// Copyright 2020 The Jujutsu Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::collections::HashMap;
use std::{error, mem};

use itertools::Itertools as _;
use jj_lib::dsl_util::{
    self, collect_similar, AliasDeclaration, AliasDeclarationParser, AliasDefinitionParser,
    AliasExpandError, AliasExpandableExpression, AliasId, AliasesMap, ExpressionFolder,
    FoldableExpression, InvalidArguments, StringLiteralParser,
};
use once_cell::sync::Lazy;
use pest::iterators::{Pair, Pairs};
use pest::pratt_parser::{Assoc, Op, PrattParser};
use pest::Parser;
use pest_derive::Parser;
use thiserror::Error;

#[derive(Parser)]
#[grammar = "template.pest"]
struct TemplateParser;

const STRING_LITERAL_PARSER: StringLiteralParser<Rule> = StringLiteralParser {
    content_rule: Rule::string_content,
    escape_rule: Rule::string_escape,
};

impl Rule {
    fn to_symbol(self) -> Option<&'static str> {
        match self {
            Rule::EOI => None,
            Rule::whitespace => None,
            Rule::string_escape => None,
            Rule::string_content_char => None,
            Rule::string_content => None,
            Rule::string_literal => None,
            Rule::raw_string_content => None,
            Rule::raw_string_literal => None,
            Rule::integer_literal => None,
            Rule::identifier => None,
            Rule::concat_op => Some("++"),
            Rule::logical_or_op => Some("||"),
            Rule::logical_and_op => Some("&&"),
            Rule::logical_not_op => Some("!"),
            Rule::negate_op => Some("-"),
            Rule::prefix_ops => None,
            Rule::infix_ops => None,
            Rule::function => None,
            Rule::function_arguments => None,
            Rule::lambda => None,
            Rule::formal_parameters => None,
            Rule::primary => None,
            Rule::term => None,
            Rule::expression => None,
            Rule::template => None,
            Rule::program => None,
            Rule::function_alias_declaration => None,
            Rule::alias_declaration => None,
        }
    }
}

pub type TemplateParseResult<T> = Result<T, TemplateParseError>;

#[derive(Debug, Error)]
#[error("{pest_error}")]
pub struct TemplateParseError {
    kind: TemplateParseErrorKind,
    pest_error: Box<pest::error::Error<Rule>>,
    source: Option<Box<dyn error::Error + Send + Sync>>,
}

#[derive(Clone, Debug, Eq, Error, PartialEq)]
pub enum TemplateParseErrorKind {
    #[error("Syntax error")]
    SyntaxError,
    #[error(r#"Keyword "{name}" doesn't exist"#)]
    NoSuchKeyword {
        name: String,
        candidates: Vec<String>,
    },
    #[error(r#"Function "{name}" doesn't exist"#)]
    NoSuchFunction {
        name: String,
        candidates: Vec<String>,
    },
    #[error(r#"Method "{name}" doesn't exist for type "{type_name}""#)]
    NoSuchMethod {
        type_name: String,
        name: String,
        candidates: Vec<String>,
    },
    #[error(r#"Function "{name}": {message}"#)]
    InvalidArguments { name: String, message: String },
    #[error("Redefinition of function parameter")]
    RedefinedFunctionParameter,
    #[error("{0}")]
    Expression(String),
    #[error(r#"Alias "{0}" cannot be expanded"#)]
    BadAliasExpansion(String),
    #[error(r#"Function parameter "{0}" cannot be expanded"#)]
    BadParameterExpansion(String),
    #[error(r#"Alias "{0}" expanded recursively"#)]
    RecursiveAlias(String),
}

impl TemplateParseError {
    pub fn with_span(kind: TemplateParseErrorKind, span: pest::Span<'_>) -> Self {
        let message = kind.to_string();
        let pest_error = Box::new(pest::error::Error::new_from_span(
            pest::error::ErrorVariant::CustomError { message },
            span,
        ));
        TemplateParseError {
            kind,
            pest_error,
            source: None,
        }
    }

    pub fn with_source(mut self, source: impl Into<Box<dyn error::Error + Send + Sync>>) -> Self {
        self.source = Some(source.into());
        self
    }

    // TODO: migrate all callers to table-based lookup_method()
    pub(crate) fn no_such_method(
        type_name: impl Into<String>,
        function: &FunctionCallNode,
    ) -> Self {
        TemplateParseError::with_span(
            TemplateParseErrorKind::NoSuchMethod {
                type_name: type_name.into(),
                name: function.name.to_owned(),
                candidates: vec![],
            },
            function.name_span,
        )
    }

    pub fn expected_type(expected: &str, actual: &str, span: pest::Span<'_>) -> Self {
        let message =
            format!(r#"Expected expression of type "{expected}", but actual type is "{actual}""#);
        TemplateParseError::expression(message, span)
    }

    /// Some other expression error.
    pub fn expression(message: impl Into<String>, span: pest::Span<'_>) -> Self {
        TemplateParseError::with_span(TemplateParseErrorKind::Expression(message.into()), span)
    }

    /// If this is a `NoSuchKeyword` error, expands the candidates list with the
    /// given `other_keywords`.
    pub fn extend_keyword_candidates<I>(mut self, other_keywords: I) -> Self
    where
        I: IntoIterator,
        I::Item: AsRef<str>,
    {
        if let TemplateParseErrorKind::NoSuchKeyword { name, candidates } = &mut self.kind {
            let other_candidates = collect_similar(name, other_keywords);
            *candidates = itertools::merge(mem::take(candidates), other_candidates)
                .dedup()
                .collect();
        }
        self
    }

