use futures::future::join_all;
use itertools::Itertools;
use language::language_settings::LanguageSettings;
use text::BufferId;
use ui::{Context, Window};

use crate::{Editor, LSP_REQUEST_DEBOUNCE_TIMEOUT};

impl Editor {
    pub(super) fn refresh_folding_ranges(
        &mut self,
        for_buffer: Option<BufferId>,
        _window: &Window,
        cx: &mut Context<Self>,
    ) {
        if !self.lsp_data_enabled() || !self.use_document_folding_ranges {
            return;
        }
        let Some(project) = self.project.clone() else {
            return;
        };

        let buffers_to_query = self
            .visible_buffers(cx)
            .into_iter()
            .filter(|buffer| self.is_lsp_relevant(buffer.read(cx).file(), cx))
            .chain(for_buffer.and_then(|id| self.buffer.read(cx).buffer(id)))
            .filter(|buffer| {
                let id = buffer.read(cx).remote_id();
                (for_buffer.is_none_or(|target| target == id))
                    && self.registered_buffers.contains_key(&id)
                    && LanguageSettings::for_buffer(buffer.read(cx), cx)
                        .document_folding_ranges
                        .enabled()
            })
            .unique_by(|buffer| buffer.read(cx).remote_id())
            .collect::<Vec<_>>();

        self.refresh_folding_ranges_task = cx.spawn(async move |editor, cx| {
            cx.background_executor()
                .timer(LSP_REQUEST_DEBOUNCE_TIMEOUT)
                .await;

            let Some(tasks) = editor
                .update(cx, |_, cx| {
                    project.read(cx).lsp_store().update(cx, |lsp_store, cx| {
                        buffers_to_query
                            .into_iter()
                            .map(|buffer| {
                                let buffer_id = buffer.read(cx).remote_id();
                                let task = lsp_store.fetch_folding_ranges(&buffer, cx);
                                async move { (buffer_id, task.await) }
                            })
                            .collect::<Vec<_>>()
                    })
                })
                .ok()
            else {
                return;
            };

            let results = join_all(tasks).await;
            if results.is_empty() {
                return;
            }

            editor
                .update(cx, |editor, cx| {
                    editor.display_map.update(cx, |display_map, cx| {
                        for (buffer_id, ranges) in results {
                            display_map.set_lsp_folding_ranges(buffer_id, ranges, cx);
                        }
                    });
                    cx.notify();
                })
                .ok();
        });
    }

    pub fn document_folding_ranges_enabled(&self, cx: &ui::App) -> bool {
        self.use_document_folding_ranges && self.display_map.read(cx).has_lsp_folding_ranges()
    }

    /// Removes LSP folding creases for buffers whose `lsp_folding_ranges`
    /// setting has been turned off, and triggers a refresh so newly-enabled
    /// buffers get their ranges fetched.
    pub(super) fn clear_disabled_lsp_folding_ranges(
        &mut self,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        if !self.use_document_folding_ranges {
            return;
        }

        let buffers_to_clear = self
            .buffer
            .read(cx)
            .all_buffers()
            .into_iter()
            .filter(|buffer| {
                let buffer = buffer.read(cx);
                !LanguageSettings::for_buffer(&buffer, cx)
                    .document_folding_ranges
                    .enabled()
            })
            .map(|buffer| buffer.read(cx).remote_id())
            .collect::<Vec<_>>();

        if !buffers_to_clear.is_empty() {
            self.display_map.update(cx, |display_map, cx| {
                for buffer_id in buffers_to_clear {
                    display_map.clear_lsp_folding_ranges(buffer_id, cx);
                }
            });
            cx.notify();
        }

        self.refresh_folding_ranges(None, window, cx);
    }
}

#[cfg(test)]
mod tests {
    use futures::StreamExt as _;
    use gpui::TestAppContext;
    use lsp::FoldingRange;
    use multi_buffer::MultiBufferRow;
    use pretty_assertions::assert_eq;
    use settings::DocumentFoldingRanges;

    use crate::{
        editor_tests::{init_test, update_test_language_settings},
        test::editor_lsp_test_context::EditorLspTestContext,
    };

