//! Channel adapters for KEZ.
//!
//! A `Channel` knows how to fetch a published proof for a given `system:` and
//! verify it against the channel's ownership rules. Each channel lives in its
//! own module (one per file) so adding a new system (`bluesky`, `web`, …) is a
//! self-contained drop-in.

use std::collections::HashMap;
use std::sync::Arc;

use async_trait::async_trait;
use kez_core::{Identity, SignedClaim, VerificationStatus};
use thiserror::Error;

pub mod activitypub;
pub mod bluesky;
pub mod dns;
pub mod github;
pub mod nostr;

/// The single error type every channel returns. Variants map directly to the
/// failure modes the spec (§8.4) requires a verifier to distinguish.
#[derive(Debug, Error)]
pub enum ChannelError {
    #[error("channel unreachable: {0}")]
    Unreachable(String),
    #[error("no KEZ proof found for {0}")]
    NotFound(Identity),
    #[error("proof failed verification: {0}")]
    Invalid(#[source] anyhow::Error),
    #[error("proof subject {found} did not match expected identity {expected}")]
    SubjectMismatch { expected: Identity, found: Identity },
    #[error("no channel registered for system: {0}")]
    NoChannelForSystem(String),
    #[error("{0}")]
    Other(#[source] anyhow::Error),
}

pub type ChannelResult<T> = Result<T, ChannelError>;

/// Output of a successful verification.
#[derive(Debug, Clone)]
pub struct ChannelHit {
    pub proof: SignedClaim,
    pub status: VerificationStatus,
}

/// A channel adapter: fetch + verify a published proof for one `system:`.
#[async_trait]
pub trait Channel: Send + Sync {
    /// The `system` prefix this channel handles (e.g. "github", "dns").
    fn system(&self) -> &'static str;

    /// Fetch the proof for `identity` from the channel and verify it.
    /// Implementations MUST confirm the proof's subject equals `identity`.
    async fn fetch_and_verify(&self, identity: &Identity) -> ChannelResult<ChannelHit>;
}

/// A small registry mapping `system:` → channel adapter. Lets the CLI (and any
/// future caller) dispatch a `verify <identifier>` request without knowing
/// which adapters are loaded.
#[derive(Default, Clone)]
pub struct Registry {
    channels: HashMap<&'static str, Arc<dyn Channel>>,
}

impl Registry {
    pub fn new() -> Self {
        Self::default()
    }

    /// Build a registry with the channels shipped in this crate.
    pub fn with_defaults() -> ChannelResult<Self> {
        let mut r = Self::new();
        r.register(Arc::new(
            github::GithubChannel::new().map_err(ChannelError::Other)?,
        ));
        r.register(Arc::new(dns::DnsChannel::new()));
        r.register(Arc::new(nostr::NostrChannel::new()));
        r.register(Arc::new(
            bluesky::BlueskyChannel::new().map_err(ChannelError::Other)?,
        ));
        let ap = Arc::new(
            activitypub::ActivityPubChannel::new().map_err(ChannelError::Other)?,
        );
        r.register(ap.clone()); // canonical: ap:
        r.register_as("mastodon", ap); // alias: mastodon:
        Ok(r)
    }

    pub fn register(&mut self, channel: Arc<dyn Channel>) {
        self.channels.insert(channel.system(), channel);
    }

    /// Register a channel under an additional alias scheme. Useful when one
    /// adapter handles multiple identifier prefixes (e.g. `ap:` and
    /// `mastodon:` both routed to `ActivityPubChannel`).
    pub fn register_as(&mut self, system: &'static str, channel: Arc<dyn Channel>) {
        self.channels.insert(system, channel);
    }

    pub fn get(&self, system: &str) -> Option<Arc<dyn Channel>> {
        self.channels.get(system).cloned()
    }

    pub async fn verify(&self, identity: &Identity) -> ChannelResult<ChannelHit> {
        let channel = self
            .get(identity.scheme())
            .ok_or_else(|| ChannelError::NoChannelForSystem(identity.scheme().to_owned()))?;
        channel.fetch_and_verify(identity).await
    }
}

/// Helper used by every channel: parse a raw proof string, verify its signature,
/// and confirm its subject matches what we asked for. Lives at the crate root
/// because it's identical for every channel.
pub fn parse_and_verify_for(raw: &str, expected: &Identity) -> ChannelResult<ChannelHit> {
    let proof = parse_proof(raw).map_err(ChannelError::Invalid)?;
    let status = proof
        .verify()
        .map_err(|err| ChannelError::Invalid(err.into()))?;
    if proof.payload.subject != *expected {
        return Err(ChannelError::SubjectMismatch {
            expected: expected.clone(),
            found: proof.payload.subject,
        });
    }
    Ok(ChannelHit { proof, status })
}

/// Best-effort parse of any of the four wire encodings (compact, JSON,
/// Markdown, legacy DNS). For the compact form, the prefix may be embedded
/// in surrounding prose (e.g. a Mastodon bio or a Bluesky post) — we extract
/// the base64url token after `kez:z1:` regardless of what comes before.
pub fn parse_proof(raw: &str) -> anyhow::Result<SignedClaim> {
    use anyhow::bail;
    use kez_core::{decode_compact_claim, extract_markdown_proof, from_json, parse_dns_txt_value};

    let trimmed = raw.trim();