    /// If this is a `NoSuchFunction` error, expands the candidates list with
    /// the given `other_functions`.
    pub fn extend_function_candidates<I>(mut self, other_functions: I) -> Self
    where
        I: IntoIterator,
        I::Item: AsRef<str>,
    {
        if let TemplateParseErrorKind::NoSuchFunction { name, candidates } = &mut self.kind {
            let other_candidates = collect_similar(name, other_functions);
            *candidates = itertools::merge(mem::take(candidates), other_candidates)
                .dedup()
                .collect();
        }
        self
    }

    /// Expands keyword/function candidates with the given aliases.
    pub fn extend_alias_candidates(self, aliases_map: &TemplateAliasesMap) -> Self {
        self.extend_keyword_candidates(aliases_map.symbol_names())
            .extend_function_candidates(aliases_map.function_names())
    }

    pub fn kind(&self) -> &TemplateParseErrorKind {
        &self.kind
    }

    /// Original parsing error which typically occurred in an alias expression.
    pub fn origin(&self) -> Option<&Self> {
        self.source.as_ref().and_then(|e| e.downcast_ref())
    }
}

impl AliasExpandError for TemplateParseError {
    fn invalid_arguments(err: InvalidArguments<'_>) -> Self {
        err.into()
    }

    fn recursive_expansion(id: AliasId<'_>, span: pest::Span<'_>) -> Self {
        Self::with_span(TemplateParseErrorKind::RecursiveAlias(id.to_string()), span)
    }

    fn within_alias_expansion(self, id: AliasId<'_>, span: pest::Span<'_>) -> Self {
        let kind = match id {
            AliasId::Symbol(_) | AliasId::Function(_) => {
                TemplateParseErrorKind::BadAliasExpansion(id.to_string())
            }
            AliasId::Parameter(_) => TemplateParseErrorKind::BadParameterExpansion(id.to_string()),
        };
        Self::with_span(kind, span).with_source(self)
    }
}

impl From<pest::error::Error<Rule>> for TemplateParseError {
    fn from(err: pest::error::Error<Rule>) -> Self {
        TemplateParseError {
            kind: TemplateParseErrorKind::SyntaxError,
            pest_error: Box::new(rename_rules_in_pest_error(err)),
            source: None,
        }
    }
}

impl From<InvalidArguments<'_>> for TemplateParseError {
    fn from(err: InvalidArguments<'_>) -> Self {
        let kind = TemplateParseErrorKind::InvalidArguments {
            name: err.name.to_owned(),
            message: err.message,
        };
        Self::with_span(kind, err.span)
    }
}

fn rename_rules_in_pest_error(err: pest::error::Error<Rule>) -> pest::error::Error<Rule> {
    err.renamed_rules(|rule| {
        rule.to_symbol()
            .map(|sym| format!("`{sym}`"))
            .unwrap_or_else(|| format!("<{rule:?}>"))
    })
}

#[derive(Clone, Debug, PartialEq)]
pub enum ExpressionKind<'i> {
    Identifier(&'i str),
    Boolean(bool),
    Integer(i64),
    String(String),
    Unary(UnaryOp, Box<ExpressionNode<'i>>),
    Binary(BinaryOp, Box<ExpressionNode<'i>>, Box<ExpressionNode<'i>>),
    Concat(Vec<ExpressionNode<'i>>),
    FunctionCall(Box<FunctionCallNode<'i>>),
    MethodCall(Box<MethodCallNode<'i>>),
    Lambda(Box<LambdaNode<'i>>),
    /// Identity node to preserve the span in the source template text.
    AliasExpanded(AliasId<'i>, Box<ExpressionNode<'i>>),
}

impl<'i> FoldableExpression<'i> for ExpressionKind<'i> {
    fn fold<F>(self, folder: &mut F, span: pest::Span<'i>) -> Result<Self, F::Error>
    where
        F: ExpressionFolder<'i, Self> + ?Sized,
    {
        match self {
            ExpressionKind::Identifier(name) => folder.fold_identifier(name, span),
            ExpressionKind::Boolean(_) | ExpressionKind::Integer(_) | ExpressionKind::String(_) => {
                Ok(self)
            }
            ExpressionKind::Unary(op, arg) => {
                let arg = Box::new(folder.fold_expression(*arg)?);
                Ok(ExpressionKind::Unary(op, arg))
            }
            ExpressionKind::Binary(op, lhs, rhs) => {
                let lhs = Box::new(folder.fold_expression(*lhs)?);
                let rhs = Box::new(folder.fold_expression(*rhs)?);
                Ok(ExpressionKind::Binary(op, lhs, rhs))
            }
            ExpressionKind::Concat(nodes) => Ok(ExpressionKind::Concat(
                dsl_util::fold_expression_nodes(folder, nodes)?,
            )),
            ExpressionKind::FunctionCall(function) => folder.fold_function_call(function, span),
            ExpressionKind::MethodCall(method) => {
                // Method call is syntactically different from function call.
                let method = Box::new(MethodCallNode {
                    object: folder.fold_expression(method.object)?,
                    function: dsl_util::fold_function_call_args(folder, method.function)?,
                });
                Ok(ExpressionKind::MethodCall(method))
            }
            ExpressionKind::Lambda(lambda) => {
                let lambda = Box::new(LambdaNode {
                    params: lambda.params,
                    params_span: lambda.params_span,
                    body: folder.fold_expression(lambda.body)?,
                });
                Ok(ExpressionKind::Lambda(lambda))
            }
            ExpressionKind::AliasExpanded(id, subst) => {
                let subst = Box::new(folder.fold_expression(*subst)?);
                Ok(ExpressionKind::AliasExpanded(id, subst))
            }
        }
    }
}

impl<'i> AliasExpandableExpression<'i> for ExpressionKind<'i> {
    fn identifier(name: &'i str) -> Self {
        ExpressionKind::Identifier(name)
    }

    fn function_call(function: Box<FunctionCallNode<'i>>) -> Self {
        ExpressionKind::FunctionCall(function)
    }

    fn alias_expanded(id: AliasId<'i>, subst: Box<ExpressionNode<'i>>) -> Self {
        ExpressionKind::AliasExpanded(id, subst)
    }
}

