use diffy::Hunk;
use ratatui::buffer::Buffer;
use ratatui::layout::Rect;
use ratatui::style::Color;
use ratatui::style::Modifier;
use ratatui::style::Style;
use ratatui::style::Stylize;
use ratatui::text::Line as RtLine;
use ratatui::text::Span as RtSpan;
use ratatui::widgets::Paragraph;
use std::collections::HashMap;
use std::path::Path;
use std::path::PathBuf;

use crate::exec_command::relativize_to_home;
use crate::render::renderable::ColumnRenderable;
use crate::render::renderable::Renderable;
use codex_core::git_info::get_git_repo_root;
use codex_core::protocol::FileChange;

const SPACES_AFTER_LINE_NUMBER: usize = 6;

// Internal representation for diff line rendering
enum DiffLineType {
    Insert,
    Delete,
    Context,
}

pub struct DiffSummary {
    changes: HashMap<PathBuf, FileChange>,
    cwd: PathBuf,
}

impl DiffSummary {
    pub fn new(changes: HashMap<PathBuf, FileChange>, cwd: PathBuf) -> Self {
        Self { changes, cwd }
    }
}

impl Renderable for FileChange {
    fn render(&self, area: Rect, buf: &mut Buffer) {
        let mut lines = vec![];
        render_change(self, &mut lines, area.width as usize);
        Paragraph::new(lines).render(area, buf);
    }

    fn desired_height(&self, width: u16) -> u16 {
        let mut lines = vec![];
        render_change(self, &mut lines, width as usize);
        lines.len() as u16
    }
}

impl From<DiffSummary> for Box<dyn Renderable> {
    fn from(val: DiffSummary) -> Self {
        let mut rows: Vec<Box<dyn Renderable>> = vec![];

        for (i, row) in collect_rows(&val.changes).into_iter().enumerate() {
            if i > 0 {
                rows.push(Box::new(RtLine::from("")));
            }
            let mut path = RtLine::from(display_path_for(&row.path, &val.cwd));
            path.push_span(" ");
            path.extend(render_line_count_summary(row.added, row.removed));
            rows.push(Box::new(path));
            rows.push(Box::new(row.change));
        }

        Box::new(ColumnRenderable::new(rows))
    }
}

pub(crate) fn create_diff_summary(
    changes: &HashMap<PathBuf, FileChange>,
    cwd: &Path,
    wrap_cols: usize,
) -> Vec<RtLine<'static>> {
    let rows = collect_rows(changes);
    render_changes_block(rows, wrap_cols, cwd)
}

// Shared row for per-file presentation
#[derive(Clone)]
struct Row {
    #[allow(dead_code)]
    path: PathBuf,
    move_path: Option<PathBuf>,
    added: usize,
    removed: usize,
    change: FileChange,
}

fn collect_rows(changes: &HashMap<PathBuf, FileChange>) -> Vec<Row> {
    let mut rows: Vec<Row> = Vec::new();
    for (path, change) in changes.iter() {
        let (added, removed) = match change {
            FileChange::Add { content } => (content.lines().count(), 0),
            FileChange::Delete { content } => (0, content.lines().count()),
            FileChange::Update { unified_diff, .. } => calculate_add_remove_from_diff(unified_diff),
        };
        let move_path = match change {
            FileChange::Update {
                move_path: Some(new),
                ..
            } => Some(new.clone()),
            _ => None,
        };
        rows.push(Row {
            path: path.clone(),
            move_path,
            added,
            removed,
            change: change.clone(),
        });
    }
    rows.sort_by_key(|r| r.path.clone());
    rows
}

fn render_line_count_summary(added: usize, removed: usize) -> Vec<RtSpan<'static>> {
    let mut spans = Vec::new();
    spans.push("(".into());
    spans.push(format!("+{added}").green());
    spans.push(" ".into());
    spans.push(format!("-{removed}").red());
    spans.push(")".into());
    spans
}

fn render_changes_block(rows: Vec<Row>, wrap_cols: usize, cwd: &Path) -> Vec<RtLine<'static>> {
    let mut out: Vec<RtLine<'static>> = Vec::new();

    let render_path = |row: &Row| -> Vec<RtSpan<'static>> {
        let mut spans = Vec::new();
        spans.push(display_path_for(&row.path, cwd).into());
        if let Some(move_path) = &row.move_path {
            spans.push(format!(" → {}", display_path_for(move_path, cwd)).into());
        }
        spans
    };

