cli.kt/src/commonMain/kotlin/com/infendro/cli/command/context/ContextParser.kt

package com.infendro.cli.command.context

import com.infendro.cli.command.Command
import com.infendro.cli.error.run.*
import com.infendro.cli.parser.Parser

internal class ContextParser(
    private val root: Command,
    private val args: Array<String>,
) {
    sealed class Result {
        data class Success(
            val context: Context,
        ) : Result()

        data class Help(
            val path: List<Command>,
        ) : Result()

        data class Failure(
            val path: List<Command>,
            val failure: RuntimeFailure,
        ) : Result()
    }

    private fun success(context: Context) = Result.Success(context)
    private fun help(path: List<Command>) = Result.Help(path)
    private fun failure(path: List<Command>, exception: RuntimeFailure) = Result.Failure(path, exception)

    private var index = 0
    private val current: String
        get() = args[index]
    private val next: String?
        get() = args.getOrNull(index + 1)

    private fun hasNext() = index < args.size
    private fun consume() {
        index++
    }

    fun parse(): Result {
        // command
        var command = root
        val path = mutableListOf(root)
        val commands = mutableMapOf<Command.Fallback.Key<*>, Any>()

        while (hasNext()) {
            if (current.startsWith("-"))
                break

            val cmd = command.commands.firstOrNull {
                (it is Command.Named && it.name == current) || it is Command.Fallback<*>
            }
            if (cmd == null) {
                when {
                    command.arguments.isEmpty() -> return failure(path, UnknownCommand(command, current))
                    else -> break
                }
            }

            command = cmd
            path += cmd
            if (cmd is Command.Fallback<*>) {
                val value = when (val result = cmd.parser.parse(current)) {
                    is Parser.Result.Success<*> -> result.value
                    is Parser.Result.Failure<*> -> return failure(path, result.failure)
                }
                commands[cmd.key] = value
            }

            consume()
        }

        // arguments and options
        val arguments = command.arguments.associateWith { mutableListOf<Any>() }
        val options = command.options.associateWith { mutableListOf<Any>() }

        var endOfOptions = false
        var argumentIndex = 0
        var argumentCount = 0

        while (hasNext()) {
            val dashes = current.takeWhile { it == '-' }.count()
            val trimmed = current.drop(dashes)

            when {
                // argument
                endOfOptions || dashes == 0 -> {
                    val argument = command.arguments.getOrNull(argumentIndex)
                        ?: return failure(path, UnexpectedArgument(current))

                    val value = when (val result = argument.parser.parse(current)) {
                        is Parser.Result.Success<*> -> result.value
                        is Parser.Result.Failure<*> -> return failure(path, result.failure)
                    }
                    arguments[argument]!! += value
                    argumentCount++

                    if (argumentCount == argument.count) {
                        argumentCount = 0
                        argumentIndex++
                    }
                }

                // option
                dashes in 1..2 -> {
                    if (dashes == 2 && trimmed.isEmpty()) {
                        endOfOptions = true
                        consume()
                        continue
                    }

                    if (dashes == 2 && trimmed == "help")
                        return help(path)

                    val (name, text) = when {
                        trimmed.contains('=') -> {
                            val (name, value) = trimmed.split('=', limit = 2)
                            name to value
                        }
                        else -> {
                            if (next?.startsWith('-') == false) {
                                consume()
                                trimmed to current
                            } else {
                                trimmed to null
                            }
                        }
                    }

                    val names = when {
                        dashes == 1 -> name.map { "$it" }
                        else -> listOf(name)
                    }

                    for (name in names) {
                        val option = command.options.firstOrNull { name in it.names }
                            ?: return failure(path, UnknownOption(command, name))

                        val value = when {
                            text != null ->
                                when (val result = option.parser.parse(text)) {
                                    is Parser.Result.Success<*> -> result.value
                                    is Parser.Result.Failure<*> -> return failure(path, result.failure)
                                }
                            option.flag -> option.fallback!!
                            else -> return failure(path, MissingOptionValue(option))
                        }
                        options[option]!! += value
                    }
                }

                // malformed option
                else -> {
                    when {
                        current.contains('=') -> {
                            val (option) = current.split('=', limit = 2)
                            return failure(path, MalformedOption(option))
                        }
                        else -> return failure(path, MalformedOption(current))
                    }
                }
            }

            consume()
        }

        // validate arguments
        for (argument in command.arguments) {
            val count = arguments[argument]!!.count()
            if (count !in argument.min..argument.count) return failure(path, InvalidArgumentCount(argument, count))
        }

        // validate options
        for (option in command.options) {
            val count = options[option]!!.count()
            if (count !in option.min..option.count) return failure(path, InvalidOptionCount(option, count))
        }

        val context = Context(path, commands, arguments, options)
        return success(context)
    }
}