sift-queue 0.8.0

use anyhow::{Context, Result};
use rustix::fs::{flock, FlockOperation};
use serde::{Deserialize, Serialize};
use std::collections::HashSet;
use std::fs::{self, File, OpenOptions};
use std::io::{BufRead, BufReader, Seek, Write};
use std::os::fd::AsFd;
use std::path::{Path, PathBuf};

/// Valid persisted status values for queue items.
pub const VALID_STATUSES: &[&str] = &["pending", "in_progress", "closed"];

/// Valid display status values surfaced by list/show output.
pub const VALID_DISPLAY_STATUSES: &[&str] = &["pending", "blocked", "in_progress", "closed"];

/// Valid source types accepted by `push` (used for validation on add).
pub const VALID_SOURCE_TYPES: &[&str] = &["diff", "file", "text", "directory"];

/// Valid priority range accepted by first-class priority fields.
pub const VALID_PRIORITY_RANGE: std::ops::RangeInclusive<u8> = 0..=4;

const ID_ALPHABET: [char; 32] = [
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'j',
    'k', 'm', 'n', 'p', 'q', 'r', 's', 't', 'v', 'w', 'x', 'y', 'z',
];
const MIN_GENERATED_ID_LENGTH: usize = 3;
// 10% is intentional for now; reduce this if collision retries become too frequent in production.
const ID_SPACE_OCCUPANCY_THRESHOLD_PERCENT: usize = 10;

// ── Types ───────────────────────────────────────────────────────────────────

#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub struct Item {
    pub id: String,

    #[serde(skip_serializing_if = "Option::is_none")]
    pub title: Option<String>,

    #[serde(skip_serializing_if = "Option::is_none")]
    pub description: Option<String>,

    pub status: String,

    #[serde(skip_serializing_if = "Option::is_none")]
    #[serde(default)]
    pub priority: Option<u8>,

    pub sources: Vec<Source>,

    pub metadata: serde_json::Value,

    pub created_at: String,
    pub updated_at: String,

    #[serde(skip_serializing_if = "is_empty_vec")]
    #[serde(default)]
    pub blocked_by: Vec<String>,

    #[serde(skip_serializing_if = "is_empty_json_vec")]
    #[serde(default)]
    pub errors: Vec<serde_json::Value>,
}

fn is_empty_vec(v: &[String]) -> bool {
    v.is_empty()
}

fn is_empty_json_vec(v: &[serde_json::Value]) -> bool {
    v.is_empty()
}

/// Serialize items through serde so the struct definition is the source of
/// truth for JSON output.
///
/// Note: this serializes the item's current `status` field verbatim. Callers
/// that want display/view semantics (for example, surfacing `blocked` as a
/// computed status in read-oriented output) must first call
/// `with_computed_status(...)`.
impl Item {
    pub fn to_json_value(&self) -> serde_json::Value {
        serde_json::to_value(self).expect("item serialization should succeed")
    }

    pub fn to_json_string(&self) -> String {
        serde_json::to_string(self).expect("item serialization should succeed")
    }

    pub fn pending(&self) -> bool {
        self.status == "pending"
    }

    pub fn blocked(&self) -> bool {
        !self.blocked_by.is_empty()
    }

    /// Compute the visible status for read-oriented views.
    ///
    /// Persisted lifecycle status remains `pending|in_progress|closed`, but
    /// pending items with open blockers are surfaced as `blocked` in display
    /// output.
    pub fn computed_status(&self, open_ids: Option<&HashSet<String>>) -> String {
        if !self.pending() || !self.blocked() {
            return self.status.clone();
        }

        match open_ids {
            None => "blocked".to_string(),
            Some(ids) => {
                if self.blocked_by.iter().any(|id| ids.contains(id)) {
                    "blocked".to_string()
                } else {
                    self.status.clone()
                }
            }
        }
    }

    pub fn with_computed_status(&self, open_ids: Option<&HashSet<String>>) -> Self {
        let mut item = self.clone();
        item.status = self.computed_status(open_ids);
        item
    }

    pub fn ready(&self, open_ids: Option<&HashSet<String>>) -> bool {
        if !self.pending() {
            return false;
        }
        if !self.blocked() {
            return true;
        }
        match open_ids {
            None => true,
            Some(ids) => self.blocked_by.iter().all(|id| !ids.contains(id)),
        }
    }
}

pub fn parse_priority_value(input: &str) -> Result<u8> {
    let trimmed = input.trim();

    let priority = trimmed
        .parse::<u8>()
        .with_context(|| format!("Invalid priority: {input}. Valid: 0-4"))?;

    if !VALID_PRIORITY_RANGE.contains(&priority) {
        anyhow::bail!("Invalid priority: {input}. Valid: 0-4");
    }

