package main

import (
	// "bytes"
	// "bufio"
	"bytes"
	"fmt"
	"html/template"
	"io"
	"net/http"
	"os"
	"os/exec"
	"os/user"
	"path/filepath"
	"strings"
	"regexp"
)

type PageData struct {
	CurrentDir  string
	CurrentUsername string
	CommandLog  []CommandOutput
}

type CommandOutput struct {
	Command string
	Output  string
	Error   string
}

type CommandNode struct {
	Operator 	string
	Left 		*CommandNode
	Right 		*CommandNode
	Command 	string
}

var commandLog []CommandOutput
var variables = make(map[string]string)

func expandCommandSubstitution(command string, currentDir string) (string, error) {
	// Do not expand single quoted strings
	reSingleQuotes := regexp.MustCompile(`'([^']*)'`)
	singleQuotedStrings := reSingleQuotes.FindAllString(command, -1)

	placeholder := "\x00PLACEHOLDER\x00"
	command = reSingleQuotes.ReplaceAllLiteralString(command, placeholder)

	// Expand variables
	reVar := regexp.MustCompile(`\$(\w+)`)
	command = reVar.ReplaceAllStringFunc(command, func(match string) string {
		varName := match[1:]
		if val, exists := variables[varName]; exists {
			return val
		}
		if envVal, exists := os.LookupEnv(varName); exists {
			return envVal
		}

		return match
	})

	// Restore single-quoted strings and avoid expansion inside them
	for _, sq := range singleQuotedStrings {
		command = strings.Replace(command, placeholder, sq, 1)
	}

	// expand $(...) command substitution
	re := regexp.MustCompile(`\$\(([^()]+)\)`)
	for {
		match := re.FindStringSubmatch(command)
		if match == nil {
			break
		}

		subCommand := strings.TrimSpace(match[1])
		subOutput, err := executeCommandTree(parseCommandTree(subCommand), currentDir)
		if err != nil {
			return "", err
		}

		command = strings.Replace(command, match[0], strings.TrimSpace(subOutput), 1)
	}
	return command, nil
}

func setVariable(command string) bool {
	re := regexp.MustCompile(`^(\w+)=(.*)$`)
	match := re.FindStringSubmatch(command)
	if match == nil {
		return false
	}

	varName := match[1]
	value := strings.Trim(match[2], `"`)

	if strings.HasPrefix(command, "export ") {
		os.Setenv(varName, value)
	} else {
		variables[varName] = value
	}

	return true
}

func parseCommandTree(command string) *CommandNode {
	if strings.Contains(command, ";") {
		parts := strings.SplitN(command, ";", 2)
		return &CommandNode{
			Operator: ";",
			Left: parseCommandTree(strings.TrimSpace(parts[0])),
			Right: parseCommandTree(strings.TrimSpace(parts[1])),
		}
	} else if strings.Contains(command, ">") {
		parts := strings.SplitN(command, ">", 2)
		return &CommandNode{
			Operator: ">",
			Left: parseCommandTree(strings.TrimSpace(parts[0])),
			Right: &CommandNode{Command: strings.TrimSpace(parts[1])},
		}
	} else if strings.Contains(command, "<") {
		parts := strings.SplitN(command, "<", 2)
		return &CommandNode{
			Operator: "<",
			Left: parseCommandTree(strings.TrimSpace(parts[0])),
			Right: &CommandNode{Command: strings.TrimSpace(parts[1])},
		}
	} else if strings.Contains(command, "|") {
		parts := strings.SplitN(command, "|", 2)
		return &CommandNode{
			Operator: "|",
			Left: parseCommandTree(strings.TrimSpace(parts[0])),
			Right: parseCommandTree(strings.TrimSpace(parts[1])),
		}
	} else if strings.Contains(command, "&&") {
		parts := strings.SplitN(command, "&&", 2)
		return &CommandNode{
			Operator: "&&",
			Left: parseCommandTree(strings.TrimSpace(parts[0])),
			Right: parseCommandTree(strings.TrimSpace(parts[1])),
		}
	} else if strings.Contains(command, "||") {
		parts := strings.SplitN(command, "||", 2)
		return &CommandNode{
			Operator: "||",
			Left: parseCommandTree(strings.TrimSpace(parts[0])),
			Right: parseCommandTree(strings.TrimSpace(parts[1])),
		}
	}
	return &CommandNode{Command: command}
}

