use anyhow::{Context, Result};
use base64::{engine::general_purpose::STANDARD as B64, Engine as _};
use chrono::{DateTime, Utc};
use ed25519_dalek::{Signature, Signer, SigningKey, Verifier, VerifyingKey};
use rand::rngs::OsRng;
use serde::{Deserialize, Serialize};
use serde_json::{json, Value};
use std::path::{Path, PathBuf};

pub const LICENSE_RELATIVE_PATH: &str = "license/license.json";
pub const PUBLIC_KEY_RELATIVE_PATH: &str = "config/license-public-key.txt";

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LicensePayload {
    pub license_id: String,
    pub product: String,
    pub edition: String,
    pub customer_name: String,
    #[serde(default)]
    pub customer_email: Option<String>,
    #[serde(default)]
    pub customer_company: Option<String>,
    pub issued_at: DateTime<Utc>,
    #[serde(default)]
    pub expires_at: Option<DateTime<Utc>>,
    #[serde(default)]
    pub max_devices: Option<u32>,
    #[serde(default)]
    pub features: Vec<String>,
    #[serde(default)]
    pub notes: Option<String>,
}

#[derive(Debug, Serialize, Deserialize)]
struct LicenseFile {
    payload_b64: String,
    signature_b64: String,
}

#[derive(Debug, Clone)]
pub struct LicenseStatus {
    pub state: &'static str,
    pub reason: Option<String>,
    pub payload: Option<LicensePayload>,
}

impl LicenseStatus {
    pub fn to_json(&self) -> Value {
        json!({
            "state": self.state,
            "licensed": self.state == "licensed",
            "reason": self.reason,
            "license": self.payload.as_ref().map(|p| json!({
                "license_id": p.license_id,
                "product": p.product,
                "edition": p.edition,
                "customer_name": p.customer_name,
                "customer_company": p.customer_company,
                "issued_at": p.issued_at.to_rfc3339(),
                "expires_at": p.expires_at.map(|d| d.to_rfc3339()),
                "features": p.features,
            })),
        })
    }
}

pub fn status(root: &Path) -> LicenseStatus {
    let verifying_key = match load_public_key(root) {
        Ok(Some(key)) => key,
        Ok(None) => {
            return LicenseStatus {
                state: "no_public_key",
                reason: Some(format!("missing {PUBLIC_KEY_RELATIVE_PATH}")),
                payload: None,
            }
        }
        Err(err) => {
            return LicenseStatus {
                state: "no_public_key",
                reason: Some(err.to_string()),
                payload: None,
            }
        }
    };
    let license_path = root.join(LICENSE_RELATIVE_PATH);
    if !license_path.exists() {
        return LicenseStatus {
            state: "unlicensed",
            reason: Some("no license file installed".to_string()),
            payload: None,
        };
    }
    let text = match std::fs::read_to_string(&license_path) {
        Ok(text) => text,
        Err(err) => {
            return LicenseStatus {
                state: "invalid",
                reason: Some(format!("cannot read license file: {err}")),
                payload: None,
            }
        }
    };
    match verify_text(&text, &verifying_key) {
        Ok(payload) => evaluate_payload(payload),
        Err(err) => LicenseStatus {
            state: "invalid",
            reason: Some(err.to_string()),
            payload: None,
        },
    }
}

pub fn install(root: &Path, content: &str) -> Result<LicenseStatus> {
    let verifying_key = load_public_key(root)?
        .with_context(|| format!("missing {PUBLIC_KEY_RELATIVE_PATH}"))?;
    let payload = verify_text(content, &verifying_key)?;
    let status = evaluate_payload(payload);
    if status.state == "invalid" {
        anyhow::bail!(
            "license rejected: {}",
            status.reason.as_deref().unwrap_or("unknown reason")
        );
    }
    let license_path = root.join(LICENSE_RELATIVE_PATH);
    if let Some(parent) = license_path.parent() {
        std::fs::create_dir_all(parent)?;
    }
    std::fs::write(&license_path, content)?;
    Ok(status)
}