    #[gpui::test]
    async fn test_lsp_folding_ranges_populates_creases(cx: &mut TestAppContext) {
        init_test(cx, |_| {});

        update_test_language_settings(cx, &|settings| {
            settings.defaults.document_folding_ranges = Some(DocumentFoldingRanges::On);
        });

        let mut cx = EditorLspTestContext::new_rust(
            lsp::ServerCapabilities {
                folding_range_provider: Some(lsp::FoldingRangeProviderCapability::Simple(true)),
                ..lsp::ServerCapabilities::default()
            },
            cx,
        )
        .await;

        let mut folding_request = cx
            .set_request_handler::<lsp::request::FoldingRangeRequest, _, _>(
                move |_, _, _| async move {
                    Ok(Some(vec![
                        FoldingRange {
                            start_line: 0,
                            start_character: Some(10),
                            end_line: 4,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: None,
                        },
                        FoldingRange {
                            start_line: 1,
                            start_character: Some(13),
                            end_line: 3,
                            end_character: Some(5),
                            kind: None,
                            collapsed_text: None,
                        },
                        FoldingRange {
                            start_line: 6,
                            start_character: Some(11),
                            end_line: 8,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: None,
                        },
                    ]))
                },
            );

        cx.set_state(
            "ˇfn main() {\n    if true {\n        println!(\"hello\");\n    }\n}\n\nfn other() {\n    let x = 1;\n}\n",
        );
        assert!(folding_request.next().await.is_some());
        cx.run_until_parked();

        cx.editor.read_with(&cx.cx.cx, |editor, cx| {
            assert!(
                editor.document_folding_ranges_enabled(cx),
                "Expected LSP folding ranges to be populated"
            );
        });

        cx.update_editor(|editor, _window, cx| {
            let snapshot = editor.display_snapshot(cx);
            assert!(
                !snapshot.is_line_folded(MultiBufferRow(0)),
                "Line 0 should not be folded before any fold action"
            );
            assert!(
                !snapshot.is_line_folded(MultiBufferRow(6)),
                "Line 6 should not be folded before any fold action"
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(0), window, cx);
        });

        cx.update_editor(|editor, _window, cx| {
            let snapshot = editor.display_snapshot(cx);
            assert!(
                snapshot.is_line_folded(MultiBufferRow(0)),
                "Line 0 should be folded after fold_at on an LSP crease"
            );
            assert_eq!(
                editor.display_text(cx),
                "fn main() ⋯\n\nfn other() {\n    let x = 1;\n}\n",
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(6), window, cx);
        });

        cx.update_editor(|editor, _window, cx| {
            let snapshot = editor.display_snapshot(cx);
            assert!(
                snapshot.is_line_folded(MultiBufferRow(6)),
                "Line 6 should be folded after fold_at on the second LSP crease"
            );
            assert_eq!(editor.display_text(cx), "fn main() ⋯\n\nfn other() ⋯\n",);
        });
    }

    #[gpui::test]
    async fn test_lsp_folding_ranges_disabled_by_default(cx: &mut TestAppContext) {
        init_test(cx, |_| {});

        let mut cx = EditorLspTestContext::new_rust(
            lsp::ServerCapabilities {
                folding_range_provider: Some(lsp::FoldingRangeProviderCapability::Simple(true)),
                ..lsp::ServerCapabilities::default()
            },
            cx,
        )
        .await;

        cx.set_state("ˇfn main() {\n    let x = 1;\n}\n");
        cx.run_until_parked();

        cx.editor.read_with(&cx.cx.cx, |editor, cx| {
            assert!(
                !editor.document_folding_ranges_enabled(cx),
                "LSP folding ranges should not be enabled by default"
            );
        });
    }

