use std::collections::VecDeque;

use codex_core::config::Config;
use ratatui::text::Line;

use crate::markdown;

/// Newline-gated accumulator that renders markdown and commits only fully
/// completed logical lines.
pub(crate) struct MarkdownNewlineCollector {
    buffer: String,
    committed_line_count: usize,
}

impl MarkdownNewlineCollector {
    pub fn new() -> Self {
        Self {
            buffer: String::new(),
            committed_line_count: 0,
        }
    }

    pub fn clear(&mut self) {
        self.buffer.clear();
        self.committed_line_count = 0;
    }

    pub fn push_delta(&mut self, delta: &str) {
        self.buffer.push_str(delta);
    }

    /// Render the full buffer and return only the newly completed logical lines
    /// since the last commit. When the buffer does not end with a newline, the
    /// final rendered line is considered incomplete and is not emitted.
    pub fn commit_complete_lines(&mut self, config: &Config) -> Vec<Line<'static>> {
        // In non-test builds, unwrap an outer ```markdown fence during commit as well,
        // so fence markers never appear in streamed history.
        let source = unwrap_markdown_language_fence_if_enabled(self.buffer.clone());
        let source = strip_empty_fenced_code_blocks(&source);

        let mut rendered: Vec<Line<'static>> = Vec::new();
        markdown::append_markdown(&source, &mut rendered, config);

        let mut complete_line_count = rendered.len();
        if complete_line_count > 0 && is_effectively_empty(&rendered[complete_line_count - 1]) {
            complete_line_count -= 1;
        }
        if !self.buffer.ends_with('\n') {
            complete_line_count = complete_line_count.saturating_sub(1);
            // If we're inside an unclosed fenced code block, also drop the
            // last rendered line to avoid committing a partial code line.
            if is_inside_unclosed_fence(&source) {
                complete_line_count = complete_line_count.saturating_sub(1);
            }
        }

        if self.committed_line_count >= complete_line_count {
            return Vec::new();
        }

        let out_slice = &rendered[self.committed_line_count..complete_line_count];
        // Strong correctness: while a fenced code block is open (no closing fence yet),
        // do not emit any new lines from inside it. Wait until the fence closes to emit
        // the entire block together. This avoids stray backticks and misformatted content.
        if is_inside_unclosed_fence(&source) {
            return Vec::new();
        }

        let out = out_slice.to_vec();
        self.committed_line_count = complete_line_count;
        out
    }

    /// Finalize the stream: emit all remaining lines beyond the last commit.
    /// If the buffer does not end with a newline, a temporary one is appended
    /// for rendering. Optionally unwraps ```markdown language fences in
    /// non-test builds.
    pub fn finalize_and_drain(&mut self, config: &Config) -> Vec<Line<'static>> {
        let mut source: String = self.buffer.clone();
        if !source.ends_with('\n') {
            source.push('\n');
        }
        let source = unwrap_markdown_language_fence_if_enabled(source);
        let source = strip_empty_fenced_code_blocks(&source);

        let mut rendered: Vec<Line<'static>> = Vec::new();
        markdown::append_markdown(&source, &mut rendered, config);

        let out = if self.committed_line_count >= rendered.len() {
            Vec::new()
        } else {
            rendered[self.committed_line_count..].to_vec()
        };

        // Reset collector state for next stream.
        self.clear();
        out
    }
}

fn is_effectively_empty(line: &Line<'_>) -> bool {
    if line.spans.is_empty() {
        return true;
    }
    line.spans
        .iter()
        .all(|s| s.content.is_empty() || s.content.chars().all(|c| c == ' '))
}

/// Remove fenced code blocks that contain no content (whitespace-only) to avoid
/// streaming empty code blocks like ```lang\n``` or ```\n```.
fn strip_empty_fenced_code_blocks(s: &str) -> String {
    // Only remove complete fenced blocks that contain no non-whitespace content.
    // Leave all other content unchanged to avoid affecting partial streams.
    let lines: Vec<&str> = s.lines().collect();
    let mut out = String::with_capacity(s.len());
    let mut i = 0usize;
    while i < lines.len() {
        let line = lines[i];
        let trimmed_start = line.trim_start();
        let fence_token = if trimmed_start.starts_with("```") {
            "```"
        } else if trimmed_start.starts_with("~~~") {
            "~~~"
        } else {
            ""
        };
        if !fence_token.is_empty() {
            // Find a matching closing fence on its own line.
            let mut j = i + 1;
            let mut has_content = false;
            let mut found_close = false;
            while j < lines.len() {
                let l = lines[j];
                if l.trim() == fence_token {
                    found_close = true;
                    break;
                }
                if !l.trim().is_empty() {
                    has_content = true;
                }
                j += 1;
            }
            if found_close && !has_content {
                // Drop i..=j and insert at most a single blank separator line.
                if !out.ends_with('\n') {
                    out.push('\n');
                }
                i = j + 1;
                continue;
            }
            // Not an empty fenced block; emit as-is.
            out.push_str(line);
            out.push('\n');
            i += 1;
        } else {
            out.push_str(line);
            out.push('\n');
            i += 1;
        }
    }
    out
}