pub fn keygen(out_dir: &Path) -> Result<(PathBuf, PathBuf)> {
    std::fs::create_dir_all(out_dir)?;
    let signing_key = SigningKey::generate(&mut OsRng);
    let private_path = out_dir.join("license-signing-key.txt");
    let public_path = out_dir.join("license-public-key.txt");
    std::fs::write(&private_path, B64.encode(signing_key.to_bytes()))?;
    std::fs::write(
        &public_path,
        B64.encode(signing_key.verifying_key().to_bytes()),
    )?;
    Ok((private_path, public_path))
}

#[allow(clippy::too_many_arguments)]
pub fn issue(
    signing_key_path: &Path,
    out_path: &Path,
    product: &str,
    edition: &str,
    customer_name: &str,
    customer_email: Option<String>,
    customer_company: Option<String>,
    expires_at: Option<DateTime<Utc>>,
    max_devices: Option<u32>,
    features: Vec<String>,
    notes: Option<String>,
) -> Result<LicensePayload> {
    let key_text = std::fs::read_to_string(signing_key_path)
        .with_context(|| format!("cannot read signing key {}", signing_key_path.display()))?;
    let key_bytes: [u8; 32] = B64
        .decode(key_text.trim())
        .context("signing key is not valid base64")?
        .try_into()
        .map_err(|_| anyhow::anyhow!("signing key must be 32 bytes"))?;
    let signing_key = SigningKey::from_bytes(&key_bytes);

    let payload = LicensePayload {
        license_id: uuid::Uuid::new_v4().to_string(),
        product: product.to_string(),
        edition: edition.to_string(),
        customer_name: customer_name.to_string(),
        customer_email,
        customer_company,
        issued_at: Utc::now(),
        expires_at,
        max_devices,
        features,
        notes,
    };
    let payload_bytes = serde_json::to_vec(&payload)?;
    let signature = signing_key.sign(&payload_bytes);
    let file = LicenseFile {
        payload_b64: B64.encode(&payload_bytes),
        signature_b64: B64.encode(signature.to_bytes()),
    };
    if let Some(parent) = out_path.parent() {
        if !parent.as_os_str().is_empty() {
            std::fs::create_dir_all(parent)?;
        }
    }
    std::fs::write(out_path, serde_json::to_string_pretty(&file)?)?;
    Ok(payload)
}

pub fn verify_path(license_path: &Path, public_key_path: &Path) -> Result<LicenseStatus> {
    let key_text = std::fs::read_to_string(public_key_path)
        .with_context(|| format!("cannot read public key {}", public_key_path.display()))?;
    let verifying_key = parse_public_key(&key_text)?;
    let text = std::fs::read_to_string(license_path)
        .with_context(|| format!("cannot read license {}", license_path.display()))?;
    let payload = verify_text(&text, &verifying_key)?;
    Ok(evaluate_payload(payload))
}

fn evaluate_payload(payload: LicensePayload) -> LicenseStatus {
    if let Some(expires_at) = payload.expires_at {
        if Utc::now() > expires_at {
            return LicenseStatus {
                state: "expired",
                reason: Some(format!("license expired {}", expires_at.to_rfc3339())),
                payload: Some(payload),
            };
        }
    }
    LicenseStatus {
        state: "licensed",
        reason: None,
        payload: Some(payload),
    }
}

fn verify_text(text: &str, verifying_key: &VerifyingKey) -> Result<LicensePayload> {
    let file: LicenseFile =
        serde_json::from_str(text).context("license file is not valid JSON")?;
    let payload_bytes = B64
        .decode(file.payload_b64.trim())
        .context("license payload is not valid base64")?;
    let signature_bytes: [u8; 64] = B64
        .decode(file.signature_b64.trim())
        .context("license signature is not valid base64")?
        .try_into()
        .map_err(|_| anyhow::anyhow!("license signature must be 64 bytes"))?;
    let signature = Signature::from_bytes(&signature_bytes);
    verifying_key
        .verify(&payload_bytes, &signature)
        .map_err(|_| anyhow::anyhow!("license signature does not match"))?;
    serde_json::from_slice(&payload_bytes).context("license payload is not valid JSON")
}