    Ok(priority)
}

#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub struct Source {
    #[serde(rename = "type")]
    pub type_: String,

    #[serde(skip_serializing_if = "Option::is_none")]
    pub path: Option<String>,

    #[serde(skip_serializing_if = "Option::is_none")]
    pub content: Option<String>,
}

impl Source {
    pub fn to_json_value(&self) -> serde_json::Value {
        serde_json::to_value(self).expect("source serialization should succeed")
    }
}

// ── Queue ───────────────────────────────────────────────────────────────────

pub struct Queue {
    pub path: PathBuf,
}

pub struct NewItem {
    pub sources: Vec<Source>,
    pub title: Option<String>,
    pub description: Option<String>,
    pub priority: Option<u8>,
    pub metadata: serde_json::Value,
    pub blocked_by: Vec<String>,
}

impl Queue {
    pub fn new(path: PathBuf) -> Self {
        Self { path }
    }

    /// Add a new item to the queue. Returns the created Item.
    pub fn push(
        &self,
        sources: Vec<Source>,
        title: Option<String>,
        description: Option<String>,
        priority: Option<u8>,
        metadata: serde_json::Value,
        blocked_by: Vec<String>,
    ) -> Result<Item> {
        let new_item = NewItem {
            sources,
            title,
            description,
            priority,
            metadata,
            blocked_by,
        };

        let mut items = self.push_many_with_description(vec![new_item])?;
        Ok(items.remove(0))
    }

    /// Add many new items to the queue under a single lock.
    pub fn push_many_with_description(&self, items: Vec<NewItem>) -> Result<Vec<Item>> {
        if items.is_empty() {
            anyhow::bail!("At least one item is required");
        }

        for item in &items {
            self.validate_new_item(item)?;
        }

        self.with_exclusive_lock(|f| {
            let existing = read_items(f, &self.path);
            let mut existing_ids: HashSet<String> = existing.iter().map(|i| i.id.clone()).collect();
            let now = now_iso8601();
            let mut created = Vec::with_capacity(items.len());

            f.seek(std::io::SeekFrom::End(0))?;
            for new_item in items {
                let id = generate_id(&existing_ids);
                existing_ids.insert(id.clone());

                let item = Item {
                    id,
                    title: new_item.title,
                    description: new_item.description,
                    status: "pending".to_string(),
                    priority: new_item.priority,
                    sources: new_item.sources,
                    metadata: new_item.metadata,
                    created_at: now.clone(),
                    updated_at: now.clone(),
                    blocked_by: new_item.blocked_by,
                    errors: Vec::new(),
                };

                writeln!(f, "{}", item.to_json_string())?;
                created.push(item);
            }
            f.flush()?;

            Ok(created)
        })
    }

    /// Get all items, skipping corrupt lines with warnings.
    pub fn all(&self) -> Vec<Item> {
        if !self.path.exists() {
            return Vec::new();
        }
        match self.with_shared_lock(|f| Ok(read_items(f, &self.path))) {
            Ok(items) => items,
            Err(_) => Vec::new(),
        }
    }

    /// Find an item by ID.
    pub fn find(&self, id: &str) -> Option<Item> {
        self.all().into_iter().find(|item| item.id == id)
    }

    /// Return IDs for all non-closed items currently in the queue.
    pub fn open_ids(&self) -> HashSet<String> {
        open_ids_for_items(&self.all())
    }

    /// Apply computed/display status semantics to a single item.
    pub fn item_with_computed_status(&self, item: Item) -> Item {
        let open_ids = self.open_ids();
        item.with_computed_status(Some(&open_ids))
    }

    /// Apply computed/display status semantics to a collection of items.
    pub fn items_with_computed_status(&self, items: Vec<Item>) -> Vec<Item> {
        let open_ids = self.open_ids();
        items
            .into_iter()
            .map(|item| item.with_computed_status(Some(&open_ids)))
            .collect()
    }

    /// Load all items and apply computed/display status semantics.
    pub fn all_with_computed_status(&self) -> Vec<Item> {
        let items = self.all();
        let open_ids = open_ids_for_items(&items);
        items
            .into_iter()
            .map(|item| item.with_computed_status(Some(&open_ids)))
            .collect()
    }

    /// Find an item by ID and apply computed/display status semantics.
    pub fn find_with_computed_status(&self, id: &str) -> Option<Item> {
        let items = self.all();
        let open_ids = open_ids_for_items(&items);
        items
            .into_iter()
            .find(|item| item.id == id)
            .map(|item| item.with_computed_status(Some(&open_ids)))
    }

