//! One-shot launcher-setting application performed the first time a game is played.
//!
//! Some games ship per-user setting files somewhere under their installed
//! `local/` tree — an `account_name.txt`, a `language.txt`, and/or a
//! `SmartSteamEmu.ini` carrying a `PersonaName = ...` line. The first time the
//! user launches a game we stamp the launcher's configured username and language
//! into whichever of those files exist, then record a per-game marker so the
//! step never runs again.
//!
//! The marker only records that we *tried*: it is written unconditionally after
//! the first attempt, whether or not any file or matching line was found. Moving
//! this out of the install transaction means already-installed games are fixed
//! up on their next play rather than only on a fresh (re)install.

use std::{
    ffi::OsStr,
    io::ErrorKind,
    path::{Path, PathBuf},
};

use eyre::WrapErr;

use crate::state_paths::launch_settings_applied_path;

const LOCAL_DIR: &str = "local";
const ACCOUNT_NAME_FILE: &str = "account_name.txt";
const LANGUAGE_FILE: &str = "language.txt";
const SMART_STEAM_EMU_INI: &str = "SmartSteamEmu.ini";
const PERSONA_NAME_KEY: &str = "PersonaName";

/// What the one-shot launcher-setting step did for a game.
///
/// These flags are an independent, observable report of each file's fate rather
/// than a state machine, so a plain record of bools is the clearest shape here.
#[allow(clippy::struct_excessive_bools)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, serde::Serialize)]
pub struct LaunchSettingsOutcome {
    /// The marker already existed, so nothing was searched or changed.
    pub already_applied: bool,
    /// An `account_name.txt` was found and overwritten with the username.
    pub account_name_written: bool,
    /// A `language.txt` was found and overwritten with the language.
    pub language_written: bool,
    /// A `SmartSteamEmu.ini` `PersonaName` line was found and rewritten.
    pub persona_name_written: bool,
}

/// Apply launcher settings once for `game_id`, then mark the attempt as done.
///
/// If the per-game marker already exists this is a no-op returning
/// `already_applied = true`. Otherwise it searches `<game_root>/local/` for the
/// known setting files, stamps `account_name` into the first `account_name.txt`
/// and first `SmartSteamEmu.ini` with a `PersonaName` line (preserving that
/// line's existing line ending) and `language` into the first `language.txt`,
/// and — whatever was or was not found — records the marker so the step never
/// runs again for this game.
pub async fn apply_launch_settings_once(
    state_dir: &Path,
    game_root: &Path,
    game_id: &str,
    account_name: Option<&str>,
    language: Option<&str>,
) -> eyre::Result<LaunchSettingsOutcome> {
    let marker = launch_settings_applied_path(state_dir, game_id);
    if tokio::fs::try_exists(&marker).await.unwrap_or(false) {
        return Ok(LaunchSettingsOutcome {
            already_applied: true,
            ..LaunchSettingsOutcome::default()
        });
    }

    let local_root = game_root.join(LOCAL_DIR);
    let outcome = LaunchSettingsOutcome {
        already_applied: false,
        account_name_written: overwrite_first_file(&local_root, ACCOUNT_NAME_FILE, account_name)
            .await?,
        language_written: overwrite_first_file(&local_root, LANGUAGE_FILE, language).await?,
        persona_name_written: rewrite_first_persona_name(&local_root, account_name).await?,
    };

    mark_applied(&marker).await?;
    Ok(outcome)
}

/// Overwrite the first file named `file_name` under `root` with `value`.
///
/// Returns `false` without touching anything when `value` is `None` or no such
/// file exists.
async fn overwrite_first_file(
    root: &Path,
    file_name: &str,
    value: Option<&str>,
) -> eyre::Result<bool> {
    let Some(value) = value else {
        return Ok(false);
    };
    let Some(path) = find_first_file(root, file_name).await? else {
        return Ok(false);
    };

    tokio::fs::write(&path, value)
        .await
        .wrap_err_with(|| format!("failed to write {}", path.display()))?;
    Ok(true)
}

