// parser.el — el self-hosting recursive descent parser
//
// Consumes the token list produced by lexer.el and builds a list of AST
// statement maps.  Each statement and expression is a Map<String, Any>.
//
// The cursor (integer position into the token list) is threaded through every
// parse function.  Functions return { "node": <map>, "pos": <int> }.
//
// The token list is passed as a parameter to all parse functions.
// native_list_get is used to index into it without cloning.
//
// Entry point: fn parse(tokens: [Map<String, Any>]) -> [Map<String, Any>]

// ── Token access helpers ──────────────────────────────────────────────────────

fn tok_at(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    native_list_get(tokens, pos)
}

fn tok_kind(tokens: [Map<String, Any>], pos: Int) -> String {
    let t = native_list_get(tokens, pos)
    t["kind"]
}

fn tok_value(tokens: [Map<String, Any>], pos: Int) -> String {
    let t = native_list_get(tokens, pos)
    t["value"]
}

fn expect(tokens: [Map<String, Any>], pos: Int, kind: String) -> Int {
    let k = tok_kind(tokens, pos)
    if k == kind {
        return pos + 1
    }
    // On mismatch just advance; error recovery is best-effort
    pos + 1
}

// ── Result helpers ────────────────────────────────────────────────────────────

fn make_result(node: Map<String, Any>, pos: Int) -> Map<String, Any> {
    { "node": node, "pos": pos }
}

// ── Type annotation parser ────────────────────────────────────────────────────
// Skips over a type annotation, returning the new position.
// Types can be: Ident, [Type], Map<K,V>, Type?, Type<Type,...>

fn skip_type(tokens: [Map<String, Any>], pos: Int) -> Int {
    let k = tok_kind(tokens, pos)
    // Array type: [Type]
    if k == "LBracket" {
        let p = pos + 1
        let p = skip_type(tokens, p)
        let p = expect(tokens, p, "RBracket")
        return p
    }
    // Named type (possibly generic)
    if k == "Ident" {
        let p = pos + 1
        let k2 = tok_kind(tokens, p)
        if k2 == "Lt" {
            // Generic params: skip until matching >
            let p = p + 1
            let depth = 1
            let running = true
            while running {
                let kk = tok_kind(tokens, p)
                if kk == "Eof" {
                    let running = false
                } else {
                    if kk == "Lt" {
                        let depth = depth + 1
                        let p = p + 1
                    } else {
                        if kk == "Gt" {
                            let depth = depth - 1
                            let p = p + 1
                            if depth <= 0 {
                                let running = false
                            }
                        } else {
                            let p = p + 1
                        }
                    }
                }
            }
            let k3 = tok_kind(tokens, p)
            if k3 == "QuestionMark" {
                let p = p + 1
            }
            return p
        }
        // Optional marker
        if k2 == "QuestionMark" {
            return p + 1
        }
        return p
    }
    pos + 1
}

// ── Parameter list ────────────────────────────────────────────────────────────
// Parses (name: Type, name: Type, ...) — returns { "params": [...], "pos": ... }

fn parse_params(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    let p = expect(tokens, pos, "LParen")
    let params: [Map<String, Any>] = native_list_empty()
    let running = true
    while running {
        let k = tok_kind(tokens, p)
        if k == "RParen" {
            let running = false
        } else {
            if k == "Eof" {
                let running = false
            } else {
                // param name
                let pname = tok_value(tokens, p)
                let p = p + 1
                let p = expect(tokens, p, "Colon")
                // Capture the leading type identifier so codegen can dispatch
                // arithmetic vs string-concat on `+` based on declared types.
                let ptype = ""
                let kt = tok_kind(tokens, p)
                if kt == "Ident" {
                    let ptype = tok_value(tokens, p)
                }
                let p = skip_type(tokens, p)
                let param = { "name": pname, "type": ptype }
                let params = native_list_append(params, param)
                let k2 = tok_kind(tokens, p)
                if k2 == "Comma" {
                    let p = p + 1
                }
            }
        }
    }
    let p = expect(tokens, p, "RParen")
    { "params": params, "pos": p }
}

// ── Expression parsing ────────────────────────────────────────────────────────

fn parse_primary(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    let k = tok_kind(tokens, pos)
    let v = tok_value(tokens, pos)

    // Integer literal
    if k == "Int" {
        return make_result({ "expr": "Int", "value": v }, pos + 1)
    }

    // Float literal
    if k == "Float" {
        return make_result({ "expr": "Float", "value": v }, pos + 1)
    }

    // String literal
    if k == "Str" {
        return make_result({ "expr": "Str", "value": v }, pos + 1)
    }

