use ring::digest::{digest, SHA256};
use serde::{Deserialize, Serialize};
use std::fs::{self, OpenOptions};
use std::io::Write;
use std::path::{Path, PathBuf};
use std::time::{SystemTime, UNIX_EPOCH};
use tauri::{AppHandle, Manager};
use uuid::Uuid;

const BRIDGE_SCHEMA: &str = "hololake.local-development-writer/v1";
const MAX_ID_BYTES: usize = 128;

#[derive(Clone, Debug, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct AcquireWriteLaneInput {
    pub account_id: String,
    pub lane_id: String,
    pub owner_instance_id: String,
    pub resume_token: Option<String>,
}

#[derive(Clone, Debug, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct InspectWriteLaneInput {
    pub account_id: String,
}

#[derive(Clone, Debug, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct ReleaseWriteLaneInput {
    pub account_id: String,
    pub lane_id: String,
    pub owner_instance_id: String,
    pub resume_token: String,
}

#[derive(Clone, Debug, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct WriteLaneReceipt {
    pub schema: &'static str,
    pub state: &'static str,
    pub account_key: String,
    pub lane_id: String,
    pub owner_instance_id: String,
    pub acquired_at_unix_ms: u128,
    pub observed_at_unix_ms: u128,
    pub resume_token: Option<String>,
    pub receipt_id: String,
}

#[derive(Clone, Debug, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct InspectWriteLaneReceipt {
    pub schema: &'static str,
    pub state: &'static str,
    pub account_key: String,
    pub lane_id: Option<String>,
    pub owner_instance_id: Option<String>,
    pub acquired_at_unix_ms: Option<u128>,
    pub observed_at_unix_ms: u128,
}

#[derive(Clone, Debug, Deserialize, Serialize)]
#[serde(rename_all = "camelCase")]
struct ActiveWriterRecord {
    schema: String,
    account_key: String,
    lane_id: String,
    owner_instance_id: String,
    resume_token_sha256: String,
    acquired_at_unix_ms: u128,
}

pub async fn acquire_development_write_lane(
    app: AppHandle,
    input: AcquireWriteLaneInput,
) -> Result<WriteLaneReceipt, String> {
    let root = bridge_root(&app)?;
    tauri::async_runtime::spawn_blocking(move || acquire_at(&root, input))
        .await
        .map_err(|error| format!("HOLOLAKE_BRIDGE_JOIN_FAILED: {error}"))?
}

pub async fn inspect_development_write_lane(
    app: AppHandle,
    input: InspectWriteLaneInput,
) -> Result<InspectWriteLaneReceipt, String> {
    let root = bridge_root(&app)?;
    tauri::async_runtime::spawn_blocking(move || inspect_at(&root, &input.account_id))
        .await
        .map_err(|error| format!("HOLOLAKE_BRIDGE_JOIN_FAILED: {error}"))?
}

pub async fn release_development_write_lane(
    app: AppHandle,
    input: ReleaseWriteLaneInput,
) -> Result<WriteLaneReceipt, String> {
    let root = bridge_root(&app)?;
    tauri::async_runtime::spawn_blocking(move || release_at(&root, input))
        .await
        .map_err(|error| format!("HOLOLAKE_BRIDGE_JOIN_FAILED: {error}"))?
}

fn bridge_root(app: &AppHandle) -> Result<PathBuf, String> {
    let app_data = app
        .path()
        .app_data_dir()
        .map_err(|error| format!("HOLOLAKE_APP_DATA_UNAVAILABLE: {error}"))?;
    let root = app_data.join("local-development-bridge-v1");
    fs::create_dir_all(&root)
        .map_err(|error| format!("HOLOLAKE_BRIDGE_STORAGE_UNAVAILABLE: {error}"))?;
    root.canonicalize()
        .map_err(|error| format!("HOLOLAKE_BRIDGE_STORAGE_UNAVAILABLE: {error}"))
}

pub(crate) fn acquire_at(
    root: &Path,
    input: AcquireWriteLaneInput,
) -> Result<WriteLaneReceipt, String> {
    validate_identifier(&input.account_id, "ACCOUNT")?;
    validate_identifier(&input.lane_id, "LANE")?;
    validate_identifier(&input.owner_instance_id, "OWNER")?;

