//! The files under `memory/` and the memory block (M5a spec, sections 3 and 4). `memoryd` creates
//! what is missing and never overwrites anything; files are 0600 in a 0700 directory.

use std::fs::{DirBuilder, OpenOptions, Permissions};
use std::io::Write;
use std::os::unix::fs::{DirBuilderExt, OpenOptionsExt, PermissionsExt};
use std::path::{Path, PathBuf};

use proto::MemoryFile;

use crate::check::{Refused, check};
use crate::entries;

/// The most characters `soul.md` may have.
pub const SOUL_LIMIT: usize = 4_000;

/// `n` with commas between thousands: `2,200`.
pub fn grouped(n: usize) -> String {
    // `let digits = n.to_string()`. Walk its chars with their index i; before each char where i > 0
    // and `(digits.len() - i).is_multiple_of(3)`, push a comma. So 2200 is "2,200" and 999 is
    // "999".
    let digits = n.to_string();
    let mut out = String::with_capacity(digits.len() + digits.len() / 3);
    for (i, c) in digits.chars().enumerate() {
        if i > 0 && (digits.len() - i).is_multiple_of(3) {
            out.push(',');
        }
        out.push(c);
    }
    out
}

/// The memory directory.
#[derive(Debug, Clone)]
pub struct Store {
    dir: PathBuf,
}

/// The block for a new session, and the identity entries left out of it because they failed the
/// check (for `memoryd` to log).
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Block {
    pub text: String,
    pub left_out: Vec<(MemoryFile, Refused)>,
}

fn fail(path: &Path, e: std::io::Error) -> String {
    format!("{}: {e}", path.display())
}

impl Store {
    pub fn new(dir: &Path) -> Store {
        Store {
            dir: dir.to_path_buf(),
        }
    }

    pub fn path(&self, name: &str) -> PathBuf {
        self.dir.join(name)
    }

    /// Create `memory/` (0700) and each missing file (0600): `soul.md` from `starter`, the others
    /// empty. Nothing that exists is changed. The error names the path.
    pub fn init(&self, starter: &Path) -> Result<(), String> {
        // 1. `DirBuilder::new().recursive(true).mode(0o700).create(&self.dir)`, then
        //    `set_permissions(&self.dir, Permissions::from_mode(0o700))`.
        // 2. When `self.path("soul.md")` does not exist: `read_to_string(starter)`, then
        //    `self.create(&soul, &text)`.
        // 3. Each of "memory.md", "user.md", "notes.md" that does not exist: `self.create(&path,
        //    "")`. Every error through `fail(path, e)`. Nothing that exists is changed. Ok(()).
        DirBuilder::new()
            .recursive(true)
            .mode(0o700)
            .create(&self.dir)
            .map_err(|e| fail(&self.dir, e))?;
        std::fs::set_permissions(&self.dir, Permissions::from_mode(0o700))
            .map_err(|e| fail(&self.dir, e))?;
        if !self.path("soul.md").exists() {
            let text = std::fs::read_to_string(starter).map_err(|e| fail(starter, e))?;
            let soul = self.path("soul.md");
            self.create(&soul, &text)?;
        }
        for name in ["memory.md", "user.md", "notes.md"] {
            let path = self.path(name);
            if !path.exists() {
                self.create(&path, "")?;
            }
        }
        Ok(())
    }

    /// Create `path` at 0600 with `text`; an existing file is an error, never overwritten.
    fn create(&self, path: &Path, text: &str) -> Result<(), String> {
        // `OpenOptions::new().write(true).create_new(true).mode(0o600).open(path)`, then
        // `write_all(text.as_bytes())`. Errors through `fail(path, e)`. create_new makes an
        // existing file an error: it is never overwritten.
        let mut file = OpenOptions::new()
            .write(true)
            .create_new(true)
            .mode(0o600)
            .open(path)
            .map_err(|e| fail(path, e))?;
        file.write_all(text.as_bytes()).map_err(|e| fail(path, e))?;
        Ok(())
    }

    /// The entries of an identity file.
    pub fn entries(&self, file: MemoryFile) -> Result<Vec<String>, String> {
        // `read_to_string(self.path(file.name()))` (an error through `fail`), then
        // `entries::parse(&text)`.
        let path = self.path(file.name());
        let text = std::fs::read_to_string(&path).map_err(|e| fail(&path, e))?;
        Ok(entries::parse(&text))
    }