    #[gpui::test]
    async fn test_lsp_folding_ranges_toggling_off_removes_creases(cx: &mut TestAppContext) {
        init_test(cx, |_| {});

        update_test_language_settings(cx, &|settings| {
            settings.defaults.document_folding_ranges = Some(DocumentFoldingRanges::On);
        });

        let mut cx = EditorLspTestContext::new_rust(
            lsp::ServerCapabilities {
                folding_range_provider: Some(lsp::FoldingRangeProviderCapability::Simple(true)),
                ..lsp::ServerCapabilities::default()
            },
            cx,
        )
        .await;

        let mut folding_request = cx
            .set_request_handler::<lsp::request::FoldingRangeRequest, _, _>(
                move |_, _, _| async move {
                    Ok(Some(vec![FoldingRange {
                        start_line: 0,
                        start_character: Some(10),
                        end_line: 4,
                        end_character: Some(1),
                        kind: None,
                        collapsed_text: None,
                    }]))
                },
            );

        cx.set_state("ˇfn main() {\n    if true {\n        println!(\"hello\");\n    }\n}\n");
        assert!(folding_request.next().await.is_some());
        cx.run_until_parked();

        cx.editor.read_with(&cx.cx.cx, |editor, cx| {
            assert!(
                editor.document_folding_ranges_enabled(cx),
                "Expected LSP folding ranges to be active before toggling off"
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(0), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            let snapshot = editor.display_snapshot(cx);
            assert!(
                snapshot.is_line_folded(MultiBufferRow(0)),
                "Line 0 should be folded via LSP crease before toggling off"
            );
            assert_eq!(editor.display_text(cx), "fn main() ⋯\n",);
        });

        update_test_language_settings(&mut cx.cx.cx, &|settings| {
            settings.defaults.document_folding_ranges = Some(DocumentFoldingRanges::Off);
        });
        cx.run_until_parked();

        cx.editor.read_with(&cx.cx.cx, |editor, cx| {
            assert!(
                !editor.document_folding_ranges_enabled(cx),
                "LSP folding ranges should be cleared after toggling off"
            );
        });
    }

    #[gpui::test]
    async fn test_lsp_folding_ranges_nested_folds(cx: &mut TestAppContext) {
        init_test(cx, |_| {});

        update_test_language_settings(cx, &|settings| {
            settings.defaults.document_folding_ranges = Some(DocumentFoldingRanges::On);
        });

        let mut cx = EditorLspTestContext::new_rust(
            lsp::ServerCapabilities {
                folding_range_provider: Some(lsp::FoldingRangeProviderCapability::Simple(true)),
                ..lsp::ServerCapabilities::default()
            },
            cx,
        )
        .await;

        let mut folding_request = cx
            .set_request_handler::<lsp::request::FoldingRangeRequest, _, _>(
                move |_, _, _| async move {
                    Ok(Some(vec![
                        FoldingRange {
                            start_line: 0,
                            start_character: Some(10),
                            end_line: 7,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: None,
                        },
                        FoldingRange {
                            start_line: 1,
                            start_character: Some(12),
                            end_line: 3,
                            end_character: Some(5),
                            kind: None,
                            collapsed_text: None,
                        },
                        FoldingRange {
                            start_line: 4,
                            start_character: Some(13),
                            end_line: 6,
                            end_character: Some(5),
                            kind: None,
                            collapsed_text: None,
                        },
                    ]))
                },
            );

        cx.set_state(
            "ˇfn main() {\n    if true {\n        a();\n    }\n    if false {\n        b();\n    }\n}\n",
        );
        assert!(folding_request.next().await.is_some());
        cx.run_until_parked();

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(1), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            let snapshot = editor.display_snapshot(cx);
            assert!(snapshot.is_line_folded(MultiBufferRow(1)));
            assert!(!snapshot.is_line_folded(MultiBufferRow(0)));
            assert_eq!(
                editor.display_text(cx),
                "fn main() {\n    if true ⋯\n    if false {\n        b();\n    }\n}\n",
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(4), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            let snapshot = editor.display_snapshot(cx);
            assert!(snapshot.is_line_folded(MultiBufferRow(4)));
            assert_eq!(
                editor.display_text(cx),
                "fn main() {\n    if true ⋯\n    if false ⋯\n}\n",
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(0), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            let snapshot = editor.display_snapshot(cx);
            assert!(snapshot.is_line_folded(MultiBufferRow(0)));
            assert_eq!(editor.display_text(cx), "fn main() ⋯\n",);
        });
    }

