use hemx_core::{Effect, EffectBatch, IntoEffect};
use serde::{de, Deserialize, Deserializer, Serialize};
use std::{error::Error, fmt};

pub const PATCH_SCHEMA_VERSION: u16 = 1;
pub const PATCH_EVENT: &str = "hemx:sync-patch";
const INTERACTION_ID: &str = "$hemx-interaction";
pub const BROWSER_RUNTIME: &str = include_str!("../runtime/hemx-sync.js");

#[derive(Clone, Debug, Eq, Hash, PartialEq)]
pub struct Channel(String);

impl Channel {
    pub fn new(value: impl Into<String>) -> Result<Self, ChannelError> {
        let value = value.into();
        if value.is_empty() {
            return Err(ChannelError::Empty);
        }
        if value.len() > 128 {
            return Err(ChannelError::TooLong);
        }
        if !value
            .bytes()
            .all(|byte| byte.is_ascii_alphanumeric() || matches!(byte, b':' | b'_' | b'-' | b'.'))
        {
            return Err(ChannelError::InvalidCharacter);
        }
        Ok(Self(value))
    }

    pub fn as_str(&self) -> &str {
        &self.0
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum ChannelError {
    Empty,
    TooLong,
    InvalidCharacter,
}

impl fmt::Display for ChannelError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Empty => formatter.write_str("sync channel must not be empty"),
            Self::TooLong => formatter.write_str("sync channel is too long"),
            Self::InvalidCharacter => {
                formatter.write_str("sync channel contains an invalid character")
            }
        }
    }
}

impl Error for ChannelError {}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Broadcast {
    channel: Channel,
    effect_batch: EffectBatch,
}

impl Broadcast {
    pub fn channel(&self) -> &Channel {
        &self.channel
    }

    pub fn effect_batch(&self) -> &EffectBatch {
        &self.effect_batch
    }

    pub fn into_parts(self) -> (Channel, EffectBatch) {
        (self.channel, self.effect_batch)
    }
}

#[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
#[serde(untagged)]
pub enum PatchValue {
    Boolean(bool),
    Integer(i64),
    String(String),
}

#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct FlatPatch {
    // req: sync/003
    schema_version: u16,
    idempotency_key: String,
    operation_id: String,
    key: String,
    value: PatchValue,
}

#[derive(Deserialize)]
#[serde(rename_all = "camelCase", deny_unknown_fields)]
struct FlatPatchWire {
    schema_version: u16,
    idempotency_key: String,
    operation_id: String,
    key: String,
    value: PatchValue,
}

impl<'de> Deserialize<'de> for FlatPatch {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        let wire = FlatPatchWire::deserialize(deserializer)?;
        let patch = Self {
            schema_version: wire.schema_version,
            idempotency_key: wire.idempotency_key,
            operation_id: wire.operation_id,
            key: wire.key,
            value: wire.value,
        };
        patch.validate().map_err(de::Error::custom)?;
        Ok(patch)
    }
}

impl FlatPatch {
    pub fn for_interaction(key: impl Into<String>, value: PatchValue) -> Result<Self, PatchError> {
        let key = key.into();
        validate_key(&key)?;
        validate_value(&value)?;
        Ok(Self {
            schema_version: PATCH_SCHEMA_VERSION,
            idempotency_key: INTERACTION_ID.to_owned(),
            operation_id: INTERACTION_ID.to_owned(),
            key,
            value,
        })
    }

    pub fn new(
        idempotency_key: impl Into<String>,
        operation_id: impl Into<String>,
        key: impl Into<String>,
        value: PatchValue,
    ) -> Result<Self, PatchError> {
        let patch = Self {
            schema_version: PATCH_SCHEMA_VERSION,
            idempotency_key: idempotency_key.into(),
            operation_id: operation_id.into(),
            key: key.into(),
            value,
        };
        patch.validate()?;
        Ok(patch)
    }

    pub fn payload(&self) -> String {
        let value = match &self.value {
            PatchValue::Boolean(value) => value.to_string(),
            PatchValue::Integer(value) => value.to_string(),
            PatchValue::String(value) => json_string(value),
        };
        format!(
            r#"{{"schemaVersion":{},"idempotencyKey":{},"operationId":{},"key":{},"value":{value}}}"#,
            self.schema_version,
            json_string(&self.idempotency_key),
            json_string(&self.operation_id),
            json_string(&self.key),
        )
    }

    pub fn validate(&self) -> Result<(), PatchError> {
        if self.schema_version != PATCH_SCHEMA_VERSION {
            return Err(PatchError::SchemaVersion(self.schema_version));
        }
        if self.idempotency_key != INTERACTION_ID || self.operation_id != INTERACTION_ID {
            validate_identifier("idempotency_key", &self.idempotency_key, 128)?;
            validate_identifier("operation_id", &self.operation_id, 128)?;
        }
        validate_key(&self.key)?;
        validate_value(&self.value)
    }
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub enum PatchError {
    Empty(&'static str),
    InvalidCharacter(&'static str),
    TooLong(&'static str),
    ReservedKey,
    SchemaVersion(u16),
    ValueTooLong,
    IntegerOutOfRange,
}