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum UnaryOp {
    /// `!`
    LogicalNot,
    /// `-`
    Negate,
}

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum BinaryOp {
    /// `||`
    LogicalOr,
    /// `&&`
    LogicalAnd,
}

pub type ExpressionNode<'i> = dsl_util::ExpressionNode<'i, ExpressionKind<'i>>;
pub type FunctionCallNode<'i> = dsl_util::FunctionCallNode<'i, ExpressionKind<'i>>;

#[derive(Clone, Debug, PartialEq)]
pub struct MethodCallNode<'i> {
    pub object: ExpressionNode<'i>,
    pub function: FunctionCallNode<'i>,
}

#[derive(Clone, Debug, PartialEq)]
pub struct LambdaNode<'i> {
    pub params: Vec<&'i str>,
    pub params_span: pest::Span<'i>,
    pub body: ExpressionNode<'i>,
}

fn parse_identifier_or_literal(pair: Pair<Rule>) -> ExpressionKind {
    assert_eq!(pair.as_rule(), Rule::identifier);
    match pair.as_str() {
        "false" => ExpressionKind::Boolean(false),
        "true" => ExpressionKind::Boolean(true),
        name => ExpressionKind::Identifier(name),
    }
}

fn parse_identifier_name(pair: Pair<Rule>) -> TemplateParseResult<&str> {
    let span = pair.as_span();
    if let ExpressionKind::Identifier(name) = parse_identifier_or_literal(pair) {
        Ok(name)
    } else {
        Err(TemplateParseError::expression("Expected identifier", span))
    }
}

fn parse_formal_parameters(params_pair: Pair<Rule>) -> TemplateParseResult<Vec<&str>> {
    assert_eq!(params_pair.as_rule(), Rule::formal_parameters);
    let params_span = params_pair.as_span();
    let params: Vec<_> = params_pair
        .into_inner()
        .map(parse_identifier_name)
        .try_collect()?;
    if params.iter().all_unique() {
        Ok(params)
    } else {
        Err(TemplateParseError::with_span(
            TemplateParseErrorKind::RedefinedFunctionParameter,
            params_span,
        ))
    }
}

fn parse_function_call_node(pair: Pair<Rule>) -> TemplateParseResult<FunctionCallNode> {
    assert_eq!(pair.as_rule(), Rule::function);
    let mut inner = pair.into_inner();
    let name_pair = inner.next().unwrap();
    let name_span = name_pair.as_span();
    let args_pair = inner.next().unwrap();
    let args_span = args_pair.as_span();
    assert_eq!(args_pair.as_rule(), Rule::function_arguments);
    let name = parse_identifier_name(name_pair)?;
    let args = args_pair
        .into_inner()
        .map(parse_template_node)
        .try_collect()?;
    Ok(FunctionCallNode {
        name,
        name_span,
        args,
        args_span,
    })
}

fn parse_lambda_node(pair: Pair<Rule>) -> TemplateParseResult<LambdaNode> {
    assert_eq!(pair.as_rule(), Rule::lambda);
    let mut inner = pair.into_inner();
    let params_pair = inner.next().unwrap();
    let params_span = params_pair.as_span();
    let body_pair = inner.next().unwrap();
    let params = parse_formal_parameters(params_pair)?;
    let body = parse_template_node(body_pair)?;
    Ok(LambdaNode {
        params,
        params_span,
        body,
    })
}

fn parse_term_node(pair: Pair<Rule>) -> TemplateParseResult<ExpressionNode> {
    assert_eq!(pair.as_rule(), Rule::term);
    let mut inner = pair.into_inner();
    let expr = inner.next().unwrap();
    let span = expr.as_span();
    let primary = match expr.as_rule() {
        Rule::string_literal => {
            let text = STRING_LITERAL_PARSER.parse(expr.into_inner());
            ExpressionNode::new(ExpressionKind::String(text), span)
        }
        Rule::raw_string_literal => {
            let (content,) = expr.into_inner().collect_tuple().unwrap();
            assert_eq!(content.as_rule(), Rule::raw_string_content);
            let text = content.as_str().to_owned();
            ExpressionNode::new(ExpressionKind::String(text), span)
        }
        Rule::integer_literal => {
            let value = expr.as_str().parse().map_err(|err| {
                TemplateParseError::expression("Invalid integer literal", span).with_source(err)
            })?;
            ExpressionNode::new(ExpressionKind::Integer(value), span)
        }
        Rule::identifier => ExpressionNode::new(parse_identifier_or_literal(expr), span),
        Rule::function => {
            let function = Box::new(parse_function_call_node(expr)?);
            ExpressionNode::new(ExpressionKind::FunctionCall(function), span)
        }
        Rule::lambda => {
            let lambda = Box::new(parse_lambda_node(expr)?);
            ExpressionNode::new(ExpressionKind::Lambda(lambda), span)
        }
        Rule::template => parse_template_node(expr)?,
        other => panic!("unexpected term: {other:?}"),
    };
    inner.try_fold(primary, |object, chain| {
        assert_eq!(chain.as_rule(), Rule::function);
        let span = object.span.start_pos().span(&chain.as_span().end_pos());
        let method = Box::new(MethodCallNode {
            object,
            function: parse_function_call_node(chain)?,
        });
        Ok(ExpressionNode::new(
            ExpressionKind::MethodCall(method),
            span,
        ))
    })
}

