using System;
using System.IO;

namespace IslaApocalypse.Core
{
	/// <summary>
	/// ⭐ EVERY PATH THE TOOLING READS OR WRITES, RESOLVED IN ONE PLACE, OVERRIDABLE BY ENVIRONMENT.
	/// → `Design - Tooling - Iteration and Batching.md` § "Tooling must be safe BY CODE, not by care".
	///
	/// ═══ WHY THIS TYPE EXISTS ═══
	///
	/// So a batch run CANNOT read over or write to the developer's live config, staged blueprints,
	/// or output directory. Not "should not" — cannot, because there is no other way to obtain a
	/// path, and each one has an environment override that a batch script sets before it starts.
	///
	/// > ⭐ THE POINT IS THAT IT IS ENFORCED BY CODE, NOT BY CARE.
	/// > A rule that depends on an executor remembering it will eventually meet an executor who
	/// > does not.
	///
	/// ⚠ This is not hypothetical. These rules were born from a real incident: an executor admitted
	/// it had been deleting the developer's staged test blueprint. It was owned and fixed IN CODE.
	/// That is why these are rules and not guidance. → <see cref="FileSafety"/>.
	///
	/// ═══ THE OVERRIDES ═══
	///
	///   ISLA_CONFIG_PATH    the generation config file        default: user://config.json
	///   ISLA_BLUEPRINT_PATH the blueprint read/written        default: user://blueprints
	///   ISLA_OUTPUT_DIR     generation output (maps, batches) default: user://output
	///
	/// ⚠ user:// RESOLUTION. Defaults sit under the project's own user data directory, which this
	/// project pins away from the old prototype's — see project.godot's user:// isolation block.
	/// Core is engine-free by design, so the caller supplies the resolved user directory (from
	/// Godot's OS.GetUserDataDir()) via <see cref="Configure"/>. Until it does, the defaults resolve
	/// under the process working directory, which is wrong for a real run and loud enough to notice.
	///
	/// No generator exists this phase. The rails are laid before it so it inherits them.
	/// </summary>
	public static class ToolingPaths
	{
		public const string ConfigPathVar    = "ISLA_CONFIG_PATH";
		public const string BlueprintPathVar = "ISLA_BLUEPRINT_PATH";
		public const string OutputDirVar     = "ISLA_OUTPUT_DIR";

		private static string _userDataDir;

		/// <summary>
		/// Hand Core the engine-resolved user data directory. Called once at startup by whichever
		/// layer owns the engine (Tools or Server); Core never asks Godot for it itself.
		/// </summary>
		public static void Configure(string userDataDir)
		{
			if (string.IsNullOrWhiteSpace(userDataDir))
				throw new ArgumentException("A user data directory is required.", nameof(userDataDir));
			_userDataDir = userDataDir;
		}

		/// <summary>The resolved user data directory, or the working directory if none was configured.</summary>
		public static string UserDataDir => _userDataDir ?? Directory.GetCurrentDirectory();

		/// <summary>Whether <see cref="Configure"/> has been called. Tooling should assert this before a run.</summary>
		public static bool IsConfigured => _userDataDir != null;

		/// <summary>The generation config file. Override: ISLA_CONFIG_PATH.</summary>
		public static string ConfigPath =>
			Override(ConfigPathVar) ?? Path.Combine(UserDataDir, "config.json");

		/// <summary>Where blueprints are read from and written to. Override: ISLA_BLUEPRINT_PATH.</summary>
		public static string BlueprintPath =>
			Override(BlueprintPathVar) ?? Path.Combine(UserDataDir, "blueprints");

		/// <summary>Where a generation run writes its output. Override: ISLA_OUTPUT_DIR.</summary>
		public static string OutputDir =>
			Override(OutputDirVar) ?? Path.Combine(UserDataDir, "output");

		/// <summary>
		/// The batches root. → `Design - Tooling - Iteration and Batching.md`:
		/// <c>batches/NN_&lt;name&gt;/&lt;seed&gt;_&lt;variant&gt;/</c>, each batch carrying an
		/// INDEX.md and a persistent scratch/. A/B comparisons are browsed by a human, and a flat
		/// directory of same-named PNGs is not browsable.
		///
		/// ⚠ PROTECTED FROM DELETION. → <see cref="FileSafety"/>.
		/// </summary>
		public static string BatchesRoot => Path.Combine(OutputDir, "batches");

