use std::collections::HashMap;
use std::path::Path;

use gix::object::tree::EntryKind;

use crate::bare::GitBare;
use crate::error::{GitError, GitResult};
use crate::pb::{GetLanguageStatsRequest, GetLanguageStatsResponse, LanguageStat, object_selector};

include!(concat!(env!("OUT_DIR"), "/linguist_generated.rs"));

/// Default max file size for line counting (512 KB).
const DEFAULT_MAX_FILE_SIZE: u32 = 512 * 1024;
const MAX_TREE_WALK_DEPTH: usize = 256;

/// Look up a language by file extension (case-insensitive, includes leading dot).
fn lookup_by_extension(ext: &str) -> Option<(&'static str, &'static str)> {
    let ext_lower = ext.to_lowercase();
    EXTENSION_MAP
        .binary_search_by(|&(e, _, _)| e.cmp(ext_lower.as_str()))
        .ok()
        .map(|idx| {
            let (_, lang, ltype) = EXTENSION_MAP[idx];
            (lang, ltype)
        })
}

/// Look up a language by exact filename.
fn lookup_by_filename(name: &str) -> Option<(&'static str, &'static str)> {
    FILENAME_MAP
        .binary_search_by(|&(f, _, _)| f.cmp(name))
        .ok()
        .map(|idx| {
            let (_, lang, ltype) = FILENAME_MAP[idx];
            (lang, ltype)
        })
}

/// Resolve the group name for a language, if any.
fn resolve_group(lang: &str) -> Option<&'static str> {
    LANG_GROUP_MAP
        .binary_search_by_key(&lang, |&(l, _)| l)
        .ok()
        .map(|idx| LANG_GROUP_MAP[idx].1)
}

/// Detect language for a file path.
/// Returns (language_name, lang_type) or None if unknown.
fn detect_language(path: &str, is_binary: bool) -> Option<(&'static str, &'static str)> {
    let file_name = Path::new(path)
        .file_name()
        .and_then(|n| n.to_str())
        .unwrap_or("");

    if let Some(result) = lookup_by_filename(file_name) {
        tracing::debug!(path = %path, lang = result.0, "matched by filename");
        return Some(result);
    }

    if let Some(ext) = Path::new(path).extension().and_then(|e| e.to_str()) {
        let ext_with_dot = format!(".{ext}");
        if let Some(result) = lookup_by_extension(&ext_with_dot) {
            tracing::debug!(path = %path, ext = %ext_with_dot, lang = result.0, "matched by extension");
            return Some(result);
        }
        tracing::debug!(path = %path, ext = %ext_with_dot, "extension not found in map");
    } else {
        tracing::debug!(path = %path, "no extension found");
    }

    if is_binary {
        if let Some(ext) = Path::new(path).extension().and_then(|e| e.to_str()) {
            let ext_lower = format!(".{ext}").to_lowercase();
            let media_type = classify_binary_extension(&ext_lower);
            return Some((media_type, "data"));
        }
        return Some(("Binary", "data"));
    }

    None
}

/// Count non-empty lines in data.
fn count_code_lines(data: &[u8]) -> u64 {
    let mut count = 0u64;
    for line in data.split(|&b| b == b'\n') {
        if !line.is_empty() && !line.iter().all(|b| b.is_ascii_whitespace()) {
            count += 1;
        }
    }
    count
}

/// Aggregated stats per language.
#[derive(Default)]
struct LangStats {
    file_count: u64,
    bytes: u64,
    lines: u64,
    lang_type: String,
}

/// Context passed through recursive tree walking.
struct WalkContext<'a> {
    max_file_size: u32,
    stats: &'a mut HashMap<String, LangStats>,
    total_files: &'a mut u64,
    total_bytes: &'a mut u64,
    total_lines: &'a mut u64,
}

impl GitBare {
    pub fn get_language_stats(
        &self,
        request: GetLanguageStatsRequest,
    ) -> GitResult<GetLanguageStatsResponse> {
        let repo = self.gix_repo()?;
        let revision = match request.revision.clone().and_then(|s| s.selector) {
            Some(object_selector::Selector::Oid(oid)) => {
                crate::sanitize::validate_oid_hex(&oid.hex)?;
                oid.hex
            }
            Some(object_selector::Selector::Revision(name)) => {
                crate::sanitize::validate_revision(&name.revision)?;
                name.revision
            }
            None => "HEAD".into(),
        };

        let max_file_size = if request.max_file_size == 0 {
            DEFAULT_MAX_FILE_SIZE
        } else {
            request.max_file_size
        };

        let mut tree = repo
            .rev_parse_single(format!("{}^{{tree}}", revision).as_str())?
            .object()?
            .try_into_tree()
            .map_err(|e| GitError::Gix(e.to_string()))?;