fn parse_expression_node(pair: Pair<Rule>) -> TemplateParseResult<ExpressionNode> {
    assert_eq!(pair.as_rule(), Rule::expression);
    static PRATT: Lazy<PrattParser<Rule>> = Lazy::new(|| {
        PrattParser::new()
            .op(Op::infix(Rule::logical_or_op, Assoc::Left))
            .op(Op::infix(Rule::logical_and_op, Assoc::Left))
            .op(Op::prefix(Rule::logical_not_op) | Op::prefix(Rule::negate_op))
    });
    PRATT
        .map_primary(parse_term_node)
        .map_prefix(|op, rhs| {
            let op_kind = match op.as_rule() {
                Rule::logical_not_op => UnaryOp::LogicalNot,
                Rule::negate_op => UnaryOp::Negate,
                r => panic!("unexpected prefix operator rule {r:?}"),
            };
            let rhs = Box::new(rhs?);
            let span = op.as_span().start_pos().span(&rhs.span.end_pos());
            let expr = ExpressionKind::Unary(op_kind, rhs);
            Ok(ExpressionNode::new(expr, span))
        })
        .map_infix(|lhs, op, rhs| {
            let op_kind = match op.as_rule() {
                Rule::logical_or_op => BinaryOp::LogicalOr,
                Rule::logical_and_op => BinaryOp::LogicalAnd,
                r => panic!("unexpected infix operator rule {r:?}"),
            };
            let lhs = Box::new(lhs?);
            let rhs = Box::new(rhs?);
            let span = lhs.span.start_pos().span(&rhs.span.end_pos());
            let expr = ExpressionKind::Binary(op_kind, lhs, rhs);
            Ok(ExpressionNode::new(expr, span))
        })
        .parse(pair.into_inner())
}

fn parse_template_node(pair: Pair<Rule>) -> TemplateParseResult<ExpressionNode> {
    assert_eq!(pair.as_rule(), Rule::template);
    let span = pair.as_span();
    let inner = pair.into_inner();
    let mut nodes: Vec<_> = inner
        .filter_map(|pair| match pair.as_rule() {
            Rule::concat_op => None,
            Rule::expression => Some(parse_expression_node(pair)),
            r => panic!("unexpected template item rule {r:?}"),
        })
        .try_collect()?;
    if nodes.len() == 1 {
        Ok(nodes.pop().unwrap())
    } else {
        Ok(ExpressionNode::new(ExpressionKind::Concat(nodes), span))
    }
}

/// Parses text into AST nodes. No type/name checking is made at this stage.
pub fn parse_template(template_text: &str) -> TemplateParseResult<ExpressionNode> {
    let mut pairs: Pairs<Rule> = TemplateParser::parse(Rule::program, template_text)?;
    let first_pair = pairs.next().unwrap();
    if first_pair.as_rule() == Rule::EOI {
        let span = first_pair.as_span();
        Ok(ExpressionNode::new(ExpressionKind::Concat(vec![]), span))
    } else {
        parse_template_node(first_pair)
    }
}

pub type TemplateAliasesMap = AliasesMap<TemplateAliasParser>;

#[derive(Clone, Debug, Default)]
pub struct TemplateAliasParser;

impl AliasDeclarationParser for TemplateAliasParser {
    type Error = TemplateParseError;

    fn parse_declaration(&self, source: &str) -> Result<AliasDeclaration, Self::Error> {
        let mut pairs = TemplateParser::parse(Rule::alias_declaration, source)?;
        let first = pairs.next().unwrap();
        match first.as_rule() {
            Rule::identifier => {
                let name = parse_identifier_name(first)?.to_owned();
                Ok(AliasDeclaration::Symbol(name))
            }
            Rule::function_alias_declaration => {
                let mut inner = first.into_inner();
                let name_pair = inner.next().unwrap();
                let params_pair = inner.next().unwrap();
                let name = parse_identifier_name(name_pair)?.to_owned();
                let params = parse_formal_parameters(params_pair)?
                    .into_iter()
                    .map(|s| s.to_owned())
                    .collect();
                Ok(AliasDeclaration::Function(name, params))
            }
            r => panic!("unexpected alias declaration rule {r:?}"),
        }
    }
}

impl AliasDefinitionParser for TemplateAliasParser {
    type Output<'i> = ExpressionKind<'i>;
    type Error = TemplateParseError;

    fn parse_definition<'i>(&self, source: &'i str) -> Result<ExpressionNode<'i>, Self::Error> {
        parse_template(source)
    }
}

/// Parses text into AST nodes, and expands aliases.
///
/// No type/name checking is made at this stage.
pub fn parse<'i>(
    template_text: &'i str,
    aliases_map: &'i TemplateAliasesMap,
) -> TemplateParseResult<ExpressionNode<'i>> {
    let node = parse_template(template_text)?;
    dsl_util::expand_aliases(node, aliases_map)
}

/// Applies the given function if the `node` is a string literal.
pub fn expect_string_literal_with<'a, 'i, T>(
    node: &'a ExpressionNode<'i>,
    f: impl FnOnce(&'a str, pest::Span<'i>) -> TemplateParseResult<T>,
) -> TemplateParseResult<T> {
    match &node.kind {
        ExpressionKind::String(s) => f(s, node.span),
        ExpressionKind::Identifier(_)
        | ExpressionKind::Boolean(_)
        | ExpressionKind::Integer(_)
        | ExpressionKind::Unary(..)
        | ExpressionKind::Binary(..)
        | ExpressionKind::Concat(_)
        | ExpressionKind::FunctionCall(_)
        | ExpressionKind::MethodCall(_)
        | ExpressionKind::Lambda(_) => Err(TemplateParseError::expression(
            "Expected string literal",
            node.span,
        )),
        ExpressionKind::AliasExpanded(id, subst) => expect_string_literal_with(subst, f)
            .map_err(|e| e.within_alias_expansion(*id, node.span)),
    }
}

