//! The document: rope, associated path, encoding state, selection, history.
//!
//! **This is the only module that touches `ropey` types directly** as an owner.
//! Confining the dependency here is the mitigation recorded in MJB-DR-006 for
//! depending on a pre-release rope crate under DAL-C.

use std::path::{Path, PathBuf};

use ropey::{Rope, RopeSlice};

use super::{
    LINE_TYPE,
    encoding::{self, DecodeError, EncodingInfo},
    history::History,
    line_ending::{self, LineEnding},
    save::{self, SaveError},
    selection::{Range, Selection},
    transaction::{ChangeError, Transaction},
};

#[derive(Debug, thiserror::Error)]
pub enum DocumentError {
    #[error("{0}")]
    Change(#[from] ChangeError),
    #[error("{0}")]
    Save(#[from] SaveError),
    // MJB-LLR-118: opening a file mojibake cannot decode is a reportable
    // failure, not something to paper over.
    #[error("{0}")]
    Decode(#[from] DecodeError),
    #[error("io error: {0}")]
    Io(#[from] std::io::Error),
}

#[derive(Debug)]
pub struct Document {
    text: Rope,
    path: Option<PathBuf>,
    encoding: EncodingInfo,
    line_ending: LineEnding,
    selection: Selection,
    history: History,
    /// The history revision the file on disk corresponds to.
    ///
    /// `modified` is derived from this rather than latched to a bool, so
    /// undoing back to the last-saved state correctly reports the buffer as
    /// clean. A latched flag would keep claiming unsaved changes for a buffer
    /// byte-identical to its file. (MJB-LLR-116)
    saved_revision: usize,
}

impl Default for Document {
    fn default() -> Self {
        Self::empty(None)
    }
}

impl Document {
    pub fn empty(path: Option<PathBuf>) -> Self {
        Self {
            text: Rope::new(),
            path,
            encoding: EncodingInfo::default(),
            line_ending: LineEnding::platform_default(),
            selection: Selection::point(0),
            history: History::new(),
            saved_revision: 0,
        }
    }

    /// MJB-LLR-111, MJB-LLR-112: load `path`.
    ///
    /// A path that does not exist yields an empty buffer that remembers it, so
    /// `:w` creates the file. Any other IO error is reported.
    pub fn open(path: &Path) -> Result<Self, DocumentError> {
        let bytes = match std::fs::read(path) {
            Ok(b) => b,
            // MJB-LLR-112
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
                return Ok(Self::empty(Some(path.to_path_buf())));
            }
            Err(e) => return Err(DocumentError::Io(e)),
        };

        // MJB-LLR-113, MJB-LLR-118: a declared encoding is transcoded; invalid
        // UTF-8 is rejected here rather than opened and later written back
        // with the damage baked in.
        let (text, encoding) = encoding::decode(&bytes)?;
        // MJB-LLR-114 is evaluated on the raw text, before normalisation
        // collapses CRLF and would erase the evidence.
        let line_ending = LineEnding::detect(&text);
        let normalized = line_ending::normalize(&text);

        Ok(Self {
            text: Rope::from_str(&normalized),
            path: Some(path.to_path_buf()),
            encoding,
            line_ending,
            selection: Selection::point(0),
            history: History::new(),
            saved_revision: 0,
        })
    }

    pub fn text(&self) -> &Rope {
        &self.text
    }

    pub fn slice(&self) -> RopeSlice<'_> {
        self.text.slice(..)
    }

    pub fn path(&self) -> Option<&Path> {
        self.path.as_deref()
    }

    pub fn set_path(&mut self, path: PathBuf) {
        self.path = Some(path);
    }

    pub fn selection(&self) -> &Selection {
        &self.selection
    }

    pub fn set_selection(&mut self, selection: Selection) {
        self.selection = selection.clamped(self.text.slice(..));
    }

