use serde::{Deserialize, Serialize};

use crate::chunk::FunctionType;

/// Manages the declaration and definition of local variables
///
/// One ResolverNode is created and pushed onto the stack for each function definition. It then gets popped off once its definition ends, so the value on top of each ResolverNode
/// on the stack will always be its parent
///
/// Normal resolution is handled by the current ResolverNode.
/// Resolution that involves closures (upvalues) is done by the Resolver (since it will potentially involve many ResolverNodes)
#[derive(Debug, Clone)]
pub struct Resolver {
    stack: Vec<ResolverNode>,
}

impl Default for Resolver {
    fn default() -> Self {
        Self::new()
    }
}

/// Used by Resolver to generate simple functions that just call the same function on the current ResolverNode
macro_rules! delegate_to_latest {
    ($fn_name: ident, $ret: ty) => {
        /// Calls this function on the current ResolverNode
        pub fn $fn_name(&mut self) -> $ret {
            self.current_node().$fn_name()
        }
    };
    ($fn_name: ident, $ret: ty, $param: ty) => {
        /// Calls this function on the current ResolverNode
        pub fn $fn_name(&mut self, x: $param) -> $ret {
            self.current_node().$fn_name(x)
        }
    };
}

impl Resolver {
    fn current_node(&mut self) -> &mut ResolverNode {
        self.stack.last_mut().unwrap()
    }

    delegate_to_latest!(begin_scope, ());
    delegate_to_latest!(end_scope, usize);
    delegate_to_latest!(is_global, bool);
    delegate_to_latest!(mark_initialized, ());
    delegate_to_latest!(declare_variable, bool, String);
    delegate_to_latest!(resolve_local, Option<Option<usize>>, &str);

    /// Calls [Resolver::recursive_resolve] to handle the flattening of upvalues
    ///
    /// Returns the index of the UpValue in the upvalues Vec
    pub fn resolve_upvalue(&mut self, name: &str) -> Option<usize> {
        let n = self.stack.len();
        if n >= 3 {
            // Depth must be 3, global scope -> function scope -> internal scope (the first place we can have upvalues)
            self.recursive_resolve(name, n - 1)
        } else {
            None
        }
    }

    /// Recursively checks parents for the given name, using child_index to index into the ResolverNode stack
    ///
    /// Attempt to resolve the variable name by looking at the locals of the parent (which sits at child_index - 1)
    /// If found, add an upvalue to self.upvalues and return the index in the UpValues vec
    fn recursive_resolve(&mut self, name: &str, child_index: usize) -> Option<usize> {
        if child_index == 0 {
            return None;
        } // Base case: Everyone failed to resolve the upvalue

        let parent = self.stack.get(child_index - 1)?;
        let mut upval_index = None;
        for (i, local) in parent.locals.iter().enumerate() {
            if local.name.eq(name) {
                upval_index = Some(i);
                break;
            }
        }

        if let Some(index) = upval_index {
            let child = self.stack.get_mut(child_index)?;
            Some(child.add_upvalue(index, true))
        } else if let Some(index) = self.recursive_resolve(name, child_index - 1) {
            let child = self.stack.get_mut(child_index)?;
            return Some(child.add_upvalue(index, false));
        } else {
            None
        }
    }

    /// Push a new ResolverNode for the new function scope
    pub fn push(&mut self, fn_type: FunctionType) {
        let mut locals = Vec::new();
        let first_local = match fn_type {
            FunctionType::Method | FunctionType::Initializer => Local {
                name: String::from("this"),
                depth: Some(1),
            }, // Fill the first slot with a magically initialized "this" which will contain the PhoenixPointer to itself
            _ => Local {
                name: String::from(""),
                depth: None,
            }, // Fill the first slot with a blank to be filled with the closure
        };
        locals.push(first_local);

        let new = ResolverNode {
            upvalues: Vec::new(),
            locals,
            scope_depth: self.stack.last().unwrap().scope_depth, // Child is responsible for calling begin and end scope
        };

        self.stack.push(new);
    }

    /// Remove the latest ResolverNode and return the UpValues resolved in that scope
    pub fn pop(&mut self) -> Vec<UpValue> {
        let latest = self.stack.pop().unwrap(); // Fixme: make this not panic?
        latest.upvalues
    }

    pub fn new() -> Resolver {
        let locals = vec![Local {
            // Placeholder local variable for VM use -> Will be filled by the corresponding PhoenixFunction for the CallFrame
            name: String::from(""),
            depth: None,
        }];

        let top = ResolverNode {
            upvalues: Vec::new(),
            locals,
            scope_depth: 0,
        };

        let stack = vec![top];