/// Applies the given function if the `node` is a lambda.
pub fn expect_lambda_with<'a, 'i, T>(
    node: &'a ExpressionNode<'i>,
    f: impl FnOnce(&'a LambdaNode<'i>, pest::Span<'i>) -> TemplateParseResult<T>,
) -> TemplateParseResult<T> {
    match &node.kind {
        ExpressionKind::Lambda(lambda) => f(lambda, node.span),
        ExpressionKind::Identifier(_)
        | ExpressionKind::Boolean(_)
        | ExpressionKind::Integer(_)
        | ExpressionKind::String(_)
        | ExpressionKind::Unary(..)
        | ExpressionKind::Binary(..)
        | ExpressionKind::Concat(_)
        | ExpressionKind::FunctionCall(_)
        | ExpressionKind::MethodCall(_) => Err(TemplateParseError::expression(
            "Expected lambda expression",
            node.span,
        )),
        ExpressionKind::AliasExpanded(id, subst) => {
            expect_lambda_with(subst, f).map_err(|e| e.within_alias_expansion(*id, node.span))
        }
    }
}

/// Looks up `table` by the given function name.
pub fn lookup_function<'a, V>(
    table: &'a HashMap<&str, V>,
    function: &FunctionCallNode,
) -> TemplateParseResult<&'a V> {
    if let Some(value) = table.get(function.name) {
        Ok(value)
    } else {
        let candidates = collect_similar(function.name, table.keys());
        Err(TemplateParseError::with_span(
            TemplateParseErrorKind::NoSuchFunction {
                name: function.name.to_owned(),
                candidates,
            },
            function.name_span,
        ))
    }
}

/// Looks up `table` by the given method name.
pub fn lookup_method<'a, V>(
    type_name: impl Into<String>,
    table: &'a HashMap<&str, V>,
    function: &FunctionCallNode,
) -> TemplateParseResult<&'a V> {
    if let Some(value) = table.get(function.name) {
        Ok(value)
    } else {
        let candidates = collect_similar(function.name, table.keys());
        Err(TemplateParseError::with_span(
            TemplateParseErrorKind::NoSuchMethod {
                type_name: type_name.into(),
                name: function.name.to_owned(),
                candidates,
            },
            function.name_span,
        ))
    }
}

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

    use super::*;

    #[derive(Debug)]
    struct WithTemplateAliasesMap(TemplateAliasesMap);

    impl WithTemplateAliasesMap {
        fn parse<'i>(&'i self, template_text: &'i str) -> TemplateParseResult<ExpressionNode<'i>> {
            parse(template_text, &self.0)
        }

        fn parse_normalized<'i>(
            &'i self,
            template_text: &'i str,
        ) -> TemplateParseResult<ExpressionNode<'i>> {
            self.parse(template_text).map(normalize_tree)
        }
    }

    fn with_aliases(
        aliases: impl IntoIterator<Item = (impl AsRef<str>, impl Into<String>)>,
    ) -> WithTemplateAliasesMap {
        let mut aliases_map = TemplateAliasesMap::new();
        for (decl, defn) in aliases {
            aliases_map.insert(decl, defn).unwrap();
        }
        WithTemplateAliasesMap(aliases_map)
    }

    fn parse_into_kind(template_text: &str) -> Result<ExpressionKind, TemplateParseErrorKind> {
        parse_template(template_text)
            .map(|node| node.kind)
            .map_err(|err| err.kind)
    }

    fn parse_normalized(template_text: &str) -> TemplateParseResult<ExpressionNode> {
        parse_template(template_text).map(normalize_tree)
    }

    /// Drops auxiliary data of AST so it can be compared with other node.
    fn normalize_tree(node: ExpressionNode) -> ExpressionNode {
        fn empty_span() -> pest::Span<'static> {
            pest::Span::new("", 0, 0).unwrap()
        }

        fn normalize_list(nodes: Vec<ExpressionNode>) -> Vec<ExpressionNode> {
            nodes.into_iter().map(normalize_tree).collect()
        }

        fn normalize_function_call(function: FunctionCallNode) -> FunctionCallNode {
            FunctionCallNode {
                name: function.name,
                name_span: empty_span(),
                args: normalize_list(function.args),
                args_span: empty_span(),
            }
        }

        let normalized_kind = match node.kind {
            ExpressionKind::Identifier(_)
            | ExpressionKind::Boolean(_)
            | ExpressionKind::Integer(_)
            | ExpressionKind::String(_) => node.kind,
            ExpressionKind::Unary(op, arg) => {
                let arg = Box::new(normalize_tree(*arg));
                ExpressionKind::Unary(op, arg)
            }
            ExpressionKind::Binary(op, lhs, rhs) => {
                let lhs = Box::new(normalize_tree(*lhs));
                let rhs = Box::new(normalize_tree(*rhs));
                ExpressionKind::Binary(op, lhs, rhs)
            }
            ExpressionKind::Concat(nodes) => ExpressionKind::Concat(normalize_list(nodes)),
            ExpressionKind::FunctionCall(function) => {
                let function = Box::new(normalize_function_call(*function));
                ExpressionKind::FunctionCall(function)
            }
            ExpressionKind::MethodCall(method) => {
                let method = Box::new(MethodCallNode {
                    object: normalize_tree(method.object),
                    function: normalize_function_call(method.function),
                });
                ExpressionKind::MethodCall(method)
            }
            ExpressionKind::Lambda(lambda) => {
                let lambda = Box::new(LambdaNode {
                    params: lambda.params,
                    params_span: empty_span(),
                    body: normalize_tree(lambda.body),
                });
                ExpressionKind::Lambda(lambda)
            }
            ExpressionKind::AliasExpanded(_, subst) => normalize_tree(*subst).kind,
        };
        ExpressionNode {
            kind: normalized_kind,
            span: empty_span(),
        }
    }

