// Feature: Postfix completion for `format`-like strings.
//
// `"Result {result} is {2 + 2}"` is expanded to the `"Result {} is {}", result, 2 + 2`.
//
// The following postfix snippets are available:
//
// - `format` -> `format!(...)`
// - `panic` -> `panic!(...)`
// - `println` -> `println!(...)`
// - `log`:
//   + `logd` -> `log::debug!(...)`
//   + `logt` -> `log::trace!(...)`
//   + `logi` -> `log::info!(...)`
//   + `logw` -> `log::warn!(...)`
//   + `loge` -> `log::error!(...)`

use crate::completion::{
    complete_postfix::postfix_snippet, completion_config::SnippetCap,
    completion_context::CompletionContext, completion_item::Completions,
};
use syntax::ast::{self, AstToken};

/// Mapping ("postfix completion item" => "macro to use")
static KINDS: &[(&str, &str)] = &[
    ("fmt", "format!"),
    ("panic", "panic!"),
    ("println", "println!"),
    ("logd", "log::debug!"),
    ("logt", "log::trace!"),
    ("logi", "log::info!"),
    ("logw", "log::warn!"),
    ("loge", "log::error!"),
];

pub(super) fn add_format_like_completions(
    acc: &mut Completions,
    ctx: &CompletionContext,
    dot_receiver: &ast::Expr,
    cap: SnippetCap,
    receiver_text: &ast::String,
) {
    let input = match string_literal_contents(receiver_text) {
        // It's not a string literal, do not parse input.
        Some(input) => input,
        None => return,
    };

    let mut parser = FormatStrParser::new(input);

    if parser.parse().is_ok() {
        for (label, macro_name) in KINDS {
            let snippet = parser.into_suggestion(macro_name);

            postfix_snippet(ctx, cap, &dot_receiver, label, macro_name, &snippet).add_to(acc);
        }
    }
}

/// Checks whether provided item is a string literal.
fn string_literal_contents(item: &ast::String) -> Option<String> {
    let item = item.text();
    if item.len() >= 2 && item.starts_with("\"") && item.ends_with("\"") {
        return Some(item[1..item.len() - 1].to_owned());
    }

    None
}

/// Parser for a format-like string. It is more allowing in terms of string contents,
/// as we expect variable placeholders to be filled with expressions.
#[derive(Debug)]
pub struct FormatStrParser {
    input: String,
    output: String,
    extracted_expressions: Vec<String>,
    state: State,
    parsed: bool,
}

#[derive(Debug, Clone, Copy, PartialEq)]
enum State {
    NotExpr,
    MaybeExpr,
    Expr,
    MaybeIncorrect,
    FormatOpts,
}

impl FormatStrParser {
    pub fn new(input: String) -> Self {
        Self {
            input: input.into(),
            output: String::new(),
            extracted_expressions: Vec::new(),
            state: State::NotExpr,
            parsed: false,
        }
    }

    pub fn parse(&mut self) -> Result<(), ()> {
        let mut current_expr = String::new();

        let mut placeholder_id = 1;

        // Count of open braces inside of an expression.
        // We assume that user knows what they're doing, thus we treat it like a correct pattern, e.g.
        // "{MyStruct { val_a: 0, val_b: 1 }}".
        let mut inexpr_open_count = 0;

