//! Contains logic for generating new file names for Instances based on their
//! middleware.

use std::borrow::Cow;

use anyhow::Context;
use rbx_dom_weak::Instance;

use crate::{snapshot::InstanceWithMeta, snapshot_middleware::Middleware};

pub fn name_for_inst<'a>(
    middleware: Middleware,
    new_inst: &'a Instance,
    old_inst: Option<InstanceWithMeta<'a>>,
) -> anyhow::Result<Cow<'a, str>> {
    if let Some(old_inst) = old_inst {
        if let Some(source) = old_inst.metadata().relevant_paths.first() {
            source
                .file_name()
                .and_then(|s| s.to_str())
                .map(Cow::Borrowed)
                .context("sources on the file system should be valid unicode and not be stubs")
        } else {
            // This is technically not /always/ true, but we want to avoid
            // running syncback on anything that has no instigating source
            // anyway.
            anyhow::bail!(
                "members of 'old' trees should have an instigating source. Somehow, {} did not.",
                old_inst.name(),
            );
        }
    } else {
        Ok(match middleware {
            Middleware::Dir
            | Middleware::CsvDir
            | Middleware::ServerScriptDir
            | Middleware::ClientScriptDir
            | Middleware::ModuleScriptDir => {
                if validate_file_name(&new_inst.name).is_err() {
                    Cow::Owned(slugify_name(&new_inst.name))
                } else {
                    Cow::Borrowed(&new_inst.name)
                }
            }
            _ => {
                let extension = extension_for_middleware(middleware);
                let slugified;
                let final_name = if validate_file_name(&new_inst.name).is_err() {
                    slugified = slugify_name(&new_inst.name);
                    &slugified
                } else {
                    &new_inst.name
                };

                Cow::Owned(format!("{final_name}.{extension}"))
            }
        })
    }
}

/// Returns the extension a provided piece of middleware is supposed to use.
pub fn extension_for_middleware(middleware: Middleware) -> &'static str {
    match middleware {
        Middleware::Csv => "csv",
        Middleware::JsonModel => "model.json",
        Middleware::Json => "json",
        Middleware::ServerScript => "server.luau",
        Middleware::ClientScript => "client.luau",
        Middleware::ModuleScript => "luau",
        Middleware::PluginScript => "plugin.luau",
        Middleware::Project => "project.json",
        Middleware::Rbxm => "rbxm",
        Middleware::Rbxmx => "rbxmx",
        Middleware::Toml => "toml",
        Middleware::Text => "txt",
        Middleware::Yaml => "yml",

        Middleware::LegacyServerScript
        | Middleware::LegacyClientScript
        | Middleware::RunContextServerScript
        | Middleware::RunContextClientScript => {
            todo!("syncback does not work on the middleware {middleware:?} yet")
        }
        // These are manually specified and not `_` to guard against future
        // middleware additions missing this function.
        Middleware::Ignore => unimplemented!("syncback does not work on Ignore middleware"),
        Middleware::Dir
        | Middleware::CsvDir
        | Middleware::ServerScriptDir
        | Middleware::ClientScriptDir
        | Middleware::ModuleScriptDir => {
            unimplemented!("directory middleware requires special treatment")
        }
    }
}

/// A list of file names that are not valid on Windows.
const INVALID_WINDOWS_NAMES: [&str; 22] = [
    "CON", "PRN", "AUX", "NUL", "COM1", "COM2", "COM3", "COM4", "COM5", "COM6", "COM7", "COM8",
    "COM9", "LPT1", "LPT2", "LPT3", "LPT4", "LPT5", "LPT6", "LPT7", "LPT8", "LPT9",
];

/// A list of all characters that are outright forbidden to be included
/// in a file's name.
const FORBIDDEN_CHARS: [char; 9] = ['<', '>', ':', '"', '/', '|', '?', '*', '\\'];

/// Slugifies a name by replacing forbidden characters with underscores
/// and ensuring the result is a valid file name
pub fn slugify_name(name: &str) -> String {
    let mut result = String::with_capacity(name.len());

    for ch in name.chars() {
        if FORBIDDEN_CHARS.contains(&ch) {
            result.push('_');
        } else {
            result.push(ch);
        }
    }

    // Handle Windows reserved names by appending an underscore
    let result_lower = result.to_lowercase();
    for forbidden in INVALID_WINDOWS_NAMES {
        if result_lower == forbidden.to_lowercase() {
            result.push('_');
            break;
        }
    }

    while result.ends_with(' ') || result.ends_with('.') {
        result.pop();
    }

    if result.is_empty() || result.chars().all(|c| c == '_') {
        result = "instance".to_string();
    }

    result
}

/// Validates a provided file name to ensure it's allowed on the file system. An
/// error is returned if the name isn't allowed, indicating why.
/// This takes into account rules for Windows, MacOS, and Linux.
///
/// In practice however, these broadly overlap so the only unexpected behavior
/// is Windows, where there are 22 reserved names.
pub fn validate_file_name<S: AsRef<str>>(name: S) -> anyhow::Result<()> {
    let str = name.as_ref();

    if str.ends_with(' ') {
        anyhow::bail!("file names cannot end with a space")
    }
    if str.ends_with('.') {
        anyhow::bail!("file names cannot end with '.'")
    }

    for char in str.chars() {
        if FORBIDDEN_CHARS.contains(&char) {
            anyhow::bail!("file names cannot contain <, >, :, \", /, |, ?, *, or \\")
        } else if char.is_control() {
            anyhow::bail!("file names cannot contain control characters")
        }
    }

    for forbidden in INVALID_WINDOWS_NAMES {
        if str == forbidden {
            anyhow::bail!("files cannot be named {str}")
        }
    }

    Ok(())
}