fn is_inside_unclosed_fence(s: &str) -> bool {
    let mut open = false;
    for line in s.lines() {
        let t = line.trim_start();
        if t.starts_with("```") || t.starts_with("~~~") {
            if !open {
                open = true;
            } else {
                // closing fence on same pattern toggles off
                open = false;
            }
        }
    }
    open
}

#[cfg(test)]
fn unwrap_markdown_language_fence_if_enabled(s: String) -> String {
    // In tests, keep content exactly as provided to simplify assertions.
    s
}

#[cfg(not(test))]
fn unwrap_markdown_language_fence_if_enabled(s: String) -> String {
    // Best-effort unwrap of a single outer ```markdown fence.
    // This is intentionally simple; we can refine as needed later.
    const OPEN: &str = "```markdown\n";
    const CLOSE: &str = "\n```\n";
    if s.starts_with(OPEN) && s.ends_with(CLOSE) {
        let inner = s[OPEN.len()..s.len() - CLOSE.len()].to_string();
        return inner;
    }
    s
}

pub(crate) struct StepResult {
    pub history: Vec<Line<'static>>, // lines to insert into history this step
}

/// Streams already-rendered rows into history while computing the newest K
/// rows to show in a live overlay.
pub(crate) struct RenderedLineStreamer {
    queue: VecDeque<Line<'static>>,
}

impl RenderedLineStreamer {
    pub fn new() -> Self {
        Self {
            queue: VecDeque::new(),
        }
    }

    pub fn clear(&mut self) {
        self.queue.clear();
    }

    pub fn enqueue(&mut self, lines: Vec<Line<'static>>) {
        for l in lines {
            self.queue.push_back(l);
        }
    }

    pub fn step(&mut self, _live_max_rows: usize) -> StepResult {
        let mut history = Vec::new();
        // Move exactly one per tick to animate gradual insertion.
        let burst = if self.queue.is_empty() { 0 } else { 1 };
        for _ in 0..burst {
            if let Some(l) = self.queue.pop_front() {
                history.push(l);
            }
        }

        StepResult { history }
    }

    pub fn drain_all(&mut self, _live_max_rows: usize) -> StepResult {
        let mut history = Vec::new();
        while let Some(l) = self.queue.pop_front() {
            history.push(l);
        }
        StepResult { history }
    }

    pub fn is_idle(&self) -> bool {
        self.queue.is_empty()
    }
}

#[cfg(test)]
pub(crate) fn simulate_stream_markdown_for_tests(
    deltas: &[&str],
    finalize: bool,
    config: &Config,
) -> Vec<Line<'static>> {
    let mut collector = MarkdownNewlineCollector::new();
    let mut out = Vec::new();
    for d in deltas {
        collector.push_delta(d);
        if d.contains('\n') {
            out.extend(collector.commit_complete_lines(config));
        }
    }
    if finalize {
        out.extend(collector.finalize_and_drain(config));
    }
    out
}

#[cfg(test)]
mod tests {
    use super::*;
    use codex_core::config::Config;
    use codex_core::config::ConfigOverrides;

    fn test_config() -> Config {
        let overrides = ConfigOverrides {
            cwd: std::env::current_dir().ok(),
            ..Default::default()
        };
        match Config::load_with_cli_overrides(vec![], overrides) {
            Ok(c) => c,
            Err(e) => panic!("load test config: {e}"),
        }
    }

    #[test]
    fn no_commit_until_newline() {
        let cfg = test_config();
        let mut c = MarkdownNewlineCollector::new();
        c.push_delta("Hello, world");
        let out = c.commit_complete_lines(&cfg);
        assert!(out.is_empty(), "should not commit without newline");
        c.push_delta("!\n");
        let out2 = c.commit_complete_lines(&cfg);
        assert_eq!(out2.len(), 1, "one completed line after newline");
    }