    #[gpui::test]
    async fn test_lsp_folding_ranges_unsorted_from_server(cx: &mut TestAppContext) {
        init_test(cx, |_| {});

        update_test_language_settings(cx, &|settings| {
            settings.defaults.document_folding_ranges = Some(DocumentFoldingRanges::On);
        });

        let mut cx = EditorLspTestContext::new_rust(
            lsp::ServerCapabilities {
                folding_range_provider: Some(lsp::FoldingRangeProviderCapability::Simple(true)),
                ..lsp::ServerCapabilities::default()
            },
            cx,
        )
        .await;

        let mut folding_request = cx
            .set_request_handler::<lsp::request::FoldingRangeRequest, _, _>(
                move |_, _, _| async move {
                    Ok(Some(vec![
                        FoldingRange {
                            start_line: 6,
                            start_character: Some(11),
                            end_line: 8,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: None,
                        },
                        FoldingRange {
                            start_line: 0,
                            start_character: Some(10),
                            end_line: 4,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: None,
                        },
                        FoldingRange {
                            start_line: 1,
                            start_character: Some(13),
                            end_line: 3,
                            end_character: Some(5),
                            kind: None,
                            collapsed_text: None,
                        },
                    ]))
                },
            );

        cx.set_state(
            "ˇfn main() {\n    if true {\n        println!(\"hello\");\n    }\n}\n\nfn other() {\n    let x = 1;\n}\n",
        );
        assert!(folding_request.next().await.is_some());
        cx.run_until_parked();

        cx.editor.read_with(&cx.cx.cx, |editor, cx| {
            assert!(
                editor.document_folding_ranges_enabled(cx),
                "Expected LSP folding ranges to be populated despite unsorted server response"
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(0), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(
                editor.display_text(cx),
                "fn main() ⋯\n\nfn other() {\n    let x = 1;\n}\n",
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(6), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(editor.display_text(cx), "fn main() ⋯\n\nfn other() ⋯\n",);
        });
    }

    #[gpui::test]
    async fn test_lsp_folding_ranges_switch_between_treesitter_and_lsp(cx: &mut TestAppContext) {
        init_test(cx, |_| {});

        let mut cx = EditorLspTestContext::new_rust(
            lsp::ServerCapabilities {
                folding_range_provider: Some(lsp::FoldingRangeProviderCapability::Simple(true)),
                ..lsp::ServerCapabilities::default()
            },
            cx,
        )
        .await;

        let source =
            "fn main() {\n    let a = 1;\n    let b = 2;\n    let c = 3;\n    let d = 4;\n}\n";
        cx.set_state(&format!("ˇ{source}"));
        cx.run_until_parked();

        // Phase 1: tree-sitter / indentation-based folding (LSP folding OFF by default).
        cx.editor.read_with(&cx.cx.cx, |editor, cx| {
            assert!(
                !editor.document_folding_ranges_enabled(cx),
                "LSP folding ranges should be off by default"
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(0), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            let snapshot = editor.display_snapshot(cx);
            assert!(
                snapshot.is_line_folded(MultiBufferRow(0)),
                "Indentation-based fold should work on the function"
            );
            assert_eq!(editor.display_text(cx), "fn main() {⋯}\n",);
        });

        cx.update_editor(|editor, window, cx| {
            editor.unfold_at(MultiBufferRow(0), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert!(
                !editor
                    .display_snapshot(cx)
                    .is_line_folded(MultiBufferRow(0)),
                "Function should be unfolded"
            );
        });

        // Phase 2: switch to LSP folding with non-syntactic ("odd") ranges.
        // The LSP returns two ranges that each cover a pair of let-bindings,
        // which is not something tree-sitter / indentation folding would produce.
        let mut folding_request = cx
            .set_request_handler::<lsp::request::FoldingRangeRequest, _, _>(
                move |_, _, _| async move {
                    Ok(Some(vec![
                        FoldingRange {
                            start_line: 1,
                            start_character: Some(14),
                            end_line: 2,
                            end_character: Some(14),
                            kind: None,
                            collapsed_text: None,
                        },
                        FoldingRange {
                            start_line: 3,
                            start_character: Some(14),
                            end_line: 4,
                            end_character: Some(14),
                            kind: None,
                            collapsed_text: None,
                        },
                    ]))
                },
            );

        update_test_language_settings(&mut cx.cx.cx, &|settings| {
            settings.defaults.document_folding_ranges = Some(DocumentFoldingRanges::On);
        });
        assert!(folding_request.next().await.is_some());
        cx.run_until_parked();

        cx.editor.read_with(&cx.cx.cx, |editor, cx| {
            assert!(
                editor.document_folding_ranges_enabled(cx),
                "LSP folding ranges should now be active"
            );
        });

