use std::path::Path;
use tokio::process::Command;

const VIDEO_EXTENSIONS: &[&str] = &["mp4", "mkv", "avi", "mov", "webm", "m4v"];

/// In-memory representation of a scanned local video file.
#[derive(Debug, Clone)]
pub struct LocalFileItem {
    /// Relative path from root, with forward slashes (used as the stable ID source).
    pub rel_path: String,
    pub title: String,
    pub duration_secs: u32,
    pub year: Option<u16>,
    /// Ancestor directory names between root and file (excluding root itself).
    pub tags: Vec<String>,
    /// First path component under root (used as collection id/name).
    pub top_dir: String,
}

/// Walk `root` and return all recognised video files with metadata.
///
/// ffprobe is called for each file to determine duration. Files that cannot be
/// probed are included with `duration_secs = 0` so they still appear in the index.
pub async fn scan_dir(root: &Path) -> Vec<LocalFileItem> {
    let mut items = Vec::new();

    let walker = walkdir::WalkDir::new(root).follow_links(true);
    for entry in walker.into_iter().filter_map(|e| e.ok()) {
        if !entry.file_type().is_file() {
            continue;
        }
        let path = entry.path();
        let ext = path
            .extension()
            .and_then(|e| e.to_str())
            .map(|e| e.to_lowercase());
        let ext = match ext {
            Some(ref e) if VIDEO_EXTENSIONS.contains(&e.as_str()) => e.clone(),
            _ => continue,
        };
        let _ = ext; // extension validated, not needed further

        let rel = match path.strip_prefix(root) {
            Ok(r) => r,
            Err(_) => continue,
        };

        // Normalise to forward-slash string for cross-platform stability.
        let rel_path: String = rel
            .components()
            .map(|c| c.as_os_str().to_string_lossy().into_owned())
            .collect::<Vec<_>>()
            .join("/");

        // Top-level directory under root.
        let top_dir = rel
            .components()
            .next()
            .filter(|_| rel.components().count() > 1) // skip if file is at root level
            .map(|c| c.as_os_str().to_string_lossy().into_owned())
            .unwrap_or_else(|| "__root__".to_string());

        // Title: stem with separator chars replaced by spaces.
        let stem = path
            .file_stem()
            .and_then(|s| s.to_str())
            .unwrap_or("")
            .to_string();
        let title = stem.replace(['_', '-', '.'], " ");
        let title = title.trim().to_string();

        // Year: first 4-digit number starting with 19xx or 20xx in filename or parent dirs.
        let search_str = format!(
            "{} {}",
            stem,
            rel.parent()
                .and_then(|p| p.to_str())
                .unwrap_or("")
        );
        let year = extract_year(&search_str);

        // Tags: ancestor directory components between root and the file.
        let tags: Vec<String> = rel
            .parent()
            .into_iter()
            .flat_map(|p| p.components())
            .map(|c| c.as_os_str().to_string_lossy().into_owned())
            .filter(|s| !s.is_empty())
            .collect();

        let duration_secs = get_duration(path).await.unwrap_or(0);

        items.push(LocalFileItem {
            rel_path,
            title,
            duration_secs,
            year,
            tags,
            top_dir,
        });
    }

    items
}

/// Extract the first plausible 4-digit year (1900–2099) from `s`.
fn extract_year(s: &str) -> Option<u16> {
    let chars: Vec<char> = s.chars().collect();
    let n = chars.len();
    if n < 4 {
        return None;
    }
    for i in 0..=(n - 4) {
        // All four chars must be ASCII digits.
        if !chars[i..i + 4].iter().all(|c| c.is_ascii_digit()) {
            continue;
        }
        // Parse and range-check.
        let s4: String = chars[i..i + 4].iter().collect();
        let num: u16 = s4.parse().ok()?;
        if !(1900..=2099).contains(&num) {
            continue;
        }
        // Word-boundary: char before and after must not be digits.
        let before_ok = i == 0 || !chars[i - 1].is_ascii_digit();
        let after_ok = i + 4 >= n || !chars[i + 4].is_ascii_digit();
        if before_ok && after_ok {
            return Some(num);
        }
    }
    None
}

/// Run ffprobe to get the duration of `path` in whole seconds.
async fn get_duration(path: &Path) -> Option<u32> {
    #[derive(serde::Deserialize)]
    struct Fmt {
        duration: Option<String>,
    }
    #[derive(serde::Deserialize)]
    struct Out {
        format: Fmt,
    }

    let output = Command::new("ffprobe")
        .args([
            "-v",
            "quiet",
            "-print_format",
            "json",
            "-show_format",
            path.to_str()?,
        ])
        .output()
        .await
        .ok()?;

    let parsed: Out = serde_json::from_slice(&output.stdout).ok()?;
    let dur: f64 = parsed.format.duration?.parse().ok()?;
    Some(dur as u32)
}