mod id;

use std::collections::{BTreeMap, HashMap};
use std::fmt::{self, Write as _};
use std::marker::PhantomData;
use std::ops::Deref;
use std::path::Path;

use nonempty::NonEmpty;
use once_cell::sync::Lazy;
use radicle_git_ext::Oid;
use serde::{Deserialize, Serialize};
use thiserror::Error;

use crate::crypto;
use crate::crypto::{Signature, Unverified, Verified};
use crate::git;
use crate::identity::Did;
use crate::storage;
use crate::storage::git::trailers;
use crate::storage::{BranchName, ReadRepository, RemoteId, WriteRepository, WriteStorage};

pub use crypto::PublicKey;
pub use id::*;

/// Untrusted, well-formed input.
#[derive(Clone, Copy, Debug)]
pub struct Untrusted;
/// Signed by quorum of the previous delegation.
#[derive(Clone, Copy, Debug)]
pub struct Trusted;

/// Path to the identity document in the identity branch.
pub static PATH: Lazy<&Path> = Lazy::new(|| Path::new("radicle.json"));
/// Maximum length of a string in the identity document.
pub const MAX_STRING_LENGTH: usize = 255;
/// Maximum number of a delegates in the identity document.
pub const MAX_DELEGATES: usize = 255;

#[derive(Error, Debug)]
pub enum DocError {
    #[error("json: {0}")]
    Json(#[from] serde_json::Error),
    #[error("git: {0}")]
    Git(#[from] git::Error),
    #[error("git: {0}")]
    RawGit(#[from] git2::Error),
    #[error("storage: {0}")]
    Storage(#[from] storage::Error),
}

impl DocError {
    /// Whether this error is caused by the document not being found.
    pub fn is_not_found(&self) -> bool {
        match self {
            Self::Git(git::Error::NotFound(_)) => true,
            Self::Git(git::Error::Git(e)) if git::is_not_found_err(e) => true,
            _ => false,
        }
    }
}

#[derive(Debug, Error)]
pub enum ProjectError {
    #[error("invalid name: {0}")]
    Name(&'static str),
    #[error("invalid description: {0}")]
    Description(&'static str),
    #[error("invalid default branch: {0}")]
    DefaultBranch(&'static str),
    #[error("json: {0}")]
    Json(#[from] serde_json::Error),
    #[error("project payload not found in identity document")]
    NotFound,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct Project {
    pub name: String,
    pub description: String,
    pub default_branch: BranchName,
}

impl From<Project> for Payload {
    fn from(proj: Project) -> Self {
        let value = serde_json::to_value(proj)
            .expect("Payload::from: could not convert project into value");

        Self { value }
    }
}

impl Project {
    /// Validate the project data.
    pub fn validate(&self) -> Result<(), ProjectError> {
        if self.name.is_empty() {
            return Err(ProjectError::Name("name cannot be empty"));
        }
        if self.name.len() > MAX_STRING_LENGTH {
            return Err(ProjectError::Name("name cannot exceed 255 bytes"));
        }
        if self.description.len() > MAX_STRING_LENGTH {
            return Err(ProjectError::Description(
                "description cannot exceed 255 bytes",
            ));
        }
        if self.default_branch.is_empty() {
            return Err(ProjectError::DefaultBranch(
                "default branch cannot be empty",
            ));
        }
        if self.default_branch.len() > MAX_STRING_LENGTH {
            return Err(ProjectError::DefaultBranch(
                "default branch cannot exceed 255 bytes",
            ));
        }
        Ok(())
    }
}

#[derive(Debug, Error)]
pub enum PayloadError {
    #[error("json: {0}")]
    Json(#[from] serde_json::Error),
    #[error("payload '{0}' not found in identity document")]
    NotFound(PayloadId),
}

/// Identifies an identity document payload type.
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
#[serde(transparent)]
// TODO: Restrict values.
pub struct PayloadId(String);

impl fmt::Display for PayloadId {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.0.fmt(f)
    }
}

impl PayloadId
where
    PayloadId: Clone,
{
    /// Project payload type.
    pub fn project() -> Self {
        Self(String::from("xyz.radicle.project"))
    }
}

