use std::{fmt, error::Error, num::IntErrorKind};
use regex::Regex;

pub mod shunting_yard;

fn normalize_string(to_normalize: String) -> String {
    let mut normalized_text = to_normalize;
    normalized_text.retain(|c| !c.is_whitespace());
    normalized_text = normalized_text.to_string();
    normalized_text
}

// In an expression like `sqrt(25)` the Task would correspond to `sqrt`. This is the enum to 
// configure possible Tasks.
// None means, the Expression doesn't send it's Value to a Task Handler
#[derive(Debug)]    // automatically generate Debug Formatter
pub enum Task {
    None,
    Root(u64),
    Power(f64),
    Log(f64),
}

// How to clone a Task, i was supprised I had to do it myself.
impl Clone for Task {
    fn clone(&self) -> Self {
        // This can probably be done cleaner than with a verbose match. FIXME
        match self {
            Task::None => Task::None,
            Task::Root(depth) => Task::Root(*depth),
            Task::Power(exp) => Task::Power(*exp),
            Task::Log(base) => Task::Log(*base), // TODO add base for log
        }
    }
}

impl Task {
    pub fn new(task_text: &str, task_param: &str) -> Task {
        if task_text.is_empty() {
            return Task::None;
        }
        let task_text = task_text.to_lowercase();
        match task_text.as_str() {
            "none" => Task::None,
            "sqrt"|"root" => {
                if task_param.is_empty() {
                    return Task::Root(2);
                }
                let pot_param = task_param.parse::<u64>();
                match pot_param {
                    Ok(value) => {Task::Root(value)},
                    Err(error) => {
                        eprintln!("could not parse task parameter: {error}"); 
                        std::process::exit(1);
                    },
                }
            },
            "power"|"pow"|"sq" => {
                if task_param.is_empty() {
                    return Task::Power(2.0);
                }
                let pot_param = task_param.parse::<f64>();
                match pot_param {
                    Ok(value) => {Task::Power(value)},
                    Err(error) => {
                        eprintln!("could not parse task parameter: {error}"); 
                        std::process::exit(1);
                    },
                }
            },
            "log"|"ln" => {
                if task_param.is_empty() {
                    return Task::Log(10.0);
                }
                let pot_param = task_param.parse::<f64>();
                match pot_param {
                    Ok(value) => {Task::Log(value)},
                    Err(error) => {
                        eprintln!("could not parse task parameter: {error}"); 
                        std::process::exit(1);
                    },
                }
            },
            // what to do if a bad task was given:
            // this would be throwing an error and aborting
            //&_ => {eprintln!("Bad Task: {}", task_text); std::process::exit(1); },
            _ => Task::None,
        }
    }
}
// An Expression is something that can be calculated. 20+5 is an expression. Expressions can 
// contain other
// Expressions and have tasks: 20+log_10(20+5)
// Tasks may have parameters, denoted using an underscore '_'
// Expressions are marked down with braces and a task before those braces:
// task(Expression)
// once the Value of the Expression got calculated, the calculated value should be sent to the 
// TaskHandler, if the Task of the Expression is not Task::None
pub struct Expression {
    pub text: String,
    full_text: String,
    task: Task,
    complex: bool,
    outer_value: Result<f64, String>,
    children: Vec<Expression>,
    depth: u8,
}

// Debug Formatter for Expression
impl fmt::Debug for Expression {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Expression")
            .field("text", &self.text)
            .field("full text", &self.full_text)
            .field("task", &self.task)
            .field("is complex?", &self.complex)
            .field("outer value", &self.outer_value)
            .field("children", &self.children)
            .field("depth", &self.depth)
            .finish()
    }
}

// implement clone by ourselves, as it's not automatically done for us.
impl Clone for Expression{
    fn clone(&self) -> Self {
        Expression { 
            text: self.text.clone(), 
            full_text: self.full_text.clone(), 
            task: self.task.clone(),
            complex: self.complex.clone(),  // TODO add support for complex numbers
            outer_value: self.outer_value.clone(),
            children: self.children.clone(),
            depth: self.depth.clone(),
        }
    }
}

fn find_brace_groups(haystack: String) -> Vec<Vec<(usize, usize)>> {

    // TODO add support for diffrent braces
    // TODO add error if not all braces are closed
    let mut parenthesis_group: Vec<(usize, usize)> = Vec::new();
    let mut parenthesis_open: usize = 0;
    let mut parenthesis_open_processed: usize = 0;
    let mut parenthesis_closed_processed: usize = 0;
    let mut parenthesis_last_opened: Vec<usize> = Vec::new();
    //let mut brackets_group: Vec<(usize, usize)> = Vec::new();
    //let mut brackets_open: usize = 0;
    //let mut square_braces_group: Vec<(usize, usize)> = Vec::new();
    //let mut square_braces_open: usize = 0;
    // first open stuff
    for (index, char) in haystack.chars().enumerate() {
        match char {
            '(' => { 
                parenthesis_group.push((index, 0)); 
                parenthesis_open = parenthesis_open + 1;
                parenthesis_last_opened.push(parenthesis_open_processed);
                parenthesis_open_processed = parenthesis_open_processed + 1;
            },
            ')' => { 
                parenthesis_group[parenthesis_last_opened[parenthesis_last_opened.len() - 1]].1 = index;
                parenthesis_open = parenthesis_open - 1;
                parenthesis_closed_processed = parenthesis_closed_processed + 1;
                parenthesis_last_opened.pop();
                // TODO add error if no parenthesis is open yet.
            },
            _ => (),
        }
    }
    // now iterate backwards and search for closing things

    let brace_groups = vec![parenthesis_group/*, square_braces_group, brackets_group*/];
    #[cfg(debug_assertions)]
    dbg!(&brace_groups);
    return brace_groups;
}

