package compose

import (
	"errors"
	"fmt"
	"slices"
	"sort"
	"strconv"
	"strings"

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

// The private network: who is on it, where, and what they are called. Ported from mesh-controller
// cmd/mesh-controller/network.go at 6c2a8d62.

// DefaultOverlayCIDR is the range the mesh allocates from when nothing says another.
const DefaultOverlayCIDR = "10.42.0.0/16"

// composer is one composition over an Input: it reads Input, changes nothing in it, and keeps what the controller
// said on its standard error as lines to return.
type composer struct {
	in   Input
	said []string
	seen map[string]bool
}

func newComposer(in Input) *composer { return &composer{in: in, seen: map[string]bool{}} }

// say keeps a line the controller would have written to its log, once.
func (c *composer) say(format string, args ...any) {
	line := fmt.Sprintf(format, args...)
	if c.seen[line] {
		return
	}
	c.seen[line] = true
	c.said = append(c.said, line)
}

// suffix is what the mesh's internal names end in: the Input's, and overlay.DefaultSuffix when it gives none. The package never calls
// overlay.Suffix or overlay.InternalName, which read the environment, so the assigner and the controller compose the same names
// from the same Input.
func (c *composer) suffix() string {
	if v := strings.TrimPrefix(strings.TrimSpace(c.in.InternalSuffix), "."); v != "" {
		return v
	}
	return overlay.DefaultSuffix
}

// internalName is a node's name inside the mesh.
func (c *composer) internalName(node string) string { return node + "." + c.suffix() }

// saidBeside is the lines already said and then every line the composer kept, once each, in the order they were found.
func (c *composer) saidBeside(lines []string) []string {
	for _, l := range c.said {
		if !slices.Contains(lines, l) {
			lines = append(lines, l)
		}
	}
	return lines
}

// overlayRange is the range the mesh allocates node addresses from: the adopted tunnel's first (novox/hq ADR 0105),
// then the range genesis was told, then the default.
func (c *composer) overlayRange() string {
	if a := c.in.Adopted; a != nil && a.Adopted {
		return a.Tunnel.Range
	}
	if v := strings.TrimSpace(c.in.OverlayCIDR); v != "" {
		return v
	}
	return DefaultOverlayCIDR
}

// network builds the private network over the machines that resolved the module for it. A machine is on it because it
// was given the module, or because it is joining with a key and an address (novox/hq ADR 0169).
func (c *composer) network(on map[string]bool, refused map[string]string) (*overlay.Generator, error) {
	tunnels := c.in.Tunnels
	carried := c.in.CarriedPeers
	isJoining := map[string]bool{}
	for _, name := range c.in.Joining {
		isJoining[name] = true
	}
	var nodes []overlay.Node
	for _, node := range c.in.sorted() {
		p := node.Place
		if !on[node.Name] && !(isJoining[node.Name] && p.Key != "" && p.Address != "") {
			continue
		}
		n := overlay.Node{
			Name: node.Name, Key: p.Key, Endpoint: p.Endpoint,
			Site: p.Site, Hub: p.Hub, Address: p.Address,
		}
		if t, takes := tunnels[node.Name]; takes && t.NodeAdopted {
			// Only an adopted node is told to take the found unit over. A hub whose placement disagrees with the tunnel is
			// refused, not composed.
			if wrong := disagrees(p, t.Tunnel); wrong != "" {
				return nil, fmt.Errorf("%s takes over the tunnel on %s and its placement disagrees with it: %s. "+
					"Re-place it — `overlay place %s --hub --endpoint <host>:%d …` — and push again; "+
					"nothing was composed", node.Name, t.Interface, wrong, node.Name, t.Port)
			}
			n.TakesOver = &overlay.TakeOver{Interface: t.Interface, Unit: t.Unit, Config: t.Config, Port: t.Port, MTU: t.MTU}
		}
		if p.Hub {
			for _, cp := range carried {
				n.Carried = append(n.Carried, overlay.Carried{Key: cp.PublicKey, Address: cp.Address})
			}
		}
		nodes = append(nodes, n)
	}
	if len(nodes) == 0 {
		// Nobody was given it: an empty network is a legitimate mesh, not a broken one.
		return overlay.Empty(), nil
	}
	g, err := overlay.From(nodes, c.overlayRange(), "")
	if err != nil && len(refused) > 0 {
		// The network is missing something, and some machines could not be resolved at all: almost always the same fact.
		var who []string
		for name, why := range refused {
			who = append(who, fmt.Sprintf("  %s: %s", name, why))
		}
		sort.Strings(who)
		return nil, fmt.Errorf("%w\n\nand %d node(s) could not be resolved at all, which is "+
			"probably why:\n%s", err, len(refused), strings.Join(who, "\n"))
	}
	return g, err
}