/// Payload value.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(transparent)]
pub struct Payload {
    value: serde_json::Value,
}

impl From<serde_json::Value> for Payload {
    fn from(value: serde_json::Value) -> Self {
        Self { value }
    }
}

impl Deref for Payload {
    type Target = serde_json::Value;

    fn deref(&self) -> &Self::Target {
        &self.value
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct Doc<V> {
    pub payload: BTreeMap<PayloadId, Payload>,
    pub delegates: NonEmpty<Did>,
    pub threshold: usize,

    #[serde(skip)]
    verified: PhantomData<V>,
}

impl Doc<Verified> {
    pub fn encode(&self) -> Result<(git::Oid, Vec<u8>), DocError> {
        let mut buf = Vec::new();
        let mut serializer =
            serde_json::Serializer::with_formatter(&mut buf, olpc_cjson::CanonicalFormatter::new());

        self.serialize(&mut serializer)?;
        let oid = git2::Oid::hash_object(git2::ObjectType::Blob, &buf)?;

        Ok((oid.into(), buf))
    }

    /// Attempt to add a new delegate to the document. Returns `true` if it wasn't there before.
    pub fn delegate(&mut self, key: crypto::PublicKey) -> bool {
        let delegate = Did::from(key);
        if self.delegates.iter().all(|id| id != &delegate) {
            self.delegates.push(delegate);
            return true;
        }
        false
    }

    /// Get the project payload, if it exists and is valid, out of this document.
    pub fn project(&self) -> Result<Project, PayloadError> {
        let value = self
            .payload
            .get(&PayloadId::project())
            .ok_or_else(|| PayloadError::NotFound(PayloadId::project()))?;
        let proj: Project = serde_json::from_value((**value).clone())?;

        Ok(proj)
    }

    pub fn sign<G: crypto::Signer>(&self, signer: &G) -> Result<(git::Oid, Signature), DocError> {
        let (oid, bytes) = self.encode()?;
        let sig = signer.sign(&bytes);

        Ok((oid, sig))
    }

    pub fn create<S: WriteStorage>(
        &self,
        remote: &RemoteId,
        msg: &str,
        storage: &S,
    ) -> Result<(Id, git::Oid, S::Repository), DocError> {
        let (doc_oid, doc) = self.encode()?;
        let id = Id::from(doc_oid);
        let repo = storage.repository(id)?;
        let tree = git::write_tree(*PATH, doc.as_slice(), repo.raw())?;
        let oid = Doc::commit(remote, &tree, msg, &[], repo.raw())?;

        drop(tree);

        Ok((id, oid, repo))
    }

    pub fn update<R: WriteRepository>(
        &self,
        remote: &RemoteId,
        msg: &str,
        signatures: &[(&PublicKey, Signature)],
        repo: &R,
    ) -> Result<git::Oid, DocError> {
        let mut msg = format!("{msg}\n\n");
        for (key, sig) in signatures {
            writeln!(&mut msg, "{}: {key} {sig}", trailers::SIGNATURE_TRAILER)
                .expect("in-memory writes don't fail");
        }

        let (_, doc) = self.encode()?;
        let tree = git::write_tree(*PATH, doc.as_slice(), repo.raw())?;
        let id_ref = git::refs::storage::id(remote);
        let head = repo.raw().find_reference(&id_ref)?.peel_to_commit()?;
        let oid = Doc::commit(remote, &tree, &msg, &[&head], repo.raw())?;

        Ok(oid)
    }

    fn commit(
        remote: &RemoteId,
        tree: &git2::Tree,
        msg: &str,
        parents: &[&git2::Commit],
        repo: &git2::Repository,
    ) -> Result<git::Oid, DocError> {
        let sig = repo
            .signature()
            .or_else(|_| git2::Signature::now("radicle", remote.to_string().as_str()))?;

        let id_ref = git::refs::storage::id(remote);
        let oid = repo.commit(Some(&id_ref), &sig, &sig, msg, tree, parents)?;

