use crate::{
    AccountField, AccountsStruct, CompositeField, Constraint, ConstraintAssociated,
    ConstraintBelongsTo, ConstraintExecutable, ConstraintLiteral, ConstraintOwner,
    ConstraintRentExempt, ConstraintSeeds, ConstraintSigner, ConstraintState, Field, Ty,
};
use heck::SnakeCase;
use quote::quote;

pub fn generate(accs: AccountsStruct) -> proc_macro2::TokenStream {
    // All fields without an `#[account(associated)]` attribute.
    let non_associated_fields: Vec<&AccountField> =
        accs.fields.iter().filter(|af| !is_associated(af)).collect();

    // Deserialization for each field
    let deser_fields: Vec<proc_macro2::TokenStream> = accs
        .fields
        .iter()
        .map(|af: &AccountField| {
            match af {
                AccountField::AccountsStruct(s) => {
                    let name = &s.ident;
                    let ty = &s.raw_field.ty;
                    quote! {
                        let #name: #ty = anchor_lang::Accounts::try_accounts(program_id, accounts)?;
                    }
                }
                AccountField::Field(f) => {
                    // Associated fields are *first* deserialized into
                    // AccountInfos, and then later deserialized into
                    // ProgramAccounts in the "constraint check" phase.
                    if is_associated(af) {
                        let name = &f.ident;
                        quote!{
                            let #name = &accounts[0];
                            *accounts = &accounts[1..];
                        }
                    } else {
                        let name = &f.typed_ident();
                        match f.is_init {
                            false => quote! {
                                let #name = anchor_lang::Accounts::try_accounts(program_id, accounts)?;
                            },
                            true => quote! {
                                let #name = anchor_lang::AccountsInit::try_accounts_init(program_id, accounts)?;
                            },
                        }
                    }
                }
            }
        })
        .collect();

    // Deserialization for each *associated* field. This must be after
    // the deser_fields.
    let deser_associated_fields: Vec<proc_macro2::TokenStream> = accs
        .fields
        .iter()
        .filter_map(|af| match af {
            AccountField::AccountsStruct(_s) => None,
            AccountField::Field(f) => match is_associated(af) {
                false => None,
                true => Some(f),
            },
        })
        .map(|field: &Field| {
            // TODO: the constraints should be sorted so that the associated
            //       constraint comes first.
            let checks = field
                .constraints
                .iter()
                .map(|c| generate_field_constraint(&field, c))
                .collect::<Vec<proc_macro2::TokenStream>>();
            quote! {
                #(#checks)*
            }
        })
        .collect();

    // Constraint checks for each account fields.
    let access_checks: Vec<proc_macro2::TokenStream> = non_associated_fields
        .iter()
        .map(|af: &&AccountField| {
            let checks: Vec<proc_macro2::TokenStream> = match af {
                AccountField::Field(f) => f
                    .constraints
                    .iter()
                    .map(|c| generate_field_constraint(&f, c))
                    .collect(),
                AccountField::AccountsStruct(s) => s
                    .constraints
                    .iter()
                    .map(|c| generate_composite_constraint(&s, c))
                    .collect(),
            };
            quote! {
                #(#checks)*
            }
        })
        .collect();

    // Each field in the final deserialized accounts struct.
    let return_tys: Vec<proc_macro2::TokenStream> = accs
        .fields
        .iter()
        .map(|f: &AccountField| {
            let name = match f {
                AccountField::AccountsStruct(s) => &s.ident,
                AccountField::Field(f) => &f.ident,
            };
            quote! {
                #name
            }
        })
        .collect();

    // Exit program code-blocks for each account.
    let on_save: Vec<proc_macro2::TokenStream> = accs
        .fields
        .iter()
        .map(|af: &AccountField| match af {
            AccountField::AccountsStruct(s) => {
                let name = &s.ident;
                quote! {
                    anchor_lang::AccountsExit::exit(&self.#name, program_id)?;
                }
            }
            AccountField::Field(f) => {
                let ident = &f.ident;
                match f.is_mut {
                    false => quote! {},
                    true => quote! {
                        anchor_lang::AccountsExit::exit(&self.#ident, program_id)?;
                    },
                }
            }
        })
        .collect();

