// Package engine implements the synchronization pipeline:
// read source -> normalize -> diff -> plan -> apply -> verify.
package engine

import (
	"context"
	"encoding/json"
	"fmt"
	"sort"
	"time"

	"pve-confsync/internal/adapter"
	"pve-confsync/internal/config"
	"pve-confsync/internal/model"
	"pve-confsync/internal/pve"
)

// Read loads and normalizes the objects of the given kinds from a cluster.
// The reference is read in ReadRunning mode (applied SDN configuration only),
// clients in ReadCurrent mode (what the next writes will modify).
func Read(ctx context.Context, c *pve.Client, kinds []model.Kind, mode adapter.ReadMode) (model.Snapshot, error) {
	snap := model.Snapshot{Cluster: c.Name(), ExportedAt: time.Now().UTC()}
	vs, err := c.CheckVersion(ctx)
	if err != nil {
		return snap, err
	}
	if len(vs) > 0 {
		snap.PVEVersion = vs[0].Version
	}
	want := map[model.Kind]bool{}
	for _, k := range kinds {
		want[k] = true
	}
	// subnets need the vnets, vnets need the zones: read the dependencies even
	// if their kind is not synchronized, but only keep the requested kinds.
	need := map[model.Kind]bool{}
	for k := range want {
		need[k] = true
	}
	if need[model.KindSubnet] {
		need[model.KindVNet] = true
	}
	if need[model.KindVNet] {
		need[model.KindZone] = true
	}
	if need[model.KindPassword] {
		need[model.KindUser] = true
	}
	var all []model.Object
	for _, a := range adapter.All() {
		if !need[a.Kind()] {
			continue
		}
		objs, warns, err := a.List(ctx, c, mode, all)
		if err != nil {
			return snap, fmt.Errorf("cluster %s: read %s: %w", c.Name(), a.Kind(), err)
		}
		snap.Warnings = append(snap.Warnings, warns...)
		all = append(all, objs...)
	}
	for _, o := range all {
		if want[o.Kind] {
			snap.Objects = append(snap.Objects, o)
		}
	}
	model.Sort(snap.Objects)
	return snap, nil
}

// Op is the action planned on one object.
type Op string

const (
	OpCreate Op = "create"
	OpUpdate Op = "update"
	OpDelete Op = "delete"
)

// Change is one planned action. Set holds the new values, Old the current ones.
type Change struct {
	Kind   model.Kind     `json:"kind"`
	ID     string         `json:"id"`
	Op     Op             `json:"op"`
	Set    map[string]any `json:"set,omitempty"`
	Unset  []string       `json:"unset,omitempty"`
	Old    map[string]any `json:"old,omitempty"`
	Target model.Object   `json:"-"`
}

// MarshalJSON hides the secret fields (password hashes): plans are shown in the
// UI and kept in the journal, the real values only live in memory until applied.
func (c Change) MarshalJSON() ([]byte, error) {
	type plain Change
	red := func(m map[string]any) map[string]any {
		if m == nil {
			return nil
		}
		out := make(map[string]any, len(m))
		for k, v := range m {
			if adapter.IsSensitive(c.Kind, k) {
				v = adapter.Redact(v)
			}
			out[k] = v
		}
		return out
	}
	p := plain(c)
	p.Set, p.Old = red(c.Set), red(c.Old)
	return json.Marshal(p)
}

// Plan is the list of changes for one client, in execution order.
type Plan struct {
	Client   string   `json:"client"`
	Changes  []Change `json:"changes"`
	Errors   []string `json:"errors,omitempty"`
	Warnings []string `json:"warnings,omitempty"`
}

// HasSDN tells whether the plan writes SDN objects (lock + reload needed).
func (p Plan) HasSDN() bool {
	for _, c := range p.Changes {
		if a, _ := adapter.ByKind(c.Kind); a != nil && a.SDN() {
			return true
		}
	}
	return false
}

// Empty tells whether there is nothing to do.
func (p Plan) Empty() bool { return len(p.Changes) == 0 }