    #[test]
    fn test_parse_tree_eq() {
        assert_eq!(
            normalize_tree(parse_template(r#" commit_id.short(1 )  ++ description"#).unwrap()),
            normalize_tree(parse_template(r#"commit_id.short( 1 )++(description)"#).unwrap()),
        );
        assert_ne!(
            normalize_tree(parse_template(r#" "ab" "#).unwrap()),
            normalize_tree(parse_template(r#" "a" ++ "b" "#).unwrap()),
        );
        assert_ne!(
            normalize_tree(parse_template(r#" "foo" ++ "0" "#).unwrap()),
            normalize_tree(parse_template(r#" "foo" ++ 0 "#).unwrap()),
        );
    }

    #[test]
    fn test_parse_whitespace() {
        let ascii_whitespaces: String = ('\x00'..='\x7f')
            .filter(char::is_ascii_whitespace)
            .collect();
        assert_eq!(
            parse_normalized(&format!("{ascii_whitespaces}f()")).unwrap(),
            parse_normalized("f()").unwrap(),
        );
    }

    #[test]
    fn test_parse_operator_syntax() {
        // Operator precedence
        assert_eq!(
            parse_normalized("!!x").unwrap(),
            parse_normalized("!(!x)").unwrap(),
        );
        assert_eq!(
            parse_normalized("!x.f() || !g()").unwrap(),
            parse_normalized("(!(x.f())) || (!(g()))").unwrap(),
        );
        assert_eq!(
            parse_normalized("x.f() || y || z").unwrap(),
            parse_normalized("((x.f()) || y) || z").unwrap(),
        );
        assert_eq!(
            parse_normalized("x || y && z.h()").unwrap(),
            parse_normalized("x || (y && (z.h()))").unwrap(),
        );

        // Logical operator bounds more tightly than concatenation. This might
        // not be so intuitive, but should be harmless.
        assert_eq!(
            parse_normalized(r"x && y ++ z").unwrap(),
            parse_normalized(r"(x && y) ++ z").unwrap(),
        );
        assert_eq!(
            parse_normalized(r"x ++ y || z").unwrap(),
            parse_normalized(r"x ++ (y || z)").unwrap(),
        );

        // Expression span
        assert_eq!(parse_template(" ! x ").unwrap().span.as_str(), "! x");
        assert_eq!(parse_template(" x ||y ").unwrap().span.as_str(), "x ||y");
    }

    #[test]
    fn test_function_call_syntax() {
        // Trailing comma isn't allowed for empty argument
        assert!(parse_template(r#" "".first_line() "#).is_ok());
        assert!(parse_template(r#" "".first_line(,) "#).is_err());

        // Trailing comma is allowed for the last argument
        assert!(parse_template(r#" "".contains("") "#).is_ok());
        assert!(parse_template(r#" "".contains("",) "#).is_ok());
        assert!(parse_template(r#" "".contains("" ,  ) "#).is_ok());
        assert!(parse_template(r#" "".contains(,"") "#).is_err());
        assert!(parse_template(r#" "".contains("",,) "#).is_err());
        assert!(parse_template(r#" "".contains("" , , ) "#).is_err());
        assert!(parse_template(r#" label("","") "#).is_ok());
        assert!(parse_template(r#" label("","",) "#).is_ok());
        assert!(parse_template(r#" label("",,"") "#).is_err());

        // Boolean literal cannot be used as a function name
        assert!(parse_template("false()").is_err());
        // Function arguments can be any expression
        assert!(parse_template("f(false)").is_ok());
    }

    #[test]
    fn test_method_call_syntax() {
        assert_eq!(
            parse_normalized("x.f().g()").unwrap(),
            parse_normalized("(x.f()).g()").unwrap(),
        );

        // Expression span
        assert_eq!(parse_template(" x.f() ").unwrap().span.as_str(), "x.f()");
        assert_eq!(
            parse_template(" x.f().g() ").unwrap().span.as_str(),
            "x.f().g()",
        );
    }

    #[test]
    fn test_lambda_syntax() {
        fn unwrap_lambda(node: ExpressionNode<'_>) -> Box<LambdaNode<'_>> {
            match node.kind {
                ExpressionKind::Lambda(lambda) => lambda,
                _ => panic!("unexpected expression: {node:?}"),
            }
        }

        let lambda = unwrap_lambda(parse_template("|| a").unwrap());
        assert_eq!(lambda.params.len(), 0);
        assert_eq!(lambda.body.kind, ExpressionKind::Identifier("a"));
        let lambda = unwrap_lambda(parse_template("|foo| a").unwrap());
        assert_eq!(lambda.params.len(), 1);
        let lambda = unwrap_lambda(parse_template("|foo, b| a").unwrap());
        assert_eq!(lambda.params.len(), 2);

        // No body
        assert!(parse_template("||").is_err());

        // Binding
        assert_eq!(
            parse_normalized("||  x ++ y").unwrap(),
            parse_normalized("|| (x ++ y)").unwrap(),
        );
        assert_eq!(
            parse_normalized("f( || x,   || y)").unwrap(),
            parse_normalized("f((|| x), (|| y))").unwrap(),
        );
        assert_eq!(
            parse_normalized("||  x ++  || y").unwrap(),
            parse_normalized("|| (x ++ (|| y))").unwrap(),
        );

        // Lambda vs logical operator: weird, but this is type error anyway
        assert_eq!(
            parse_normalized("x||||y").unwrap(),
            parse_normalized("x || (|| y)").unwrap(),
        );
        assert_eq!(
            parse_normalized("||||x").unwrap(),
            parse_normalized("|| (|| x)").unwrap(),
        );

        // Trailing comma
        assert!(parse_template("|,| a").is_err());
        assert!(parse_template("|x,| a").is_ok());
        assert!(parse_template("|x , | a").is_ok());
        assert!(parse_template("|,x| a").is_err());
        assert!(parse_template("| x,y,| a").is_ok());
        assert!(parse_template("|x,,y| a").is_err());

