use proc_macro2::{Ident, Span, TokenStream};
use quote::{quote, ToTokens};
use syn::Type;

use sqlx_core::describe::{Column, Describe};

use crate::database::DatabaseExt;

use crate::query::QueryMacroInput;
use std::fmt::{self, Display, Formatter};
use syn::parse::{Parse, ParseStream};
use syn::Token;

pub struct RustColumn {
    pub(super) ident: Ident,
    pub(super) type_: Option<TokenStream>,
}

struct DisplayColumn<'a> {
    // zero-based index, converted to 1-based number
    idx: usize,
    name: &'a str,
}

struct ColumnDecl {
    ident: Ident,
    // TIL Rust still has OOP keywords like `abstract`, `final`, `override` and `virtual` reserved
    r#override: Option<ColumnOverride>,
}

enum ColumnOverride {
    NonNull,
    Nullable,
    Wildcard,
    Exact(Type),
}

impl Display for DisplayColumn<'_> {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        write!(f, "column #{} ({:?})", self.idx + 1, self.name)
    }
}

pub fn columns_to_rust<DB: DatabaseExt>(describe: &Describe<DB>) -> crate::Result<Vec<RustColumn>> {
    describe
        .columns
        .iter()
        .enumerate()
        .map(|(i, column)| -> crate::Result<_> {
            // add raw prefix to all identifiers
            let decl = ColumnDecl::parse(&column.name)
                .map_err(|e| format!("column name {:?} is invalid: {}", column.name, e))?;

            let type_ = match decl.r#override {
                Some(ColumnOverride::Exact(ty)) => Some(ty.to_token_stream()),
                Some(ColumnOverride::Wildcard) => None,
                // these three could be combined but I prefer the clarity here
                Some(ColumnOverride::NonNull) => Some(get_column_type(i, column)),
                Some(ColumnOverride::Nullable) => {
                    let type_ = get_column_type(i, column);
                    Some(quote! { Option<#type_> })
                }
                None => {
                    let type_ = get_column_type(i, column);

                    if column.not_null.unwrap_or(false) {
                        Some(type_)
                    } else {
                        Some(quote! { Option<#type_> })
                    }
                }
            };

            Ok(RustColumn {
                ident: decl.ident,
                type_,
            })
        })
        .collect::<crate::Result<Vec<_>>>()
}

pub fn quote_query_as<DB: DatabaseExt>(
    input: &QueryMacroInput,
    out_ty: &Type,
    bind_args: &Ident,
    columns: &[RustColumn],
) -> TokenStream {
    let instantiations = columns.iter().enumerate().map(
        |(
            i,
            &RustColumn {
                ref ident,
                ref type_,
                ..
            },
        )| {
            match (input.checked, type_) {
                // we guarantee the type is valid so we can skip the runtime check
                (true, Some(type_)) => quote! {
                    #ident: row.try_get_unchecked::<#type_, _>(#i).try_unwrap_optional()?
                },
                // type was overridden to be a wildcard so we fallback to the runtime check
                (true, None) => quote! ( #ident: row.try_get(#i)? ),
                // macro is the `_unchecked!()` variant so this will die in decoding if it's wrong
                (false, _) => quote!( #ident: row.try_get_unchecked(#i)? ),
            }
        },
    );

    let db_path = DB::db_path();
    let row_path = DB::row_path();
    let sql = &input.src;

    quote! {
        sqlx::query_with::<#db_path, _>(#sql, #bind_args).try_map(|row: #row_path| {
            use sqlx::Row as _;
            use sqlx::result_ext::ResultExt as _;

            Ok(#out_ty { #(#instantiations),* })
        })
    }
}

fn get_column_type<DB: DatabaseExt>(i: usize, column: &Column<DB>) -> TokenStream {
    if let Some(type_info) = &column.type_info {
        <DB as DatabaseExt>::return_type_for_id(&type_info).map_or_else(
            || {
                let message =
                    if let Some(feature_gate) = <DB as DatabaseExt>::get_feature_gate(&type_info) {
                        format!(
                            "optional feature `{feat}` required for type {ty} of {col}",
                            ty = &type_info,
                            feat = feature_gate,
                            col = DisplayColumn {
                                idx: i,
                                name: &*column.name
                            }
                        )
                    } else {
                        format!(
                            "unsupported type {ty} of {col}",
                            ty = type_info,
                            col = DisplayColumn {
                                idx: i,
                                name: &*column.name
                            }
                        )
                    };
                syn::Error::new(Span::call_site(), message).to_compile_error()
            },
            |t| t.parse().unwrap(),
        )
    } else {
        syn::Error::new(
            Span::call_site(),
            format!(
                "database couldn't tell us the type of {col}; \
                     this can happen for columns that are the result of an expression",
                col = DisplayColumn {
                    idx: i,
                    name: &*column.name
                }
            ),
        )
        .to_compile_error()
    }
}

impl ColumnDecl {
    fn parse(col_name: &str) -> crate::Result<Self> {
        // find the end of the identifier because we want to use our own logic to parse it
        // if we tried to feed this into `syn::parse_str()` we might get an un-great error
        // for some kinds of invalid identifiers
        let (ident, remainder) = if let Some(i) = col_name.find(&[':', '!', '?'][..]) {
            let (ident, remainder) = col_name.split_at(i);

            (parse_ident(ident)?, remainder)
        } else {
            (parse_ident(col_name)?, "")
        };

        Ok(ColumnDecl {
            ident,
            r#override: if !remainder.is_empty() {
                Some(syn::parse_str(remainder)?)
            } else {
                None
            },
        })
    }
}

impl Parse for ColumnOverride {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let lookahead = input.lookahead1();

        if lookahead.peek(Token![:]) {
            input.parse::<Token![:]>()?;

            let ty = Type::parse(input)?;

            if let Type::Infer(_) = ty {
                Ok(ColumnOverride::Wildcard)
            } else {
                Ok(ColumnOverride::Exact(ty))
            }
        } else if lookahead.peek(Token![!]) {
            input.parse::<Token![!]>()?;

            Ok(ColumnOverride::NonNull)
        } else if lookahead.peek(Token![?]) {
            input.parse::<Token![?]>()?;

            Ok(ColumnOverride::Nullable)
        } else {
            Err(lookahead.error())
        }
    }
}

fn parse_ident(name: &str) -> crate::Result<Ident> {
    // workaround for the following issue (it's semi-fixed but still spits out extra diagnostics)
    // https://github.com/dtolnay/syn/issues/749#issuecomment-575451318

    let is_valid_ident = name.chars().all(|c| c.is_alphanumeric() || c == '_');

    if is_valid_ident {
        let ident = String::from("r#") + name;
        if let Ok(ident) = syn::parse_str(&ident) {
            return Ok(ident);
        }
    }

    Err(format!("{:?} is not a valid Rust identifier", name).into())
}