// SPDX-License-Identifier: GPL-3.0-or-later
// src/document/manager.rs
//
// Document Manager – single entry point via DocumentCommand.

use crate::document::loader::{load_document, scan_directory_into};
use crate::document::session::{SessionData, SessionKind};
use crate::document::store;
use crate::document::DocumentContent;
use crate::error::Error;
use log::warn;
use std::path::{Path, PathBuf};

#[allow(dead_code)]
#[derive(Debug)]
pub enum DocumentState {
    Empty,
    Loading,
    Loaded(DocumentContent),
    Error(Error),
}

/// All actions the UI can request from the manager.
/// The manager executes; the UI decides.
#[derive(Debug)]
pub enum DocumentCommand {
    /// Create a new session. Does nothing if a session with that name already exists.
    CreateSession {
        name: String,
        kind: SessionKind,
        path: Option<PathBuf>,
    },
    /// Scan a directory into an existing session, replacing its current items.
    ScanDirectory { session: String, dir: PathBuf },
    /// Load a file and make it the active item in the given session.
    AddFileToSession { session: String, path: PathBuf },
    /// Set the active session by name.
    SetActive(String),
    /// Open a session file (.ron): loads all sessions and activates the DirectoryBrowser.
    OpenSession(PathBuf),
    /// Navigate to the next item in the active session.
    NavigateNext,
    /// Navigate to the previous item in the active session.
    NavigatePrevious,
    /// Select a specific item by index in the active session.
    SelectItem(usize),
    /// Copy an item from one session to another.
    CopyItemToSession {
        source_session: String,
        target_session: String,
        source_item_index: usize,
        target_item_index: Option<usize>,
    },
    /// Delete an item from a session.
    DeleteItemFromSession {
        session: String,
        item_index: Option<usize>,
    },
}

pub struct DocumentManager {
    sessions: Vec<SessionData>,
    pub active_session_name: Option<String>,
    pub state: DocumentState,
}

impl Default for DocumentManager {
    fn default() -> Self {
        Self {
            sessions: Vec::new(),
            active_session_name: None,
            state: DocumentState::Empty,
        }
    }
}

impl DocumentManager {
    pub fn new() -> Self {
        Self::default()
    }

    /// The single public entry point for all state changes.
    pub fn handle(&mut self, command: DocumentCommand) {
        match command {
            DocumentCommand::CreateSession { name, kind, path } => {
                if self.session(&name).is_none() {
                    self.sessions
                        .push(SessionData::new(&name, kind, path, Vec::new()));
                }
            }

            DocumentCommand::ScanDirectory { session, dir } => {
                if let Some(s) = self.session_mut(&session) {
                    scan_directory_into(s, &dir);
                }
            }

            DocumentCommand::AddFileToSession { session, path } => {
                self.active_session_name = Some(session);
                self.load_file(&path);
            }

            DocumentCommand::SetActive(name) => {
                if self.session(&name).is_some() {
                    self.active_session_name = Some(name);
                }
            }

            DocumentCommand::OpenSession(path) => {
                self.load_all_sessions(&path);
            }

            DocumentCommand::NavigateNext => self.next(),
            DocumentCommand::NavigatePrevious => self.previous(),
            DocumentCommand::SelectItem(index) => self.select_item(index),

            DocumentCommand::CopyItemToSession {
                source_session,
                target_session,
                source_item_index,
                target_item_index,
            } => {
                self.copy_item_to_session(
                    &source_session,
                    &target_session,
                    source_item_index,
                    target_item_index,
                );
            }

            DocumentCommand::DeleteItemFromSession {
                session,
                item_index,
            } => {
                self.delete_item_from_session(&session, item_index);
            }
        }
    }

    /// Read-only access to a session by name.
    pub fn session(&self, name: &str) -> Option<&SessionData> {
        self.sessions.iter().find(|s| s.name == name)
    }

    // Mutable access to a session by name.
    fn session_mut(&mut self, name: &str) -> Option<&mut SessionData> {
        self.sessions.iter_mut().find(|s| s.name == name)
    }

    // Mutable access to the currently active session.
    // The name is cloned to satisfy the borrow checker – it is a cheap String copy.
    fn active_session_mut(&mut self) -> Option<&mut SessionData> {
        let name = self.active_session_name.clone()?;
        self.sessions.iter_mut().find(|s| s.name == name)
    }