        // Formal parameter can't be redefined
        assert_eq!(
            parse_template("|x, x| a").unwrap_err().kind,
            TemplateParseErrorKind::RedefinedFunctionParameter
        );

        // Boolean literal cannot be used as a parameter name
        assert!(parse_template("|false| a").is_err());
    }

    #[test]
    fn test_keyword_literal() {
        assert_eq!(parse_into_kind("false"), Ok(ExpressionKind::Boolean(false)));
        assert_eq!(parse_into_kind("(true)"), Ok(ExpressionKind::Boolean(true)));
        // Keyword literals are case sensitive
        assert_eq!(
            parse_into_kind("False"),
            Ok(ExpressionKind::Identifier("False")),
        );
        assert_eq!(
            parse_into_kind("tRue"),
            Ok(ExpressionKind::Identifier("tRue")),
        );
    }

    #[test]
    fn test_string_literal() {
        // "\<char>" escapes
        assert_eq!(
            parse_into_kind(r#" "\t\r\n\"\\\0" "#),
            Ok(ExpressionKind::String("\t\r\n\"\\\0".to_owned())),
        );

        // Invalid "\<char>" escape
        assert_eq!(
            parse_into_kind(r#" "\y" "#),
            Err(TemplateParseErrorKind::SyntaxError),
        );

        // Single-quoted raw string
        assert_eq!(
            parse_into_kind(r#" '' "#),
            Ok(ExpressionKind::String("".to_owned())),
        );
        assert_eq!(
            parse_into_kind(r#" 'a\n' "#),
            Ok(ExpressionKind::String(r"a\n".to_owned())),
        );
        assert_eq!(
            parse_into_kind(r#" '\' "#),
            Ok(ExpressionKind::String(r"\".to_owned())),
        );
        assert_eq!(
            parse_into_kind(r#" '"' "#),
            Ok(ExpressionKind::String(r#"""#.to_owned())),
        );
    }

    #[test]
    fn test_integer_literal() {
        assert_eq!(parse_into_kind("0"), Ok(ExpressionKind::Integer(0)));
        assert_eq!(parse_into_kind("(42)"), Ok(ExpressionKind::Integer(42)));
        assert_eq!(
            parse_into_kind("00"),
            Err(TemplateParseErrorKind::SyntaxError),
        );

        assert_eq!(
            parse_into_kind(&format!("{}", i64::MAX)),
            Ok(ExpressionKind::Integer(i64::MAX)),
        );
        assert_matches!(
            parse_into_kind(&format!("{}", (i64::MAX as u64) + 1)),
            Err(TemplateParseErrorKind::Expression(_))
        );
    }

    #[test]
    fn test_parse_alias_decl() {
        let mut aliases_map = TemplateAliasesMap::new();
        aliases_map.insert("sym", r#""is symbol""#).unwrap();
        aliases_map.insert("func(a)", r#""is function""#).unwrap();

        let (id, defn) = aliases_map.get_symbol("sym").unwrap();
        assert_eq!(id, AliasId::Symbol("sym"));
        assert_eq!(defn, r#""is symbol""#);

        let (id, params, defn) = aliases_map.get_function("func").unwrap();
        assert_eq!(id, AliasId::Function("func"));
        assert_eq!(params, ["a"]);
        assert_eq!(defn, r#""is function""#);

        // Formal parameter 'a' can't be redefined
        assert_eq!(
            aliases_map.insert("f(a, a)", r#""""#).unwrap_err().kind,
            TemplateParseErrorKind::RedefinedFunctionParameter
        );

        // Boolean literal cannot be used as a symbol, function, or parameter name
        assert!(aliases_map.insert("false", r#"""#).is_err());
        assert!(aliases_map.insert("true()", r#"""#).is_err());
        assert!(aliases_map.insert("f(false)", r#"""#).is_err());

        // Trailing comma isn't allowed for empty parameter
        assert!(aliases_map.insert("f(,)", r#"""#).is_err());
        // Trailing comma is allowed for the last parameter
        assert!(aliases_map.insert("g(a,)", r#"""#).is_ok());
        assert!(aliases_map.insert("h(a ,  )", r#"""#).is_ok());
        assert!(aliases_map.insert("i(,a)", r#"""#).is_err());
        assert!(aliases_map.insert("j(a,,)", r#"""#).is_err());
        assert!(aliases_map.insert("k(a  , , )", r#"""#).is_err());
        assert!(aliases_map.insert("l(a,b,)", r#"""#).is_ok());
        assert!(aliases_map.insert("m(a,,b)", r#"""#).is_err());
    }

    #[test]
    fn test_expand_symbol_alias() {
        assert_eq!(
            with_aliases([("AB", "a ++ b")])
                .parse_normalized("AB ++ c")
                .unwrap(),
            parse_normalized("(a ++ b) ++ c").unwrap(),
        );
        assert_eq!(
            with_aliases([("AB", "a ++ b")])
                .parse_normalized("if(AB, label(c, AB))")
                .unwrap(),
            parse_normalized("if((a ++ b), label(c, (a ++ b)))").unwrap(),
        );

        // Multi-level substitution.
        assert_eq!(
            with_aliases([("A", "BC"), ("BC", "b ++ C"), ("C", "c")])
                .parse_normalized("A")
                .unwrap(),
            parse_normalized("b ++ c").unwrap(),
        );

        // Operator expression can be expanded in concatenation.
        assert_eq!(
            with_aliases([("AB", "a || b")])
                .parse_normalized("AB ++ c")
                .unwrap(),
            parse_normalized("(a || b) ++ c").unwrap(),
        );

        // Operands should be expanded.
        assert_eq!(
            with_aliases([("A", "a"), ("B", "b")])
                .parse_normalized("A || !B")
                .unwrap(),
            parse_normalized("a || !b").unwrap(),
        );