        // The indentation fold at row 0 should no longer be available;
        // only the LSP ranges exist.
        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(0), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert!(
                !editor
                    .display_snapshot(cx)
                    .is_line_folded(MultiBufferRow(0)),
                "Row 0 has no LSP crease, so fold_at should be a no-op"
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(1), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert!(
                editor
                    .display_snapshot(cx)
                    .is_line_folded(MultiBufferRow(1)),
                "First odd LSP range should fold"
            );
            assert_eq!(
                editor.display_text(cx),
                "fn main() {\n    let a = 1;⋯\n    let c = 3;\n    let d = 4;\n}\n",
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(3), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert!(
                editor
                    .display_snapshot(cx)
                    .is_line_folded(MultiBufferRow(3)),
                "Second odd LSP range should fold"
            );
            assert_eq!(
                editor.display_text(cx),
                "fn main() {\n    let a = 1;⋯\n    let c = 3;⋯\n}\n",
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.unfold_at(MultiBufferRow(1), window, cx);
            editor.unfold_at(MultiBufferRow(3), window, cx);
        });

        // Phase 3: switch back to tree-sitter by disabling LSP folding ranges.
        update_test_language_settings(&mut cx.cx.cx, &|settings| {
            settings.defaults.document_folding_ranges = Some(DocumentFoldingRanges::Off);
        });
        cx.run_until_parked();

        cx.editor.read_with(&cx.cx.cx, |editor, cx| {
            assert!(
                !editor.document_folding_ranges_enabled(cx),
                "LSP folding ranges should be cleared after switching back"
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(0), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            let snapshot = editor.display_snapshot(cx);
            assert!(
                snapshot.is_line_folded(MultiBufferRow(0)),
                "Indentation-based fold should work again after switching back"
            );
            assert_eq!(editor.display_text(cx), "fn main() {⋯}\n",);
        });
    }

    #[gpui::test]
    async fn test_lsp_folding_ranges_collapsed_text(cx: &mut TestAppContext) {
        init_test(cx, |_| {});

        update_test_language_settings(cx, &|settings| {
            settings.defaults.document_folding_ranges = Some(DocumentFoldingRanges::On);
        });

        let mut cx = EditorLspTestContext::new_rust(
            lsp::ServerCapabilities {
                folding_range_provider: Some(lsp::FoldingRangeProviderCapability::Simple(true)),
                ..lsp::ServerCapabilities::default()
            },
            cx,
        )
        .await;

        let mut folding_request = cx
            .set_request_handler::<lsp::request::FoldingRangeRequest, _, _>(
                move |_, _, _| async move {
                    Ok(Some(vec![
                        // main: custom collapsed text
                        FoldingRange {
                            start_line: 0,
                            start_character: Some(10),
                            end_line: 4,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: Some("{ fn body }".to_string()),
                        },
                        // other: collapsed text longer than the original folded content
                        FoldingRange {
                            start_line: 6,
                            start_character: Some(11),
                            end_line: 8,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: Some("{ this collapsed text is intentionally much longer than the original function body it replaces }".to_string()),
                        },
                        // emoji: collapsed text WITH emoji and multi-byte chars
                        FoldingRange {
                            start_line: 10,
                            start_character: Some(11),
                            end_line: 13,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: Some("{ 🦀…café }".to_string()),
                        },
                        // outer: collapsed text on the outer fn
                        FoldingRange {
                            start_line: 15,
                            start_character: Some(11),
                            end_line: 22,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: Some("{ outer… }".to_string()),
                        },
                        // inner_a: nested inside outer, with collapsed text
                        FoldingRange {
                            start_line: 16,
                            start_character: Some(17),
                            end_line: 18,
                            end_character: Some(5),
                            kind: None,
                            collapsed_text: Some("{ a }".to_string()),
                        },
                        // inner_b: nested inside outer, no collapsed text
                        FoldingRange {
                            start_line: 19,
                            start_character: Some(17),
                            end_line: 21,
                            end_character: Some(5),
                            kind: None,
                            collapsed_text: None,
                        },
                        // newline: collapsed text containing \n
                        FoldingRange {
                            start_line: 24,
                            start_character: Some(13),
                            end_line: 27,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: Some("{\n  …\n}".to_string()),
                        },
                    ]))
                },
            );

