use crate::expr::constrain_decls;
use roc_builtins::std::StdLib;
use roc_can::constraint::{Constraint, LetConstraint};
use roc_can::def::Declaration;
use roc_collections::all::{MutMap, MutSet, SendMap};
use roc_module::symbol::{ModuleId, Symbol};
use roc_region::all::{Loc, Region};
use roc_types::solved_types::{FreeVars, SolvedType};
use roc_types::subs::{VarStore, Variable};
use roc_types::types::{Alias, Problem};

pub type SubsByModule = MutMap<ModuleId, ExposedModuleTypes>;

#[derive(Clone, Debug)]
pub enum ExposedModuleTypes {
    Invalid,
    Valid(MutMap<Symbol, SolvedType>, MutMap<Symbol, Alias>),
}

pub struct ConstrainedModule {
    pub unused_imports: MutMap<ModuleId, Region>,
    pub constraint: Constraint,
}

pub fn constrain_module(declarations: &[Declaration], home: ModuleId) -> Constraint {
    constrain_decls(home, declarations)
}

#[derive(Debug, Clone)]
pub struct Import {
    pub loc_symbol: Loc<Symbol>,
    pub solved_type: SolvedType,
}

pub fn constrain_imported_values(
    imports: Vec<Import>,
    body_con: Constraint,
    var_store: &mut VarStore,
) -> (Vec<Variable>, Constraint) {
    use Constraint::*;
    let mut def_types = SendMap::default();
    let mut rigid_vars = Vec::new();

    for import in imports {
        let mut free_vars = FreeVars::default();
        let loc_symbol = import.loc_symbol;

        // an imported symbol can be either an alias or a value
        match import.solved_type {
            SolvedType::Alias(symbol, _, _, _) if symbol == loc_symbol.value => {
                // do nothing, in the future the alias definitions should not be in the list of imported values
            }
            _ => {
                let typ = roc_types::solved_types::to_type(
                    &import.solved_type,
                    &mut free_vars,
                    var_store,
                );

                def_types.insert(
                    loc_symbol.value,
                    Loc {
                        region: loc_symbol.region,
                        value: typ,
                    },
                );

                for (_, var) in free_vars.named_vars {
                    rigid_vars.push(var);
                }

                for var in free_vars.wildcards {
                    rigid_vars.push(var);
                }

                // Variables can lose their name during type inference. But the unnamed
                // variables are still part of a signature, and thus must be treated as rigids here!
                for (_, var) in free_vars.unnamed_vars {
                    rigid_vars.push(var);
                }
            }
        }
    }

    (
        rigid_vars.clone(),
        Let(Box::new(LetConstraint {
            rigid_vars,
            flex_vars: Vec::new(),
            def_types,
            defs_constraint: True,
            ret_constraint: body_con,
        })),
    )
}

/// Run pre_constrain_imports to get imported_symbols and imported_aliases.
pub fn constrain_imports(
    imported_symbols: Vec<Import>,
    constraint: Constraint,
    var_store: &mut VarStore,
) -> Constraint {
    let (_introduced_rigids, constraint) =
        constrain_imported_values(imported_symbols, constraint, var_store);

    // TODO determine what to do with those rigids
    //    for var in introduced_rigids {
    //        output.ftv.insert(var, format!("internal_{:?}", var).into());
    //    }

    constraint
}

pub struct ConstrainableImports {
    pub imported_symbols: Vec<Import>,
    pub imported_aliases: MutMap<Symbol, Alias>,
    pub unused_imports: MutMap<ModuleId, Region>,
}

/// Run this before constraining imports.
///
/// Constraining imports is split into two different functions, because this
/// part of the work needs to be done on the main thread, whereas the rest of it
/// can be done on a different thread.
pub fn pre_constrain_imports(
    home: ModuleId,
    references: &MutSet<Symbol>,
    imported_modules: MutMap<ModuleId, Region>,
    exposed_types: &mut SubsByModule,
    stdlib: &StdLib,
) -> ConstrainableImports {
    let mut imported_symbols = Vec::with_capacity(references.len());
    let mut imported_aliases = MutMap::default();
    let mut unused_imports = imported_modules; // We'll remove these as we encounter them.