    // Header
    let total_added: usize = rows.iter().map(|r| r.added).sum();
    let total_removed: usize = rows.iter().map(|r| r.removed).sum();
    let file_count = rows.len();
    let noun = if file_count == 1 { "file" } else { "files" };
    let mut header_spans: Vec<RtSpan<'static>> = vec!["• ".into()];
    if let [row] = &rows[..] {
        let verb = match &row.change {
            FileChange::Add { .. } => "Added",
            FileChange::Delete { .. } => "Deleted",
            _ => "Edited",
        };
        header_spans.push(verb.bold());
        header_spans.push(" ".into());
        header_spans.extend(render_path(row));
        header_spans.push(" ".into());
        header_spans.extend(render_line_count_summary(row.added, row.removed));
    } else {
        header_spans.push("Edited".bold());
        header_spans.push(format!(" {file_count} {noun} ").into());
        header_spans.extend(render_line_count_summary(total_added, total_removed));
    }
    out.push(RtLine::from(header_spans));

    for (idx, r) in rows.into_iter().enumerate() {
        // Insert a blank separator between file chunks (except before the first)
        if idx > 0 {
            out.push("".into());
        }
        // File header line (skip when single-file header already shows the name)
        let skip_file_header = file_count == 1;
        if !skip_file_header {
            let mut header: Vec<RtSpan<'static>> = Vec::new();
            header.push("  └ ".dim());
            header.extend(render_path(&r));
            header.push(" ".into());
            header.extend(render_line_count_summary(r.added, r.removed));
            out.push(RtLine::from(header));
        }

        render_change(&r.change, &mut out, wrap_cols);
    }

    out
}

fn render_change(change: &FileChange, out: &mut Vec<RtLine<'static>>, width: usize) {
    match change {
        FileChange::Add { content } => {
            for (i, raw) in content.lines().enumerate() {
                out.extend(push_wrapped_diff_line(
                    i + 1,
                    DiffLineType::Insert,
                    raw,
                    width,
                ));
            }
        }
        FileChange::Delete { content } => {
            for (i, raw) in content.lines().enumerate() {
                out.extend(push_wrapped_diff_line(
                    i + 1,
                    DiffLineType::Delete,
                    raw,
                    width,
                ));
            }
        }
        FileChange::Update { unified_diff, .. } => {
            if let Ok(patch) = diffy::Patch::from_str(unified_diff) {
                let mut is_first_hunk = true;
                for h in patch.hunks() {
                    if !is_first_hunk {
                        out.push(RtLine::from(vec!["    ".into(), "⋮".dim()]));
                    }
                    is_first_hunk = false;

                    let mut old_ln = h.old_range().start();
                    let mut new_ln = h.new_range().start();
                    for l in h.lines() {
                        match l {
                            diffy::Line::Insert(text) => {
                                let s = text.trim_end_matches('\n');
                                out.extend(push_wrapped_diff_line(
                                    new_ln,
                                    DiffLineType::Insert,
                                    s,
                                    width,
                                ));
                                new_ln += 1;
                            }
                            diffy::Line::Delete(text) => {
                                let s = text.trim_end_matches('\n');
                                out.extend(push_wrapped_diff_line(
                                    old_ln,
                                    DiffLineType::Delete,
                                    s,
                                    width,
                                ));
                                old_ln += 1;
                            }
                            diffy::Line::Context(text) => {
                                let s = text.trim_end_matches('\n');
                                out.extend(push_wrapped_diff_line(
                                    new_ln,
                                    DiffLineType::Context,
                                    s,
                                    width,
                                ));
                                old_ln += 1;
                                new_ln += 1;
                            }
                        }
                    }
                }
            }
        }
    }
}