    // Bool literal
    if k == "Bool" {
        return make_result({ "expr": "Bool", "value": v }, pos + 1)
    }

    // Identifier
    if k == "Ident" {
        return make_result({ "expr": "Ident", "name": v }, pos + 1)
    }

    // Grouped expression
    if k == "LParen" {
        let r = parse_expr(tokens, pos + 1)
        let node = r["node"]
        let p = r["pos"]
        let p = expect(tokens, p, "RParen")
        return make_result(node, p)
    }

    // Array literal: [e1, e2, ...]
    if k == "LBracket" {
        let p = pos + 1
        let elems: [Map<String, Any>] = native_list_empty()
        let running = true
        while running {
            let k2 = tok_kind(tokens, p)
            if k2 == "RBracket" {
                let running = false
            } else {
                if k2 == "Eof" {
                    let running = false
                } else {
                    let r = parse_expr(tokens, p)
                    let elem = r["node"]
                    let p = r["pos"]
                    let elems = native_list_append(elems, elem)
                    let k3 = tok_kind(tokens, p)
                    if k3 == "Comma" {
                        let p = p + 1
                    }
                }
            }
        }
        let p = expect(tokens, p, "RBracket")
        return make_result({ "expr": "Array", "elems": elems }, p)
    }

    // Map literal: { "key": val, ... }
    if k == "LBrace" {
        let p = pos + 1
        let pairs: [Map<String, Any>] = native_list_empty()
        let running = true
        while running {
            let k2 = tok_kind(tokens, p)
            if k2 == "RBrace" {
                let running = false
            } else {
                if k2 == "Eof" {
                    let running = false
                } else {
                    // key: Str token
                    let key = tok_value(tokens, p)
                    let p = p + 1
                    let p = expect(tokens, p, "Colon")
                    let r = parse_expr(tokens, p)
                    let val_node = r["node"]
                    let p = r["pos"]
                    let pair = { "key": key, "value": val_node }
                    let pairs = native_list_append(pairs, pair)
                    let k3 = tok_kind(tokens, p)
                    if k3 == "Comma" {
                        let p = p + 1
                    }
                }
            }
        }
        let p = expect(tokens, p, "RBrace")
        return make_result({ "expr": "Map", "pairs": pairs }, p)
    }

    // if expression
    if k == "If" {
        let r = parse_if(tokens, pos)
        return r
    }

    // match expression
    if k == "Match" {
        let r = parse_match(tokens, pos)
        return r
    }

    // for expression (used as statement)
    if k == "For" {
        let r = parse_for_expr(tokens, pos)
        return r
    }

    // Unary not
    if k == "Not" {
        let r = parse_primary(tokens, pos + 1)
        let inner = r["node"]
        let p = r["pos"]
        return make_result({ "expr": "Not", "inner": inner }, p)
    }

    // Unary minus
    if k == "Minus" {
        let r = parse_primary(tokens, pos + 1)
        let inner = r["node"]
        let p = r["pos"]
        return make_result({ "expr": "Neg", "inner": inner }, p)
    }

    // Fallback: skip unknown token
    make_result({ "expr": "Nil" }, pos + 1)
}

fn parse_if(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    let p = expect(tokens, pos, "If")
    let r = parse_expr(tokens, p)
    let cond = r["node"]
    let p = r["pos"]
    let r2 = parse_block(tokens, p)
    let then_stmts = r2["stmts"]
    let p = r2["pos"]
    let has_else = false
    let else_stmts: [Map<String, Any>] = native_list_empty()
    let k2 = tok_kind(tokens, p)
    if k2 == "Else" {
        let p = p + 1
        let k3 = tok_kind(tokens, p)
        if k3 == "If" {
            // else-if chain: parse as nested if
            let r3 = parse_if(tokens, p)
            let nested = r3["node"]
            let p = r3["pos"]
            let else_stmts = native_list_append(else_stmts, { "stmt": "Expr", "value": nested })
            let has_else = true
        } else {
            let r3 = parse_block(tokens, p)
            let else_stmts = r3["stmts"]
            let p = r3["pos"]
            let has_else = true
        }
    }
    make_result({ "expr": "If", "cond": cond, "then": then_stmts, "else": else_stmts, "has_else": has_else }, p)
}

