//! Fast, side-effect-free status for shell prompts.
//!
//! Every snapshot and checkout writes a manifest of the working copy as it
//! was last seen: `size`, `mtime`, and BLAKE3 of each file. `quick_status`
//! walks the working copy and compares against that manifest, reading a
//! file's content only when its size or mtime changed, and records no
//! operation. Ahead/behind counts come from walking the store between the
//! local bookmark and its `origin` tracking state.

use super::*;
use std::time::UNIX_EPOCH;

#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub struct PromptInfo {
    pub bookmark: String,
    /// Working-copy ChangeId prefix.
    pub change_id: String,
    pub heads: usize,
    pub dirty: bool,
    pub conflicted: bool,
    /// Changes local `main` has that `origin/main` lacks, when tracking exists.
    pub ahead: Option<usize>,
    pub behind: Option<usize>,
}

impl PromptInfo {
    /// Expand `%b` bookmark, `%c` change id, `%h` heads, `%d` dirty marker
    /// (`*`), `%x` conflict marker (`!`), `%a`/`%B` ahead/behind counts
    /// (empty when unknown), `%A`/`%D` `+n`/`-n` when non-zero, `%%` percent.
    pub fn format(&self, fmt: &str) -> String {
        let mut out = String::new();
        let mut chars = fmt.chars();
        while let Some(c) = chars.next() {
            if c != '%' {
                out.push(c);
                continue;
            }
            match chars.next() {
                Some('b') => out.push_str(&self.bookmark),
                Some('c') => out.push_str(&self.change_id),
                Some('h') => out.push_str(&self.heads.to_string()),
                Some('d') => {
                    if self.dirty {
                        out.push('*');
                    }
                }
                Some('x') => {
                    if self.conflicted {
                        out.push('!');
                    }
                }
                Some('a') => out.push_str(&self.ahead.map(|n| n.to_string()).unwrap_or_default()),
                Some('B') => out.push_str(&self.behind.map(|n| n.to_string()).unwrap_or_default()),
                Some('A') => {
                    if let Some(n) = self.ahead.filter(|n| *n > 0) {
                        out.push_str(&format!("+{n}"));
                    }
                }
                Some('D') => {
                    if let Some(n) = self.behind.filter(|n| *n > 0) {
                        out.push_str(&format!("-{n}"));
                    }
                }
                Some('%') => out.push('%'),
                Some(other) => {
                    out.push('%');
                    out.push(other);
                }
                None => out.push('%'),
            }
        }
        out
    }
}

/// Path → (size, mtime in nanoseconds, BLAKE3 hex) as last seen.
/// One manifest entry: the file's stat, its content hash, and the stored
/// blob for an opaque file.
#[derive(Clone, Debug)]
pub(crate) struct ManifestEntry {
    pub size: u64,
    pub mtime_ns: u128,
    pub hash: String,
    pub blob: Option<ObjectRef>,
}

#[derive(Clone, Debug, Default)]
pub(crate) struct Manifest {
    /// When the manifest was written, for the racy-stat guard.
    pub written_ns: u128,
    pub entries: BTreeMap<String, ManifestEntry>,
}

pub(crate) fn mtime_ns(m: &fs::Metadata) -> u128 {
    m.modified().ok().and_then(|t| t.duration_since(UNIX_EPOCH).ok()).map(|d| d.as_nanos()).unwrap_or(0)
}

pub const DEFAULT_PROMPT_FORMAT: &str = "%b %c%d%x%A%D";

/// One manifest line per file: size, mtime in nanoseconds, hash, blob ref
/// or `-`, path.
fn manifest_line(path: &str, size: u64, mtime_ns: u128, hash: &str, blob: Option<ObjectRef>) -> String {
    format!("{size}\t{mtime_ns}\t{hash}\t{}\t{path}\n", blob.map(|b| b.to_hex()).unwrap_or_else(|| "-".into()))
}

impl Repo {
    fn manifest_path(&self) -> PathBuf {
        self.oxy.join("workspaces").join(self.workspace.to_hex()).join("manifest")
    }

    /// Record the working copy as it is now (after a snapshot, commit, or
    /// checkout), with header lines saying whether the base state is
    /// conflicted and whether the working-copy change holds uncommitted work.
    pub(crate) fn write_manifest(&self, conflicted: bool, uncommitted: bool) -> Result<()> {
        let entries = self.walk_working_copy()?;
        self.write_manifest_entries(conflicted, uncommitted, &entries, &HashMap::new())
    }

    /// Write the manifest from entries already walked; `blobs` names the
    /// stored blob of each opaque path so the next walk can skip reading it.
    pub(crate) fn write_manifest_entries(&self, conflicted: bool, uncommitted: bool, entries: &BTreeMap<String, FsEntry>, blobs: &HashMap<String, ObjectRef>) -> Result<()> {
        let written = std::time::SystemTime::now().duration_since(UNIX_EPOCH).map(|d| d.as_nanos()).unwrap_or(0);
        let mut text = format!("# conflicted={}\n# uncommitted={}\n# written={written}\n", conflicted as u8, uncommitted as u8);
        for (path, e) in entries {
            let full = self.root.join(path);
            let (size, mtime_ns) = match fs::symlink_metadata(&full) {
                Ok(m) => (m.len(), mtime_ns(&m)),
                Err(_) => (e.content.len() as u64, 0),
            };
            let hash = match &e.content_hash {
                Some(h) => h.clone(),
                None => blake3::hash(&e.content).to_hex().to_string(),
            };
            let blob = blobs.get(path).copied().or(e.blob);
            text.push_str(&manifest_line(path, size, mtime_ns, &hash, blob));
        }
        let p = self.manifest_path();
        fs::create_dir_all(p.parent().unwrap())?;
        write_atomic(&p, text.as_bytes())
    }