/// Rewrite the first `PersonaName` line found in any `SmartSteamEmu.ini` under `root`.
async fn rewrite_first_persona_name(root: &Path, persona_name: Option<&str>) -> eyre::Result<bool> {
    let Some(persona_name) = persona_name else {
        return Ok(false);
    };

    for path in find_files(root, SMART_STEAM_EMU_INI).await? {
        let content = tokio::fs::read_to_string(&path)
            .await
            .wrap_err_with(|| format!("failed to read {}", path.display()))?;
        let Some(rewritten) = rewrite_persona_name_content(&content, persona_name) else {
            continue;
        };

        tokio::fs::write(&path, rewritten)
            .await
            .wrap_err_with(|| format!("failed to write {}", path.display()))?;
        return Ok(true);
    }

    Ok(false)
}

/// Find the first regular file named `file_name` anywhere under `root`.
///
/// A missing `root` (for example an uninstalled game with no `local/`) yields
/// `None`. Directories are visited in sorted order for deterministic results.
async fn find_first_file(root: &Path, file_name: &str) -> eyre::Result<Option<PathBuf>> {
    let mut pending_dirs = vec![root.to_path_buf()];
    while let Some(dir) = pending_dirs.pop() {
        let mut entries = match tokio::fs::read_dir(&dir).await {
            Ok(entries) => entries,
            Err(err) if err.kind() == ErrorKind::NotFound => continue,
            Err(err) => {
                return Err(err).wrap_err_with(|| format!("failed to read {}", dir.display()));
            }
        };

        let mut child_dirs = Vec::new();
        while let Some(entry) = entries.next_entry().await? {
            let file_type = entry.file_type().await?;
            let path = entry.path();
            if file_type.is_dir() {
                child_dirs.push(path);
            } else if file_type.is_file() && entry.file_name() == OsStr::new(file_name) {
                return Ok(Some(path));
            }
        }

        child_dirs.sort();
        child_dirs.reverse();
        pending_dirs.extend(child_dirs);
    }

    Ok(None)
}

/// Find every regular file named `file_name` anywhere under `root`.
///
/// A missing `root` yields an empty list. Directories are visited in sorted
/// order for deterministic results.
async fn find_files(root: &Path, file_name: &str) -> eyre::Result<Vec<PathBuf>> {
    let mut matches = Vec::new();
    let mut pending_dirs = vec![root.to_path_buf()];
    while let Some(dir) = pending_dirs.pop() {
        let mut entries = match tokio::fs::read_dir(&dir).await {
            Ok(entries) => entries,
            Err(err) if err.kind() == ErrorKind::NotFound => continue,
            Err(err) => {
                return Err(err).wrap_err_with(|| format!("failed to read {}", dir.display()));
            }
        };

        let mut child_dirs = Vec::new();
        while let Some(entry) = entries.next_entry().await? {
            let file_type = entry.file_type().await?;
            let path = entry.path();
            if file_type.is_dir() {
                child_dirs.push(path);
            } else if file_type.is_file() && entry.file_name() == OsStr::new(file_name) {
                matches.push(path);
            }
        }

        child_dirs.sort();
        child_dirs.reverse();
        pending_dirs.extend(child_dirs);
    }

    Ok(matches)
}

/// Rewrite the first `PersonaName` line in `content`, preserving its line ending.
///
/// Returns `None` when no matching line exists, so the caller can skip writing.
fn rewrite_persona_name_content(content: &str, persona_name: &str) -> Option<String> {
    let mut output = String::with_capacity(content.len() + persona_name.len());
    let mut replaced = false;
    for segment in content.split_inclusive('\n') {
        if replaced {
            output.push_str(segment);
            continue;
        }

        let (body, ending) = split_trailing_newline(segment);
        if let Some(new_body) = rewrite_persona_line(body, persona_name) {
            output.push_str(&new_body);
            output.push_str(ending);
            replaced = true;
        } else {
            output.push_str(segment);
        }
    }

    replaced.then_some(output)
}

/// Split a `split_inclusive('\n')` segment into its body and trailing newline.
fn split_trailing_newline(segment: &str) -> (&str, &str) {
    if let Some(body) = segment.strip_suffix("\r\n") {
        (body, "\r\n")
    } else if let Some(body) = segment.strip_suffix('\n') {
        (body, "\n")
    } else {
        (segment, "")
    }
}