    let account_key = sha256_hex(input.account_id.as_bytes());
    let account_root = prepare_account_root(root, &account_key)?;
    let active_path = account_root.join("active-writer.json");

    if active_path.exists() {
        let active = read_active_record(&active_path)?;
        return resume_existing(active, &input.lane_id, input.resume_token.as_deref());
    }

    if input.resume_token.is_some() {
        return Err("HOLOLAKE_WRITER_RESUME_TOKEN_STALE".into());
    }

    let resume_token = Uuid::new_v4().to_string();
    let acquired_at_unix_ms = now_unix_ms()?;
    let record = ActiveWriterRecord {
        schema: BRIDGE_SCHEMA.to_string(),
        account_key: account_key.clone(),
        lane_id: input.lane_id.clone(),
        owner_instance_id: input.owner_instance_id.clone(),
        resume_token_sha256: sha256_hex(resume_token.as_bytes()),
        acquired_at_unix_ms,
    };
    let bytes = serde_json::to_vec_pretty(&record)
        .map_err(|error| format!("HOLOLAKE_WRITER_RECORD_INVALID: {error}"))?;
    let mut file = match OpenOptions::new()
        .write(true)
        .create_new(true)
        .open(&active_path)
    {
        Ok(file) => file,
        Err(error) if error.kind() == std::io::ErrorKind::AlreadyExists => {
            let active = read_active_record(&active_path)?;
            return resume_existing(active, &input.lane_id, input.resume_token.as_deref());
        }
        Err(error) => return Err(format!("HOLOLAKE_WRITER_ACQUIRE_FAILED: {error}")),
    };
    file.write_all(&bytes)
        .and_then(|_| file.sync_all())
        .map_err(|error| format!("HOLOLAKE_WRITER_ACQUIRE_FAILED: {error}"))?;

    Ok(receipt_for(
        "ACQUIRED",
        &record,
        Some(resume_token),
        acquired_at_unix_ms,
    ))
}

fn resume_existing(
    record: ActiveWriterRecord,
    requested_lane_id: &str,
    resume_token: Option<&str>,
) -> Result<WriteLaneReceipt, String> {
    if record.lane_id != requested_lane_id {
        return Err("HOLOLAKE_ACCOUNT_WRITER_ALREADY_ACTIVE".into());
    }
    let supplied = resume_token.ok_or("HOLOLAKE_ACCOUNT_WRITER_ALREADY_ACTIVE")?;
    if sha256_hex(supplied.as_bytes()) != record.resume_token_sha256 {
        return Err("HOLOLAKE_ACCOUNT_WRITER_ALREADY_ACTIVE".into());
    }
    let observed_at = now_unix_ms()?;
    Ok(receipt_for("RESUMED", &record, None, observed_at))
}

pub(crate) fn inspect_at(root: &Path, account_id: &str) -> Result<InspectWriteLaneReceipt, String> {
    validate_identifier(account_id, "ACCOUNT")?;
    let account_key = sha256_hex(account_id.as_bytes());
    let active_path = root
        .join("accounts")
        .join(&account_key)
        .join("active-writer.json");
    let observed_at_unix_ms = now_unix_ms()?;
    if !active_path.exists() {
        return Ok(InspectWriteLaneReceipt {
            schema: BRIDGE_SCHEMA,
            state: "AVAILABLE",
            account_key,
            lane_id: None,
            owner_instance_id: None,
            acquired_at_unix_ms: None,
            observed_at_unix_ms,
        });
    }
    let record = read_active_record(&active_path)?;
    Ok(InspectWriteLaneReceipt {
        schema: BRIDGE_SCHEMA,
        state: "ACTIVE",
        account_key,
        lane_id: Some(record.lane_id),
        owner_instance_id: Some(record.owner_instance_id),
        acquired_at_unix_ms: Some(record.acquired_at_unix_ms),
        observed_at_unix_ms,
    })
}

