package cisco

import (
	"fmt"
	"strings"
)

// commandResult holds the output of a command and whether the session should end.
type commandResult struct {
	output string
	exit   bool
}

// commandEntry defines a single command with its name and optional sub-commands.
type commandEntry struct {
	name string
	subs []commandEntry // nil for leaf commands
}

// userExecCommands defines the command tree for user EXEC mode.
var userExecCommands = []commandEntry{
	{name: "show", subs: []commandEntry{
		{name: "version"},
		{name: "clock"},
		{name: "ip", subs: []commandEntry{
			{name: "route"},
			{name: "interface", subs: []commandEntry{
				{name: "brief"},
			}},
		}},
		{name: "interfaces"},
		{name: "vlan", subs: []commandEntry{
			{name: "brief"},
		}},
	}},
	{name: "enable"},
	{name: "exit"},
	{name: "?"},
}

// privilegedExecCommands extends user commands for privileged mode.
var privilegedExecCommands = []commandEntry{
	{name: "show", subs: []commandEntry{
		{name: "version"},
		{name: "clock"},
		{name: "ip", subs: []commandEntry{
			{name: "route"},
			{name: "interface", subs: []commandEntry{
				{name: "brief"},
			}},
		}},
		{name: "interfaces"},
		{name: "running-config"},
		{name: "startup-config"},
		{name: "vlan", subs: []commandEntry{
			{name: "brief"},
		}},
	}},
	{name: "configure", subs: []commandEntry{
		{name: "terminal"},
	}},
	{name: "write", subs: []commandEntry{
		{name: "memory"},
	}},
	{name: "copy"},
	{name: "reload"},
	{name: "disable"},
	{name: "terminal", subs: []commandEntry{
		{name: "length"},
	}},
	{name: "exit"},
	{name: "?"},
}

// globalConfigCommands defines the command tree for global config mode.
var globalConfigCommands = []commandEntry{
	{name: "hostname"},
	{name: "interface"},
	{name: "ip", subs: []commandEntry{
		{name: "route"},
	}},
	{name: "no"},
	{name: "end"},
	{name: "exit"},
	{name: "?"},
}

// interfaceConfigCommands defines the command tree for interface config mode.
var interfaceConfigCommands = []commandEntry{
	{name: "ip", subs: []commandEntry{
		{name: "address"},
	}},
	{name: "description"},
	{name: "shutdown"},
	{name: "no", subs: []commandEntry{
		{name: "shutdown"},
	}},
	{name: "switchport", subs: []commandEntry{
		{name: "mode"},
	}},
	{name: "end"},
	{name: "exit"},
	{name: "?"},
}

// commandsForMode returns the command tree for the given IOS mode.
func commandsForMode(mode iosMode) []commandEntry {
	switch mode {
	case modeUserExec:
		return userExecCommands
	case modePrivilegedExec:
		return privilegedExecCommands
	case modeGlobalConfig:
		return globalConfigCommands
	case modeInterfaceConfig:
		return interfaceConfigCommands
	default:
		return userExecCommands
	}
}

// resolveAbbreviation attempts to match an abbreviated word against a list of
// command entries. It returns the matched entry name, or an error string if
// ambiguous or unknown.
func resolveAbbreviation(word string, entries []commandEntry) (string, error) {
	word = strings.ToLower(word)
	var matches []string
	for _, e := range entries {
		if strings.ToLower(e.name) == word {
			return e.name, nil // exact match
		}
		if strings.HasPrefix(strings.ToLower(e.name), word) {
			matches = append(matches, e.name)
		}
	}
	switch len(matches) {
	case 0:
		return "", fmt.Errorf("unknown")
	case 1:
		return matches[0], nil
	default:
		return "", fmt.Errorf("ambiguous")
	}
}