    /// Convenience: replace the primary range.
    pub fn set_range(&mut self, range: Range) {
        let clamped = range.clamped(self.text.slice(..));
        self.selection.set_primary(clamped);
    }

    pub fn range(&self) -> Range {
        self.selection.primary()
    }

    /// MJB-LLR-116: whether the buffer differs from the file on disk.
    ///
    /// Derived by comparing the current history revision against the one the
    /// file was written at, so undoing back to the saved state reports clean.
    pub fn is_modified(&self) -> bool {
        self.history.revision() != self.saved_revision
    }

    pub fn line_ending(&self) -> LineEnding {
        self.line_ending
    }

    pub fn len_lines(&self) -> usize {
        self.text.len_lines(LINE_TYPE)
    }

    pub fn history_mut(&mut self) -> &mut History {
        &mut self.history
    }

    /// MJB-LLR-117: apply `transaction`, recording its inverse for undo.
    pub fn apply(&mut self, transaction: &Transaction) -> Result<(), DocumentError> {
        // The inverse must be computed against the pre-change rope.
        let inverse = Transaction::new(transaction.changes.invert(&self.text));

        transaction.changes.apply(&mut self.text)?;

        if let Some(sel) = &transaction.selection {
            self.selection = sel.clone().clamped(self.text.slice(..));
        } else {
            self.selection = self.selection.clone().clamped(self.text.slice(..));
        }

        self.history.commit(transaction.clone(), inverse);
        Ok(())
    }

    /// Apply without recording history — used to replay an undo or redo, whose
    /// own bookkeeping is already handled by [`History`].
    fn apply_without_history(&mut self, transaction: &Transaction) -> Result<(), DocumentError> {
        transaction.changes.apply(&mut self.text)?;
        if let Some(sel) = &transaction.selection {
            self.selection = sel.clone().clamped(self.text.slice(..));
        } else {
            self.selection = self.selection.clone().clamped(self.text.slice(..));
        }
        Ok(())
    }

    /// MJB-LLR-052: revert the most recent change. `false` if there was none.
    pub fn undo(&mut self) -> Result<bool, DocumentError> {
        let Some(t) = self.history.undo().cloned() else {
            return Ok(false);
        };
        self.apply_without_history(&t)?;
        Ok(true)
    }

    /// MJB-LLR-053: reapply the most recently reverted change.
    pub fn redo(&mut self) -> Result<bool, DocumentError> {
        let Some(t) = self.history.redo().cloned() else {
            return Ok(false);
        };
        self.apply_without_history(&t)?;
        Ok(true)
    }

    /// MJB-LLR-115: the document as it should appear on disk.
    ///
    /// Assembles the text once. Chaining `to_string` → `with_final_newline` →
    /// `apply` → `encode` would copy the whole document at each step; the
    /// terminator rewrite and the final newline are folded into a single pass
    /// so only the encode step copies, and only when the encoding is not the
    /// UTF-8 the rope already holds.
    pub fn encode(&self, insert_final_newline: bool) -> Vec<u8> {
        let ending = self.line_ending.as_str();
        let needs_rewrite = self.line_ending != LineEnding::Lf;

        let mut text = String::with_capacity(self.text.len() + 1);
        for chunk in self.text.chunks() {
            if needs_rewrite {
                // The rope stores LF only, so a plain split is sufficient.
                let mut parts = chunk.split('\n');
                if let Some(first) = parts.next() {
                    text.push_str(first);
                }
                for part in parts {
                    text.push_str(ending);
                    text.push_str(part);
                }
            } else {
                text.push_str(chunk);
            }
        }

        if insert_final_newline && !text.is_empty() && !text.ends_with(ending) {
            text.push_str(ending);
        }

        encoding::encode(&text, self.encoding)
    }

    /// MJB-LLR-137: write to the associated path and mark it clean.
    pub fn save(&mut self, force: bool, insert_final_newline: bool) -> Result<(), DocumentError> {
        let path = self.path.clone().ok_or(SaveError::NoPath)?;
        let bytes = self.encode(insert_final_newline);
        save::write_atomic(&path, &bytes, force)?;
        self.saved_revision = self.history.revision();
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::buffer::selection::Range;

    fn doc(text: &str) -> Document {
        let mut d = Document::empty(None);
        d.text = Rope::from_str(text);
        d
    }

    #[test]
    fn mjb_llr_112_missing_file_yields_empty_buffer_that_remembers_the_path() {
        let d = tempfile::tempdir().unwrap();
        let p = d.path().join("not-created-yet.txt");
        let doc = Document::open(&p).unwrap();
        assert_eq!(doc.text().len(), 0);
        assert_eq!(doc.path(), Some(p.as_path()));
        assert!(!doc.is_modified());
    }

    #[test]
    fn mjb_llr_111_loads_contents() {
        let d = tempfile::tempdir().unwrap();
        let p = d.path().join("f.txt");
        std::fs::write(&p, "hello\nworld\n").unwrap();
        let doc = Document::open(&p).unwrap();
        assert_eq!(doc.text().to_string(), "hello\nworld\n");
    }

