package catalogue

import (
	"encoding/json"
	"fmt"
	"reflect"
	"sort"
	"strings"
)

// What a move does to a module's containers (novox/hq ADR 0245).
//
// A container whose declaration changes is recreated, whatever changed in it: an image, an environment
// variable, a health check adopted. A module whose containers are recreated in one send is down while
// they start again — on 2026-10-07 a catalogue change that only adopted the images' own health checks
// recreated nine of mail's containers at once, and the operator's phone could not reach the mail. So a
// send says, per module, how many of its containers it recreates and whether any image changed, before
// it is sent and in the plan that sent it.

// Recreation is what moving a module from one build's manifest to another's does to its containers.
type Recreation struct {
	// Containers is how many containers the new build declares.
	Containers int
	// Recreated are the ids of the containers whose declaration differs — changed, added or gone —
	// sorted.
	Recreated []string
	// Images are the ids among them whose image changed (or that are added or gone).
	Images []string
}

// Recreates compares two builds of a module, container by container, by resource id.
func Recreates(from, to Manifest) Recreation {
	before := containersByID(from)
	after := containersByID(to)
	var r Recreation
	r.Containers = len(after)
	for id, now := range after {
		was, held := before[id]
		switch {
		case !held:
			r.Recreated = append(r.Recreated, id)
			r.Images = append(r.Images, id)
		case !sameDeclaration(was, now):
			r.Recreated = append(r.Recreated, id)
			if !sameDeclaration(was["image"], now["image"]) {
				r.Images = append(r.Images, id)
			}
		}
	}
	for id := range before {
		if _, kept := after[id]; !kept {
			r.Recreated = append(r.Recreated, id)
			r.Images = append(r.Images, id)
		}
	}
	sort.Strings(r.Recreated)
	sort.Strings(r.Images)
	return r
}

// SpecOnly is whether the move recreates containers without any new image: a change to how they are
// declared only — a health check adopted, a variable — which a person may well not expect to interrupt.
func (r Recreation) SpecOnly() bool { return len(r.Recreated) > 0 && len(r.Images) == 0 }

// Say is the recreation in the mesh's words, for a module: empty when the move recreates nothing.
func (r Recreation) Say(module string) string {
	if len(r.Recreated) == 0 {
		return ""
	}
	what := "with a new image"
	switch {
	case r.SpecOnly():
		what = "no new image, only their declaration"
	case len(r.Images) < len(r.Recreated):
		what = fmt.Sprintf("%d with a new image", len(r.Images))
	}
	whole := ""
	if len(r.Recreated) > 1 && len(r.Recreated) >= r.Containers {
		whole = ", every one at once: its service is interrupted until they are up again"
	} else if len(r.Recreated) > 1 {
		whole = ", at once: what they serve is interrupted until they are up again"
	}
	return fmt.Sprintf("recreates %d of %s's %d container(s) (%s: %s)%s", len(r.Recreated), module, r.Containers,
		what, strings.Join(r.Recreated, ", "), whole)
}

func containersByID(m Manifest) map[string]map[string]any {
	out := map[string]map[string]any{}
	for _, r := range m.Resources {
		if t, _ := r["type"].(string); t != "container" {
			continue
		}
		id, _ := r["id"].(string)
		out[id] = r
	}
	return out
}

// sameDeclaration compares two declarations as JSON, so a number read as an int and one read as a
// float are one value.
func sameDeclaration(a, b any) bool {
	ra, errA := json.Marshal(a)
	rb, errB := json.Marshal(b)
	if errA != nil || errB != nil {
		return reflect.DeepEqual(a, b)
	}
	var na, nb any
	_ = json.Unmarshal(ra, &na)
	_ = json.Unmarshal(rb, &nb)
	return reflect.DeepEqual(na, nb)
}

// What a move under a module's own `record` may do without a person (novox/hq ADR 0377).
//
// A module records because its manifest says so or because it keeps irreplaceable data: mail, whose containers
// recreated together interrupt everyone's mail, and the database server, whose restart drops every consumer. That
// hold also held the moves that interrupt nothing — on 2026-10-15 the database server moved with only its tools
// bundle changed, its walk said it "recreates none of its containers", and the machine stayed behind until a
// person pushed. So such a move rolls out like any other, and only a move that recreates a container or touches
// data still waits.