// resolveCommand resolves a sequence of abbreviated words into the canonical
// command path (e.g., ["sh", "run"] → ["show", "running-config"]).
// It returns the resolved path, any remaining arguments, and an error if
// resolution fails.
func resolveCommand(words []string, entries []commandEntry) ([]string, []string, error) {
	var resolved []string
	current := entries

	for i, w := range words {
		name, err := resolveAbbreviation(w, current)
		if err != nil {
			if err.Error() == "unknown" && len(resolved) > 0 {
				// Remaining words are arguments to the resolved command.
				return resolved, words[i:], nil
			}
			return resolved, words[i:], err
		}
		resolved = append(resolved, name)

		// Find sub-commands for the matched entry.
		var nextLevel []commandEntry
		for _, e := range current {
			if e.name == name {
				nextLevel = e.subs
				break
			}
		}
		if nextLevel == nil {
			// Leaf command — rest are arguments.
			return resolved, words[i+1:], nil
		}
		current = nextLevel
	}
	return resolved, nil, nil
}

// dispatch processes a command line in the context of the current IOS state.
func (s *iosState) dispatch(input string) commandResult {
	words := strings.Fields(input)
	if len(words) == 0 {
		return commandResult{}
	}

	// Handle "?" as a help request.
	if words[0] == "?" {
		return s.cmdHelp()
	}

	cmds := commandsForMode(s.mode)
	resolved, args, err := resolveCommand(words, cmds)
	if err != nil {
		if err.Error() == "ambiguous" {
			return commandResult{output: fmt.Sprintf("%% Ambiguous command:  \"%s\"", input)}
		}
		return commandResult{output: invalidInput(input)}
	}

	if len(resolved) == 0 {
		return commandResult{output: invalidInput(input)}
	}

	cmd := strings.Join(resolved, " ")

	switch s.mode {
	case modeUserExec:
		return s.dispatchUserExec(cmd, args)
	case modePrivilegedExec:
		return s.dispatchPrivilegedExec(cmd, args)
	case modeGlobalConfig:
		return s.dispatchGlobalConfig(cmd, args)
	case modeInterfaceConfig:
		return s.dispatchInterfaceConfig(cmd, args)
	}
	return commandResult{output: invalidInput(input)}
}

func (s *iosState) dispatchUserExec(cmd string, args []string) commandResult {
	switch cmd {
	case "show version":
		return commandResult{output: showVersion(s)}
	case "show clock":
		return commandResult{output: showClock()}
	case "show ip route":
		return commandResult{output: showIPRoute(s)}
	case "show ip interface brief":
		return commandResult{output: showIPInterfaceBrief(s)}
	case "show interfaces":
		return commandResult{output: showInterfaces(s)}
	case "show vlan brief":
		return commandResult{output: showVLANBrief()}
	case "enable":
		return commandResult{} // handled in Handle() loop
	case "exit":
		return commandResult{exit: true}
	}
	return commandResult{output: invalidInput(cmd)}
}

func (s *iosState) dispatchPrivilegedExec(cmd string, args []string) commandResult {
	switch cmd {
	case "show version":
		return commandResult{output: showVersion(s)}
	case "show clock":
		return commandResult{output: showClock()}
	case "show ip route":
		return commandResult{output: showIPRoute(s)}
	case "show ip interface brief":
		return commandResult{output: showIPInterfaceBrief(s)}
	case "show interfaces":
		return commandResult{output: showInterfaces(s)}
	case "show running-config":
		return commandResult{output: showRunningConfig(s)}
	case "show startup-config":
		return commandResult{output: showRunningConfig(s)} // same as running
	case "show vlan brief":
		return commandResult{output: showVLANBrief()}
	case "configure terminal":
		s.mode = modeGlobalConfig
		return commandResult{output: "Enter configuration commands, one per line.  End with CNTL/Z."}
	case "write memory":
		return commandResult{output: "[OK]"}
	case "copy":
		return commandResult{output: "[OK]"}
	case "reload":
		return commandResult{output: "System configuration has been modified. Save? [yes/no]: ", exit: true}
	case "disable":
		s.mode = modeUserExec
		return commandResult{}
	case "terminal length":
		return commandResult{} // accept silently
	case "exit":
		return commandResult{exit: true}
	}
	return commandResult{output: invalidInput(cmd)}
}