        for chr in self.input.chars() {
            match (self.state, chr) {
                (State::NotExpr, '{') => {
                    self.output.push(chr);
                    self.state = State::MaybeExpr;
                }
                (State::NotExpr, '}') => {
                    self.output.push(chr);
                    self.state = State::MaybeIncorrect;
                }
                (State::NotExpr, _) => {
                    self.output.push(chr);
                }
                (State::MaybeIncorrect, '}') => {
                    // It's okay, we met "}}".
                    self.output.push(chr);
                    self.state = State::NotExpr;
                }
                (State::MaybeIncorrect, _) => {
                    // Error in the string.
                    return Err(());
                }
                (State::MaybeExpr, '{') => {
                    self.output.push(chr);
                    self.state = State::NotExpr;
                }
                (State::MaybeExpr, '}') => {
                    // This is an empty sequence '{}'. Replace it with placeholder.
                    self.output.push(chr);
                    self.extracted_expressions.push(format!("${}", placeholder_id));
                    placeholder_id += 1;
                    self.state = State::NotExpr;
                }
                (State::MaybeExpr, _) => {
                    current_expr.push(chr);
                    self.state = State::Expr;
                }
                (State::Expr, '}') => {
                    if inexpr_open_count == 0 {
                        self.output.push(chr);
                        self.extracted_expressions.push(current_expr.trim().into());
                        current_expr = String::new();
                        self.state = State::NotExpr;
                    } else {
                        // We're closing one brace met before inside of the expression.
                        current_expr.push(chr);
                        inexpr_open_count -= 1;
                    }
                }
                (State::Expr, ':') => {
                    if inexpr_open_count == 0 {
                        // We're outside of braces, thus assume that it's a specifier, like "{Some(value):?}"
                        self.output.push(chr);
                        self.extracted_expressions.push(current_expr.trim().into());
                        current_expr = String::new();
                        self.state = State::FormatOpts;
                    } else {
                        // We're inside of braced expression, assume that it's a struct field name/value delimeter.
                        current_expr.push(chr);
                    }
                }
                (State::Expr, '{') => {
                    current_expr.push(chr);
                    inexpr_open_count += 1;
                }
                (State::Expr, _) => {
                    current_expr.push(chr);
                }
                (State::FormatOpts, '}') => {
                    self.output.push(chr);
                    self.state = State::NotExpr;
                }
                (State::FormatOpts, _) => {
                    self.output.push(chr);
                }
            }
        }

        if self.state != State::NotExpr {
            return Err(());
        }

        self.parsed = true;
        Ok(())
    }

    pub fn into_suggestion(&self, macro_name: &str) -> String {
        assert!(self.parsed, "Attempt to get a suggestion from not parsed expression");

        let expressions_as_string = self.extracted_expressions.join(", ");
        format!(r#"{}("{}", {})"#, macro_name, self.output, expressions_as_string)
    }
}

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

    #[test]
    fn format_str_parser() {
        let test_vector = &[
            ("no expressions", Some(("no expressions", vec![]))),
            ("{expr} is {2 + 2}", Some(("{} is {}", vec!["expr", "2 + 2"]))),
            ("{expr:?}", Some(("{:?}", vec!["expr"]))),
            ("{malformed", None),
            ("malformed}", None),
            ("{{correct", Some(("{{correct", vec![]))),
            ("correct}}", Some(("correct}}", vec![]))),
            ("{correct}}}", Some(("{}}}", vec!["correct"]))),
            ("{correct}}}}}", Some(("{}}}}}", vec!["correct"]))),
            ("{incorrect}}", None),
            ("placeholders {} {}", Some(("placeholders {} {}", vec!["$1", "$2"]))),
            ("mixed {} {2 + 2} {}", Some(("mixed {} {} {}", vec!["$1", "2 + 2", "$2"]))),
            (
                "{SomeStruct { val_a: 0, val_b: 1 }}",
                Some(("{}", vec!["SomeStruct { val_a: 0, val_b: 1 }"])),
            ),
            ("{expr:?} is {2.32f64:.5}", Some(("{:?} is {:.5}", vec!["expr", "2.32f64"]))),
            (
                "{SomeStruct { val_a: 0, val_b: 1 }:?}",
                Some(("{:?}", vec!["SomeStruct { val_a: 0, val_b: 1 }"])),
            ),
            ("{     2 + 2        }", Some(("{}", vec!["2 + 2"]))),
        ];

        for (input, output) in test_vector {
            let mut parser = FormatStrParser::new((*input).to_owned());
            let outcome = parser.parse();

            if let Some((result_str, result_args)) = output {
                assert!(
                    outcome.is_ok(),
                    "Outcome is error for input: {}, but the expected outcome is {:?}",
                    input,
                    output
                );
                assert_eq!(parser.output, *result_str);
                assert_eq!(&parser.extracted_expressions, result_args);
            } else {
                assert!(
                    outcome.is_err(),
                    "Outcome is OK for input: {}, but the expected outcome is error",
                    input
                );
            }
        }
    }

    #[test]
    fn test_into_suggestion() {
        let test_vector = &[
            ("println!", "{}", r#"println!("{}", $1)"#),
            (
                "log::info!",
                "{} {expr} {} {2 + 2}",
                r#"log::info!("{} {} {} {}", $1, expr, $2, 2 + 2)"#,
            ),
            ("format!", "{expr:?}", r#"format!("{:?}", expr)"#),
        ];

        for (kind, input, output) in test_vector {
            let mut parser = FormatStrParser::new((*input).to_owned());
            parser.parse().expect("Parsing must succeed");

            assert_eq!(&parser.into_suggestion(*kind), output);
        }
    }
}