use sha2::{Digest, Sha256};

use crate::SchedulerMinimalCandidateSelectionCandidate;

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SchedulerAffinityTarget {
    pub provider_id: String,
    pub endpoint_id: String,
    pub key_id: String,
}

#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub struct ClientSessionAffinity {
    pub client_family: Option<String>,
    pub session_key: Option<String>,
}

impl ClientSessionAffinity {
    pub fn new(client_family: Option<String>, session_key: Option<String>) -> Self {
        Self {
            client_family,
            session_key,
        }
    }

    pub fn from_session_key(session_key: impl Into<String>) -> Self {
        Self {
            client_family: None,
            session_key: Some(session_key.into()),
        }
    }

    pub fn has_session_key(&self) -> bool {
        self.session_key
            .as_deref()
            .map(str::trim)
            .is_some_and(|value| !value.is_empty())
    }
}

pub fn build_scheduler_affinity_cache_key_for_api_key_id(
    api_key_id: &str,
    api_format: &str,
    global_model_name: &str,
) -> Option<String> {
    build_scheduler_affinity_cache_key_for_api_key_id_with_client_session(
        api_key_id,
        api_format,
        global_model_name,
        None,
    )
}

pub fn build_scheduler_affinity_cache_key_for_api_key_id_with_client_session(
    api_key_id: &str,
    api_format: &str,
    global_model_name: &str,
    client_session_affinity: Option<&ClientSessionAffinity>,
) -> Option<String> {
    let api_key_id = api_key_id.trim();
    if api_key_id.is_empty() {
        return None;
    }
    let api_format = crate::normalize_api_format(api_format);
    let global_model_name = global_model_name.trim();
    if api_format.is_empty() || global_model_name.is_empty() {
        return None;
    }

    let legacy_key = format!("scheduler_affinity:{api_key_id}:{api_format}:{global_model_name}");
    let Some(client_session_affinity) = client_session_affinity else {
        return Some(legacy_key);
    };
    let Some(session_key) = client_session_affinity
        .session_key
        .as_deref()
        .map(str::trim)
        .filter(|value| !value.is_empty())
    else {
        return Some(legacy_key);
    };
    let client_family = client_session_affinity
        .client_family
        .as_deref()
        .map(str::trim)
        .filter(|value| !value.is_empty())
        .map(str::to_ascii_lowercase)
        .unwrap_or_else(|| "generic".to_string());
    let session_hash = hash_session_key(session_key);

    Some(format!(
        "scheduler_affinity:v2:{api_key_id}:{api_format}:{global_model_name}:{client_family}:{session_hash}"
    ))
}

fn hash_session_key(session_key: &str) -> String {
    let mut hasher = Sha256::new();
    hasher.update(session_key.as_bytes());
    let digest = hasher.finalize();
    digest.iter().map(|byte| format!("{byte:02x}")).collect()
}

pub fn candidate_affinity_hash(
    affinity_key: &str,
    candidate: &SchedulerMinimalCandidateSelectionCandidate,
) -> u64 {
    let mut hasher = Sha256::new();
    hasher.update(affinity_key.as_bytes());
    hasher.update(b":");
    hasher.update(candidate.provider_id.as_bytes());
    hasher.update(b":");
    hasher.update(candidate.endpoint_id.as_bytes());
    hasher.update(b":");
    hasher.update(candidate.key_id.as_bytes());
    let digest = hasher.finalize();
    u64::from_be_bytes([
        digest[0], digest[1], digest[2], digest[3], digest[4], digest[5], digest[6], digest[7],
    ])
}

pub fn matches_affinity_target(
    candidate: &SchedulerMinimalCandidateSelectionCandidate,
    target: &SchedulerAffinityTarget,
) -> bool {
    candidate.provider_id == target.provider_id
        && candidate.endpoint_id == target.endpoint_id
        && candidate.key_id == target.key_id
}

pub fn candidate_key(
    candidate: &SchedulerMinimalCandidateSelectionCandidate,
) -> (String, String, String) {
    (
        candidate.provider_id.clone(),
        candidate.endpoint_id.clone(),
        candidate.key_id.clone(),
    )
}