    // Implementation for `ToAccountInfos` trait.
    let to_acc_infos: Vec<proc_macro2::TokenStream> = accs
        .fields
        .iter()
        .map(|f: &AccountField| {
            let name = match f {
                AccountField::AccountsStruct(s) => &s.ident,
                AccountField::Field(f) => &f.ident,
            };
            quote! {
                account_infos.extend(self.#name.to_account_infos());
            }
        })
        .collect();

    // Implementation for `ToAccountMetas` trait.
    let to_acc_metas: Vec<proc_macro2::TokenStream> = accs
        .fields
        .iter()
        .map(|f: &AccountField| {
            let (name, is_signer) = match f {
                AccountField::AccountsStruct(s) => (&s.ident, quote! {None}),
                AccountField::Field(f) => {
                    let is_signer = match f.is_signer {
                        false => quote! {None},
                        true => quote! {Some(true)},
                    };
                    (&f.ident, is_signer)
                }
            };
            quote! {
                account_metas.extend(self.#name.to_account_metas(#is_signer));
            }
        })
        .collect();

    let name = &accs.ident;
    let (combined_generics, trait_generics, strct_generics) = match accs.generics.lt_token {
        None => (quote! {<'info>}, quote! {<'info>}, quote! {}),
        Some(_) => {
            let g = &accs.generics;
            (quote! {#g}, quote! {#g}, quote! {#g})
        }
    };

    let account_mod_name: proc_macro2::TokenStream = format!(
        "__client_accounts_{}",
        accs.ident.to_string().to_snake_case()
    )
    .parse()
    .unwrap();

    let account_struct_fields: Vec<proc_macro2::TokenStream> = accs
        .fields
        .iter()
        .map(|f: &AccountField| match f {
            AccountField::AccountsStruct(s) => {
                let name = &s.ident;
                let symbol: proc_macro2::TokenStream = format!(
                    "__client_accounts_{0}::{1}",
                    s.symbol.to_snake_case(),
                    s.symbol,
                )
                .parse()
                .unwrap();
                quote! {
                    pub #name: #symbol
                }
            }
            AccountField::Field(f) => {
                let name = &f.ident;
                quote! {
                    pub #name: anchor_lang::solana_program::pubkey::Pubkey
                }
            }
        })
        .collect();

    let account_struct_metas: Vec<proc_macro2::TokenStream> = accs
        .fields
        .iter()
        .map(|f: &AccountField| match f {
            AccountField::AccountsStruct(s) => {
                let name = &s.ident;
                quote! {
                    account_metas.extend(self.#name.to_account_metas(None));
                }
            }
            AccountField::Field(f) => {
                let is_signer = match f.is_signer {
                    false => quote! {false},
                    true => quote! {true},
                };
                let meta = match f.is_mut {
                    false => quote! { anchor_lang::solana_program::instruction::AccountMeta::new_readonly },
                    true => quote! { anchor_lang::solana_program::instruction::AccountMeta::new },
                };
                let name = &f.ident;
                quote! {
                    account_metas.push(#meta(self.#name, #is_signer));
                }
            }
        })
        .collect();

    // Re-export all composite account structs (i.e. other structs deriving
    // accounts embedded into this struct. Required because, these embedded
    // structs are *not* visible from the #[program] macro, which is responsible
    // for generating the `accounts` mod, which aggregates all the the generated
    // accounts used for structs.
    let re_exports: Vec<proc_macro2::TokenStream> = {
        // First, dedup the exports.
        let mut re_exports = std::collections::HashSet::new();
        for f in accs.fields.iter().filter_map(|f: &AccountField| match f {
            AccountField::AccountsStruct(s) => Some(s),
            AccountField::Field(_) => None,
        }) {
            re_exports.insert(format!(
                "__client_accounts_{0}::{1}",
                f.symbol.to_snake_case(),
                f.symbol,
            ));
        }

        re_exports
            .iter()
            .map(|symbol: &String| {
                let symbol: proc_macro2::TokenStream = symbol.parse().unwrap();
                quote! {
                    pub use #symbol;
                }
            })
            .collect()
    };