    #[test]
    fn finalize_commits_partial_line() {
        let cfg = test_config();
        let mut c = MarkdownNewlineCollector::new();
        c.push_delta("Line without newline");
        let out = c.finalize_and_drain(&cfg);
        assert_eq!(out.len(), 1);
    }

    #[test]
    fn heading_starts_on_new_line_when_following_paragraph() {
        let cfg = test_config();

        // Stream a paragraph line, then a heading on the next line.
        // Expect two distinct rendered lines: "Hello." and "Heading".
        let mut c = MarkdownNewlineCollector::new();
        c.push_delta("Hello.\n");
        let out1 = c.commit_complete_lines(&cfg);
        let s1: Vec<String> = out1
            .iter()
            .map(|l| {
                l.spans
                    .iter()
                    .map(|s| s.content.clone())
                    .collect::<Vec<_>>()
                    .join("")
            })
            .collect();
        assert_eq!(
            out1.len(),
            1,
            "first commit should contain only the paragraph line, got {}: {:?}",
            out1.len(),
            s1
        );

        c.push_delta("## Heading\n");
        let out2 = c.commit_complete_lines(&cfg);
        let s2: Vec<String> = out2
            .iter()
            .map(|l| {
                l.spans
                    .iter()
                    .map(|s| s.content.clone())
                    .collect::<Vec<_>>()
                    .join("")
            })
            .collect();
        assert_eq!(
            s2,
            vec!["", "## Heading"],
            "expected a blank separator then the heading line"
        );

        let line_to_string = |l: &ratatui::text::Line<'_>| -> String {
            l.spans
                .iter()
                .map(|s| s.content.clone())
                .collect::<Vec<_>>()
                .join("")
        };

        assert_eq!(line_to_string(&out1[0]), "Hello.");
        assert_eq!(line_to_string(&out2[1]), "## Heading");
    }

    #[test]
    fn heading_not_inlined_when_split_across_chunks() {
        let cfg = test_config();

        // Paragraph without trailing newline, then a chunk that starts with the newline
        // and the heading text, then a final newline. The collector should first commit
        // only the paragraph line, and later commit the heading as its own line.
        let mut c = MarkdownNewlineCollector::new();
        c.push_delta("Sounds good!");
        // No commit yet
        assert!(c.commit_complete_lines(&cfg).is_empty());

        // Introduce the newline that completes the paragraph and the start of the heading.
        c.push_delta("\n## Adding Bird subcommand");
        let out1 = c.commit_complete_lines(&cfg);
        let s1: Vec<String> = out1
            .iter()
            .map(|l| {
                l.spans
                    .iter()
                    .map(|s| s.content.clone())
                    .collect::<Vec<_>>()
                    .join("")
            })
            .collect();
        assert_eq!(
            s1,
            vec!["Sounds good!", ""],
            "expected paragraph followed by blank separator before heading chunk"
        );

        // Now finish the heading line with the trailing newline.
        c.push_delta("\n");
        let out2 = c.commit_complete_lines(&cfg);
        let s2: Vec<String> = out2
            .iter()
            .map(|l| {
                l.spans
                    .iter()
                    .map(|s| s.content.clone())
                    .collect::<Vec<_>>()
                    .join("")
            })
            .collect();
        assert_eq!(
            s2,
            vec!["## Adding Bird subcommand"],
            "expected the heading line only on the final commit"
        );

        // Sanity check raw markdown rendering for a simple line does not produce spurious extras.
        let mut rendered: Vec<ratatui::text::Line<'static>> = Vec::new();
        crate::markdown::append_markdown("Hello.\n", &mut rendered, &cfg);
        let rendered_strings: Vec<String> = rendered
            .iter()
            .map(|l| {
                l.spans
                    .iter()
                    .map(|s| s.content.clone())
                    .collect::<Vec<_>>()
                    .join("")
            })
            .collect();
        assert_eq!(
            rendered_strings,
            vec!["Hello."],
            "unexpected markdown lines: {rendered_strings:?}"
        );

        let line_to_string = |l: &ratatui::text::Line<'_>| -> String {
            l.spans
                .iter()
                .map(|s| s.content.clone())
                .collect::<Vec<_>>()
                .join("")
        };

        assert_eq!(line_to_string(&out1[0]), "Sounds good!");
        assert_eq!(line_to_string(&out1[1]), "");
        assert_eq!(line_to_string(&out2[0]), "## Adding Bird subcommand");
    }

    fn lines_to_plain_strings(lines: &[ratatui::text::Line<'_>]) -> Vec<String> {
        lines
            .iter()
            .map(|l| {
                l.spans
                    .iter()
                    .map(|s| s.content.clone())
                    .collect::<Vec<_>>()
                    .join("")
            })
            .collect()
    }