    // Loads all sessions from a RON file and activates the DirectoryBrowser.
    fn load_all_sessions(&mut self, path: &Path) {
        match store::load_sessions(path) {
            Ok(mut loaded) => {
                // Re-scan every DirectoryBrowser's source directory on load.
                // Validate every DocumentCollection: remove items whose files no longer exist.
                for session in loaded.iter_mut() {
                    match session.kind {
                        SessionKind::DirectoryBrowser => {
                            if let Some(dir) = session.path.clone() {
                                scan_directory_into(session, &dir);
                            }
                        }
                        SessionKind::DocumentCollection => {
                            session.items.retain(|item| {
                                if item.path.exists() {
                                    true
                                } else {
                                    warn!(
                                        "Session '{}': {}",
                                        session.name,
                                        Error::NotFound(item.path.display().to_string())
                                    );
                                    false
                                }
                            });

                            // Reset index if it pointed to a now-removed item.
                            session.current_index = match session.current_index {
                                Some(i) if i < session.items.len() => Some(i),
                                _ if !session.items.is_empty() => Some(0),
                                _ => None,
                            };
                        }
                    }
                }

                // Activate the DirectoryBrowser as the default entry point.
                let browser_name = loaded
                    .iter()
                    .find(|s| s.kind == SessionKind::DirectoryBrowser)
                    .map(|s| s.name.clone());

                self.sessions = loaded;
                self.active_session_name = browser_name;
                self.state = DocumentState::Empty;
            }
            Err(e) => {
                self.state = DocumentState::Error(e);
            }
        }
    }

    fn select_item(&mut self, index: usize) {
        if let Some(session) = self.active_session_mut() {
            if index < session.items.len() {
                session.current_index = Some(index);
            }
        }
    }

    fn next(&mut self) {
        if let Some(session) = self.active_session_mut() {
            if let Some(idx) = session.current_index {
                if idx + 1 < session.items.len() {
                    session.current_index = Some(idx + 1);
                }
            }
        }
    }

    fn previous(&mut self) {
        if let Some(session) = self.active_session_mut() {
            if let Some(idx) = session.current_index {
                if idx > 0 {
                    session.current_index = Some(idx - 1);
                }
            }
        }
    }

    fn load_file(&mut self, path: &Path) {
        self.state = DocumentState::Loading;

        match load_document(path) {
            Ok(content) => {
                // Align current_index to the loaded file's position in the session.
                if let Some(session) = self.active_session_mut() {
                    if let Some(idx) = session.items.iter().position(|item| item.path == path) {
                        session.current_index = Some(idx);
                    }
                }
                self.state = DocumentState::Loaded(content);
            }
            Err(e) => {
                self.state = DocumentState::Error(e);
            }
        }
    }

    fn copy_item_to_session(
        &mut self,
        source_session: &str,
        target_session: &str,
        source_item_index: usize,
        target_item_index: Option<usize>,
    ) {
        let source = match self.session(source_session) {
            Some(s) => s,
            None => {
                self.state = DocumentState::Error(Error::Session(format!(
                    "Session '{}' not found",
                    source_session
                )));
                return;
            }
        };

        let target = match self.session(target_session) {
            Some(s) => s,
            None => {
                self.state = DocumentState::Error(Error::Session(format!(
                    "Session '{}' not found",
                    target_session
                )));
                return;
            }
        };

        if target.kind != SessionKind::DocumentCollection {
            self.state = DocumentState::Error(Error::Session(
                "Target must be a DocumentCollection".to_string(),
            ));
            return;
        }

        let item = match source.items.get(source_item_index) {
            Some(item) => item.clone(),
            None => {
                return;
            }
        };

        if target
            .items
            .iter()
            .any(|i| i.path == item.path && i.page_index == item.page_index)
        {
            self.state = DocumentState::Error(Error::Session("Item already exists".to_string()));
            return;
        }

        let insert_index = match target_item_index {
            Some(idx) if idx <= target.items.len() => idx,
            _ => target.items.len(),
        };

        if let Some(target) = self.session_mut(target_session) {
            target.items.insert(insert_index, item);
        }
    }

    fn delete_item_from_session(&mut self, session: &str, item_index: Option<usize>) {
        let target = match self.session(session) {
            Some(s) => s,
            None => {
                self.state = DocumentState::Error(Error::Session(format!(
                    "Session '{}' not found",
                    session
                )));
                return;
            }
        };

        if target.kind != SessionKind::DocumentCollection {
            self.state = DocumentState::Error(Error::Session(
                "Session must be a DocumentCollection".to_string(),
            ));
            return;
        }

        let idx = match item_index {
            Some(i) => i,
            None => match target.current_index {
                Some(i) => i,
                None => return,
            },
        };

        if let Some(target) = self.session_mut(session) {
            if idx < target.items.len() {
                target.items.remove(idx);

                let new_len = target.items.len();
                if new_len == 0 {
                    target.current_index = None;
                } else if let Some(current) = target.current_index {
                    if current >= new_len {
                        target.current_index = Some(new_len - 1);
                    }
                }
            }
        }
    }
}