use std::borrow::Cow;
use std::time::{SystemTime, UNIX_EPOCH};

use serde_json::Value;
use tracing::warn;

use crate::ai_serving::ExecutionRuntimeAuthContext;
use crate::privacy::{
    build_redaction_session_config, read_chat_pii_redaction_runtime_config,
    try_mask_chat_pii_request_json_with_cache_options, ChatPiiRedactionRequestFormat,
    MaskChatRequestOptions, RedactionMaskError, RedactionSessionSlot, RedisRedactionMappingCache,
};
use crate::{AppState, GatewayError};

pub(crate) struct ProviderRequestRedaction<'a> {
    pub(crate) body_json: Cow<'a, Value>,
    pub(crate) redacted: bool,
}

impl<'a> ProviderRequestRedaction<'a> {
    fn disabled(body_json: &'a Value) -> Self {
        Self {
            body_json: Cow::Borrowed(body_json),
            redacted: false,
        }
    }
}

#[derive(Clone, Copy, Debug, Default)]
struct ChatPiiRedactionFeatureSettings {
    enabled: Option<bool>,
    inject_model_instruction: Option<bool>,
}

impl ChatPiiRedactionFeatureSettings {
    fn merge_from_value(&mut self, value: Option<&Value>) {
        let Some(settings) = value
            .and_then(Value::as_object)
            .and_then(|features| features.get("chat_pii_redaction"))
            .and_then(Value::as_object)
        else {
            return;
        };
        if let Some(enabled) = settings.get("enabled").and_then(Value::as_bool) {
            self.enabled = Some(enabled);
        }
        if let Some(inject_model_instruction) = settings
            .get("inject_model_instruction")
            .and_then(Value::as_bool)
        {
            self.inject_model_instruction = Some(inject_model_instruction);
        }
    }

    fn effective_enabled(self) -> bool {
        self.enabled.unwrap_or(false)
    }

    fn effective_inject_model_instruction(self) -> bool {
        self.inject_model_instruction.unwrap_or(true)
    }
}

pub(crate) fn request_identity_response_encoding_when_redacted(
    headers: &mut std::collections::BTreeMap<String, String>,
    redacted: bool,
) {
    if redacted {
        headers.insert("accept-encoding".to_string(), "identity".to_string());
    }
}

pub(crate) async fn resolve_provider_chat_pii_redaction<'a>(
    state: &AppState,
    parts: &http::request::Parts,
    body_json: &'a Value,
    auth_context: &ExecutionRuntimeAuthContext,
    client_api_format: &str,
    candidate_id: &str,
) -> Result<ProviderRequestRedaction<'a>, GatewayError> {
    let Some(format) = ChatPiiRedactionRequestFormat::from_api_format(client_api_format) else {
        return Ok(ProviderRequestRedaction::disabled(body_json));
    };
    let Some(slot) = parts.extensions.get::<RedactionSessionSlot>() else {
        return Ok(ProviderRequestRedaction::disabled(body_json));
    };
    let runtime_config = read_chat_pii_redaction_runtime_config(state)
        .await
        .map_err(|err| {
            warn!(
                error = ?err,
                "gateway failed to read chat pii redaction runtime config"
            );
            GatewayError::Internal("chat pii redaction setup failed".to_string())
        })?;
    if !runtime_config.enabled {
        return Ok(ProviderRequestRedaction::disabled(body_json));
    }
    let feature_settings = resolve_chat_pii_redaction_feature_settings(state, auth_context).await?;
    if !feature_settings.effective_enabled() {
        return Ok(ProviderRequestRedaction::disabled(body_json));
    }
    let Some(hmac_key) = state.encryption_key().map(str::as_bytes).map(Vec::from) else {
        warn!("gateway chat pii redaction is enabled but encryption key is unavailable");
        return Err(GatewayError::Internal(
            "chat pii redaction setup failed".to_string(),
        ));
    };
    let body_bytes = serde_json::to_vec(body_json).map_err(|err| {
        warn!(
            error = ?err,
            "gateway failed to serialize provider chat pii redaction body"
        );
        GatewayError::Internal("chat pii redaction setup failed".to_string())
    })?;
    let now_unix_secs = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap_or_default()
        .as_secs();
    let cache = RedisRedactionMappingCache::new(state.runtime_state.as_ref());
    let masked = try_mask_chat_pii_request_json_with_cache_options(
        &body_bytes,
        format,
        build_redaction_session_config(hmac_key, &runtime_config, now_unix_secs),
        MaskChatRequestOptions::runtime(feature_settings.effective_inject_model_instruction()),
        Some(&cache),
    )
    .await
    .map_err(redaction_mask_error_to_gateway_error)?;
    if !masked.redacted {
        return Ok(ProviderRequestRedaction {
            body_json: Cow::Borrowed(body_json),
            redacted: false,
        });
    }
    let masked_body_json = serde_json::from_slice::<Value>(&masked.body).map_err(|err| {
        warn!(
            error = ?err,
            "gateway failed to decode redacted provider chat pii body"
        );
        GatewayError::Internal("chat pii redaction setup failed".to_string())
    })?;
    slot.put_for_candidate(candidate_id, masked.session);
    Ok(ProviderRequestRedaction {
        body_json: Cow::Owned(masked_body_json),
        redacted: true,
    })
}

async fn resolve_chat_pii_redaction_feature_settings(
    state: &AppState,
    auth_context: &ExecutionRuntimeAuthContext,
) -> Result<ChatPiiRedactionFeatureSettings, GatewayError> {
    let user_settings = state
        .read_user_feature_settings(&auth_context.user_id)
        .await
        .map_err(|err| {
            warn!(
                error = ?err,
                "gateway failed to read user chat pii redaction feature settings"
            );
            GatewayError::Internal("chat pii redaction setup failed".to_string())
        })?;
    let key_settings = state
        .read_auth_api_key_feature_settings(
            &auth_context.user_id,
            &auth_context.api_key_id,
            auth_context.api_key_is_standalone,
        )
        .await
        .map_err(|err| {
            warn!(
                error = ?err,
                "gateway failed to read api key chat pii redaction feature settings"
            );
            GatewayError::Internal("chat pii redaction setup failed".to_string())
        })?;

    let mut settings = ChatPiiRedactionFeatureSettings::default();
    settings.merge_from_value(user_settings.as_ref());
    settings.merge_from_value(key_settings.as_ref());
    Ok(settings)
}

fn redaction_mask_error_to_gateway_error(error: RedactionMaskError) -> GatewayError {
    match error {
        RedactionMaskError::Limit(limit) => GatewayError::Client {
            status: limit.client_status(),
            message: limit.safe_message().to_string(),
        },
    }
}