        Ok(oid.into())
    }
}

#[derive(Error, Debug)]
pub enum VerificationError {
    #[error("invalid delegates: {0}")]
    Delegates(&'static str),
    #[error("invalid version `{0}`")]
    Version(u32),
    #[error("invalid threshold `{0}`: {1}")]
    Threshold(usize, &'static str),
}

impl Doc<Unverified> {
    pub fn initial(project: Project, delegate: Did) -> Self {
        Self::new(project, NonEmpty::new(delegate), 1)
    }

    pub fn new(project: Project, delegates: NonEmpty<Did>, threshold: usize) -> Self {
        let project =
            serde_json::to_value(project).expect("Doc::initial: payload must be serializable");

        Self {
            payload: BTreeMap::from_iter([(PayloadId::project(), Payload::from(project))]),
            delegates,
            threshold,
            verified: PhantomData,
        }
    }

    pub fn from_json(bytes: &[u8]) -> Result<Self, DocError> {
        serde_json::from_slice(bytes).map_err(DocError::from)
    }

    pub fn verified(self) -> Result<Doc<Verified>, VerificationError> {
        if self.delegates.len() > MAX_DELEGATES {
            return Err(VerificationError::Delegates(
                "number of delegates cannot exceed 255",
            ));
        }
        if self.delegates.is_empty() {
            return Err(VerificationError::Delegates(
                "delegate list cannot be empty",
            ));
        }
        if self.threshold > self.delegates.len() {
            return Err(VerificationError::Threshold(
                self.threshold,
                "threshold cannot exceed number of delegates",
            ));
        }
        if self.threshold == 0 {
            return Err(VerificationError::Threshold(
                self.threshold,
                "threshold cannot be zero",
            ));
        }

        Ok(Doc {
            payload: self.payload,
            delegates: self.delegates,
            threshold: self.threshold,
            verified: PhantomData,
        })
    }

    pub fn blob_at<R: ReadRepository>(commit: Oid, repo: &R) -> Result<git2::Blob, DocError> {
        repo.blob_at(commit, Path::new(&*PATH))
            .map_err(DocError::from)
    }

    pub fn load_at<R: ReadRepository>(commit: Oid, repo: &R) -> Result<(Self, Oid), DocError> {
        let blob = Self::blob_at(commit, repo)?;
        let doc = Doc::from_json(blob.content())?;

        Ok((doc, blob.id().into()))
    }

    pub fn load<R: ReadRepository>(remote: &RemoteId, repo: &R) -> Result<(Self, Oid), DocError> {
        let oid = Self::head(remote, repo)?;

        Self::load_at(oid, repo)
    }
}

impl<V> Doc<V> {
    pub fn head<R: ReadRepository>(remote: &RemoteId, repo: &R) -> Result<Oid, DocError> {
        repo.reference_oid(remote, &git::refs::storage::IDENTITY_BRANCH)
            .map_err(DocError::from)
    }
}

#[derive(Error, Debug)]
pub enum IdentityError {
    #[error("git: {0}")]
    GitRaw(#[from] git2::Error),
    #[error("git: {0}")]
    Git(#[from] git::Error),
    #[error("verification: {0}")]
    Verification(#[from] VerificationError),
    #[error("root hash `{0}` does not match project")]
    MismatchedRoot(Oid),
    #[error("commit signature for {0} is invalid: {1}")]
    InvalidSignature(PublicKey, crypto::Error),
    #[error("commit message for {0} is invalid")]
    InvalidCommitMessage(Oid),
    #[error("commit trailers for {0} are invalid: {1}")]
    InvalidCommitTrailers(Oid, trailers::Error),
    #[error("quorum not reached: {0} signatures for a threshold of {1}")]
    QuorumNotReached(usize, usize),
    #[error("identity document error: {0}")]
    Doc(#[from] DocError),
    #[error("the document root is missing")]
    MissingRoot,
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Identity<I> {
    /// The head of the identity branch. This points to a commit that
    /// contains the current document blob.
    pub head: Oid,
    /// The canonical identifier for this identity.
    /// This is the object id of the initial document blob.
    pub root: I,
    /// The object id of the current document blob.
    pub current: Oid,
    /// Revision number. The initial document has a revision of `0`.
    pub revision: u32,
    /// The current document.
    pub doc: Doc<Verified>,
    /// Signatures over this identity.
    pub signatures: HashMap<PublicKey, Signature>,
}

impl radicle_cob::identity::Identity for Identity<Oid> {
    type Identifier = Oid;

    fn content_id(&self) -> Oid {
        self.current
    }
}

impl Identity<Oid> {
    pub fn verified(self, id: Id) -> Result<Identity<Id>, IdentityError> {
        // The root hash must be equal to the id.
        if self.root != *id {
            return Err(IdentityError::MismatchedRoot(self.root));
        }

