//! Verification framework for building trust in decentralized services.
//!
//! Verification levels:
//! - 0: None (bare announce)
//! - 1: Self-asserted (profile URL, metadata)
//! - 2: Endorsed by trusted peers
//! - 3: Registry-verified (KBV for therapists, trade registry for craftsmen)

use serde::{Deserialize, Serialize};

use crate::identity::ServiceIdentity;

/// Verification levels (higher = more trusted).
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Default)]
#[repr(u8)]
pub enum VerificationLevel {
    #[default]
    None = 0,
    SelfAsserted = 1,
    PeerEndorsed = 2,
    RegistryVerified = 3,
}

impl From<u8> for VerificationLevel {
    fn from(value: u8) -> Self {
        match value {
            1 => VerificationLevel::SelfAsserted,
            2 => VerificationLevel::PeerEndorsed,
            3.. => VerificationLevel::RegistryVerified,
            _ => VerificationLevel::None,
        }
    }
}

/// A verification attestation attached to a service message.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Verification {
    /// Verification level.
    pub level: u8,
    /// Verifier's mesh address.
    pub verifier_address: [u8; 16],
    /// What is being verified (e.g., "license", "identity").
    pub claim: String,
    /// Optional external reference (URL, registry ID).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub reference: Option<String>,
    /// Signature over (level || sender_address || claim).
    pub signature: Vec<u8>,
    /// Timestamp of verification.
    pub timestamp: u64,
    /// Optional expiry timestamp.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub expires: Option<u64>,
}

impl Verification {
    /// Create a new peer endorsement.
    pub fn peer_endorsement(
        verifier: &ServiceIdentity,
        subject_address: &[u8; 16],
        claim: impl Into<String>,
    ) -> Self {
        Self::new(
            verifier,
            VerificationLevel::PeerEndorsed,
            subject_address,
            claim,
            None,
        )
    }

    /// Create a registry verification.
    pub fn registry(
        verifier: &ServiceIdentity,
        subject_address: &[u8; 16],
        claim: impl Into<String>,
        reference: impl Into<String>,
    ) -> Self {
        Self::new(
            verifier,
            VerificationLevel::RegistryVerified,
            subject_address,
            claim,
            Some(reference.into()),
        )
    }

    /// Create a new verification.
    pub fn new(
        verifier: &ServiceIdentity,
        level: VerificationLevel,
        subject_address: &[u8; 16],
        claim: impl Into<String>,
        reference: Option<String>,
    ) -> Self {
        use std::time::{SystemTime, UNIX_EPOCH};

        let claim = claim.into();
        let timestamp = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs();

        let signable = Self::signable_bytes(level as u8, subject_address, &claim);
        let signature = verifier.sign(&signable).to_vec();

        Self {
            level: level as u8,
            verifier_address: verifier.address(),
            claim,
            reference,
            signature,
            timestamp,
            expires: None,
        }
    }

    /// Set expiry time.
    pub fn with_expiry(mut self, expires: u64) -> Self {
        self.expires = Some(expires);
        self
    }

    /// Create signable bytes.
    fn signable_bytes(level: u8, subject_address: &[u8; 16], claim: &str) -> Vec<u8> {
        let mut buf = Vec::with_capacity(17 + claim.len());
        buf.push(level);
        buf.extend_from_slice(subject_address);
        buf.extend_from_slice(claim.as_bytes());
        buf
    }

    /// Verify this attestation.
    pub fn verify(&self, verifier_public_key: &[u8; 32], subject_address: &[u8; 16]) -> bool {
        use crate::identity::compute_address;

        // Verify verifier address matches key
        if compute_address(verifier_public_key) != self.verifier_address {
            return false;
        }

        // Check expiry
        if let Some(expires) = self.expires {
            use std::time::{SystemTime, UNIX_EPOCH};
            let now = SystemTime::now()
                .duration_since(UNIX_EPOCH)
                .unwrap_or_default()
                .as_secs();
            if now > expires {
                return false;
            }
        }

        let sig: [u8; 64] = match self.signature.as_slice().try_into() {
            Ok(s) => s,
            Err(_) => return false,
        };

        let signable = Self::signable_bytes(self.level, subject_address, &self.claim);
        ServiceIdentity::verify(verifier_public_key, &signable, &sig)
    }
}