pub(crate) fn release_at(
    root: &Path,
    input: ReleaseWriteLaneInput,
) -> Result<WriteLaneReceipt, String> {
    validate_identifier(&input.account_id, "ACCOUNT")?;
    validate_identifier(&input.lane_id, "LANE")?;
    validate_identifier(&input.owner_instance_id, "OWNER")?;
    let account_key = sha256_hex(input.account_id.as_bytes());
    let account_root = root.join("accounts").join(&account_key);
    let active_path = account_root.join("active-writer.json");
    let record = read_active_record(&active_path)?;
    if record.lane_id != input.lane_id
        || record.owner_instance_id != input.owner_instance_id
        || record.resume_token_sha256 != sha256_hex(input.resume_token.as_bytes())
    {
        return Err("HOLOLAKE_WRITER_RELEASE_NOT_AUTHORIZED".into());
    }

    let released_at = now_unix_ms()?;
    let receipt_id = receipt_id("RELEASED", &record, released_at);
    let receipts_root = account_root.join("receipts");
    fs::create_dir_all(&receipts_root)
        .map_err(|error| format!("HOLOLAKE_WRITER_RELEASE_FAILED: {error}"))?;
    let released_path = receipts_root.join(format!("{receipt_id}.json"));
    fs::rename(&active_path, &released_path)
        .map_err(|error| format!("HOLOLAKE_WRITER_RELEASE_FAILED: {error}"))?;

    Ok(WriteLaneReceipt {
        schema: BRIDGE_SCHEMA,
        state: "RELEASED",
        account_key: record.account_key,
        lane_id: record.lane_id,
        owner_instance_id: record.owner_instance_id,
        acquired_at_unix_ms: record.acquired_at_unix_ms,
        observed_at_unix_ms: released_at,
        resume_token: None,
        receipt_id,
    })
}

fn prepare_account_root(root: &Path, account_key: &str) -> Result<PathBuf, String> {
    let accounts_root = root.join("accounts");
    fs::create_dir_all(&accounts_root)
        .map_err(|error| format!("HOLOLAKE_BRIDGE_STORAGE_UNAVAILABLE: {error}"))?;
    let account_root = accounts_root.join(account_key);
    fs::create_dir_all(&account_root)
        .map_err(|error| format!("HOLOLAKE_BRIDGE_STORAGE_UNAVAILABLE: {error}"))?;
    Ok(account_root)
}

fn read_active_record(path: &Path) -> Result<ActiveWriterRecord, String> {
    let bytes = fs::read(path).map_err(|error| {
        if error.kind() == std::io::ErrorKind::NotFound {
            "HOLOLAKE_WRITER_NOT_ACTIVE".to_string()
        } else {
            format!("HOLOLAKE_WRITER_RECORD_UNREADABLE: {error}")
        }
    })?;
    let record: ActiveWriterRecord = serde_json::from_slice(&bytes)
        .map_err(|error| format!("HOLOLAKE_WRITER_RECORD_INVALID: {error}"))?;
    if record.schema != BRIDGE_SCHEMA {
        return Err("HOLOLAKE_WRITER_RECORD_SCHEMA_UNSUPPORTED".into());
    }
    Ok(record)
}

fn receipt_for(
    state: &'static str,
    record: &ActiveWriterRecord,
    resume_token: Option<String>,
    observed_at_unix_ms: u128,
) -> WriteLaneReceipt {
    WriteLaneReceipt {
        schema: BRIDGE_SCHEMA,
        state,
        account_key: record.account_key.clone(),
        lane_id: record.lane_id.clone(),
        owner_instance_id: record.owner_instance_id.clone(),
        acquired_at_unix_ms: record.acquired_at_unix_ms,
        observed_at_unix_ms,
        resume_token,
        receipt_id: receipt_id(state, record, observed_at_unix_ms),
    }
}

fn receipt_id(state: &str, record: &ActiveWriterRecord, observed_at_unix_ms: u128) -> String {
    sha256_hex(
        format!(
            "{state}\n{}\n{}\n{}\n{}\n{observed_at_unix_ms}",
            record.account_key,
            record.lane_id,
            record.owner_instance_id,
            record.acquired_at_unix_ms
        )
        .as_bytes(),
    )
}