        cx.set_state(
            &[
                "ˇfn main() {\n",
                "    if true {\n",
                "        println!(\"hello\");\n",
                "    }\n",
                "}\n",
                "\n",
                "fn other() {\n",
                "    let x = 1;\n",
                "}\n",
                "\n",
                "fn emoji() {\n",
                "    let a = \"🦀🔥\";\n",
                "    let b = \"café\";\n",
                "}\n",
                "\n",
                "fn outer() {\n",
                "    fn inner_a() {\n",
                "        let x = 1;\n",
                "    }\n",
                "    fn inner_b() {\n",
                "        let y = 2;\n",
                "    }\n",
                "}\n",
                "\n",
                "fn newline() {\n",
                "    let a = 1;\n",
                "    let b = 2;\n",
                "}\n",
            ]
            .concat(),
        );
        assert!(folding_request.next().await.is_some());
        cx.run_until_parked();

        let unfolded_text = [
            "fn main() {\n",
            "    if true {\n",
            "        println!(\"hello\");\n",
            "    }\n",
            "}\n",
            "\n",
            "fn other() {\n",
            "    let x = 1;\n",
            "}\n",
            "\n",
            "fn emoji() {\n",
            "    let a = \"🦀🔥\";\n",
            "    let b = \"café\";\n",
            "}\n",
            "\n",
            "fn outer() {\n",
            "    fn inner_a() {\n",
            "        let x = 1;\n",
            "    }\n",
            "    fn inner_b() {\n",
            "        let y = 2;\n",
            "    }\n",
            "}\n",
            "\n",
            "fn newline() {\n",
            "    let a = 1;\n",
            "    let b = 2;\n",
            "}\n",
        ]
        .concat();

        // Fold newline fn — collapsed text that itself contains \n
        // (newlines are sanitized to spaces to keep folds single-line).
        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(24), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(
                editor.display_text(cx),
                [
                    "fn main() {\n",
                    "    if true {\n",
                    "        println!(\"hello\");\n",
                    "    }\n",
                    "}\n",
                    "\n",
                    "fn other() {\n",
                    "    let x = 1;\n",
                    "}\n",
                    "\n",
                    "fn emoji() {\n",
                    "    let a = \"🦀🔥\";\n",
                    "    let b = \"café\";\n",
                    "}\n",
                    "\n",
                    "fn outer() {\n",
                    "    fn inner_a() {\n",
                    "        let x = 1;\n",
                    "    }\n",
                    "    fn inner_b() {\n",
                    "        let y = 2;\n",
                    "    }\n",
                    "}\n",
                    "\n",
                    "fn newline() { … }\n",
                ]
                .concat(),
            );
        });

        cx.update_editor(|editor, window, cx| {
            editor.unfold_all(&crate::actions::UnfoldAll, window, cx);
        });

        // Fold main — custom collapsed text.
        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(0), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(
                editor.display_text(cx),
                [
                    "fn main() { fn body }\n",
                    "\n",
                    "fn other() {\n",
                    "    let x = 1;\n",
                    "}\n",
                    "\n",
                    "fn emoji() {\n",
                    "    let a = \"🦀🔥\";\n",
                    "    let b = \"café\";\n",
                    "}\n",
                    "\n",
                    "fn outer() {\n",
                    "    fn inner_a() {\n",
                    "        let x = 1;\n",
                    "    }\n",
                    "    fn inner_b() {\n",
                    "        let y = 2;\n",
                    "    }\n",
                    "}\n",
                    "\n",
                    "fn newline() {\n",
                    "    let a = 1;\n",
                    "    let b = 2;\n",
                    "}\n",
                ]
                .concat(),
            );
        });