/// Set of known trusted verifiers (registries, endorsers).
#[derive(Default)]
pub struct TrustedVerifiers {
    /// Known public keys with their trust level.
    verifiers: Vec<TrustedVerifier>,
}

/// A trusted verifier entry.
#[derive(Clone)]
pub struct TrustedVerifier {
    pub public_key: [u8; 32],
    pub address: [u8; 16],
    pub name: String,
    pub max_level: VerificationLevel,
}

impl TrustedVerifiers {
    /// Create empty set.
    pub fn new() -> Self {
        Self::default()
    }

    /// Add a trusted verifier.
    pub fn add(
        &mut self,
        public_key: [u8; 32],
        name: impl Into<String>,
        max_level: VerificationLevel,
    ) {
        use crate::identity::compute_address;
        
        self.verifiers.push(TrustedVerifier {
            public_key,
            address: compute_address(&public_key),
            name: name.into(),
            max_level,
        });
    }

    /// Find a verifier by address.
    pub fn find_by_address(&self, address: &[u8; 16]) -> Option<&TrustedVerifier> {
        self.verifiers.iter().find(|v| &v.address == address)
    }

    /// Verify a verification against known trusted verifiers.
    /// Returns the effective level (or 0 if not trusted).
    pub fn check(&self, verification: &Verification, subject_address: &[u8; 16]) -> u8 {
        let Some(verifier) = self.find_by_address(&verification.verifier_address) else {
            return 0;
        };

        // Level cannot exceed verifier's max
        let claimed_level = verification.level.min(verifier.max_level as u8);

        // Actually verify the signature
        if verification.verify(&verifier.public_key, subject_address) {
            claimed_level
        } else {
            0
        }
    }

    /// Get the highest trusted verification level from a list.
    pub fn highest_level(
        &self,
        verifications: &[Verification],
        subject_address: &[u8; 16],
    ) -> VerificationLevel {
        verifications
            .iter()
            .map(|v| self.check(v, subject_address))
            .max()
            .map(VerificationLevel::from)
            .unwrap_or(VerificationLevel::None)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn peer_endorsement_roundtrip() {
        let verifier = ServiceIdentity::generate();
        let subject_address = [1u8; 16];

        let v = Verification::peer_endorsement(&verifier, &subject_address, "good_actor");
        assert!(v.verify(&verifier.public_key(), &subject_address));
        assert_eq!(v.level, VerificationLevel::PeerEndorsed as u8);
    }

    #[test]
    fn trusted_verifiers_check() {
        let verifier = ServiceIdentity::generate();
        let subject_address = [2u8; 16];

        let mut trusted = TrustedVerifiers::new();
        trusted.add(verifier.public_key(), "Test Registry", VerificationLevel::RegistryVerified);

        let v = Verification::registry(&verifier, &subject_address, "licensed", "REG-12345");
        let level = trusted.check(&v, &subject_address);
        assert_eq!(level, VerificationLevel::RegistryVerified as u8);
    }

    #[test]
    fn untrusted_verifier_returns_zero() {
        let verifier = ServiceIdentity::generate();
        let subject_address = [3u8; 16];

        let trusted = TrustedVerifiers::new(); // Empty

        let v = Verification::registry(&verifier, &subject_address, "licensed", "REG-999");
        let level = trusted.check(&v, &subject_address);
        assert_eq!(level, 0);
    }

    #[test]
    fn expired_verification_fails() {
        let verifier = ServiceIdentity::generate();
        let subject_address = [4u8; 16];

        let v = Verification::peer_endorsement(&verifier, &subject_address, "trusted")
            .with_expiry(1); // Expired in 1970

        assert!(!v.verify(&verifier.public_key(), &subject_address));
    }
}