    /// Change only the header flags of the current manifest (after a commit
    /// the files are as the snapshot left them).
    pub(crate) fn rewrite_manifest_flags(&self, conflicted: bool, uncommitted: bool) -> Result<()> {
        let p = self.manifest_path();
        let text = match fs::read_to_string(&p) {
            Ok(t) => t,
            Err(_) => return self.write_manifest(conflicted, uncommitted),
        };
        let mut out = String::with_capacity(text.len());
        for line in text.lines() {
            if line.starts_with("# conflicted=") {
                out.push_str(&format!("# conflicted={}\n", conflicted as u8));
            } else if line.starts_with("# uncommitted=") {
                out.push_str(&format!("# uncommitted={}\n", uncommitted as u8));
            } else {
                out.push_str(line);
                out.push('\n');
            }
        }
        write_atomic(&p, out.as_bytes())
    }

    /// Forget the manifest after an operation that changed the working-copy
    /// change without a snapshot (undo, rewrites); the prompt shows blank
    /// markers until the next snapshot.
    pub(crate) fn drop_manifest(&self) {
        let _ = fs::remove_file(self.manifest_path());
    }

    pub(crate) fn read_manifest(&self) -> Result<Option<(bool, bool, Manifest)>> {
        let text = match fs::read_to_string(self.manifest_path()) {
            Ok(t) => t,
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(None),
            Err(e) => return Err(e.into()),
        };
        let mut out = Manifest::default();
        let mut conflicted = false;
        let mut uncommitted = false;
        for line in text.lines() {
            if let Some(v) = line.strip_prefix("# conflicted=") {
                conflicted = v.trim() == "1";
                continue;
            }
            if let Some(v) = line.strip_prefix("# uncommitted=") {
                uncommitted = v.trim() == "1";
                continue;
            }
            if let Some(v) = line.strip_prefix("# written=") {
                out.written_ns = v.trim().parse().unwrap_or(u128::MAX);
                continue;
            }
            let f: Vec<&str> = line.splitn(5, '\t').collect();
            if f.len() == 5 {
                out.entries.insert(
                    f[4].to_string(),
                    ManifestEntry { size: f[0].parse().unwrap_or(0), mtime_ns: f[1].parse().unwrap_or(0), hash: f[2].to_string(), blob: ObjectRef::from_hex(f[3]) },
                );
            }
        }
        Ok(Some((conflicted, uncommitted, out)))
    }

    /// Whether the working copy differs from the last manifest. Without a
    /// manifest the answer is `None`.
    pub fn quick_dirty(&self) -> Result<Option<bool>> {
        let Some((_, uncommitted, manifest)) = self.read_manifest()? else { return Ok(None) };
        if uncommitted {
            return Ok(Some(true));
        }
        let mut seen = 0usize;
        let mut wb = ignore::WalkBuilder::new(&self.root);
        wb.hidden(false).git_ignore(false).git_global(false).git_exclude(false).require_git(false).follow_links(false).add_custom_ignore_filename(".oxyignore");
        wb.filter_entry(|e| e.file_name() != OXY_DIR);
        for entry in wb.build() {
            let Ok(entry) = entry else { continue };
            let Some(ft) = entry.file_type() else { continue };
            if ft.is_dir() {
                continue;
            }
            let rel: String = entry.path().strip_prefix(&self.root).unwrap().components().map(|c| c.as_os_str().to_string_lossy().to_string()).collect::<Vec<_>>().join("/");
            if !self.in_scope(&rel) {
                continue;
            }
            let Some(me) = manifest.entries.get(&rel) else { return Ok(Some(true)) };
            seen += 1;
            let m = fs::symlink_metadata(entry.path())?;
            let now_mtime = mtime_ns(&m);
            if ft.is_symlink() {
                let target = fs::read_link(entry.path())?;
                if blake3::hash(target.to_string_lossy().as_bytes()).to_hex().as_str() != me.hash {
                    return Ok(Some(true));
                }
                continue;
            }
            if m.len() != me.size {
                return Ok(Some(true));
            }
            if now_mtime != me.mtime_ns && blake3::hash(&fs::read(entry.path())?).to_hex().as_str() != me.hash {
                return Ok(Some(true));
            }
        }
        Ok(Some(seen != manifest.entries.len()))
    }

    /// Prompt information without recording anything.
    pub fn quick_status(&self) -> Result<PromptInfo> {
        let view = self.view()?;
        let bookmark = self.config.bookmark.clone();
        let heads = self.heads_of(&view, &bookmark)?;
        let wc_hash = view.workspaces.get(&self.workspace).copied();
        let change_id = match wc_hash {
            Some(h) => self.store.get_change(&h)?.change_id.short(8),
            None => String::new(),
        };
        // Conflictedness was recorded by the last snapshot; without a
        // manifest (never snapshotted) both flags are unknown and shown clear.
        let manifest = self.read_manifest()?;
        let conflicted = manifest.as_ref().map(|(c, _, _)| *c).unwrap_or(false);
        let dirty = self.quick_dirty()?.unwrap_or(false);
        let (ahead, behind) = match view.remotes.get("origin").and_then(|b| b.get(&bookmark)) {
            Some(st) => {
                let remote_heads = self.store.get_state(st)?.heads;
                let ahead = self.negotiate(&remote_heads, &heads).map(|v| v.len()).ok();
                let behind = self.negotiate(&heads, &remote_heads).map(|v| v.len()).ok();
                (ahead, behind)
            }
            None => (None, None),
        };
        Ok(PromptInfo { bookmark, change_id, heads: heads.len(), dirty, conflicted, ahead, behind })
    }
}