use crate::ir_core::ids::SigId;
use crate::ir_core::types::Type;
use std::collections::HashMap;
use std::sync::{Mutex, OnceLock};

/// Canonical function signature: params + return type.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct Signature {
    pub params: Vec<Type>,
    pub return_type: Type,
}

impl Signature {
    /// Stable, deterministic descriptor. Example:
    /// fn(int;string)->void
    /// fn(array{int;4};optional{string})->result{void;error{E}}
    pub fn descriptor(&self) -> String {
        let mut s = String::new();
        s.push_str("fn(");
        for (i, p) in self.params.iter().enumerate() {
            if i > 0 {
                s.push(';');
            }
            encode_type(p, &mut s);
        }
        s.push(')');
        s.push_str("->");
        encode_type(&self.return_type, &mut s);
        s
    }

    /// Parse a descriptor previously produced by `descriptor()`
    pub fn from_descriptor(desc: &str) -> Result<Self, String> {
        // Expect prefix: fn( ... )-> ...
        if !desc.starts_with("fn(") {
            return Err("Invalid descriptor: missing fn(".to_string());
        }
        let rest = &desc[3..];
        let close = rest.find(')').ok_or_else(|| "Invalid descriptor: missing ')'".to_string())?;
        let params_blob = &rest[..close];
        let after = &rest[close + 1..];
        let arrow = after.strip_prefix("->").ok_or_else(|| "Invalid descriptor: missing '->'".to_string())?;

        let params = if params_blob.is_empty() {
            Vec::new()
        } else {
            let mut v = Vec::new();
            for part in split_top_level(params_blob, ';')? {
                let (ty, consumed) = decode_type(part)?;
                if consumed != part.len() {
                    return Err("Trailing garbage in parameter".to_string());
                }
                v.push(ty);
            }
            v
        };

        let (return_type, consumed) = decode_type(arrow)?;
        if consumed != arrow.len() {
            return Err("Trailing garbage after return type".to_string());
        }

        Ok(Signature { params, return_type })
    }
}

/// Global signature interner. Thread-safe and process-wide for this compiler instance.
pub struct SignatureInterner {
    map: HashMap<Signature, SigId>,
    rev: Vec<Signature>,
}

impl SignatureInterner {
    pub fn new() -> Self {
        Self { map: HashMap::new(), rev: Vec::new() }
    }

    pub fn intern(&mut self, sig: Signature) -> SigId {
        if let Some(id) = self.map.get(&sig) {
            return *id;
        }
        let id = SigId(self.rev.len() as u32);
        self.rev.push(sig.clone());
        self.map.insert(sig, id);
        id
    }

    pub fn resolve(&self, id: SigId) -> Option<&Signature> {
        self.rev.get(id.0 as usize)
    }
}

static GLOBAL_INTERNER: OnceLock<Mutex<SignatureInterner>> = OnceLock::new();

pub fn global_signature_interner() -> &'static Mutex<SignatureInterner> {
    GLOBAL_INTERNER.get_or_init(|| Mutex::new(SignatureInterner::new()))
}

// ==============
// Encoding/Decoding helpers for `Type`
// Canonical grammar (EBNF-ish):
// Type := "void" | "int" | "bounded" | "float" | "bool" | "string"
//       | "struct{" Name "}" | "service{" Name "}" | "contract{" Name "}"
//       | "error{" Name "}" | "array{" Type ";" UInt "}"
//       | "optional{" Type "}" | "result{" Type ";" Type "}"
//       | "fn(" [Type { ";" Type }] ")" "->" Type
// Name := escaped UTF-8 without '}' and ';' (escape via '\')