        Resolver { stack }
    }
}

#[derive(Debug, Clone)]
struct ResolverNode {
    upvalues: Vec<UpValue>,
    locals: Vec<Local>,
    scope_depth: usize,
}

impl ResolverNode {
    pub fn begin_scope(&mut self) {
        self.scope_depth += 1;
    }

    /// MUST BE CALLED BY Compiler::end_scope()
    ///
    /// Decrements the scope depth and pops off the values that went out of scope
    /// Todo:
    /// *  Make this less uggo
    /// *  Use a trait or something to limit the visibility somehow?
    pub fn end_scope(&mut self) -> usize {
        self.scope_depth -= 1;
        let mut pops = 0;
        for local in self.locals.iter().rev() {
            if let Some(x) = local.depth {
                if x > self.scope_depth {
                    pops += 1;
                } else {
                    break;
                }
            }
        }
        for _ in 0..pops {
            self.locals.pop();
        }
        pops
    }

    pub fn is_global(&self) -> bool {
        self.scope_depth == 0
    }

    fn add_local(&mut self, name: String) {
        let local = Local { name, depth: None };
        self.locals.push(local);
    }

    /// Marks the last local variable as initialized by giving it a depth
    /// if the current scope is not global
    pub fn mark_initialized(&mut self) {
        if self.scope_depth == 0 {
            return;
        }
        self.locals.last_mut().unwrap().depth = Some(self.scope_depth);
    }

    /// MUST BE CALLED BY Compiler::declare_variable()
    /// Declare new local variables by pushing them onto self.locals
    ///
    /// New locals are set to a special "uninitialized" state until define_variable() is called
    ///
    /// If the scope is global, do nothing
    pub fn declare_variable(&mut self, str_val: String) -> bool {
        if !self.is_global() {
            // Must not be in the global scope in order to define local vars
            let mut found_eq = false; // Is this the idiomatic way of doing this?? I have no idea

            for local in self.locals.iter() {
                if let Some(x) = local.depth {
                    if x < self.scope_depth {
                        break;
                    }
                }
                if str_val.eq(&local.name) {
                    found_eq = true;
                    break;
                }
            }

            self.add_local(str_val);
            !found_eq
        } else {
            true
        }
    }

    /// Walk and look for a local variable with the same name, None if the var is not found (treat as global)
    ///
    /// *  Err(_) => Syntax error detected, throw an error
    /// *  Ok(None) => Resolution failed
    /// *  Ok(Some(index)) => found
    ///
    /// Fixme: Should probably make this a Option<Option<usize>>
    pub fn resolve_local(&self, name: &str) -> Option<Option<usize>> {
        let mut error = false;
        for (i, local) in self.locals.iter().enumerate() {
            if local.name.eq(name) {
                if local.depth.is_none() {
                    error = true;
                    break;
                } else {
                    return Some(Some(i));
                }
            }
        }

        if error {
            None
        } else {
            Some(None)
        }
    }

    fn add_upvalue(&mut self, index: usize, is_local: bool) -> usize {
        for (i, existing_upvalue) in self.upvalues.iter().enumerate() {
            if existing_upvalue.index == index {
                return i;
            }
        }

        self.upvalues.push(UpValue { is_local, index });
        self.upvalues.len() - 1
    }
}

#[derive(Debug, Clone)]
pub struct Local {
    name: String,
    depth: Option<usize>,
}

/// Similar to local, but for upvalues
/// An upvalue refers to a local variable in an enclosing function
#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
pub struct UpValue {
    pub is_local: bool,
    pub index: usize,
}