        // Fold emoji fn — multi-byte / emoji collapsed text (main still folded).
        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(10), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(
                editor.display_text(cx),
                [
                    "fn main() { fn body }\n",
                    "\n",
                    "fn other() {\n",
                    "    let x = 1;\n",
                    "}\n",
                    "\n",
                    "fn emoji() { 🦀…café }\n",
                    "\n",
                    "fn outer() {\n",
                    "    fn inner_a() {\n",
                    "        let x = 1;\n",
                    "    }\n",
                    "    fn inner_b() {\n",
                    "        let y = 2;\n",
                    "    }\n",
                    "}\n",
                    "\n",
                    "fn newline() {\n",
                    "    let a = 1;\n",
                    "    let b = 2;\n",
                    "}\n",
                ]
                .concat(),
            );
        });

        // Fold a nested range (inner_a) while outer is still unfolded.
        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(16), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(
                editor.display_text(cx),
                [
                    "fn main() { fn body }\n",
                    "\n",
                    "fn other() {\n",
                    "    let x = 1;\n",
                    "}\n",
                    "\n",
                    "fn emoji() { 🦀…café }\n",
                    "\n",
                    "fn outer() {\n",
                    "    fn inner_a() { a }\n",
                    "    fn inner_b() {\n",
                    "        let y = 2;\n",
                    "    }\n",
                    "}\n",
                    "\n",
                    "fn newline() {\n",
                    "    let a = 1;\n",
                    "    let b = 2;\n",
                    "}\n",
                ]
                .concat(),
            );
        });

        // Unfold everything to reset.
        cx.update_editor(|editor, window, cx| {
            editor.unfold_all(&crate::actions::UnfoldAll, window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(editor.display_text(cx), unfolded_text);
        });

        // Fold ALL at once and verify every fold.
        cx.update_editor(|editor, window, cx| {
            editor.fold_all(&crate::actions::FoldAll, window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(
                editor.display_text(cx),
                [
                    "fn main() { fn body }\n",
                    "\n",
                    "fn other() { this collapsed text is intentionally much longer than the original function body it replaces }\n",
                    "\n",
                    "fn emoji() { 🦀…café }\n",
                    "\n",
                    "fn outer() { outer… }\n",
                    "\n",
                    "fn newline() { … }\n",
                ]
                .concat(),
            );
        });

        // Unfold all again, then fold only the outer, which should swallow inner folds.
        cx.update_editor(|editor, window, cx| {
            editor.unfold_all(&crate::actions::UnfoldAll, window, cx);
        });
        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(15), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(
                editor.display_text(cx),
                [
                    "fn main() {\n",
                    "    if true {\n",
                    "        println!(\"hello\");\n",
                    "    }\n",
                    "}\n",
                    "\n",
                    "fn other() {\n",
                    "    let x = 1;\n",
                    "}\n",
                    "\n",
                    "fn emoji() {\n",
                    "    let a = \"🦀🔥\";\n",
                    "    let b = \"café\";\n",
                    "}\n",
                    "\n",
                    "fn outer() { outer… }\n",
                    "\n",
                    "fn newline() {\n",
                    "    let a = 1;\n",
                    "    let b = 2;\n",
                    "}\n",
                ]
                .concat(),
            );
        });

        // Unfold the outer, then fold both inners independently.
        cx.update_editor(|editor, window, cx| {
            editor.unfold_all(&crate::actions::UnfoldAll, window, cx);
        });
        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(16), window, cx);
            editor.fold_at(MultiBufferRow(19), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(
                editor.display_text(cx),
                [
                    "fn main() {\n",
                    "    if true {\n",
                    "        println!(\"hello\");\n",
                    "    }\n",
                    "}\n",
                    "\n",
                    "fn other() {\n",
                    "    let x = 1;\n",
                    "}\n",
                    "\n",
                    "fn emoji() {\n",
                    "    let a = \"🦀🔥\";\n",
                    "    let b = \"café\";\n",
                    "}\n",
                    "\n",
                    "fn outer() {\n",
                    "    fn inner_a() { a }\n",
                    "    fn inner_b() ⋯\n",
                    "}\n",
                    "\n",
                    "fn newline() {\n",
                    "    let a = 1;\n",
                    "    let b = 2;\n",
                    "}\n",
                ]
                .concat(),
            );
        });
    }