    #[test]
    fn lists_and_fences_commit_without_duplication() {
        let cfg = test_config();

        // List case
        let deltas = vec!["- a\n- ", "b\n- c\n"];
        let streamed = simulate_stream_markdown_for_tests(&deltas, true, &cfg);
        let streamed_str = lines_to_plain_strings(&streamed);

        let mut rendered_all: Vec<ratatui::text::Line<'static>> = Vec::new();
        crate::markdown::append_markdown("- a\n- b\n- c\n", &mut rendered_all, &cfg);
        let rendered_all_str = lines_to_plain_strings(&rendered_all);

        assert_eq!(
            streamed_str, rendered_all_str,
            "list streaming should equal full render without duplication"
        );

        // Fenced code case: stream in small chunks
        let deltas2 = vec!["```", "\nco", "de 1\ncode 2\n", "```\n"];
        let streamed2 = simulate_stream_markdown_for_tests(&deltas2, true, &cfg);
        let streamed2_str = lines_to_plain_strings(&streamed2);

        let mut rendered_all2: Vec<ratatui::text::Line<'static>> = Vec::new();
        crate::markdown::append_markdown("```\ncode 1\ncode 2\n```\n", &mut rendered_all2, &cfg);
        let rendered_all2_str = lines_to_plain_strings(&rendered_all2);

        assert_eq!(
            streamed2_str, rendered_all2_str,
            "fence streaming should equal full render without duplication"
        );
    }

    #[test]
    fn utf8_boundary_safety_and_wide_chars() {
        let cfg = test_config();

        // Emoji (wide), CJK, control char, digit + combining macron sequences
        let input = "🙂🙂🙂\n汉字漢字\nA\u{0003}0\u{0304}\n";
        let deltas = vec![
            "🙂",
            "🙂",
            "🙂\n汉",
            "字漢",
            "字\nA",
            "\u{0003}",
            "0",
            "\u{0304}",
            "\n",
        ];

        let streamed = simulate_stream_markdown_for_tests(&deltas, true, &cfg);
        let streamed_str = lines_to_plain_strings(&streamed);

        let mut rendered_all: Vec<ratatui::text::Line<'static>> = Vec::new();
        crate::markdown::append_markdown(input, &mut rendered_all, &cfg);
        let rendered_all_str = lines_to_plain_strings(&rendered_all);

        assert_eq!(
            streamed_str, rendered_all_str,
            "utf8/wide-char streaming should equal full render without duplication or truncation"
        );
    }

    #[test]
    fn empty_fenced_block_is_dropped_and_separator_preserved_before_heading() {
        let cfg = test_config();
        // An empty fenced code block followed by a heading should not render the fence,
        // but should preserve a blank separator line so the heading starts on a new line.
        let deltas = vec!["```bash\n```\n", "## Heading\n"]; // empty block and close in same commit
        let streamed = simulate_stream_markdown_for_tests(&deltas, true, &cfg);
        let texts = lines_to_plain_strings(&streamed);
        assert!(
            texts.iter().all(|s| !s.contains("```")),
            "no fence markers expected: {texts:?}"
        );
        // Expect the heading and no fence markers. A blank separator may or may not be rendered at start.
        assert!(
            texts.iter().any(|s| s == "## Heading"),
            "expected heading line: {texts:?}"
        );
    }

    #[test]
    fn paragraph_then_empty_fence_then_heading_keeps_heading_on_new_line() {
        let cfg = test_config();
        let deltas = vec!["Para.\n", "```\n```\n", "## Title\n"]; // empty fence block in one commit
        let streamed = simulate_stream_markdown_for_tests(&deltas, true, &cfg);
        let texts = lines_to_plain_strings(&streamed);
        let para_idx = match texts.iter().position(|s| s == "Para.") {
            Some(i) => i,
            None => panic!("para present"),
        };
        let head_idx = match texts.iter().position(|s| s == "## Title") {
            Some(i) => i,
            None => panic!("heading present"),
        };
        assert!(
            head_idx > para_idx,
            "heading should not merge with paragraph: {texts:?}"
        );
    }
}