func executeCommandTree(node *CommandNode, currentDir string) (string, error) {
	if node == nil {
		return "", nil
	}

	switch node.Operator {
	case "&&":
		leftOutput, err := executeCommandTree(node.Left, currentDir)
		if err != nil {
			return "", err
		}
		if leftOutput != "" {
			return executeCommandTree(node.Right, currentDir)
		}
		return executeCommandTree(node.Right, currentDir)

	case "||":
		leftOutput, err := executeCommandTree(node.Left, currentDir)
		if err == nil && leftOutput != "" {
			return leftOutput, nil
		}
		return executeCommandTree(node.Right, currentDir)

	case "|":
		leftOutput, err := executeCommandTree(node.Left, currentDir)
		if err != nil {
			return "", err
		}
		cmdArgs := parseCommandWithQuotes(node.Right.Command)
		if len(cmdArgs) == 0 {
			return "", fmt.Errorf("Invalid Command")
		}
		cmd := exec.Command(cmdArgs[0], cmdArgs[1:]...)
		cmd.Dir = currentDir
		cmd.Stdin = strings.NewReader(leftOutput)
		var outputBuffer bytes.Buffer
		cmd.Stdout = &outputBuffer
		cmd.Stderr = &outputBuffer
		if err := cmd.Run(); err != nil {
			return "", err
		}
		return outputBuffer.String(), nil

	case ">":
		leftOutput, err := executeCommandTree(node.Left, currentDir)
		if err != nil {
			return "", err
		}
		file, err := os.Create(strings.TrimSpace(node.Right.Command))
		if err != nil {
			return "", err
		}
		defer file.Close()
		_, err = file.WriteString(leftOutput)
		return "", err

	case "<":
		file, err := os.Open(strings.TrimSpace(node.Right.Command))
		if err != nil {
			return "", err
		}
		defer file.Close()
		cmdArgs := parseCommandWithQuotes(node.Left.Command)
		if len(cmdArgs) == 0 {
			return "", fmt.Errorf("Invalid command")
		}
		cmd := exec.Command(cmdArgs[0], cmdArgs[1:]...)
		cmd.Dir = currentDir
		cmd.Stdin = file
		var outputBuffer bytes.Buffer
		cmd.Stdout = &outputBuffer
		cmd.Stderr = &outputBuffer
		if err := cmd.Run(); err != nil {
			return "", err
		}
		return outputBuffer.String(), nil

	case ";":
		leftOutput, _ := executeCommandTree(node.Left, currentDir)
		rightOutput, _ := executeCommandTree(node.Right, currentDir)
		return leftOutput + rightOutput, nil
	}
	return executeSimpleCommand(node.Command, currentDir).Output, nil
}

func executeCommand(command string, args []string, dir string) (string, error) {
	cmd := exec.Command(command, args...)
	cmd.Dir = dir
	output, err := cmd.CombinedOutput()
	return string(output), err
}

func executeSimpleCommand(command string, currentDir string) CommandOutput {
	var cmdOutput CommandOutput
	// args := strings.Fields(command)
	args := parseCommandWithQuotes(command)
	if len(args) == 0 {
		return cmdOutput
	}

	cmd := exec.Command(args[0], args[1:]...)
	cmd.Dir = currentDir
	output, err := cmd.CombinedOutput()
	cmdOutput.Command = command
	cmdOutput.Output = string(output)
	if err != nil {
		cmdOutput.Error = err.Error()
	}
	return cmdOutput
}

func changeDirectory(command string, args []string, currentDir *string) CommandOutput {
	var cmdOutput CommandOutput

