package main

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"os/exec"
	"slices"
	"strings"

	"github.com/novox/mesh-controller/internal/inventory"
	"github.com/novox/mesh-controller/internal/link"
)

// The operator's command, `mesh-cli` (alias `nox`), answered here (novox/hq ADR 0272).
//
// mesh-cli asks the node-engine on its own machine; the engine reads the asking account from the kernel and asks
// this controller on its own node's subject. Here it is judged — the controller's terminal, an ordinary call, or
// nothing — and run as every verb's line is: a fresh process of this binary, with this process's environment.
//
// **The terminal** is a line from a node's operator account, on the control-node (§4). Phase 2 adds a node whose
// agents run under an account of their own, judged unable to become root (ADR 0266, not built yet); until then no
// other node is the terminal, because agents there run as its operator. **An ordinary call** is a line from that
// account elsewhere: it meets every refusal of the generic `command` verb and runs with `MESH_VERB=mesh-cli`, so a
// terminal-only change is refused with its reason. **Any other account is refused**, root included: those two
// accounts already reach the mesh's verbs through the mesh MCP server, and no other account gains anything here.

// cliVerb is what a line from mesh-cli that is not the terminal runs as: the verb its process names, so every
// terminal-only refusal applies and says it came through mesh-cli.
const cliVerb = "mesh-cli"

// cliServers are commands that serve until stopped. Run for mesh-cli they would hold a second server under this
// one until the call's bound killed it.
var cliServers = map[string]bool{"serve": true, "api": true, "board": true}

// cliVerdict is how a line is run, or why it is not.
type cliVerdict struct {
	terminal bool
	// why says why the line is or is not the terminal, in words the operator reads under the answer.
	why string
	// refused says why nothing runs.
	refused string
}

// judgeCLI decides how a line from mesh-cli runs (ADR 0272 §4). nodes is every node the mesh knows; control is
// every node the controller's module is assigned to, which is exactly one in a mesh that is well.
func judgeCLI(node string, asked link.CLIAsked, nodes []inventory.Node, control []string) cliVerdict {
	var record *inventory.Node
	for i := range nodes {
		if nodes[i].Name == node {
			record = &nodes[i]
			break
		}
	}
	switch {
	case record == nil:
		return cliVerdict{refused: fmt.Sprintf("%s is not a node this mesh knows, so nothing ran", node)}
	case asked.UID == 0 || asked.Account == "root":
		return cliVerdict{refused: "mesh-cli answers the operator's own account, never root: run it as yourself, " +
			"not under sudo. Nothing ran"}
	case record.Account == "":
		return cliVerdict{refused: fmt.Sprintf("the mesh does not know %s's operator account (`node account <node> <login>`), "+
			"so no account there is answered. Nothing ran", node)}
	case asked.Account != record.Account:
		return cliVerdict{refused: fmt.Sprintf("mesh-cli answers %s's operator account (%s) only, and this line came "+
			"from %s. Nothing ran", node, record.Account, asked.Account)}
	}
	if len(control) != 1 {
		return cliVerdict{why: fmt.Sprintf("not the controller's terminal: the mesh names %d control-nodes, and the "+
			"terminal is the one control-node's operator account", len(control))}
	}
	if control[0] == node {
		// **A person at a terminal, not a service of the operator's** (review of ADR 0272): the tool runner and the
		// account's user units run as the operator too, and only a login session is the terminal.
		if asked.Session == "" {
			return cliVerdict{why: fmt.Sprintf("not the controller's terminal: %s on %s asked from no login session — a "+
				"service or a user unit running as the operator, not a person at a terminal", asked.Account, node)}
		}
		return cliVerdict{terminal: true, why: fmt.Sprintf("the controller's terminal: %s on the control-node %s, "+
			"login session %s", asked.Account, node, asked.Session)}
	}
	return cliVerdict{why: fmt.Sprintf("not the controller's terminal: agents on %s may run as %s, so a "+
		"terminal-only change is made from the control-node %s (novox/hq ADR 0272)", node, asked.Account, control[0])}
}