// Graph is the whole mesh's network, for showing it: the nodes on it and each one's peers.
func Graph(in Input) ([]overlay.Node, overlay.Graph, error) {
	c := newComposer(in)
	on, refused, err := c.whoResolves(overlay.Requirement)
	if err != nil {
		return nil, nil, err
	}
	g, err := c.network(on, refused)
	if err != nil {
		return nil, nil, err
	}
	return g.Nodes(), g.Graph(), nil
}

// whoResolves is the machines whose resolution answers a requirement, and why the others did not: by what a module
// provides, not by its name, resolved rather than read from the assignments.
func (c *composer) whoResolves(requirement string) (map[string]bool, map[string]string, error) {
	on := map[string]bool{}
	// Why a node could not be resolved, kept rather than raised: one broken node must not stop the rest being described.
	refused := map[string]string{}
	for _, n := range c.in.sorted() {
		resolved, err := c.planFor(n.Name)
		switch {
		case unresolvable(err):
			refused[n.Name] = err.Error()
			continue
		case err != nil:
			// Not a node that does not resolve: a question that went unanswered.
			return nil, nil, fmt.Errorf("whether %s answers %q cannot be read: %w", n.Name, requirement, err)
		}
		for _, m := range resolved.Plan.Modules {
			for _, offered := range m.Offers() {
				if offered == requirement {
					on[n.Name] = true
				}
			}
		}
	}
	return on, refused, nil
}

// Generators is what every node's declaration is composed with, over the whole mesh: the private network's generator
// (one generator now; the names and a resolver's zone file are facts a module asks for in its manifest).
func Generators(in Input) (map[string]catalogue.Generator, error) {
	c := newComposer(in)
	return c.generators()
}

func (c *composer) generators() (map[string]catalogue.Generator, error) {
	on, refused, err := c.whoResolves(overlay.Addressing)
	if err != nil {
		return nil, err
	}
	net, err := c.network(on, refused)
	if err != nil {
		return nil, err
	}
	return map[string]catalogue.Generator{overlay.Name: net}, nil
}

// disagrees says how a node's placement differs from the tunnel it takes over — its address not the tunnel's, its
// endpoint not on the tunnel's port — or nothing when both agree.
func disagrees(p Place, t Tunnel) string {
	var wrong []string
	want := t.Address
	if i := strings.Index(want, "/"); i >= 0 {
		want = want[:i]
	}
	if p.Address != want {
		wrong = append(wrong, fmt.Sprintf("its address is %s and the tunnel's is %s", orNothing(p.Address), want))
	}
	if p.Reachable() && portOfEndpoint(p.Endpoint) != strconv.Itoa(t.Port) {
		wrong = append(wrong, fmt.Sprintf("its endpoint %s is not on the tunnel's port %d", p.Endpoint, t.Port))
	}
	return strings.Join(wrong, "; ")
}

func orNothing(s string) string {
	if s == "" {
		return "unset"
	}
	return s
}

// portOfEndpoint is the port in host:port, or empty.
func portOfEndpoint(endpoint string) string {
	if i := strings.LastIndex(endpoint, ":"); i >= 0 {
		return endpoint[i+1:]
	}
	return ""
}

// whereEveryoneIs is each machine's name on the private network, for the ones on it. Resolved without consulting the
// rest of the mesh (it is called from that path), and refused without the catalogue.
func (c *composer) whereEveryoneIs() (map[string]string, error) {
	if c.in.Catalogue == nil {
		return nil, errors.New("asked where everyone is without the catalogue, which cannot be answered")
	}
	out := map[string]string{}
	for _, p := range c.onTheNetwork() {
		out[p.Name] = c.internalName(p.Name)
	}
	return out, nil
}

// onTheNetwork is every placed machine that resolves the private network: has an address AND runs what puts it there
// (novox/hq issue 079). A machine that does not resolve is not counted, and said.
func (c *composer) onTheNetwork() []Node {
	var out []Node
	for _, n := range c.in.sorted() {
		if n.Place.Address == "" {
			continue
		}
		if len(n.Assigned) == 0 {
			continue
		}
		got, err := catalogue.Resolve(c.in.Catalogue, n.Assigned,
			catalogue.Node{Name: n.Name, Site: n.Place.Site, Capabilities: n.Capabilities},
			catalogue.World{Unchecked: true, Holdings: c.in.Holdings})
		if err != nil {
			c.say("%s is not counted as on the network: it does not resolve: %v", n.Name, err)
			continue
		}
		for _, m := range got.Modules {
			for _, offered := range m.Offers() {
				if offered == overlay.Requirement {
					out = append(out, n)
				}
			}
		}
	}
	return out
}