        Ok(Identity {
            root: id,
            head: self.head,
            current: self.current,
            revision: self.revision,
            doc: self.doc,
            signatures: self.signatures,
        })
    }
}

impl Identity<Untrusted> {
    pub fn load<R: ReadRepository>(
        remote: &RemoteId,
        repo: &R,
    ) -> Result<Identity<Oid>, IdentityError> {
        let head = Doc::<Untrusted>::head(remote, repo)?;
        let mut history = repo.revwalk(head)?.collect::<Vec<_>>();

        // Retrieve root document.
        let root_oid = history.pop().ok_or(IdentityError::MissingRoot)??.into();
        let root_blob = Doc::blob_at(root_oid, repo)?;
        let root: git::Oid = root_blob.id().into();
        let trusted = Doc::from_json(root_blob.content())?;
        let revision = history.len() as u32;

        let mut trusted = trusted.verified()?;
        let mut current = root;
        let mut signatures = Vec::new();

        // Traverse the history chronologically.
        for oid in history.into_iter().rev() {
            let oid = oid?;
            let blob = Doc::blob_at(oid.into(), repo)?;
            let untrusted = Doc::from_json(blob.content()).map_err(DocError::from)?;
            let untrusted = untrusted.verified()?;
            let commit = repo.commit(oid.into())?;
            let msg = commit
                .message_raw()
                .ok_or_else(|| IdentityError::InvalidCommitMessage(oid.into()))?;

            // Keys that signed the *current* document version.
            signatures = trailers::parse_signatures(msg)
                .map_err(|e| IdentityError::InvalidCommitTrailers(oid.into(), e))?;
            for (pk, sig) in &signatures {
                if let Err(err) = pk.verify(blob.content(), sig) {
                    return Err(IdentityError::InvalidSignature(*pk, err));
                }
            }

            // Check that enough delegates signed this next version.
            let quorum = signatures
                .iter()
                .filter(|(key, _)| trusted.delegates.iter().any(|d| &**d == key))
                .count();
            if quorum < trusted.threshold {
                return Err(IdentityError::QuorumNotReached(quorum, trusted.threshold));
            }

            trusted = untrusted;
            current = blob.id().into();
        }

        Ok(Identity {
            root,
            head,
            current,
            revision,
            doc: trusted,
            signatures: signatures.into_iter().collect(),
        })
    }
}

#[cfg(test)]
mod test {
    use radicle_crypto::test::signer::MockSigner;
    use radicle_crypto::Signer as _;

    use crate::rad;
    use crate::storage::git::transport;
    use crate::storage::git::Storage;
    use crate::storage::{ReadStorage, WriteStorage};
    use crate::test::arbitrary;
    use crate::test::fixtures;

    use super::*;
    use qcheck_macros::quickcheck;

    #[test]
    fn test_canonical_example() {
        let tempdir = tempfile::tempdir().unwrap();
        let storage = Storage::open(tempdir.path().join("storage")).unwrap();

        transport::local::register(storage.clone());

        let delegate = MockSigner::from_seed([0xff; 32]);
        let (repo, _) = fixtures::repository(tempdir.path().join("working"));
        let (id, _, _) = rad::init(
            &repo,
            "heartwood",
            "Radicle Heartwood Protocol & Stack",
            git::refname!("master"),
            &delegate,
            &storage,
        )
        .unwrap();

        assert_eq!(
            delegate.public_key().to_human(),
            String::from("z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi")
        );
        assert_eq!(
            (*id).to_string(),
            "d96f425412c9f8ad5d9a9a05c9831d0728e2338d"
        );
        assert_eq!(
            id.to_human(),
            String::from("rad:z42hL2jL4XNk6K8oHQaSWfMgCL7ji")
        );
    }