// controlNodes is every node the controller's module is assigned to.
func controlNodes(ctx context.Context, inv *inventory.Inventory, nodes []inventory.Node) ([]string, error) {
	var out []string
	for _, n := range nodes {
		modules, err := inv.Assigned(ctx, n.Name)
		if err != nil {
			return nil, err
		}
		if slices.Contains(modules, controllerModule) {
			out = append(out, n.Name)
		}
	}
	return out, nil
}

// controllerModule is the module that runs the controller, and so marks the control-node.
const controllerModule = "mesh-controller"

// answerMeshCLI is the serving controller's answer to mesh-cli.
func answerMeshCLI(inv *inventory.Inventory) link.CLIHandler {
	return func(ctx context.Context, node string, asked link.CLIAsked) link.CLIAnswer {
		if handingOver.Load() {
			return link.CLIRefusal("this controller is stopping and runs no new command; ask again in a moment. Nothing ran")
		}
		nodes, err := inv.Nodes(ctx)
		if err != nil {
			return link.CLIRefusal("the mesh's nodes cannot be read, so nothing ran: " + err.Error())
		}
		control, err := controlNodes(ctx, inv, nodes)
		if err != nil {
			return link.CLIRefusal("which node is the control-node cannot be read, so nothing ran: " + err.Error())
		}
		return runForMeshCLI(ctx, node, asked, judgeCLI(node, asked, nodes, control))
	}
}

// cliJournal says one line in the controller's journal (its standard output); a variable so a test can read it.
var cliJournal = func(line string) { fmt.Println(line) }

// runForMeshCLI runs a judged line and answers what it said. Every line is said in the journal first: its call,
// who asked on which node, its command word only, and how it runs (review of ADR 0272).
func runForMeshCLI(ctx context.Context, node string, asked link.CLIAsked, v cliVerdict) link.CLIAnswer {
	how := "as an ordinary call"
	switch {
	case v.refused != "":
		how = "refused: " + v.refused
	case v.terminal:
		how = "as the controller's terminal"
	}
	call := link.CallIDIn(ctx)
	if call == "" {
		call = "(no call)"
	}
	cliJournal(fmt.Sprintf("mesh-cli %s: %s on %s asked %q, %s", call, asked.Account, node, asked.Line[0], how))
	if v.refused != "" {
		return link.CLIRefusal(v.refused)
	}
	// Standard input is the terminal's alone: a secret given at the terminal reaches `secret accept`, and no ordinary
	// call is handed what the asker's standard input held (novox/hq ADR 0259 §10, ADR 0272).
	if len(asked.Stdin) > 0 && !v.terminal {
		return link.CLIAnswer{Exit: 1, Why: v.why, Refused: "standard input is given to a line that runs as the " +
			"controller's terminal alone, and this one does not. Nothing ran"}
	}
	if cliServers[asked.Line[0]] {
		return link.CLIAnswer{Exit: 1, Why: v.why, Refused: fmt.Sprintf("%s serves until stopped, and is not a "+
			"command line mesh-cli runs. Nothing ran", asked.Line[0])}
	}
	verb, line := "", asked.Line
	if !v.terminal {
		composed, err := ordinaryLine(asked.Line)
		if err != nil {
			return link.CLIAnswer{Exit: 1, Why: v.why, Refused: err.Error()}
		}
		verb, line = cliVerb, composed
	}
	cmd := selfCommand(ctx, line)
	cmd.Env = commandEnvironment(fmt.Sprintf("%s through mesh-cli on %s", asked.Account, node), verb, v.terminal)
	// No standard input unless mesh-cli carried one for a terminal line: a command that reads one gets nothing, and
	// fails saying so (ADR 0272 §5).
	cmd.Stdin = nil
	if len(asked.Stdin) > 0 {
		cmd.Stdin = bytes.NewReader(asked.Stdin)
	}
	var stdout, stderr bytes.Buffer
	cmd.Stdout, cmd.Stderr = &stdout, &stderr
	err := cmd.Run()
	answer := link.CLIAnswer{Stdout: stdout.Bytes(), Stderr: stderr.Bytes(), Terminal: v.terminal, Why: v.why}
	var exit *exec.ExitError
	switch {
	case err == nil:
	case errors.As(err, &exit):
		answer.Exit = exit.ExitCode()
		if answer.Exit < 0 {
			// Killed: by the call's bound, or by this controller stopping.
			answer.Exit = 1
			answer.Stderr = append(answer.Stderr, []byte(fmt.Sprintf("\nmesh-cli: the command was stopped (%v)\n",
				exit))...)
		}
	default:
		answer.Exit = 1
		answer.Refused = fmt.Sprintf("could not run %s from this controller's own build: %v", strings.Join(asked.Line, " "), err)
	}
	return answer
}