    #[gpui::test]
    async fn test_lsp_folding_ranges_with_multibyte_characters(cx: &mut TestAppContext) {
        init_test(cx, |_| {});

        update_test_language_settings(cx, &|settings| {
            settings.defaults.document_folding_ranges = Some(DocumentFoldingRanges::On);
        });

        let mut cx = EditorLspTestContext::new_rust(
            lsp::ServerCapabilities {
                folding_range_provider: Some(lsp::FoldingRangeProviderCapability::Simple(true)),
                ..lsp::ServerCapabilities::default()
            },
            cx,
        )
        .await;

        // √ is 3 bytes in UTF-8 but 1 code unit in UTF-16.
        // LSP character offsets are UTF-16, so interpreting them as byte
        // offsets lands inside a multi-byte character and panics.
        let mut folding_request = cx
            .set_request_handler::<lsp::request::FoldingRangeRequest, _, _>(
                move |_, _, _| async move {
                    Ok(Some(vec![
                        // Outer fold: start/end on ASCII-only lines (sanity check).
                        FoldingRange {
                            start_line: 0,
                            start_character: Some(16),
                            end_line: 8,
                            end_character: Some(1),
                            kind: None,
                            collapsed_text: None,
                        },
                        // Inner fold whose start_character falls among multi-byte chars.
                        // Line 1 is "    //√√√√√√√√√√"
                        //   UTF-16 offsets: 0-3=' ', 4='/', 5='/', 6-15='√'×10
                        //   Byte offsets:   0-3=' ', 4='/', 5='/', 6..35='√'×10 (3 bytes each)
                        // start_character=8 (UTF-16) → after "    //√√", byte offset would be 12
                        //   but naively using 8 as byte offset hits inside the first '√'.
                        FoldingRange {
                            start_line: 1,
                            start_character: Some(8),
                            end_line: 3,
                            end_character: Some(5),
                            kind: None,
                            collapsed_text: None,
                        },
                    ]))
                },
            );

        // Line 0: "fn multibyte() {"       (16 UTF-16 units)
        // Line 1: "    //√√√√√√√√√√"       (16 UTF-16 units, 36 bytes)
        // Line 2: "    let y = 2;"          (14 UTF-16 units)
        // Line 3: "    //√√√|end"           (13 UTF-16 units; '|' is just a visual marker)
        // Line 4: "    if true {"           (14 UTF-16 units)
        // Line 5: "        let a = \"√√\";" (22 UTF-16 units, 28 bytes)
        // Line 6: "    }"                   (5 UTF-16 units)
        // Line 7: "    let z = 3;"          (14 UTF-16 units)
        // Line 8: "}"                       (1 UTF-16 unit)
        cx.set_state(
            &[
                "ˇfn multibyte() {\n",
                "    //√√√√√√√√√√\n",
                "    let y = 2;\n",
                "    //√√√|end\n",
                "    if true {\n",
                "        let a = \"√√\";\n",
                "    }\n",
                "    let z = 3;\n",
                "}\n",
            ]
            .concat(),
        );
        assert!(folding_request.next().await.is_some());
        cx.run_until_parked();

        // Fold the inner range whose start_character lands among √ chars.
        // Fold spans from line 1 char 8 ("    //√√" visible) to line 3 char 5
        // ("/√√√|end" visible after fold marker).
        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(1), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(
                editor.display_text(cx),
                [
                    "fn multibyte() {\n",
                    "    //√√⋯/√√√|end\n",
                    "    if true {\n",
                    "        let a = \"√√\";\n",
                    "    }\n",
                    "    let z = 3;\n",
                    "}\n",
                ]
                .concat(),
            );
        });

        // Unfold, then fold the outer range to make sure it works too.
        cx.update_editor(|editor, window, cx| {
            editor.unfold_all(&crate::actions::UnfoldAll, window, cx);
        });
        cx.update_editor(|editor, window, cx| {
            editor.fold_at(MultiBufferRow(0), window, cx);
        });
        cx.update_editor(|editor, _window, cx| {
            assert_eq!(editor.display_text(cx), "fn multibyte() {⋯\n",);
        });
    }
}