fn parse_match(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    let p = expect(tokens, pos, "Match")
    let r = parse_expr(tokens, p)
    let subject = r["node"]
    let p = r["pos"]
    let p = expect(tokens, p, "LBrace")
    let arms: [Map<String, Any>] = native_list_empty()
    let running = true
    while running {
        let k = tok_kind(tokens, p)
        if k == "RBrace" {
            let running = false
        } else {
            if k == "Eof" {
                let running = false
            } else {
                // parse pattern => body
                let r2 = parse_pattern(tokens, p)
                let pattern = r2["node"]
                let p = r2["pos"]
                let p = expect(tokens, p, "FatArrow")
                let r3 = parse_expr(tokens, p)
                let body = r3["node"]
                let p = r3["pos"]
                let arm = { "pattern": pattern, "body": body }
                let arms = native_list_append(arms, arm)
                let k2 = tok_kind(tokens, p)
                if k2 == "Comma" {
                    let p = p + 1
                }
            }
        }
    }
    let p = expect(tokens, p, "RBrace")
    make_result({ "expr": "Match", "subject": subject, "arms": arms }, p)
}

fn parse_pattern(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    let k = tok_kind(tokens, pos)
    if k == "Ident" {
        let v = tok_value(tokens, pos)
        if v == "_" {
            return make_result({ "pattern": "Wildcard" }, pos + 1)
        }
        return make_result({ "pattern": "Binding", "name": v }, pos + 1)
    }
    if k == "Int" {
        return make_result({ "pattern": "LitInt", "value": tok_value(tokens, pos) }, pos + 1)
    }
    if k == "Str" {
        return make_result({ "pattern": "LitStr", "value": tok_value(tokens, pos) }, pos + 1)
    }
    if k == "Bool" {
        return make_result({ "pattern": "LitBool", "value": tok_value(tokens, pos) }, pos + 1)
    }
    // Wildcard _
    make_result({ "pattern": "Wildcard" }, pos + 1)
}

fn parse_for_expr(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    let p = expect(tokens, pos, "For")
    let item_name = tok_value(tokens, p)
    let p = p + 1
    let p = expect(tokens, p, "In")
    let r = parse_expr(tokens, p)
    let list_expr = r["node"]
    let p = r["pos"]
    let r2 = parse_block(tokens, p)
    let body = r2["stmts"]
    let p = r2["pos"]
    make_result({ "expr": "For", "item": item_name, "list": list_expr, "body": body }, p)
}

fn parse_block(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    let p = expect(tokens, pos, "LBrace")
    let stmts: [Map<String, Any>] = native_list_empty()
    let running = true
    while running {
        let k = tok_kind(tokens, p)
        if k == "RBrace" {
            let running = false
        } else {
            if k == "Eof" {
                let running = false
            } else {
                let r = parse_stmt(tokens, p)
                let stmt = r["node"]
                let p = r["pos"]
                let stmts = native_list_append(stmts, stmt)
            }
        }
    }
    let p = expect(tokens, p, "RBrace")
    { "stmts": stmts, "pos": p }
}

// ── Postfix expressions (calls, field access, index) ─────────────────────────

fn parse_postfix(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    let r = parse_primary(tokens, pos)
    let node = r["node"]
    let p = r["pos"]
    let running = true
    while running {
        let k = tok_kind(tokens, p)
        if k == "LParen" {
            // function call
            let p = p + 1
            let args: [Map<String, Any>] = native_list_empty()
            let run2 = true
            while run2 {
                let k2 = tok_kind(tokens, p)
                if k2 == "RParen" {
                    let run2 = false
                } else {
                    if k2 == "Eof" {
                        let run2 = false
                    } else {
                        let r2 = parse_expr(tokens, p)
                        let arg = r2["node"]
                        let p = r2["pos"]
                        let args = native_list_append(args, arg)
                        let k3 = tok_kind(tokens, p)
                        if k3 == "Comma" {
                            let p = p + 1
                        }
                    }
                }
            }
            let p = expect(tokens, p, "RParen")
            let node = { "expr": "Call", "func": node, "args": args }
        } else {
            if k == "Dot" {
                let field = tok_value(tokens, p + 1)
                let p = p + 2
                let node = { "expr": "Field", "object": node, "field": field }
            } else {
                if k == "LBracket" {
                    let r2 = parse_expr(tokens, p + 1)
                    let idx = r2["node"]
                    let p = r2["pos"]
                    let p = expect(tokens, p, "RBracket")
                    let node = { "expr": "Index", "object": node, "index": idx }
                } else {
                    if k == "QuestionMark" {
                        let p = p + 1
                        let node = { "expr": "Try", "inner": node }
                    } else {
                        let running = false
                    }
                }
            }
        }
    }
    make_result(node, p)
}