fn load_public_key(root: &Path) -> Result<Option<VerifyingKey>> {
    let path = root.join(PUBLIC_KEY_RELATIVE_PATH);
    if !path.exists() {
        return Ok(None);
    }
    let text = std::fs::read_to_string(&path)
        .with_context(|| format!("cannot read public key {}", path.display()))?;
    Ok(Some(parse_public_key(&text)?))
}

fn parse_public_key(text: &str) -> Result<VerifyingKey> {
    let bytes: [u8; 32] = B64
        .decode(text.trim())
        .context("public key is not valid base64")?
        .try_into()
        .map_err(|_| anyhow::anyhow!("public key must be 32 bytes"))?;
    VerifyingKey::from_bytes(&bytes).context("public key is not a valid Ed25519 key")
}

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

    #[test]
    fn issued_license_verifies_and_round_trips() {
        let dir = std::env::temp_dir().join(format!("jkl-license-test-{}", std::process::id()));
        std::fs::create_dir_all(&dir).unwrap();
        let (private_path, public_path) = keygen(&dir).unwrap();
        let license_path = dir.join("license.json");
        issue(
            &private_path,
            &license_path,
            "JackAILocal",
            "pro",
            "Test Customer",
            Some("test@example.com".to_string()),
            None,
            None,
            Some(3),
            vec!["chat".to_string()],
            None,
        )
        .unwrap();
        let status = verify_path(&license_path, &public_path).unwrap();
        assert_eq!(status.state, "licensed");
        assert_eq!(status.payload.unwrap().customer_name, "Test Customer");
        std::fs::remove_dir_all(&dir).ok();
    }

    #[test]
    fn tampered_license_is_rejected() {
        let dir = std::env::temp_dir().join(format!("jkl-license-tamper-{}", std::process::id()));
        std::fs::create_dir_all(&dir).unwrap();
        let (private_path, public_path) = keygen(&dir).unwrap();
        let license_path = dir.join("license.json");
        issue(
            &private_path,
            &license_path,
            "JackAILocal",
            "personal",
            "Honest Customer",
            None,
            None,
            None,
            None,
            vec![],
            None,
        )
        .unwrap();
        let text = std::fs::read_to_string(&license_path).unwrap();
        let mut file: LicenseFile = serde_json::from_str(&text).unwrap();
        let mut payload: LicensePayload =
            serde_json::from_slice(&B64.decode(&file.payload_b64).unwrap()).unwrap();
        payload.edition = "whitelabel".to_string();
        file.payload_b64 = B64.encode(serde_json::to_vec(&payload).unwrap());
        std::fs::write(&license_path, serde_json::to_string(&file).unwrap()).unwrap();
        assert!(verify_path(&license_path, &public_path).is_err());
        std::fs::remove_dir_all(&dir).ok();
    }

    #[test]
    fn expired_license_reports_expired() {
        let dir = std::env::temp_dir().join(format!("jkl-license-exp-{}", std::process::id()));
        std::fs::create_dir_all(&dir).unwrap();
        let (private_path, public_path) = keygen(&dir).unwrap();
        let license_path = dir.join("license.json");
        issue(
            &private_path,
            &license_path,
            "JackAILocal",
            "pro",
            "Late Customer",
            None,
            None,
            Some(Utc::now() - chrono::Duration::days(1)),
            None,
            vec![],
            None,
        )
        .unwrap();
        let status = verify_path(&license_path, &public_path).unwrap();
        assert_eq!(status.state, "expired");
        std::fs::remove_dir_all(&dir).ok();
    }
}