pub(crate) fn display_path_for(path: &Path, cwd: &Path) -> String {
    let path_in_same_repo = match (get_git_repo_root(cwd), get_git_repo_root(path)) {
        (Some(cwd_repo), Some(path_repo)) => cwd_repo == path_repo,
        _ => false,
    };
    let chosen = if path_in_same_repo {
        pathdiff::diff_paths(path, cwd).unwrap_or_else(|| path.to_path_buf())
    } else {
        relativize_to_home(path).unwrap_or_else(|| path.to_path_buf())
    };
    chosen.display().to_string()
}

fn calculate_add_remove_from_diff(diff: &str) -> (usize, usize) {
    if let Ok(patch) = diffy::Patch::from_str(diff) {
        patch
            .hunks()
            .iter()
            .flat_map(Hunk::lines)
            .fold((0, 0), |(a, d), l| match l {
                diffy::Line::Insert(_) => (a + 1, d),
                diffy::Line::Delete(_) => (a, d + 1),
                diffy::Line::Context(_) => (a, d),
            })
    } else {
        // For unparsable diffs, return 0 for both counts.
        (0, 0)
    }
}

fn push_wrapped_diff_line(
    line_number: usize,
    kind: DiffLineType,
    text: &str,
    width: usize,
) -> Vec<RtLine<'static>> {
    let indent = "    ";
    let ln_str = line_number.to_string();
    let mut remaining_text: &str = text;

    // Reserve a fixed number of spaces after the line number so that content starts
    // at a consistent column. Content includes a 1-character diff sign prefix
    // ("+"/"-" for inserts/deletes, or a space for context lines) so alignment
    // stays consistent across all diff lines.
    let gap_after_ln = SPACES_AFTER_LINE_NUMBER.saturating_sub(ln_str.len());
    let prefix_cols = indent.len() + ln_str.len() + gap_after_ln;

    let mut first = true;
    let (sign_char, line_style) = match kind {
        DiffLineType::Insert => ('+', style_add()),
        DiffLineType::Delete => ('-', style_del()),
        DiffLineType::Context => (' ', style_context()),
    };
    let mut lines: Vec<RtLine<'static>> = Vec::new();

    loop {
        // Fit the content for the current terminal row:
        // compute how many columns are available after the prefix, then split
        // at a UTF-8 character boundary so this row's chunk fits exactly.
        let available_content_cols = width.saturating_sub(prefix_cols + 1).max(1);
        let split_at_byte_index = remaining_text
            .char_indices()
            .nth(available_content_cols)
            .map(|(i, _)| i)
            .unwrap_or_else(|| remaining_text.len());
        let (chunk, rest) = remaining_text.split_at(split_at_byte_index);
        remaining_text = rest;

        if first {
            // Build gutter (indent + line number + spacing) as a dimmed span
            let gutter = format!("{indent}{ln_str}{}", " ".repeat(gap_after_ln));
            // Content with a sign ('+'/'-'/' ') styled per diff kind
            let content = format!("{sign_char}{chunk}");
            lines.push(RtLine::from(vec![
                RtSpan::styled(gutter, style_gutter()),
                RtSpan::styled(content, line_style),
            ]));
            first = false;
        } else {
            // Continuation lines keep a space for the sign column so content aligns
            let gutter = format!("{indent}{} ", " ".repeat(ln_str.len() + gap_after_ln));
            lines.push(RtLine::from(vec![
                RtSpan::styled(gutter, style_gutter()),
                RtSpan::styled(chunk.to_string(), line_style),
            ]));
        }
        if remaining_text.is_empty() {
            break;
        }
    }
    lines
}