    #[test]
    fn test_not_found() {
        let tempdir = tempfile::tempdir().unwrap();
        let storage = Storage::open(tempdir.path().join("storage")).unwrap();
        let remote = arbitrary::gen::<RemoteId>(1);
        let proj = arbitrary::gen::<Id>(1);
        let repo = storage.repository(proj).unwrap();
        let oid = git2::Oid::from_str("2d52a53ce5e4f141148a5f770cfd3ead2d6a45b8").unwrap();

        let err = Doc::<Unverified>::head(&remote, &repo).unwrap_err();
        assert!(err.is_not_found());

        let err = Doc::load_at(oid.into(), &repo).unwrap_err();
        assert!(err.is_not_found());
    }

    #[test]
    fn test_valid_identity() {
        let tempdir = tempfile::tempdir().unwrap();
        let mut rng = fastrand::Rng::new();

        let alice = MockSigner::new(&mut rng);
        let bob = MockSigner::new(&mut rng);
        let eve = MockSigner::new(&mut rng);

        let storage = Storage::open(tempdir.path().join("storage")).unwrap();
        let (id, _, _, _) =
            fixtures::project(tempdir.path().join("copy"), &storage, &alice).unwrap();

        // Bob and Eve fork the project from Alice.
        rad::fork_remote(id, alice.public_key(), &bob, &storage).unwrap();
        rad::fork_remote(id, alice.public_key(), &eve, &storage).unwrap();

        // TODO: In some cases we want to get the repo and the project, but don't
        // want to have to create a repository object twice. Perhaps there should
        // be a way of getting a project from a repo.
        let mut doc = storage.get(alice.public_key(), id).unwrap().unwrap();
        let mut prj = doc.project().unwrap();
        let repo = storage.repository(id).unwrap();

        // Make a change to the description and sign it.
        prj.description += "!";
        doc.payload.insert(PayloadId::project(), prj.clone().into());
        doc.sign(&alice)
            .and_then(|(_, sig)| {
                doc.update(
                    alice.public_key(),
                    "Update description",
                    &[(alice.public_key(), sig)],
                    &repo,
                )
            })
            .unwrap();

        // Add Bob as a delegate, and sign it.
        doc.delegate(*bob.public_key());
        doc.threshold = 2;
        doc.sign(&alice)
            .and_then(|(_, sig)| {
                doc.update(
                    alice.public_key(),
                    "Add bob",
                    &[(alice.public_key(), sig)],
                    &repo,
                )
            })
            .unwrap();

        // Add Eve as a delegate, and sign it.
        doc.delegate(*eve.public_key());
        doc.sign(&alice)
            .and_then(|(_, alice_sig)| {
                doc.sign(&bob).and_then(|(_, bob_sig)| {
                    doc.update(
                        alice.public_key(),
                        "Add eve",
                        &[(alice.public_key(), alice_sig), (bob.public_key(), bob_sig)],
                        &repo,
                    )
                })
            })
            .unwrap();

        // Update description again with signatures by Eve and Bob.
        prj.description += "?";
        doc.payload.insert(PayloadId::project(), prj.into());
        let (current, head) = doc
            .sign(&bob)
            .and_then(|(_, bob_sig)| {
                doc.sign(&eve).and_then(|(blob_id, eve_sig)| {
                    doc.update(
                        alice.public_key(),
                        "Update description",
                        &[(bob.public_key(), bob_sig), (eve.public_key(), eve_sig)],
                        &repo,
                    )
                    .map(|head| (blob_id, head))
                })
            })
            .unwrap();

        let identity: Identity<Id> = Identity::load(alice.public_key(), &repo)
            .unwrap()
            .verified(id)
            .unwrap();

        assert_eq!(identity.signatures.len(), 2);
        assert_eq!(identity.revision, 4);
        assert_eq!(identity.root, id);
        assert_eq!(identity.current, current);
        assert_eq!(identity.head, head);
        assert_eq!(identity.doc, doc);

        let doc = storage.get(alice.public_key(), id).unwrap().unwrap();
        assert_eq!(doc.project().unwrap().description, "Acme's repository!?");
    }

    #[quickcheck]
    fn prop_encode_decode(doc: Doc<Verified>) {
        let (_, bytes) = doc.encode().unwrap();
        assert_eq!(Doc::from_json(&bytes).unwrap().verified().unwrap(), doc);
    }
}