package delivery

import (
	"bytes"
	"encoding/json"
	"strconv"
	"strings"

	"git.novox.be/novox/mesh-sdk/go/catalogue"
)

// Comparison is what CompareComposed finds, module by module: the same, differing, added by what was composed (not run
// now) and removed by it (run now, not composed). Each list is sorted by module.
type Comparison struct {
	Same    []string
	Differs []ModuleDiffers
	Added   []ModuleAdded
	Removed []string
}

// CompareComposed compares the compositions a node composed (by key, as compose.Compositions answers them) with the ones
// it runs, as its agent would (ADR 0559 §4: a node's answer to a placement candidate). A module is the same when its
// composition's digest is the one it runs (ComposedDigestOf, the signature left out), so the agent would apply nothing
// of it; it differs when the digests differ (both named); it is added when composed and not run, removed when run and
// not composed. The node's own composition is named HaveNodeWord. The bus's user list (catalogue.BusUsersID) is left out
// on both sides: the bus node follows it alone and never applies it from a composition it made (ADR 0547 §2, §8). A
// difference names the first resource, by its id, whose content differs or that one side alone holds; when every
// resource is equal it says what else differs (their order, the files filled, the data, the node's own parts, a file
// carried by digest).
func CompareComposed(composed map[string]Composed, running []Composed) Comparison {
	name := func(c Composed) string {
		if c.Module == "" {
			return HaveNodeWord
		}
		return c.Module
	}
	ours := map[string]Composed{}
	for _, c := range composed {
		ours[name(c)] = c
	}
	theirs := map[string]Composed{}
	for _, c := range running {
		theirs[name(c)] = c
	}
	modules := map[string]bool{}
	for m := range ours {
		modules[m] = true
	}
	for m := range theirs {
		modules[m] = true
	}
	var out Comparison
	for _, m := range sortedKeys(modules) {
		a, composedHere := ours[m]
		b, runs := theirs[m]
		switch {
		case !runs:
			dig, _ := ComposedDigestOf(withoutBusUsers(a))
			out.Added = append(out.Added, ModuleAdded{Module: m, Composed: dig})
		case !composedHere:
			out.Removed = append(out.Removed, m)
		default:
			if d, ok := compareOne(m, a, b); ok {
				out.Same = append(out.Same, m)
			} else {
				out.Differs = append(out.Differs, d)
			}
		}
	}
	return out
}

// compareOne is one module's comparison: true when the digests agree, else what differs first.
func compareOne(module string, composed, running Composed) (ModuleDiffers, bool) {
	composed, running = withoutBusUsers(composed), withoutBusUsers(running)
	dc, errC := ComposedDigestOf(composed)
	dr, errR := ComposedDigestOf(running)
	if errC != nil {
		return ModuleDiffers{Module: module, Running: dr, Why: "the composition has no digest: " + errC.Error()}, false
	}
	if errR == nil && dc == dr {
		return ModuleDiffers{}, true
	}
	differs := func(resource, why string) (ModuleDiffers, bool) {
		return ModuleDiffers{Module: module, Composed: dc, Running: dr, Resource: resource, Why: why}, false
	}
	// Words for the difference: resource by resource, each side with its large files by digest, so a file carried whole
	// and the same file carried by digest read as one.
	a, _, errA := composed.ByDigest()
	b, _, errB := running.ByDigest()
	if errA != nil || errB != nil {
		return differs("", "the compositions differ and cannot be read resource by resource")
	}
	ra, rb := resourcesByID(a.Resources), resourcesByID(b.Resources)
	ids := map[string]bool{}
	for id := range ra {
		ids[id] = true
	}
	for id := range rb {
		ids[id] = true
	}
	for _, id := range sortedKeys(ids) {
		x, inA := ra[id]
		y, inB := rb[id]
		switch {
		case !inB:
			return differs(id, "composed, and not in what runs")
		case !inA:
			return differs(id, "in what runs, and not composed")
		case !bytes.Equal(x, y):
			return differs(id, "the resource differs")
		}
	}
	switch {
	case !jsonEqual(a.Filled, b.Filled):
		return differs("", "the files the provisioner fills differ")
	case a.Data != b.Data:
		return differs("", "whether it declares data differs")
	case !jsonEqual(a.Own, b.Own):
		return differs("", "the node's own parts differ")
	case a.FP != b.FP:
		return differs("", "the fingerprint differs")
	}
	if dA, err := ComposedDigestOf(a); err == nil {
		if dB, err := ComposedDigestOf(b); err == nil && dA == dB {
			return differs("", "the same content, a large file carried whole on one side and by digest on the other")
		}
	}
	return differs("", "the same resources in another order")
}

// withoutBusUsers is c without the bus's user list resource (its id `bus-users`, or `<module>.bus-users`).
func withoutBusUsers(c Composed) Composed {
	out := c
	out.Resources = nil
	for _, raw := range c.Resources {
		var head struct {
			ID string `json:"id"`
		}
		if json.Unmarshal(raw, &head) == nil && (head.ID == catalogue.BusUsersID() || strings.HasSuffix(head.ID, "."+catalogue.BusUsersID())) {
			continue
		}
		out.Resources = append(out.Resources, raw)
	}
	return out
}

// resourcesByID is each resource canonical, by its id (a resource without one by its place).
func resourcesByID(resources []json.RawMessage) map[string][]byte {
	out := make(map[string][]byte, len(resources))
	for i, raw := range resources {
		var head struct {
			ID string `json:"id"`
		}
		_ = json.Unmarshal(raw, &head)
		id := head.ID
		if id == "" {
			id = "#" + strconv.Itoa(i)
		}
		canon, err := canonicalJSON(raw)
		if err != nil {
			canon = raw
		}
		out[id] = canon
	}
	return out
}