//! Artifacts (Cylinder, docs/cylinder.md §4.1, oxygen#108): an immutable
//! object naming a tree of files, each an ordinary blob of FastCDC BLAKE3
//! chunks, so an image rebuilt with one changed file moves only that file's
//! changed chunks, and a binary in an archive and in an image is the same
//! chunks. An artifact is an object of its own (`artifact`) in canonical
//! CBOR; its tree is a blob. The `cylinder` crate packs, unpacks and keeps
//! them.

use crate::cbor::{self, Value};
use crate::hash::{hash_object, ObjectRef, ObjectType};
use crate::objects::{schema, ObjectError};
use std::collections::BTreeMap;

type R<T> = std::result::Result<T, ObjectError>;

/// The encoding's version this crate writes and reads.
pub const VERSION: u64 = 1;

/// What an artifact is for.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Kind {
    Container,
    RunnerImage,
    Package,
    Archive,
    Report,
}

impl Kind {
    pub const ALL: [Kind; 5] = [
        Kind::Container,
        Kind::RunnerImage,
        Kind::Package,
        Kind::Archive,
        Kind::Report,
    ];

    pub fn as_str(self) -> &'static str {
        match self {
            Kind::Container => "container",
            Kind::RunnerImage => "runner-image",
            Kind::Package => "package",
            Kind::Archive => "archive",
            Kind::Report => "report",
        }
    }

    pub fn parse(s: &str) -> R<Kind> {
        Kind::ALL.into_iter().find(|k| k.as_str() == s).map_or_else(
            || {
                schema(format!(
                    "{s:?} is not a kind of artifact: {}",
                    Kind::ALL.map(|k| k.as_str()).join(", ")
                ))
            },
            Ok,
        )
    }
}

/// A file's mode in a tree: a regular file, an executable one, or a
/// symbolic link (whose blob is its target).
pub const MODE_FILE: u32 = 0o100644;
pub const MODE_EXEC: u32 = 0o100755;
pub const MODE_LINK: u32 = 0o120000;

/// A file of an artifact's tree.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Entry {
    /// `/`-separated, relative, never `.` or `..` parts.
    pub path: String,
    pub mode: u32,
    pub blob: ObjectRef,
    pub size: u64,
}

/// An artifact's files, in path order: paths, modes, blobs and sizes.
#[derive(Clone, Debug, Default, PartialEq, Eq)]
pub struct DirTree {
    pub entries: Vec<Entry>,
}

fn path_ok(p: &str) -> bool {
    !p.is_empty()
        && !p.starts_with('/')
        && p.split('/').all(|s| !s.is_empty() && s != "." && s != "..")
}

fn obj(r: &ObjectRef) -> Value {
    Value::Bytes(r.0.to_vec())
}

fn get_obj(v: &Value, what: &str) -> R<ObjectRef> {
    match v.as_bytes() {
        Some(b) if b.len() == 32 => {
            let mut a = [0u8; 32];
            a.copy_from_slice(b);
            Ok(ObjectRef(a))
        }
        _ => schema(format!("{what} is not an object reference")),
    }
}

fn get_text(v: &Value, what: &str) -> R<String> {
    v.as_text()
        .map(str::to_string)
        .map_or_else(|| schema(format!("{what} is not text")), Ok)
}

fn get_uint(v: &Value, what: &str) -> R<u64> {
    v.as_uint()
        .map_or_else(|| schema(format!("{what} is not a number")), Ok)
}

impl DirTree {
    pub fn encode(&self) -> Vec<u8> {
        let entries = self
            .entries
            .iter()
            .map(|e| {
                Value::Array(vec![
                    Value::Text(e.path.clone()),
                    Value::Uint(e.mode as u64),
                    obj(&e.blob),
                    Value::Uint(e.size),
                ])
            })
            .collect();
        cbor::encode(&Value::map([
            (0, Value::Uint(VERSION)),
            (1, Value::Array(entries)),
        ]))
    }

    /// Read and check a tree: a known version, clean paths, each once, in
    /// order, with a known mode.
    pub fn decode(bytes: &[u8]) -> R<DirTree> {
        let v = cbor::decode(bytes)?;
        let m = v.as_map().map_or_else(|| schema("a tree is a map"), Ok)?;
        if m.get(&0).and_then(Value::as_uint) != Some(VERSION) {
            return schema(format!(
                "tree version {:?} is not known; this reads {VERSION}",
                m.get(&0)
            ));
        }
        let mut entries = Vec::new();
        for item in m.get(&1).and_then(Value::as_array).unwrap_or_default() {
            let [p, mode, blob, size] = item.as_array().unwrap_or_default() else {
                return schema("a tree entry is [path, mode, blob, size]");
            };
            let path = get_text(p, "a path")?;
            let mode = get_uint(mode, "a mode")? as u32;
            if !path_ok(&path) {
                return schema(format!("{path:?} is not a clean relative path"));
            }
            if ![MODE_FILE, MODE_EXEC, MODE_LINK].contains(&mode) {
                return schema(format!(
                    "{path}: mode {mode:o} is not a file, an executable or a link"
                ));
            }
            if entries.last().is_some_and(|l: &Entry| l.path >= path) {
                return schema(format!(
                    "{path}: entries are not in path order, or one is there twice"
                ));
            }
            entries.push(Entry {
                path,
                mode,
                blob: get_obj(blob, "a blob")?,
                size: get_uint(size, "a size")?,
            });
        }
        Ok(DirTree { entries })
    }
}