	if len(args) == 0 {
		homeDir, _ := os.UserHomeDir()
		err := os.Chdir(homeDir)
		if err != nil {
			cmdOutput = CommandOutput {
				Command: command,
				Error: "Failed to change to home directory: " + err.Error(),
			}
		} else {
			cmdOutput = CommandOutput {
				Command: command,
				Output: "Changed to home directory: " +  homeDir,
			}
			*currentDir = homeDir
		}
	} else {
		newDir := args[0]
		err := os.Chdir(newDir)
		if err != nil {
			cmdOutput = CommandOutput {
				Command: command + " " + newDir,
				Error: "Failed to change to directory: " + err.Error(),
			}
		} else {
			cmdOutput = CommandOutput {
				Command: command + " " + newDir,
				Output: "Changed to directory: " + newDir,
			}
			*currentDir = newDir
		}
	}
	return cmdOutput
}

func fileUploadHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method == http.MethodPost {
		file, header, err := r.FormFile("file")
		if err != nil {
			http.Error(w, "Failed to upload file", http.StatusInternalServerError)
			return
		}
		defer file.Close()

		uploadDir := r.FormValue("uploadDir")
		if uploadDir == "" {
			uploadDir = "./"
		}

		out, err := os.Create(filepath.Join(uploadDir, header.Filename))
		if err != nil {
			http.Error(w, "Failed to save file", http.StatusInternalServerError)
			return
		}
		defer out.Close()

		_, err = io.Copy(out, file)
		if err != nil {
			http.Error(w, "Failed to write file", http.StatusInternalServerError)
			return
		}
		cmdOutput := CommandOutput{Command: "upload", Output: "File saved successfully", Error: ""}
		// fmt.Fprintf(w, "File %s uploaded successfully to %s", header.Filename, uploadDir)
		commandLog = append(commandLog, cmdOutput)

	}
}

// func fileDownloadHandler(w http.ResponseWriter, r *http.Request) {
// 	if r.Method == http.MethodPost {
// 		file, header, err := r.FormFile("file")

func processCommand(command string, currentDir string) CommandOutput {
	var errorMsg string

	// Handle variable assignments before execution
	if setVariable(command) {
		return CommandOutput{Command: command, Output: "", Error: ""}
	}

	// This handles command substitution which is $(...) in bash
	expandedCommand, err := expandCommandSubstitution(command, currentDir)
	if err != nil {
		errorMsg = err.Error()
		return CommandOutput{Command: command, Output: "", Error: errorMsg}
	}

	tree := parseCommandTree(expandedCommand)
	output, err := executeCommandTree(tree, currentDir)
	if err != nil {
		errorMsg = err.Error()
	}
	return CommandOutput{Command: command, Output: output, Error: errorMsg}
}

func parseCommandWithQuotes(command string) []string {
	var args []string
	var current strings.Builder
	inSingleQuote, inDoubleQuote := false, false

	for i := 0; i < len(command); i++ {
		c := command[i]

		switch c {
		case '\'':
			if !inDoubleQuote {
				inSingleQuote = !inSingleQuote
				continue
			}
		case '"':
			if !inSingleQuote {
				inDoubleQuote = !inDoubleQuote
				continue
			}
		case ' ':
			if !inSingleQuote && !inDoubleQuote {
				if current.Len() > 0 {
					args = append(args, current.String())
					current.Reset()
				}
				continue
			}
		case '\\':
			// Handle escaped characters
			if i+1 < len(command) {
				next := command[i+1]
				if next == '"' || next == '\'' || next == '\\' {
					current.WriteByte(next)
					i++
					continue
				}
			}
		}

		current.WriteByte(c)
	}

	// Add the last argument
	if current.Len() > 0 {
		args = append(args, current.String())
	}

	return args
}

func handler(w http.ResponseWriter, r *http.Request) {
	currentDir, _ := os.Getwd()
	currentUser, _ := user.Current()
	currentUsername := currentUser.Username

	if r.Method == http.MethodPost {
		input := r.FormValue("command")
		parts := strings.Fields(input)
		if len(parts) > 0 {
			command := parts[0]
			args := parts[1:]
			if  command == "cd" {
				cmdOutput := changeDirectory(command, args, &currentDir)
				commandLog = append(commandLog, cmdOutput)
			} else {
				cmdOutput := processCommand(input, currentDir)
				commandLog = append(commandLog, cmdOutput)
			}
		}
	}

