {
			continue
		}
		for _, g := range u.Groups {
			if w[u.Name] == nil {
				w[u.Name] = map[string][]string{}
			}
			w[u.Name][g] = append(w[u.Name][g], u.ID)
		}
	}
	return w
}

// othersAsk is every resource other than one that asks for an account to be in a group.
func (w Wanted) othersAsk(account, group, except string) []string {
	var others []string
	for _, id := range w[account][group] {
		if id != except {
			others = append(others, id)
		}
	}
	return others
}

// applyGroups makes the account be in every group the resource declares, and takes it out of every group
// this resource put it in and no longer asks for. What the mesh put the account in is recorded on out.
func applyGroups(ctx context.Context, sys system.System, r *declaration.User, run Runner,
	previous store.Applied, wanted Wanted, out *Outcome) error {
	// What this resource put the account in before, for this account only: a declaration that renamed its
	// user says nothing about the new one's groups.
	var added []string
	if previous.Target == r.Name {
		added = append(added, previous.Groups...)
	}
	if len(r.Groups) == 0 && len(added) == 0 {
		return nil
	}
	in, err := system.GroupsOf(ctx, system.Runner(run), r.Name)
	if err != nil {
		return err
	}
	already := setOf(in)
	declared := setOf(r.Groups)

	var put []string
	for _, want := range r.Groups {
		if already[want] {
			continue
		}
		exists, err := system.GroupExists(ctx, system.Runner(run), want)
		if err != nil {
			return err
		}
		if !exists {
			return fmt.Errorf("%q was not put in the group %q: this machine has no such group yet. The package "+
				"that makes it is not installed, or is declared after the account", r.Name, want)
		}
		if err := sys.AddUserToGroup(ctx, system.Runner(run), r.Name, want); err != nil {
			return err
		}
		already[want] = true
		put = append(put, want)
		if !contains(added, want) {
			added = append(added, want)
		}
	}

	// What this resource put the account in and no longer asks for.
	var kept, said []string
	for _, g := range added {
		switch {
		case declared[g]:
			kept = append(kept, g)
		case !already[g]:
			// Taken out since, by a person: nothing to give back.
		case len(wanted.othersAsk(r.Name, g, r.ID)) > 0:
			said = append(said, fmt.Sprintf("left in %s, which %s still asks for", g,
				strings.Join(wanted.othersAsk(r.Name, g, r.ID), ", ")))
		default:
			gone, why := leaveGroup(ctx, sys, r.Name, g, run)
			if !gone {
				kept = append(kept, g)
			}
			said = append(said, why)
		}
	}
	out.groups = kept
	if len(put) > 0 {
		said = append([]string{fmt.Sprintf("put in %s; a session that began before has %s only after a new "+
			"login", strings.Join(put, ", "), them(len(put)))}, said...)
	}
	if len(put) > 0 || len(said) > 0 {
		if out.Action == "unchanged" {
			out.Action = "updated"
		}
		out.Detail = joinDetail(out.Detail, strings.Join(said, "; "))
	}
	return nil
}

// giveGroupsBack is removeUser's groups: every group the mesh put the account in, taken back unless
// another declared resource still asks for it. Never fatal, for the shell's reason: a removal that failed
// would stay recorded and fail the same way on every apply after. Empty when there was nothing to say.
func giveGroupsBack(ctx context.Context, sys system.System, a store.Applied, run Runner, wanted Wanted) (bool, string) {
	if len(a.Groups) == 0 {
		return false, ""
	}
	in, err := system.GroupsOf(ctx, system.Runner(run), a.Target)
	if err != nil {
		return false, fmt.Sprintf("the groups the mesh put it in (%s) were not given back: %v",
			strings.Join(a.Groups, ", "), err)
	}
	already := setOf(in)
	gave := false
	var said []string
	for _, g := range a.Groups {
		if !already[g] {
			continue
		}
		if others := wanted.othersAsk(a.Target, g, a.ID); len(others) > 0 {
			said = append(said, fmt.Sprintf("left in %s, which %s still asks for", g, strings.Join(others, ", ")))
			continue
		}
		gone, why := leaveGroup(ctx, sys, a.Target, g, run)
		gave = gave || gone
		said = append(said, why)
	}
	return gave, strings.Join(said, "; ")
}

// leaveGroup takes an account out of one group the mesh put it in, read back from the machine, and says
// what came of it.
func leaveGroup(ctx context.Context, sys system.System, account, group string, run Runner) (bool, string) {
	l, ok := sys.(system.GroupLeaver)
	if !ok {
		return false, fmt.Sprintf("left in %s: this machine's system cannot take an account out of one group", group)
	}
	if err := l.RemoveUserFromGroup(ctx, system.Runner(run), account, group); err != nil {
		return false, fmt.Sprintf("left in %s: %v", group, err)
	}
	in, err := system.GroupsOf(ctx, system.Runner(run), account)
	if err != nil {
		return false, fmt.Sprintf("taken out of %s, and the group database could not be read back: %v", group, err)
	}
	if setOf(in)[group] {
		return false, fmt.Sprintf("taken out of %s, and the group database still lists it there", group)
	}
	return true, fmt.Sprintf("taken out of %s, which the mesh had put it in", group)
}

func setOf(items []string) map[string]bool {
	s := map[string]bool{}
	for _, i := range items {
		s[i] = true
	}
	return s
}

func contains(items []string, want string) bool {
	for _, i := range items {
		if i == want {
			return true
		}
	}
	return false
}

func them(n int) string {
	if n == 1 {
		return "it"
	}
	return "them"
}

func joinDetail(a, b string) string {
	switch {
	case a == "":
		return b
	case b == "":
		return a
	}
	return a + "; " + b
}