// ── Binary expression precedence climbing ────────────────────────────────────

fn op_precedence(kind: String) -> Int {
    if kind == "Or" { return 1 }
    if kind == "And" { return 2 }
    if kind == "EqEq" { return 3 }
    if kind == "NotEq" { return 3 }
    if kind == "Lt" { return 4 }
    if kind == "Gt" { return 4 }
    if kind == "LtEq" { return 4 }
    if kind == "GtEq" { return 4 }
    if kind == "Plus" { return 5 }
    if kind == "Minus" { return 5 }
    if kind == "Star" { return 6 }
    if kind == "Slash" { return 6 }
    0
}

fn is_binop(kind: String) -> Bool {
    if kind == "Or" { return true }
    if kind == "And" { return true }
    if kind == "EqEq" { return true }
    if kind == "NotEq" { return true }
    if kind == "Lt" { return true }
    if kind == "Gt" { return true }
    if kind == "LtEq" { return true }
    if kind == "GtEq" { return true }
    if kind == "Plus" { return true }
    if kind == "Minus" { return true }
    if kind == "Star" { return true }
    if kind == "Slash" { return true }
    false
}

fn parse_binop(tokens: [Map<String, Any>], pos: Int, min_prec: Int) -> Map<String, Any> {
    let r = parse_postfix(tokens, pos)
    let left = r["node"]
    let p = r["pos"]
    let running = true
    while running {
        let k = tok_kind(tokens, p)
        let prec = op_precedence(k)
        if is_binop(k) {
            if prec >= min_prec {
                let op = k
                let r2 = parse_binop(tokens, p + 1, prec + 1)
                let right = r2["node"]
                let p = r2["pos"]
                let left = { "expr": "BinOp", "op": op, "left": left, "right": right }
            } else {
                let running = false
            }
        } else {
            let running = false
        }
    }
    make_result(left, p)
}

fn parse_expr(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    parse_binop(tokens, pos, 1)
}

// ── Statement parsing ─────────────────────────────────────────────────────────

fn parse_stmt(tokens: [Map<String, Any>], pos: Int) -> Map<String, Any> {
    let k = tok_kind(tokens, pos)

    // let binding
    if k == "Let" {
        let p = pos + 1
        let name = tok_value(tokens, p)
        let p = p + 1
        let ltype = ""
        let k2 = tok_kind(tokens, p)
        // optional type annotation: name: Type — capture the leading
        // identifier so codegen can dispatch arithmetic vs concat on
        // `+` between two typed Idents.
        if k2 == "Colon" {
            let p = p + 1
            let kt = tok_kind(tokens, p)
            if kt == "Ident" {
                let ltype = tok_value(tokens, p)
            }
            let p = skip_type(tokens, p)
        }
        let p = expect(tokens, p, "Eq")
        let r = parse_expr(tokens, p)
        let val = r["node"]
        let p = r["pos"]
        return make_result({ "stmt": "Let", "name": name, "value": val, "type": ltype }, p)
    }

    // return statement
    if k == "Return" {
        let p = pos + 1
        let k2 = tok_kind(tokens, p)
        if k2 == "RBrace" {
            return make_result({ "stmt": "Return", "value": { "expr": "Nil" } }, p)
        }
        if k2 == "Eof" {
            return make_result({ "stmt": "Return", "value": { "expr": "Nil" } }, p)
        }
        let r = parse_expr(tokens, p)
        let val = r["node"]
        let p = r["pos"]
        return make_result({ "stmt": "Return", "value": val }, p)
    }

    // fn definition
    if k == "Fn" {
        let p = pos + 1
        let name = tok_value(tokens, p)
        let p = p + 1
        let r = parse_params(tokens, p)
        let params = r["params"]
        let p = r["pos"]
        // return type annotation: -> Type. Capture the leading identifier
        // so codegen can distinguish Void-returning functions from value-
        // returning ones. Anything not "Void" is treated as a value type.
        let ret_type = ""
        let k2 = tok_kind(tokens, p)
        if k2 == "Arrow" {
            let p = p + 1
            let kt = tok_kind(tokens, p)
            if kt == "Ident" {
                let ret_type = tok_value(tokens, p)
            }
            let p = skip_type(tokens, p)
        }
        let r2 = parse_block(tokens, p)
        let body = r2["stmts"]
        let p = r2["pos"]
        return make_result({ "stmt": "FnDef", "name": name, "params": params, "body": body, "ret_type": ret_type }, p)
    }