	tmpl := template.Must(template.New("index").Parse(`
		<!DOCTYPE html>
		<html lang="en">
		<head>
			<meta charset="UTF-8">
			<meta name="viewport" content="width=device-width, initial-scale=1.0">
			<title>Go Web Shell</title>
			<script>
				document.addEventListener("DOMContentLoaded", function() {
					const input = document.getElementById("command-input");
					if (!input) return;
					let commandHistory = JSON.parse(sessionStorage.getItem("commandHistory")) || [];
					let historyIndex = commandHistory.length;
					let tabIndex = -1;
					let tabMatches = [];

					document.querySelector("form").addEventListener("submit", function(event) {
						const command = input.value.trim();
						if (command) {
							commandHistory.push(command);
							sessionStorage.setItem("commandHistory", JSON.stringify(commandHistory));
							historyIndex = commandHistory.length;
						}
					});

					window.addEventListener("keydown", function(event) {
						if (document.activeElement !== input) return;

						const cursorPos = input.selectionStart;
						const textLength = input.value.length;

						// Prevent default behavior for specific Ctrl+Key shortcuts
						if (event.ctrlKey && ["w", "n", "p", "h", "e", "a", "k", "u", "d", "r", "t"].includes(event.key.toLowerCase())) {
							event.preventDefault();
							event.stopPropagation();
						}

						// Ctrl+A: Move cursor to the beginning
						if (event.ctrlKey && event.key === "a") {
							input.setSelectionRange(0, 0);
						}

						// Ctrl+E: Move cursor to the end
						else if (event.ctrlKey && event.key === "e") {
							input.setSelectionRange(textLength, textLength);
						}

						// Ctrl+U: Clear the input field
						else if (event.ctrlKey && event.key === "u") {
							input.value = "";
						}

						// Ctrl+K: Delete everything after the cursor
						else if (event.ctrlKey && event.key === "k") {
							input.value = input.value.substring(0, cursorPos);
						}

						// Ctrl+W: Delete the previous word
						else if (event.ctrlKey && event.key === "w") {
							const beforeCursor = input.value.substring(0, cursorPos);
							const afterCursor = input.value.substring(cursorPos);
							const newBeforeCursor = beforeCursor.replace(/\S+\s*$/, ""); // Delete last word
							input.value = newBeforeCursor + afterCursor;
							input.setSelectionRange(newBeforeCursor.length, newBeforeCursor.length);
						}

						// Ctrl+H: Delete the previous character (Backspace)
						else if (event.ctrlKey && event.key === "h") {
							if (cursorPos > 0) {
								input.value = input.value.substring(0, cursorPos - 1) + input.value.substring(cursorPos);
								input.setSelectionRange(cursorPos - 1, cursorPos - 1);
							}
						}

						// Ctrl+D: Delete character under cursor (or clear input if empty)
						else if (event.ctrlKey && event.key === "d") {
							if (textLength === 0) {
								console.log("Ctrl+D: No input, simulating EOF");
							} else if (cursorPos < textLength) {
								input.value = input.value.substring(0, cursorPos) + input.value.substring(cursorPos + 1);
								input.setSelectionRange(cursorPos, cursorPos);
							}
						}

						// Ctrl+P: Previous command (up)
						else if (event.ctrlKey && event.key === "p") {
							if (historyIndex > 0) {
								historyIndex--;
								input.value = commandHistory[historyIndex];
							} else if (historyIndex === 0) {
								input.value = commandHistory[0];
							}
						}

						// Ctrl+N: Next command (down)
						else if (event.ctrlKey && event.key === "n") {
							if (historyIndex < commandHistory.length - 1) {
								historyIndex++;
								input.value = commandHistory[historyIndex];
							} else {
								historyIndex = commandHistory.length;
								input.value = "";
							}
						}

						// Ctrl+R: Prevent page reload (for future reverse search)
						else if (event.ctrlKey && event.key === "r") {
							console.log("Reverse search triggered (not yet implemented)");
						}