    quote! {
        /// An internal, Anchor generated module. This is used (as an
        /// implementation detail), to generate a struct for a given
        /// `#[derive(Accounts)]` implementation, where each field is a Pubkey,
        /// instead of an `AccountInfo`. This is useful for clients that want
        /// to generate a list of accounts, without explicitly knowing the
        /// order all the fields should be in.
        ///
        /// To access the struct in this module, one should use the sibling
        /// `accounts` module (also generated), which re-exports this.
        mod #account_mod_name {
            use super::*;
            use anchor_lang::prelude::borsh;
            #(#re_exports)*

            #[derive(anchor_lang::AnchorSerialize)]
            pub struct #name {
                #(#account_struct_fields),*
            }

            impl anchor_lang::ToAccountMetas for #name {
                fn to_account_metas(&self, is_signer: Option<bool>) -> Vec<anchor_lang::solana_program::instruction::AccountMeta> {
                    let mut account_metas = vec![];

                    #(#account_struct_metas)*

                    account_metas
                }
            }
        }

        impl#combined_generics anchor_lang::Accounts#trait_generics for #name#strct_generics {
            #[inline(never)]
            fn try_accounts(program_id: &anchor_lang::solana_program::pubkey::Pubkey, accounts: &mut &[anchor_lang::solana_program::account_info::AccountInfo<'info>]) -> std::result::Result<Self, anchor_lang::solana_program::program_error::ProgramError> {
                // Deserialize each account.
                #(#deser_fields)*
                // Deserialize each associated account.
                //
                // Associated accounts are treated specially, because the fields
                // do deserialization + constraint checks in a single go,
                // whereas all other fields, i.e. the `deser_fields`, first
                // deserialize, and then do constraint checks.
                #(#deser_associated_fields)*
                // Perform constraint checks on each account.
                #(#access_checks)*
                // Success. Return the validated accounts.
                Ok(#name {
                    #(#return_tys),*
                })
            }
        }

        impl#combined_generics anchor_lang::ToAccountInfos#trait_generics for #name#strct_generics {
            fn to_account_infos(&self) -> Vec<anchor_lang::solana_program::account_info::AccountInfo<'info>> {
                let mut account_infos = vec![];

                #(#to_acc_infos)*

                account_infos
            }
        }

        impl#combined_generics anchor_lang::ToAccountMetas for #name#strct_generics {
            fn to_account_metas(&self, is_signer: Option<bool>) -> Vec<anchor_lang::solana_program::instruction::AccountMeta> {
                let mut account_metas = vec![];

                #(#to_acc_metas)*


                account_metas
            }
        }

        impl#combined_generics anchor_lang::AccountsExit#trait_generics for #name#strct_generics {
            fn exit(&self, program_id: &anchor_lang::solana_program::pubkey::Pubkey) -> anchor_lang::solana_program::entrypoint::ProgramResult {
                #(#on_save)*
                Ok(())
            }
        }
    }
}

// Returns true if the given AccountField has an associated constraint.
fn is_associated(af: &AccountField) -> bool {
    match af {
        AccountField::AccountsStruct(_s) => false,
        AccountField::Field(f) => f
            .constraints
            .iter()
            .filter(|c| match c {
                Constraint::Associated(_c) => true,
                _ => false,
            })
            .next()
            .is_some(),
    }
}

pub fn generate_field_constraint(f: &Field, c: &Constraint) -> proc_macro2::TokenStream {
    match c {
        Constraint::BelongsTo(c) => generate_constraint_belongs_to(f, c),
        Constraint::Signer(c) => generate_constraint_signer(f, c),
        Constraint::Literal(c) => generate_constraint_literal(c),
        Constraint::Owner(c) => generate_constraint_owner(f, c),
        Constraint::RentExempt(c) => generate_constraint_rent_exempt(f, c),
        Constraint::Seeds(c) => generate_constraint_seeds(f, c),
        Constraint::Executable(c) => generate_constraint_executable(f, c),
        Constraint::State(c) => generate_constraint_state(f, c),
        Constraint::Associated(c) => generate_constraint_associated(f, c),
    }
}