fn encode_type(ty: &Type, out: &mut String) {
    match ty {
        Type::Void => out.push_str("void"),
        Type::Int => out.push_str("int"),
        Type::Bounded => out.push_str("bounded"),
        Type::Float => out.push_str("float"),
        Type::Bool => out.push_str("bool"),
        Type::String => out.push_str("string"),
        Type::Optional(inner) => {
            out.push_str("optional{");
            encode_type(inner, out);
            out.push('}');
        }
        Type::Result(ok, err) => {
            out.push_str("result{");
            encode_type(ok, out);
            out.push(';');
            encode_type(err, out);
            out.push('}');
        }
        Type::Struct(name) => {
            out.push_str("struct{");
            encode_name(name, out);
            out.push('}');
        }
        Type::Service(name) => {
            out.push_str("service{");
            encode_name(name, out);
            out.push('}');
        }
        Type::Contract(name) => {
            out.push_str("contract{");
            encode_name(name, out);
            out.push('}');
        }
        Type::ErrorType(name) => {
            out.push_str("error{");
            encode_name(name, out);
            out.push('}');
        }
        Type::Array(inner, n) => {
            out.push_str("array{");
            encode_type(inner, out);
            out.push(';');
            out.push_str(&n.to_string());
            out.push('}');
        }
        Type::Function { params, return_type } => {
            out.push_str("fn(");
            for (i, p) in params.iter().enumerate() {
                if i > 0 { out.push(';'); }
                encode_type(p, out);
            }
            out.push(')');
            out.push_str("->");
            encode_type(return_type, out);
        }
    }
}

fn encode_name(name: &str, out: &mut String) {
    for ch in name.chars() {
        match ch {
            '\\' => out.push_str("\\\\"),
            '}' => out.push_str("\\}"),
            ';' => out.push_str("\\;"),
            _ => out.push(ch),
        }
    }
}

fn decode_name(s: &str) -> Result<(String, usize), String> {
    let mut out = String::new();
    let mut chars = s.chars().peekable();
    let mut consumed = 0;
    while let Some(&c) = chars.peek() {
        if c == '}' { break; }
        consumed += 1;
        chars.next();
        if c == '\\' {
            let next = chars.next().ok_or_else(|| "Invalid escape in name".to_string())?;
            consumed += 1;
            out.push(next);
        } else {
            out.push(c);
        }
    }
    Ok((out, consumed))
}

fn split_top_level(input: &str, sep: char) -> Result<Vec<&str>, String> {
    let mut parts = Vec::new();
    let mut depth_brace = 0i32;
    let mut depth_fn = 0i32; // counts '(' nesting for nested fn types
    let mut start = 0usize;
    for (i, ch) in input.char_indices() {
        match ch {
            '{' => depth_brace += 1,
            '}' => depth_brace -= 1,
            '(' => depth_fn += 1,
            ')' => depth_fn -= 1,
            _ => {}
        }
        if ch == sep && depth_brace == 0 && depth_fn == 0 {
            parts.push(&input[start..i]);
            start = i + ch.len_utf8();
        }
    }
    parts.push(&input[start..]);
    if depth_brace != 0 || depth_fn != 0 {
        return Err("Unbalanced delimiters".to_string());
    }
    Ok(parts)
}

fn decode_type(s: &str) -> Result<(Type, usize), String> {
    // Order matters; check longer keywords first to avoid prefix issues
    let keywords = [
        "optional{",
        "result{",
        "struct{",
        "service{",
        "contract{",
        "error{",
        "array{",
        "fn(",
        "void",
        "int",
        "bounded",
        "float",
        "bool",
        "string",
    ];