#[cfg(test)]
mod tests {
    use super::{
        build_scheduler_affinity_cache_key_for_api_key_id,
        build_scheduler_affinity_cache_key_for_api_key_id_with_client_session,
        candidate_affinity_hash, candidate_key, matches_affinity_target, ClientSessionAffinity,
        SchedulerAffinityTarget,
    };
    use crate::SchedulerMinimalCandidateSelectionCandidate;

    fn sample_candidate(id: &str) -> SchedulerMinimalCandidateSelectionCandidate {
        SchedulerMinimalCandidateSelectionCandidate {
            provider_id: format!("provider-{id}"),
            provider_name: format!("Provider {id}"),
            provider_type: "custom".to_string(),
            provider_priority: 1,
            endpoint_id: format!("endpoint-{id}"),
            endpoint_api_format: "openai:chat".to_string(),
            key_id: format!("key-{id}"),
            key_name: format!("Key {id}"),
            key_auth_type: "api_key".to_string(),
            key_internal_priority: 1,
            key_global_priority_for_format: Some(1),
            key_capabilities: None,
            model_id: format!("model-{id}"),
            global_model_id: format!("global-model-{id}"),
            global_model_name: "gpt-5".to_string(),
            selected_provider_model_name: "gpt-5".to_string(),
            mapping_matched_model: None,
        }
    }

    #[test]
    fn builds_normalized_scheduler_affinity_cache_key() {
        assert_eq!(
            build_scheduler_affinity_cache_key_for_api_key_id("api-key-1", "OPENAI:CHAT", "gpt-5"),
            Some("scheduler_affinity:api-key-1:openai:chat:gpt-5".to_string())
        );
    }

    #[test]
    fn rejects_blank_affinity_key_components() {
        assert_eq!(
            build_scheduler_affinity_cache_key_for_api_key_id("", "openai:chat", "gpt-5"),
            None
        );
        assert_eq!(
            build_scheduler_affinity_cache_key_for_api_key_id("api-key-1", "", "gpt-5"),
            None
        );
        assert_eq!(
            build_scheduler_affinity_cache_key_for_api_key_id("api-key-1", "openai:chat", ""),
            None
        );
    }

    #[test]
    fn builds_session_aware_scheduler_affinity_cache_key_without_raw_session() {
        let affinity = ClientSessionAffinity::new(
            Some(" Generic ".to_string()),
            Some("conversation-123:agent-7".to_string()),
        );

        let cache_key = build_scheduler_affinity_cache_key_for_api_key_id_with_client_session(
            "api-key-1",
            "OPENAI:CHAT",
            "gpt-5",
            Some(&affinity),
        )
        .expect("cache key should build");

        assert!(cache_key.starts_with("scheduler_affinity:v2:api-key-1:openai:chat:gpt-5:generic:"));
        assert!(!cache_key.contains("conversation-123"));
        assert!(!cache_key.contains("agent-7"));
    }

    #[test]
    fn session_aware_scheduler_affinity_key_falls_back_without_session_key() {
        let affinity = ClientSessionAffinity::new(Some("generic".to_string()), None);

        assert_eq!(
            build_scheduler_affinity_cache_key_for_api_key_id_with_client_session(
                "api-key-1",
                "openai:chat",
                "gpt-5",
                Some(&affinity),
            ),
            Some("scheduler_affinity:api-key-1:openai:chat:gpt-5".to_string())
        );
    }

    #[test]
    fn session_aware_scheduler_affinity_key_splits_sessions_and_clients() {
        let left =
            ClientSessionAffinity::new(Some("generic".to_string()), Some("session-a".to_string()));
        let right =
            ClientSessionAffinity::new(Some("generic".to_string()), Some("session-b".to_string()));
        let other_client =
            ClientSessionAffinity::new(Some("other".to_string()), Some("session-a".to_string()));

        let left_key = build_scheduler_affinity_cache_key_for_api_key_id_with_client_session(
            "api-key-1",
            "openai:chat",
            "gpt-5",
            Some(&left),
        );
        let right_key = build_scheduler_affinity_cache_key_for_api_key_id_with_client_session(
            "api-key-1",
            "openai:chat",
            "gpt-5",
            Some(&right),
        );
        let other_client_key =
            build_scheduler_affinity_cache_key_for_api_key_id_with_client_session(
                "api-key-1",
                "openai:chat",
                "gpt-5",
                Some(&other_client),
            );

        assert_ne!(left_key, right_key);
        assert_ne!(left_key, other_client_key);
    }

    #[test]
    fn affinity_hash_is_candidate_specific() {
        let left = sample_candidate("1");
        let right = sample_candidate("2");

        assert_ne!(
            candidate_affinity_hash("api-key-1", &left),
            candidate_affinity_hash("api-key-1", &right)
        );
    }

    #[test]
    fn affinity_target_and_candidate_key_reuse_candidate_identity() {
        let candidate = sample_candidate("1");
        let target = SchedulerAffinityTarget {
            provider_id: candidate.provider_id.clone(),
            endpoint_id: candidate.endpoint_id.clone(),
            key_id: candidate.key_id.clone(),
        };

        assert!(matches_affinity_target(&candidate, &target));
        assert_eq!(
            candidate_key(&candidate),
            (
                "provider-1".to_string(),
                "endpoint-1".to_string(),
                "key-1".to_string()
            )
        );
    }
}