    /// Replace an identity file's entries: written to a temporary file at 0600, then renamed.
    pub fn write_entries(&self, file: MemoryFile, list: &[String]) -> Result<(), String> {
        // The file is `self.path(file.name())`; the temporary file is
        // `self.path(&format!(".{}.tmp", file.name()))`. Remove the temporary file if it is there
        // (ignore the result), `self.create(&temp, &entries::render(list))?`, then
        // `std::fs::rename(&temp, &path)` (an error through `fail(&path, e)`).
        let path = self.path(file.name());
        let temp = self.path(&format!(".{}.tmp", file.name()));
        let _ = std::fs::remove_file(&temp);
        self.create(&temp, &entries::render(list))?;
        std::fs::rename(&temp, &path).map_err(|e| fail(&path, e))?;
        Ok(())
    }

    /// Append `text` to a file (0600, created if missing), as one write.
    pub fn append(&self, name: &str, text: &str) -> Result<(), String> {
        // `OpenOptions::new().append(true).create(true).mode(0o600).open(&path)` for
        // `self.path(name)`, then one `write_all(text.as_bytes())`. Errors through `fail`.
        let path = self.path(name);
        let mut file = OpenOptions::new()
            .append(true)
            .create(true)
            .mode(0o600)
            .open(&path)
            .map_err(|e| fail(&path, e))?;
        file.write_all(text.as_bytes())
            .map_err(|e| fail(&path, e))?;
        Ok(())
    }

    /// The block for a new session (M5a spec, section 4). A file over its limit, or unreadable,
    /// is an error: no session starts without its memory and no sign of it. Identity entries that
    /// fail the check are left out and reported; `soul.md` is the owner's and is not checked.
    pub fn block(&self) -> Result<Block, String> {
        // 1. Read `self.path("soul.md")` (an error through `fail`) and trim() it. When its
        //    chars().count() > SOUL_LIMIT: Err(format!("{}: {} characters; its limit is {}",
        //    path.display(), grouped(chars), grouped(SOUL_LIMIT))).
        // 2. `text` starts as format!("# soul.md\n{}", soul), with "(empty)" in place of an empty
        //    soul.
        // 3. For file in [MemoryFile::Memory, MemoryFile::User]: `self.entries(file)?`; `size =
        //    entries::size(&list)`; when size > file.limit(), the same Err sentence with the path,
        //    size and limit of that file. Each entry: `check(&entry)` Ok -> kept; Err(refused) ->
        //    push (file, refused) onto `left_out`. The body is "(empty)" when nothing is kept, else
        //    `entries::render(&kept).trim_end()`. Append format!("\n\n# {} ({} of {}
        //    characters)\n{body}", file.name(), grouped(size), grouped(file.limit())) to `text`.
        //    `size` counts the whole file, entries left out included.
        // 4. Ok(Block { text, left_out }).
        let soul_path = self.path("soul.md");
        let soul = std::fs::read_to_string(&soul_path).map_err(|e| fail(&soul_path, e))?;
        let soul = soul.trim();
        let chars = soul.chars().count();
        if chars > SOUL_LIMIT {
            return Err(format!(
                "{}: {} characters; its limit is {}",
                soul_path.display(),
                grouped(chars),
                grouped(SOUL_LIMIT)
            ));
        }

        let mut text = if soul.is_empty() {
            "# soul.md\n(empty)".to_string()
        } else {
            format!("# soul.md\n{soul}")
        };

        let mut left_out = Vec::new();
        for file in [MemoryFile::Memory, MemoryFile::User] {
            let list = self.entries(file)?;
            let size = entries::size(&list);
            if size > file.limit() {
                let path = self.path(file.name());
                return Err(format!(
                    "{}: {} characters; its limit is {}",
                    path.display(),
                    grouped(size),
                    grouped(file.limit())
                ));
            }
            let mut kept = Vec::new();
            for entry in &list {
                match check(entry) {
                    Ok(()) => kept.push(entry.clone()),
                    Err(refused) => left_out.push((file, refused)),
                }
            }
            let body = if kept.is_empty() {
                "(empty)".to_string()
            } else {
                entries::render(&kept).trim_end().to_string()
            };
            text.push_str(&format!(
                "\n\n# {} ({} of {} characters)\n{body}",
                file.name(),
                grouped(size),
                grouped(file.limit())
            ));
        }

        Ok(Block { text, left_out })
    }
}