/// Rewrite a single line matching `^\s*PersonaName\s*=\s*...` to use `persona_name`.
///
/// Leading whitespace and the spacing around `=` are preserved; everything after
/// the separator's trailing whitespace is replaced with `persona_name`.
fn rewrite_persona_line(line: &str, persona_name: &str) -> Option<String> {
    let leading_len = line.len() - line.trim_start().len();
    let (leading, rest) = line.split_at(leading_len);

    let rest = rest.strip_prefix(PERSONA_NAME_KEY)?;
    let mid_len = rest.len() - rest.trim_start().len();
    let (mid_ws, after_mid) = rest.split_at(mid_len);

    let after_eq = after_mid.strip_prefix('=')?;
    let post_len = after_eq.len() - after_eq.trim_start().len();
    let post_ws = &after_eq[..post_len];

    Some(format!(
        "{leading}{PERSONA_NAME_KEY}{mid_ws}={post_ws}{persona_name}"
    ))
}

async fn mark_applied(marker: &Path) -> eyre::Result<()> {
    if let Some(parent) = marker.parent() {
        tokio::fs::create_dir_all(parent)
            .await
            .wrap_err_with(|| format!("failed to create {}", parent.display()))?;
    }
    tokio::fs::write(marker, [])
        .await
        .wrap_err_with(|| format!("failed to write {}", marker.display()))?;
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::test_support::TempDir;

    #[test]
    fn rewrites_simple_line_and_preserves_unix_ending() {
        let content = "[User]\nPersonaName = stubname\nLanguage = english\n";
        let rewritten =
            rewrite_persona_name_content(content, "realuser").expect("line should be rewritten");
        assert_eq!(
            rewritten,
            "[User]\nPersonaName = realuser\nLanguage = english\n"
        );
    }

    #[test]
    fn preserves_crlf_line_ending() {
        let content = "[User]\r\nPersonaName = stubname\r\nLanguage = english\r\n";
        let rewritten =
            rewrite_persona_name_content(content, "realuser").expect("line should be rewritten");
        assert_eq!(
            rewritten,
            "[User]\r\nPersonaName = realuser\r\nLanguage = english\r\n"
        );
    }

    #[test]
    fn preserves_leading_whitespace_and_separator_spacing() {
        let content = "\tPersonaName=stubname\n";
        let rewritten =
            rewrite_persona_name_content(content, "realuser").expect("line should be rewritten");
        assert_eq!(rewritten, "\tPersonaName=realuser\n");
    }

    #[test]
    fn rewrites_final_line_without_trailing_newline() {
        let content = "PersonaName = stubname";
        let rewritten =
            rewrite_persona_name_content(content, "realuser").expect("line should be rewritten");
        assert_eq!(rewritten, "PersonaName = realuser");
    }

    #[test]
    fn ignores_similar_keys() {
        assert!(rewrite_persona_line("PersonaNameExtra = x", "realuser").is_none());
        assert!(rewrite_persona_line("MyPersonaName = x", "realuser").is_none());
        assert!(rewrite_persona_line("PersonaName foo", "realuser").is_none());
    }

    #[test]
    fn returns_none_when_no_persona_line() {
        let content = "[User]\nLanguage = english\n";
        assert!(rewrite_persona_name_content(content, "realuser").is_none());
    }

    #[tokio::test]
    async fn applies_username_to_both_files_then_marks_done() {
        let state = TempDir::new("lanspread-launch-state");
        let game = TempDir::new("lanspread-launch-game");
        let root = game.path();
        let account = root.join(LOCAL_DIR).join("profile").join(ACCOUNT_NAME_FILE);
        let ini = root
            .join(LOCAL_DIR)
            .join("config")
            .join("emu")
            .join(SMART_STEAM_EMU_INI);
        let language = root.join(LOCAL_DIR).join(LANGUAGE_FILE);
        write_file(&account, b"stubname");
        write_file(&ini, b"[User]\r\nPersonaName = stubname\r\n");
        write_file(&language, b"english");

        let outcome = apply_launch_settings_once(
            state.path(),
            root,
            "game",
            Some("realuser"),
            Some("german"),
        )
        .await
        .expect("apply should succeed");

        assert_eq!(
            outcome,
            LaunchSettingsOutcome {
                already_applied: false,
                account_name_written: true,
                language_written: true,
                persona_name_written: true,
            }
        );
        assert_eq!(
            std::fs::read_to_string(&account).expect("account file should be readable"),
            "realuser"
        );
        assert_eq!(
            std::fs::read_to_string(&ini).expect("ini should be readable"),
            "[User]\r\nPersonaName = realuser\r\n"
        );
        assert_eq!(
            std::fs::read_to_string(&language).expect("language file should be readable"),
            "german"
        );
        assert!(launch_settings_applied_path(state.path(), "game").is_file());
    }