        // Method receiver and arguments should be expanded.
        assert_eq!(
            with_aliases([("A", "a")])
                .parse_normalized("A.f()")
                .unwrap(),
            parse_normalized("a.f()").unwrap(),
        );
        assert_eq!(
            with_aliases([("A", "a"), ("B", "b")])
                .parse_normalized("x.f(A, B)")
                .unwrap(),
            parse_normalized("x.f(a, b)").unwrap(),
        );

        // Lambda expression body should be expanded.
        assert_eq!(
            with_aliases([("A", "a")]).parse_normalized("|| A").unwrap(),
            parse_normalized("|| a").unwrap(),
        );
        // No matter if 'A' is a formal parameter. Alias substitution isn't scoped.
        // If we don't like this behavior, maybe we can turn off alias substitution
        // for lambda parameters.
        assert_eq!(
            with_aliases([("A", "a ++ b")])
                .parse_normalized("|A| A")
                .unwrap(),
            parse_normalized("|A| (a ++ b)").unwrap(),
        );

        // Infinite recursion, where the top-level error isn't of RecursiveAlias kind.
        assert_eq!(
            with_aliases([("A", "A")]).parse("A").unwrap_err().kind,
            TemplateParseErrorKind::BadAliasExpansion("A".to_owned()),
        );
        assert_eq!(
            with_aliases([("A", "B"), ("B", "b ++ C"), ("C", "c ++ B")])
                .parse("A")
                .unwrap_err()
                .kind,
            TemplateParseErrorKind::BadAliasExpansion("A".to_owned()),
        );

        // Error in alias definition.
        assert_eq!(
            with_aliases([("A", "a(")]).parse("A").unwrap_err().kind,
            TemplateParseErrorKind::BadAliasExpansion("A".to_owned()),
        );
    }

    #[test]
    fn test_expand_function_alias() {
        assert_eq!(
            with_aliases([("F(  )", "a")])
                .parse_normalized("F()")
                .unwrap(),
            parse_normalized("a").unwrap(),
        );
        assert_eq!(
            with_aliases([("F( x )", "x")])
                .parse_normalized("F(a)")
                .unwrap(),
            parse_normalized("a").unwrap(),
        );
        assert_eq!(
            with_aliases([("F( x, y )", "x ++ y")])
                .parse_normalized("F(a, b)")
                .unwrap(),
            parse_normalized("a ++ b").unwrap(),
        );

        // Arguments should be resolved in the current scope.
        assert_eq!(
            with_aliases([("F(x,y)", "if(x, y)")])
                .parse_normalized("F(a ++ y, b ++ x)")
                .unwrap(),
            parse_normalized("if((a ++ y), (b ++ x))").unwrap(),
        );
        // F(a) -> if(G(a), y) -> if((x ++ a), y)
        assert_eq!(
            with_aliases([("F(x)", "if(G(x), y)"), ("G(y)", "x ++ y")])
                .parse_normalized("F(a)")
                .unwrap(),
            parse_normalized("if((x ++ a), y)").unwrap(),
        );
        // F(G(a)) -> F(x ++ a) -> if(G(x ++ a), y) -> if((x ++ (x ++ a)), y)
        assert_eq!(
            with_aliases([("F(x)", "if(G(x), y)"), ("G(y)", "x ++ y")])
                .parse_normalized("F(G(a))")
                .unwrap(),
            parse_normalized("if((x ++ (x ++ a)), y)").unwrap(),
        );

        // Function parameter should precede the symbol alias.
        assert_eq!(
            with_aliases([("F(X)", "X"), ("X", "x")])
                .parse_normalized("F(a) ++ X")
                .unwrap(),
            parse_normalized("a ++ x").unwrap(),
        );

        // Function parameter shouldn't be expanded in symbol alias.
        assert_eq!(
            with_aliases([("F(x)", "x ++ A"), ("A", "x")])
                .parse_normalized("F(a)")
                .unwrap(),
            parse_normalized("a ++ x").unwrap(),
        );

        // Function and symbol aliases reside in separate namespaces.
        assert_eq!(
            with_aliases([("A()", "A"), ("A", "a")])
                .parse_normalized("A()")
                .unwrap(),
            parse_normalized("a").unwrap(),
        );

        // Method call shouldn't be substituted by function alias.
        assert_eq!(
            with_aliases([("F()", "f()")])
                .parse_normalized("x.F()")
                .unwrap(),
            parse_normalized("x.F()").unwrap(),
        );

        // Formal parameter shouldn't be substituted by alias parameter, but
        // the expression should be substituted.
        assert_eq!(
            with_aliases([("F(x)", "|x| x")])
                .parse_normalized("F(a ++ b)")
                .unwrap(),
            parse_normalized("|x| (a ++ b)").unwrap(),
        );

        // Invalid number of arguments.
        assert_matches!(
            with_aliases([("F()", "x")]).parse("F(a)").unwrap_err().kind,
            TemplateParseErrorKind::InvalidArguments { .. }
        );
        assert_matches!(
            with_aliases([("F(x)", "x")]).parse("F()").unwrap_err().kind,
            TemplateParseErrorKind::InvalidArguments { .. }
        );
        assert_matches!(
            with_aliases([("F(x,y)", "x ++ y")])
                .parse("F(a,b,c)")
                .unwrap_err()
                .kind,
            TemplateParseErrorKind::InvalidArguments { .. }
        );

        // Infinite recursion, where the top-level error isn't of RecursiveAlias kind.
        assert_eq!(
            with_aliases([("F(x)", "G(x)"), ("G(x)", "H(x)"), ("H(x)", "F(x)")])
                .parse("F(a)")
                .unwrap_err()
                .kind,
            TemplateParseErrorKind::BadAliasExpansion("F()".to_owned()),
        );
    }
}