fn validate_identifier(value: &str, kind: &str) -> Result<(), String> {
    if value.is_empty()
        || value.len() > MAX_ID_BYTES
        || !value
            .bytes()
            .all(|byte| byte.is_ascii_alphanumeric() || matches!(byte, b'-' | b'_' | b'.' | b':'))
    {
        return Err(format!("HOLOLAKE_{kind}_ID_INVALID"));
    }
    Ok(())
}

fn now_unix_ms() -> Result<u128, String> {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|duration| duration.as_millis())
        .map_err(|error| format!("HOLOLAKE_SYSTEM_CLOCK_INVALID: {error}"))
}

fn sha256_hex(value: &[u8]) -> String {
    digest(&SHA256, value)
        .as_ref()
        .iter()
        .map(|byte| format!("{byte:02x}"))
        .collect()
}

pub(crate) fn account_key_for(account_id: &str) -> Result<String, String> {
    validate_identifier(account_id, "ACCOUNT")?;
    Ok(sha256_hex(account_id.as_bytes()))
}

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

    fn acquire_input(lane_id: &str) -> AcquireWriteLaneInput {
        AcquireWriteLaneInput {
            account_id: "human-BS-0001".into(),
            lane_id: lane_id.into(),
            owner_instance_id: "codex-instance-1".into(),
            resume_token: None,
        }
    }

    #[test]
    fn one_account_cannot_open_two_write_lanes() {
        let temp = TempDir::new().unwrap();
        let first = acquire_at(temp.path(), acquire_input("DEV-001")).unwrap();
        assert_eq!(first.state, "ACQUIRED");
        assert_eq!(
            acquire_at(temp.path(), acquire_input("DEV-002")).unwrap_err(),
            "HOLOLAKE_ACCOUNT_WRITER_ALREADY_ACTIVE"
        );
    }

    #[test]
    fn the_same_lane_resumes_after_the_ai_reconnects() {
        let temp = TempDir::new().unwrap();
        let first = acquire_at(temp.path(), acquire_input("DEV-001")).unwrap();
        let mut reconnect = acquire_input("DEV-001");
        reconnect.resume_token = first.resume_token.clone();
        let resumed = acquire_at(temp.path(), reconnect).unwrap();
        assert_eq!(resumed.state, "RESUMED");
        assert_eq!(resumed.lane_id, "DEV-001");
        assert!(resumed.resume_token.is_none());
    }

    #[test]
    fn a_resume_token_cannot_be_used_to_switch_to_another_lane() {
        let temp = TempDir::new().unwrap();
        let first = acquire_at(temp.path(), acquire_input("DEV-001")).unwrap();
        let mut impostor = acquire_input("DEV-002");
        impostor.resume_token = first.resume_token;
        assert_eq!(
            acquire_at(temp.path(), impostor).unwrap_err(),
            "HOLOLAKE_ACCOUNT_WRITER_ALREADY_ACTIVE"
        );
    }

    #[test]
    fn explicit_release_creates_a_receipt_then_allows_the_next_lane() {
        let temp = TempDir::new().unwrap();
        let first = acquire_at(temp.path(), acquire_input("DEV-001")).unwrap();
        let released = release_at(
            temp.path(),
            ReleaseWriteLaneInput {
                account_id: "human-BS-0001".into(),
                lane_id: "DEV-001".into(),
                owner_instance_id: "codex-instance-1".into(),
                resume_token: first.resume_token.unwrap(),
            },
        )
        .unwrap();
        assert_eq!(released.state, "RELEASED");
        assert!(temp
            .path()
            .join("accounts")
            .join(released.account_key)
            .join("receipts")
            .join(format!("{}.json", released.receipt_id))
            .is_file());

        let second = acquire_at(temp.path(), acquire_input("DEV-002")).unwrap();
        assert_eq!(second.state, "ACQUIRED");
    }

    #[test]
    fn inspect_never_discloses_the_resume_token() {
        let temp = TempDir::new().unwrap();
        acquire_at(temp.path(), acquire_input("DEV-001")).unwrap();
        let observed = inspect_at(temp.path(), "human-BS-0001").unwrap();
        assert_eq!(observed.state, "ACTIVE");
        assert_eq!(observed.lane_id.as_deref(), Some("DEV-001"));
    }
}