		/// <summary>
		/// The scratch subfolder of a batch. INTERMEDIATES PERSIST HERE AND ARE NEVER CLEANED —
		/// the whole point is that a run's intermediates survive it, so a surprising result can be
		/// investigated instead of regenerated.
		/// </summary>
		public static string BatchScratch(string batchDir) => Path.Combine(batchDir, "scratch");

		/// <summary>
		/// ⭐ A BATCH ROOT: <c>batches/&lt;task&gt;_&lt;descriptor&gt;/</c>.
		///
		/// ═══ ⚠⚠ THE PREFIX IS THE AUTHORING TASK NUMBER. IT IS NOT A COUNTER. ═══
		///
		/// <c>04_review</c> means "the batch task 04 authored". It does NOT mean "the fifth batch".
		/// A task that produces six batches produces six <c>04_*</c> folders, not <c>04_</c> through
		/// <c>09_</c>.
		///
		/// This is enforced here, in code, because it already drifted once: tasks 02 and 03 used the
		/// prefix as a global running counter and produced <c>00_smoke</c> … <c>05_trophy_10240</c>
		/// across two tasks, so nothing in the folder name said which task made what. Passing the
		/// task number as an explicit argument — rather than letting a caller compose a free-form
		/// string — is what makes the convention unbreakable rather than remembered.
		/// → `Design - Tooling - Iteration and Batching.md`.
		///
		/// The descriptor must NOT carry its own numeric prefix; that is the mistake this method
		/// exists to prevent, so it is refused rather than silently accepted.
		/// </summary>
		public static string BatchRoot(int taskNumber, string descriptor)
		{
			if (taskNumber < 0)
				throw new ArgumentOutOfRangeException(nameof(taskNumber), taskNumber,
					"A batch is named for the task that authored it; there is no negative task.");
			if (string.IsNullOrWhiteSpace(descriptor))
				throw new ArgumentException("A batch needs a descriptor — '04_' alone is not browsable.", nameof(descriptor));

			string d = descriptor.Trim();

			// Refuse "04_review", "4_review", "05_foo" — the caller is re-adding a prefix, which is
			// exactly how the counter drifted. The task number is this method's job, not theirs.
			int us = d.IndexOf('_');
			if (us > 0 && int.TryParse(d.Substring(0, us), out _))
				throw new ArgumentException(
					$"Descriptor '{d}' starts with its own numeric prefix. Pass the task number as " +
					$"taskNumber and the descriptor WITHOUT one (e.g. \"review\", not \"04_review\") — " +
					"the prefix is composed here so it cannot drift.", nameof(descriptor));

			return Path.Combine(BatchesRoot, $"{taskNumber:D2}_{d}");
		}

		/// <summary>
		/// A variant directory inside a batch:
		/// <c>batches/&lt;task&gt;_&lt;descriptor&gt;/&lt;seed&gt;_&lt;variant&gt;/</c>.
		/// </summary>
		public static string BatchDir(int taskNumber, string descriptor, long seed, string variant)
			=> Path.Combine(BatchRoot(taskNumber, descriptor), $"{seed}_{variant}");

		private static string Override(string variable)
		{
			string v = Environment.GetEnvironmentVariable(variable);
			return string.IsNullOrWhiteSpace(v) ? null : v;
		}

		/// <summary>Every resolved path, for a run report's header. Print this; it is cheap and it has caught things.</summary>
		public static string Describe() =>
			$"user data : {UserDataDir}{(IsConfigured ? "" : "   ⚠ NOT CONFIGURED — falling back to CWD")}\n" +
			$"config    : {ConfigPath}{Marker(ConfigPathVar)}\n" +
			$"blueprints: {BlueprintPath}{Marker(BlueprintPathVar)}\n" +
			$"output    : {OutputDir}{Marker(OutputDirVar)}\n" +
			$"batches   : {BatchesRoot}";

		private static string Marker(string variable) => Override(variable) != null ? $"   [{variable}]" : "";
	}
}