    // Markdown fence is the most specific marker — check it first.
    if trimmed.contains("```kez") {
        return Ok(extract_markdown_proof(trimmed)?);
    }
    // Raw JSON envelope.
    if trimmed.starts_with('{') {
        return Ok(from_json(trimmed)?);
    }
    // Legacy DNS prefix — JSON payload, won't be embedded in prose.
    if trimmed.starts_with("kez1:") {
        return Ok(parse_dns_txt_value(trimmed)?);
    }
    // Compact: extract the kez:z1:<base64url> token anywhere in the input.
    if let Some(token) = extract_compact_token(trimmed) {
        return Ok(decode_compact_claim(&token)?);
    }
    bail!("unknown KEZ proof format")
}

/// Pure: find a `kez:z1:<base64url>` token anywhere in `text` and return it.
/// The token ends at the first non-base64url-alphabet character.
pub fn extract_compact_token(text: &str) -> Option<String> {
    use kez_core::COMPACT_PROOF_PREFIX;
    let idx = text.find(COMPACT_PROOF_PREFIX)?;
    let after = &text[idx + COMPACT_PROOF_PREFIX.len()..];
    let body: String = after
        .chars()
        .take_while(|c| c.is_ascii_alphanumeric() || *c == '_' || *c == '-')
        .collect();
    if body.is_empty() {
        None
    } else {
        Some(format!("{COMPACT_PROOF_PREFIX}{body}"))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use chrono::Utc;
    use kez_core::{ClaimPayload, NostrSecret, SignedClaim};

    fn make_signed(subject: &str) -> SignedClaim {
        let secret = NostrSecret::generate();
        let primary = Identity::parse(format!("nostr:{}", secret.npub())).unwrap();
        let subject = Identity::parse(subject).unwrap();
        SignedClaim::sign(
            ClaimPayload::new(subject, primary, Utc::now()),
            &secret,
        )
        .unwrap()
    }

    #[test]
    fn parse_proof_handles_all_four_encodings() {
        let signed = make_signed("github:jason");

        // JSON
        let json = signed.to_pretty_json().unwrap();
        let p_json = parse_proof(&json).unwrap();
        assert_eq!(p_json, signed);

        // Compact
        let compact = signed.to_compact().unwrap();
        let p_compact = parse_proof(&compact).unwrap();
        assert_eq!(p_compact, signed);

        // Markdown
        let md = signed.to_markdown_proof().unwrap();
        let p_md = parse_proof(&md).unwrap();
        assert_eq!(p_md, signed);

        // Legacy DNS (`kez1:` prefix)
        let dns = kez_core::dns_txt_value(&signed).unwrap();
        let p_dns = parse_proof(&dns).unwrap();
        assert_eq!(p_dns, signed);
    }

    #[test]
    fn parse_proof_rejects_unknown_format() {
        let err = parse_proof("just some text").unwrap_err();
        assert!(err.to_string().contains("unknown"));
    }

    #[test]
    fn parse_proof_extracts_compact_token_from_surrounding_prose() {
        let signed = make_signed("ap:@jason@mastodon.social");
        let compact = signed.to_compact().unwrap();
        let bio = format!("hello world! my proof: {compact} — verify it");
        let parsed = parse_proof(&bio).unwrap();
        assert_eq!(parsed, signed);
    }

    #[test]
    fn extract_compact_token_stops_at_non_base64url_char() {
        let text = "before kez:z1:KLUv_QBYabc. after";
        let token = extract_compact_token(text).unwrap();
        assert_eq!(token, "kez:z1:KLUv_QBYabc");
    }

    #[test]
    fn extract_compact_token_returns_none_when_missing() {
        assert!(extract_compact_token("nothing here").is_none());
        assert!(extract_compact_token("kez:z1:").is_none(), "empty body");
    }

    #[test]
    fn parse_and_verify_for_flags_subject_mismatch() {
        let signed = make_signed("github:jason");
        let json = signed.to_pretty_json().unwrap();
        let wrong = Identity::parse("github:mallory").unwrap();
        let err = parse_and_verify_for(&json, &wrong).unwrap_err();
        assert!(matches!(err, ChannelError::SubjectMismatch { .. }));
    }

    #[test]
    fn parse_and_verify_for_passes_on_match() {
        let signed = make_signed("github:jason");
        let json = signed.to_pretty_json().unwrap();
        let expected = Identity::parse("github:jason").unwrap();
        let hit = parse_and_verify_for(&json, &expected).unwrap();
        assert_eq!(hit.proof, signed);
    }

    #[test]
    fn registry_dispatches_by_scheme() {
        let registry = Registry::with_defaults().unwrap();
        assert!(registry.get("github").is_some());
        assert!(registry.get("dns").is_some());
        assert!(registry.get("nostr").is_some());
        assert!(registry.get("bluesky").is_some());
        assert!(registry.get("ap").is_some());
        assert!(
            registry.get("mastodon").is_some(),
            "mastodon: must alias to ap:"
        );
        assert!(registry.get("did").is_none(), "did: is not implemented yet");
    }

    #[tokio::test]
    async fn registry_reports_unknown_system() {
        let registry = Registry::new();
        let identity = Identity::parse("github:jason").unwrap();
        let err = registry.verify(&identity).await.unwrap_err();
        assert!(matches!(err, ChannelError::NoChannelForSystem(_)));
    }
}