pub fn generate_composite_constraint(
    _f: &CompositeField,
    c: &Constraint,
) -> proc_macro2::TokenStream {
    match c {
        Constraint::Literal(c) => generate_constraint_literal(c),
        _ => panic!("Composite fields can only use literal constraints"),
    }
}

pub fn generate_constraint_belongs_to(
    f: &Field,
    c: &ConstraintBelongsTo,
) -> proc_macro2::TokenStream {
    let target = c.join_target.clone();
    let ident = &f.ident;
    quote! {
        if &#ident.#target != #target.to_account_info().key {
            return Err(anchor_lang::solana_program::program_error::ProgramError::Custom(1)); // todo: error codes
        }
    }
}

pub fn generate_constraint_signer(f: &Field, _c: &ConstraintSigner) -> proc_macro2::TokenStream {
    let ident = &f.ident;
    let info = match f.ty {
        Ty::AccountInfo => quote! { #ident },
        Ty::ProgramAccount(_) => quote! { #ident.to_account_info() },
        _ => panic!("Invalid syntax: signer cannot be specified."),
    };
    quote! {
        // Don't enforce on CPI, since usually a program is signing and so
        // the `try_accounts` deserializatoin will fail *if* the one
        // tries to manually invoke it.
        //
        // This check will be performed on the other end of the invocation.
        if cfg!(not(feature = "cpi")) {
            if !#info.is_signer {
                return Err(anchor_lang::solana_program::program_error::ProgramError::MissingRequiredSignature);
            }
        }
    }
}

pub fn generate_constraint_literal(c: &ConstraintLiteral) -> proc_macro2::TokenStream {
    let tokens = &c.tokens;
    quote! {
        if !(#tokens) {
            return Err(anchor_lang::solana_program::program_error::ProgramError::Custom(1)); // todo: error codes
        }
    }
}

pub fn generate_constraint_owner(f: &Field, c: &ConstraintOwner) -> proc_macro2::TokenStream {
    let ident = &f.ident;
    let owner_target = c.owner_target.clone();
    quote! {
        if #ident.to_account_info().owner != #owner_target.to_account_info().key {
            return Err(ProgramError::Custom(76)); // todo: proper error.
        }
    }
}

pub fn generate_constraint_rent_exempt(
    f: &Field,
    c: &ConstraintRentExempt,
) -> proc_macro2::TokenStream {
    let ident = &f.ident;
    let info = match f.ty {
        Ty::AccountInfo => quote! { #ident },
        Ty::ProgramAccount(_) => quote! { #ident.to_account_info() },
        _ => panic!("Invalid syntax: rent exemption cannot be specified."),
    };
    match c {
        ConstraintRentExempt::Skip => quote! {},
        ConstraintRentExempt::Enforce => quote! {
            if !rent.is_exempt(#info.lamports(), #info.try_data_len()?) {
                return Err(anchor_lang::solana_program::program_error::ProgramError::Custom(2)); // todo: error codes
            }
        },
    }
}

pub fn generate_constraint_seeds(f: &Field, c: &ConstraintSeeds) -> proc_macro2::TokenStream {
    let name = &f.ident;
    let seeds = &c.seeds;
    quote! {
        let program_signer = Pubkey::create_program_address(
            &#seeds,
            program_id,
        ).map_err(|_| anchor_lang::solana_program::program_error::ProgramError::Custom(1))?; // todo
        if #name.to_account_info().key != &program_signer {
            return Err(anchor_lang::solana_program::program_error::ProgramError::Custom(1)); // todo
        }
    }
}

pub fn generate_constraint_executable(
    f: &Field,
    _c: &ConstraintExecutable,
) -> proc_macro2::TokenStream {
    let name = &f.ident;
    quote! {
        if !#name.to_account_info().executable {
            return Err(anchor_lang::solana_program::program_error::ProgramError::Custom(5)) // todo
        }
    }
}