						// Tab Completion
						else if (event.key === "Tab") {
							event.preventDefault();
							const currentText = input.value.trim();

							if (currentText === "") return;

							// Find all matching commands from history
							if (tabIndex === -1) {
								tabMatches = commandHistory.filter(cmd => cmd.startsWith(currentText));
								if (tabMatches.length === 0) return;
							}

							// Cycle through matches
							if (event.shiftKey) {
								tabIndex = tabIndex > 0 ? tabIndex - 1 : tabMatches.length - 1; // Shift+Tab goes backward
							} else {
								tabIndex = (tabIndex + 1) % tabMatches.length;
							}

							input.value = tabMatches[tabIndex];
						}

						// Allow Enter key to submit form
						if (event.key === "Enter") {
							tabIndex = -1; // Reset tab completion cycle
							return;
						}
					}, true);
				});
			</script>
			<script>
				document.addEventListener("DOMContentLoaded", function() {
					document.getElementById("command-input").addEventListener("keydown", function(event) {
						if (event.key === "Enter") {
							let inputVal = this.value.trim();
							if (inputVal === "upload") {
								document.getElementById("inputFile").click();
							}
						}
					});

					function requestUpload() {
						let fileInput = document.getElementById("inputFile");
						console.log("file is");
						console.log(fileInput);
						if (fileInput.files.length === 0) {
							console.error("No file selected.");
							return;
						}
						let file = fileInput.files[0];
						let formData = new FormData();
						formData.append("file", file);

						fetch("http://localhost:8080/upload", {
							method: "POST",
							body: formData
						})
						.then(response => response.text())
						.then(data => {
							console.log("Upload succesful:", data);
							document.getElementById("command-input").value = "";
						})
						.catch(error => console.error("Upload failed:", error));
						}
				});
			</script>
			<style>
				body {
					background-color: #222;
					color: #eee;
					font-family: monospace;
					font-size: 14pt;
					margin: 0;
					padding: 0;
					height: 100vh;
					display: flex;
					flex-direction: column;
				}
				#terminal {
					flex: 1;
					padding: 12px;
					overflow-y: auto;
					white-space: pre-wrap;
					border: 1px solid white;
					margin: 10px;
					display: flex;
					flex-direction: column;
				}
				input {
					font-size: 14pt;
					background: #222;
					color: #eee;
					border: none;
					width: 80%;
					font-family: monospace;
				}
				input:focus {
					outline: none;
				}
				span.command {
					color: #75df0b;
				}
				span.error {
					color: #ff5555;
				}
				span.directory {
					color: #1bc9e7;
				}
			</style>
		</head>
		<body>
			<div id="terminal">
				<span>Current Directory: {{.CurrentDir}}</span>
				{{range .CommandLog}}
				<div><span class="command">gommand:$ {{.Command}}</span></div>
				{{if .Output}}
				<div>{{.Output}}</div>
				{{end}}
				{{if .Error}}
				<div class="error">{{.Error}}</div>
				{{end}}
				{{end}}
				<form method="POST" autocomplete="off">
					<div style="display: flex; align-items: center;">
						<span class="command">{{.CurrentUsername}}:<span class="directory">{{.CurrentDir}}</span>$ </span>
						<input id="command-input" type="text" name="command" placeholder="Type a command here..." autofocus required>
					</div>
				</form>
			</div>
			<div>
				<form id="fileUpload" action="/upload" method="POST" enctype="multipart/form-data">
					<label for="inputFile">Select a file to upload:</label>
					<input name="inputFile" id="inputFile" type="file">
					<button id="fileUploadButton" onclick="document.getElementById('inputFile').click()">Upload</button>
				</form>
				</div>
		</body>
		</html>
	`))

	data := PageData{
		CurrentDir: currentDir,
		CurrentUsername: currentUsername,
		CommandLog: commandLog,
	}
	tmpl.Execute(w, data)
}

func main() {
	http.HandleFunc("/", handler)
	http.HandleFunc("/upload", fileUploadHandler)
	fmt.Println("Starting server on :8080")
	http.ListenAndServe(":8080", nil)
}