// Holds is why a move from one build's manifest to another's still waits for a person under a module's own
// `record` (ADR 0377 §3), empty when it recreates none of its containers and moves none of its data: no container
// changed, added or gone; no file or directory changed, added or gone that a container mounts, or that holds or
// lies within a path of the module's declared data; no change to its `data` declaration, nor to what it provides,
// requires or contributes; and, for a module that declares data of its own, no change to a long-running process.
// Its tools bundles, a file nothing mounts that holds none of its data, and manifest fields that recreate
// nothing — its tool list — may differ.
func Holds(from, to Manifest) string {
	module := to.Module
	if module == "" {
		module = from.Module
	}
	if said := Recreates(from, to).Say(module); said != "" {
		return said
	}
	if !sameDeclaration(from.Data, to.Data) {
		return "it changes " + module + "'s data declaration"
	}
	for _, f := range []struct {
		what   string
		was, s any
	}{
		{"what it provides", from.Provides, to.Provides},
		{"what it requires", from.Requires, to.Requires},
		{"which of its requirements are optional", from.OptionalRequires, to.OptionalRequires},
		{"what it contributes to a provider", from.Contributes, to.Contributes},
		{"what it contributes to a provider", from.ContributesMany, to.ContributesMany},
		// A setting is filled into the files the module writes: a changed default changes what a container may
		// mount without the file's own declaration changing.
		{"its settings, which the files it writes are filled from", from.Settings, to.Settings},
	} {
		if !sameDeclaration(emptyAsNil(f.was), emptyAsNil(f.s)) {
			return "it changes " + f.what
		}
	}
	mounted := append(mountSources(from), mountSources(to)...)
	data := append(dataPaths(from), dataPaths(to)...)
	keepsData := (from.Data != nil && len(from.Data.Own) > 0) || (to.Data != nil && len(to.Data.Own) > 0)
	before, after := resourcesByID(from), resourcesByID(to)
	var changed []string
	for id, r := range after {
		if was, held := before[id]; !held || !sameDeclaration(was, r) {
			changed = append(changed, id)
		}
	}
	for id := range before {
		if _, kept := after[id]; !kept {
			changed = append(changed, id)
		}
	}
	sort.Strings(changed)
	dirs := absoluteDirectories(from, to)
	for _, key := range changed {
		for _, r := range []map[string]any{before[key], after[key]} {
			if r == nil {
				continue
			}
			kind, id := fmt.Sprint(r["type"]), fmt.Sprint(r["id"])
			switch kind {
			case "file", "directory":
				for _, p := range pathsOf(r, dirs) {
					for _, m := range mounted {
						if pathsMeet(p, expandDir(m.source, dirs)) {
							return fmt.Sprintf("it changes the %s %s, which its container %s mounts", kind, id, m.container)
						}
					}
					for _, d := range data {
						if pathsMeet(p, expandDir(d.path, dirs)) {
							return fmt.Sprintf("it changes the %s %s, which holds or lies within its data %s", kind, id, d.id)
						}
					}
				}
			case "process", "service":
				if keepsData {
					return fmt.Sprintf("it changes its long-running %s %s, and it keeps data of its own", kind, id)
				}
			}
		}
	}
	return ""
}

type mountSource struct{ container, source string }

// mountSources is every path a container of the module reads from its machine: its volumes' sources and its
// environment files.
func mountSources(m Manifest) []mountSource {
	var out []mountSource
	for _, r := range m.Resources {
		if fmt.Sprint(r["type"]) != "container" {
			continue
		}
		id := fmt.Sprint(r["id"])
		vols, _ := r["volumes"].([]any)
		for _, v := range vols {
			s, _ := v.(string)
			if mount := volumeMount.FindStringSubmatch(s); mount != nil {
				out = append(out, mountSource{id, mount[1]})
			}
		}
		switch files := r["env-file"].(type) {
		case string:
			out = append(out, mountSource{id, files})
		case []any:
			for _, f := range files {
				if s, ok := f.(string); ok {
					out = append(out, mountSource{id, s})
				}
			}
		}
	}
	return out
}

type dataPath struct{ id, path string }

func dataPaths(m Manifest) []dataPath {
	if m.Data == nil {
		return nil
	}
	var out []dataPath
	for _, it := range m.Data.Own {
		out = append(out, dataPath{it.ID, it.Path})
	}
	return out
}

func resourcesByID(m Manifest) map[string]map[string]any {
	out := map[string]map[string]any{}
	for _, r := range m.Resources {
		out[fmt.Sprint(r["type"])+":"+fmt.Sprint(r["id"])] = r
	}
	return out
}

// absoluteDirectories is, per directory id, the absolute path a directory of either build states.
func absoluteDirectories(ms ...Manifest) map[string]string {
	out := map[string]string{}
	for _, m := range ms {
		for _, r := range m.Resources {
			if fmt.Sprint(r["type"]) != "directory" {
				continue
			}
			if p, ok := r["path"].(string); ok && strings.HasPrefix(p, "/") {
				out[fmt.Sprint(r["id"])] = strings.TrimRight(p, "/")
			}
		}
	}
	return out
}

// pathsOf is every way a file or directory resource is named: its path, and a directory's `${dir:<id>}`.
func pathsOf(r map[string]any, dirs map[string]string) []string {
	var out []string
	if p, ok := r["path"].(string); ok && p != "" {
		out = append(out, expandDir(p, dirs))
	}
	if fmt.Sprint(r["type"]) == "directory" {
		out = append(out, expandDir("${dir:"+fmt.Sprint(r["id"])+"}", dirs))
	}
	return out
}

// expandDir writes a leading `${dir:<id>}` as the directory's absolute path when one is stated, so a path named
// either way is one path.
func expandDir(p string, dirs map[string]string) string {
	p = strings.TrimRight(p, "/")
	if ref := dirPlain.FindStringSubmatch(p); ref != nil {
		if abs, ok := dirs[ref[1]]; ok {
			return abs
		}
		return p
	}
	if strings.HasPrefix(p, "${dir:") {
		end := strings.Index(p, "}")
		if abs, ok := dirs[p[len("${dir:"):end]]; ok {
			return abs + p[end+1:]
		}
	}
	return p
}

// pathsMeet is whether one path is the other or lies within it.
func pathsMeet(a, b string) bool {
	if a == "" || b == "" {
		return false
	}
	return a == b || strings.HasPrefix(a, b+"/") || strings.HasPrefix(b, a+"/")
}

// emptyAsNil reads an empty list or map as nothing, so a field written empty is no change from one left out.
func emptyAsNil(v any) any {
	rv := reflect.ValueOf(v)
	switch rv.Kind() {
	case reflect.Slice, reflect.Map:
		if rv.Len() == 0 {
			return nil
		}
	case reflect.Ptr:
		if rv.IsNil() {
			return nil
		}
	}
	return v
}