// settingsForms is what an ordinary `settings` line may say: the settings verb's own forms.
const settingsForms = "settings set <module> <values> [--replace] [--node <node>], settings clear <module> " +
	"[--node <node>], settings show <module> [--history] [--node <node>], or settings preferences [<module>] " +
	"[--node <node>]"

// ordinaryLine is the command line an ordinary call runs (ADR 0272 §4): a `settings` line composed exactly as the
// settings verb composes its own, so its refusals — the terminal-only keys among them — are that verb's (review of
// ADR 0272); any other line as the generic `command` verb takes it, with its refusals.
func ordinaryLine(argv []string) ([]string, error) {
	if len(argv) == 0 || argv[0] != "settings" {
		// What the generic verb runs, and nothing it would refuse: its reading forms only, and never a command that
		// is the terminal's alone (novox/hq ADR 0266) — the two checks argvFor makes of the `command` verb's line,
		// made of the words as given rather than re-split from one string.
		if err := refusedAsTheGenericCommand(argv); err != nil {
			return nil, err
		}
		if err := terminalOnly(argv); err != nil {
			return nil, err
		}
		return argv, nil
	}
	args := map[string]any{}
	var words []string
	rest := argv[1:]
	for i := 0; i < len(rest); i++ {
		w := rest[i]
		switch {
		case w == "--replace" || w == "-replace":
			args["replace"] = "true"
		case w == "--history" || w == "-history":
			args["history"] = "true"
		case w == "--node" || w == "-node":
			if i+1 >= len(rest) {
				return nil, fmt.Errorf("--node names no node; settings takes %s. Nothing ran", settingsForms)
			}
			i++
			args["node"] = rest[i]
		case strings.HasPrefix(w, "--node=") || strings.HasPrefix(w, "-node="):
			_, args["node"], _ = strings.Cut(w, "=")
		case strings.HasPrefix(w, "-"):
			return nil, fmt.Errorf("settings takes no %s through mesh-cli outside the terminal; it takes %s. "+
				"Nothing ran", w, settingsForms)
		default:
			words = append(words, w)
		}
	}
	wrong := fmt.Errorf("through mesh-cli outside the terminal, settings takes the settings verb's forms: %s. "+
		"Nothing ran", settingsForms)
	if len(words) == 0 {
		return nil, wrong
	}
	switch words[0] {
	case "set":
		if len(words) != 3 {
			return nil, wrong
		}
		args["module"], args["values"] = words[1], words[2]
	case "clear":
		if len(words) != 2 {
			return nil, wrong
		}
		args["module"], args["clear"] = words[1], "true"
	case "show":
		if len(words) != 2 {
			return nil, wrong
		}
		args["module"] = words[1]
	case "preferences":
		if len(words) > 2 {
			return nil, wrong
		}
		args["list"] = "preferences"
		if len(words) == 2 {
			args["module"] = words[1]
		}
	default:
		return nil, wrong
	}
	return argvFor("settings", args)
}