fn style_gutter() -> Style {
    Style::default().add_modifier(Modifier::DIM)
}

fn style_context() -> Style {
    Style::default()
}

fn style_add() -> Style {
    Style::default().fg(Color::Green)
}

fn style_del() -> Style {
    Style::default().fg(Color::Red)
}

#[cfg(test)]
mod tests {
    use super::*;
    use insta::assert_snapshot;
    use ratatui::Terminal;
    use ratatui::backend::TestBackend;
    use ratatui::text::Text;
    use ratatui::widgets::Paragraph;
    use ratatui::widgets::WidgetRef;
    use ratatui::widgets::Wrap;
    fn diff_summary_for_tests(changes: &HashMap<PathBuf, FileChange>) -> Vec<RtLine<'static>> {
        create_diff_summary(changes, &PathBuf::from("/"), 80)
    }

    fn snapshot_lines(name: &str, lines: Vec<RtLine<'static>>, width: u16, height: u16) {
        let mut terminal = Terminal::new(TestBackend::new(width, height)).expect("terminal");
        terminal
            .draw(|f| {
                Paragraph::new(Text::from(lines))
                    .wrap(Wrap { trim: false })
                    .render_ref(f.area(), f.buffer_mut())
            })
            .expect("draw");
        assert_snapshot!(name, terminal.backend());
    }

    fn snapshot_lines_text(name: &str, lines: &[RtLine<'static>]) {
        // Convert Lines to plain text rows and trim trailing spaces so it's
        // easier to validate indentation visually in snapshots.
        let text = lines
            .iter()
            .map(|l| {
                l.spans
                    .iter()
                    .map(|s| s.content.as_ref())
                    .collect::<String>()
            })
            .map(|s| s.trim_end().to_string())
            .collect::<Vec<_>>()
            .join("\n");
        assert_snapshot!(name, text);
    }

    #[test]
    fn ui_snapshot_wrap_behavior_insert() {
        // Narrow width to force wrapping within our diff line rendering
        let long_line = "this is a very long line that should wrap across multiple terminal columns and continue";

        // Call the wrapping function directly so we can precisely control the width
        let lines = push_wrapped_diff_line(1, DiffLineType::Insert, long_line, 80);

        // Render into a small terminal to capture the visual layout
        snapshot_lines("wrap_behavior_insert", lines, 90, 8);
    }

    #[test]
    fn ui_snapshot_apply_update_block() {
        let mut changes: HashMap<PathBuf, FileChange> = HashMap::new();
        let original = "line one\nline two\nline three\n";
        let modified = "line one\nline two changed\nline three\n";
        let patch = diffy::create_patch(original, modified).to_string();

        changes.insert(
            PathBuf::from("example.txt"),
            FileChange::Update {
                unified_diff: patch,
                move_path: None,
            },
        );

        for name in ["apply_update_block", "apply_update_block_manual"] {
            let lines = diff_summary_for_tests(&changes);

            snapshot_lines(name, lines, 80, 12);
        }
    }

    #[test]
    fn ui_snapshot_apply_update_with_rename_block() {
        let mut changes: HashMap<PathBuf, FileChange> = HashMap::new();
        let original = "A\nB\nC\n";
        let modified = "A\nB changed\nC\n";
        let patch = diffy::create_patch(original, modified).to_string();

        changes.insert(
            PathBuf::from("old_name.rs"),
            FileChange::Update {
                unified_diff: patch,
                move_path: Some(PathBuf::from("new_name.rs")),
            },
        );

        let lines = diff_summary_for_tests(&changes);

        snapshot_lines("apply_update_with_rename_block", lines, 80, 12);
    }

    #[test]
    fn ui_snapshot_apply_multiple_files_block() {
        // Two files: one update and one add, to exercise combined header and per-file rows
        let mut changes: HashMap<PathBuf, FileChange> = HashMap::new();

        // File a.txt: single-line replacement (one delete, one insert)
        let patch_a = diffy::create_patch("one\n", "one changed\n").to_string();
        changes.insert(
            PathBuf::from("a.txt"),
            FileChange::Update {
                unified_diff: patch_a,
                move_path: None,
            },
        );