        if !request.path.is_empty() {
            crate::sanitize::validate_file_path(&request.path)?;
            let entry = tree
                .lookup_entry_by_path(&request.path)?
                .ok_or_else(|| GitError::NotFound(request.path.clone()))?;
            tree = entry
                .object()?
                .try_into_tree()
                .map_err(|e| GitError::Gix(e.to_string()))?;
        }

        let prefix = request.path.trim_matches('/').to_string();
        let mut stats: HashMap<String, LangStats> = HashMap::new();
        let mut total_files = 0u64;
        let mut total_bytes = 0u64;
        let mut total_lines = 0u64;

        let mut ctx = WalkContext {
            max_file_size,
            stats: &mut stats,
            total_files: &mut total_files,
            total_bytes: &mut total_bytes,
            total_lines: &mut total_lines,
        };
        self.walk_tree(&repo, &tree, &prefix, 0, &mut ctx)?;

        tracing::info!(
            total_files,
            total_bytes,
            total_lines,
            languages_found = stats.len(),
            "raw language stats before group resolution"
        );
        let mut resolved: HashMap<String, LangStats> = HashMap::new();
        for (lang, s) in stats {
            let target = resolve_group(&lang).unwrap_or(&lang);
            let entry = resolved
                .entry(target.to_string())
                .or_insert_with(|| LangStats {
                    lang_type: s.lang_type.clone(),
                    ..Default::default()
                });
            entry.file_count = entry.file_count.saturating_add(s.file_count);
            entry.bytes = entry.bytes.saturating_add(s.bytes);
            entry.lines = entry.lines.saturating_add(s.lines);
            if entry.lang_type.is_empty() {
                entry.lang_type = s.lang_type;
            }
        }

        let mut languages: Vec<LanguageStat> = resolved
            .into_iter()
            .map(|(language, s)| {
                let percentage = if total_bytes > 0 {
                    (s.bytes as f64 / total_bytes as f64) * 100.0
                } else {
                    0.0
                };
                LanguageStat {
                    language,
                    lang_type: s.lang_type,
                    file_count: s.file_count,
                    bytes: s.bytes,
                    lines: s.lines,
                    percentage,
                }
            })
            .collect();

        languages.sort_by(|a, b| {
            b.bytes
                .cmp(&a.bytes)
                .then_with(|| a.language.cmp(&b.language))
        });

        Ok(GetLanguageStatsResponse {
            languages,
            total_files,
            total_bytes,
            total_lines,
        })
    }

    fn walk_tree(
        &self,
        _repo: &gix::Repository,
        tree: &gix::Tree<'_>,
        prefix: &str,
        depth: usize,
        ctx: &mut WalkContext<'_>,
    ) -> GitResult<()> {
        if depth > MAX_TREE_WALK_DEPTH {
            return Err(GitError::InvalidArgument(format!(
                "tree depth exceeds maximum of {MAX_TREE_WALK_DEPTH}"
            )));
        }

        for entry in tree.iter() {
            let entry = entry?;
            let name = String::from_utf8_lossy(entry.filename()).into_owned();
            let path = if prefix.is_empty() {
                name.clone()
            } else {
                format!("{prefix}/{name}")
            };

            match entry.kind() {
                EntryKind::Tree => {
                    let child_tree = entry
                        .object()?
                        .try_into_tree()
                        .map_err(|e| GitError::Gix(e.to_string()))?;
                    self.walk_tree(_repo, &child_tree, &path, depth + 1, ctx)?;
                }
                EntryKind::Blob | EntryKind::BlobExecutable => {
                    let blob = entry
                        .object()?
                        .try_into_blob()
                        .map_err(|e| GitError::Gix(e.to_string()))?;
                    let data = &blob.data;
                    let size = data.len() as u64;

                    if size == 0 {
                        continue;
                    }

                    let is_binary = data.contains(&0);

                    let Some((lang_name, lang_type)) = detect_language(&path, is_binary) else {
                        tracing::debug!(path = %path, is_binary, "no language detected");
                        continue;
                    };

                    let lang_key = lang_name.to_string();

                    let lines = if !is_binary && size <= u64::from(ctx.max_file_size) {
                        count_code_lines(data)
                    } else {
                        0
                    };

                    *ctx.total_files = ctx.total_files.saturating_add(1);
                    *ctx.total_bytes = ctx.total_bytes.saturating_add(size);
                    *ctx.total_lines = ctx.total_lines.saturating_add(lines);

                    let s = ctx
                        .stats
                        .entry(lang_key.clone())
                        .or_insert_with(|| LangStats {
                            lang_type: lang_type.to_string(),
                            ..Default::default()
                        });
                    s.file_count = s.file_count.saturating_add(1);
                    s.bytes = s.bytes.saturating_add(size);
                    s.lines = s.lines.saturating_add(lines);
                }
                _ => {} // Skip symlinks, submodules
            }
        }

        Ok(())
    }
}