    #[test]
    fn mjb_llr_114_crlf_is_detected_and_normalized_for_storage() {
        let d = tempfile::tempdir().unwrap();
        let p = d.path().join("crlf.txt");
        std::fs::write(&p, "a\r\nb\r\n").unwrap();

        let doc = Document::open(&p).unwrap();
        assert_eq!(doc.line_ending(), LineEnding::Crlf);
        assert_eq!(doc.text().to_string(), "a\nb\n", "stored as LF");
    }

    /// MJB-LLR-115, MJB-HLR-003: a CRLF file saved back is still CRLF.
    #[test]
    fn mjb_llr_115_crlf_round_trips_through_save() {
        let d = tempfile::tempdir().unwrap();
        let p = d.path().join("crlf.txt");
        std::fs::write(&p, "a\r\nb\r\n").unwrap();

        let mut doc = Document::open(&p).unwrap();
        doc.save(false, true).unwrap();
        assert_eq!(std::fs::read(&p).unwrap(), b"a\r\nb\r\n");
    }

    /// MJB-LLR-118: a file that is not valid UTF-8 is refused, and the file on
    /// disk is left exactly as it was.
    #[test]
    fn mjb_llr_118_invalid_utf8_file_is_refused() {
        let d = tempfile::tempdir().unwrap();
        let p = d.path().join("bad.bin");
        let original = [b'a', 0xFF, b'b'];
        std::fs::write(&p, original).unwrap();

        let err = Document::open(&p).expect_err("must refuse to open");
        assert!(matches!(err, DocumentError::Decode(_)), "got {err:?}");
        assert!(
            err.to_string().contains("UTF-8"),
            "message must explain why, got: {err}"
        );
        assert_eq!(
            std::fs::read(&p).unwrap(),
            original,
            "a refused open must not touch the file"
        );
    }

    /// MJB-LLR-113: a BOM-declared non-UTF-8 file still opens.
    #[test]
    fn mjb_llr_113_declared_utf16_file_opens() {
        let d = tempfile::tempdir().unwrap();
        let p = d.path().join("u16.txt");
        // UTF-16LE BOM + "hi".
        std::fs::write(&p, [0xFF, 0xFE, b'h', 0x00, b'i', 0x00]).unwrap();

        let doc = Document::open(&p).expect("a declared encoding must open");
        assert_eq!(doc.text().to_string(), "hi");
    }

    #[test]
    fn mjb_llr_116_modified_flag_lifecycle() {
        let d = tempfile::tempdir().unwrap();
        let p = d.path().join("f.txt");
        std::fs::write(&p, "abc").unwrap();

        let mut doc = Document::open(&p).unwrap();
        assert!(!doc.is_modified(), "freshly opened");

        let t = Transaction::insert(doc.text(), doc.selection(), "X");
        doc.apply(&t).unwrap();
        assert!(doc.is_modified(), "set by an applied transaction");

        doc.save(false, false).unwrap();
        assert!(!doc.is_modified(), "cleared by a successful write");
    }

    /// MJB-LLR-137: a successful write clears `modified`; a failed one must
    /// not, or the user would be told their unsaved work is safe.
    #[test]
    fn mjb_llr_137_failed_write_leaves_modified_set() {
        let mut doc = doc("content");
        // No path: the save cannot succeed.
        let t = Transaction::insert(doc.text(), doc.selection(), "X");
        doc.apply(&t).unwrap();
        assert!(doc.is_modified());

        assert!(doc.save(false, true).is_err());
        assert!(
            doc.is_modified(),
            "a failed write must not clear the modified flag"
        );
    }

    /// MJB-LLR-116: undoing back to the saved state reports the buffer clean.
    /// A latched flag would keep claiming unsaved changes for content that is
    /// byte-identical to the file.
    #[test]
    fn mjb_llr_116_undo_back_to_saved_state_is_clean() {
        let d = tempfile::tempdir().unwrap();
        let p = d.path().join("f.txt");
        std::fs::write(&p, "abc").unwrap();
        let mut doc = Document::open(&p).unwrap();

        doc.save(false, false).unwrap();
        assert!(!doc.is_modified());

        let t = Transaction::insert(doc.text(), doc.selection(), "X");
        doc.apply(&t).unwrap();
        assert!(doc.is_modified(), "an edit dirties the buffer");

        doc.undo().unwrap();
        assert!(
            !doc.is_modified(),
            "undoing back to the saved content must report clean"
        );

        doc.redo().unwrap();
        assert!(doc.is_modified(), "redoing dirties it again");
    }