    /// Filter items by persisted lifecycle status (optional).
    ///
    /// This method intentionally does not apply computed/display status
    /// semantics. Callers that want view-oriented filtering (for example,
    /// treating `blocked` as a visible status in list/show output) should load
    /// items, call `with_computed_status(...)`, and then filter those results.
    pub fn filter(&self, status: Option<&str>) -> Vec<Item> {
        let items = self.all();
        match status {
            Some(s) => items.into_iter().filter(|item| item.status == s).collect(),
            None => items,
        }
    }

    /// Return pending items that are not blocked by any non-closed item.
    pub fn ready(&self) -> Vec<Item> {
        let items = self.all();
        let open_ids: HashSet<String> = items
            .iter()
            .filter(|i| i.status != "closed")
            .map(|i| i.id.clone())
            .collect();
        items
            .into_iter()
            .filter(|item| item.ready(Some(&open_ids)))
            .collect()
    }

    /// Update an item by ID. Returns the updated Item or None.
    pub fn update(&self, id: &str, attrs: UpdateAttrs) -> Result<Option<Item>> {
        self.with_exclusive_lock(|f| {
            let mut items = read_items(f, &self.path);
            let index = items.iter().position(|item| item.id == id);
            let index = match index {
                Some(i) => i,
                None => return Ok(None),
            };

            let original = items[index].clone();
            let item = &mut items[index];

            if let Some(status) = &attrs.status {
                if !VALID_STATUSES.contains(&status.as_str()) {
                    anyhow::bail!(
                        "Invalid status: {}. Valid: {}",
                        status,
                        VALID_STATUSES.join(", ")
                    );
                }
                item.status = status.clone();
            }
            if let Some(title) = attrs.title {
                item.title = Some(title);
            }
            if let Some(description) = attrs.description {
                item.description = Some(description);
            }
            if let Some(priority) = attrs.priority {
                if let Some(value) = priority {
                    validate_priority(value)?;
                }
                item.priority = priority;
            }
            if let Some(metadata) = attrs.metadata {
                item.metadata = metadata;
            }
            if let Some(blocked_by) = attrs.blocked_by {
                validate_blocked_by(id, &blocked_by)?;
                item.blocked_by = blocked_by;
            }
            if let Some(sources) = attrs.sources {
                self.validate_source_types(&sources)?;
                item.sources = sources;
            }

            if *item == original {
                return Ok(Some(original));
            }

            item.updated_at = now_iso8601();

            let updated = item.clone();
            rewrite_items(f, &items)?;
            Ok(Some(updated))
        })
    }

    /// Remove an item by ID. Returns the removed Item or None.
    pub fn remove(&self, id: &str) -> Result<Option<Item>> {
        self.with_exclusive_lock(|f| {
            let mut items = read_items(f, &self.path);
            let index = items.iter().position(|item| item.id == id);
            match index {
                Some(i) => {
                    let removed = items.remove(i);
                    rewrite_items(f, &items)?;
                    Ok(Some(removed))
                }
                None => Ok(None),
            }
        })
    }

    // ── Private helpers ─────────────────────────────────────────────────

    fn validate_new_item(&self, item: &NewItem) -> Result<()> {
        if let Some(priority) = item.priority {
            validate_priority(priority)?;
        }

        if item.sources.is_empty() && item.title.is_none() && item.description.is_none() {
            anyhow::bail!("Item requires at least one source, title, or description");
        }

        self.validate_source_types(&item.sources)
    }

    fn validate_source_types(&self, sources: &[Source]) -> Result<()> {
        for source in sources {
            if !VALID_SOURCE_TYPES.contains(&source.type_.as_str()) {
                anyhow::bail!(
                    "Invalid source type: {}. Valid: {}",
                    source.type_,
                    VALID_SOURCE_TYPES.join(", ")
                );
            }
        }
        Ok(())
    }

    fn ensure_directory(&self) -> Result<()> {
        if let Some(parent) = self.path.parent() {
            if !parent.exists() {
                fs::create_dir_all(parent)?;
            }
        }
        Ok(())
    }

    fn with_exclusive_lock<T, F>(&self, f: F) -> Result<T>
    where
        F: FnOnce(&mut File) -> Result<T>,
    {
        self.ensure_directory()?;
        let mut file = OpenOptions::new()
            .read(true)
            .write(true)
            .create(true)
            .truncate(false)
            .open(&self.path)
            .with_context(|| format!("Failed to open queue file: {}", self.path.display()))?;

        flock(&file.as_fd(), FlockOperation::LockExclusive)
            .with_context(|| "Failed to acquire exclusive lock")?;

        let result = f(&mut file);