    #[tokio::test]
    async fn is_noop_once_marker_exists() {
        let state = TempDir::new("lanspread-launch-state");
        let game = TempDir::new("lanspread-launch-game");
        let root = game.path();
        let ini = root.join(LOCAL_DIR).join(SMART_STEAM_EMU_INI);
        write_file(&ini, b"PersonaName = stubname\n");

        let first = apply_launch_settings_once(state.path(), root, "game", Some("realuser"), None)
            .await
            .expect("first apply should succeed");
        assert!(first.persona_name_written);
        assert!(!first.already_applied);

        // Externally reset the value; a second apply must not touch it again.
        write_file(&ini, b"PersonaName = stubname\n");
        let second = apply_launch_settings_once(state.path(), root, "game", Some("realuser"), None)
            .await
            .expect("second apply should succeed");

        assert!(second.already_applied);
        assert!(!second.persona_name_written);
        assert_eq!(
            std::fs::read_to_string(&ini).expect("ini should be readable"),
            "PersonaName = stubname\n"
        );
    }

    #[tokio::test]
    async fn marks_done_even_when_nothing_found() {
        let state = TempDir::new("lanspread-launch-state");
        let game = TempDir::new("lanspread-launch-game");
        let root = game.path();
        write_file(
            &root.join(LOCAL_DIR).join("readme.txt"),
            b"no settings here",
        );

        let outcome = apply_launch_settings_once(
            state.path(),
            root,
            "game",
            Some("realuser"),
            Some("german"),
        )
        .await
        .expect("apply should succeed");

        assert_eq!(outcome, LaunchSettingsOutcome::default());
        assert!(launch_settings_applied_path(state.path(), "game").is_file());
    }

    #[tokio::test]
    async fn marks_done_when_local_missing() {
        let state = TempDir::new("lanspread-launch-state");
        let game = TempDir::new("lanspread-launch-game");

        let outcome = apply_launch_settings_once(
            state.path(),
            game.path(),
            "game",
            Some("realuser"),
            Some("german"),
        )
        .await
        .expect("apply should succeed");

        assert_eq!(outcome, LaunchSettingsOutcome::default());
        assert!(launch_settings_applied_path(state.path(), "game").is_file());
    }

    #[tokio::test]
    async fn overwrites_first_account_file_in_sorted_order() {
        let state = TempDir::new("lanspread-launch-state");
        let game = TempDir::new("lanspread-launch-game");
        let root = game.path();
        let first = root.join(LOCAL_DIR).join("a").join(ACCOUNT_NAME_FILE);
        let second = root.join(LOCAL_DIR).join("z").join(ACCOUNT_NAME_FILE);
        write_file(&first, b"old-a");
        write_file(&second, b"old-z");

        apply_launch_settings_once(state.path(), root, "game", Some("realuser"), None)
            .await
            .expect("apply should succeed");

        assert_eq!(
            std::fs::read_to_string(&first).expect("first account file should be readable"),
            "realuser"
        );
        assert_eq!(
            std::fs::read_to_string(&second).expect("second account file should be readable"),
            "old-z"
        );
    }

    #[tokio::test]
    async fn searches_past_ini_files_without_persona_name() {
        let state = TempDir::new("lanspread-launch-state");
        let game = TempDir::new("lanspread-launch-game");
        let root = game.path();
        let first = root.join(LOCAL_DIR).join("a").join(SMART_STEAM_EMU_INI);
        let second = root.join(LOCAL_DIR).join("b").join(SMART_STEAM_EMU_INI);
        write_file(&first, b"[User]\nLanguage = english\n");
        write_file(&second, b"PersonaName = stubname\n");

        let outcome =
            apply_launch_settings_once(state.path(), root, "game", Some("realuser"), None)
                .await
                .expect("apply should succeed");

        assert!(outcome.persona_name_written);
        assert_eq!(
            std::fs::read_to_string(&first).expect("first ini should be readable"),
            "[User]\nLanguage = english\n"
        );
        assert_eq!(
            std::fs::read_to_string(&second).expect("second ini should be readable"),
            "PersonaName = realuser\n"
        );
        assert!(launch_settings_applied_path(state.path(), "game").is_file());
    }

    fn write_file(path: &Path, bytes: &[u8]) {
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent).expect("parent dir should be created");
        }
        std::fs::write(path, bytes).expect("file should be written");
    }
}