    // Translate referenced symbols into constraints. We do this on the main
    // thread because we need exclusive access to the exposed_types map, in order
    // to get the necessary constraint info for any aliases we imported. We also
    // resolve builtin types now, so we can use a reference to stdlib instead of
    // having to either clone it or recreate it from scratch on the other thread.
    for &symbol in references.iter() {
        let module_id = symbol.module_id();

        // We used this module, so clearly it is not unused!
        unused_imports.remove(&module_id);

        if module_id.is_builtin() {
            // For builtin modules, we create imports from the
            // hardcoded builtin map.
            match stdlib.types.get(&symbol) {
                Some((solved_type, region)) => {
                    let loc_symbol = Loc {
                        value: symbol,
                        region: *region,
                    };

                    imported_symbols.push(Import {
                        loc_symbol,
                        solved_type: solved_type.clone(),
                    });
                }
                None => {
                    if module_id == home {
                        continue;
                    }

                    if module_id == ModuleId::RESULT {
                        let region = Region::zero(); // TODO this should be the region where this symbol was declared in its home module. Look that up!
                        let loc_symbol = Loc {
                            value: symbol,
                            region,
                        };

                        match exposed_types.get(&module_id) {
                            Some(ExposedModuleTypes::Valid(solved_types, new_aliases)) => {
                                // If the exposed value was invalid (e.g. it didn't have
                                // a corresponding definition), it won't have an entry
                                // in solved_types
                                if let Some(solved_type) = solved_types.get(&symbol) {
                                    // TODO should this be a union?
                                    for (k, v) in new_aliases.clone() {
                                        imported_aliases.insert(k, v);
                                    }

                                    imported_symbols.push(Import {
                                        loc_symbol,
                                        solved_type: solved_type.clone(),
                                    });
                                }
                            }
                            Some(ExposedModuleTypes::Invalid) => {
                                // If that module was invalid, use True constraints
                                // for everything imported from it.
                                imported_symbols.push(Import {
                                    loc_symbol,
                                    solved_type: SolvedType::Erroneous(Problem::InvalidModule),
                                });
                            }
                            None => {
                                panic!(
                                    "Could not find module {:?} in exposed_types {:?}",
                                    module_id, exposed_types
                                );
                            }
                        }

                        continue;
                    }

                    let is_valid_alias = stdlib.applies.contains(&symbol)
                        // This wasn't a builtin value or Apply; maybe it was a builtin alias.
                        || roc_types::builtin_aliases::aliases().contains_key(&symbol);

                    if !is_valid_alias {
                        panic!(
                            "Could not find {:?} in builtin types {:?} or builtin aliases",
                            symbol, stdlib.types,
                        );
                    }
                }
            }
        } else if module_id != home {
            // We already have constraints for our own symbols.
            let region = Region::zero(); // TODO this should be the region where this symbol was declared in its home module. Look that up!
            let loc_symbol = Loc {
                value: symbol,
                region,
            };

            match exposed_types.get(&module_id) {
                Some(ExposedModuleTypes::Valid(solved_types, new_aliases)) => {
                    // If the exposed value was invalid (e.g. it didn't have
                    // a corresponding definition), it won't have an entry
                    // in solved_types
                    if let Some(solved_type) = solved_types.get(&symbol) {
                        // TODO should this be a union?
                        for (k, v) in new_aliases.clone() {
                            imported_aliases.insert(k, v);
                        }

                        imported_symbols.push(Import {
                            loc_symbol,
                            solved_type: solved_type.clone(),
                        });
                    }
                }
                Some(ExposedModuleTypes::Invalid) => {
                    // If that module was invalid, use True constraints
                    // for everything imported from it.
                    imported_symbols.push(Import {
                        loc_symbol,
                        solved_type: SolvedType::Erroneous(Problem::InvalidModule),
                    });
                }
                None => {
                    panic!(
                        "Could not find module {:?} in exposed_types {:?}",
                        module_id, exposed_types
                    );
                }
            }
        }
    }

    ConstrainableImports {
        imported_symbols,
        imported_aliases,
        unused_imports,
    }
}