    // type definition
    if k == "Type" {
        let p = pos + 1
        let name = tok_value(tokens, p)
        let p = p + 1
        let p = expect(tokens, p, "LBrace")
        let fields: [Map<String, Any>] = native_list_empty()
        let running = true
        while running {
            let k2 = tok_kind(tokens, p)
            if k2 == "RBrace" {
                let running = false
            } else {
                if k2 == "Eof" {
                    let running = false
                } else {
                    let fname = tok_value(tokens, p)
                    let p = p + 1
                    let p = expect(tokens, p, "Colon")
                    let p = skip_type(tokens, p)
                    let fields = native_list_append(fields, { "name": fname })
                    let k3 = tok_kind(tokens, p)
                    if k3 == "Comma" {
                        let p = p + 1
                    }
                }
            }
        }
        let p = expect(tokens, p, "RBrace")
        return make_result({ "stmt": "TypeDef", "name": name, "fields": fields }, p)
    }

    // enum definition
    if k == "Enum" {
        let p = pos + 1
        let name = tok_value(tokens, p)
        let p = p + 1
        let p = expect(tokens, p, "LBrace")
        let variants: [Map<String, Any>] = native_list_empty()
        let running = true
        while running {
            let k2 = tok_kind(tokens, p)
            if k2 == "RBrace" {
                let running = false
            } else {
                if k2 == "Eof" {
                    let running = false
                } else {
                    let vname = tok_value(tokens, p)
                    let p = p + 1
                    let variants = native_list_append(variants, { "name": vname })
                    let k3 = tok_kind(tokens, p)
                    if k3 == "Comma" {
                        let p = p + 1
                    }
                }
            }
        }
        let p = expect(tokens, p, "RBrace")
        return make_result({ "stmt": "EnumDef", "name": name, "variants": variants }, p)
    }

    // import statement
    if k == "Import" {
        let p = pos + 1
        let path = tok_value(tokens, p)
        let p = p + 1
        return make_result({ "stmt": "Import", "path": path }, p)
    }

    // from ... import { ... }
    if k == "From" {
        let p = pos + 1
        let module_name = tok_value(tokens, p)
        let p = p + 1
        // skip "import" keyword
        let k2 = tok_kind(tokens, p)
        if k2 == "Import" {
            let p = p + 1
        }
        // skip { Name, ... }
        let k3 = tok_kind(tokens, p)
        if k3 == "LBrace" {
            let p = p + 1
            let running = true
            while running {
                let k4 = tok_kind(tokens, p)
                if k4 == "RBrace" {
                    let running = false
                } else {
                    if k4 == "Eof" {
                        let running = false
                    } else {
                        let p = p + 1
                        let k5 = tok_kind(tokens, p)
                        if k5 == "Comma" {
                            let p = p + 1
                        }
                    }
                }
            }
            let p = expect(tokens, p, "RBrace")
        }
        return make_result({ "stmt": "Import", "path": module_name }, p)
    }

    // while loop
    if k == "While" {
        let p = pos + 1
        let r = parse_expr(tokens, p)
        let cond = r["node"]
        let p = r["pos"]
        let r2 = parse_block(tokens, p)
        let body = r2["stmts"]
        let p = r2["pos"]
        return make_result({ "stmt": "While", "cond": cond, "body": body }, p)
    }

    // for loop
    if k == "For" {
        let p = pos + 1
        let item_name = tok_value(tokens, p)
        let p = p + 1
        let p = expect(tokens, p, "In")
        let r = parse_expr(tokens, p)
        let list_expr = r["node"]
        let p = r["pos"]
        let r2 = parse_block(tokens, p)
        let body = r2["stmts"]
        let p = r2["pos"]
        return make_result({ "stmt": "For", "item": item_name, "list": list_expr, "body": body }, p)
    }

    // @decorator — skip and parse next stmt
    if k == "At" {
        let p = pos + 1
        // skip decorator name
        let p = p + 1
        return parse_stmt(tokens, p)
    }

    // bare expression or if/match statement
    let r = parse_expr(tokens, pos)
    let val = r["node"]
    let p = r["pos"]
    make_result({ "stmt": "Expr", "value": val }, p)
}

// ── Top-level parse ────────────────────────────────────────────────────────────

fn parse(tokens: [Map<String, Any>]) -> [Map<String, Any>] {
    let total: Int = native_list_len(tokens)
    let stmts: [Map<String, Any>] = native_list_empty()
    let pos: Int = 0
    let running = true
    while running {
        if pos >= total {
            let running = false
        } else {
            let k = tok_kind(tokens, pos)
            if k == "Eof" {
                let running = false
            } else {
                let r = parse_stmt(tokens, pos)
                let stmt = r["node"]
                let new_pos: Int = r["pos"]
                let stmts = native_list_append(stmts, stmt)
                // Guard against infinite loops — if pos didn't advance, force it
                if new_pos <= pos {
                    let pos = pos + 1
                } else {
                    let pos = new_pos
                }
            }
        }
    }
    stmts
}