        // File b.txt: newly added with one line
        changes.insert(
            PathBuf::from("b.txt"),
            FileChange::Add {
                content: "new\n".to_string(),
            },
        );

        let lines = diff_summary_for_tests(&changes);

        snapshot_lines("apply_multiple_files_block", lines, 80, 14);
    }

    #[test]
    fn ui_snapshot_apply_add_block() {
        let mut changes: HashMap<PathBuf, FileChange> = HashMap::new();
        changes.insert(
            PathBuf::from("new_file.txt"),
            FileChange::Add {
                content: "alpha\nbeta\n".to_string(),
            },
        );

        let lines = diff_summary_for_tests(&changes);

        snapshot_lines("apply_add_block", lines, 80, 10);
    }

    #[test]
    fn ui_snapshot_apply_delete_block() {
        // Write a temporary file so the delete renderer can read original content
        let tmp_path = PathBuf::from("tmp_delete_example.txt");
        std::fs::write(&tmp_path, "first\nsecond\nthird\n").expect("write tmp file");

        let mut changes: HashMap<PathBuf, FileChange> = HashMap::new();
        changes.insert(
            tmp_path.clone(),
            FileChange::Delete {
                content: "first\nsecond\nthird\n".to_string(),
            },
        );

        let lines = diff_summary_for_tests(&changes);

        // Cleanup best-effort; rendering has already read the file
        let _ = std::fs::remove_file(&tmp_path);

        snapshot_lines("apply_delete_block", lines, 80, 12);
    }

    #[test]
    fn ui_snapshot_apply_update_block_wraps_long_lines() {
        // Create a patch with a long modified line to force wrapping
        let original = "line 1\nshort\nline 3\n";
        let modified = "line 1\nshort this_is_a_very_long_modified_line_that_should_wrap_across_multiple_terminal_columns_and_continue_even_further_beyond_eighty_columns_to_force_multiple_wraps\nline 3\n";
        let patch = diffy::create_patch(original, modified).to_string();

        let mut changes: HashMap<PathBuf, FileChange> = HashMap::new();
        changes.insert(
            PathBuf::from("long_example.txt"),
            FileChange::Update {
                unified_diff: patch,
                move_path: None,
            },
        );

        let lines = create_diff_summary(&changes, &PathBuf::from("/"), 72);

        // Render with backend width wider than wrap width to avoid Paragraph auto-wrap.
        snapshot_lines("apply_update_block_wraps_long_lines", lines, 80, 12);
    }

    #[test]
    fn ui_snapshot_apply_update_block_wraps_long_lines_text() {
        // This mirrors the desired layout example: sign only on first inserted line,
        // subsequent wrapped pieces start aligned under the line number gutter.
        let original = "1\n2\n3\n4\n";
        let modified = "1\nadded long line which wraps and_if_there_is_a_long_token_it_will_be_broken\n3\n4 context line which also wraps across\n";
        let patch = diffy::create_patch(original, modified).to_string();

        let mut changes: HashMap<PathBuf, FileChange> = HashMap::new();
        changes.insert(
            PathBuf::from("wrap_demo.txt"),
            FileChange::Update {
                unified_diff: patch,
                move_path: None,
            },
        );

        let mut lines = create_diff_summary(&changes, &PathBuf::from("/"), 28);
        // Drop the combined header for this text-only snapshot
        if !lines.is_empty() {
            lines.remove(0);
        }
        snapshot_lines_text("apply_update_block_wraps_long_lines_text", &lines);
    }

    #[test]
    fn ui_snapshot_apply_update_block_relativizes_path() {
        let cwd = std::env::current_dir().unwrap_or_else(|_| PathBuf::from("/"));
        let abs_old = cwd.join("abs_old.rs");
        let abs_new = cwd.join("abs_new.rs");

        let original = "X\nY\n";
        let modified = "X changed\nY\n";
        let patch = diffy::create_patch(original, modified).to_string();

        let mut changes: HashMap<PathBuf, FileChange> = HashMap::new();
        changes.insert(
            abs_old,
            FileChange::Update {
                unified_diff: patch,
                move_path: Some(abs_new),
            },
        );

        let lines = create_diff_summary(&changes, &cwd, 80);

        snapshot_lines("apply_update_block_relativizes_path", lines, 80, 10);
    }
}