    for kw in keywords {
        if s.starts_with(kw) {
            match kw {
                "void" => return Ok((Type::Void, 4)),
                "int" => return Ok((Type::Int, 3)),
                "bounded" => return Ok((Type::Bounded, 7)),
                "float" => return Ok((Type::Float, 5)),
                "bool" => return Ok((Type::Bool, 4)),
                "string" => return Ok((Type::String, 6)),
                "optional{" => {
                    let (inner, used) = decode_type(&s[9..])?;
                    let rest = &s[9 + used..];
                    if !rest.starts_with('}') { return Err("Missing '}' for optional".to_string()); }
                    return Ok((Type::Optional(Box::new(inner)), 9 + used + 1));
                }
                "result{" => {
                    let (ok, used_ok) = decode_type(&s[7..])?;
                    let rest = &s[7 + used_ok..];
                    if !rest.starts_with(';') { return Err("Missing ';' in result".to_string()); }
                    let (err, used_err) = decode_type(&rest[1..])?;
                    let rest2 = &rest[1 + used_err..];
                    if !rest2.starts_with('}') { return Err("Missing '}' for result".to_string()); }
                    return Ok((Type::Result(Box::new(ok), Box::new(err)), 7 + used_ok + 1 + used_err + 1));
                }
                "struct{" => {
                    let (name, used) = decode_name(&s[7..])?;
                    let rest = &s[7 + used..];
                    if !rest.starts_with('}') { return Err("Missing '}' for struct".to_string()); }
                    return Ok((Type::Struct(name), 7 + used + 1));
                }
                "service{" => {
                    let (name, used) = decode_name(&s[8..])?;
                    let rest = &s[8 + used..];
                    if !rest.starts_with('}') { return Err("Missing '}' for service".to_string()); }
                    return Ok((Type::Service(name), 8 + used + 1));
                }
                "contract{" => {
                    let (name, used) = decode_name(&s[9..])?;
                    let rest = &s[9 + used..];
                    if !rest.starts_with('}') { return Err("Missing '}' for contract".to_string()); }
                    return Ok((Type::Contract(name), 9 + used + 1));
                }
                "error{" => {
                    let (name, used) = decode_name(&s[6..])?;
                    let rest = &s[6 + used..];
                    if !rest.starts_with('}') { return Err("Missing '}' for error".to_string()); }
                    return Ok((Type::ErrorType(name), 6 + used + 1));
                }
                "array{" => {
                    let (inner, used) = decode_type(&s[6..])?;
                    let rest = &s[6 + used..];
                    if !rest.starts_with(';') { return Err("Missing ';' in array".to_string()); }
                    // parse UInt
                    let rest_num = &rest[1..];
                    let mut n_str = String::new();
                    let mut consumed = 0usize;
                    for ch in rest_num.chars() {
                        if ch.is_ascii_digit() { n_str.push(ch); consumed += 1; } else { break; }
                    }
                    if n_str.is_empty() { return Err("Missing array size".to_string()); }
                    let n: u32 = n_str.parse().map_err(|_| "Invalid array size".to_string())?;
                    let rest2 = &rest_num[consumed..];
                    if !rest2.starts_with('}') { return Err("Missing '}' for array".to_string()); }
                    return Ok((Type::Array(Box::new(inner), n), 6 + used + 1 + consumed + 1));
                }
                "fn(" => {
                    // parse params until ')'
                    let after = &s[3..];
                    let close = after.find(')').ok_or_else(|| "Missing ')' in fn type".to_string())?;
                    let params_blob = &after[..close];
                    let mut params = Vec::new();
                    if !params_blob.is_empty() {
                        for part in split_top_level(params_blob, ';')? {
                            let (p, used) = decode_type(part)?;
                            if used != part.len() { return Err("Trailing data in fn param".to_string()); }
                            params.push(p);
                        }
                    }
                    let rest = &after[close + 1..];
                    if !rest.starts_with("->") { return Err("Missing '->' in fn type".to_string()); }
                    let (ret, used_ret) = decode_type(&rest[2..])?;
                    return Ok((Type::Function { params, return_type: Box::new(ret) }, 3 + close + 1 + 2 + used_ret));
                }
                _ => {}
            }
        }
    }
    Err("Unknown type in descriptor".to_string())
}

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

    #[test]
    fn descriptors_are_different_for_overloads() {
        let sig_i = Signature {
            params: vec![Type::Int],
            return_type: Type::Void,
        };
        let sig_s = Signature {
            params: vec![Type::String],
            return_type: Type::Void,
        };
        assert_ne!(sig_i.descriptor(), sig_s.descriptor());
    }

    #[test]
    fn descriptor_round_trip_stable() {
        let sig = Signature {
            params: vec![
                Type::Array(Box::new(Type::Int), 4),
                Type::Optional(Box::new(Type::String)),
                Type::Result(Box::new(Type::Int), Box::new(Type::ErrorType("E42".into()))),
            ],
            return_type: Type::Void,
        };
        let d1 = sig.descriptor();
        let parsed = Signature::from_descriptor(&d1).expect("parse ok");
        let d2 = parsed.descriptor();
        assert_eq!(d1, d2);
        assert_eq!(sig, parsed);
    }
}