pub fn generate_constraint_state(f: &Field, c: &ConstraintState) -> proc_macro2::TokenStream {
    let program_target = c.program_target.clone();
    let ident = &f.ident;
    let account_ty = match &f.ty {
        Ty::CpiState(ty) => &ty.account_ident,
        _ => panic!("Invalid syntax"),
    };
    quote! {
        // Checks the given state account is the canonical state account for
        // the target program.
        if #ident.to_account_info().key != &anchor_lang::CpiState::<#account_ty>::address(#program_target.to_account_info().key) {
            return Err(ProgramError::Custom(1)); // todo: proper error.
        }
        if #ident.to_account_info().owner != #program_target.to_account_info().key {
            return Err(ProgramError::Custom(1)); // todo: proper error.
        }
    }
}

pub fn generate_constraint_associated(
    f: &Field,
    c: &ConstraintAssociated,
) -> proc_macro2::TokenStream {
    let associated_target = c.associated_target.clone();
    let field = &f.ident;
    let account_ty = match &f.ty {
        Ty::ProgramAccount(ty) => &ty.account_ident,
        _ => panic!("Invalid syntax"),
    };

    let space = match &f.space {
        None => quote! {
            let space = 8 + #account_ty::default().try_to_vec().unwrap().len();
        },
        Some(s) => quote! {
            let space = #s;
        },
    };

    let payer = match &f.payer {
        None => quote! {
            let payer = #associated_target.to_account_info();
        },
        Some(p) => quote! {
            let payer = #p.to_account_info();
        },
    };

    let seeds_no_nonce = match f.associated_seeds.len() {
        0 => quote! {
            [
                &b"anchor"[..],
                #associated_target.to_account_info().key.as_ref(),
            ]
        },
        _ => {
            let seeds = to_seeds_tts(&f.associated_seeds);
            quote! {
                [
                    &b"anchor"[..],
                    #associated_target.to_account_info().key.as_ref(),
                    #seeds
                ]
            }
        }
    };
    let seeds_with_nonce = match f.associated_seeds.len() {
        0 => quote! {
            [
                &b"anchor"[..],
                #associated_target.to_account_info().key.as_ref(),
                &[nonce],
            ]
        },
        _ => {
            let seeds = to_seeds_tts(&f.associated_seeds);
            quote! {
                [
                    &b"anchor"[..],
                    #associated_target.to_account_info().key.as_ref(),
                    #seeds
                    &[nonce],
                ]
            }
        }
    };

    quote! {
        let #field: anchor_lang::ProgramAccount<#account_ty> = {
            #space
            #payer

            let (associated_field, nonce) = Pubkey::find_program_address(
                &#seeds_no_nonce,
                program_id,
            );
            if &associated_field != #field.key {
                return Err(ProgramError::Custom(45)); // todo: proper error.
            }
            let lamports = rent.minimum_balance(space);
            let ix = anchor_lang::solana_program::system_instruction::create_account(
                payer.key,
                #field.key,
                lamports,
                space as u64,
                program_id,
            );

            let seeds = #seeds_with_nonce;
            let signer = &[&seeds[..]];
            anchor_lang::solana_program::program::invoke_signed(
                &ix,
                &[

                    #field.clone(),
                    payer.clone(),
                    system_program.clone(),
                ],
                signer,
            ).map_err(|e| {
                anchor_lang::solana_program::msg!("Unable to create associated account");
                e
            })?;
            // For now, we assume all accounts created with the `associated`
            // attribute have a `nonce` field in their account.
            let mut pa: anchor_lang::ProgramAccount<#account_ty> = anchor_lang::ProgramAccount::try_from_init(
                &#field,
            )?;
            pa.__nonce = nonce;
            pa
        };
    }
}

// Returns the inner part of the seeds slice as a token stream.
fn to_seeds_tts(seeds: &[syn::Ident]) -> proc_macro2::TokenStream {
    assert!(seeds.len() > 0);
    let seed_0 = &seeds[0];
    let mut tts = quote! {
        #seed_0.to_account_info().key.as_ref(),
    };
    for seed in &seeds[1..] {
        tts = quote! {
            #tts
            #seed.to_account_info().key.as_ref(),
        };
    }
    tts
}