        // Lock released when file is dropped
        result
    }

    fn with_shared_lock<T, F>(&self, f: F) -> Result<T>
    where
        F: FnOnce(&mut File) -> Result<T>,
    {
        let mut file = File::open(&self.path)
            .with_context(|| format!("Failed to open queue file: {}", self.path.display()))?;

        flock(&file.as_fd(), FlockOperation::LockShared)
            .with_context(|| "Failed to acquire shared lock")?;

        f(&mut file)
    }
}

fn open_ids_for_items(items: &[Item]) -> HashSet<String> {
    items
        .iter()
        .filter(|item| item.status != "closed")
        .map(|item| item.id.clone())
        .collect()
}

/// Read items from an open file, skipping corrupt lines.
fn read_items(file: &mut File, path: &Path) -> Vec<Item> {
    file.seek(std::io::SeekFrom::Start(0)).ok();
    let reader = BufReader::new(file);
    let mut items = Vec::new();

    for (line_num, line) in reader.lines().enumerate() {
        let line = match line {
            Ok(l) => l,
            Err(_) => continue,
        };
        let trimmed = line.trim();
        if trimmed.is_empty() {
            continue;
        }
        match serde_json::from_str::<Item>(trimmed) {
            Ok(item) => items.push(item),
            Err(e) => {
                eprintln!(
                    "Warning: Skipping corrupt line {} in {}: {}",
                    line_num + 1,
                    path.display(),
                    e
                );
            }
        }
    }
    items
}

/// Truncate and rewrite all items to the file.
fn rewrite_items(file: &mut File, items: &[Item]) -> Result<()> {
    file.seek(std::io::SeekFrom::Start(0))?;
    file.set_len(0)?;
    for item in items {
        writeln!(file, "{}", item.to_json_string())?;
    }
    file.flush()?;
    Ok(())
}

/// Generate a random lowercase ID using adaptive length and retry on collision.
fn generate_id(existing_ids: &HashSet<String>) -> String {
    let length = generated_id_length(existing_ids.len());

    loop {
        let id = nanoid::nanoid!(length, &ID_ALPHABET);
        if !existing_ids.contains(&id) {
            return id;
        }
    }
}

fn generated_id_length(active_or_reserved_ids: usize) -> usize {
    let mut length = MIN_GENERATED_ID_LENGTH;

    loop {
        let total_space = id_space_for_length(length);
        let occupancy_threshold = total_space * ID_SPACE_OCCUPANCY_THRESHOLD_PERCENT / 100;

        if active_or_reserved_ids < occupancy_threshold {
            return length;
        }

        length += 1;
    }
}

fn id_space_for_length(length: usize) -> usize {
    ID_ALPHABET
        .len()
        .checked_pow(length as u32)
        .expect("generated ID space should fit in usize")
}

/// Current UTC time in ISO 8601 with millisecond precision.
fn now_iso8601() -> String {
    chrono::Utc::now()
        .format("%Y-%m-%dT%H:%M:%S%.3fZ")
        .to_string()
}

fn validate_priority(priority: u8) -> Result<()> {
    if VALID_PRIORITY_RANGE.contains(&priority) {
        Ok(())
    } else {
        anyhow::bail!("Invalid priority: {}. Valid: 0-4", priority);
    }
}

fn validate_blocked_by(item_id: &str, blocked_by: &[String]) -> Result<()> {
    if blocked_by.iter().any(|blocker_id| blocker_id == item_id) {
        anyhow::bail!("Item cannot block itself: {}", item_id);
    }
    Ok(())
}

/// Attributes for updating an item.
#[derive(Default)]
pub struct UpdateAttrs {
    pub status: Option<String>,
    pub title: Option<String>,
    pub description: Option<String>,
    pub priority: Option<Option<u8>>,
    pub metadata: Option<serde_json::Value>,
    pub blocked_by: Option<Vec<String>>,
    pub sources: Option<Vec<Source>>,
}

#[cfg(test)]
mod tests {
    use super::{generated_id_length, id_space_for_length};

    #[test]
    fn id_space_matches_base32_lengths() {
        assert_eq!(id_space_for_length(3), 32_768);
        assert_eq!(id_space_for_length(4), 1_048_576);
        assert_eq!(id_space_for_length(5), 33_554_432);
        assert_eq!(id_space_for_length(6), 1_073_741_824);
    }

    #[test]
    fn generated_ids_start_at_three_characters() {
        assert_eq!(generated_id_length(0), 3);
        assert_eq!(generated_id_length(3_275), 3);
    }

    #[test]
    fn generated_id_length_grows_at_documented_thresholds() {
        assert_eq!(generated_id_length(3_276), 4);
        assert_eq!(generated_id_length(104_857), 5);
        assert_eq!(generated_id_length(3_355_443), 6);
        assert_eq!(generated_id_length(107_374_182), 7);
    }
}