    /// MJB-LLR-116: same history depth, different content, must stay dirty.
    #[test]
    fn mjb_llr_116_divergent_edit_at_the_same_depth_stays_modified() {
        let d = tempfile::tempdir().unwrap();
        let p = d.path().join("f.txt");
        std::fs::write(&p, "abc").unwrap();
        let mut doc = Document::open(&p).unwrap();

        let t = Transaction::insert(doc.text(), doc.selection(), "X");
        doc.apply(&t).unwrap();
        doc.save(false, false).unwrap();
        assert!(!doc.is_modified());

        doc.undo().unwrap();
        // A *different* edit, returning to the same history depth.
        let t = Transaction::insert(doc.text(), doc.selection(), "Y");
        doc.apply(&t).unwrap();

        assert!(
            doc.is_modified(),
            "content differs from the file despite equal history depth"
        );
        assert_eq!(doc.text().to_string(), "Yabc");
    }

    #[test]
    fn mjb_llr_137_successful_write_clears_modified() {
        let d = tempfile::tempdir().unwrap();
        let p = d.path().join("f.txt");
        let mut doc = Document::open(&p).unwrap();

        let t = Transaction::insert(doc.text(), doc.selection(), "hello");
        doc.apply(&t).unwrap();
        assert!(doc.is_modified());

        doc.save(false, true).unwrap();
        assert!(!doc.is_modified());
        assert_eq!(std::fs::read_to_string(&p).unwrap(), "hello\n");
    }

    #[test]
    fn mjb_llr_117_apply_updates_text_and_records_history() {
        let mut doc = doc("hello");
        let t = Transaction::change(doc.text(), [(0, 5, Some("goodbye".into()))]);
        doc.apply(&t).unwrap();
        assert_eq!(doc.text().to_string(), "goodbye");
        assert!(doc.history.can_undo());
    }

    #[test]
    fn mjb_llr_052_undo_restores_previous_text() {
        let mut doc = doc("hello");
        let t = Transaction::change(doc.text(), [(0, 5, Some("goodbye".into()))]);
        doc.apply(&t).unwrap();

        assert!(doc.undo().unwrap());
        assert_eq!(doc.text().to_string(), "hello");
    }

    #[test]
    fn mjb_llr_053_redo_reapplies() {
        let mut doc = doc("hello");
        let t = Transaction::change(doc.text(), [(0, 5, Some("goodbye".into()))]);
        doc.apply(&t).unwrap();
        doc.undo().unwrap();

        assert!(doc.redo().unwrap());
        assert_eq!(doc.text().to_string(), "goodbye");
    }

    /// MJB-LLR-052: undoing past the start is a no-op, not an error.
    #[test]
    fn mjb_llr_052_undo_past_history_start_is_a_noop() {
        let mut doc = doc("hello");
        assert!(!doc.undo().unwrap(), "nothing to undo");
        assert_eq!(doc.text().to_string(), "hello");
        assert!(!doc.undo().unwrap(), "still nothing, still safe");
    }

    #[test]
    fn mjb_llr_053_redo_past_end_is_a_noop() {
        let mut doc = doc("hello");
        assert!(!doc.redo().unwrap());
        assert_eq!(doc.text().to_string(), "hello");
    }

    #[test]
    fn multiple_undo_redo_cycles_are_stable() {
        let mut doc = doc("");
        for c in ["a", "b", "c"] {
            let t = Transaction::insert(doc.text(), doc.selection(), c);
            doc.apply(&t).unwrap();
            let end = doc.text().len();
            doc.set_range(Range::point(end));
        }
        assert_eq!(doc.text().to_string(), "abc");

        for _ in 0..3 {
            assert!(doc.undo().unwrap());
        }
        assert_eq!(doc.text().to_string(), "");

        for _ in 0..3 {
            assert!(doc.redo().unwrap());
        }
        assert_eq!(doc.text().to_string(), "abc");
    }

    #[test]
    fn mjb_llr_185_final_newline_added_on_encode_when_requested() {
        let doc = doc("no trailing newline");
        assert!(doc.encode(true).ends_with(b"\n"));
        assert!(!doc.encode(false).ends_with(b"\n"));
    }

    #[test]
    fn mjb_llr_185_empty_document_encodes_empty() {
        let doc = doc("");
        assert!(doc.encode(true).is_empty(), "must not invent a newline");
    }

    #[test]
    fn saving_without_a_path_is_an_error_not_a_panic() {
        let mut doc = doc("x");
        assert!(doc.save(false, true).is_err());
    }
}