func (s *iosState) dispatchGlobalConfig(cmd string, args []string) commandResult {
	switch cmd {
	case "hostname":
		if len(args) < 1 {
			return commandResult{output: "% Incomplete command."}
		}
		s.hostname = args[0]
		return commandResult{}
	case "interface":
		if len(args) < 1 {
			return commandResult{output: "% Incomplete command."}
		}
		ifName := strings.Join(args, "")
		s.currentIf = ifName
		s.mode = modeInterfaceConfig
		return commandResult{}
	case "ip route":
		return commandResult{} // accept silently
	case "no":
		return commandResult{} // accept silently
	case "end":
		s.mode = modePrivilegedExec
		return commandResult{}
	case "exit":
		s.mode = modePrivilegedExec
		return commandResult{}
	}
	return commandResult{output: invalidInput(cmd)}
}

func (s *iosState) dispatchInterfaceConfig(cmd string, args []string) commandResult {
	switch cmd {
	case "ip address":
		if len(args) < 2 {
			return commandResult{output: "% Incomplete command."}
		}
		if iface := s.findInterface(s.currentIf); iface != nil {
			iface.ip = args[0]
			iface.mask = args[1]
		}
		return commandResult{}
	case "description":
		if len(args) < 1 {
			return commandResult{output: "% Incomplete command."}
		}
		if iface := s.findInterface(s.currentIf); iface != nil {
			iface.desc = strings.Join(args, " ")
		}
		return commandResult{}
	case "shutdown":
		if iface := s.findInterface(s.currentIf); iface != nil {
			iface.shutdown = true
			iface.status = "administratively down"
			iface.protocol = "down"
		}
		return commandResult{}
	case "no shutdown":
		if iface := s.findInterface(s.currentIf); iface != nil {
			iface.shutdown = false
			iface.status = "up"
			iface.protocol = "up"
		}
		return commandResult{}
	case "switchport mode":
		return commandResult{} // accept silently
	case "end":
		s.mode = modePrivilegedExec
		s.currentIf = ""
		return commandResult{}
	case "exit":
		s.mode = modeGlobalConfig
		s.currentIf = ""
		return commandResult{}
	}
	return commandResult{output: invalidInput(cmd)}
}

func (s *iosState) cmdHelp() commandResult {
	cmds := commandsForMode(s.mode)
	var b strings.Builder
	for _, e := range cmds {
		if e.name == "?" {
			continue
		}
		b.WriteString(fmt.Sprintf("  %-20s %s\n", e.name, helpText(e.name)))
	}
	return commandResult{output: b.String()}
}

func helpText(name string) string {
	switch name {
	case "show":
		return "Show running system information"
	case "enable":
		return "Turn on privileged commands"
	case "disable":
		return "Turn off privileged commands"
	case "exit":
		return "Exit from the EXEC"
	case "configure":
		return "Enter configuration mode"
	case "write":
		return "Write running configuration to memory"
	case "copy":
		return "Copy from one file to another"
	case "reload":
		return "Halt and perform a cold restart"
	case "terminal":
		return "Set terminal line parameters"
	case "hostname":
		return "Set system's network name"
	case "interface":
		return "Select an interface to configure"
	case "ip":
		return "Global IP configuration subcommands"
	case "no":
		return "Negate a command or set its defaults"
	case "end":
		return "Exit from configure mode"
	case "description":
		return "Interface specific description"
	case "shutdown":
		return "Shutdown the selected interface"
	case "switchport":
		return "Set switching mode characteristics"
	default:
		return ""
	}
}

func invalidInput(input string) string {
	return fmt.Sprintf("%% Invalid input detected at '^' marker.\n\n%s\n^", input)
}