// MakePlan computes the changes that bring the client in line with the reference.
func MakePlan(cfg *config.Config, cl *config.Client, ref, actual []model.Object) Plan {
	plan := Plan{Client: cl.Name}
	var deletes []Change
	for _, k := range cfg.Kinds {
		a, err := adapter.ByKind(k)
		if err != nil {
			plan.Errors = append(plan.Errors, err.Error())
			continue
		}
		cur := map[string]model.Object{}
		for _, o := range actual {
			if o.Kind == k {
				cur[o.ID] = o
			}
		}
		inRef := map[string]bool{}
		for _, r := range ref {
			if r.Kind != k || !cfg.Selected(k, r.ID) {
				continue
			}
			inRef[r.ID] = true
			mapping := model.Normalize(cl.Mapping[k][r.ID])
			a.Canonicalize(mapping)
			desired, managed := desiredFields(cfg, cl, a, r, mapping)
			o, exists := cur[r.ID]
			if !exists {
				if a.Singleton() {
					plan.Errors = append(plan.Errors, fmt.Sprintf("%s: not found on client", r.Key()))
					continue
				}
				for _, f := range a.Required(model.Object{Kind: k, ID: r.ID, Fields: desired}) {
					if _, ok := desired[f]; !ok {
						plan.Errors = append(plan.Errors,
							fmt.Sprintf("%s: field %q required for creation, add it to the mapping of client %s", r.Key(), f, cl.Name))
					}
				}
				plan.Changes = append(plan.Changes, Change{Kind: k, ID: r.ID, Op: OpCreate, Set: desired,
					Target: model.Object{Kind: k, ID: r.ID, Fields: desired}})
				continue
			}
			ch := Change{Kind: k, ID: r.ID, Op: OpUpdate, Set: map[string]any{}, Old: map[string]any{}, Target: o}
			for f, v := range desired {
				if !model.Equal(v, o.Fields[f]) {
					if a.Immutable(f) {
						plan.Errors = append(plan.Errors, fmt.Sprintf("%s: field %q differs (%s -> %s) and cannot be changed, re-creation needed",
							r.Key(), f, model.Format(o.Fields[f]), model.Format(v)))
						continue
					}
					ch.Set[f] = v
					if old, ok := o.Fields[f]; ok {
						ch.Old[f] = old
					}
				}
			}
			// fields only present on the client are managed too when their policy is "sync"
			for f := range o.Fields {
				if cfg.Policy(cl, a, f) == adapter.Sync {
					managed[f] = true
				}
			}
			for f := range managed {
				if _, want := desired[f]; want {
					continue
				}
				if old, has := o.Fields[f]; has {
					ch.Unset = append(ch.Unset, f)
					ch.Old[f] = old
				}
			}
			sort.Strings(ch.Unset)
			if len(ch.Set) > 0 || len(ch.Unset) > 0 {
				plan.Changes = append(plan.Changes, ch)
			}
		}
		if cfg.Prune && !a.Singleton() {
			for id, o := range cur {
				if !inRef[id] && cfg.Selected(k, id) {
					deletes = append(deletes, Change{Kind: k, ID: id, Op: OpDelete, Old: o.Fields, Target: o})
				}
			}
		}
	}
	checkParents(&plan, cl.Name, actual)
	// deletions last, dependents first (subnets, vnets, zones)
	sort.SliceStable(deletes, func(i, j int) bool {
		if deletes[i].Kind != deletes[j].Kind {
			return kindRank(deletes[i].Kind) > kindRank(deletes[j].Kind)
		}
		return deletes[i].ID < deletes[j].ID
	})
	plan.Changes = append(plan.Changes, deletes...)
	return plan
}

// checkParents blocks the objects whose parents (groups of an account, account
// of a password) are neither on the target nor created by the plan.
func checkParents(plan *Plan, client string, actual []model.Object) {
	have := map[string]bool{}
	for _, o := range actual {
		have[o.Key()] = true
	}
	for _, c := range plan.Changes {
		if c.Op == OpCreate {
			have[c.Key()] = true
		}
	}
	for _, c := range plan.Changes {
		if c.Op == OpDelete {
			continue
		}
		for _, p := range adapter.Parents(Desired(c)) {
			if !have[p] {
				plan.Errors = append(plan.Errors, fmt.Sprintf("%s: %s absent on target %s and not replicated", c.Key(), p, client))
			}
		}
	}
}

// Desired is the object as it will be after the change (fields of the target
// with the new values).
func Desired(c Change) model.Object {
	f := map[string]any{}
	for k, v := range c.Target.Fields {
		f[k] = v
	}
	for _, k := range c.Unset {
		delete(f, k)
	}
	for k, v := range c.Set {
		f[k] = v
	}
	return model.Object{Kind: c.Kind, ID: c.ID, Fields: f}
}

func kindRank(k model.Kind) int {
	for i, x := range model.Kinds {
		if x == k {
			return i
		}
	}
	return len(model.Kinds)
}

// desiredFields returns the field values the client must have, and the set of
// fields the tool manages on this object (absent from desired => to delete).
func desiredFields(cfg *config.Config, cl *config.Client, a adapter.Adapter, r model.Object, mapping map[string]any) (map[string]any, map[string]bool) {
	desired := map[string]any{}
	managed := map[string]bool{}
	// a field is managed when its policy is "sync", whatever its presence
	for f, v := range r.Fields {
		if cfg.Policy(cl, a, f) == adapter.Sync {
			desired[f] = v
		}
	}
	for f := range cfg.Policies[a.Kind()] {
		if cfg.Policy(cl, a, f) == adapter.Sync {
			managed[f] = true
		}
	}
	for f := range cl.Policies[a.Kind()] {
		if cfg.Policy(cl, a, f) == adapter.Sync {
			managed[f] = true
		}
	}
	for f := range r.Fields {
		if cfg.Policy(cl, a, f) == adapter.Sync {
			managed[f] = true
		}
	}
	// the client mapping wins over the reference (except forbidden fields)
	for f, v := range mapping {
		if a.Forbidden(f) || cfg.Policy(cl, a, f) == adapter.Ignore {
			continue
		}
		desired[f] = v
		managed[f] = true
	}
	return desired, managed
}