impl fmt::Display for PatchError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Empty(field) => write!(formatter, "{field} must not be empty"),
            Self::InvalidCharacter(field) => {
                write!(formatter, "{field} contains an invalid character")
            }
            Self::TooLong(field) => write!(formatter, "{field} is too long"),
            Self::ReservedKey => formatter.write_str("patch key is reserved"),
            Self::SchemaVersion(version) => {
                write!(formatter, "unsupported patch schema version {version}")
            }
            Self::ValueTooLong => formatter.write_str("patch string value is too long"),
            Self::IntegerOutOfRange => {
                formatter.write_str("patch integer value exceeds JavaScript's safe range")
            }
        }
    }
}

impl Error for PatchError {}

fn json_string(value: &str) -> String {
    const HEX: &[u8; 16] = b"0123456789abcdef";
    let mut encoded = String::with_capacity(value.len() + 2);
    encoded.push('"');
    for character in value.chars() {
        match character {
            '"' => encoded.push_str("\\\""),
            '\\' => encoded.push_str("\\\\"),
            '\n' => encoded.push_str("\\n"),
            '\r' => encoded.push_str("\\r"),
            '\t' => encoded.push_str("\\t"),
            character if character <= '\u{1f}' => {
                let byte = character as u8;
                encoded.push_str("\\u00");
                encoded.push(HEX[(byte >> 4) as usize] as char);
                encoded.push(HEX[(byte & 0x0f) as usize] as char);
            }
            character => encoded.push(character),
        }
    }
    encoded.push('"');
    encoded
}

fn validate_value(value: &PatchValue) -> Result<(), PatchError> {
    match value {
        PatchValue::String(value) if value.len() > 4096 => Err(PatchError::ValueTooLong),
        PatchValue::Integer(value) if value.unsigned_abs() > 9_007_199_254_740_991 => {
            Err(PatchError::IntegerOutOfRange)
        }
        _ => Ok(()),
    }
}

fn validate_identifier(field: &'static str, value: &str, maximum: usize) -> Result<(), PatchError> {
    if value.is_empty() {
        return Err(PatchError::Empty(field));
    }
    if value.len() > maximum {
        return Err(PatchError::TooLong(field));
    }
    if !value
        .bytes()
        .all(|byte| byte.is_ascii_alphanumeric() || matches!(byte, b':' | b'_' | b'-' | b'.'))
    {
        return Err(PatchError::InvalidCharacter(field));
    }
    Ok(())
}

fn validate_key(key: &str) -> Result<(), PatchError> {
    if key.is_empty() {
        return Err(PatchError::Empty("key"));
    }
    if key.len() > 64 {
        return Err(PatchError::TooLong("key"));
    }
    if matches!(
        key,
        "schemaVersion" | "idempotencyKey" | "operationId" | "key" | "value"
    ) {
        return Err(PatchError::ReservedKey);
    }
    let mut bytes = key.bytes();
    if !bytes.next().is_some_and(|byte| byte.is_ascii_alphabetic())
        || !bytes.all(|byte| byte.is_ascii_alphanumeric() || matches!(byte, b'_' | b'-'))
    {
        return Err(PatchError::InvalidCharacter("key"));
    }
    Ok(())
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct SyncEffect(Effect); // req: sync/002

impl SyncEffect {
    // req: sync/004
    pub fn broadcast(channel: Channel, effect_batch: EffectBatch) -> Broadcast {
        Broadcast {
            channel,
            effect_batch,
        }
    }

    pub fn send_patch(patch: FlatPatch) -> Self {
        patch.validate().expect("FlatPatch must remain valid");
        Self(Effect::Emit {
            name: PATCH_EVENT.to_owned(),
            payload: patch.payload(),
        })
    }
}

impl IntoEffect for SyncEffect {
    fn append_to(self, ops: &mut Vec<Effect>) {
        self.0.append_to(ops);
    }
}

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

    #[test]
    fn broadcast_preserves_typed_channel_and_ordinary_batch() {
        let channel = Channel::new("board:alpha").unwrap();
        let batch = EffectBatch {
            abi_version: 1,
            fingerprint: hemx_core::BuildFingerprint(7),
            ops: vec![],
        };
        let broadcast = SyncEffect::broadcast(channel.clone(), batch.clone());
        assert_eq!(broadcast.into_parts(), (channel, batch));
        assert_eq!(
            Channel::new("board alpha"),
            Err(ChannelError::InvalidCharacter)
        );
    }

    #[test]
    fn schema_is_flat_and_rejects_reserved_keys() {
        let patch = FlatPatch::new(
            "actor:1",
            "move-card-to-done",
            "cardColumn",
            PatchValue::String("done".to_owned()),
        )
        .unwrap();
        assert_eq!(
            patch.payload(),
            r#"{"schemaVersion":1,"idempotencyKey":"actor:1","operationId":"move-card-to-done","key":"cardColumn","value":"done"}"#
        );
        assert_eq!(
            FlatPatch::new("actor:1", "move", "value", PatchValue::Integer(1)),
            Err(PatchError::ReservedKey)
        );
        assert_eq!(
            FlatPatch::new(
                "actor:1",
                "move",
                "rank",
                PatchValue::Integer(9_007_199_254_740_992),
            ),
            Err(PatchError::IntegerOutOfRange)
        );
        assert!(serde_json::from_str::<FlatPatch>(
            r#"{"schemaVersion":1,"idempotencyKey":"actor:1","operationId":"move","key":"rank","value":9007199254740992}"#,
        )
        .unwrap_err()
        .to_string()
        .contains("safe range"));
    }
}