/// An artifact (docs/cylinder.md §4.1).
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Artifact {
    pub kind: Kind,
    /// `x86_64`, `riscv64`, `aarch64`.
    pub arch: Option<String>,
    /// `linux`, `darwin`, `none`.
    pub os: Option<String>,
    /// The [`DirTree`]'s blob.
    pub tree: ObjectRef,
    /// The default command, for a container or an image.
    pub entrypoint: Option<Vec<String>>,
    pub env: BTreeMap<String, String>,
    pub labels: BTreeMap<String, String>,
    /// The files' bytes together.
    pub total_size: u64,
    /// The receipt of the Flow job that built it, when one did.
    pub receipt: Option<ObjectRef>,
}

fn pairs(m: &BTreeMap<String, String>) -> Value {
    if m.is_empty() {
        return Value::Null;
    }
    Value::Array(
        m.iter()
            .map(|(k, v)| Value::Array(vec![Value::Text(k.clone()), Value::Text(v.clone())]))
            .collect(),
    )
}

fn get_pairs(v: Option<&Value>, what: &str) -> R<BTreeMap<String, String>> {
    let mut out = BTreeMap::new();
    let Some(v) = v.filter(|v| !v.is_null()) else {
        return Ok(out);
    };
    for p in v
        .as_array()
        .map_or_else(|| schema(format!("{what} is a list of pairs")), Ok)?
    {
        let [k, val] = p.as_array().unwrap_or_default() else {
            return schema(format!("{what}: a pair is [key, value]"));
        };
        let k = get_text(k, what)?;
        if out.insert(k.clone(), get_text(val, what)?).is_some() {
            return schema(format!("{what}: {k} is there twice"));
        }
    }
    Ok(out)
}

fn opt_text(v: &Option<String>) -> Value {
    v.as_ref().map_or(Value::Null, |s| Value::Text(s.clone()))
}

impl Artifact {
    /// Its canonical CBOR, keys as in docs/cylinder.md §4.1.
    pub fn encode(&self) -> Vec<u8> {
        let entry = self.entrypoint.as_ref().map_or(Value::Null, |a| {
            Value::Array(a.iter().cloned().map(Value::Text).collect())
        });
        cbor::encode(&Value::map([
            (0, Value::Uint(VERSION)),
            (1, Value::Text(self.kind.as_str().into())),
            (2, opt_text(&self.arch)),
            (3, opt_text(&self.os)),
            (4, obj(&self.tree)),
            (5, entry),
            (6, pairs(&self.env)),
            (7, pairs(&self.labels)),
            (8, Value::Uint(self.total_size)),
            (9, self.receipt.as_ref().map_or(Value::Null, obj)),
        ]))
    }

    pub fn decode(bytes: &[u8]) -> R<Artifact> {
        let v = cbor::decode(bytes)?;
        let m = v
            .as_map()
            .map_or_else(|| schema("an artifact is a map"), Ok)?;
        if m.get(&0).and_then(Value::as_uint) != Some(VERSION) {
            return schema(format!(
                "artifact version {:?} is not known; this reads {VERSION}",
                m.get(&0)
            ));
        }
        if let Some(k) = m.keys().find(|k| **k > 9) {
            return schema(format!("key {k} is not part of an artifact"));
        }
        let text = |k: u64, what: &str| -> R<Option<String>> {
            match m.get(&k) {
                None | Some(Value::Null) => Ok(None),
                Some(v) => get_text(v, what).map(Some),
            }
        };
        let entrypoint = match m.get(&5) {
            None | Some(Value::Null) => None,
            Some(v) => Some(
                v.as_array()
                    .unwrap_or_default()
                    .iter()
                    .map(|a| get_text(a, "the entrypoint"))
                    .collect::<R<_>>()?,
            ),
        };
        let receipt = match m.get(&9) {
            None | Some(Value::Null) => None,
            Some(v) => Some(get_obj(v, "the receipt")?),
        };
        Ok(Artifact {
            kind: Kind::parse(&text(1, "the kind")?.unwrap_or_default())?,
            arch: text(2, "the architecture")?,
            os: text(3, "the system")?,
            tree: get_obj(m.get(&4).unwrap_or(&Value::Null), "the tree")?,
            entrypoint,
            env: get_pairs(m.get(&6), "env")?,
            labels: get_pairs(m.get(&7), "labels")?,
            total_size: get_uint(m.get(&8).unwrap_or(&Value::Null), "the size")?,
            receipt,
        })
    }

    /// Its name: its object's hash, as every Oxygen object is named.
    pub fn name(&self) -> ObjectRef {
        hash_object(ObjectType::Artifact, &self.encode())
    }
}