/*
 * Main logic for the Expression struct
 */
impl Expression {
    /*
     * Main function for making text into Expression
     * example: "12 + log_10(10 + 15) + 3"
     * has a sub expression log_10(10 + 5), which has Task::Log with base 10
     */
    pub fn new(expression_text: String, expression_full_text: String, task: Task, depth: u8) -> Expression {

        // check if we are too deep
        if depth > 254 {
            eprintln!("Expression '{}' has a too deep family tree. Maximum generations are 254.", expression_text);
            std::process::exit(1);
        }

        let expression_text = normalize_string(expression_text);
        let mut task_text_full: String;
        let mut children: Vec<Expression> = Vec::new();

        let re_contains_sub_expression= Regex::new(r"(\(.*\))|(\[.*\])|(\{.*\})").unwrap();

        if re_contains_sub_expression.is_match(expression_text.as_str()) {
            let brace_groups: Vec<Vec<(usize, usize)>> = find_brace_groups(expression_text.clone());

            let mut brace_groups_texts: Vec<String> = Vec::new();

            // 1 brace group per possible combination, by default, this is only (), so 1 iteration.
            // This is still O(n¹) 
            for brace_group in brace_groups {
                for pair in brace_group {
                    let text = &expression_text[pair.0..pair.1 + 1];
                    let text = &text[1..text.len() - 1];
                    brace_groups_texts.push(text.to_string());
                    // we have the expression_text, now we just need to get the task until we can
                    // pass these parameters into Expression::new(). This is the recursive part.
                    let possible_task = &expression_text[..pair.0].chars().rev().collect::<String>();
                    let mut stop_at: usize = 0;
                    for (index, char) in possible_task.chars().enumerate() {
                        if !(char.is_alphanumeric()) {
                            break;
                        }
                        stop_at = index;
                    }
                    dbg!(&stop_at);
                    // needed for none task: '1 + (1 + 1)'
                    let fixup = if stop_at == 0 { 0 } else { 1 };
                    task_text_full = possible_task.clone()[..stop_at+ fixup].chars().rev().collect::<String>();
                    let task: Task;
                    if task_text_full.contains('_') {
                        let split: Vec<&str> = task_text_full.split('_').collect();
                        task = Task::new(split[0], split[1]);
                    }
                    else {
                        task = Task::new(task_text_full.as_str(), "");
                    }
                    let child_full_text = task_text_full + "(" + text + ")";
                    let child = Expression::new(text.to_string(), child_full_text, task, depth+1);
                    children.push(child);
                }
            }
        } 

        let expression = Expression {
            text: expression_text,
            full_text: normalize_string(expression_full_text),
            task,
            complex: false,
            outer_value: Err("Value not yet calculated.".to_string()),
            children,
            depth,
        };
        expression
    }

    // calculate value for expression.
    pub fn process(self) -> Result<f64, String> {
        let mut normalized_text = self.normalize_text();
        //let re_numeric = Regex::new(r"\d+(\.\d+)?");
        /*
         *  Algorithm:
         *  
         *  First, search child expressions in normalized_text by searching for the text of all
         *  children in normalized_text. If an expression is found, a value for it should be
         *  calculated (recursive!) and the text should be substituted with the calculated value.
         *  If a child expression is not found in the normalized_text, throw an error, as an
         *  expression has a child but does not contain it's text. (note: a childs child
         *  expressions are not the child expression of the original expression, so no need to
         *  worry about the order of substituting texts for values.)
         *
         *  Once there are no more child expressions in the normalized_text, we can use the
         *  shunting yards algorithm to calculate the result. I'm not yet sure, if I want to use
         *  another developers shunting yard algorithm or implement it by myself.
         */ 
       
        // TODO check if we have any unknown values.
        
        // iterate through children, substitute childrens text with childrens results (as string
        // slice).
        for child in self.children {
            //normalized_text = normalized_text.replace(child.full_text.clone().as_str(), child.process().expect(self.text).as_str());
            let child_full_text = match child.clone().process() {
                Ok(result) => result.to_string(),
                Err(err) => { 
                    eprintln!(
                        "Could not calculate result of child expression '{}': {}", 
                        child.text,
                        "error placeholder TODO"
                        );
                    std::process::exit(2);
                }
            };
            dbg!(&child.full_text);
            dbg!(&child_full_text);
            normalized_text = normalized_text.replace(child.full_text.as_str(), child_full_text.as_str());
        }
        dbg!(&normalized_text);
        // TODO Shunting yards algorithm, as we now have only calculatable values left.
        // Implement this as public module in shunting_yard.rs
        // self.result = MYRESULT
        let rpn = shunting_yard::form_reverse_polish_notation(&normalized_text);
        match rpn {
            Ok(valid_rpn) => {
                dbg!(&valid_rpn);
                return shunting_yard::calc_reverse_polish_notation(&valid_rpn);
            },
            Err(err) => {
                eprintln!("Could not calculate a result for expression '{}': {err}", self.text);
                std::process::exit(2);
            },
        }
    }

    // wrapper for normalize_string()
    fn normalize_text(&self) -> String {
        normalize_string(self.text.clone())
    }
}